# Crossovers, a Step Further



## Patrick Bateman (Sep 11, 2006)

I am working on a new system, and I am a fan of loudspeakers that keep the drivers in phase.
There is only one type of filter that can do this: a first order filter.
This is why first order filters are used by Vandersteen, Dunlavy, Thiel, Dynaudio, and numerous others.

I do not think that it is a coincidence that those speakers are known for their startling imaging and wide soundstages; to my ears the biggest improvement rendered by drivers that are in-phase is the soundstage. (My home speakers are Vandersteen and I use first order filters almost exclusively in my projects.)

There are a couple designers who use high order crossovers that are in-phase, or close to it. Tom Danley is one, Jean Michael LeCleach is another.

I've been avoiding trying to learn how to do this, because phase makes my head hurt, but I decided it's about time to learn.

I'm not 100% sure if the two designers are using the same method, in fact one of the reasons I'm posting this is to get an understanding of how it works.

Some caveats:

1) The material in this thread is Jean Michael LeCleach's
2) I don't see a copyright on it, but if I missed it, please let me know. I'll take down the images and link directly to the source.
3) The reason that I don't just post a link to the source is that Mr LeCleach passed away last year, and I've seen many times when good solid information fell into obscurity because the author died. So this thread is definitely an attempt to keep this method in the limelight.


----------



## Patrick Bateman (Sep 11, 2006)

Here's the source of the original paper, from the ETF Triode Show in France, ten years ago, as presented by the late Jean Michael LeCleach:

http://www.melaudia.net/zdoc/jml_crossovers_etf04.pdf


----------



## Patrick Bateman (Sep 11, 2006)




----------



## Patrick Bateman (Sep 11, 2006)

​


----------



## Patrick Bateman (Sep 11, 2006)

​


----------



## Patrick Bateman (Sep 11, 2006)

​
More posts to come, there's about fifty more slides in the presentation. (Entire file available from link in second post.)


----------



## sqnut (Dec 24, 2009)

Good to have you back, hope you had fun . Reading and picking up on some things.



> Phase is chaotic in reverberant environments, yes, but the direct sound is not affected by reverberation. In some situations such as choral music in a cathedral from the back of the audience, phase is totally messed up, but in most other cases it still matters!


So, the relevance of phase depends on the environment. Not only are you at the back of the cathedral, the roof is 6" above your head and the furthest wall is like 3 feet away. The amt of direct energy you're hearing is WAY less than what you would in a room. It is a phase nightmare. Phase matters in a room but in a car.....



> Three experiments were performed which confirm the audibility of time offset in loudspeaker drivers but indicate that this audibility is due only to the frequency response aberrations resulting from the time offset. Implications of these results are discussed.


You're hearing phase anomalies in the response domain. Response is the way one hears phase. 



> Given that the response alone can explain time offset audibility and time delay alone cannot explain this audibility it seems inescapable to conclude that arrival time compensation by itself has no audible value.


Again room vs room. Timing is of vital importance in a car as it is the only way to make the speakers equi-distance from you. Something that is taken for granted in a room. I think in a car getting the timing right and then smoothing out the phase by using the eq is the way to go. IMHO eq around the xover point is basically to ensure a smooth transition from one set of drivers to the next. 



> "A frequent argument to justify why phase distortion is insignificant for material recorded and/or reproduced in a reverberant environment is that reflections cause gross, position sensitive phase distortion themselves. "
> "*Although this is true, it is also true that the first-arrival direct sound is not subject to these distortions*


Environment. In a car we are getting precious little of that direct sound. Not only is the quantum of direct sound vs reflected radically different between a room and a car, the time interval between the direct and the first reflection (gating?) is much smaller in a car. 



> 4th order LR crossover have always sounded "disjointed" to me - transients sound blurred, and high frequencies don't match up with low frequencies.


In a room, speakers that use shallow slopes image, stage great and are tonally decent in a small spot X. Creating and *staying* in that small X is just not possible in a car. 

In a room outside that X, the stage and image collapse a bit and acoustical interference? makes the speakers sound 'darker' in the mid range. B&O is a bad example to use because they are playing with timing on most of their speakers, iirc. 

Attributes like space, air, etc in a car, is better achieved on the back of wider dispersion on steeper slopes vs narrow dispersion on shallow slopes.

It's beginning to get too technical for me.


----------



## Patrick Bateman (Sep 11, 2006)

I've never heard a speaker with high order slopes that could image as well as a speaker with first order slopes.

Getting the phase flat from 250hz to 20khz would be tricky; it basically requires us to eliminate all reflections within almost half a meter(!)
But if you limit yourself to 1khz-20khz, it's pretty easy to do with first order slopes.

I think flat phase is probably the main reason that Hybrid wins so many prizes, their designs use high order xovers but their xover points maintain flat phase in the midrange.

LeCleach offers a tantalizing possibility here, the ability to use high order slopes *and* have (close to) flat phase.

Another bonus is that it requires the midrange to be closer than the tweeter, which is exactly how most cars are set up.


----------



## thehatedguy (May 4, 2007)

"Quasi-optimal" crossover for high-efficiency loudspeaker system - diyAudio


----------



## 2010hummerguy (Oct 7, 2009)

Subscribed, this is the stuff that keeps me up at night.


----------



## ErinH (Feb 14, 2007)

the bit about low order crossovers being better transiently is true to some extent (various types change) *BUT only in the absolute term of the crossover itself*. *When you pair the crossover with a driver things change. * * When you pair a driver+crossover with another driver+crossover, things change.* A 1st order BW (with 0ms GD) added to driver paired with another crossover will alter the transient (GD) and can just as easily result in as high GD as using a higher order crossover slope. 

The *summed response *(frequency, phase/polarity, time) is the important aspect and evaluating a single crossover type on its own is only a piece of the puzzle. Don't get caught up the crossover types themselves. It's important to know what they do, but the interaction with the driver you're using it on and other crossovers in the network is what matters.

One cool thing is in the car we have the luxury of DSP. Practically everyone on this site has DSP. Heck, I'd venture to say that more people in car audio use T/A than those in home audio do. Therefore, if we set a crossover network to foremost limit the driver's bandwidth (for reasons such as beaming, distortion, or breakup) then you have the luxury of adjusting time of one driver relative to the other to lessen GD IF you feel that's of utmost importance. Maybe between a tweeter/mid at higher frequency this isn't as much a concern as it is with low frequency crossovers where the wavelength is so long that phase is more impactful on group delay.

For example, if you had a midrange that needed to be low passed at 3khz with a steep filter and the tweeter network you have resulted in you having a 90deg phase shift at the summed crossover point of, say, 2.5khz, you could delay the tweeter by 0.10ms and achieve a 90deg phase transformation that would *theoretically, in this hypothetical case* get you in phase at the crossover.


----------



## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> the bit about low order crossovers being better transiently is true to some extent (various types change) *BUT only in the absolute term of the crossover itself*. *When you pair the crossover with a driver things change. * * When you pair a driver+crossover with another driver+crossover, things change.* A 1st order BW (with 0ms GD) added to driver paired with another crossover will alter the transient (GD) and can just as easily result in as high GD as using a higher order crossover slope.
> 
> The *summed response *(frequency, phase/polarity, time) is the important aspect and evaluating a single crossover type on its own is only a piece of the puzzle. Don't get caught up the crossover types themselves. It's important to know what they do, but the interaction with the driver you're using it on and other crossovers in the network is what matters.
> 
> ...


Yeah phase response is a skull crusher. Here's an example:

In my Synergy horns I use first order electrical crossovers nearly 100% of the time. Occasionally I find that I have to flip the polarity of one driver to get the phase flat. *This is always kind of a bummer, because theoretically you can't get a midrange and tweeter in-phase with a first order slope UNLESS the drivers are both connected in positive polarity.* But my microphone doesn't lie, and many times I have to flip the polarity to get a phase response that measures flat.

But now I can see what's going on:

What's happening is that the combination of the natural rolloff of the tweeter and the electrical rolloff of the filter is combining to create a slope that's more like third order, not first order. Combine that with the fact that the midrange is about 10cm in front of the tweeter, *and I accidentally had a configuration that was pretty close to what LeCleach is recommending in this paper.*

This is way cool, because it's very difficult to get a "true" first order rolloff with a tweeter. Tweeters typically have a 'Q' that's between 1.0 and 2.0, and due to that, they tend to rolloff steeply. If I'm not mistaken, this is one of the reasons that the Dynaudio, Thiel and Vandersteen crossovers are so insanely complex; they use a pile of components to create a "true" first order slope.


----------



## 2010hummerguy (Oct 7, 2009)

bikinpunk said:


> For example, if you had a midrange that needed to be low passed at 3khz with a steep filter and the tweeter network you have resulted in you having a 90deg phase shift at the summed crossover point of, say, 2.5khz, you could delay the tweeter by 0.10ms and achieve a 90deg phase transformation that would *theoretically, in this hypothetical case* get you in phase at the crossover.


This is something I am learning about, would the .1ms delay affect the rest of the tweeter's phase? IE everything above the xover point...


----------



## Patrick Bateman (Sep 11, 2006)

Architect7 said:


> This is something I am learning about, would the .1ms delay affect the rest of the tweeter's phase? IE everything above the xover point...


What he recommended will work... *at the crossover point.*

That's the problem with high order crossovers: the phase shifts dramatically and the phase shift changes with frequency. *So if you fix it at one frequency, you may well make it worse at another.

The higher the order, the more the shift. First order has 90 degrees of phase rotation, 2nd is 180 degrees, 4th is 360 degrees, etc.

If you really want to make your head explode, there is a piece of software named 'RePhase' that can apply delay that varies with frequency... IE you can basically flatten the phase of any filter! This is some Next Level ****, and it used to require a whole rack of processing and about $100,000 in gear, but RePhase is free.

*


----------



## quietfly (Mar 23, 2011)

subbed to see where this ends up.....


----------



## 2010hummerguy (Oct 7, 2009)

Patrick Bateman said:


> What he recommended will work... *at the crossover point.*
> 
> That's the problem with high order crossovers: the phase shifts dramatically and the phase shift changes with frequency. *So if you fix it at one frequency, you may well make it worse at another.
> 
> ...


*

Funny enough, I just learned about RePhase a couple weeks ago...definitely planning to use it with my home 2 channel build.*


----------



## Patrick Bateman (Sep 11, 2006)

Architect7 said:


> Funny enough, I just learned about RePhase a couple weeks ago...definitely planning to use it with my home 2 channel build.


I was babbling about Synergy Horns over at diyaudio* and the inventor was kind enough to post a pic of what RePhase can do to his invention:










This shows the frequency response, impulse response, and phase response.
Check out the impulse response in particular, see how it 'fades to black' almost instantaneously? *This is something that's literally impossible with the LR4 filters that are so popular.* Basically the proaudio guys mostly don't care about phase, but they care a LOT about power handling, so LR4 is the pro audio default. IMHO AudioControl made it popular in the car audio world, and AudioControl is a few miles from Rane, which is a pro audio company. (I used to live a few miles away from both of them.)

TLDR: I think LR4 filters are used WAY too much, and I think AudioControl was influenced by Rane, due to their physical proximity.









If you Google "perfect impulse response", this is the pic that comes up. It's a Dunlavy SC-IV which uses, you guessed it, first order filters. Both Dunlavy and LeCleach have passed away, so hopefully I can keep some of these ideas out there.

* original discussion, with Geddes, Danley and myself here : http://www.diyaudio.com/forums/multi-way/178187-great-waveguide-list-22.html#post3912653


Also, that phase response is just completely ridiculous too. Basically flat from 100hz to 13,500hz. The only reason there's a blip at 13,500hz is because that's the end of the horn! (13,500hz = 1")


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> What he recommended will work... *at the crossover point.*
> 
> That's the problem with high order crossovers: the phase shifts dramatically and the phase shift changes with frequency. *So if you fix it at one frequency, you may well make it worse at another.
> 
> The higher the order, the more the shift. First order has 90 degrees of phase rotation, 2nd is 180 degrees, 4th is 360 degrees, etc. *


*

iirc, with both a LP and HP the phase shift occurs in frequencies below the xover point. Now, with the same xover point and the same order for both LP and HP, the phase shift on the both drivers is identical. 

