# Improve Your Midbass.



## Patrick Bateman (Sep 11, 2006)

There was a thread on here that gave me an idea on how to improve your midbass.

First, let's talk about phase plugs.



















When you look at a phase plug, it's easy to think that the shape of the phase plug is the important part. IMHO, *it's the shape of the cone.*

Here's why:

Picture yourself listening to a loudspeaker in your living room. The woofers are five inches in diameter. You are seated five feet away. 

The EDGES of the cone are five feet from you.
But the CENTER of the cones are 1.5 inches further away. (Because of the cone's shape.)


One and a half inches, who cares right?
There's no way that 1.5 inches will make any difference will it?

Unfortunately, it will.

Here's why:

Sound travels at 13,500 inches per second. 4500Hz is three inches long. *This means that the sound radiating from the center of that five inch cone is out-of-phase with the rest of the cone.* (Because 4500Hz is three inches long, a distance of 1.5 inches means that the two parts of the cone are out-of-phase with each other.)


OK, does that make sense?

That's why there's a phase plug on these Focals. The shape of the plug is mostly unimportant; the main idea is to literally eliminate the center of the cone. If the center of the cone is gone, there's nothing radiating from it, and now our loudspeaker plays higher than it played before.

Note that there is no free lunch; although our woofer will play higher in frequency, it now has less cone area. 

For instance, a 5" woofer with a 1.5" phase plug has the same cone area as a 4.22" woofer with no phase plug. This means that if you purchase a loudspeaker with a phase plug, you probably want to get something bigger than you would normally use.

If you've made it this far, let's talk about what happens in your car.









In a car, we have the same issues. But now they're more extreme, and they're assymetrical. (Because the left driver is closer than the right.)

Here's what the distances are in a car. This assumes the speaker is five feet away:

1) The center of the loudspeaker is five feet away
2) The far side of the loudspeaker is 2.5" further
3) The near side of the loudspeaker is 2.5" closer

This geometry limits our speaker to just 1,350Hz!

Here's why:

When our 5" loudspeaker is playing 1,350Hz the sound coming from the NEAR side is out-of-phase with the sound coming from the FAR side. This is because 1,350Hz is ten inches long. Which means that a distance of five inches will put the two sources out-of-phase.

Will a phase plug fix this?

NO. It will improve the upper limit for the PASSENGER, but it will do nothing for the driver. This is because the issue is geometric; the sound that's out-of-phase is coming from the edge of the driver, not the center, so a phase plug does no good.









How about one of these NEXO waveguides? Will they fix things?

NO. This would actually make things worse. The NEXO waveguide works well if you're listening ON AXIS, but we're not.









Here's a waveguide that Douglas Winker from JBL made. *Now we're getting warmer.* The Winker Waveguide is taking a 8" woofer and making it behave like one that's about 6" in diameter. This pushes the upper limit of the woofer from 844Hz to 1125Hz.

A difference of 300Hz probably doesn't sound like a lot, but when you're pushing your tweeters this low, it can really improve the response a lot. *Particularly off-axis - which is how we are listening.*

It is going to require some trial and error, but I personally believe that the ultimate solution would take the spherical wavefront of the midbass and "squeeze" it into a narrow column.

The reason that we want a narrow column is because we're listening off-axis. Taken to the extreme, the column would be about 1" long.

The reason that we can't shrink the waveguide that small is that *the smaller we make the aperture, the more it rolls off our highs.*

So we have a juggling act here. A small aperture gives us the beamwidth we want, but it also rolls off the highs. No aperture at all gives us wide beamwidth ON AXIS, but off axis we have dips. (Due to the pathlength difference.)

I know this post is probably massively confusing, but the end result would look like this:



















Basically we are taking the output of a midbass, and "squeezing" it through an aperture which makes the midbass behave like it's a ribbon. (narrow vertical beamwidth, wide horizontal beamwidth.)

This gives us exactly what we want:

1) a wider horizontal beamwidth, so that the driver can hear the highs from the midbass
2) a narrow vertical beamwidth, so that we're not sending much output into the floor and the ceiling.


----------



## tonny (Dec 4, 2010)

A normal Phase plug can improve the mid bass also, because is gets rid off the resonances under the dust cap and there for you will have a cleaner sound.


----------



## backousis (Feb 22, 2014)

i think beaming is a big problem too and can't be fixed with waveguides


----------



## SkizeR (Apr 19, 2011)

is the title of the thread a mistake? i dont see how any of this improves midbass and nowhere did you talk about midbass. do you mean midrange?


----------



## Patrick Bateman (Sep 11, 2006)

SkizeR said:


> is the title of the thread a mistake? i dont see how any of this improves midbass and nowhere did you talk about midbass. do you mean midrange?


