# Shapeways Acoustic Lens



## Patrick Bateman (Sep 11, 2006)

A forum member was interested in having some acoustic lenses printed.

If anyone else would be interested, let me know what you're looking for and I'll throw something together, upload it to Shapeways, and measure it.

This would be an easy way to get a version of the system that B&O sells in Audis, Mercedes and Aston Martins.

I have a solid grasp on how the lens works. It is a waveguide, similar to the HLCDs from the 90s, but which does not require a compression driver.









Another forum member posted this a few years back.


Before I go and design something I'd need to know what tweeter people would prefer. Due to the fact that the tweeter fires UP, you probably want a neodymium tweeter. (That'll keep the depth to a minimum.)

Having said that, you could also load it with a compression driver to get some redonkulous SPL. (Don't take my word for it - it's right in the patent.)

If you want to read up on it, google "manny carruba" or "Sausalito Audio Works." (Manny is here in Cali, invented it and licensed it to Bang & Olufsen in Copenhagen.)


----------



## depthsounder (May 19, 2008)

What about this tweeter? 

Tymphany OC25SC65-04
(Can't post links or photos yet)

It might be low profile enough to be contained in the bottom of the unit, allowing a flat bottom which could be mounted anywhere on the dash without needing a mounting hole.

Another option would be a blank flange on the bottom and a cutout for a typical 1" tweeter with screw mounted faceplate. The screw holes can be drilled by the end user to accommodate their tweeter of choice. 

I would be interested in a pair of waveguides if you are printing them. 

-David


----------



## SkizeR (Apr 19, 2011)

**** yes! ive been thinking about trying to make a mold out of these somehow, but wasnt sure. how do you think it would work for the scanspeak R2904? i highly doubt you will be making a large amount for that tweeter since i only know one or two other people with this tweeter, but i would definitely buy a pair, or even just pay for the 3d model of it.


----------



## depthsounder (May 19, 2008)

What frequency range do you estimate the waveguide to have pattern control over? Also, could the rear top portion of the assembly be tapered to more closely match the profile of the waveguide? This would allow it to be pushed further into the corner of the windshield and would look less like a coke can sitting on the dash.


----------



## Orion525iT (Mar 6, 2011)

Dayton Audio AMT Mini-8 Air Motion Transformer Tweeter 8 Ohm

The AMTPOD I think is the the same physical dimensions once out of the cups. I can measure mine sometime today. You need diaphragm size? They are made by 

Edit: Found the diaphragm size of the AMTPOD on Madisound website 19mm x 19mm (they are made by Tianle and rebadged as Dayton at parts express)


----------



## Kevmoso (Jun 4, 2013)

What is the lowest frequency playing neo tweeter that there is? I vote for that one.


----------



## oabeieo (Feb 22, 2015)

Orion525iT said:


> Dayton Audio AMT Mini-8 Air Motion Transformer Tweeter 8 Ohm
> 
> The AMTPOD I think is the the same physical dimensions once out of the cups. I can measure mine sometime today. You need diaphragm size? They are made by
> 
> Edit: Found the diaphragm size of the AMTPOD on Madisound website 19mm x 19mm (they are made by Tianle and rebadged as Dayton at parts express)


I have neo3 b&g and neo8 b&g I have used as tea tweeter and love the way they sound as a tweeter however , I have wanted to try this one, it says very high output , but a 15w rms rating worries me especially at 88db. 
Do these really get loud without blowing? Could you put a 100w car amp on them safely?


----------



## thehatedguy (May 4, 2007)

I think they look the same, but other folks who I think are in the know say the Daytons are not the same as the Tianle.



Orion525iT said:


> Dayton Audio AMT Mini-8 Air Motion Transformer Tweeter 8 Ohm
> 
> The AMTPOD I think is the the same physical dimensions once out of the cups. I can measure mine sometime today. You need diaphragm size? They are made by
> 
> Edit: Found the diaphragm size of the AMTPOD on Madisound website 19mm x 19mm (they are made by Tianle and rebadged as Dayton at parts express)


----------



## Orion525iT (Mar 6, 2011)

thehatedguy said:


> I think they look the same, but other folks who I think are in the know say the Daytons are not the same as the Tianle.


