# Ported midbass and creating phantom sources



## Orion525iT (Mar 6, 2011)

So it seems I am on another experimental journey to get one more better than my last. I have been concentrating a lot on creating imaging that goes beyond the boundaries of the interior. 

In my previous install, I had built PPSL enclosures for my subs and stuffed them into the rear quarters and fed them a stereo signal. I crossed them at 150hz to the midbass in door pods. Although the stereo signal to the subs + higher than normal xover did add some width cues (maybe just from higher freq harmonics), it was marginal. I also found that the manifolds sent too much energy into the car body directly. A final issue was a rattle on the right bank that I could not track down. That rattle ended up to be a blown sub. So I decide to pull both manifolds to try something different. 

In place of the manifolds I started to experiment with midbasses in the same location. Nothing radical here, it's been done before. But I really wanted to see how slight changes in driver location impacted stage width. I set the passband for 80-300hz. I started low in the quarters (rear bench height) and shifted the midbass higher over a few listening sessions. There was a noticeable difference with each position. The closer the midbass was to ear height, the wider the stage. Placing the midbass further back narrowed the stage. Improvements to width is apparent with very small shifts in midbass placement. Also, rearward shift lessened as stage width increased. This all makes sense from an ITD and C of C perspective. 

Because small changes in position make significant differences, I want to maximize ITD. But, at some point I am hindered by where I can physically position the drivers (quarter window). So, the idea was to try to use a slot to create a phantom driver in a position that is impossible for the driver itself to reside. 

I modeled various drivers that I had laying around, and it seems that the best option is to use two per side parallel PM180-8 in a ported enclosure. The port will be tuned to 80hz. My RS225-4 did not model well especially with the higher tuned port.


The easiest solution to creating phantom source would be to build bandpass enclosures and direct the port to the optimal position. But I couldn't get the 80-300hz passband I wanted. So I came up with the idea of using a slot with a ported enclosure. In Hornresp, the GP with the ported enclosure is about 8 ms, which I think will be acceptable. I tried, in Hornresp, to model the ported enclosure with the slot in front of the drivers by using an offset driver layout and then manipulated the horn to make it more like a slot. It seems that it will work, but there are some issues and I am not even sure I modeled it correctly. I will post the models tonight when I get home.

Thoughts and opinions?


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## bugsplat (Nov 7, 2014)

My only concern might be the limited freq range a ported enclosure would give but admittedly I have not built or tested many. I guess you could lift the lacking areas or tame the peak with a DSP. I like sealed boxes because of the more even levels they give but require more watts. I run two 6.5 mid-woofers to bridge the gap between my sub and 3" full range. They sit just behind the driver and passenger in the wheel wells.


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## Orion525iT (Mar 6, 2011)

bugsplat said:


> My only concern might be the limited freq range a ported enclosure would give but admittedly I have not built or tested many. I guess you could lift the lacking areas or tame the peak with a DSP. I like sealed boxes because of the more even levels they give but require more watts. I run two 6.5 mid-woofers to bridge the gap between my sub and 3" full range. They sit just behind the driver and passenger in the wheel wells.


The range of the ported enclosure is not really limited for this application (except below tuning off course). Output from the ported enclosure is 6 db higher at the tuning frequency. More importantly, driver excursion is reduced greatly at the lower end of the targeted passband. The benefit with that is greatly reduced distortion. This is very important, as distortion has the potential to pull the stage rearward.

The real question is whether a slot can be utilized to create a phantom source to maximize ITD. Eventually, the slot will act as a bandpass enclosure. The goal is to make sure that any potential bandpass created by the slot is outside the targeted response. It's all pretty tricky stuff. I'll get the Hornresp sims up tonight so you can see what I mean.


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## Hanatsu (Nov 9, 2010)

Dual bandpass enclosures each side, one slightly lower and one slightly higher.

Not sure what you mean really, you wanna build a ported enclosure and place the port somewhere else... ?

I'm running my mids to about 200Hz, 24dB LR. I didn't notice that much of a difference of moving them back and forth in the door, never tried different height since it would be impossible to install them higher in my car anyway. I think the most important thing is getting midrange and tweeters in ear height.


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## Orion525iT (Mar 6, 2011)

Hanatsu said:


> Dual bandpass enclosures each side, one slightly lower and one slightly higher.
> 
> Not sure what you mean really, you wanna build a ported enclosure and place the port somewhere else... ?
> 
> I'm running my mids to about 200Hz, 24dB LR. I didn't notice that much of a difference of moving them back and forth in the door, never tried different height since it would be impossible to install them higher in my car anyway. I think the most important thing is getting midrange and tweeters in ear height.


Not just the port, I want to use a slot on the front side of the driver to create a phantom source in a different location without allowing the slot act like a true port.


Interesting thought with the dual bandpass, although I shiver at the thought of trying to get that to integrate with everything else.

At 150hz there was a subtle difference running stereo. 200hz might still fall in the marginal sphere. But at 300hz, the effect was definitely detectable. It may not matter when the midbass is in front, but rearward pull is mitigated by maximizing ITD. There is a significant change in approach angle by moving the drivers from the bottom to the top of the rear quarters. 



I agree that the midrange is also an important factor. But, I have a different solution for that . However, there are limitations (output for one) that makes/forces me to use a 300hz, or higher, highpass.


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## Hanatsu (Nov 9, 2010)

Ah I see. I never run midbass drivers above 200Hz. I even try to push my 3-3,5" widebanders to 160Hz if the distortion is acceptable. Mids low in doors generally just mess up staging imo 


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> The easiest solution to creating phantom source would be to build bandpass enclosures and direct the port to the optimal position. But I couldn't get the 80-300hz passband I wanted. So I came up with the idea of using a slot with a ported enclosure. In Hornresp, the GP with the ported enclosure is about 8 ms, which I think will be acceptable. I tried, in Hornresp, to model the ported enclosure with the slot in front of the drivers by using an offset driver layout and then manipulated the horn to make it more like a slot. It seems that it will work, but there are some issues and I am not even sure I modeled it correctly. I will post the models tonight when I get home.
> 
> Thoughts and opinions?


A plain ol' bandpass will get you 1.5 octaves of bandwidth. 81hz - 322hz to be exact.

Set the rear chamber to 0.14 cf, the front chamber to 0.08 cf, port tuned to 150hz. I'm using this calculator : http://www.carstereo.com/help/Articles.cfm?id=28

This is pretty darn similar to what I am doing in my car right now. I have a B&C 8NDL51 in a bandpass box. The Dayton is very similar to the B&C, just a bit smaller.

I personally made the back chamber as small as possible; the problem that I run into with these boxes isn't getting them to play LOW enough, but getting them to play HIGH enough.

