# DIY - reducing speaker beaming



## mitchyz250f (May 14, 2005)

First off I want to say that I am way over my head here and may have a few facts wrong. I would really like the big brained guys on the forum to discuss this.

I while back I read about Mark Eldridge using JBL 2118 off axis to 2500 Hz or so. Beaming occurs on the JBL 2118 at around 1200 Hz. By 2500 Hz the difference between on axis and off is pretty dramatic. Mark was able to do this with the aid of some type of foam with a star shaped cut out that went in front of the speaker. Ever since then I have been trying to find out more about this but haven't been able to. 

Wouldn’t it be great to use a 2118 or 2123 to 2500 or 3500 Hz. Wouldn't it be great to get the dynamics over that entire range without having to use several speakers and still be flush mount?

Recently while doing my weekly search on the topic I found an article that describes a foam piece with a 3” hole in the middle that goes in front of the speaker to reduce beaming. Interestingly he has plots of before and after. 

Speaker Directivity Modifier :: TGP Webzine


Below are some threads that where individual talk about their success with the DIY device.
Beam Blocker vs Foam cutout? [Archive] - Telecaster Guitar Forum
Welcome to FrugalGuitarist.com | Taming the Beam
The Amp Garage :: View topic - Beam Blockers


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## MarkZ (Dec 5, 2005)

Nice find. It's always cool when the processing isn't digital.


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## subwoofery (Nov 9, 2008)

Just wondering if the 3" hole applies to any size speaker or does it diminishes the smaller you go? 

Kelvin


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## Volenti (Feb 17, 2010)

subwoofery said:


> Just wondering if the 3" hole applies to any size speaker or does it diminishes the smaller you go?
> 
> Kelvin


The thinking behind this suggests that you would scale the hole smaller on smaller drivers, a circle of foam with a 3'' hole in it wouldn't make much sence (and would have little effect) on say, a 4'' driver.

I would assume a little exprimentation would be in order to determine an effective thickness/hole size for a particular driver and application.


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## subwoofery (Nov 9, 2008)

Volenti said:


> The thinking behind this suggests that you would scale the hole smaller on smaller drivers, a circle of foam with a 3'' hole in it wouldn't make much sence (and would have little effect) on say, a 4'' driver.
> 
> I would assume a little exprimentation would be in order to determine an effective thickness/hole size for a particular driver and application.


I thought so lol... Guess one's can make this to replace speaker grill  

Kelvin


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## mitchyz250f (May 14, 2005)

I read some more about this last night. For a 10 inch hole it was recommend to use a 2.5" hole. But that doesn't really make sense to me, as I would think the hole would be a ration to the speaker diameter.

For all the reading I have done it seems to be used by guitarist the most.

I wish some of the big brains (you know who you are) would comment on this.


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## Oliver (Jun 25, 2007)

http://www.diymobileaudio.com/forum...orum/27665-please-define-explain-beaming.html


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## chad (Jun 30, 2005)

guitarists need to discover that they don't have ears on their ankles or ass.

When they manage to accomplish this then they won't have soundmen throwing bottles at them while they drill holes thru the audience's eyelids with their glory of dick guitar aimed for kill.


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## 14642 (May 19, 2008)

Interesting. Looks like a combination of an acoustic low pass filter and some reduction of the "radiating area". It gives flatter response and wider bandwidth, but the only way to realize that flatter response and higher extension is to reduce the output at lower frequencies a lot. Doesn't look like an appropriate compromise to me.


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## mitchyz250f (May 14, 2005)

What did Mark Aldridge do exactly? Does anyone know?


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## BigRed (Aug 12, 2007)

All the cars / trucks I've seen Mark build that used the 2118, used them as a midbass. THen again, I never asked or read about crossover points 

Alma Gates I believe had the 2118's playing with the 6" and tweeter. I couldn't imagine the benefits of running the 2118 up to 2500hz.

anybody else know? Andy?


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## chad (Jun 30, 2005)

I can't imagine the benefits of using the 2118 as a midbass as generally they make a superb midrange 

Yep they beam like crazy.. but generally we call the "pattern control"


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## thehatedguy (May 4, 2007)

It wasn't Mark or Alma, it was Doug Winker who played his 2118s up that high in a 2 way front stage. How Doug did it is explained in his dissertation- probably in the U Texas- Austin archives. 

Or for a clue, look at the star pattern on Manger drivers and the diffraction rings that were pictured in Gary Bigg's Regal


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## thehatedguy (May 4, 2007)

That's not how Doug's idea works.


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## thehatedguy (May 4, 2007)

Really look at the Manger drivers and the star pattern on the parameter.


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## thehatedguy (May 4, 2007)

Sorry, just looked over his dissertation, it's not in there...must be his Master's Thesis that I am thinking about.

It's not a car stereo white paper, but a Master's Thesis...so there is plenty of research and data to back his claims up, or he wouldn't have been awarded the degree.

Dr. Doug now works for Harmon International where his research a long with others concentrated on constant beam width arrays.


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## jonnyanalog (Nov 14, 2007)

if you have his thesis paper I would like to read it.


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## chad (Jun 30, 2005)

I'm still a proponent of beaming=pattern control 


Anyone care to prove that wrong?


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## 14642 (May 19, 2008)

Unfortunately, Doug doesn't work for Harman. 

Why not just use an additional midrange in a three way?


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## thehatedguy (May 4, 2007)

I thought he did, or did at one point.

I don't have his Master's Thesis, but Dr. Doug does frequent a couple of the car audio boards like Dynamic Mobile Acoustics.

I'm with you Chad.

One thing to thing about is the cone of a speaker is composed of hundreds of "point sources." As you get higher in frequencies to get the speaker to beam, think of all of those point sources has little flash lights focusing from hundreds of single lights to one big light. Now, you have to take that focused beam and disperse it by diffraction. Since high frequencies usually travel along the edges of the cone (from how I understand it), you need need to introduce diffraction artifacts along the edge to widen the beam back out.

Look at the kick panels in Gary Bigg's Regal feature and look at the Manger MSW speakers. See what they have in common. That should get you pointed in the right direction.


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## thehatedguy (May 4, 2007)

So basically you can widen the beam or use the beaming to your advantage like Chad as stated.

Or you could do like Andy stated and use another midrange. I would use a compression driver.


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## dubbreak (May 9, 2008)

I'd like to see harmonic distortion graphs on the before and after as well (see if there are any compromises there). It would also be interesting to test with different power levels.

By the graphs it definitely looks like it's removing extra on axis energy so that the on axis response more closely resembles the off axis response. Cool find.

Wonder how small you'd have to go with a 6.5" driver. Just under 2.5"?


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## mitchyz250f (May 14, 2005)

I think it would be great to be able to run a JBL 2118 or something else off axis in the kicks to 2500 Hz, and then run tweeters up high. A simple 2 way that would give pretty good dynamics and imaging. Besides, everytime I don't have to install a new (3rd) speaker it is a good thing.

IF there was no more distortion.
IF it really possible.
Isn't this what Doug did?


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## thehatedguy (May 4, 2007)

That's exactly what he did.

2118s and Scan 60000s in the kicks with a pair of JBL tweeters in the sail panels. He was using his diffraction ring though.

Why would there be more distortion? 2118 is technically a midrange.


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## Dangerranger (Apr 12, 2006)

Wouldn't it be better to mimic (or just test effectiveness of) an actual diffraction device in production on speakers now, and see the functionality? such as Boston's tweeter in the ProSE and Z6 designs, or the SEAS neo tweeter? granted they're domes, but the physics still exist. Boston also had the AMD woofers in home audio uses and such

Though admittedly, the AMD devices and such seem to be more geared toward cancelling out unwanted spectral content like cone resonances than controlling beaming. But that in itself would be in interesting experiment if tuned correctly (I'm looking at you, SEAS Excel W18EX )


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## mitchyz250f (May 14, 2005)

Isn't there anyone out there (with the needed equipment) willing to do a few experiments on this. I am sure the foam thickness and hole diameter can be modified to effect the final output.