Hmm, really? Well they look identical. The housing look the same. The box was identical. The packaging material is identical. They come with the same half - moon 3M sticky pads. Same sensitivity, same rms. appeared on Madisound at around the same time as the Daytons on PE.

I de - cupped mine to get a smaller profile, so if anyone is willing to do the same with a pair from Madisound, it should be pretty easy to compare.


----------



## Orion525iT (Mar 6, 2011)

oabeieo said:


> I have neo3 b&g and neo8 b&g I have used as tea tweeter and love the way they sound as a tweeter however , I have wanted to try this one, it says very high output , but a 15w rms rating worries me especially at 88db.
> Do these really get loud without blowing? Could you put a 100w car amp on them safely?


I don't know about the 8 ohm vereion, I have the 4 ohm. I have them crossed at 7000 hz 24db LR fed off 125 rms amp channels. How much they are actually getting, I don't know. But they get loud enough for me; louder than any reasonable listening level.


----------



## stills (Apr 13, 2008)

I vote the SEAS Prestige 27TFFNC/G (H1396) 1" Textile Dome Tweeter
Or the hard dome. Common size & shape. Well known performance.


----------



## SkizeR (Apr 19, 2011)

i think the best choice for this would be the scan d3004 or r3004 since 1) theyre amazing tweeters for a good price, and 2) theyre definitely the most popular


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> What about this tweeter?
> 
> Tymphany OC25SC65-04
> (Can't post links or photos yet)
> ...











This works for me.

For a SAW lens you want as little flange as possible. For instance, I have some Dayton RS28s here, and they don't work so hot for this stuff because the exit on the dome is actually close to two inches across, even though the dome itself is just a bit over 1" in diameter. The extra space at the exit screws up the wavefront, because you need a small exit for a good wavefront.


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> What frequency range do you estimate the waveguide to have pattern control over?
> 
> 
> 
> ...


----------



## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> Dayton Audio AMT Mini-8 Air Motion Transformer Tweeter 8 Ohm
> 
> The AMTPOD I think is the the same physical dimensions once out of the cups. I can measure mine sometime today. You need diaphragm size? They are made by
> 
> Edit: Found the diaphragm size of the AMTPOD on Madisound website 19mm x 19mm (they are made by Tianle and rebadged as Dayton at parts express)


Ribbons have the right shape, but the output level sucks.
That's why NEO3s are so big; they basically have to use a large surface area to compensate for the lack of xmax. (Displacement = surface area x xmax)

So basically a NEO3 would have enough output to work, but it's too large
Those little AMTs would have the right size, but not enough output.

Domes and compression drivers are the hot ticket here.


----------



## Mic10is (Aug 20, 2007)

Id definitely be interested once overall dimensions are know. I agree on using the Scan Tweeter


----------



## hot9dog (Mar 23, 2013)

Im getting turned on by reading this thread! Lol but seriously, im very interested in seeing where this goes! I know typically the lens is positioned on the dash, but how would it work if it was rotated 90 degrees and positioned on the A pillar?


----------



## SkizeR (Apr 19, 2011)

hot9dog said:


> Im getting turned on by reading this thread! Lol but seriously, im very interested in seeing where this goes! I know typically the lens is positioned on the dash, but how would it work if it was rotated 90 degrees and positioned on the A pillar?


i was just about to ask this. my tweeters are 4 inches in diameter and pretty much need to be on axis, so it makes for some ****ty blind sponts, especially in a small 2 seater sports car. i was thinking maybe mount them firing across the dash, but the lens sideways towards the center


----------



## Guest (Jun 11, 2015)

I believe Mercedes used a similar technique


----------



## hot9dog (Mar 23, 2013)

Oh wow!!!!!! That looks bad ass!!!