I know this sounds like crazy talk; most people have a hard time getting enough midbass in the car. But IMHO, a tiny sealed box works really well. You lose a lot of low frequency output when you put a speaker in a door. Using a proper sealed box fixes this. And of course, a single reflex bandpass is simply a sealed box with a chamber in front that filters out the highs.









My box is shaped like this. Basically the woofer is in the center, in a tube. The tube is inside a box. The air in the box is the front chamber. The air in the tube is the back chamber. The use of a tube allows me to make the box smaller, because a tube is stronger than a box. I use sonotube.

The port on mine is barely there; I basically just cut a couple of 2" holes in the side of the box.

I didn't design any of this with hornresp, I just started building. If you have a WT3 or DATS it's pretty easy to build a nice bandpass box. All you have to do is keep working on the box until the impedance curve looks right. If the impedance curve looks wrong, there's something wrong with the box, so fix it. For instance, I had to use about half a tube of liquid nails to make the box absolutely 110% airtight. Even the tiniest leak screws up vented and bandpass boxes.


Oh, you'll also notice that the "real world" bandwidth of the bandpass box is wider than the sims predict. The reason for this is cabin gain. Basically we *think* that cabin gain starts around 80hz, but it's actually quite a bit higher, and it varies depending on where the midbass enclosure is located. For instance, you can make a bandpass box that covers 150hz - 400hz in the sim, and then put it in the car and find that the F3 has dropped from 150hz to 80hz. *So it's quite possible to get 2-3 octaves of bandwidth out of a single reflex bandpass if you leverage these tricks.* You can extend even further if you use damping in the box, but I generally avoid that because damping just wastes your output, it's fairly easy to extend the bandwidth another half an octave, but at the expense of 2-3dB of overall output.


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## Hanatsu (Nov 9, 2010)

I got a tiny tiny 2liter box for two 5,5in Seas l12 drivers. Creates a huge peak around 150Hz, I think Qt is like 2,0. With EQ you can get tons of output down to 80-100Hz. It's a giant upgrade from the oem door mounting. Door IB is actually a form of leaky sealed or even some form of halfassed dipole. You lose output no matter how good you dampen the door... :/


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## Orion525iT (Mar 6, 2011)

I'll try to model the bandpass again. It was my hope that a simple bandpass would do the trick, but I couldn't get it to model right. I am in the practice of modeling in Winisd first to ball park, and then using Hornresp to fine tune (doing this because I don't have a good feel for ported, bandpass boxes). But that might be a flawed approach. 

Patrick, that's a neat trick with the sonotube. If you pay attention, those tubes have a wide tolerance with their diameters. I think "they" do this so one 8" tube can slip inside another for shipping. But this allows you to easily laminate several tubes together to increase wall thickness. You just have to peel off the outer paper and inner waxed layer first. I did this for the rounded sections of my last midbass pods.

I've been arguing for the merits of sealed midbass. Dipoles might have their place in mobile audio, but not if you are sitting at the edge of the dipole...like a door card.


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> I got a tiny tiny 2liter box for two 5,5in Seas l12 drivers. Creates a huge peak around 150Hz, I think Qt is like 2,0. With EQ you can get tons of output down to 80-100Hz. It's a giant upgrade from the oem door mounting. Door IB is actually a form of leaky sealed or even some form of halfassed dipole. You lose output no matter how good you dampen the door... :/
> 
> 
> Sent from my iPhone 6 using Tapatalk.


Yep.

I have this mess of midbasses in my car, because I wanted to do an array, and I'm now finding that I really don't need 8" midbasses. The array of drivers produces more output than I need. I bought some 6" Pyles that I'm going to try out.

The idea being that I'll still have a midbass array, the enclosures will simply be smaller.

I'm not excited about building MORE enclosures, but the B&C enclosure is about 12mm too tall, and I can't squeeze it under the seats. (I intended to hide it there.)


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## Orion525iT (Mar 6, 2011)

Some sims from Hornresp with my original plan of using a slot in attempt to create a phantom source.










This first picture is the acoustic power. This is on 60 watts going into 2 PM180-8 wired in parallel. Light grey is just a ported box tuned to 80hz. The black line is the same box with a slot in front to create a phantom source. The slot depth is 34 cm, which is the length of the two drivers if arranged side by side (driver baskets are 17cm diameter), and the slot slowly expands towards the mouth. 










Second picture is group delay. It appears the slot does some nasty stuff here. Again, light grey is just the ported box and black is the ported box with the slot in front. 
I don't think that will work. I can handle some GD from the ported box, but it seems that adding the slot in an attempt to create a phantom source will nearly double GD at the crossover near 80hz. I wonder what a plain old sealed or even IB would behave with the slot.


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## Orion525iT (Mar 6, 2011)

Did some sims with plain old sealed 



















If I am doing the sims correctly, it looks like having that slot adds to group delay. I would say that the sealed plus the slot has acceptable GD, as does ported alone without the slot. But ported with the slot is a non-starter. 

*GD looks worse here, but pay attention to the scale compared to the previous screenshots* 

I will see what things look like where I eliminate the slot and use the port on bandpass for the phantom source instead.


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## Patrick Bateman (Sep 11, 2006)

For the longest time I thought group delay was audible. But after lots and lots of measuring, I'm starting to think that what I *thought* was the sound of high group delay was simply problems with frequency response.

For instance, I've built at least ten bandpass boxes. Most of them had that 'one-note' bass that bandpass boxes are infamous for. This time around, I used everything in my arsenal to make sure the box came out right. I tuned the port to exactly the same frequency as the sealed side, I measured the frequency response, I set the EQ so that the sub blends seamlessly with the mains.

And you know what? It sounds great. Doesn't sound anything like the 'one-note' bandpass boxes that used to plague me.


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> For the longest time I thought group delay was audible. But after lots and lots of measuring, I'm starting to think that what I *thought* was the sound of high group delay was simply problems with frequency response.
> 
> For instance, I've built at least ten bandpass boxes. Most of them had that 'one-note' bass that bandpass boxes are infamous for. This time around, I used everything in my arsenal to make sure the box came out right. I tuned the port to exactly the same frequency as the sealed side, I measured the frequency response, I set the EQ so that the sub blends seamlessly with the mains.
> 
> And you know what? It sounds great. Doesn't sound anything like the 'one-note' bandpass boxes that used to plague me.


Ya, I didn't really want to go down the GD rabbit hole. Might not be much _there_ there.

So, is that really the key to BP? Make the sealed side tune the same as the port tune? I am totally new to BP as I never saw the need until now. What about the ported chamber size?


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## Hanatsu (Nov 9, 2010)

I've messed around with GD audibility too. EQ fixes most of the issues, the phase shifts not created by sharp transitions in the mag response can be altered by allpass filters.

Posted this before...




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## Hanatsu (Nov 9, 2010)

I think GD is audible when there's large swings up and down. If you smooth it out over a wide range I noticed differences in the subwoofer staging. The largest difference still is when phase affects the mag response in a maximum summing or nulling situation...