But still, other than looking at pictures, is there any reading material regarding Mark's E. device It worked for him, it has usefulness.


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## dubbreak (May 9, 2008)

mitchyz250f said:


> Isn't there anyone out there (with the needed equipment) willing to do a few experiments on this. I am sure the foam thickness and hole diameter can be modified to effect the final output.
> 
> But still, other than looking at pictures, is there any reading material regarding Mark's E. device It worked for him, it has usefulness.


I have a mic, drivers, space in my house to do the measurement, can get foam from work etc.. but it's time I am usually lacking.

I'd like to give it a try with some peerless mids I have (6.5") that have a hump on axis that isn't present off axis.


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> First off I want to say that I am way over my head here and may have a few facts wrong. I would really like the big brained guys on the forum to discuss this.
> 
> I while back I read about Mark Eldridge using JBL 2118 off axis to 2500 Hz or so. Beaming occurs on the JBL 2118 at around 1200 Hz. By 2500 Hz the difference between on axis and off is pretty dramatic. Mark was able to do this with the aid of some type of foam with a star shaped cut out that went in front of the speaker. Ever since then I have been trying to find out more about this but haven't been able to.
> 
> ...











The directivity of a radiator - any radiator - is dependent on size.

This is why small speakers tend to sound brighter off-axis than large speakers. Their small size improves their off-axis response.

All radiators begin to beam at a predictable frequency - typically one wavelength. So an eight inch woofer with a seven inch cone starts to beam at 1928hz. (speed of sound / diameter)

Once you know that, you can do two tricks.

The first is to control the beamwidth of a small radiator. For instance, my home speakers (Gedlee Summas) have a 3" diaphragm coupled to a 15" waveguide. The waveguide transforms the output so that it beams like a 15" woofer. Not coincidentally, the Summa uses a 15" woofer. Now you see why 

Winker's invention isn't designed to make the 8" woofer "look" like a smaller woofer. I believe it's simply designed to reduce peaks and dips off axis. You see, the off-axis peaks and dips are caused by the geometry of the cone. Because the cone is symmetrical, the dips and peaks are unavoidable.

Winker's invention breaks up the symmetry. That's it.

By doing that, you flatten the off-axis response.

There *are* ways to make a large woofer "look" like a small woofer, which I can get into if you want. I've tried them myself; it's a lot of trial and error, and not very rewarding.

Another way to manipulate the off-axis response of a loudspeaker is to use an array. I personally use the array simulator from FRD tools all the time - it's invaluable.

HTH


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## mitchyz250f (May 14, 2005)

Thanks Patrick. OK, let try to set some parameters. 
-Nine pointed star
-The largest portion of the “star” is at the cone/surround interface
-The star points and cutouts are one 6th the dia of the star itself
-the star material appears to be a solid
-???

This is completely different than the approach it initially posted. Does anyone have plots for this speaker?


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Thanks Patrick. OK, let try to set some parameters.
> -Nine pointed star
> -The largest portion of the “star” is at the cone/surround interface
> -The star points and cutouts are one 6th the dia of the star itself
> ...


There are a number of reviews on the web. I believe John Atkinson at Stereophile measured it also.

But building a clone of a Manger seems like an awful lot of work if all you're trying to do is improve the off-axis response to 4khz or so. According to my calculator, a 3.375" radiator will be omnipolar up to 4khz.
















​Why not just clone the woofer array from a Nexo Geo? These guys are using a simple phase plug to make a single eight inch woofer look like a pair of four inch woofers. And it's documented to death (google it!)

_"Midrange frequencies are usually reproduced using small-diameter cone transducers. The cones are fairly small in relation to the frequencies they radiate, so the direction the cone is aimed doesn't matter much.

The line will have a front firing lobe as long as the wavelengths are shorter than 1/2 the height of the line . Below that frequency it will transition to an omnidirectional point source. So the effect of curvature shading is simply to shorten the line slightly, thereby raising the frequency at which it loses directional control.


It's also critical to maintain intra-driver spacing that is smaller than 1/2 wavelength at crossover. Above that distance each driver will produce an individual lobe and the array will produce a series of main and side lobes rather than a coherent wavefront with curvature shading that fits the audience.

We've shown how conventional horns make it impossible to align multiple points of origin, and how the patented GEO wavesource uses hyperboloid acoustic reflectors to solve these problems. GEO S Series and T Series Tangent Array Modules use 8-inch cone midrange drivers to reproduce frequencies up to at least 1200 or 1300 Hz.


The relationship between wavelength, time and distance will always be an issue to overcome with any form of direct radiating speaker. It's just a question of “what frequency and how much interference”
Of course, we can't expect to get 8-inch cones in adjacent enclosures any closer than 10 inches on centre. This means that they will be a full wavelength apart at 1300 Hz. Adjacent cones will start to become separate sources at 325 Hz (1/4 wavelength spacing) and will be developing individual lobes at 625 Hz: far too low to cross over into the compression driver.

The DPD is a simple phase plug that causes each 8-inch cone to behave acoustically like a pair of 4-inch drivers. By creating two acoustical centres with 5 to 6 inch spacing, the phase plug raises the upper frequency limit for line source coupling between adjacent midrange transducers. We don't lose the power handling or low frequency extension of the 8-inch cone driver in the process."_







Here's one of the midbasses from my old Accord. Look familiar?  They Nexo guys have good taste 

B&C 8NDL51 8" Neodymium Woofer | B&C 8NDL51 8" Neodymium Woofer midrange midbass line array 2-way horn loaded pa system | Parts-Express.com
$121 at Parts Express


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## Douglas WInker (Jun 18, 2010)

Hi all. I posted a long explanation with a picture of my kicks and was told it was being sent to a moderator for deletion because I did not have enough posts.

Doug


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## Douglas WInker (Jun 18, 2010)

Here is the text from my post. Let's see if it works.

I see from this thread that people were asking questions about the setup in my BMW. Here are some answers to your questions. 

First, my dissertation was on a constant beamwidth, wide bandwidth array and had nothing to do with my car. JBL was nice enough to send me a bunch of speakers to use in the array though. I think it is cool that some of your have actually found and downloaded it btw. 

No, I don't work for Harman. I work for this company ETS-Lindgren | EMC and RF Microwave Testing, Measurement and Shielding We build test chambers and I do all of the chamber design for the acoustics side of the business - anechoic chambers, reverberation rooms, noise control rooms, studios, audiometric rooms, etc.... So I live primarily in the industrial test and measurement world. If you are ever in the Austin area, send me a PM and I can give you a tour of our factory and our lab. We have a very large hemi-anechoic chamber with a >0dBA noise floor. Nice and quiet in there. Anyway, on to the 2118 setup I ran.

So the 7 series is no more. It was in a fire at Audio FX in Georgetown, Texas. Some of the equipment was recovered and I was able to save the diffraction rings for the mids. I gave them to someone in Florida with a Civic as long as he promised to be nice to them. That was a few years ago.

No this was not part of a thesis and was never published. I lost all of my test data when my old school pc died and don't have a need/desire to test again. I have the math and my notes somewhere but no promises on finding that and posting.

Yes, it what Gary used in his Regal, but due to the crossover points and size of his mids, it was more for points that sound. The technique I used only works when trying to mate a large speaker with a tweeter. If I had the room, I would have run the 2118 with a 2105 and then the Scan tweet, but I did not have the room. So unless you are going to run an 8 in a 2 way setup, don't waste your time trying this.