----------



## SkizeR (Apr 19, 2011)

i worked on (i think a mercedes) back when i was working in the city, and when you turned the radio on, two of these lenses rose up out of the corner of the dash. it was pretty sweet


----------



## hot9dog (Mar 23, 2013)

The audi A8 had the lens that rose from the dash. Impressive to see in person.


----------



## SkizeR (Apr 19, 2011)

hot9dog said:


> The audi A8 had the lens that rose from the dash. Impressive to see in person.


That might have been it. It was either a Benz, Audi, or Lexus

Sent from my HTC6525LVW using Tapatalk


----------



## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> This works for me.
> 
> For a SAW lens you want as little flange as possible. For instance, I have some Dayton RS28s here, and they don't work so hot for this stuff because the exit on the dome is actually close to two inches across, even though the dome itself is just a bit over 1" in diameter. The extra space at the exit screws up the wavefront, because you need a small exit for a good wavefront.












I'm thinking the DQ25 instead of the OC25. Here's why:

1) DQ25 has a phase plug. That usually works nicely when you're trying to shape the wavefront. B&O uses one.
2) DQ25 is pretty well known and respected. (Zaph uses 'em.)
3) price is good.

Here's my thought :

If I went ahead and bought ten of these, stuck 'em in a lens, then offered the finish product in this thread, I have a feeling there would be four people interested in a pair. (I'll keep one set for myself  )

Totaly price would be around $50 for the drivers, $20-ish for shipping, and $20-ish for the plastic.

Call it fifty bucks per item, shipped, so I don't end up taking a loss on this.

Thoughts?


----------



## Mic10is (Aug 20, 2007)

any way to just make the lenses "universal" fit for a 1" tweeter? I think youd get more takers that way. Also gives people more options without having to hack something apart to get to what they want.


----------



## hot9dog (Mar 23, 2013)

Dibs on a set.....im in.


----------



## SkizeR (Apr 19, 2011)

mr bateman, is there a specific and exact shape and width/length, or tuning to these lenses?


----------



## Patrick Bateman (Sep 11, 2006)

Mic10is said:


> any way to just make the lenses "universal" fit for a 1" tweeter? I think youd get more takers that way. Also gives people more options without having to hack something apart to get to what they want.


Sure. 

Just pick your entrance diameter and that determines everything else. 

For instance, you could have a one inch entrance for compression drivers and 3/4" tweeters. 

A 1.25" entrance for 1" tweeters. Etc...


----------



## Mic10is (Aug 20, 2007)

Patrick Bateman said:


> Sure.
> 
> Just pick your entrance diameter and that determines everything else.
> 
> ...


I was just thinking that for most car audio applications, a 1" tweeter is pretty standard, so if you were mass producing them, the simplest route would be to do for a 1" tweeter with a a 1.25 or 1.5" flange. basically large enough to fit something like the Scan tweeter which is a pretty standard sized housing etc..


----------



## deeppinkdiver (Feb 4, 2011)

Sub'd! Very interesting project..


----------



## deeppinkdiver (Feb 4, 2011)

Perhaps something for the Sinfoni T25T tweeter.. I know of a few guys that would try it


----------



## Guest (Jun 11, 2015)

I'd be on board with a lens for the T25T....


----------



## gijoe (Mar 25, 2008)

I was in a friends BMW the other day with the B&O sound package. She has a single center speaker with this lens that drops down flush with the dash, the lens intrigued me, and the single, center driver reminded me of an old thread here (also started by Patrick, I believe) about the effectiveness of only using a single tweeter in the center of the dash.

I would be interested in trying both of these concepts out simultaneously in my car.


----------



## Patrick Bateman (Sep 11, 2006)

gijoe said:


> I was in a friends BMW the other day with the B&O sound package. She has a single center speaker with this lens that drops down flush with the dash, the lens intrigued me, and the single, center driver reminded me of an old thread here (also started by Patrick, I believe) about the effectiveness of only using a single tweeter in the center of the dash.
> 
> I would be interested in trying both of these concepts out simultaneously in my car.