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## sqnut (Dec 24, 2009)

Hanatsu said:


> It's a giant upgrade from the oem door mounting. Door IB is actually a form of leaky sealed or even some form of halfassed dipole. You lose output no matter how good you dampen the door... :/
> 
> 
> Sent from my iPhone 6 using Tapatalk.


That is so true and I realized that the first time I tuned a car with kicks, wow!!


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## bugsplat (Nov 7, 2014)

Orion525iT said:


> Ya, I didn't really want to go down the GD rabbit hole. Might not be much _there_ there.
> 
> So, is that really the key to BP? Make the sealed side tune the same as the port tune? I am totally new to BP as I never saw the need until now. What about the ported chamber size?


Thats why I have just stayed with sealed and feed it more. I found it too hard to try and hit my goals AND stay in the right form factor. Its one thing to build a box in your trunk, its another to try and build in a quarter panel. I applaud you for your efforts. Thats not easy.


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## sqnut (Dec 24, 2009)

Hanatsu said:


> I think GD is audible when there's large swings up and down. If you smooth it out over a wide range I noticed differences in the subwoofer staging. The largest difference still is when phase affects the mag response in a maximum summing or nulling situation...
> 
> 
> Sent from my iPhone 6 using Tapatalk.


I don't get it, you feel GD down low is audible and yet you prefer ported boxes

But seriously, I think you may be on to something because there is an inherent difference in sound between a sealed and ported box, no matter how much eq is applied.


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## Hanatsu (Nov 9, 2010)

Vented is superior to sealed mainly because of higher output, efficiency and lower distortion (imo).

Main part of peaking GD comes from irregular FR, the excess delay is a more subtle effect and relates more to how good sub/mids integrate... again imo 


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## sqnut (Dec 24, 2009)

Hanatsu said:


> Vented is superior to sealed mainly because of higher output, efficiency and lower distortion (imo).
> 
> Main part of peaking GD comes from irregular FR, the excess delay is a more subtle effect and relates more to how good sub/mids integrate... again imo
> 
> ...


It's the real world and you can't have your cake and eat it too. So you can either have higher output and higher GD or a lower and more linear output with 75% lower GD. Distortion is meaningless in 20-80hz region imo. ......sorry about the derail.


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## Hanatsu (Nov 9, 2010)

I think distortion is very important in the 20-80Hz region. Listen to velodyne! 

I can have the cake and eat it too, answer is FIR processing or creative use of APF 


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## Orion525iT (Mar 6, 2011)

Hanatsu said:


> Vented is superior to sealed mainly because of higher output, efficiency and lower distortion (imo).
> 
> Main part of peaking GD comes from irregular FR, the excess delay is a more subtle effect and relates more to how good sub/mids integrate... again imo
> 
> ...


It's your opinion that it is superior, however it is fact that distortion is lowered by reducing excursion.

We aren't talking about 20 - 80hz in any case. So any discussion there is a red herring. I am dealing with 80 - 300hz. Does anybody think distortion isn't audible in that range? 

Which is why I was looking into ported and bandpass. In my specific application, distortion could potentially cause rearward cues and destroy the very reason I am trying this in the first place. Interestingly, BP boxes only marginally lower excursion over sealed; but does the BP effectively filter this distortion out?


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## Hanatsu (Nov 9, 2010)

Orion525iT said:


> It's your opinion that it is superior, however it is fact that distortion is lowered by reducing excursion.
> 
> We aren't talking about 20 - 80hz in any case. So any discussion there is a red herring. I am dealing with 80 - 300hz. Does anybody think distortion isn't audible in that range?
> 
> Which is why I was looking into ported and bandpass. In my specific application, distortion could potentially cause reward cues and destroy the very reason I am trying this in the first place. Interestingly, BP boxes only marginally lower excursion over sealed; but does the BP effectively filter this distortion out?


Lower excursion = lower distortion. Yep

Harmonic distortion is audible to about 8-9kHz. IMD basically any frequency. BP is a physical bandpass filter, any distortion outside the passband is lowpassed out. 4th order BP got as low excursion as a vented at Fb but usually we put Fb higher in a 4th order box. 6th order is more intresting, dual Fb and ten times the work to get right. A 6th order BP done right with the right processing should theoretically be an amazing thing. Too bad I've rarely seen any, IIRC Bose holds some patent over this tech.

Sorry for the derail...


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## thehatedguy (May 4, 2007)

Can you not put a sealed 10 in there and be done?


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## Orion525iT (Mar 6, 2011)

thehatedguy said:


> Can you not put a sealed 10 in there and be done?



Sure, could even do a 12" .......and Bob's your Uncle. 

But that completely ignores the reasons I started the thread.


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## thehatedguy (May 4, 2007)

It doesn't ignore them...you get everything you want- low group delay, low distortion, and good output.

And it saves you a **** ton of work.

There isn't a way to discern height cues between 80-300 hertz...maybe 300 you can localize height with deep male voices and such.


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## Orion525iT (Mar 6, 2011)

thehatedguy said:


> It doesn't ignore them...you get everything you want- low group delay, low distortion, and good output.
> 
> And it saves you a **** ton of work.
> 
> There isn't a way to discern height cues between 80-300 hertz...maybe 300 you can localize height with deep male voices and such.


Yes GD, distortion, and output are all concerns. Distortion is a real issue because it is a huge limiting factor as it has the potential to pull the stage. You are correct, you can't discern height cues before ~300hz, *but you are ignoring something that is associated with height*; approach angle (most likely a more accurate term for this) and associated ITD. If you raise the driver vertically in the same plane, you increase ITD until you reach ear height. If you slide the driver closer to you in the same plane, you increase ITD. You do both as much as space will allow, and you have maximized the ITD. 

But here is the kicker, I have found that increasing ITD not only widens the stage, *it seems to also impact how everything stages front to rear*. Any problems here will be exasperated by distortion and other artifacts. All of this becomes really important when your speakers are behind you, and you want to create the illusion that they are in front. If your midbass is in front, this goes out the window, and you really only need to focus on whether decreases in ITD impacts stage width. 

From the only guy I know of here that has midbasses in his rear quarters (JBL 2204) said this in another thread:



mitchyz250f said:


> Just wanted to make a correction to something I have said many times. With the crossover of from my quarter panel mounted midbass at 400Hz the stage will wander from front to back. Sometimes it sounds like ambience and other times it sounds like the guitar player, singer whatever is walking from the back to the front of the car. Most people think it is cool but we know it is wrong. If you want a solid front stage you have to cross below 300Hz.


.

From my experiments, I know exactly what he is talking about here. He is using very good set of 12" in my opinion. Yet 300hz is the bleeding edge of what he can really get away with.

Here's a question; where do you think the acoustic center of a 12" driver will be when mounted flush in a quarter panel?