Now for the educational portion of the program....(no math)

If you look at sound radiation from a baffled piston (loudspeaker), you will see a relationship between loudspeaker diameter and wavelength as they relate to beamwidth. As the wavelength approaches the diameter of the piston, the main lobe narrows and side lobes appear. Now that is a simple algebraic relationship and nothing in acoustics starts out as a simple algebraic equation. It starts with differential equations with certain boundary conditions. One of the boundary conditions is that the edge of the loudspeaker in not clamped, which is what you have with a loudspeaker that moves freely at the edge. The other boundary condition is that the distance from the center of the loudspeaker to the edge of the loudspeaker is constant. It is this condition that determines loudspeaker beam patterns. If you are at a point directly in front of a speaker (say 1 m) and measure to the center of the dust cap, you get a distance of 1m. Now if you measure from the same point to the edge of the cone, you get a longer measurement. The difference between the two is the key because that difference if the same for any point at the edge of the cone. When the speaker moves (assuming pistonic motion), a wave front appears about the surface of the cone and travels toward you. The wave motion from the center of the cone gets there first and the wave from the edge (called the edge wave) gets there a little later. This difference or delay is also a phase shift. When you combine both waves at your position, they can combine constructively and destructively depending on the amount of delay. If the wave length is very large, there is little or no change in the directivity. If the difference is on the order of a wavelength, then you get interference and the beam pattern changes.

Now, if the edge of the loudspeaker is random, then the interference is reduced and the beamwidth stays omni-directional at higher frequencies. Also, the side lobes, when they appear, are 27 dB below the main lobe in amplitude. Since it is hard to build a random edge woofer and make it work well, you build the next best thing – a lens or diffraction ring as I call it. Of course, if you do the math you will see that an 8” speaker is good to about 1 kHz before you need this. My 8s play to almost 3 k so I need a ring. When you get to a 6”, you are at ~3k before this would do you any good so it is not necessary. They work for me because I go from an 8 to a tweeter. If you put them on anything smaller, they are not worth the effort.

I have to give credit where credit is due on these. Gary Biggs helped me make mine. Actually he made them because my aluminum skills at the time were not so hot. I did polish them myself though. 

So....who wants to see a picture? I would like to post one.

Feel free to ask questions, but I don't spend much time on forums. So send me a PM if I don't reply.

-Doug


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## Douglas WInker (Jun 18, 2010)

The forum keeps deleting my posts!


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## Douglas WInker (Jun 18, 2010)

So it seems I have to wait between posts. So who here saw Transformers 2 (yes, it was awful) Well, do you remember the room that was the HQ for the good guys? The one with all the blue wedges? The is an RF room we did for the govt. It is an entire hanger.


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## thehatedguy (May 4, 2007)

Dr Doug! Nice to have you. It was a mistake on my part to say you were with Harman...I latter talked to Matt Bogart who said you were doing what you were doing. Sorry for the confusion.

That buster Steve will never use those things, he should send them to me lol.

Thanks for joining, hope to see more from you here!

Oh, the 7 series made an impression on me when you were at IASCA Finals with it that I haven't forgotten.


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## Douglas WInker (Jun 18, 2010)

Here is an article I wrote on an anechoic chamber. In case anyone is interested.

http://www.ets-lindgren.com/pdf/AD_DW_0809.pdf


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## Douglas WInker (Jun 18, 2010)

Ok, that is five posts. Let's try for the picture of my kicks.

It worked.

-Doug


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## thehatedguy (May 4, 2007)

I need that front stage in my car.


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## colt45 (Apr 21, 2007)

Welcome, Doug and thanks for sharing on the forum!


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## mitchyz250f (May 14, 2005)

Thanks so much for the detail about your defraction rings. When I look at the rings the cutouts look random. Is there a general rule for makeing these? 

For example, 
-The largest part ofthe opening seems to start at the interface between the surrond and the basket,
-The small teeth go inward towards the center of the speaker to the surround/cone interface, 
-Every fourth tooth is twice as tall as the smaller teeth. If you want the beaming characteristics of a 6" speaker than the largest 'star tips' should be 6" from tip to tip. 

I wouldn't be surprised if everything I said was wrong, just trying to create a starting point.


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## MarkZ (Dec 5, 2005)

Thanks for the post, Doug. 

What are you gaining by smearing the cone-edge distance with the jagged ring as opposed to simply using a smooth ring to push the cone-edge distance out of the passband?


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## Douglas WInker (Jun 18, 2010)

The answer to both of the posts above is.. random distance. There was no order to how things were cut. Don't try to find a pattern or make any sense of one if you can find one. Just make it random. The idea is to break up the edge wave. You don't want some curve or continuous function


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## mitchyz250f (May 14, 2005)

Is there a sonic downside? Loss of volume for example. Did you try to reduce the edge from 8" to 6". How do you determine the size of the 'largest teeth'?


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## thehatedguy (May 4, 2007)

If there was a loss of output, I never knew it. It had impact and volume like a horn car.


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## MarkZ (Dec 5, 2005)

Doug, I'm still not so sure I understand. If you set up the diffraction so as to mimic a smaller driver, like the original link aims to do, and your passband is well within those constraints, then how is the jagged ring advantageous?

Also, you used metal to build yours. The article says that reflections from a hard surface back to the cone could introduce undesirable effects. Would a foam backing be useful?


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## Douglas WInker (Jun 18, 2010)

It does not mimic a smaller driver. Who said reflections from a hard surface can introduce undesirable effects? It depends on how one defines undesirable. Someone might say that putting 16 15-inch woofers in a truck with 48000 watts could "introduce undesirable effects." And no, foam is not recommended.

A loudspeaker is a vibrating piston. For a vibrating piston the on-axis radiation can be simplified as the sum of two two plane wave signals of the same amplitude. One coming from the center of the piston and one coming from the edge, which is often called the "edge wave." This edge wave is 180 degrees out of phase with the primary signal coming from the center. When the combine you get beaming as wavelength approached piston diameter. 

Here are some references for further reading. I think you can view these pages at amazon or you can buy the books there as well. There is always the safe fallback of a library too.

"Fundamentals of Physical Acoustics" by David T. Blackstock - Chapter 13 - Radiation from a baffled piston.

"Theoretical Acoustics" by P.M. Morse and K.U. Ingard - Chapter 7.4 - Radiation from a circular piston - p.381

"Fundamentals of Acoustics" by Kinsler, Frey, Coppens, and Sanders - Chapter 7 - Radiation and Reception of Acoustic Waves

"Acoustics - An introduction to its physical priciples and applications" - by Allan Pierce - Chapter 4-8 - Radiation from a circular disk

"Acoustics" by Leo Beranek - Chapter 4 - Radiation of sound

Pierce and Morse & Ingard are a bit heavy on the math but none of these are light on the math. I listed several because you should be able to find one of these at a library. They all cover the same thing more or less. If you have any trouble finding one of them, let me know. Those are just the books that are on my desk right now. I have a bunch of loudspeaker and transducer books, but they are at home right now.

-Doug


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## MarkZ (Dec 5, 2005)

Douglas WInker said:


> It does not mimic a smaller driver. Who said reflections from a hard surface can introduce undesirable effects? It depends on how one defines undesirable. Someone might say that putting 16 15-inch woofers in a truck with 48000 watts could "introduce undesirable effects." And no, foam is not recommended.


Doug, I'm referencing the concept that started this thread. They talked about comb-filtering resulting from reflections from a hard surface directly in front of the cone. At least, I _think_ it's the same link. I read one earlier today that had the same pictures, so I assume it is. They used foam over the edges with a circle cut out at the center smaller than the diameter of the driver. 

I understood that the way your design works is to vary the edge-center distance radially so that you're essentially smearing the phase differences when you integrate around the whole thing. Is that right? My question is, if you plan to run the speaker up to 3kHz, could you not create a smooth ring instead whose diameter was one wavelength at 6kHz (or thereabouts)? This is how I understood the original concept described at the beginning of this thread.

Sorry, no time to read acoustics books. I'm hoping for the abridged version from someone on this forum.


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## 2DEEP2 (Jul 9, 2007)

Doug, sad to hear the BMW is no longer with us.