We hear phase anomalies in the response domain. Therefore in a car that is where they should be corrected along with timing. In a car you need timing and response to correct for any 'phassy' issues Also, any significant phase issue will more likely be heard on the driver with the LP simply because the anomalies are occurring in the drivers pass band. With the HP driver, these anomalies occur beyond the pass band and are rolling off steeply on a fourth order slope. With fourth order slopes, I will eq each driver an octave above and below the xover point for a smooth combined response in this region as measured and finally as heard. Getting these zones right is finally what gives that sense of flowing and connected unity of sound and source. 

This range of an octave above and below, could fall in any zone of your overall response curve, i.e. one that is flat, sloping down or up. The transition has to be smooth the range itself does not have to be flat.

Additionally since it's a car, the environment and install ensure that a 4th order electronic slope does not normally translate into a 4th order measured / acoustic slope. So you need to eq for that as well. 

You don't need to do any of the above in a room. In a car nearly everything, comes down to response one way or the other, like Erin mentioned. A good sounding car is almost always about micromanaging the perceived response.*


----------



## 2010hummerguy (Oct 7, 2009)

Patrick Bateman said:


> I was babbling about Synergy Horns over at diyaudio* and the inventor was kind enough to post a pic of what RePhase can do to his invention:
> 
> 
> 
> ...


Reading this gave me goose bumps. Can't wait to try it next week when I get my computer system set up. Your Rane/AC conjecture is totally plausible. Employee cross pollenation is certainly a cause for this trend. RePhase lets us cross steep but retain power handling, right? We get our cake and eat it too?



sqnut said:


> iirc, with both a LP and HP the phase shift occurs in frequencies below the xover point. Now, with the same xover point and the same order for both LP and HP, the phase shift on the both drivers is identical.
> 
> We hear phase anomalies in the response domain. Therefore in a car that is where they should be corrected along with timing. In a car you need timing and response to correct for any 'phassy' issues Also, any significant phase issue will more likely be heard on the driver with the LP simply because the anomalies are occurring in the drivers pass band. With the HP driver, these anomalies occur beyond the pass band and are rolling off steeply on a fourth order slope. With fourth order slopes, I will eq each driver an octave above and below the xover point for a smooth combined response in this region as measured and finally as heard. Getting these zones right is finally what gives that sense of flowing and connected unity of sound and source.
> 
> ...


This is how I have approached it for years because I am uneducated when it comes to understanding phase. And I have felt like I have been missing something in my DIY home speaker designs. I am attempting to address this by:

1. No more 4-way designs. Instead, one big planar for 200hz-4khz to address human vocal range and most instruments. I do not like large full range drivers due to a number of issues so that is not an option. And I love ribbons so they will round out the top end. TA will come into play for blending with woofers at 200hz but not a big deal being under 300hz. Will need to play with the higher xover point to match dispersion...

2. 1st order x-overs...easy for the 4khz xover, not for the 200hz xover...might bump to 300hz and try for 1st order...or rely on RePhase.

3. Rephase. I would also like to try Dirac though that is $$$. But I will attempt the trial.

I am also considering bagging my grandiose ideas and just get big Magnepans like 3.7 with the dedicated ribbons. Mmmmmmm. Just maybe...


----------



## sqnut (Dec 24, 2009)

You heard and liked the Magic Bus right? That is all 4th order LR. Sure there are a lot of other things going on in the bus and even the environment it is very different to our daily drives. So fourth order can be made to sound good, even in the region where we are most sensitive to phase. You highlighted the quality of low end in the bus. Again, the size of the bus has a lot to do with how accurate and articulate you can get the low end. But yeah, it's a fourth order LR. Timing and response coherence are key, phase is accounted for between those two. Anything beyond that is a mirage.

Our hearing is geared to hearing relative differences in timing, amplitude, and pitch rather than absolutes. Anytime we saturate one area eg listening at 120db (amplitude) the ears ability to hear 'difference' degrades rapidly, which is why we won't hear 10% distortion at 120db etc. 

By running shallow slopes in a car, not only are you spreading the combing but also making a comb with much finer teeth. So you are actually saturating two fields pitch and amplitude (peak/dip). You're pushing the ear out of its comfort zone, chasing something that is a mirage in *this* environment.


----------



## Patrick Bateman (Sep 11, 2006)

Architect7 said:


> Reading this gave me goose bumps. Can't wait to try it next week when I get my computer system set up. Your Rane/AC conjecture is totally plausible. Employee cross pollenation is certainly a cause for this trend. RePhase lets us cross steep but retain power handling, right? We get our cake and eat it too?
> 
> 
> 
> ...


Ack.

Hate to be the bearer of bad news, but all line sources have massive phase problems. *Basically, if it's a line, you can't get flat phase, or at least not over a wide bandwidth.*

Here's why:

Every octave we go up in frequency, the wavelengths get shorter. As we approach the last three octaves, the wavelengths are so short, the sound radiated from one side of the diaphragm is out of phase with the sound radiated from the center. Complicating this further is that many line sources are dipoles.

I didn't really understand this until 2013. I was measuring some Monsoon planars, and couldn't figure out why the phase was an absolute mess at high frequencies. And then it clicked: *it's the diaphragm size and shape.*

If you're interested in planars and ribbons, about the only solution to the problem is what Quad does. Basically the diaphragm is in rings, like the "Target" logo, and each ring plays a different bandwidth.









Dunlavy SC-IV step response









Quad ESL 989 step response









Magnepan MG3.6/R step response

Here's some measurements to illustrate this. The first is a Dunlavy SC-IV, which has a step response that's about as good as you can get with passive crossovers. The second is a Quad - *see how it's similar to the Dunlavy and the Synergy Horn?* But then check out the Magnepan; it's step response illustrates that the phase is not flat.



I definitely sympathize with wanting to use planars. They sound great, and their CSD response is particularly excellent. But phase? Not so much.




























BTW, the reason that full-range speakers with good phase are so freaken' HUUUUGE is because of this situation. Every octave you go lower, the design gets exponentially larger. Some of these designs weigh upwards of 500lbs.

I listened to Keele's CBT at CES, and the first thing I noticed was that diffuse phasiness that's endemic to all line sources. Since Keele is literally one of the pioneers in horn design, I'd be really curious to learn why he switched from horns to arrays.


TLDR : line sources have phase problems that are un-fixable. It's plain ol' geometry. You can make an array sound like a full range if you're clever though, which is exactly how the Quad ESL, Synergy Horn, Dynaudio and Dunlavy speakers all work. I don't think it's a coincidence that these speakers are classics, it's the phase.


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> You heard and liked the Magic Bus right? That is all 4th order LR. Sure there are a lot of other things going on in the bus and even the environment it is very different to our daily drives. So fourth order can be made to sound good, even in the region where we are most sensitive to phase. You highlighted the quality of low end in the bus. Again, the size of the bus has a lot to do with how accurate and articulate you can get the low end. But yeah, it's a fourth order LR. Timing and response coherence are key, phase is accounted for between those two. Anything beyond that is a mirage.
> 
> Our hearing is geared to hearing relative differences in timing, amplitude, and pitch rather than absolutes. Anytime we saturate one area eg listening at 120db (amplitude) the ears ability to hear 'difference' degrades rapidly, which is why we won't hear 10% distortion at 120db etc.
> 
> By running shallow slopes in a car, not only are you spreading the combing but also making a comb with much finer teeth. So you are actually saturating two fields pitch and amplitude (peak/dip). You're pushing the ear out of its comfort zone, chasing something that is a mirage in *this* environment.


I know the whole phase thing is a skull crusher, and people love to debate it on the Internet. Here's some things to consider:

1) Dynaudio, Dunlavy, Vandersteen and Thiel speakers consistently rank among the best regarded speakers for musical fidelity
2) All use first order crossovers exclusively
3) The freaken' INVENTOR of the LR4 crossover no longer uses his own topology, or at least not in the midrange. A quote from his own website: _"Passive 1st order crossover between lower midrange and upper midrange at 1 kHz,
located in base of midrange/tweeter baffle_"

IMHO, the main reason people use LR4 is because it's ubiquitous and passive first order crossovers have a bad rep. But the INVENTOR of LR4 doesn't even use it. Makes you think, right? http://www.linkwitzlab.com/LX521/Description.htm


----------



## sqnut (Dec 24, 2009)

All I'm saying is you have to take into account your equipment, the environment you're listening in and the way we hear, when we talk about reproducing good sound in a car. So what works in a room environment may not work in a car for reasons explained. 

I've heard dyns and vandys the flow of music is buttery smooth. You don't get that liquid flow with Scans and Wilsons for instance, that is an effect of phase. Good imaging but in a very small area. BUT Both the Dyns and Vandys sound dark and closed while the Scans and Wilsons are more open and again this is in a room.


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> All I'm saying is you have to take into account your equipment, the environment you're listening in and the way we hear, when we talk about reproducing good sound in a car. So what works in a room environment may not work in a car for reasons explained.
> 
> I've heard dyns and vandys the flow of music is buttery smooth. You don't get that liquid flow with Scans and Wilsons for instance, that is an effect of phase. Good imaging but in a very small area. BUT Both the Dyns and Vandys sound dark and closed while the Scans and Wilsons are more open and again this is in a room.


I'm listening to Vandersteens off-axis as I write this, and yes, they're dark. The reason for this is because shallow slopes means that two or even three drivers are all covering the same bandwidth at relatively similar SPL levels. Here's an example:

Let's say you have a three way with first order slopes. Tweeter is crossed at 4khz, midrange is crossed at 1khz. In this scenario, here are the SPL levels at 2khz:

1) The midrange is playing at 100dB
2) The woofer is playing at 91dB
3) The tweeter is playing at 91dB

Pretty crazy right? The woofer is as loud as the tweeter! And only nine dB below the midrange. That's due to the crazy amount of overlap between drivers. (Which is a "thing" with first order slopes.)

All of this is just simple geometry; when you have multiple drivers playing the same thing and the pathlengths aren't equal, *you get comb filtering.* There are two solutions to comb filtering:

1) steep slopes
2) or equalize the pathlengths

*But the LeCleach and Danley solutions solve all that.*

That's what's so tantalizing about this. They let you have your cake and eat it too. Nearly flat phase, along with high SPL, directivity, and steep slopes.

The Danley solution definitely goes a step further than LeCleach; the pathlengths are equalized to an insane degree, all the way down to the diaphragm of the tweeter. Danley could make wheelbarrows full of cash if he sold line arrays, but he refuses to, because you can't have an equalized path length with a line array. It is not physically possible. The company is so committed to this, they even did engineering for two companies on their line arrays, but they refuse to sell them under the Danley badge.

The thing is, 99.9% of the world hasn't even heard these designs. Despite the fact that I've studied Danley's work for over a decade, I've never actually heard one of his Synergy horns. I *have* heard one of his Unity horns, but I had to literally look someone up on the Internet and ask them if I could hear them to get that opportunity. I also have a friend that used to run Unity horns at raves in Oregon and Washington in the early 00's.


----------



## sqnut (Dec 24, 2009)

Click on this link and scroll down to the section where he compares the power distribution between 1st order BW and 4th order LR.

Music and the Human Ear


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> *But the LeCleach and Danley solutions solve all that.*
> 
> That's what's so tantalizing about this. They let you have your cake and eat it too. Nearly flat phase, along with high SPL, directivity, and steep slopes.


In a room, not in a car. You cant have flat phase in a car no matter what you do.


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> In a room, not in a car. You cant have flat phase in a car no matter what you do.


lolwhut?

Of course you can have flat phase. 1khz is only 34cm long. It's not even difficult to achieve flat phase down to 1khz.

If you measure a speaker with flat phase in a car, and the phase measurement isn't flat, then your measurement has issues.

But is it impossible to achieve? No, not at all. It's not even difficult really.

On top of that, I've noticed a distinct improvement in percussion when I use subs with low group delay. And we're talking about frequencies that exceed the length of the car. Now I'll admit it's basically impossible to measure phase in a car at 100hz, but why does a sub with low group delay sound better on percussion than one with high group delay?

Perhaps our ears are more sensitive to phase than the software we use to measure.

I am *definitely* of the opinion that phase is more audible than frequency response problems. For instance, I can easily measure a 3dB peak in response at 5khz with a microphone, *but I have a hard time hearing it.* OTOH, if I am listening to a drummer keep time, and that drummer is off by even 5%, *I can hear the change in the beat.* And a difference of 5% is literally a fraction of a second. Difficult to measure, easy to hear.

When I play around with the digital delay on my MiniDSP I can hear difference of *microseconds!* Timing is something we are very VERY attuned to.