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## Orion525iT (Mar 6, 2011)

The more I look at this and run the sims, it seems that everything is starting to tilt towards a 4th order BP. 

Running a slot to create a phantom source has issues because it adds to group delay. If I use a ported box _and_ a slot, it starts to behave like some sort of quasi-6th order. The port plus the slot creates a sharp GD spike at the port tuning frequency (16 milliseconds). Too complex and too much to go wrong here.

A 4th order has some additional group delay over a sealed, but it is less than ported at around 5 or so milliseconds. The GD is also much more gradual and spread out without any sharp spikes. I loose output over a straight forward ported and gain some over sealed. But I can put the port exactly where I want it.

I'll post some sims when I get the chance.


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> The more I look at this and run the sims, it seems that everything is starting to tilt towards a 4th order BP.
> 
> Running a slot to create a phantom source has issues because it adds to group delay. If I use a ported box _and_ a slot, it starts to behave like some sort of quasi-6th order. The port plus the slot creates a sharp GD spike at the port tuning frequency (16 milliseconds). Too complex and too much to go wrong here.
> 
> ...


Another thing that's handy about single reflex bandpass is that the group delay is at a maximum in the center of the bandwidth.

IE, if you have a bandpass midbass covering 100hz to 400hz, the maximum group delay will be at the tuning frequency, which will be something like 200hz.

Now it would *seem* that the last thing you'd want is to have a bunch of group delay right in the middle there. But the reason it's good is that you can fix it with DSP.

IE, if there's two milliseconds of group delay right in the middle of the bandwidth, you can 'line up' the wavefronts by simply delaying the midrange.

If you want to go crazy, you could completely flatten the group delay using those all-pass filters that Hanatsu posted.


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> Another thing that's handy about single reflex bandpass is that the group delay is at a maximum in the center of the bandwidth.
> 
> IE, if you have a bandpass midbass covering 100hz to 400hz, the maximum group delay will be at the tuning frequency, which will be something like 200hz.
> 
> ...


I meant to ask Hanatsu about that when he posted it. How does that all-pass work?

I am finding that driver selection makes a huge impact on GD. Most references to 4th order suggest that you aim for low FS and qts around .50. I assume this is geared towards subs. But what I am finding is the opposite with midbass. A driver with higher FS and lower qts (higher EBP) lowers GD substantially while also allowing for small boxes. There is a tradeoff, I am guessing in frequency response and gain?


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> I meant to ask Hanatsu about that when he posted it. How does that all-pass work?
> 
> I am finding that driver selection makes a huge impact on GD. Most references to 4th order suggest that you aim for low FS and qts around .50. I assume this is geared towards subs. But what I am finding is the opposite with midbass. A driver with higher FS and lower qts (higher EBP) lowers GD substantially while also allowing for small boxes. There is a tradeoff, I am guessing in frequency response and gain?


IIRC, group delay is based on frequency and Q. If Q goes up, group delay goes up. If frequency goes down, group delay goes up. And I *think* that hornresp is smart enough to calculate the delay that occurs due to port length. For instance, a 27" port will have one more millisecond of group delay than a 13.5" port, because sound travels 13.5" in one millisecond.

What Hanatsu posted is fairly simple; it's a filter that shapes the TIME response, not the FREQUENCY response. For instance, picture a bandpass filter centered at 300hz. There's going to be a high pass filter, and a low pass filter, and that gives you a bandpass frequency response. Now take that idea, and do it in the TIME domain. So you can have a filter that has a delay that varies with frequency.

This is kinda similar to how FIR filters work.


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## sqnut (Dec 24, 2009)

I think of FIR filters as fine tuning the TA, it's not going to affect tonality but it will help a lot with cohesion.


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## Patrick Bateman (Sep 11, 2006)

sqnut said:


> I think of FIR filters as fine tuning the TA, it's not going to affect tonality but it will help a lot with cohesion.


My home speakers have flat phase (Vandersteens) and most of my Synergy Horns do too. Once you adjust your brain to hear it, it's REALLY difficult not to notice when the phase response of a speaker is screwed up. I'll bet if you put a blindfold on me, and played ten different speakers, and *one* of them had flat phase, I could pick that one out.

I've only heard a couple speakers with FIR filters. The Beolab 90 - which is the best speaker I've ever heard. And Bill Waslo's Synergy Horns. (Which are very good too.)

I'm really curious to see how much improvement can be rendered with FIR filters on speakers that are a little more modest, like a simple two way.


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## oabeieo (Feb 22, 2015)

sqnut said:


> I think of FIR filters as fine tuning the TA, it's not going to affect tonality but it will help a lot with cohesion.


It completely alters tonality. Totally changes a speakers behavior.


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## sqnut (Dec 24, 2009)

oabeieo said:


> It completely alters tonality. Totally changes a speakers behavior.


Tonality in pure and simple terms is frequency response and you are not changing that. What will improve with FIR filters are things like resolution and depth, better separation between direct and ambient sound (aka recordings in a large room and hearing the room), better dynamics, etc etc. You're hearing all these as better tonality.


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## Patrick Bateman (Sep 11, 2006)

I kinda agree with both of you.

I agree that depth improves and there's a better definition of the elements in the soundstage.

But when speakers have non-flat phase, I can tell even if I'm not in front of the speakers. There's a 'swishy' sound to the upper midrange. The closest thing to it is the sound of heavy compression, like you get when you overcompress an mpeg.

I think what's causing this sound is the rapid phase shift at the xover point. Basically the speaker is *acoustically* flat at the crossover point, but it's *not* in phase in the time domain, which leads to that 'swishy' sound.


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## oabeieo (Feb 22, 2015)

sqnut said:


> Tonality in pure and simple terms is frequency response and you are not changing that. What will improve with FIR filters are things like resolution and depth, better separation between direct and ambient sound (aka recordings in a large room and hearing the room), better dynamics, etc etc. You're hearing all these as better tonality.


Sorta , yeah. Well if you say it that way than yes

However , a change in phase will change the frequency responce at the listening position


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## Hanatsu (Nov 9, 2010)

Orion525iT said:


> I meant to ask Hanatsu about that when he posted it. How does that all-pass work?
> 
> I am finding that driver selection makes a huge impact on GD. Most references to 4th order suggest that you aim for low FS and qts around .50. I assume this is geared towards subs. But what I am finding is the opposite with midbass. A driver with higher FS and lower qts (higher EBP) lowers GD substantially while also allowing for small boxes. There is a tradeoff, I am guessing in frequency response and gain?


Allpass is IIR filtering, can be done with a MiniDSP by programming biquads. They got a spreadsheet. By altering the Q of the filter you can add an arbitrary amount of group delay at a specific frequency.


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## SSSnake (Mar 8, 2007)

> Tonality in pure and simple terms is frequency response and you are not changing that.