It was a great car to listen to. I always took pointers for my own Seas 8 with TLR set up.


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## thehatedguy (May 4, 2007)

Doctor



cajunner said:


> oh, and welcome to the forum, Mr. Winker, or is it Dr.?


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## thehatedguy (May 4, 2007)

Thesis for masters

Dissertation for Ph.D

Geddes would flip out at the idea of adding diffraction artifacts to a speaker design.


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## SSSnake (Mar 8, 2007)

Flipout, meltdown, go postal... take your pick. 

Besides a critical aspect of his solution is the speaker beaming matches the directivity of the horn at the xover frequency (so at least some beaming is REQUIRED).


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## benny (Apr 7, 2008)

Wouldn't the close proximity of the cone edge to the diffraction ring make any reflections/distortions occur higher than the drivers intended passband?


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## mitchyz250f (May 14, 2005)

benny - If I understand what you are saying, then that is the intent.

I wonder if the beaming could be controled sort of like a horn by making the oval defraction ring?


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## Patrick Bateman (Sep 11, 2006)

SSSnake said:


> Flipout, meltdown, go postal... take your pick.
> 
> Besides a critical aspect of his solution is the speaker beaming matches the directivity of the horn at the xover frequency (so at least some beaming is REQUIRED).


Even though I own a set of Geddes speakers, and I wrote a few hundred posts on their use in a car, I'm really starting to shy away from their use. The problem is that you have to be seated a "minimum distance" for an array to sum properly, and that minimum distance gets further and further as the center-to-center spacing distance between the drivers grows. This isn't to say that all waveguides are useless - but in a car, the giant ones may be. JBL probably figured this out a while ago, since their components use a very modest waveguide.

Too bad I didn't actually listen to Geddes when he told me as much half a decade ago:

"_Sorry, but this application seems absurd to me. You would not see any
difference between any waveguide in this application. Waveguides need
several wavelengths of sound to achieve their directivity control. You are
always in the nearfield of the device in a car. You may as well just use
whatever contour fits the space.

Earl
GedLee LLC

> -----Original Message-----
> From: anonymous [mailto:[email protected]]
> Sent: Tuesday, October 05, 2004 6:39 PM
> To: [email protected]
> Subject: Re: Oblate Spheroidal Waveguide Question
>
> Dr Geddes,
>
> If I can kep the waveguide down to a manageable size, I intend to use
> a JBL 2470.
>
> 2470
>
> If the size requirements are too much, I'll scale down the waveguide
> and go with a B&C DE25. Certainly the 2470 should go lower.
>
> This is for my Honda Accord, which currently has Radian 475PEBs in
> handmade tractrix horns. Originally the Radians were in CD horns
> manufactured by Welcome to SpeakerWorks/USD Audio.
>
> I'm looking forward to seeing what kind of results I can attain with a
> waveguide! The tractrix horns measure very very good, but I will
> admit that they beam the high frequencies. Subjectively, this means
> that the soundstage in the car is very dependent on aiming of the
> horns, and collapses if you move your head a few inches, or your legs
> get in the way!
>
> I'll bet you haven't run across a lot of people putting waveguides in a
> car?
>
_


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## Patrick Bateman (Sep 11, 2006)

Douglas WInker said:


> It does not mimic a smaller driver. Who said reflections from a hard surface can introduce undesirable effects? It depends on how one defines undesirable. Someone might say that putting 16 15-inch woofers in a truck with 48000 watts could "introduce undesirable effects." And no, foam is not recommended.
> 
> A loudspeaker is a vibrating piston. For a vibrating piston the on-axis radiation can be simplified as the sum of two two plane wave signals of the same amplitude. One coming from the center of the piston and one coming from the edge, which is often called the "edge wave." This edge wave is 180 degrees out of phase with the primary signal coming from the center. When the combine you get beaming as wavelength approached piston diameter.
> 
> ...


Hopefully I got the basic idea right when I said that _"Winker's invention isn't designed to make the 8" woofer "look" like a smaller woofer. I believe it's simply designed to reduce peaks and dips off axis. You see, the off-axis peaks and dips are caused by the geometry of the cone. Because the cone is symmetrical, the dips and peaks are unavoidable.

Winker's invention breaks up the symmetry. That's it.

By doing that, you flatten the off-axis response._


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## mitchyz250f (May 14, 2005)

If the top and bottom (12 and 6 oclock) of membrane had no peaks or interuption but the sides did (3 and 9 oclock), wouldn't the speaker beam verticaly soon the in did horizontally?

THe design of the Manger and Mark's speaker are somewhat similar. This is a paper I found on the Manger design:

http://www.soundlabsgroup.com.au/mm5/graphics/manger/downloads/manger_talk_asa.pdf


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## silent_riot (Apr 18, 2007)

Thank you, Dr. Doug.


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## MarkZ (Dec 5, 2005)

Patrick Bateman said:


> Hopefully I got the basic idea right when I said that _"Winker's invention isn't designed to make the 8" woofer "look" like a smaller woofer._


_




I believe it's simply designed to reduce peaks and dips off axis.

Click to expand...

What's the difference?_


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## Douglas WInker (Jun 18, 2010)

Patrick said it correctly. Just break up the symmetry. 

Side lobes are suppressed. The main lobe does not beam as quickly as frequency increases but it does beam. The main benefit is a suppressed side lobe. Side lobes alternate phase so the first is out of phase with the main lobe by 180 degrees. The second is in phase and so on. The idea is not to make the speaker behave like a 6 or a 5. The idea is to take a large driver and inhibit the side lobes up to a point where a tweeter can take over. I wanted to put a 2118 in my kick panel and I wanted a 2 way system. I wanted something that was very dynamic. The 2118 was able to do that but I had a trade off in directionality and beaming that I had to overcome and this was my solution. One thing to note. The 8 did beam and did have problems at high frequency. I just pushed these problems up a couple of octaves and used a tweeter in that range.  As I said before, I would not try this with a smaller mid because there is no point. 

Since there were a few questions about me. I have a PhD and a MS in Acoustics from the Dept. of Electrical and Computer Engineering at the University of Texas at Austin. I did not write a Masters thesis since I knew I was going for a PhD. UT offers several ways to get from Masters to PhD and one of them is course work. I did more course work for a broader experience. I did write a dissertation for my PhD called *Improving speech intelligibility with a constant-beamwidth, wide-bandwidth loudspeaker array* if you want to read it, here's a link. Click on Full Text to download. Note: it is 150 MB 

University of Texas Libraries /All Locations

Doug


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## cyberdraven (Oct 28, 2009)

Gosh! This is a whole new ball game for newbies.

Question: Im having my 6.5" mids in door stock location with 5" opening diameter. Do you suggest better to leave it that way to control beaming? This thread opens a new dimension, all the while Im leaning towards customizing my doors to widen the opening for my mids.


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## rawdawg (Apr 27, 2007)

If I'm reading correctly, according to the good Dr., it is useless to try this with a Mid smaller than 8", so his edge diffraction Audiobahn flame looking metal cover(jk!) is not applicable to your situation.


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## mitchyz250f (May 14, 2005)

Why would this be useless on anything smaller than an 8'? 

Mark was able to push the usable off axis crossover point of the 8" from 1000 Hz to 3000Hz. I should mention that the JBL 2118 still sounds VERY good at 3000 Hz. If you had a 6" that started beam at 1500 Hz and you could push that so that you could crossover at 4500 Hz off axis and there could be benefit, depending on your setup, to that also.

I think this could be especially helpful when trying to do stealth installations when you may want to keep speaker off axis.


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## SSSnake (Mar 8, 2007)

Thanks Doc! I have been wondering about this famed ring for quite some time. Particularly if there was any pattern to the points. Completely random seemed too easy.