----------



## Patrick Bateman (Sep 11, 2006)

Also, I know Andy Wehmeyer has generally been dismissive of phase. But keep in mind he worked at JBL, hardly a proponent of phase response. The Prosound community is focused on an entirely different set of criteria than the studio community, car audio community, or home community. As soon as you use more than one tweeter your phase is going to go to ****, and could you imagine a football stadium, movie theater or nightclub that only used one tweeter? The entire reason that Danley made the layered combiner was to concentrate the power of four, six, or even sixty four tweeters into a single spot, so that his designs would work in stadiums. For 95% of the pro audio companies, flat phase is an impossible goal. They have no need to study it, talk about it, or advertise it, because they simply cannot achieve it.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> lolwhut?
> 
> Of course you can have flat phase. 1khz is only 34cm long. It's not even difficult to achieve flat phase down to 1khz.
> 
> ...


You know, at the end of the day it comes down to triggers. Of all the things that we are sensitive to, response, timing, phase, pitch etc, one of them is always a trigger. Wherein if everything else is perfect but this is slightly off, it's never going to sound right. For you that trigger is the audible effect of phase (which is basically heard as response and timing) and for me it's response. A 3db peak at 5khz is seriously ouch territory. 

I agree that we are very sensitive to timing differences. But at the end of the day we are chasing our own triggers, is that fair?


----------



## 14642 (May 19, 2008)

Patrick Bateman said:


> Also, I know Andy Wehmeyer has generally been dismissive of phase. But keep in mind he worked at JBL, hardly a proponent of phase response. The Prosound community is focused on an entirely different set of criteria than the studio community, car audio community, or home community. As soon as you use more than one tweeter your phase is going to go to ****, and could you imagine a football stadium, movie theater or nightclub that only used one tweeter? The entire reason that Danley made the layered combiner was to concentrate the power of four, six, or even sixty four tweeters into a single spot, so that his designs would work in stadiums. For 95% of the pro audio companies, flat phase is an impossible goal. They have no need to study it, talk about it, or advertise it, because they simply cannot achieve it.


Patrick,
I used to work at HARMAN. JBL is but one part of that company. However, I never worked very closely on any projects with any of the pro audio guys, except that we shared a transducer engineer (Who also develops transducers for REVEL). Stadiums and studios are very different than cars. It isn't fair for you to assume that because one of the brands owned by my former employer uses a design goal that doesn't apply to cars that my 30 years of experience in cars is somehow not valuable. 

I'm dismissive of phase because we developed a phase EQ FOR CARS and the benefit was miniscule. So small as to not be audible to anyone who listened to it.

So, my question, and I'll go back and read the thread to see if this is addressed, is how are you measuring phase?


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> lolwhut?
> 
> Of course you can have flat phase. 1khz is only 34cm long. It's not even difficult to achieve flat phase down to 1khz.





Andy Wehmeyer said:


> Patrick,
> 
> I'm dismissive of phase because we developed a phase EQ FOR CARS and the benefit was miniscule. So small as to not be audible to anyone who listened to it.
> 
> So, my question, and I'll go back and read the thread to see if this is addressed, is how are you measuring phase?


Since Andy has bumped the thread, I'm curious too. I wanted to ask you did you measure the phase at speaker level or ear level? There in no way that you can keep flat phase at ear level in the car. Reflections are totally messing up the phase in a car, if you measured at ear level how did you separate the direct sound from reflected sound?


----------



## 14642 (May 19, 2008)

OK. So I read the whole thread. 

There's a big difference between the room in which you listen to your Vandersteens and the inside of your car. Nowhere is this more apparent than in viewing an impulse response measurement of any single driver in a big room (like your living room) and in the car. 

The beauty of gated measurements is that they make it possible to make a sort of anechoic measurement in a nonanechoic space. In a large enough room, it's possible to make that measurement, window the response to remove the first reflection (often from the floor) and view the anechoic response. Of course, the window compromises the low frequency resolution, but you can certainly view the shape of the curve with reasonable accuracy.

Try that in a car. Good luck with that. From an audibility standpoint, ALL of the reflections are so short that they are processed by us as part of the initial sound. Well, the Magic Bus may be different. It' big and it's treated as a room. I don't even consider that car audio, but I've also never heard it. Any phase EQ that operates at high frequencies has to work in one tiny point in space. It is possible to EQ the phase at lower frequencies over a reasonable area, and that's what we tried. Very little benefit. 

My point is that in a car it's pointless to consider the phase of the loudspeaker itself without the effect of all the reflections that arrive so soon after the initial response that we don't even hear them separately.


----------



## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Patrick,
> I used to work at HARMAN. JBL is but one part of that company. However, I never worked very closely on any projects with any of the pro audio guys, except that we shared a transducer engineer (Who also develops transducers for REVEL). Stadiums and studios are very different than cars. It isn't fair for you to assume that because one of the brands owned by my former employer uses a design goal that doesn't apply to cars that my 30 years of experience in cars is somehow not valuable.
> 
> I'm dismissive of phase because we developed a phase EQ FOR CARS and the benefit was miniscule. So small as to not be audible to anyone who listened to it.
> ...


I may be out-of-my-mind, but I'm not stupid; I would never say that 'your 30 years of experience in cars is somehow not valuable.'

But I *am* saying that loudspeakers without phase shift at the xover point do three things:

1) To me, they tend to be the speakers that image the best. Is that due to the xover, or something else? Unknown. My money is on the xover.
2) It is undeniable that these designs are commercially successful. If you look at a copy of Stereophile from twenty years ago, you will see a lot of brands that have gone kaput. Mach 1 Acoustics, Apogee, Clearfield Audio. But Dynaudio, Thiel, and Vandersteen keep chugging along, and every one of them use first order crossovers. The only exception to this rule is Dunlavy. But I'll give Dunlavy a pass, because he died. It's challenging to build speakers from the grave. Thiel will be celebrating their fortieth anniversary in two years; that's quite an accomplishment in an industry where companies rarely last ten years.

If I really wanted to get crazy with the statistics, it would be interesting to see if there's a correlation between the use of first order crossovers, and the longevity of a loudspeaker manufacturer. But I digress...

3) Don't let anyone find out, but I actually don't listen to audiophile recordings. *I basically listen to podcasts and EDM.* To my ears, first order filters are more intelligible in the midrange. Basically voices sound closer to a human being; the phase shift in high order crossovers creates a ringing that's readily audible on male voices. Put a blindfold on me and play thirty seconds of Johnny Cash and I can tell you if the crossover is first order or not.
EDM uses a lot of studio effects, and the imaging of first order xovers is readily noticeable.





Here's the thing I find so mystifying about the debate about phase. There are three camps. Some say it is inaudible. Some say it is audible. Most seem to fall somewhere in the middle; they say "yes it's audible, but the effect is miniscule."


So here's the thing I don't get: if we agree it's audible, why not optimize for it? There are SO MANY things in audio that are demonstrably inaudible, yet people fetishize over them. Study after study has shown that differences between amplifiers are inaudible, yet amp threads get 50,000 hits. I come out and say that I think phase is important, and everybody acts like I just kicked their dog


----------



## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> OK. So I read the whole thread.
> 
> There's a big difference between the room in which you listen to your Vandersteens and the inside of your car. Nowhere is this more apparent than in viewing an impulse response measurement of any single driver in a big room (like your living room) and in the car.
> 
> ...


Waveguides.


I really need to get my Mazda finished and give you a demo.

It's doing some things that I don't think people have heard before. I was totally bummed that I blew up a midrange before the MECA show.



Basically with a waveguide we can get the car 'out of the equation' for the first millisecond or two. According to Haas, *the imaging cues are formed in the first 0.62ms.*


IMHO, the Haas effect is the reason that you see all of these winning cars using the same formula: midrange and tweeter very close together, mounted at eye level, with DSP delay to get the drivers aligned as tightly as possible. It is basically a recipe for a loudspeaker that can pass the Haas test. I am taking a step further by wrapping the drivers in a waveguide (thank you JBL) and also flattening the phase.


----------



## sqnut (Dec 24, 2009)

I'm glad the thread is up and running again considering I brought it to a grinding halt



Patrick Bateman said:


> Basically with a waveguide we can get the car 'out of the equation' for the first millisecond or two. According to Haas, *the imaging cues are formed in the first 0.62ms.*
> 
> 
> IMHO, the Haas effect is the reason that you see all of these winning cars using the same formula: midrange and tweeter very close together, mounted at eye level, with DSP delay to get the drivers aligned as tightly as possible. It is basically a recipe for a loudspeaker that can pass the Haas test. I am taking a step further by wrapping the drivers in a waveguide (thank you JBL) and also flattening the phase.


We need to hear 0.62ms of direct sound before the first reflection hits us, that allows us to accurately lock location cues and hence imaging. In a room that is not an issue. IIRC in a room the distribution of sound between direct, early and late reflections is something like 20%/40%/40%. I'm not sure and maybe Andy can confirm this, but in a car the direct sound would probably be in single digits. Everything else is early reflections. 

Early reflections arriving 0.2-1ms from direct sound makes the location cues (imaging) fuzzier. I think no matter where you mount the waveguide its hard to imagine getting a 1-2ms delay between direct and reflected sound. You're essentially saying that with waveguides there are no reflection points 17-20cm from both the waveguide and your ears. That is tough to imagine.

Reflections from 1ms-25ms are largely ignored by the brain for any location cues, BUT the brain perceives the direct sound as 'louder'.


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> I'm glad the thread is up and running again considering I brought it to a grinding halt
> 
> 
> 
> ...


A waveguide doesn't eliminate reflections off of the floor, the ceiling, the side windows. *But it attenuates them a great deal.*

It would be great if we could knock them down by 20dB, and that *is* possible with a dipole, but even 6dB of attenuation is enough to make it seem like we're no longer in a car.


















Here's how the sound radiates from something like Gary's Mercedes.
This is simulated at the crossover point, which I assume is somewhere around 3khz.
In the sim, we see that the two drivers are radiating. *the reflection off of the back wall (aka the windshield) is basically nil because the drivers are flush.* This is what I was talking about in the thread titled 'Everything Counts in Large Amounts'

Note what happens when the sound is reflected; *the angle doesn't really matter. Wherever the sound hits, there is a reflection.*


















When you stick a waveguide in front of your speaker, the energy that would normally get reflected off of the walls is reflected off of the walls of the waveguide. Designed carefully, those early reflections merge with the initial wavefront, and the waveguide seems to "disappear." All horns are not created equal, and some horns don't pull off this trick. The ones that don't have bad imaging; this is caused by re-radiation off of sharp edges and rapid transitions in the horn.


In the radiation, note how the reflection off of the back wall is MUCH worse than off the sidewalls. *This is a feature of waveguides; they are directional, you can point them to maximize the SPL in a specific location.*


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> *A waveguide doesn't eliminate reflections off of the floor, the ceiling, the side windows*. But it attenuates them a great deal.
> 
> It would be great if we could knock them down by 20dB, and that *is* possible with a dipole, but even 6dB of attenuation is enough to make it seem like we're no longer in a car.


Precisely, since we will always have reflective surfaces ~ 10" from your ears, the directivity of the waveguide (even if placed to give an unblocked path to your ears) is not helping in resolving the 0.2-0.6ms period between direct and reflected sound. The effect of attenuating the reflected energy gives you a sense of space, sure.

What is helping a LOT is the thick dashmat like cover on everything in Garys car. A nice 1.5cm thick covering will cut the energy of reflections 5khz and up. This takes care of the 0.05ms-0.2 ms zone. 0.625ms is 1600hz and to cut these reflection, the absorbing material needs to be over two inches thick. The attenuation of the 5Khz+ reflections by itself will make a huge difference in terms of space.

I agree with you that while you cant eliminate reflections you can absorb the reflective energy to a point where you can hear a big difference.



Patrick Bateman said:


> When you stick a waveguide in front of your speaker, the energy that would normally get reflected off of the walls is reflected off of the walls of the waveguide. Designed carefully, those early reflections merge with the initial wavefront, and the waveguide seems to "disappear." All horns are not created equal, and some horns don't pull off this trick. The ones that don't have bad imaging; this is caused by re-radiation off of sharp edges and rapid transitions in the horn.
> 
> 
> In the radiation, note how the reflection off of the back wall is MUCH worse than off the sidewalls. *This is a feature of waveguides; they are directional, you can point them to maximize the SPL in a specific location.*


All the HLCD I have heard in a room, a car or even pro audio, had this signature sound. There is something about the 500-2khz range done by a horn. It's just very, very different. I think this timbrel change is linked to the summing of the direct and reflected sound ~6khz and up in the mouth of the horn. Then the car's environment takes over.