This is true if you are only considering one channel. We are not. The summed response will be and is different if the phase changes. Therefore the system freq response IS altered by implementing an all pass filter to fix the phase alignment in the midbass.


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> Most references to 4th order suggest that you aim for low FS and qts around .50. I assume this is geared towards subs. But what I am finding is the opposite with midbass. A driver with higher FS and lower qts (higher EBP) lowers GD substantially while also allowing for small boxes. There is a tradeoff, I am guessing in frequency response and gain?


Oh, here's something interesting about bandpass:

In the literature, you *do* see a lot of recommendations like that, to use a low FS and a fairly high Q.

Here's the interesting thing : it really doesn't matter how you get there, all that matters is the Fb and the Qb of the sealed side of the chamber. For instance, let's say you're aiming for a Qb of 0.707 and a Fb of 60hz. You could use a big ol' prosound woofer with an FS of 30hz and a Qts of 0.25, and just put that big prosound woofer in a tiny tiny enclosure to 'push' the Q from 0.25 to 0.707. *But you could also use a TINY woofer, like a 4" woofer, that has a Qts of 0.5 and a FS of 50hz.* It doesn't matter how you arrive at the target Fb and Qb, all that matters is that you get there.

This leads to some really strange designs. For instance, I've simmed bandpass boxes using 5" woofers that played as deep as bandpass boxes using 18" woofers.

If all of that makes sense, then tapped horns and back loaded horns become very easy to understand. *They're exactly like a bandpass box, except you have ZERO control over the Qb and the Fb.* The Qb and the Fb are set in stone, they're the Qts and the Fs of the woofer that you put in the horn.

Those statements may be obvious to some, but I really didn't understand that was how it works until five years ago or so. (And I've been making bandpass boxes for 25 years.)

It's the reason that some horns are the size of a mini-fridge, while other horns are the size of a small car, all the while using the same size woofer. With bandpass boxes and horns you can basically 'dial-in' the efficiency and the bandwidth. Taken to the extreme, it IS possible to raise the output by 20, even 25dB.









^^ Cerwin Vega single eighteen, 159lbs per box









^^ Danley Dual 18, one quarter ton per side


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## Orion525iT (Mar 6, 2011)

Hanatsu said:


> Allpass is IIR filtering, can be done with a MiniDSP by programming biquads. They got a spreadsheet. By altering the Q of the filter you can add an arbitrary amount of group delay at a specific frequency.


Ok, thanks. I was seriously looking into plugins for foobar in case I needed it. I'll have to look into what I can do with my MiniDSP and try to get my head around it.


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## Orion525iT (Mar 6, 2011)

I ran a few more sims comparing BR to 4th order BP. Both sims are at a whopping 20 watts. Light gray is BR and BP is black. BR is tuned to 80hz and BP is tuned to 150hz




























Patrick had predicted the largest GD where the port is tuned. This is certainly the case with the BR, but not with the BP.

Phase Response graph for the BP is interesting. Anybody care to explain it?


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## Orion525iT (Mar 6, 2011)

Forgot to mention; the rear chamber/front chamber on the BP box is ~.29 cubic ft/ .20 cubic ft respectively. The BR box is actually larger at .67 cubic ft.


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## oabeieo (Feb 22, 2015)

Just a guess here , but I think I read somewhere that GD on a 4th order is slightly higher than that of a sealed box. The port on a 4th order is the high side cutoff , the low side is the sealed side. In a 6th order the low side is ported and would exhibit large amounts of GD at tuning due to the wavelength at which its tuned is so long along with the long port. Same goes for a T-line. We calculate the distance of the port on the low side of a ported box and assume that the distance of the port in speed of sound numbers, when actually it's a 1/4wave principle. So the leinght of the port has to be the square root (or something x4) so a 10" port is 40"(or 80"I can't remember I think it's 80" I remember reading square root) of GD PLUS the GD from fb. 

A 4th order port has nothing to do with low frequency extension so subsequently wouldn't have the GD that would be compared to a "ported/vented" box or a 6th order because it's tuning it much higher and would account for shorter wavelength.


It made sence when I read it and I probably just botched it it's been a while. 
But it makes sence when a port tuned around 30hz could have up to 30ms of delay.


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## T3mpest (Dec 25, 2005)

I just caught up to this thread. As I was reading, I was going to suggest a 4th order, but looks like you guys figured that out. The main advantage I see over other direct radiation options is that the 4th order will physically filter out the higher order distortion components that would otherwise draw your staging back.. 

For something like this it would be my first choice, especially since you don't need it to go really low.

Also the tune the port at sealed resonance has been used by the SPL guys for years as a rule of thumb and it works fine for them.


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## Hanatsu (Nov 9, 2010)

Orion525iT said:


> Ok, thanks. I was seriously looking into plugins for foobar in case I needed it. I'll have to look into what I can do with my MiniDSP and try to get my head around it.



I did a thread a little while back about it. Dunno how to link to it via tapatalk... 


Sent from my iPhone 6 using Tapatalk.


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## Orion525iT (Mar 6, 2011)

I think I am going to give this a shot. It seems the 4th order will do everything I want and give me a little something different to try.

With that said. I have a few questions in regard to driver selection. The Dayton PM180-8 model great I can get the frequency response I want and they seem to have lower group delay than other options. And, I already own them. However, the PM180-8 were never intended for the car. I bought them at nearly 1/2 price, when PE had a sale, with the intent of using them in horns or OB projects in the house.

With that said, what worries me is the cones on those drivers are very light weight material. I am concerned about how they will behave in a 4th order bandpass. Do I need a stiffer and stronger material like aluminum? These aren't subs, so I don't think they need to be that beefy, but I worry I would blow holes in the PM180-8s.

As a side note, everything in the 6.5" Peerless HDS line models very ( a bit less output) well and I think they all use stronger cone material. 

Any thoughts?


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## thehatedguy (May 4, 2007)

Cone folding has happened in bandpass enclosures before. But that takes a ton of power.

Could you build a proof of concept and try it out in your house to see how well they take the abuse? I am guessing the cones will be fine. I would guess that these are such low distortion drivers and the bandpass is filtering distortion, you could drive these pretty hard without hearing them cry for help.


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## Hanatsu (Nov 9, 2010)

Any driver good in a sealed box is basically good in a 4th order bp. I don't think the light cone is an issue.


Sent from my iPhone 6 using Tapatalk.


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## Orion525iT (Mar 6, 2011)

thehatedguy said:


> Cone folding has happened in bandpass enclosures before. But that takes a ton of power.
> 
> Could you build a proof of concept and try it out in your house to see how well they take the abuse? I am guessing the cones will be fine. I would guess that these are such low distortion drivers and the bandpass is filtering distortion, you could drive these pretty hard without hearing them cry for help.


Thats kind of what got me a bit worried. The drivers themselves are very low distortion and the BP will lower it further. But really all I need is about 20 watts to hit 110db; which is plenty for me, and my mids will have a hard time matching that. 