> Question: Im having my 6.5" mids in door stock location with 5" opening diameter. Do you suggest better to leave it that way to control beaming? This thread opens a new dimension, all the while Im leaning towards customizing my doors to widen the opening for my mids.


Do you need to run the 6.5" higher than 2.4k?
No? Then you don't want to do this.


Yes, well then maybe...

I have not done the math but a symmetric smaller opening is likely to set up additional resonances. These resonances are likely to be higher in freq but more pronounced. The short answer is you may have to use a steeper filter on the mid to kill the increased out of band distortion.

From a practical standpoint... unless the sheet metal in your particular door is pretty stout you are likely to setup additional vibrations in the door. This would also require you to bottom mount the mid to the door (typically pretty hard and causes you to give up significant mounting depth after you consider cone clearance/throw).

Besides for every gain there is typically a loss (in this case I'm sure there is a loss as well - I'm just not sure what - maybe the generation of HOMs  ). The goal of a intelligent system designer is to minimize losses/maiximize gains affecting system objectives. If one of your objectives includes getting the 6.5" mid above 2.4Khz then look into this otherwise this is NOT for you.


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## mosconiac (Nov 12, 2009)

I have a simple (verging on dumb) question, but if we are fitting a (seemingly thin) metal diffusor on the face of the woofer, how do we ensure the metal diffusor itself doesn't introduce mechanical resonance into the equation? That is, how to do we ensure these random points don't vibrate & produce a gawdawful racket?!?


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## Patrick Bateman (Sep 11, 2006)

cyberdraven said:


> Gosh! This is a whole new ball game for newbies.
> 
> Question: Im having my 6.5" mids in door stock location with 5" opening diameter. Do you suggest better to leave it that way to control beaming? This thread opens a new dimension, all the while Im leaning towards customizing my doors to widen the opening for my mids.


The hole is symmetrical. So you'll get a bunch of lovely symmetrical peaks and nulls off axis :O

Reason #1,428 that I *hate* putting midranges in doors...


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## Douglas WInker (Jun 18, 2010)

mosconiac said:


> I have a simple (verging on dumb) question, but if we are fitting a (seemingly thin) metal diffusor on the face of the woofer, how do we ensure the metal diffusor itself doesn't introduce mechanical resonance into the equation? That is, how to do we ensure these random points don't vibrate & produce a gawdawful racket?!?


Design them so they don't add an audible ring. Use a fairly heavy material (I used aluminum). Screw them down tight. Mine attached through the speaker mounting holes with the same bolts that held the speakers in place. There was also a wood spacer ring behind them so the cone did not hit the diffraction ring during maximum excursion.

-Doug


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## Douglas WInker (Jun 18, 2010)

You can do this for higher frequencies as well but what is the point in 20 Hz to 20 kHz audio. There is an ultrasonic application for something like this with microphones.

-Doug


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## mitchyz250f (May 14, 2005)

What is he downside of doing this?


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## cyberdraven (Oct 28, 2009)

Patrick Bateman said:


> The hole is symmetrical. So you'll get a bunch of lovely symmetrical peaks and nulls off axis :O
> 
> Reason #1,428 that I *hate* putting midranges in doors...


Thanks Pat. Unfortunately, im having 5.5" midrange in my kicks. Im running the Alpine SPX-F17T btw. Read much of your thread about waveguides but havent adopted any yet as I couldnt comprehend much. 

Would midbass under the seat in AP much better? Thanks!


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## CraigMBA (Nov 19, 2010)

Douglas WInker said:


> Ok, that is five posts. Let's try for the picture of my kicks.


Wow. Thanks Doug. I know I pestered you about this a bunch of times over the years, but I sincerely appreciate you sharing with the public. In an odd way, you made my install a TON easier.


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## 14642 (May 19, 2008)

Hey Doug. Nice to see you here.


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## Douglas WInker (Jun 18, 2010)

CraigMBA said:


> Wow. Thanks Doug. I know I pestered you about this a bunch of times over the years, but I sincerely appreciate you sharing with the public. In an odd way, you made my install a TON easier.


You are welcome.


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## Douglas WInker (Jun 18, 2010)

Andy Wehmeyer said:


> Hey Doug. Nice to see you here.


Hi Andy. I get by here but very rarely. Hence the 6 months since my last post. 

-Doug


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## Lars Ulriched (Oct 31, 2009)

Any more infos on this? Really ineresting reading...


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## cvjoint (Mar 10, 2006)

Good read, somebody put lots of effort into it.


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## mitchyz250f (May 14, 2005)

Patrick Bateman said:


> ​Why not just clone the woofer array from a Nexo Geo? These guys are using a simple phase plug to make a single eight inch woofer look like a pair of four inch woofers. And it's documented to death (google it!)


Patrick, with proper time alignment would that baffle/phase plug be a good place for a tweeter?


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## motomech (Nov 12, 2014)

Fascinating!
Sub'ed


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Patrick, with proper time alignment would that baffle/phase plug be a good place for a tweeter?


Not just good, GREAT. 
Dave Smith is one of a handful of people who's worked on the worlds best coaxes at Kef and Tad. (Look him up on LinkedIn). Dave mentioned that a lowly ceiling speaker from Snell, which looks like that Nexo speaker from the last post, outperformed some of the worlds best coaxes by putting the tweeter on that 'bridge' that's over the woofer. 

IMHO, here's how this works:

1) if you have a midrange with a crossover of 2000hz, it basically doesn't "see" the bridge because the wavelengths are so long. 2000hz is 17cm long; the sound wraps around the bridge. BUT the air UNDER the bridge creates an acoustic low pass filter which reduces distortion. (Same way that the front chamber in a bandpass subwoofer works.)
2) in a coax, the tweeter "sees" the woofer cone, because the wavelengths are so short. This isn't the end of the world, but you can definitely see the effect. If you look at the frequency response plots of coaxial speakers, the tweeters are always pretty rough. I mess around a lot with coaxes and Synergy horns - my measurements show this too. 

By putting the tweeter on the bridge, you "hide" the woofer from the tweeter over most of its bandwidth. 

So you get:
1) the incredible clarity and articulation of a coax
2) lower midrange distortion
3) the smooth treble response of a tweeter on a flat baffle


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## Patrick Bateman (Sep 11, 2006)

Forgot to mention the downside - you must delay the tweeter. 
This can be done via DSP.
You could also use a 4th order over on the tweeter and a 2nd order on the woofer, which would generate a large delay fir the tweeter and a small delay for the woofer. With an xover of 2000 he you'd get a delay of 3.5 inches, enough to offset the tweeter.


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## thehatedguy (May 4, 2007)

KEF was doing the Nexo-like phase plug in 1966.

DIY woofer wave guides, They work! - diyAudio

Also, JBL is mounting the tweeters in the center of a waveguide in the Control 40 ceiling speakers...making it almost Unity-like in the bandpass entry of the midbass. And you can buy the waveguides from JBL Pro Parts if you have the S/N...which isn't hard to find.


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## Focused4door (Aug 15, 2015)

Patrick Bateman said:


> Not just good, GREAT.
> Dave Smith is one of a handful of people who's worked on the worlds best coaxes at Kef and Tad. (Look him up on LinkedIn). Dave mentioned that a lowly ceiling speaker from Snell, which looks like that Nexo speaker from the last post, outperformed some of the worlds best coaxes by putting the tweeter on that 'bridge' that's over the woofer.
> 
> IMHO, here's how this works:
> ...


I have thought of doing this to use a component speaker for locations that pretty much only has room for a coaxial but never actually tried it. Either lived with a coaxial or ending up mounting the tweeter in a less than ideal location.

It seems easy and cheap enough that I am surprised a manufacturer hasn't offered something similar.


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## mitchyz250f (May 14, 2005)

I know that the wave will re-form around the phase plug; but is there any audible or inaudible distortion/defraction created?


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## oabeieo (Feb 22, 2015)

I don't know how I missed this one, great read !! Subbed


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> I know that the wave will re-form around the phase plug; but is there any audible or inaudible distortion/defraction created?