Those B&O guys know what they're doing. I've long thought that the SAW lens would work nicely as a coaxial. But I'd always put them right on top of each other. (I made a couple, I can probably dig up the pics.)

The problem with a coax, in this situation, is that it gets tall in a hurry. The ones that I made were something like 6" tall.

It hadn't occurred to me that if you offset it, you're still within one wavelength at the xover point. So it's fairly simple to get good polar response. (A little DSP would go a long way here too.)









Heres the lenses from the Aston Martin









The Mercedes version always seemed a bit silly to me. A plain ol' tweeter in the A-Pillar would be cheaper and work just as well or better. One of the big advantages of the SAW lenses is that you can line up all the drivers on the same axis, and you can keep the height to a minimum.


----------



## Patrick Bateman (Sep 11, 2006)

SkizeR said:


> i think the best choice for this would be the scan d3004 or r3004 since 1) theyre amazing tweeters for a good price, and 2) theyre definitely the most popular


I haven't paid more than $75 for a tweeter in a decade :O

I could probably throw together something generic that would work with a ScanSpeak, but I can't figure out why they're five times more expensive than Vifa. (Besides the obvious - they're made in Denmark.)


----------



## Guest (Jun 12, 2015)

These SAW lenses really do look to be a great option... relatively compact with controlled dispersersion... 

I like it...


----------



## Patrick Bateman (Sep 11, 2006)

SkizeR said:


> mr bateman, is there a specific and exact shape and width/length, or tuning to these lenses?


Yeah, the whole thing is fairly simple.









You start with this, your basic spiral designed by mother nature









Do the math, you got yourself a Fibonacci Spiral









Overlaid with the real thing










read more here : Cloning a $3200 Speaker for $400 - diyAudio


----------



## Patrick Bateman (Sep 11, 2006)

deeppinkdiver said:


> Perhaps something for the Sinfoni T25T tweeter.. I know of a few guys that would try it


The faceplate messes it up.

I have no idea what these cost, but they don't look cheap, and I wouldn't ruin an expensive tweeter just to cram it into a lens.

Stick with the $25 Vifa, it's nice


----------



## Mic10is (Aug 20, 2007)

If this thing over 3" in diameter then my interest starts waning. too large and much work to integrate how I would want to in the dash

http://www.ebay.com/itm/No-3-Audi-A...set-/321753736158?hash=item4aea0463de&vxp=mtr


----------



## deeppinkdiver (Feb 4, 2011)

So you would need a "naked" driver? Just the magnet assembly and soft dome with no housing to do the SAW application? Hmmm.. That would be a pricy trial.

I have a few BNIB pairs of Vifa ring tweeters around here


----------



## Patrick Bateman (Sep 11, 2006)

deeppinkdiver said:


> So you would need a "naked" driver? Just the magnet assembly and soft dome with no housing to do the SAW application? Hmmm.. That would be a pricy trial.
> 
> I have a few BNIB pairs of Vifa ring tweeters around here


Yep.

When something is close to a tweeter, a difference of 1/4" makes a huge difference, because 20khz is less than an inch long.

That's why the 'naked' Vifa tweeters suggested on the first page are such a good fit.

Plus, lets be realistic here, 80% of the expense of the B&O lenses are those ridiculous CNC milled aluminum bits. You can get the same results for $50 if you make it out of plastic.


----------



## Patrick Bateman (Sep 11, 2006)

Mic10is said:


> If this thing over 3" in diameter then my interest starts waning. too large and much work to integrate how I would want to in the dash
> 
> No 3 Audi A4 A5 A6 A7 A8 Q5 All Fitted B O Type Auto Rising Tweeters Set | eBay


What's the plan? Add some 'sparkle' to your compression drivers? Or are you thinking about going with dome tweeters?

A dome tweeter with high power handling would be a good match for either option.