----------



## 14642 (May 19, 2008)

Yes, waveguides help to eliminate the reflections from the adjacent boundaries. Those cause 
image spread. 

Now back to the phase thing. Is the suggestion that making a speaker in a box with an anechoically measured response and then transporting that speaker and its crossover to the car is the right way?

Or, are you suggesting that the speakers should be measured in their locations and a crossover developed from that set of measurements?


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> Precisely, since we will always have reflective surfaces ~ 10" from your ears, the directivity of the waveguide (even if placed to give an unblocked path to your ears) is not helping in resolving the 0.2-0.6ms period between direct and reflected sound. The effect of attenuating the reflected energy gives you a sense of space, sure.
> 
> What is helping a LOT is the thick dashmat like cover on everything in Garys car. A nice 1.5cm thick covering will cut the energy of reflections 5khz and up. This takes care of the 0.05ms-0.2 ms zone. 0.625ms is 1600hz and to cut these reflection, the absorbing material needs to be over two inches thick. The attenuation of the 5Khz+ reflections by itself will make a huge difference in terms of space.


Your statement in the first paragraph is based on the idea that all reflections are bad. This is not true. *If the reflective surface is within 1/4 wavelength, and the shape is right, the reflected energy is reflected right back into the initial wavefront.*









^^ watch the video I made. See how the wavefront hits the walls, but integrates with what's going down the center of the waveguide? *This is the key. This is the reason that people listen to modern studio monitors and say "I didn't know that horns could image. These don't sound like the horns I had in the 80s."* 

















It's the reason that pro speakers changed from the first pic, to the second pic. It's the reason that waveguides like the second pic are basically the 'default' now, when ten years ago the first type was the norm.









Here's a frequency response measurement and phase measurement of one of my Synergy horns. The phase isn't perfect - the crossover needs some refinement - but you can see that it's doesn't have the massive rotation you get with a high order xover. So what I'm arguing here isn't academic; here's a phase and frequency response done by yours truly.









For comparison's sake, here's the frequency response and phase of a JBL Control Now loudspeaker (red) and a Vandersteen (blue.) *See how the phase of the Vandy doesn't have that big rotation at the xover point?* Both are smoother than my design, because direct radiator simply have smoother response than compression drivers.





TLDR: A properly designed waveguide takes the energy that would normally get reflected off of the walls, and it focuses it back into the initial wavefront. Similar to how headlights work on a car. We can't get flat phase with an old-school horn, but with a modern waveguide, we can.





sqnut said:


> I agree with you that while you cant eliminate reflections you can absorb the reflective energy to a point where you can hear a big difference.
> 
> 
> 
> All the HLCD I have heard in a room, a car or even pro audio, had this signature sound. There is something about the 500-2khz range done by a horn. It's just very, very different. I think this timbrel change is linked to the summing of the direct and reflected sound ~6khz and up in the mouth of the horn. Then the car's environment takes over.



The reason that car HLCDs sound wonky is because of pattern flip.
The sound of pattern flip has always been irritating to me, and it's one of the reasons that I run midbass arrays.
Basically the wavefront from car HLCDs is assymettrical, while the wavefront from a circular driver is symmetrical. At the xover point the difference in wavefronts means that the response on-axis will be different off-axis.


Ever read reviews of planar speakers in Stereophile, and they talk about how it's hard to integrate a conventional woofer with a planar? Yep, same problem : pattern flip.


----------



## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Yes, waveguides help to eliminate the reflections from the adjacent boundaries. Those cause
> image spread.
> 
> Now back to the phase thing. Is the suggestion that making a speaker in a box with an anechoically measured response and then transporting that speaker and its crossover to the car is the right way?
> ...


When measuring phase, as soon as we get a major reflection, it's going to pollute our phase measurement. For instance, if I am measuring a speaker 3' off the ground, the 'bounce' off the ground is going to determin how low in frequency that I can measure phase.

Due to that, *I'm only focused on getting the phase flat from about 500hz to 13,500hz.* I'd love it if I could get it to work down to 100hz, but the dimensions of a car are simply too small to make that realistic.

My measurement method goes like this:

1) All of my waveguides use a boundary in the car to extend the waveguide. Ideally I don't want *anything* between the diaphragm and my ear; that's why speakers on the dash sound better than speakers under the dash; the steering wheel and the driver mess up the phase and frequency response.
2) I measure frequency response and phase outside, and optimize it for 500hz-13,500hz
3) Then I put it in the car. Generally if it measures well anechoically, it will sound good in-car. Occasionally I have to apply a little EQ, and *yes* I understand that EQ will change the phase.


Synergy horns are kind of unique in this respect, that we have the entire front stage on a single waveguide. It would be difficult to replicate this trick with direct radiators, unless you built a replica of the dash and measured that outside.


----------



## ErinH (Feb 14, 2007)

Patrick Bateman said:


> When measuring phase, as soon as we get a major reflection, it's going to pollute our phase measurement. For instance, if I am measuring a speaker 3' off the ground, the 'bounce' off the ground is going to determin how low in frequency that I can measure phase.
> 
> Due to that, *I'm only focused on getting the phase flat from about 500hz to 13,500hz.* I'd love it if I could get it to work down to 100hz, but the dimensions of a car are simply too small to make that realistic.


A word of caution…
While the floor bounce mitigates you typically to the only 3ms or so of quasi-anechoic data, the resolution is important. *At 3ms, your resolution in data is 333hz intervals.* At 10ms you have 100hz intervals. At 20ms you are measuring down to 50hz intervals. Now, imagine what this is doing to your lower frequency accuracy when you only have 333hz resolution. Naturally, the more resolution you have, the more accurate the data. If you have 333hz resolution then you have 333, 666, 999hz, etc as your data points. What happens if there’s a high Q peak at 800hz? Your data isn’t going to show that. This is why anechoic measurements are still performed. For the rest of us in the hobby of measuring and providing data, we just live with this tradeoff (and typically will perform NF/FF merges, even though that has it’s own set of issues). 

Point: Be careful of how explicitly you trust your data when it’s gated to 3ms impulse.





Patrick Bateman said:


> My measurement method goes like this:
> Generally if it measures well anechoically, it will sound good in-car.


This is the same rationale I used when I went with the Kefs in my car. The notion that power response is critical and in a reflective environment what you want for timbre is to have the reflected sound “play nice” with the direct sound. IOW, smooth polars and no dip at the crossover in power response will result in a replicated reflection that won’t differ from the initial (direct) sound. It’s the same thing Toole/Linkwitz/et al have been saying for years. It just took me a while to really bite. I actually did measure mine on my test baffle and came up with a crossover that worked well on that large 4x2’ baffle. 

This is even more key in installs where the aiming axis is not on-axis with the listener and therefore there would be no ‘direct’ sound in this instance. The more alike the response in all axes is, the less difference there is between reflected sounds and less marring of things like timbre. I’d also say that this plays a significant role in soundstage as well, though, my readings have found this stated otherwise (wish I could talk with these authors to understand any caveats).

Now, with that said, my answer to Andy’s question is:
It would depend. First and foremost, there is no way to replicate the car environment easily. I’m NOT talking about reflections - building angles out of wood and cardboard to simulate the windshield or dash - but the placement and aiming of a midrange on a dash and a tweeter in a corner, or some other car install. If we concede that power response is key then the next step is to determine what spacing and crossover network is necessary to achieve the desired response (assuming you have good drivers that don't have their own issues). But, good luck replicating your car install outside of the car. I think your only real option is to measure the response (spatially averaging) in the car and play with different settings. 

Luckily, for me, it’s easier: the concentric design keeps the tweeter and mid at the same location so there is no physical separation and/or aiming difference to account for. Of course, I’m still honestly not sure how well anechoically measuring the response is and plopping that in to a car is. In my case, I adjusted the network to optimize it as best I could and then used that same network in the car. I think it works very, very well. There’s slight left/right imbalance but it’s very minimal compared to my previous setups. But, again, I think that has more to do with the whole than the single sum. The driver itself is superb and it’s really hard to screw it up (though, it can be done… trust me ).


----------



## Patrick Bateman (Sep 11, 2006)

bikinpunk said:


> Luckily, for me, it’s easier: the concentric design keeps the tweeter and mid at the same location so there is no physical separation and/or aiming difference to account for. Of course, I’m still honestly not sure how well anechoically measuring the response is and plopping that in to a car is. In my case, I adjusted the network to optimize it as best I could and then used that same network in the car. I think it works very, very well. There’s slight left/right imbalance but it’s very minimal compared to my previous setups. But, again, I think that has more to do with the whole than the single sum. The driver itself is superb and it’s really hard to screw it up (though, it can be done… trust me ).












The JBL Control Now was a speaker that really got me thinking about this. The idea that you could get almost everything right, but ruin a design with a poor choice of crossover slope. It does SO MANY things right:
1) it's efficient
2) it's smooth
3) it's dynamic

*But it just doesn't image. At all.*










And when I look at that measurement, of the Vandy (blue) versus the JBL (red), my main take away is that there's a huge phase rotation right in the midle of the midrange, due to the steep crossover from midrange to tweeter. I'm not convinced that the phase has to be perfectly flat, but the JBL has a MASSIVE phase shift, at a frequency where we're insanely sensitive to problems. 180 degrees of shift in the octave from 1250hz to 2500hz. I'm not saying that all high-order xovers are bad, but putting the xover right in the octave where we're sensitive to it isn't a good idea IMHO.









This is my Vandersteen btw. Felt on the tweeter for diffraction reduction, minimum baffle for diffraction reduction, first order xovers to achieve flat phase.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> Your statement in the first paragraph is based on the idea that all reflections are bad. This is not true. *If the reflective surface is within 1/4 wavelength, and the shape is right, the reflected energy is reflected right back into the initial wavefront.*


Well with 99.9% of installs reflections are bad and absorbing a chunk of them 5K and above cleans up the 0.05-0.3ms for a start. Just doing this will make the space you're listening in seem larger. Even though you're only getting the direct sound for only half the desired time. Realistically this is about the best that you can do. In theory I see that adding a waveguide to this would help push the 0.3 closer to the 0.6 point, but now we have created another problem while trying to solve this one, that of trying to blend two different wave fronts, as you explained. 



Patrick Bateman said:


> Here's a frequency response measurement and phase measurement of one of my Synergy horns. The phase isn't perfect - the crossover needs some refinement - but you can see that it's doesn't have the massive rotation you get with a high order xover. So what I'm arguing here isn't academic; here's a phase and frequency response done by yours truly.
> 
> 
> 
> ...


Yes but the corkscrew is taking place 45db down. 



Patrick Bateman said:


> The reason that car HLCDs sound wonky is because of pattern flip.
> The sound of pattern flip has always been irritating to me, and it's one of the reasons that I run midbass arrays.
> Basically the wavefront from car HLCDs is assymettrical, while the wavefront from a circular driver is symmetrical. At the xover point the difference in wavefronts means that the response on-axis will be different off-axis.
> 
> ...


Pattern flip. Just learned a new term, thanks for explaining it. You would rather try and combine sound waves with different wavefronts even though it has audible artifacts, as long as you think you're getting closer to the mirage of flat phase in a car.


----------



## Patrick Bateman (Sep 11, 2006)

1) the shift in phase, aka 'corkscrew' isn't happening at 45dB down. It's happening at full volume, where the two drivers meet. SPL is measured in decibels, phase is measured in degrees. The phase scale is on the right hand side of the graph, the SPL level is on the left.

2) To attenuate down to 5khz with a dash mat, you'd need one about 3/4" thick. Most of the ones I've seen are thin felt about 1/4" thick. They won't do much outside of the very top octave. Plus, they do nothing to treat the windshield. By far the easiest and simplest way to deal with the reflections off the dash and windshield is with a dipole or cardioid, but waveguides are a close second. It doesn't take much of a waveguide to get down to 5khz; in fact it's less than 3" wide.