Actually the opposite; it reduces distortion.

In my current project I was tinkering with the xover between midrange and tweeter, and it was starting to look like I'd need six components for the xover. I said "screw that" and went out and made a phase plug for the midranges.

Basically it's way less hassle to make a phase plug then to deal with a 3rd order lowpass on the midrange. On top of that, it's cheap. An 18dB xover is about $15 in components. And that really sucks if you're using $4 midranges.

The main reason *not* to use a phase plug is bandwidth. All of these contraptions definitely reduce the bandwidth of the driver. So it depends on whether you see that as a defect or a feature. I see it as a feature.










Let me take a minute hear and talk about the distortion question. I know that when you look at a loudspeaker with a big hunk of plywood across the face of the driver, you'd think "that's a bad idea." Logically, it seems like putting a piece of plywood right in front of the midrange would have some ill effect. You'd think that the sound would hit the plywood, and get reflect back into the driver, and that can't possibly be A Good Thing right?

Here's the reason that this works:
Air doesn't "care" if it bounces back into the midrange cone, and those reflections won't have any ill effect on the midrange. If you make the duct REALLY small you'll run into compression issues. But it has to be REALLY small for that to happen; that hunk of plywood would have to cover up 75%-100% of the cone before things get ugly. (And this IS a real problem by the way; when you make the compression too high you'll start to hear ugly mechanical sounds from the midrange, because the pressure is so high it's pushing back on the face of the cone. But, again, you REALLY have to use a lot of compression to get to that point.)









Now let's think about what happens when you mask off that cone:
*The main thing that happens is that you're going to create unequal path lengths for some of the sound.* IE, the sound radiation from the CENTER of the cone is going to travel further to get to your ears than the sound from the EDGE of the cone. For the most part, *that difference in pathlength will determine the highest frequency that the speaker can play.* IE, if you have an 8" woofer and you slap a hunk of plywood across the center, the sound at the center of the speaker is going to travel an extra 4" to get to your ears than the sound at the edge of the driver. That 4" difference in pathlength will put a notch in the output at 1687hz, and a peak in the output at 3375hz.

OK, at this point you might be thinking "I don't want a notch in my midrange at 1687hz and a peak at 3375hz."

The thing is, some of the sound is delayed by 4", some is delayed by 3", some is delayed by 2"... The delay isn't constant; the delay depends on how much extra the sound has to travel to get around that plywood bridge that's across the cone.

*Put all of that together, and you wind up with a nicely behaved lowpass on the midrange.* The bridge basically acts as a low pass filter on the midrange. The low pass frequency is going to vary.








If you wanted to get high tech you could probably model this in Abec, a piece of software from http://www.randteam.de/ABEC3/Index.html

But these things behave predictably; I generally find that the hunk of wood acts as a first order low pass filter. The frequency of the lowpass is generally somewhere around the additional distance that the sound has to travel. IE, if you stick a hunk of plywood across an 8" woofer, the sound has to travel an additional 4". 3375hz is four inches. You start to get a low pass at one half of that, because that's when the sound is 180 degrees out of phase. So a plywood bridge on an 8" woofer will give you a lowpass of about 1688hz, which is just about perfect if you're crossing over to a waveguide.

OK, if all of that made sense, then now you understand how they low pass filter works.

Now lets talk about distortion. Distortion is generally a product of the driver itself. If you have a really crummy enclosure, the enclosure can radiate distortion too. The bridge isn't going to add distortion to the driver; how could it? The only way it could add distortion is if the bridge was so large, it created compression. That's easy to avoid; just make sure that at least 25% of the loudspeaker cone is exposed.

Now the cool thing is that the bridge can REDUCE distortion. The way that this works is that the bridge is creating a low pass filter. (As described a couple of paragraphs above.) So if you have an 8" woofer that's generating 70dB of distortion at 4000hz, and your bridge is lowpassing the speaker, *well you just reduced the distortion significantly.* The really cool thing about this is that this is one of the only ways I can think of to reduce distortion without buying expensive drivers. You can't reduce harmonic distortion with an electronic lowpass filter. IE, if you have an 8" woofer generating 70dB of distortion at 4000hz, and you lowpass the woofer, the electronic lowpass does nothing to reduce the distortion. But a MECHANICAL lowpass filter CAN.

I know my little experiments look a little ridiculous; there aren't many car audio dudes using $4 woofers. The thing is, the combination of an electronic highpass and a mechanical lowpass can seriously nuke the distortion in a driver. Scanspeak will sell you a $100 midrange with a copper shorting ring, and that copper shorting ring can reduce distortion by 10dB. But a hunk of plywood can reduce it even further, and plywood is way cheaper than Scanspeak. I still have to deal with the power handling problem, which is why I tend to use arrays of cheap drivers.









BTW, you can do this at any frequency; here's one of these devices on a tweeter from Erin's KEF speakers. Same idea, just much smaller dimensions.


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## mitchyz250f (May 14, 2005)

Thanks for that very detailed and instructive response. I see this solving many problems. Some more questions:

In the KEF coax example it looks as though they tried to get the baffle as close to the tweeter as possible. Is that correct? Is it beneficial with cone speakers?

How does this affect time alignment? Is the source of the sound still the voice coil? For example if I have a tweeter and midrange time aligned with the tweeter directly in front of the mid, after 'phase plugging' are the speakers still time aligned? How about with the tweeter time aligned but above the mid?

My mid-basses are in my rear quarter panels which are not at an ideal location for maximum stage width. Could I move the perceived sound past the edge of the mid bass? Could I make a phase plug that completely covered the MB and turned into a 'rectangular slot' like a slot port on a subwoofer? As long as the area was 25% of the area of the cone? Would the calculations you provided still apply? What are the limits of the length of the port?

Would that technique work on midranges also?

Is it beneficial to radius the edges of the phase plugs to reduce detraction?


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Thanks for that very detailed and instructive response. I see this solving many problems. Some more questions:
> 
> In the KEF coax example it looks as though they tried to get the baffle as close to the tweeter as possible. Is that correct?


That's correct. The volume of air and the pathlength difference creates a low pass filter. So if you want to increase the frequency of that low pass filter, you'll want to make the chamber as small as possible, and you'd want to equalize the pathlengths as much as possible.

High frequency phase plugs are serious business; I've mostly avoided them lately because they're so easy to screw up. But phase plugs for all other frequencies are pretty easy, because the wavelengths are long, which gives you more margin for error.

















Editorializing for a minute, modern phase plugs are moving away from high compression ratios. If you look at old phase plugs, from twenty years ago, they were extremely complex and used very high compression. (First pic is a TAD, from about 20 years ago.) Modern phase plugs are more 'open' with lower compression. The second pic, of a JBL D2, you can see that though it's newer, it's actually a simpler phase plug.



mitchyz250f said:


> Is it beneficial with cone speakers?


Absolutely. JBL and the prosound companies are using it all over the place now.








EAW ANYA uses it on every single driver








Arguably, Danley got this ball rolling fifteen years ago. They used it on every driver, and they always have








JBL uses it in their ceiling speakers.








In the JBL Vertec they use it on the midrange and tweeter




mitchyz250f said:


> How does this affect time alignment? Is the source of the sound still the voice coil?


The source of the sound in a loudspeaker is very rarely the voice coil.
Let's say that you have a 6.5" midrange. The source of the sound is the entire surface of the cone. You can hear this for yourself; a 3" speaker "sounds" smaller than a 6.5" speaker. But this is complicated by the low pass filter; a lowpass filter adds significantly delay, and it's almost guaranteed that the sound from the midrange will be delayed a LOT. A fourth order low pass filter at 2200hz adds a full millisecond of delay.