I mean midbass.

With one of the JBL or Doug Winger waveguides, you can run a midbass high enough to reach a tweeter, even 45-60 degrees off axis.




















In the home audio world, there are monitors that have 6.5" and even 8" midbass that cross over to a 1" tweeter. In the car, the reason we have to do a three way with these configs is because we're listening so far off axis. Back in the day, speaker pods were popular, and they 'fixed' the issue by putting the midbasses ON axis.

But speaker pods have gone out of favor, because we use DSP to fix the pathlength problem.

But DSP can't fix the beaming problem, which is where waveguides come in. But this time, they're on the midbass not the tweeter. Though, ideally, they WOULD be on both, to match the directivity at the crossover point.


----------



## Patrick Bateman (Sep 11, 2006)

backousis said:


> i think beaming is a big problem too and can't be fixed with waveguides


Beaming is caused by the size and the shape of the loudspeaker wavefront.
Waveguides change the size and the shape of the loudspeaker wavefront, and can fix beaming.

Phase plugs come in handy too.


----------



## backousis (Feb 22, 2014)

Patrick Bateman said:


> Beaming is caused by the size and the shape of the loudspeaker wavefront.
> Waveguides change the size and the shape of the loudspeaker wavefront, and can fix beaming.
> 
> Phase plugs come in handy too.


they need to make it smaller.


----------



## Alrojoca (Oct 5, 2012)

Will changing the phase just on one speaker time align them either more or less aggressively or EQuing the channel affected fix the issue using waveguides then?


----------



## Patrick Bateman (Sep 11, 2006)

Alrojoca said:


> Will changing the phase just on one speaker time align them either more or less aggressively or EQuing the channel affected fix the issue using waveguides then?


All the waveguide does is making the speaker appear to be a different size.

For instance, a 5" waveguide on a 1" tweeter makes the tweeter behave as if it was 5" in diameter.

The thing that's a bit unusual about the JBL waveguide pictured in post #1 is that it makes a large speaker appear SMALLER, instead of making a small speaker appear LARGER.


This CAN make DSP and EQ more effective. For instance, when you're using DSP to alter the perceived location of a 7" midbass, the DSP is never perfect because there's a pathlength difference from one side of the cone to the other. If that speaker was just 1" in diameter, that would be less of an issue. And a waveguide CAN make the speaker "appear" to be smaller.

Note that there's no free lunch, the waveguide will affect the frequency response.


----------



## Alrojoca (Oct 5, 2012)

What about using using a midbass larger than the other side to compensate for the different response and just compensate or fix the other issues with the DSP?

It's getting more complicated than simply go with a 3 way front or a 2way with a 4-5" on the dash and a sub in the front.

I know it's about improving the midbass, but it seems that the listener's position messes up the benefits


----------



## grinkeeper (Jun 26, 2015)

The Phase plugs on my Focal Utopias are rather big. I never actually understood why and thanks to Patrick Bateman, now I know. Thanks.

Here is some pictures for comparison.

6.5” 6W2 and 7” 7W2, both have the same mounting depth by the way, just an interesting side note.


----------



## SkizeR (Apr 19, 2011)

Patrick Bateman said:


> I mean midbass.
> 
> With one of the JBL or Doug Winger waveguides, you can run a midbass high enough to reach a tweeter, even 45-60 degrees off axis.
> 
> ...


Oh so it's "how to improve A mid bass speakers top end response" 

Sent from my SM-G920V using Tapatalk


----------



## sqnut (Dec 24, 2009)

Yes, the 100 hz fundamental of an A2 pluck on a guitar and all its harmonics, is closer to our ear from the near edge of the mid bass cone, than the far edge. This is precisely why I always recommend using the tape measure to the nearest part of the cone. The brain takes all phase and location information from the first arriving sound and everything else that follows till about 0.3 ms is treated as just another reflection. 

The phase plug on a woofer allows it to play the mid range frequencies better, while on say a tweeter, it's just a decoration piece. Also, I'm not sure how the wave guides would give better mid bass?? In real life tuning scenarios, a tight snappy and dynamic mid bass is purely down to timing the drivers, and the response balance between the mid bass and mid range frequencies. YMMV.


----------



## backousis (Feb 22, 2014)

so a flange in front of a 6.5inch midbass driver with a rectangular opening 6x3 inch would cause a dispertion similar to a ribbon.
it could be placed with an angle so the would have high dispersion only towards the driver.
this could easily raise beaming equaly to a 3 inch driver.
that would be about 4.5khz and could make a good match with almost any tweeter.
can we calculate how something like that would affect the high frequencies of the midbass?


----------



## Fetus (Apr 14, 2011)

backousis said:


> it could be placed with an angle so they would have high dispersion only towards the driver...