Hanatsu said:


> Any driver good in a sealed box is basically good in a 4th order bp. I don't think the light cone is an issue.


Good to know. I have hit these guy pretty hard in the .16 cu foot door pods. They did fine. 

Thanks to both of ya, time to make sawdust for a test box!


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## Orion525iT (Mar 6, 2011)

Work on this has been slowed because I have to carve out the sub bank enclosures that are glued in with polyurethane construction adhesive. That **** won't budge!

Messing around with 4th order BP is an interesting exercise. It's kind of fun to push the numbers around and try different drivers, ect. Hopefully Hornresp is doing a good job with the sims. Hornresp sims mostly match those in Winisd. In fact I am using Winisd for initial sims and then transfer the numbers to Hornresp. 

I'll post the Hornresp numbers at some point so everyone can see what I am working with. The enclosure is actually pretty small, maybe .5 cu ft total. I have also found that if I optimize everything, that the maximum group delay is around 80hz at ~6ms. But the group delay tapers off to ~2 ms at 300hz. So if am thinking about this correctly, the maximum _net_ group delay is only ~4 ms. That should be below the threshold of audibility. Even so, I can do some processing to knock it down further or if I am having integration problems. I should be able to hit ~110dB from 80-300hz with about 30 watts (actually almost 113 db at the ends of the bandpass).


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## Orion525iT (Mar 6, 2011)

Anybody have an idea of what the maximum peak velocity I should aim for at the throat mouth (bandpass port)? I keep finding conflicting information and ugly tales of port coloration.

3" port makes things really easy because I can just get a stock 3" Precision port from PE and cut it to length. If I need to go to a 4" port, the port length doubles and routing of the port gets tricky.


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## Hanatsu (Nov 9, 2010)

I wouldn't go above 15m/s for flanged both sides. I think 20m/s might be ok, depends.


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## thehatedguy (May 4, 2007)

Keep in mind the output is going to be directly related to the size of the port since it is the only column of air moving.


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## Orion525iT (Mar 6, 2011)

Hanatsu said:


> I wouldn't go above 15m/s for flanged both sides. I think 20m/s might be ok, depends.


82 sq cm port (4" round) port is around 13.6 m/sec. Can't easily do a round port that large so I am going to have to use a slot. Which isn't all bad because I can push the mouth closer to ear height. The odd thing is that the front chamber is so small and I am using two 17 cm diameter drivers per box that the dimensions of the box get weird. I am going to have to get creative to stop the chamber itself from acting like part of the port.


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## Orion525iT (Mar 6, 2011)

It seems you have to really push the numbers around to optimize something like this. 

To give you an idea of the size of the box. The rear chamber is 7.8 liters and the front chamber is 4000 cubic cm. That puts the entire volume of the BP box at a hair under .42 cubic feet (not including driver displacement). Box is tuned to 152.14 hz

As port cross sectional area increases, you must increase port length for a given tune. A larger cross sectional area reduces port velocity. Great, no problem we just increase area and make the port longer as long as we can still make room for the port.

But the sims are showing me something else that might be a problem.










Acoustic output with a 3" port. Doesn't look bad, but peak port velocity at the mouth is around 23 m/s at ~98 hz.










3.5" port peak port velocity is 17.2 m/s at ~93 hz.










Last image is 4.0" port. Peak port velocity is 13.6 m/s at ~90.5 hz

The largest port (4") only needs a port length of 7.48". That should be easy to fit. So whats the problem? Well, as port diameter increases and likewise port length, a high Q peak appears and gets closer to the bandpass of the midbass. I assume that peak is some sort of 1/4 wave resonance building in the port itself? Is Hornresp modeling this accurately and is this something I need to be worried about?


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## thehatedguy (May 4, 2007)

Hornresp will exaggerate things like that...often times ripples and peaks will be worse in the sim than in real life.

But I can't see the screen shots here at work to tell you much more than that.

How does the resonance look when you apply he desired XO filter?


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## Hanatsu (Nov 9, 2010)

That sharp peak will be smoothed out in a real world example...

What you need is; Violent Bass Air. lol


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## thehatedguy (May 4, 2007)

VBA FTW


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## Orion525iT (Mar 6, 2011)

Lolz ok guys. 

I haven't messed with xover filters yet because it's likely to be another level of learning curve when combined with the 4th order. I'll cross that bridge when I get there I suppose.

Hopefully I'll get some cabin gain help on the low end. I don't need all the acoustic power that these boxes will give me, mainly because I don't think the Aura Whispers that I will be in using in an array (of sorts ) will keep pace. It will be nice to have the dynamic reserve, however. So it is very likely that with some eq and crossover work the peak port velocity will be lower than what the sims show.

Just a rough application of a low pass kills that peak in the frequency responce btw. Some work on the high pass lowers driver displacement by several mm too. All this without reducing overall output by more than 1 db at both ends.


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## oabeieo (Feb 22, 2015)

Really want to know it how turns out. Sounds like a super fun project


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## Orion525iT (Mar 6, 2011)

I haven't had much time to mess around with this lately, but I recently reexamined my approach. I decided to go back to having the subs in the quarters, which leaves no room for the midbass. The subs will be ported 8" Alpine type Rs, one in each quarter. I still believe that a 4th order bandpass is the way to go for the midbass, for reasons stated earlier in the thread. But I also think I can improve upon the basic concept.

One of the drawbacks of the 4th order, is the limited bandwidth. You can push the chamber sizes and volumes around to spread the peak, but you loose efficiency in the process. Ultimately, there is a limit as to how far you can take things. But a quote from earlier in the thread got me thinking.




Hanatsu said:


> Dual bandpass enclosures each side, one slightly lower and one slightly higher.


What about dual bandpass? One covering the lower range, and one covering a higher range? Seems possible. One huge problem is that I am limited to 8 DSP channels. Subs x2, midbass x2, mids x2, tweeters x2. *So, the trick is to get the dual bandpass boxes to work off the same channel!*

In order to get the dual bandpass to operate off the same channel, the boxes need to match in terms of output and time. I modeled a bunch of different drivers in WinISD. I used WinISD instead of Hornresp, because I found WinISD gives very similar basic results and for me it's quicker to use and easier to compare results.


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## Orion525iT (Mar 6, 2011)

So this is what I came up with. It covers ~140hz to ~750hz easily. The lower range is covered by eight HiWave BMR12 per box. Those little 2" drivers have 3mm xmax and have been on clearance at PE for some time. At $4.40 a piece, they are a steal and will work great based on the models. The high range is covered by dual Aura Whispers. You can see that output is matched nicely. You will also noticed that I spent considerable time trying to match or come close to matching the group delay where the low range box and the high range box naturally roll off.