In summary, the 'source' of the sound is the surface of the cone, but that sound is likely delayed by a low pass filter. (Unless you happen to be using symmetrical first order filters.)



mitchyz250f said:


> For example if I have a tweeter and midrange time aligned with the tweeter directly in front of the mid, after 'phase plugging' are the speakers still time aligned? How about with the tweeter time aligned but above the mid?


An electronic low pass filter adds a delay, and so does a mechanical low pass filter. So there's a couple of ways to go about this. The easy way is to build it, measure it, and then apply time delay with your mic.

The hard way is to realize that the phase plug will give you a first order acoustical low pass. And based on that, you simply move the midranges forward of the tweeter to a point that's equal to the xover filter. For instance, if you had a xover point of 1350hz, you'd move the midranges to a point that's 13.5" ahead of the tweeter. If you increase the order of the filter to 2nd order, you'd move it to 6.75"
If you increase the order to 3rd order, it would be 4.5" away

Hope that makes sense? Each order of low pass is one wavelength. The tighter you pack the midrange and the tweeter, the higher the order. The looser you pack the midrange and tweeter, the lower the order.








Do that, and it's going to look a lot like a Synergy horn, or a JBL Vertec, or an EAW Anya. The reason that the midranges in the Synergy horn aren't quite 13.5" ahead is because you always have to add the distance from the surface of the cone to the exit of the phase plug, and that's about 2.5". And there's also another 3" or so in the phase plug of the compression driver. And the filter order is something like 3rd order. (A combination of an acoustic low pas from the phase plug and an electrical low pass from the passive crossover filter.)










That last paragraph was hideously technical. The main point here is that JBL and EAW and Danley are using the phase plug to create an acoustic low pass filter, and to change the apparent size of the midranges. In the Danley, they have four midranges which have as much output as a single 10" midrange, but those drivers are radiating through eight 3/4" ports. So it behaves as if it was being driven by speakers the size of a tweeter, but it has output like a 10" midrange. You can see how this is really attractive for a high output system; the polar response of a driver that's tiny, with the output of a driver that's large.



mitchyz250f said:


> My mid-basses are in my rear quarter panels which are not at an ideal location for maximum stage width. Could I move the perceived sound past the edge of the mid bass? Could I make a phase plug that completely covered the MB and turned into a 'rectangular slot' like a slot port on a subwoofer? As long as the area was 25% of the area of the cone? Would the calculations you provided still apply? What are the limits of the length of the port?


Are they firing UP or firing sideways? If they're firing UP you could widen the stage by masking off 75% of the cone. Basically make it so that it behaves like a 3" driver that's mounted at the edge of the car.

If they're firing sideways, like the old Buick Grand National, I'm not sure a phase plug could do a lot. You could probably raise the stage by making it behave like a smaller driver that's mounted higher.



mitchyz250f said:


> Would that technique work on midranges also?
> 
> Is it beneficial to radius the edges of the phase plugs to reduce detraction?


Yes, it works at all frequencies. Many companies use phase plugs on every single driver. IMHO, it's far easier on midranges, midbasses and woofers. On woofers it has limited use, because woofers are tiny compared to the frequencies that they generate. It still has the ability to reduce distortion and to create an acoustic low pass though, even on subs.

IMHO, the real 'bang for the buck' is for midrange and midbass duty. If you have a 3D printer you could take a crack at high frequency phase plugs, but it's a real art. At midrange and midbass it's pretty simple, just decide what size and shape of the wavefront you want and cut a hole.









The JBL phase plugs are pretty darn simple. They have a ribbon shaped wavefront for the high frequencies, and a ribbon shaped wavefront for the midranges.

















The Lambda Unity has a 1" circular wavefront for the tweeter, and an array of 3/4" circular wavefronts from the midranges. That's your humble narrator. Not my speakers, they're the speakers for a Grammy award winner who lives by my house in Oregon.

Word on the street is that Steven Spielberg uses Danley for mastering his movies too*. (No, Gary didn't tell me that, don't blame him  )

* http://www.avsforum.com/forum/89-sp...12ht-vs-danley-synergy-sh50.html#post35834946


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## mitchyz250f (May 14, 2005)

A lot of information there to digest.

Regarding my attempt to move the sound closer to my direct left and right from my mid-basses that are in my rear quarter panels. Could I use a slot (phase plug?) like the one in the image below to move the sound beyond the perimeter of the speaker?

I got confused in your response between 'crossover induced delay' and 'phase plug induced delay' so I hope you don't mind if I use a drawing from your '28 weeks later' thread to ask a question. If have two 6.5" mids (with 5" cones) and effectively I block off 1/2 the cone as in the image below; what is my phase change at a 2000Hz crossover?

And finally what is JBL trying to accomplish with the ceiling speakers?


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> A lot of information there to digest.
> 
> Regarding my attempt to move the sound closer to my direct left and right from my mid-basses that are in my rear quarter panels. Could I use a slot (phase plug?) like the one in the image below to move the sound beyond the perimeter of the speaker?


Yes, you could.

Here's how I always explain this:

Let's say that someone is speaking into a piece of pipe that's a meter long. Where will the sound emanate from? *The sound will emanate from the exit of the pipe, not the entrance.*

BUT, there WILL be a delay.

So you have to compensate for both. You've changed the origin of the sound from one side of the pipe to the other, but the delay is still there.


This stuff gets really confusing when you realize that the origin is actually frequency dependent. For instance, if you've ever heard sound emanating from a heating duct, you'll notice that the high frequencies sound like they're coming from far away, and the low frequencies don't.

Don't get too worried about that; we're dealing with ducts that are so small, you won't have to sweat it.

If anyone is curious, the way that this works is that the origin depends on the wavelength; if the wavelength is smaller than the duct, the origin will appear to be in the part of the duct where the wave will fit. IE, high frequencies are short and they'll sound like they're coming from the origin.

But, again, don't sweat that, it won't affect us because the ducts are small.


mitchyz250f said:


> I got confused in your response between 'crossover induced delay' and 'phase plug induced delay' so I hope you don't mind if I use a drawing from your '28 weeks later' thread to ask a question. If have two 6.5" mids (with 5" cones) and effectively I block off 1/2 the cone as in the image below; what is my phase change at a 2000Hz crossover?


It doesn't matter if the delay is caused by an electrical crossover filter, an electronic crossover filter, or an acoustic filter. Low pass crossovers introduce 90 degrees of delay per order.

So a 2000hz lowpass would introduce 90 degrees of delay with a first order filter, 180 with a 2nd order, etc.
2000hz is 6.75" long, so that would have the net effect of delaying the driver by 3.375" for a 2nd order, 6.75" for a fourth order, etc.

Sound travels 13.5" in one millisecond, so 6.75" is half a millisecond. 


mitchyz250f said:


> And finally what is JBL trying to accomplish with the ceiling speakers?


They're using a phase plug on the midranges to low pass the midranges acoustically, reduce distortion, and reduce the apparent size of the radiator. Reducing the apparent size of the radiator improves the off-axis response. Which means that the JBL ceiling speaker with a phase plug will probably sound better off axis than a competitor's ceiling speaker that doesn't have a phase plug.

This is the main reason that all drivers have phase plugs, especially tweeters. You want to make the apparent source of the driver to be smaller than it really is.


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## oabeieo (Feb 22, 2015)

Patrick Bateman said:


> Yes, you could.
> 
> Here's how I always explain this:
> 
> ...



So Patrick , 

That is VERY very intresting and I have a question if you don't mind. 

So the delay that is inherent in a filter of any sort is because the level of attenuation no matter how it is done , via. Electrical , passive, acoustical . I get that . So my question is this . 


And this may be off subject but sorta on subject so sorry in advance . 