3) Pattern Flip is A Thing. That's why my waveguides are generally symmetrical, or close to it. Pattern Flip isn't a problem if you keep the vertical and horizontal dimensions relatively similar. For instance, you won't hear patter flip with a 6"x9" radiator, but with a 16" x 2" you will.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> The JBL Control Now was a speaker that really got me thinking about this. The idea that you could get almost everything right, but ruin a design with a poor choice of crossover slope. It does SO MANY things right:
> 1) it's efficient
> 2) it's smooth
> 3) it's dynamic
> ...


IMHO speakers that don't image well in a normal room normally have a timing issue. The phase angle is largely down to timing. In addition to shallow slopes on your Vandys notice how with you in your sweet-spot the woofer / mid and tweet are at different distances from your ear.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> 1) the shift in phase, aka 'corkscrew' isn't happening at 45dB down. It's happening at full volume, where the two drivers meet. SPL is measured in decibels, phase is measured in degrees. The phase scale is on the right hand side of the graph, the SPL level is on the left.


You're right I'm not sure why my brain started thinking 45 db down:blush:. There is a 360deg twist at 3khz a typical 4th order slope. Since we hear phase shifts in our response we can eq an octave above and below 3khz to mitigate this. 



Patrick Bateman said:


> 2) To attenuate down to 5khz with a dash mat, you'd need one about 3/4" thick. Most of the ones I've seen are thin felt about 1/4" thick. They won't do much outside of the very top octave. Plus, they do nothing to treat the windshield. By far the easiest and simplest way to deal with the reflections off the dash and windshield is with a dipole or cardioid, but waveguides are a close second. It doesn't take much of a waveguide to get down to 5khz; in fact it's less than 3" wide.


 Yes you would need to use something 3/4" thick which you could then cover to make it more aesthetic. For us dudes who don't use waveguides or dipoles etc and mount speakers on dash/pillars, reflections off the windshield are a fact of life. But the more you can absorb, the better it will sound while giving the perception of a larger space.


----------



## Hanatsu (Nov 9, 2010)

My my... Phase again 

Those who know me are probably aware of me disliking the idea of using swallow sloped filters within car audio. Using 4th order L-R acoustic slopes will align drivers perfectly in both magnitude and phase at the crossover if the drivers are time aligned towards each other. 

*As long as you EQ in a minimum phase region, you fix the magnitude and phase response at the same time with an ordinary EQ. 

*Absolute phase is inaudible.

*Swallow filter slopes will create combing in the frequency response in the passband where two or more drivers interact. That's audible and generally not a good thing.

*Swallow highpass filters decrease power handling

*Swallow lowpass filters needs to be placed several octaves below the beaming point so all drivers play within their optimal power response range

*Driver characteristics can't deviate too much from each other within the passband where they interact. 

*Home audio and car audio is different. Focus on the acoustic response and the distortion induced by the environment. I'm familiar with phaseEQ and I can say that it's only good for one thing - that's integrating drivers in the lower frequencies by altering phase other than the linear vs freq-way that T/A does. It can create some "interesting" illusions in terms of staging.

*Flat phase response is impossible to archive in a car.


----------



## sqnut (Dec 24, 2009)

Hanatsu said:


> My my... Phase again
> 
> Those who know me are probably aware of me disliking the idea of using swallow sloped filters within car audio. Using 4th order L-R acoustic slopes will align drivers perfectly in both magnitude and phase at the crossover if the drivers are time aligned towards each other.
> 
> ...


^^ thanks for summing it up:thumbsup:. My single biggest take away from a year and a half of tuning at 12db slopes all round was, that I needed an eq at 1/6 oct and 0.2db resolution to make shallow slopes work. In a car steeper slopes work fine.


----------



## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> <snip>
> *Flat phase response is impossible to archive in a car.












Not only is it possible, *it's not even difficult*

1) get your drivers within 1/4 WL at the xover.
2) use a first order xover

This isn't rocket science. Yes, Danley was a rocket scientist but you don't have to be one to get flat phase. Waeguides help because of the reflective environment of a car.

The important thing to realize is that you don't need to eliminate all reflections in the car... It's only the first fraction of a millisecond that counts, as far as imaging goes. *If you can clean up everything within 17cm, or so, that goes a long way.*


----------



## sqnut (Dec 24, 2009)

Patrick, your in car measurements are at speaker level or ear level?


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> Patrick, your in car measurements are at speaker level or ear level?


Ear level.










But it doesn't matter a whole lot. Here's a measurement of the $14 JBL constant directivity horn. Even 45 degrees off axis, the response shape is basically the same.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> [ *If you can clean up everything within 17cm, or so, that goes a long way.*


You need to clear stuff 17 cm from the driver *and* your ears. How do we do that in a car?


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> You need to clear stuff 17 cm from the driver *and* your ears. How do we do that in a car?


What's within 17cm of your ears?


----------



## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> Not only is it possible, *it's not even difficult*
> 
> 1) get your drivers within 1/4 WL at the xover.
> 2) use a first order xover
> ...


But that's not what I talk about. Even if you do that, the phase response will be nowhere to flat 20-20kHz, you're lucky if you can get 2 octaves somewhat "flat". The easiest way to prove this is by looking at the minimum phase part of the group delay. Anywhere it's not close to zero means that the area ain't minimum phase and every car is full of those areas. What I mean is that the environment screw phase so hard so it's pointless even trying to "fix" it, even if we did, phase is only audible in an area where two drivers interact. A sleep slope will make this passband very small and everything outside is not affected by the crossover.


----------



## sqnut (Dec 24, 2009)

The roof, driver window....


----------



## ErinH (Feb 14, 2007)

Hanatsu said:


> phase is only audible in an area where two drivers interact.


and that's because their summation = frequency response. so it's not the phase you're hearing, per se; it's the frequency response (magnitude+phase).


----------



## thehatedguy (May 4, 2007)

With horns and waveguides-

You can't have a shallow sloped acoustical crossover and have an electrical crossover component too. You can have a shallow electrical crossover slope. The electrical filter is going to combine with the already intrinsic semi-steep roll off of the acoustically loaded speaker at some point to produce a fairly steep final acoustical roll off.

And old school horns? I would think the conical horns used by Tom are the oldest of the oldest in terms of geometry.


----------



## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> What's within 17cm of your ears?


Reflections?


----------



## thehatedguy (May 4, 2007)

Erin (bikinpunk) is a rocket scientist by day


----------



## Patrick Bateman (Sep 11, 2006)

sqnut said:


> The roof, driver window....












THIS IS AMERICA, WE DON'T DRIVE TRABANTS

But seriously, the roof is about 25cm from my ears and the side of the car is about the same. Roof treatment helps, and rolling down the window helps too.

IMHO one of the biggest problems is the headrest.


----------



## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> But that's not what I talk about. Even if you do that, the phase response will be nowhere to flat 20-20kHz, you're lucky if you can get 2 octaves somewhat "flat". The easiest way to prove this is by looking at the minimum phase part of the group delay. Anywhere it's not close to zero means that the area ain't minimum phase and every car is full of those areas. What I mean is that the environment screw phase so hard so it's pointless even trying to "fix" it, even if we did, phase is only audible in an area where two drivers interact. A sleep slope will make this passband very small and everything outside is not affected by the crossover.


You live in Sweden right? Go listen to some Dynaudios and tell me phase doesn't matter.

It's trivially easy to fix two or three octaves, but personally my goal is to fix four:
625hz -1250-hz
1250hz - 2500hz
2.5khz-5khz
5khz-10khz

Fixing phase to 2khz isn't even hard.


----------



## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> You live in Sweden right? Go listen to some Dynaudios and tell me phase doesn't matter.
> 
> It's trivially easy to fix two or three octaves, but personally my goal is to fix four:
> 625hz -1250-hz
> ...


I don't say phase doesn't matter, I'm saying if you fix the frequency response, the phase will be fixed at the same time. In all areas except those which ain't minimum phase.

I've built several home audio speakers and made quite a few crossover designs. Nowadays I use active filters, all my drivers are crossed with 4th order L-R and I got among the best drivers you can get from Scan-Speak. I've only noticed a slight change in staging with shallow slope filters (very easy to test since I use a MiniDSP). Regarding DynAudio I don't find them to be very special, my favorite speakers before those I built myself was the B&W Nautilus 801. I believe (for home audio) that 'flat' frequency response is far more important than perfect phase coherency, but that's just my opinion. 

Here's a measurement of my car, non-EQed response:





There's like 1500deg phase shift. That due to the destructive interference of the environment. Even if it looks like crap, it sounds good and stage perfect.

I forgot to save the picture after EQ but it went down to 150-200deg phase shift between 100-2000Hz. My opinion is that it doesn't matter in this sense, the frequency response is the thing we should focus at.

The one things that's interesting with phase is that it doesn't matter how "off" it is as long as the other speaker that plays the same passband is just as "off". That's essentially the "absolute phase" I'm talking about. That is inaudible, there's several studies that can back that up


----------



## Patrick Bateman (Sep 11, 2006)

It looks to me that your gate is set wrong. Probably set the start of the gate too soon, and the end of the gate too late.









A high order xover will have a phase shift that looks like this JBL Control Now (red line.) 1st order has 90 degrees of phase shift, 2nd order 180, 3rd 270, and 4th order 360 degrees.









Here's another one showing a phase shift at the xover. (Not my measurement.) The phase shift seems to indicate an xover around 2khz.

Either the gate is wrong, or the mids and tweets are separated by a few wavelengths. For instance, with a 3khz crossover a distance of 34cm (13.3") would be equivalent to three wavelengths.

If it's the latter there isn't much you can do; can't phase align drivers that are seperated by more than about a third of a wavelength.


----------



## Hanatsu (Nov 9, 2010)

Nah, it's just one driver playing 

I don't gate the response in the car. We don't hear a 'gated' response. We hear the power response, the sum of all reflections. Of course it's easy to get a theoretical "perfect" phase display by doing quasi anechoic measurements but I don't see the point. Am I missing something?

Tapaaatalk!!


----------



## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> Nah, it's just one driver playing
> 
> I don't gate the response in the car. We don't hear a 'gated' response. We hear the power response, the sum of all reflections. Of course it's easy to get a theoretical "perfect" phase display by doing quasi anechoic measurements but I don't see the point. Am I missing something?
> 
> Tapaaatalk!!


You can't measure phase without a gate

Check out HolmImpulse, it shows you the frequency that your response is "valid" to.










For instance, in this measurement, the data is "valid" to 400hz. (See at bottom right?)

And I put "valid" in quotes, because Erin is correct, the granularity of the measurement improves as you use a longer gate. IE, the gate used above may be valid to 400hz, but a gate that's twice as long, or ten times as long, would be even better.

Of course, that's very very hard to do in a car, which is why I basically don't sweat any phase measurement below 500hz or so.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> THIS IS AMERICA, WE DON'T DRIVE TRABANTS
> 
> But seriously, the roof is about 25cm from my ears and the side of the car is about the same. Roof treatment helps, and rolling down the window helps too.
> 
> IMHO one of the biggest problems is the headrest.


Growing up, I was surrounded by Trabants and Volgas, the daily ride is a plain jane Fiesta. So I measured, I'm 6'2" with the seat pushed back my ears are 8" from my the roof and my right ear is 4" from the B pillar. Windows down is not an option when it's 44/112. What headrest? Been driving around for 5 years with no headrests. Will have to buy a pair when I sell the car. If you hang around long enough in this hobby, chances are you're slightly cuckoo and OCD stricken.


----------



## Patrick Bateman (Sep 11, 2006)

44 degrees? OMG

Did you see the pic of what Gary did to his B Pillar?


----------



## Patrick Bateman (Sep 11, 2006)

Here's an interesting article about phase.
I'm generally using an iPad or a Nexus as a source, and it looks like some of these devices may wreck the phase response:

Fun with Phase – iPod vs iPhone « Synergetic Audio Concepts

The author also wrote some free tools that can measure and determine whether your device is screwing up the phase.


----------



## thehatedguy (May 4, 2007)

I just don't know how to get true 6 dB acoustic slopes especially with a horn or waveguide. It would require notches and probably multiple cascaded filters to shape the response at different frequencies...I know (or have a really good idea I should say) that is how Danley is doing them on his horns. You would want some shunt to ground at the outer edge of each passband to physically keep the driver from playing for protection...that I know Tom does and I have simmed a few crossovers like that but never built them because I at that time had never seen anyone else do that and didn't know it would work or blow my amp up.