I think this is where this is heading. Have the mouth of the waveguide at the angle (as in, rotated against the cone) that keeps the edge of the waveguide equidistant to your ears...

Edit: I could be wrong, though. This is a Patrick Bateman thread after all...


----------



## backousis (Feb 22, 2014)

just an opening like the picture of the eon600 last picture of the first post.
that should be placed at an angle about 45 degrees related to the floor we assume the driver is at the door factory location.
that should give a wide dispersion to the drivers head and to the pedals and a narrower
dispersion to the seat and dash.
i hope you can visual it now.


----------



## Patrick Bateman (Sep 11, 2006)

backousis said:


> so a flange in front of a 6.5inch midbass driver with a rectangular opening 6x3 inch would cause a dispertion similar to a ribbon.
> it could be placed with an angle so the would have high dispersion only towards the driver.
> this could easily raise beaming equaly to a 3 inch driver.
> that would be about 4.5khz and could make a good match with almost any tweeter.
> can we calculate how something like that would affect the high frequencies of the midbass?


I don't think aiming it would be a good idea

This "aperture waveguide" from JBL is only intended to change the SHAPE of the wavefront, not the direction

If you wanted to change the *direction* of the wavefront, you would have to physically tilt the driver (with the aperture waveguide attached.)


Having said all that, there's no real reason to tilt the midbass upwards. On the driver's side, we're listening about 70 degrees off axis (Horizontall.) That's a problem; we're WAY off-axis.

But VERTICALLY, we're only 30-40 degrees off axis. IE, we're still inside of the vertical beamwidth, it's the horizontal beamwidth that's the issue.


----------



## backousis (Feb 22, 2014)

i don;t mean aim it.
just turn the waveguide on the driver to make the pattern not narrow vertical and widehorizontal but something inbetween.
we are sittiing much higher than the midbass but we are sitting and to the back.
maybe i should make a draw.


----------



## Patrick Bateman (Sep 11, 2006)

backousis said:


> i don;t mean aim it.
> just turn the waveguide on the driver to make the pattern not narrow vertical and widehorizontal but something inbetween.
> we are sittiing much higher than the midbass but we are sitting and to the back.
> maybe i should make a draw.


True, the shape doesn't have to be long and skinny like a ribbon. 
JBL went that route because of what they were using for a tweeter.

If you simply wanted it to behave like a smaller driver, the shape would basically be the same as what Doug Winker used. (See post #1, with the pic of the 8" midbass in Doug's car.)


----------



## backousis (Feb 22, 2014)

yes but to make it behave like a 3 inch we should make the opening to small.
emulating a ribbons pattern would probably be more suitable to lead it towards the driver
and still the opening be big enough for the lower frequencies.
the only think we don't know is how much something like that will roll off the highs.


----------



## mitchyz250f (May 14, 2005)

Patrick Bateman said:


> Basically we are taking the output of a mid-bass, and "squeezing" it through an aperture which makes the mid-bass behave like it's a ribbon. (narrow vertical beam width, wide horizontal beam width.)


Patrick why don't the edges of the waveguide create diffraction.


----------



## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Patrick why don't the edges of the waveguide create diffraction.
> 
> I guess the reason mid-bass response is improved is because the power response is matched.


Geddes and Danley have argued about this one over at diyaudio.

One school of thought says that you're going to get diffraction because you're putting an aperture in front of the woofer that creates a discontinuity. Similar to a diffraction slot, but not quite the same.

Another school of thought (which I tend to agree with) says that the wavefront simply won't form until it exits the aperture.

For instance:

3000Hz is 4.5" long. The gap under the cone is well under 4.5", so the waveform simply doesn't form until the air exits the aperture. The wavefront forms at the aperture's exit, *as if there was a loudspeaker there.*


----------



## Patrick Bateman (Sep 11, 2006)

backousis said:


> yes but to make it behave like a 3 inch we should make the opening to small.
> emulating a ribbons pattern would probably be more suitable to lead it towards the driver
> and still the opening be big enough for the lower frequencies.
> the only think we don't know is how much something like that will roll off the highs.


I'll make a model in Hornresp and post it


----------



## Patrick Bateman (Sep 11, 2006)

OK, I made a hornresp model of the JBL style aperture, like this:










Hornresp is one-dimensional, *so if you really want to examine how these behave, you'd want to use a 2D program like ABEC.*

But I'm confident that Hornresp can get us 'in the ballpark.'

To make the model, I took a 6.5" woofer (SB Acoustics SB17RNXC35).
And then I created a chamber in front of the woofer, *and I varied the size of the exit.*









"A picture is worth a thousand words." Here's an animation showing what happens as you make the aperture smaller and smaller and smaller. I was surprised to see that it really doesn't filter the highs very much at all. The main effect is that it creates a rise in the upper treble, right where the woofer is starting to beam.