I like point source arrays, but I can understand if some people want to spread the drivers apart.


----------



## deeppinkdiver (Feb 4, 2011)

Patrick Bateman said:


> Yep.
> 
> When something is close to a tweeter, a difference of 1/4" makes a huge difference, because 20khz is less than an inch long.
> 
> ...


Id be happy to send you my Vifa's to build me a pair, this is something id love to play with..


Im one of the guys that can model and make one of those ridiculous CNC milled bits, maybe.. But it is certainly cheaper, easier and more realistic to print exactly what is needed. Ive really thought about getting a printer, I have expierience with them from work, thats about all I can say.


----------



## gijoe (Mar 25, 2008)

Patrick Bateman said:


> Those B&O guys know what they're doing. I've long thought that the SAW lens would work nicely as a coaxial. But I'd always put them right on top of each other. (I made a couple, I can probably dig up the pics.)
> 
> The problem with a coax, in this situation, is that it gets tall in a hurry. The ones that I made were something like 6" tall.
> 
> ...



Patrick, does the shape of the lens change depending on whether or not you use a single, center tweeter, or a traditional 2-tweeter setup? I didn't get a close look in the BMW, nor can I tell from the photo you posted, but I wonder if in order to optimize a single center tweeter the lens would need to focus the waves to two locations, left and right, of if there is still a single focal point.


----------



## Patrick Bateman (Sep 11, 2006)

gijoe said:


> Patrick, does the shape of the lens change depending on whether or not you use a single, center tweeter, or a traditional 2-tweeter setup? I didn't get a close look in the BMW, nor can I tell from the photo you posted, but I wonder if in order to optimize a single center tweeter the lens would need to focus the waves to two locations, left and right, of if there is still a single focal point.


Take a loudspeaker and put it on your dash. It's going to sound like the sound is coming from a point in space that's a few inches above the driver. Also, the location of the driver will be 'blurred', the sound won't seem to be radiating from a single point in space. 

All of this happens because of early reflections. 

Early reflections are A Bad Thing, because they shrink the soundstage. But they're also kinda hard to avoid, particularly in a small environment like a car. So facing the loudspeaker UP doesn't avoid those reflections, but it scattered them in space and time. 

You can listen for yourself; go get some tweeters and put them face up on the dash, then try different locations until you find one you like. 

You'll notice the top octave is rolled off. *All the lens doors is take that top octave and it bends it 90 degrees.* So that the tweeter doesn't sound rolled off when its face up.

Basically there's no need for more than one shape because there's only one shape that will bend it 90 degrees.


----------



## Jepalan (Jun 27, 2013)

This is probably a really stupid question, but is there any advantage to using this acoustic lens versus mounting similar tweeters in "orbs" (same dash location) and aiming at the listener on-axis? 

What are the pros/cons comparing these two mounting methods? Since the lens dispersion is still essentially cardioid, what is the diff?


----------



## cajunner (Apr 13, 2007)

it goes back to the box shapes, with diffractive changes for most shapes but the pretty response curves goes to the cylinder (a-la-Pluto) and the sphere, or orb.

when you put the thing in an omni mount, but cut the back half of radiation out, it concentrates the acoustic energy in the forward field, whether or not you "sausalito" it out or just add a baffle.

the nice thing about this design is that the windshield and the dash, in some vehicles form a natural waveguide that should address lower frequencies, there's no need for platters above and below. The sausalito itself throwing the top octave forward means there is a portion of the audio that is naturally narrowing the vertical dispersion, and the normal dash sound of early reflections is tamed and the clear response of the tweeter can play through. The only problem is that the baffle will block some people's vision of the road, based on how they sit in a car. Having a dash with factory holes that you could squeeze a compression driver into, then using the Sausalito principle of reflector/baffle logistics above the drivers, could bring some extra definition to the highs and possibly upper mids as well.