----------



## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> I just don't know how to get true 6 dB acoustic slopes especially with a horn or waveguide. It would require notches and probably multiple cascaded filters to shape the response at different frequencies...I know (or have a really good idea I should say) that is how Danley is doing them on his horns. You would want some shunt to ground at the outer edge of each passband to physically keep the driver from playing for protection...that I know Tom does and I have simmed a few crossovers like that but never built them because I at that time had never seen anyone else do that and didn't know it would work or blow my amp up.


Tom isn't using first order xovers.
He sent me an email describing how he does it, but I don't want to post it as I figure it's a trade secret.

The LeCleach method is similar, but different, and the whole reason I posted this thread was to publicize that there's a way of flattening the phase that doesn't require first order filters.









^^ This phase response was achieve with a single capacitor. That's the whole crossover, one cap.

So it's surprisingly easy to achieve.

This is one of the 'neat' things about getting your mid and tweet really close together. EVERYTHING gets easier. Less comb filtering, easier to get the phase right, easier to get the frequency response right.


IMHO, Bill Waslo has probably built the most faithful replica of a Synergy xover, and Bill was *also* using a minimal xover. In his case, he was using two components on the tweeter, not one.



To tell the truth, the main challenge with my Synergy xovers is the midrange taps. If your midrange taps are 'off' by half an inch, then you can't get the phase to sum properly. So if you get the location wrong (and you usually do), you have to either rebuild the horn, or use DSP to delay one driver. VTC does the latter in their Synergies.


----------



## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> You can't measure phase without a gate
> 
> Check out HolmImpulse, it shows you the frequency that your response is "valid" to.
> 
> ...


Yes. I'm aware of that but my point is that we don't hear the "gated response". It's like measuring a driver 5cm from the cone and saying, both the magnitude and phase response is flat. Well, it won't be at listening position. Since the FR change, phase change along with it. If the excess group delay remains close to zero, all issues will be resolved by having an ordinary EQ, phase will "follow" the frequency response. I still don't understand what's wrong with a 4th order L-R filter, it sums perfectly at the crossover point.

Can we conclude that absolute phase is inaudible? (Which means if all drivers have the SAME phase response, it won't matter how much the phase is off, well until it affects the group delay enough, at least). The conclusion I draw from this is that phase only matters when it differs from driver to driver and most in the ITD range of our hearing. In the lower frequencies we use relative phase shifts to steer the image, as the wavelengths get smaller we lose the ability to hear phase differences, even relative ones. In the IID range, the only effect the phase will have is on the actual magnitude response (which is used to steer the image in the highs). 

As far as I understand you are arguing that absolute phase is audible. I say it's not. If a crossover inserts a delay big enough to impact group delay by a significant amount it might very well be audible. A 4th order LR filter introduces like 0,5ms of group delay, which still is inaudible in any frequency range. 



> Dr. Floyd Toole:
> "It turns out that, within very generous tolerances, humans are insensitive to phase shifts. Under carefully contrived circumstances, special signals auditioned in anechoic conditions, or through headphones, people have heard slight differences. However, even these limited results have failed to provide clear evidence of a 'preference' for a lack of phase shift. When auditioned in real rooms, these differences disappear ..."


This site is the best explanation I've seen so far:

Phase, Time and Distortion in Loudspeakers


----------



## Regus (Feb 1, 2011)

Patrick Bateman said:


> 2) It is undeniable that these designs are commercially successful. If you look at a copy of Stereophile from twenty years ago, you will see a lot of brands that have gone kaput. Mach 1 Acoustics, Apogee, Clearfield Audio. But Dynaudio, Thiel, and Vandersteen keep chugging along, and every one of them use first order crossovers. The only exception to this rule is Dunlavy. But I'll give Dunlavy a pass, because he died. It's challenging to build speakers from the grave. Thiel will be celebrating their fortieth anniversary in two years; that's quite an accomplishment in an industry where companies rarely last ten years.
> 
> If I really wanted to get crazy with the statistics, it would be interesting to see if there's a correlation between the use of first order crossovers, and the longevity of a loudspeaker manufacturer.


Actually IMVHO it's not crazy - in fact what we really need to establish is whether there is a causal link (as opposed to a correlation) between commercial success/longevity and the use of first order crossovers - some form of meta-analysis perhaps.

Sounds like something an electronic engineering student working on acoustics could write a thesis on...


----------



## Rybaudio (May 23, 2008)

The task of a crossover is not simply to sum at a single point in space - speakers put out entire sound fields and any time you are listening in an enclosed space you will hear the entire sound field in the form of reflections and reverberation. When you consider the sound field put out by a pair of non-coincident speakers, the LR crossover is almost always superior to the first order option.

If you were summing two signals electronically, sure, a 1st order crossover gets the phase and amplitude right. That might also work if you have a unity horn or coaxial driver with the tweeter inside the voice coil of the woofer. 

But typically you are dealing with two sources that are non-coincident and their center to center distance is significant at the crossover frequency. What this means is that as you move around the sound field, the path length differences between the two sources varies, and the variation is large enough to correspond to 180+ degrees of phase (some points sum perfect, some points cancel).

Take a 6.5" woofer crossed to a 1" dome at 2 kHz. The center to center spacing here is at least 3.75." A 2 kHz wave has a wavelength of around 6", so a 3" path length difference will give 180 degrees of phase difference. At 90 degrees off-axis vertically (thinking of them in a bookshelf), we are at 3.75" path length difference, so even if you get them summing perfectly on-axis, there is going to be a big null at a bit under 90 deg off-axis. If the summation is not perfect on-axis, the null will occur closer to on-axis.

That was a fairly optimistic example - the numbers are often worse. The point is that having both drivers playing at the crossover is not generally a good scenario from the perspective of the sound field generated. The combination is usually more directive than the individuals, and if the center to center spacing is large, you get nulls and side lobes. 

The steepness of the filter determines the size (in frequency) of the region over which this happens. The steeper the filter, the smaller the region. Steeper filters also have more complexity (especially if doing passively) and group delay so there is a trade-off.

The question is if that group delay is audible and how bad it is. If you take a few music samples and send them through an LR4/LR8/LR16 filter (send through HP, LP, and then sum the two) and try to hear a difference, I think you will be hard pressed to hear anything until you get to a fairly high order. If you have access to matlab, you can pull music in, do the processing, and rewrite as a wav file to compare on whatever playback system you choose. Maybe with specialized program material you can hear a difference, but even then, it's generally not that objectionable. OTOH, if you try running those samples through filters that have dips in the response at the crossover frequency, those are clearly audible. This isn't an entirely fair comparison because it's spatially dependent in the physical system and you hear the entire sound field not just one point, but I feel it at least gives you an idea of the audibility of using the phase shift involved in the crossover.

A LR crossover, which is simply two even order Butterworth filters cascaded, has special properties. First, the phases of the high and low-pass sections align at all frequencies, so if no additional shifts are present, the outputs will sum coherently at all frequencies through the crossover region. This means that as you move away from on-axis, you will not get any peaks in the off-axis responses - they will only drop. It's far more offensive to have a reflection with a 3 dB bump in it than a 3 dB dip, so this is a good thing. Some people have commented that this subjectively makes the sound more "coherent" and I agree, although I don't really have any data to back it up. The second property of the LR crossover is that it sums flat. So on-axis (or same PLD), two sources crossed over LR will sum flat, and if the path lengths change (say off-axis), there will not be any bumps.

Even order Butterworths have the same phase property, but they sum to +3 dB at the crossover frequency since each source is only down 3 dB. Nobody wants a 3 dB bump in the response at the crossover frequency. Odd-order Butterworths sum flat, but they are not in-phase at the crossover frequency, so as you go off-axis you get a 3 dB peak at some angle where the phases align. From a polar point of view, the main lobe is actually tilted at the crossover point. People doing MTM have used that property to cheat a little but in general it is not a good thing.

First order crossovers are shallow-sloped and in the odd-order butterworth category. What does that mean? Basically it means they suck balls at everything except making a single axis phase perfect. If you sum them flat on-axis they are each - 3 dB at the crossover frequency. That means as you move to other parts of the sound field you get peaks of 3 dB and big nulls, and further, these occur over very large frequency ranges. From a sound field perspective, they are a disaster both in frequency response magnitude and phase. On-axis they may sum fine and be phase coherence, but you don't just hear on-axis, you hear the entire sound field in the form of reflections, reverberation, etc.

There's also the issue of power handling, and realizing the filters in practice since most drivers roll off at at least 12 dB/oct below the cross point. Generally speaking, first order crossovers are just not a good option. You end up trading off huge losses for trivial gains. The exception may be coincident drivers if power handling is not an issue. An LR4 crossover has good properties and group delay that is at best maybe audible.


----------



## Rybaudio (May 23, 2008)

^ pardon the novel

TL/DR: first order no good


----------



## Rybaudio (May 23, 2008)

Patrick Bateman said:


> 1) get your drivers within 1/4 WL at the xover.


I agree that would work although you can still get a peak off-axis. However, this is a nontrivial requirement that is not generally met in practice. Let's look at some quarter wavelength numbers:

500 Hz 6.8"
1 kHz 3.4"
2 kHz 1.7"
3 kHz 1.1"

Given these have to be center to center spacing, this is not possible under most circumstances.


----------



## ErinH (Feb 14, 2007)

I read. Great post. Though, I honestly have the feeling that it'll get lost in the shuffle. Hopefully I'm wrong.


----------



## Patrick Bateman (Sep 11, 2006)

Rybaudio said:


> I agree that would work although you can still get a peak off-axis. However, this is a nontrivial requirement that is not generally met in practice. Let's look at some quarter wavelength numbers:
> 
> 500 Hz 6.8"
> 1 kHz 3.4"
> ...


To me, that's one of the mysteries about first order xovers: the fact that they measure poorly off axis *if the drivers are spaced more than about 1/3wl apart* but the speakers still sound good.

But on axis? *As long as you're within one wavelength you can get flat response.*

If you follow *that* rule of thumb, things get easier:

2 kHz 6.8"
3 kHz 4.5"

This is what 90% of the companies do. (Dynaudio, Thiel, Vandersteen, Spica, etc.)

Danley is an oddball, because the drivers are so tightly spaced. Kef and TAD use tight spacing but they do not use first order xovers.

































Here's the frequency response, step response and xover points of a TAD CR1. You can see that the drivers aren't in phase.

















Same battery of tests, but from the KEF RS50. One thing I notice about the Kef is that they've optimized for phase over frequency. The step response isn't ideal, *but it is better than the TAD.* 


I have heard both speakers, and one thing that mystified me about the Kef was how it costs a fraction of what the TAD costs, but in many ways I preferred it. Maybe I have my answer here.


----------



## Patrick Bateman (Sep 11, 2006)

Actually I may have answered my own question:

Loudspeakers with first order xovers measure terribly off axis *if the drivers are spaced more than about 1/3WL apart.*

BUT...










The reason this happens is due to pathlength differences. For instance, if you have a midrange crossing over to a tweeter at 3khz, and you're six inches off axis, *that's a full one and one quarter wavelength out-of-phase.* This is what causes the comb filtering; it's pathlength differences.

High order xovers minimize this, because you simply have much less overlap between the drivers. Even half an octave above the xover point you have about 12dB of attenuation with a LR4 xover.



But the thing I didn't consider; and the reasons that my Vandersteens sound great off-axis; is that the pathlength differences only happen when you stand up. As long as your ears are on-axis with the midrange and tweeter there's isn't a pathlength difference.




TLDR: horizontal arrays with low-order xovers and one wavelength spacing is A Bad Idea. Vertical arrays with low order xovers and 1WL spacing sounds fine to me. YMMV


----------



## Regus (Feb 1, 2011)

I've just come up with an interesting (to me at least) experiment which could be performed, which would draw on the threads by Hanatsu (on measuring your system) and Bikinpunk (essentials of SQ) and hopefully address some of the points raised on crossovers and acoustic response - it's probably been done before, but it could be good to add some objective data to the subjective impressions on the effects of phase on SQ. I will post more on it later, once I have gone through it again in my head, so people can comment on it and refine it, if necessary - Patrick _et al._ let me know if it needs to be a separate thread or whether you are happy to keep it in this one.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> 44 degrees? OMG
> 
> Did you see the pic of what Gary did to his B Pillar?


Could sure do with some temperate Cali weather! Checked out a couple of the videos but didn't get a clear view of the B pillar treatment.


----------



## TOOSTUBBORN2FAIL (Jan 31, 2011)

Last time I remember, I "think" he had a thick felt covering them. I know multiple surfaces in his car were covered in the stuff last time I saw it.