In the graph, we start out with no aperture, and then the exit of the aperture is gradually shrunk, from 10% of the cone until it's covering 50% of the cone. The animation 'jumps' at the beginning because the SCALE on the left moves by 5dB. 

You would want to EQ that out. There's two ways to do it:
1) Use a miniDSP or an EQ to 'cut' the peak
or
2) Use a low pass filter to accomplish the same thing

The advantage of an EQ is that you can preserver the high frequency response. You can basically 'cut' the peak on it's center.

Either will work, one is more elegant though.

Also, a note about Hornresp:









This is the actual MEASURED response of the SB Acoustics SB17. Hornresp tends to exaggerate the high frequency rolloff of drivers. It does this because it treats them as a perfect piston, and in the real world, speaker manufacturers tend to build drivers that 'decouple' at high frequency, so that they play higher than a perfect piston would. You can see this effect if you compare the frequency response of a paper coned woofer with an aluminum coned woofer, the aluminum cone is closer to a perfect piston and tends to roll off earlier than paper.


----------



## Patrick Bateman (Sep 11, 2006)

JBL is using this technology across nearly their whole line. The first pic is from their ceiling speakers, the second pic is from their Vertec line arrays.

In both, note that the midrange is masked off with a device similar to what was in post #1.


Let me translate JBL marketing-speak into english:

In a conventional two-way speaker, with a 1" tweeter and a 5" woofer, there is a directivity mismatch at the crossover point. This is because the tweeter has the beamwidth of a 1" driver, and the woofer has the beamwidth of a 5" driver.

In other words, *even if you put the tweeter an inch in front of the woofer, the pattern isn't going to match.* To get the pattern to match, we need to figure out a way to make the tweeter seem bigger or make the woofer seem smaller.

Probably the most common solution is to slap the tweeter on a waveguide, making it behave as if it's the same size as the woofer.

The JBL "Radiation Boundary Integrator" does a little bit of both. You can see that it's making the woofer SEEM smaller than it really is; the sound of the woofer is 'funneled' through those holes. But at the same time, it is also a waveguide for the tweeter.

It basically kills two birds with one stone.

In the pic of JBL's ceiling speakers, note that you can get the RBI in a series of different beamwidths. Some are as wide as 120 degrees, but others have half the beamwidth.


----------



## mitchyz250f (May 14, 2005)

I think these are the JBL patents.


----------



## mitchyz250f (May 14, 2005)

I think think this is one of the JBL patents. The waveguide is actually doing a few more things.


https://www.google.com/patents/US8130994


----------



## backousis (Feb 22, 2014)

i guess at the animation is the output on axis?
maybe it,s better at 60degree off axis?

i will use some duct tape over the grills to see what happens.


----------



## backousis (Feb 22, 2014)

i used some duct tape and really boosts the midrange a bit but not enough.
and it causes rumbling which is annoying.


----------



## req (Aug 4, 2007)

backousis said:


> i used some duct tape and really boosts the midrange a bit but not enough.
> and it causes rumbling which is annoying.


try something solid like a piece of 1\4" board or ABS plastic. i bet the tape is flopping all over the place causing that kind of noise.

interesting concept tho patrick. never seen this used in car audio before.


----------



## backousis (Feb 22, 2014)

req said:


> try something solid like a piece of 1\4" board or ABS plastic. i bet the tape is flopping all over the place causing that kind of noise.
> 
> interesting concept tho patrick. never seen this used in car audio before.


yes but i need to remove the door panels to do that.

i don,t think i will.


----------



## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> I think these are the JBL patents.


In post 24, I posted a Hornresp sim of this device

I don't think Hornresp is simulating it properly. Here's why:









In this picture from the patent that you posted, *we can see that the RBI basically acts like an inductor.* It's a low pass filter, albeit an acoustic one, not an electronic one.

Here's what the three curves are:

1) the curve that extends out to 10,000 is the bare driver (#802)
2) the curve that has a midrange peak is with an RBI (#804)
3) the curve that looks like #2, but is flatter, is with an RBI with a spacer added. The spacer basically makes the chamber in front of the woofer larger. (#806)










The patent indicates that tighter spacing between the midrange taps extends the high frequencies.


----------



## Picassotheimpaler (Sep 21, 2014)

Thread resurrection!
Curious if anyone has ever done any real world testing on any of these ideas.
I have some very dense CCF that I may make some donuts with and stuff on the back of my speaker grills just to see what sort of difference is made.
Would be an interesting experiment if no one has beaten me to it.


----------