So I'll start by saying the helix DSP has the ability to shift midrange in phase by 22.5 deg steps IIRC . So my question is this , 
Let's say you don't have a helix but do have a pioneer p99 which has phase shifts in 180 deg increments. If you wanted to shift 90 degrees you can't . But if you simply set the crossover to Left side 18db crossover and RIght side to 24 db crossover, should that be your 90degree phase shift? I realize it could sound funny but in certian midrange bands it may be beneficial and worth the anomaly in the crossover between Left and Right. Also how could one manipulate a electrical and acoustical/passive combo to get a 22.5 deg shift or 180+22.5 . 

Thank in advance 
Andy


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## mitchyz250f (May 14, 2005)

Thanks again Patrick.

I took a closer look at the JBL ceiling speaker 'Control 47HC' . It appears they are using the phase plugs as a waveguide for the the coaxial tweeter. This limits the interaction of the tweeter frequencies with the cones surface which is the problem that ErinH was seeing with coincident coaxial. Sort of like, kinda like a synergy horn...right?


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## thehatedguy (May 4, 2007)

Exactly like one...or that's what I have been saying for a couple of years now.


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Thanks again Patrick.
> 
> I took a closer look at the JBL ceiling speaker 'Control 47HC' . It appears they are using the phase plugs as a waveguide for the the coaxial tweeter. This limits the interaction of the tweeter frequencies with the cones surface which is the problem that ErinH was seeing with coincident coaxial. Sort of like, kinda like a synergy horn...right?


Unfortunately, no.

If you look at the frequency response plots of the KEF speakers and the Danley Speakers, they both suffer from raggedness in the tweeter range.









This is a measurement of a Danley SH50, this is basically as good as it gets when it comes to Danley Synergy horns. Note the high frequency response; those 4dB dips are audible.









By comparison's sake, here's a QSC waveguide driven. Noticeably smoother.

So, unfortunately, that might be the achilles heel of the design.

If you've followed my projects lately, you'll notice I stopped using compression drivers. This is mostly because I think that SAW lens can do what waveguides do, but cheaper and smoother. Initially I thought that the point of the SAW lens was to bend sound ninety degrees. But the more that I use them, the more I think that they combine the best features of domes (smooth frequency response, small, cheap) without the drawbacks (low efficiency, no directivity control.) I have a plan on the backburner to do a full-on Synergy Horn with a SAW lens, and not a tiny one like the one in my Mazda, a big one for the home.

I believe that those dips and peaks in the response of the Synergy Horn are caused by two things. First, reflection and diffraction off the midrange taps. But also due to plain ol' geometry; it's really difficult to get everything equidistant when you're using a compression driver that's the size of a grapefruit.

It might be possible to achieve smoother response than Danley and Kef with a smaller compression driver. But I haven't been able to achieve it myself, and I've mostly given up on that as a goal.



On a side note, in a 'real' Synergy Horn the tweeter needs to be quite a bit behind the woofer. The difference between a Unity Horn and a Synergy Horn is mostly in the crossover, and the crossover requires a tweeter that's a few inches behind the midrange. That's why you can't do a Synergy Horn with a KEF coaxial. All of the Danley Synergy horns, even the ones that use coaxes, have the tweeter behind the magnet or further.

I have two different KEF speakers at my house, and the Synergy Horn sounds way different than them. Definitely better. (I rented an SH50 for half a week.)









Here's what I mean when I say "tweeter behind the magnet"









On a side note, one of the ideas I've been kicking around is to do a Synergy Horn without the horn. Basically my idea is that you could do something like Voxativ's speaker, but you would drive it with one of those $150 B&C coaxials, instead of a $2000 boutique full-range, like Voxativ uses. The way that this works is that the Voxativ enclosure is so tall and wide, it eliminates radiation to the back wall. By doing that, it eliminates those early cues that 'smear' the image of a conventional speaker. The net effect is that the Voxativ images nearly as good as a Synergy Horn (not quite, but it's in the ballpark.) The advantage of driving it with a B&C coax is that you can use the Synergy Horn xover concept to get the B&C to behave like it's a full range driver. If done right, it won't sound like a two-way, it will sound like one unit. (That's the whole idea of the Synergy thing, it looks like one unit and it sounds like one unit.) I think the Synergy Horn images better, but the Synergy Horn is freaking humongous. The Voxativ is as wide and as tall, but it's much MUCH less deep. The volume is much smaller.

If anyone gets an opportunity to audition either one, I'd say that they're the best imaging speakers there are, plus Quads. (Quads, not coincidentally, also work like Synergy Horns.)



[/font]


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## mitchyz250f (May 14, 2005)

Found this pretty interesting read about phase plugs used with horns;

Phase Plugs


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## mitchyz250f (May 14, 2005)

Upto this point we have only talked about cone speakers. Nothing about domes. 

I want to use a Dayton RS-52 for my rear surrounds without a tweeter. Looks like they are only down 5 db at 15k. My MS8 should take out the peak at 12K and fix the top end to 15K or so which should be fine for rears. Would I use the the same basic techniques on the domes as we use on the cones. One of the issues is that at 15K the frequencies as so short I think I could run into cancelation issues. Cool thing about the RS-52's is that they have a metal grill that might form the basis for this work.

Any suggestion or comments?


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## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> Upto this point we have only talked about cone speakers. Nothing about domes.
> 
> I want to use a Dayton RS-52 for my rear surrounds without a tweeter. Looks like they are only down 5 db at 15k. My MS8 should take out the peak at 12K and fix the top end to 15K or so which should be fine for rears. Would I use the the same basic techniques on the domes as we use on the cones. One of the issues is that at 15K the frequencies as so short I think I could run into cancelation issues. Cool thing about the RS-52's is that they have a metal grill that might form the basis for this work.
> 
> Any suggestion or comments?












The dude over at David Ralph's Speaker Pages - Home of the Windows Passive Crossover Designer (WinPCD) tried that, didn't make much of a difference unfortunately.

Those aluminum drivers can be a real p.i.t.a. at high frequencies due to ringing.

You might try sandwiching felt between the dome and the grill. That could dampen the ringing. Ralph just placed it right on the grill itself.


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## Patrick Bateman (Sep 11, 2006)

Looks like JBL is putting these "radiation boundary integrators" into more and more of their speakers.










Here's their new speaker - note the RBI that's used to change the radiation of the 12" woofer.


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## Patrick Bateman (Sep 11, 2006)

Looks like Tom Danley may have noticed this technology, or he may have stumbled across the idea independently.










Here is Doug Winker's car



















Here's the new "Studio One" monitors from Danley Sound Labs. Same idea.

Danley is using a much higher compression ratio. In other words, he's masking off more of the cone. This is no problem, Doug could have used a much higher compression ratio also. I've used compression ratios as high as ten to one (90% of the diaphragm masked off.)


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## Jscoyne2 (Oct 29, 2014)

Can you change the direction of subwoofer waves that easily?

Sent from my XT1710-02 using Tapatalk


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## Patrick Bateman (Sep 11, 2006)

Jscoyne2 said:


> Can you change the direction of subwoofer waves that easily?
> 
> Sent from my XT1710-02 using Tapatalk


This does the opposite: it makes a large driver behave like a smaller one. For instance, if you mask off 75% of the cone of a 6" woofer, you can get it to behave as if it's 3" in diameter.

This is particularly useful with coaxials, because you can get a fairly large coax to behave as if it's a small point source.

If you wanted to change the direction of a subwoofer, easiest way to do that would probably be with a dipole or cardioid.


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## vonbraun (Sep 13, 2018)

Hello, greetings from Argentina. What do you think about Jay Mitchell Directivity Mod (the foam donut) , it´s about guitar speaker.... but... could it be applied in a hi-fi sound system? The mod is mentioned at the first post of this thread.


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## Patrick Bateman (Sep 11, 2006)

vonbraun said:


> Hello, greetings from Argentina. What do you think about Jay Mitchell Directivity Mod (the foam donut) , it´s about guitar speaker.... but... could it be applied in a hi-fi sound system? The mod is mentioned at the first post of this thread.


Yes. The article linked in post #1 is consistent with everything else posted in this thread.


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