Careful what you wish for^. Its only temperate in socal. Here in central cal it will be over 100 this week, and the worst drought since records were kept.


----------



## Patrick Bateman (Sep 11, 2006)

TOOSTUBBORN2FAIL said:


> Last time I remember, I "think" he had a thick felt covering them. I know multiple surfaces in his car were covered in the stuff last time I saw it.
> 
> 
> 
> ...


Last night I ordered twelve square feet of pressed felt:

F26 SAE Pressed Wool Felt Plain 72" Wide | eBay

Will probably do the same thing to my car.


----------



## ErinH (Feb 14, 2007)

I tried roxul in the pillars. that was a mess. I think it may have worked... I don't really know anymore. but it was the full 2" thick stuff and it was right above and down the pillar where the mid/tweeter were located.

Gary also has some foam (or he did at MECA Finals 2010) on his door panel. I asked him about it and he said it helped resolve a reflection there. I'll let him talk about it since it's his car.


----------



## garysummers (Oct 25, 2010)

The pictures show the current state of the benz interior. I sometimes experiment with foams and felt on different surfaces to see what can be done to remove some of the unwanted reflections. Sometimes it works others not!
The "b" pillars have felt on them at ear level covering the hard plastic surfaces(sorry no photo). The entire dash is tightly stuffed with foam to remove any resonance.
These worked!


----------



## Patrick Bateman (Sep 11, 2006)

this dude is not ****ing around : Making Acoustic Panels


----------



## quietfly (Mar 23, 2011)

Damn...


----------



## ErinH (Feb 14, 2007)

The real question there is... How much was really necessary and how did he go about determining what he needed? IOW, did he do it "right". I will say, the air gaps he has makes me think he knew what he was doing... Most people have no idea about those and fewer have any idea why they're used (and it what configuration makes the most sense to use them). 

I see a LOT of posts on home audio forums where people slap up panels but they have no rationale why other than they thought they should. 


I'll actually be building some panels for my HT soon but I have to measure the room first. I'll be posting all the info in my build log to hopefully illustrate that it's not just something you throw on a wall.


----------



## Orion525iT (Mar 6, 2011)

garysummers said:


> I sometimes experiment with foams and felt on different surfaces to see what can be done to remove some of the unwanted reflections. Sometimes it works others not!


I have several sheets of various thicknesses acoustic foam that I moved around my car. I had a kick panel install, and placing foam under the dash, at the knee board, and against the center console greatly improved the driverside bias. I also had a good bit of rainbowing, that many experience with kickpanels. On a hunch, I placed a 24" x 18" piece of foam _in the center only_ where the headliner meets the windshield above my head. As a result, the stage lowered from hairline (not all hairlines are equal) to nose level, but the rainbowing was mitigated. 

I wonder if a really clever guy could create a panel with micro perforations that would act as high frequency helmholtz resonators. The panel could be transparent.


----------



## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> IMHO one of the biggest problems is the headrest.


I think so too. It just so happens that my new daily driver has recaro seats which narrow to slightly wider than my neck to form the headrest. So it will be interesting to see how much difference they make over normal headrests.


----------



## ErinH (Feb 14, 2007)

Orion525iT said:


> I wonder if a really clever guy could create a panel with micro perforations that would act as high frequency helmholtz resonators. The panel could be transparent.


but why? resonators are a narrow band acoustic treatment. and by narrow band, I'm talking Q's of >10. They are intended to target modal issues in low frequency response. Broadband absorption is used in midrange to high frequency response and this is done with more typical acoustical absorption panels.


----------



## sqnut (Dec 24, 2009)

Patrick Bateman said:


> Last night I ordered twelve square feet of pressed felt:
> 
> F26 SAE Pressed Wool Felt Plain 72" Wide | eBay
> 
> Will probably do the same thing to my car.


True story from about 5 years ago.

I took two 1/2" sheets like that and got 5 mtrs of it quilted, so that I could use it as a 3/4-1" layer. I neatly cut 3x3 squares and started applying it 1/3 octave for each drivers pass band. 500hz is 26" and 1/2 wave is 13", so everything that was 13" from each mid and my ears (in all directions) got covered. I did this for each driver till 1/2 and octave above/below its crossover point. 

At this point the interior looked like a mosaic art deco disaster. BUT it sounded cleaner, much cleaner. The sound was more open and I started to feel and see space around the instruments for the first time. The aural benefits over rode the visual disaster that stared at me everyday. 

I had about 40% of the dash / door panels / centre console / roof etc covered with the patches. I figured if 40% makes so much of a difference, what would happen if I covered EVERYTHING, so I did it. I think I used close to 70sqft and covered everything. Got rid of the head rest for good measure (bad safety decision). It looked ugly as sin, but instead of making things better, it made the sound dull. I needed to rework L/R a bit and and open up the 4Khz+ range more. Some additional tweaking in the 400-1khz range. Took a month or so to dial it in, but it was the best the car _*ever*_ sounded.

All good things must come to an end and one day while dropping my 8yr old girl to school she tells me, "Dad, do you mind if Mom drops me to school from tomorrow? Your car is ugly and it's embarrassing." The boss had spoken. Everything was gone by EOD. 

TLDR: The covering needs to be thick, cover as much as you can, make it look aesthetic like Garys car, when you go from an untreated to a fully treated interior you may need to open up the top end a bit.


----------



## sqnut (Dec 24, 2009)

TOOSTUBBORN2FAIL said:


> Careful what you wish for^. Its only temperate in socal. *Here in central cal it will be over 100 this week, and the worst drought since records were kept.*


The effects of El Nino. We're both in for a long hot and dry summer. Don't think we will have much rains either. How's that for global connectivity.


----------



## Regus (Feb 1, 2011)

I've just been reading that Britain is set to have severe weather this weekend, with cricket ball sized hail, thunderstorms and tornadoes all forecast from tomorrow night onwards...


----------



## TOOSTUBBORN2FAIL (Jan 31, 2011)

Our farmers here are getting ZERO water this year. We've been in drought for 4 years now. Combine that with some of the worst air in the country and it sucks. It is funny how everything is connected.


Patrick, how thick is that felt? I've been looking for something for my wifes dash.


----------



## Patrick Bateman (Sep 11, 2006)

TOOSTUBBORN2FAIL said:


> Our farmers here are getting ZERO water this year. We've been in drought for 4 years now. Combine that with some of the worst air in the country and it sucks. It is funny how everything is connected.
> 
> 
> Patrick, how thick is that felt? I've been looking for something for my wifes dash.


I believe the stuff I've been using is 3/4". I got it off of eBay. I think the link is somewhere in this thread.


----------



## Patrick Bateman (Sep 11, 2006)

Last night I did some experimentation with this crossover topology.

First, I did a 'normal' crossover, where the goal is to get the frequency response flat.
Then, I tried to do a crossover with flat phase, by using first order filters. *That wasn't possible to achieve; basically no matter how I EQ'd the drivers, their inherent rolloff was too steep to achieve a first order filter.* For instance, even with no filter whatsoever, my tweeter was rolling off at about 18dB octave at the bottom of it's passband.

So then I tried doing the LeCleach approach. While the phase wasn't as good as the first order, it definitely had a lot of the same aspects that I like. I've noticed with a first order filter, it's much more difficult to pinpoint the location of the drivers. Basically when you close your eyes, the sound seems to be coming from a point in space that's larger and more diffuse.

Neat.

It takes a fair amount of trial and error to get it right. I didn't bother using the spreadsheet. Basically you have to experiment with small amounts of delay until the phase rotation at the xover point is minimized. For instance, I'd add 250 microseconds of delay to the tweeter (8.5cm), measure the phase, then repeat, until I got the phase close to the target. It's similar to using delay to smooth out the frequency response at the xover point, but instead of smoothing the frequency response you're smoothing the phase response.


----------



## Patrick Bateman (Sep 11, 2006)

DSP has come a long, long way in the last five years. The things we can do with miniDSP, rephase, and miniDSP HD were unheard of a decade ago.

That's created a little problem, which is that I'm not 110% sure exactly what my phase curves should look like. I've generally set things so that the amount of phase rotation is minimized at the crossover point.

IE, I don't want to see a big 'jump' in phase at the crossover point. Which is exactly what you get with the LR4 crossovers that everyone uses, and the reason that Linkwitz himself stopped using them in the midrange. (IMHO.)

I've learned a lot from Bill Waslo, and I think his speakers sound fabulous, and he posted this the other day:

"Chris,

Impressive setup, wish I could hear something like that someday (not sure I have room for a pair of 402s in my small room, though).

One technical quibble, of probably little importance, though: the phase graph you show in the first post of this long thread:









Is not really showing a linear phase. The frequency scale of that plot is log, not linear, so a straight line that is other than 0 or 180 degrees doesn't mean the phase is linear. Linear phase (waveform faithful) would require a straight line for of the phase when the frequency scale is constant in units of Hz (not in octaves, as the slope with a log-frequency plot would show). Delay (seconds) would be proportional to the negative of that slope -- linear phase implies constant delay.

Here is a (rough) plot of what your data might look like in a linear-frequency graph: 









As shown, the delay (i.e., downward slope) below about 2kHz is much larger than it is above 2kHz. 

Here is the same linear-frequency plot with the usual phase wrapping (to get the vertical down to a more visible scale):









The phase response is quite linear from 2kHz to about 12k and likely minimum phase above that (phase dropping due to magnitude rolloff). Typical rule of thumb for "reproducing square waves" to the eye is that the phase be linear and magnitude need to be flat from 1/10x to 10x the square wave frequency (and the phase must also flatten near 0 degrees when delay is compensated to achieve a horizontal line).

I won't say that this is actually very important, though, just being technically picky. I went to a fair bit of trouble to get my Synergyish speakers to be relatively linear phase in the crossover -- and then added a FIR equalizer to smooth the phase further-- but the difference didn't cause a golden glow with angels appearing in the room or anything. I'm pretty sure (but, from an uncontrolled test) that there's a positive difference in the midbass sound on transients when phase was linearized, but it's still not something I'd bet much money on. At the high frequencies, magnitude fixes are definitely audible, but phase differences (comparing to a system with an impulse response that was already pretty compact) didn't seem to make much difference to me. Possibly if the HF phase had been initially really screwed up then HF phase linearization might have been audible.

Bill"

Some food for thought there. I think this is one of the most concise explanations of what the phase curve should look like.

Bill's post is from here: https://community.klipsch.com/index...based-full-range-multiple-entry-horn/&page=22


----------



## Patrick Bateman (Sep 11, 2006)

Reflecting on Bill's post above, I can make a couple of observations:

1) Based on the math in Bill's post, if you wanted to reproduce a square wave at 1000hz, you'd need flat frequency response from 100hz to 10,000hz, and flat phase also. I'm too lazy to look up the curves, but the Danley SH-50 should be able to do this; in fact it can achieve that goal all the way to 13,500hz. (Above 13,500hz the pattern collapses because the wavelength radiated by the tweeter is smaller than the throat.)

2) In Bill's post, he's downplayed the effect of flat phase. I wonder if he's just grown accustomed to the effect? Or maybe the audibility of phase varies from person to person? I have personally listened to the old Unity horns back-to-back with the new Synergy Horns, and I found that the most notable difference between the two was that the Synergy Horns image better. They create a real solid center image, as if there was a center channel there. And when you close your eyes it's hard to tell where the stage begins or ends. (Arguably the biggest difference between the Unity horns from fifteen years ago, and the Synergy horns from ten years ago, is the phase response.)

I've heard hundreds of speakers, everything from Dynaudio to Focal to TAD, and the only speakers that have drop dead imaging like that are the Danley SH-50 and the Quad Electrostatics. Both speakers work on the exact same principle, so that's seems to be a winning formula.


----------



## thehatedguy (May 4, 2007)

He's questioned the importance of flat phase a couple of times in his build posts.


----------



## oabeieo (Feb 22, 2015)

That's why I love using a 1st order filter cornered well into the passband , leaving plenty of usable frequency response to roll off.

Good post .


----------



## Patrick Bateman (Sep 11, 2006)

As my threads tend to do, this one went off-topic pretty fast.

Here's the formula for LeCleach's crossover. It is *specifically* designed to improve the nearfield listening experience, so it's particularly well suited to car audio, computer audio, or home audio in a small space.