Anything that controls the dash/windshield sound field to allow dash mounting a driver but getting 180 degree forward radiation from it, sounds like a step in the right direction.

pointing the tweeter in an orb is doing nothing at all to suppress those first bounces above and below the pod, and leaves the "veil" in place.


----------



## Jepalan (Jun 27, 2013)

So, I *think* you said..

While horizontal dispersion is similar between this lens design and an orb, the vertical dispersion is more controlled and therefore reduces *some* of the early reflections (and the the bad things that come along with them).

Yes?


----------



## cajunner (Apr 13, 2007)

Jepalan said:


> So, I *think* you said..
> 
> While horizontal dispersion is similar between this lens design and an orb, the vertical dispersion is more controlled and therefore reduces *some* of the early reflections (and the the bad things that come along with them).
> 
> Yes?


pretty much?

I'm just guessing, that Patrick's now all-inclusive use of "wave guide" extends to whatever is being put above, behind, and around the dome tweeter or compression driver exit.

Since it's been said the Sausalito adds at least 2 db to a dome's regular sensitivity, I would assume that it is because of the concentration of acoustic energy into a half pie, or steradian mess?

Having fun with words. Anyways, I believe the use of the Sausalito is a definite improvement to the regular upfire into the angled windshield by a dash mounted driver.

I haven't heard it, of course but there are a few manufacturers out there who are betting it's better, to put them in the spotlight of motorized panels and pods.


so, if I had to guess, the use of the sausalito in a more invested size like say, a 2" dome midrange and 6" of lens height, would work better if it could be partially recessed into the dash, along with the cool driven motorized pods.

for that matter, a drop-down dash that reveals the large-sized Sausalito acting in the cardioid fashion, brought forward just a couple of inches and with enough rear space to give "air" around the instruments, haha...


----------



## rimshot (May 17, 2005)

Goodness! That makes me want to throw my pillar plans out of the window!!! I need two of these for my sails. I dont mind the idea of a modular tweeter setup, iam so indecisive anyway. Patrick, thank you for clarifying that this won't work well for wide bandwidth.


----------



## Patrick Bateman (Sep 11, 2006)

Jepalan said:


> So, I *think* you said..
> 
> While horizontal dispersion is similar between this lens design and an orb, the vertical dispersion is more controlled and therefore reduces *some* of the early reflections (and the the bad things that come along with them).
> 
> Yes?


No.









According to Floyd Toole*, we want loudspeakers with WIDE horizontal directivity, and NARROW vertical directivity. This is why JBL speakers have waveguides that are WIDE horizontally and NARROW vertically. *The shape of the wave matches the shape of the waveguide.*

In the JBL pic, you can see that there's a small waveguide stacked on top of a large waveguide. The reason why the waveguides are a different size is because the waves are longer as you go lower. For instance, 1khz is 13.5" long, and 10khz is 1.35" long. *As you go lower, the waveguides gotta get bigger.* But note that the ratios stay the same : wide and short. That wide and short shape gives you the wavefront shape they're after.









Those crazy Danes are doing the same thing as JBL, but they can't have a speaker that looks utilitarian, so this is what they came up with. The platters in the design do the exact same thing that the waveguide in the JBL design does. It 'squashes' the wave into a wide and short shape. (Remember, wide horizontal directivity, narrow vertical.)

Though the speakers look different, the goals are the same. Where the Danes take a left-turn is that the Danish speaker radiates to the front *and* the back. I've heard the Beolabs, and I've heard tons of JBL speakers. The Beolabs sound more 'spacious' because you're getting some early reflections off of the back wall. The JBLs sound more 'dry', it's closer to a giant pair of headphones than the Beolabs.









Those Danes are wacky. I was in Copenhagen for my honeymoon. This hotel was across the street from me. They're very serious about their modern design.



TLDR:
The beolab lens works like a waveguide. It uses a nearby surface to achieve the goals outlined by Harman's Floyd Toole: narrow verticaly directivity and wide horizontal directivity. It's easy to get wrapped up in the "lens" that sits in front of the tweeter, but the platters in the Beolab speaker do most of the heavy lifting. In the car environment, the speaker is designed to use the dash to narrow the vertical directivity.