The problem with the modeling is that it doesn't seem that WinISD factors in port length when it calculates group delay. Patrick stated that Hornresp _might_ do that. So eventually I will model this again in Hornresp to see.

The cool thing is that the BMR12s and the Whispers are both narrow 2" drivers. This means I can fit these boxes where normal boxes would not go. In this case, I can fit them under the door panel with only slight modifications.

Another interesting aspect is that box design needs to be thoroughly considered. This is because these boxes are tiny, especially in the case of the box for the Whispers (3.1 cu inches for the rear chamber, and 5.0 cu inches for the front chamber). The problem you run into is that the line between port and box become more ambiguous. You don't what your box to act like a port, or the port to act like a box. So you have to play with the box geometry and port geometry a bit. 

Thoughts?


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## Patrick Bateman (Sep 11, 2006)

I've tried a bunch of different ways to do this, here's my thoughts:









This was my first attempt. Basically two woofers in push pull, with a port setup so that I could cut the port length until I got the desired tuning frequency.

DON'T DO THIS

It worked, but I seriously came close to just giving up on this hobby entirely. It was SO MUCH WORK. Those boxes look tiny, but they were actually more work than building a full size subwoofer, because all of the tolerances were so ridiculous.

I threw them away a few months ago.









This was another attempt. It is a Danley Sound Labs BDEAP subwoofer, scaled down for midbass use. It uses the same drivers as the other midbass box. The box is larger because it's a horn, not a bandpass. But this one actually worked damn well. It came together super-fast, because Danley is a freaken rocket scientist and his designs are really elegant. I built this thing in less than four hours, and I could've done it even faster if I'd moved a couple things around. Highly recommended. The obvious dowside is that it's quite big, measuring 13" x 13" x 6.5" IIRC.









The predicted response is ugly









But the measured response is quite good (the upper trace in this measurement)

http://www.diyaudio.com/forums/subwoofers/258609-ikea-midbass-horn.html

Here's more info on it ^^

One thing you might notice is that you can push these designs to three or even four octaves of bandwidth. The way you do this is to simply shape the response with EQ. Because the efficiency is high and the response is smooth (except for that 4dB dip at 210hz), they're very "EQ friendly."

IE, you could probably cover the entire midbass range


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## Patrick Bateman (Sep 11, 2006)

Here's another method that works well. This is the B&C 8NDL51 bandpass midbass that's in my car right now. Basically the sealed part of the bandpass is a sonotube. The ported part is the box around it. The 'neat' part is that you can tune the bandpass by drilling holes in the exterior. IIRC, I am using dual 2" holes. (Note that the top of the box is absent in this photo, to allow you to see the insides.)

I thought I would need some PVC pipe to extend the exit, but I didn't.

The only real downside to this box is that you need a woofer that's particularly shallow. I am currently using B&C, but it's about 1/4" too tall. I bought some Pyle 6.5" woofers, and I plan on rebuilding the box using those instead, to reduce the height.









A bandpass midbass like the one pictured has several advantages over a setup like Earl Zausmer's:

1) the bandpass enclosure reduces harmonic distortion, allowing you to use a smaller woofer. (The eight I used is utter overkill.)
2) the bandpass enclosure allows us to move the source of the sound. For instance, orienting the port to the side 'pushes' it towards the edge of the car, widening the soundstage
3) In a bandpass enclosure, the apparent source of the sound is the port, not the woofer. This helps with the xover, by improving pathlength differences. For instance, if you have a 10" woofer in the door of your car, the near edge of the woofer is ten inches closer than the far edge of the woofer. That pathlength difference creates issues with the polar response, the off-axis frequency response, and muddies imaging cues. For instance, if you have a 1,350hz crossover from your 10" midbass to your tweeter, then a 10" pathlength difference is ONE FULL WAVELENGTH from one edge of the cone to the other. Even a half wavelength difference is bad, and a full wavelength difference is terrible. (There will be a null at one-half-wavelength.)


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> I've tried a bunch of different ways to do this, here's my thoughts:
> 
> 
> 
> ...


Ok, fair enough warning. Obviously, the boxes for the whispers will be the most challenging, because of the tolerances. But,with the Whispers, I can easily use 2" PVC for the front chamber (it slips nearly perfectly over the front of the driver), 1-1/2" PVC for the rear chamber, and a PVC port. It would easy to hot snot the thing together for testing and tweaking. Because the Whisper uses a titanium cone and a rubber surround, I can accurately measure driver displacement and chamber volume with water and a syringe (which I have done already). I can also check chamber volumes with water after assembly. 

Obviously, there will be much more room for error with the low range boxes.



Patrick Bateman said:


> A bandpass midbass like the one pictured has several advantages over a setup like Earl Zausmer's:
> 
> 1) the bandpass enclosure reduces harmonic distortion, allowing you to use a smaller woofer. (The eight I used is utter overkill.)
> 2) the bandpass enclosure allows us to move the source of the sound. For instance, orienting the port to the side 'pushes' it towards the edge of the car, widening the soundstage
> 3) In a bandpass enclosure, the apparent source of the sound is the port, not the woofer. This helps with the xover, by improving pathlength differences. For instance, if you have a 10" woofer in the door of your car, the near edge of the woofer is ten inches closer than the far edge of the woofer. That pathlength difference creates issues with the polar response, the off-axis frequency response, and muddies imaging cues. For instance, if you have a 1,350hz crossover from your 10" midbass to your tweeter, then a 10" pathlength difference is ONE FULL WAVELENGTH from one edge of the cone to the other. Even a half wavelength difference is bad, and a full wavelength difference is terrible. (There will be a null at one-half-wavelength.)


I agree with all those points and I think that if it works, the effort will be worth it.


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## strong*I*bumpin (Oct 3, 2005)

How the heck the brake pedal don't come in contact with the grill?....or is it the angle of the pic?


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## Orion525iT (Mar 6, 2011)

I guess I am all in on trying this out.

I got the BMR12s yesterday. Weird, they came by postal but were shipped out UPS . In any case, they are pretty nice little buggers. QC could be a bit better, but at such a low price they are a steal. Also, although they are listed as 2", the actual diaphragm is much larger than the 2" Whispers. Cone seems pretty stout and I think they will take some abuse despite the low RMS rating. 

I have some 7781 E-glass and some vinyl ester resin coming on Monday. I have to make a mold of a small portion of the interior sheet metal so I can restructure the door a bit to fit the boxes. Luckly, I have a spare set of complete doors so I can do all the work on a bench. 

I should know soon if I am in way over my head.


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## Orion525iT (Mar 6, 2011)

I checked my work in HornResp today. I spent several hours pushing things around and triple checking my parameters. Good thing I did.