From his document:

settings of a 2 ways system according the proposed method
1..........Only Butterworth 3rd order filters are used.
2..........The relay frequency Fr between the low-pass and the high-pass
is defined at -5dB.
3..........The cut-off frequency Fl (at -3dB) of the low-pass filter is
calculated by: Fl = 0.87 x Fr
4..........The cut-off frequency F
h (at -3dB) of the high-pass filter is
calculated by: F
h = 1.14 x Fr
5..........If the 2 drivers are aligned at the same distance of the listener,
then the low-freqeuncy loudspeaker has to be moved toward the listener
of a distance equal to 0.22 x wavelength at Fr
.
6..........The polarity of the high frequency loudspeaker has to be
reversed.

The entire thing is here : http://www.melaudia.net/zdoc/jml_crossovers_etf04.pdf

At some point I need to post the whole thing, in the event that the original goes offline. (The author died a few years ago.)


----------



## Patrick Bateman (Sep 11, 2006)

It's a bummer this topology never really caught on. Likely because the author is in France and he passed away a few years ago. This topology works really well.

This afternoon I noticed something interesting: *The vertical polars are nearly as good as the horizontal polars.*

This was really interesting to me, because most two-way loudspeakers work terribly on one axis and really nice on the other. I've measured two way loudspeakers where the response has a massive suckout, right in the upper midrange, as you move vertically off-axis.

The reason that this happens is because our crossover is typically in the upper midrange. For instance, with a crossover point of 2000hz, as you move above the loudspeaker you may see a 'hole' in the response. The 'hole' happens because of phase shift. 2000Hz is 6.75" long, so if the pathlength between midrange and tweeter changes by just 3.38", you get a suckout because the mid and tweet are out-of-phase. If you've ever heard a two way where the midrange sounds a bit dark, particularly off-axis, that's what you're hearing.









Here's the horizontal polar response of a two-way loudspeaker using the crossover described in this thread.(1) Note that there's a bit of a dip at the xover point, but the polars are really well behaved. Not that the dip could be easily fixed with EQ. (The dip is inherent to this topology, I can explain why if anyone's curious.)

To me, the thing that's interesting here is that the polars are really well behaved all the way to 4khz.










Because they're well behaved to 4khz, it means that the addition of a modest waveguide can clean up the polars all the way to 20khz. Basically just add a small waveguide to narrow the beamwidth above 4khz. 4khz is 3.375" long, so you don't need a big waveguide to make this work.









Here's the vertical polars. These really surprised me, they're really well behaved. This is unusual for a two way with wide spacing like I'm using in this sim.

(1) Here's the specs for this sim:

The woofer is 8" in diameter with a 7" cone.
The xover point of the speaker is 1316hz.
Due to the unique topology of the LeCleach xover, the low pass is set at 1145Hz.
The high pass is set at 1500Hz.
The tweeter is recessed by 2.26" and it's polarity is reversed.
The center-to-center spacing is a whopping 10.26"! I did this on purpose, basically to see "how far can you take it?" Reducing the CTC spacing will improve everything here. But I wanted to experiment with large CTC distances, as that's frequently the case in car audio.

Note that the 'recess' of the tweeter can be done physically, or electronically via DSP.










This might be an interesting option for a setup like Gary Biggs had, where the speakers are a full 90 degrees off-axis and the tweeter is loaded in a waveguide.


----------



## Holmz (Jul 12, 2017)

With the ease of digital filters it would be interesting to see this revisited using digital techniques.
In addition to altering filter steepness, there is phase correction and the impulse response EQ filters going under the name Dirac.


----------



## Patrick Bateman (Sep 11, 2006)

Holmz said:


> With the ease of digital filters it would be interesting to see this revisited using digital techniques.
> In addition to altering filter steepness, there is phase correction and the impulse response EQ filters going under the name Dirac.


Yeah, the thing that got me curious about these filters was this set of Yamaha speakers I bought last week.

Here's the response that I measured:










If you look at the phase response, there's less than 45 degrees of phase shift over about 60% of the audible bandwidth, from about 400Hz to 15khz.

The Yamaha uses FIR filters. I can get this kind of phase response with Unity horns, but I've never seen a conventional two-way with phase response like this. Even the Dynaudios and the Vandersteens fall apart if you measure them off-axis. They have really great phase response ON axis but get ugly off-axis because of the low order filters they use.

So the LeCleach xovers look intriguing. They're not as perfect on axis as a first order xover, but they're much better off-axis. They're not as perfect as a FIR filter, but they can be implemented with a $80 miniDSP or implemented passively.

Subjectively, the Yamahas sound better on percussion than my Behringers do, and I think that's because of the excellent phase response.


----------



## Holmz (Jul 12, 2017)

Patrick Bateman said:


> ...
> Here's the response that I measured:
> 
> 
> ...


Those wild swings seem like an artefact which would be hard to achieve.
Maybe they are intentionally twiddled in a FIR, but to me the data looks questionable.

It would be interesting to see what is happening with better resolution closer to the big jumps.


----------



## Patrick Bateman (Sep 11, 2006)

Those 'swings' at 3khz and 10khz are just the phase 'wrapping' around. The scale is measured in degrees, so when it hits 180 it 'wraps' to the other side.

If you measure a fourth order xover the wraps get really insane, because there's 360 degrees of rotation at the xover point!

You also see this with ribbons, because the surface area is so large. The software basically loses it's mind trying to measure phase, because the wavefront is planar, so if you move the mic by the teeniest amount the phase measurement goes nuts. (Because the wavefront is so flat, even the tiniest bit off axis screws up the phase measurement.)










That's why the "PDR" versions of the BG ribbons 'mask off' part of the diaphragm with felt. The felt acts as an acoustic low pass filter. This lowers the overall efficiency, but makes a ribbon behave more like a dome. You can also do it asymmetrically. For instance, if you don't care about the vertical polars, you can just mask off the vertical edges of the ribbon.

The foam in the Gedlee waveguides was originally based on the same idea. At first he was trying to use foam to manipulate the polar response.


----------



## subterFUSE (Sep 21, 2009)

Patrick Bateman said:


> Yeah, the thing that got me curious about these filters was this set of Yamaha speakers I bought last week.
> 
> Here's the response that I measured:
> 
> ...




That phase plot is showing an almost ideal, linear phase system, which can only be achieved with FIR filters. Aside from the low end, the phase response is ostensibly linear, and the low end response is pretty damned close to linear. My guess is that the FIR filters don't have enough taps to get the low bass region fully linear.... but it's so close that it's probably inconsequential to improve any further.


----------



## Patrick Bateman (Sep 11, 2006)

While watching movies, my wife was complaining that the audio was out-of-sync. Someone over at diyaudio clued me in:

Because Yamaha is using FIR filters, they've limited the number of taps to keep the delay from getting out-of-control. So when I'm watching movies, there's a bit of delay, but not enough to drive me up a wall.


----------



## subterFUSE (Sep 21, 2009)

Patrick Bateman said:


> While watching movies, my wife was complaining that the audio was out-of-sync. Someone over at diyaudio clued me in:
> 
> 
> 
> Because Yamaha is using FIR filters, they've limited the number of taps to keep the delay from getting out-of-control. So when I'm watching movies, there's a bit of delay, but not enough to drive me up a wall.




I have an Anthem processor with FIR filters. It has a video delay setting to sync the picture with the audio, if you have that issue. Maybe your processor has that, too?

Obviously, you must be running your video through the processor for this to work.

Sent from my iPhone using Tapatalk


----------



## Holmz (Jul 12, 2017)

Patrick Bateman said:


> Those 'swings' at 3khz and 10khz are just the phase 'wrapping' around. The scale is measured in degrees, so when it hits 180 it 'wraps' to the other side.
> ...




Yeah but... The Y-axis shows them going from 0 to 20, so should I assume that is degrees radians, cycles (?)...

If it was -180 to 180, or 0 to 360, or 2-radians, or 1-cycle... Then I would not be scratching the chins.

But it does appear to be as you say.




Patrick Bateman said:


> ...
> If you measure a fourth order xover the wraps get really insane, because there's 360 degrees of rotation at the xover point!
> ,,,




And it could even be more like 2 or 3 cycles if it is unwrapped. That however does not bear sanity to see an immediate jump like that.




Patrick Bateman said:


> ...
> You also see this with ribbons, because the surface area is so large. The software basically loses it's mind trying to measure phase, because the wavefront is planar, so if you move the mic by the teeniest amount the phase measurement goes nuts. (Because the wavefront is so flat, even the tiniest bit off axis screws up the phase measurement.)
> ...




^Poppycock^
The microphone does not know that the speaker is a planer, so the mic will have no effect upon the phase measurement in a relative sense. The phase measurement is a phase measurement and the S/W and microphone does not know what the speaker is. It is solely based in mathamatics which every other "plane wave sensor system" in the world relies on from radio astronomy to radar, to geo and ocean sounding.

Assuming that the mic is 1M away from the speaker then the wavefront is bent into a convex wave with a radius of 1M. This is almost nothing across a 1" microphone, and many are much smaller than 1".

If anything a planar speaker should be a better measurement than a phase measurement from a pistonic speaker.


----------



## subterFUSE (Sep 21, 2009)

I might give this a shot in my car, although I have a 3 way front setup.

Do we think this might work if I run the midbass in positive polarity, the midrange inverted, and the tweeters positive?


Sent from my iPhone using Tapatalk


----------



## Patrick Bateman (Sep 11, 2006)

subterFUSE said:


> I might give this a shot in my car, although I have a 3 way front setup.
> 
> Do we think this might work if I run the midbass in positive polarity, the midrange inverted, and the tweeters positive?
> 
> ...


Here's some food for thought:









Here's the measured response of one of my recent projects, with the mids IN phase and OUT of phase. You can see that there's a ridiculously deep null at the xover frequency. This indicates that I kinda lucked out here, I got the geometry just perfect, so that when you flipped the polarity, POW! A perfect null.









Here's a cutaway of the speaker, a Unity horn with six midranges and a ribbon tweeter. I put a lot of work into getting all the drivers into a tightly focused array, the tweeter is literally two inches from the mid.


What I think is going on in the LeCleach xover is basically the OPPOSITE of this. In my Unity horns, the midrange and the tweeter are incredibly close together. In the LeCleach crossover, the spacing is quite large. Normally, large spacing will produce a polar response that's a mess. But the combination of physically moving the tweeter backwards, plus flipping the polarity, leads to a response that isn't perfect but it's pretty good.

I did some tinkering with the crossover in ARPE and found that the setback distance wasn't critical. With a microphone you could find the optimum setback distance, but the response didn't completely fall apart if things were off by 50%. 

In regards to your original question, I would start from the top:

1) decide what the tweeter polarity will be: positive or negative

2) The midrange polarity will be the opposite

3) The polarity of the midbass will largely come down to what measures best, and it could be positive OR negative. A lot will depend on your delay settings. Personally, I would be inclined to set the midbass and the midrange polarity the same, and use DSP delay to get the wavefronts in-phase at the xover.


----------



## Holmz (Jul 12, 2017)

Patrick Bateman said:


> Here's some food for thought:
> 
> 
> 
> ...




^That^ is tortuous.

If you are doing a phase measurement from pseudo random noise, then just plot the normal and inverted phase measurements.
You essentially threw out the complex information, to go to dB response,,, whereas almost the whole point here has been a discussion oñ phase.

Once we see the phase 180 degrees would we can sum them in our heads to zero.


----------



## Patrick Bateman (Sep 11, 2006)

Holmz said:


> ^That^ is tortuous.
> 
> If you are doing a phase measurement from pseudo random noise, then just plot the normal and inverted phase measurements.
> You essentially threw out the complex information, to go to dB response,,, whereas almost the whole point here has been a discussion oñ phase.
> ...


This isn't a phase measurement, it's a frequency response measurement.

One measurement is in phase, one is out-of-phase.

The intention is to illustrate that the spacing and the phase of the xover is correct; that's what creates the deep null at the xover frequency.

The measurement was done with a swept swine in REW


----------



## Holmz (Jul 12, 2017)

Patrick Bateman said:


> This isn't a phase measurement, it's a frequency response measurement.
> 
> One measurement is in phase, one is out-of-phase.
> 
> ...


Exactly - But in phase space one trace should rock over to be 180 degree out from the proper one.

Which may be just as interesting as it shows "the cause", rather than "the effect".

Hence the two plots work together in a logical way.
(And yes... I know you can see the null and just right to the reason behind it being there)


----------