It turns out that the upper range bandpass box offers little benefit over using the Whispers as direct radiators in small sealed enclosures. By using a small sealed enclosure, and pushing up Qtc, I was able to increase output on the Whispers where the BMR12 BP4 rolls off. Instead of just allowing the sealed enclosure to roll off the Whispers, I also added a 2nd order BW high pass filter on the Whispers, centered at 300hz. The filter lowers excursion, increases power handling, and will hopefully reduce distortion from the Whispers. The filter also adds GD, but this actually helps because it better matches the group delay of the BP4 box at the crossover point. 

Using a BP4 on the Whispers for the upper range would have reduced excursion and also reduced distortion, but the tolerances on the boxes would have been absurd. The BP4 box for the BMR12s will be challenging enough, but then I would have needed to use water at a specific temperature and pipette syringes to accurately measure the chambers! Good results would have assumed extremely accurate published T/S parameters. Way to much to wrong here. I just have to hope that the Whispers are well behaved enough as direct radiators to not draw attention to themselves. 










Predicted response of the BMR12 BP4 boxes plus the sealed Whisper.


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## Orion525iT (Mar 6, 2011)

I built a test box. It's a half sized box from what I plan to use, but it is scaled down for similar response. 

I took some measurements in a small room in the house. Not ideal, but I have no way of doing field measurements. I am not sure how useful these measurements will be, but hopefully they can show if I am heading in the right direction. 



















First measurement is the BP4 flat out. It is intended to cover ~130hz-300hz and is tuned to 212hz.

The second measurment is the BP4 plus the sealed whispers. Again my target range is ~130hz to 600-800hz combined. 

The BP4 plays flat out without a low pass filter but _will have_ an active high pass in application. The sealed Whispers have a passive 12db high pass at 300hz and _will have_ an active low pass at 600-800hz (yet to be determined). The idea here is to let me use a single channel per side. The BP4 plus the sealed Whispers and the passive filter are all designed to work together to have similar phase response and group delay, especially where the BP4 naturally rolls off to the sealed Whispers. There are no filters in the measurements other than the 12db passive; just a 80-800hz sweep. 

Any thoughts?

Edit: I should mention the port on the BP4 is undersized. It is that way because of the PVC pipe I had on hand.


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## Patrick Bateman (Sep 11, 2006)

How are you doing the measurements?

I've found it's really hard to get a clean measurement at low frequency in a room, that's generally why I only post measurements down to about 250hz.

A couple of things you might try to make for a better measurement:

1) put the mic on the floor and put the speaker on the floor too. ("ground plane measurement.") This basically eliminates the first reflection. You'll still get reflections off the wall and the ceiling, but putting the mic on the floor gives you about eight milliseconds of clean data, assuming you can get the mic and the speaker about eight feet away from the walls. (Sound travels 13.5" in one millisecond.)

2) Taking it a step further, one thing that can really help is if you can get it outdoors, or at least close to it. For instance, I lived in a condo for the last three years, and I'd open up the garage door and do ground plane measurements close to the garage door. This one is a bit dicey because it pisses off the neighbors, but it definitely gets you a cleaner measurement.

Back when I used to live on a river in Oregon, my midbass measurements were easily audible from the *other* side of the river :O I'm kinda lucky no one ever called the cops.


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## Orion525iT (Mar 6, 2011)

I'll try to get a "yard" measurement. Though, between the cicadas and the freeway hum, the noise floor will be high. I might be better off trying an car measurement with approximate locations.

My biggest concerns are the dip out at 166hz and the weird response ripple through the passband.


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> My biggest concerns are the dip out at 166hz and the weird response ripple through the passband.



Those are probably reflections.

Take a look at my measurements of midbasses, and you won't see them. One strong reflection will add peaks and dips across the entire bandwidth, which is what I see in your measurements.


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## Orion525iT (Mar 6, 2011)

I am still working on this. I decided to deviate a bit from my original plan. I have pushed up the tuning on the box. The reasons for this are many. First, my subs should be able to play out to at least 150 because they are located in the quarters. That allows me to have the cutoff point on the band pass at a similar spot. Second, the length of the port needed to hit a lower high pass also limited the low pass. This is due to port resonance; the longer the port, the lower the port resonance. I didn't want any chance that port resonance would color the sound. Tuning the box higher allows for a shorter port, and all possible port resonance is far outside the passband at >2000hz. Add a filter, and the port resonance disappears completely. The additional bonus to all this is that port velocity is also decreased substantially, which in turn reduced the risk of port noise.

You can do all sorts of stuff to widen the output with bandpass boxes. But there is a price. As you widen the bandpass, you increase group delay and phase shift. My research seems to indicate that the reason that transients can suffer with bandpass boxes is because of the group delay and phase shift. A better approach, which was something that Patrick had hinted at earlier, is to Eq down the peak. Band pass boxes are so darn efficient, that a little Eq goes a long way. So you Eq the peak to effectively widen the bandpass. You lose efficiency that way in a sense, but you have output to spare.

The end result of all this is that I can easily hit 95db between 150-400hz at one watt and 105db in the same range before I run out of excursion or power handling. I should be able to get some boundary boost at the low end too.

Some pictures of the progress so you can get an idea of what the boxes look like.


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## Patrick Bateman (Sep 11, 2006)

I kinda have a soft spot for bandpass boxes because my enthusiasm for box building began with an article in Car Audio and Electronics from the late great Peter Mitchell, where an MTX bandpass box with dual tens beat everything in it's league.


















Kef was a big influence too. Their nineties speakers used bandpass alignments for the bass. If you watch closely in American Psycho, Patrick Bateman's speakers are Kef Reference Threes. I have Kefs in my office and in my family room.










Based on all that, it kinda warmed my heart that the new Elac speakers are using a bandpass midbass. This is basically a three way speaker. The mids and highs are coaxial and in a sealed box. The woofer is a 6.5" unit in a bandpass box, that is coupled to an 8" passive radiator. Andrew Jones, the designer, used to work for Kef and TAD.

There's an interesting angle here, if you look closely. This is a series tuned reflex bandpass. These are really unusual. Bose owned the patent on this one for ages. It's possible that Elac is using a passive radiator to circumvent the Bose patent, or perhaps the Bose patent has expired. The series reflex bandpass is an interesting design, it basically offers efficiency levels that approach a horn, but it's less sensitive to tuning issues than a dual reflex bandpass. I believe you can sim it in Hornresp. You can definitely sim it in Bandpass Box Model, but that's a seriously old program.


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## Patrick Bateman (Sep 11, 2006)

Out of curiosity, I did some sims of a series tuned dual reflex bandpass here:

Parallel vs Series Tuned 6th order bandpass boxes - Page 4 - diyAudio

This is hardly a "simple" design, but if you want to squeeze as much bass out of a 4" woofer it's compelling. It's not going to take a lot of power though.

Do NOT build one of these boxes if you don't have tools to measure them. Dual reflex bandpass is hideously complex. But I'll bet you could get a 3" woofer down to 40Hz with one of these boxes, they go REALLY low.


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