* https://www.google.com/search?q=directivity+floyd+toole


----------



## Patrick Bateman (Sep 11, 2006)

I'm going to start with something inspired by this B&O lens in the Mercedes.
The earlier lenses, from about eight years back, were larger.
To me, it looks like they reduced the area of the waveguide entrance, which has the effect of reducing the overall size.

I'll see if I can knock something out quickly and get it printed tonight. I'm working out of state this month so it's hard to get a lot of 3D printing done.


----------



## Patrick Bateman (Sep 11, 2006)

For the longest time I thought the SAW lens was a Fibonacci spiral









After staring at it for a while, I think it's simply a circle

Here's the start of the lens.


----------



## Jepalan (Jun 27, 2013)

Patrick Bateman said:


> TLDR:
> The beolab lens works like a waveguide. It uses a nearby surface to achieve the goals outlined by Harman's Floyd Toole: narrow verticaly directivity and wide horizontal directivity. It's easy to get wrapped up in the "lens" that sits in front of the tweeter, but the platters in the Beolab speaker do most of the heavy lifting. In the car environment, the speaker is designed to use the dash to narrow the vertical directivity.


Thanks Patrick! I found this paper particularly enlightening...
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White%20Papers/LoudspeakersandRoomsPt2.pdf


----------



## depthsounder (May 19, 2008)

The SAW waveguide is a circular rotation of an ellipse according to the patent: US5615176 A

Interestingly enough the inventors recently sold the patent to B&O. They have continued development of a similar waveguide, see patent application US20140119588 A1

-David


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> The SAW waveguide is a circular rotation of an ellipse according to the patent: US5615176 A
> 
> Interestingly enough the inventors recently sold the patent to B&O. They have continued development of a similar waveguide, see patent application US20140119588 A1
> 
> -David


Are you Speakerdave from diyaudio? Or a different Dave? Just curious, you seem to know this well.









It took me a day to sort out why the lens is shaped the way it is, but I think I figured it out:

1) If you wanted a vertical coverage angle of zero, you'd use something that looked like one quarter of an ellipse. As I demonstrated in the earlier post, *the lens isn't an ellipse; it's a quarter circle.*
2) The 'trick' here is twofold. First, the vertical coverage angle isn't zero degrees. Second, the part of the quarter-circle that extends beyond the mouth of the waveguide probably isn't doing a whole lot. 









This illustration from the Paraline patent shows how this works









Here's an illustration that I made which shows how you can use the lens to vary the vertical coverage. IE, you can get a vertical coverage of anywhere from 90 degrees to zero degrees. You could even have a NEGATIVE coverage angle, which would basically focus it to the BACK of the room (or the car.)









I made this animation a while ago that shows how the lens works.


----------



## depthsounder (May 19, 2008)

I go by gtforme00 on diyaudio. I only skimmed the patent to find out what the shape was, you seem to have a more comprehensive understanding of the design. I've been interested in the SAW waveguide since it was made famous by B&O and I happened upon your shapeways thread as I was looking for tweeter mounting ideas in my truck. The OEM locations are upfiring toward the windshield in the dash, the drivers side reflection path puts you directly on axis with the tweeter, and makes it very easy to localize. The SAW lens seems like a clever way to avoid some of those early reflections and it piqued my interest.

-David


----------



## Jepalan (Jun 27, 2013)

Another noob question: what keeps the reflected paths from combining in bad ways with the direct paths? Won't the small PLDs cause combing in the freq response?

Also, wouldn't a parabolic section be required to properly focus parallel paths into a point source (like a solar cooker in reverse)?


----------



## Patrick Bateman (Sep 11, 2006)

Jepalan said:


> Another noob question: what keeps the reflected paths from combining in bad ways with the direct paths? Won't the small PLDs cause combing in the freq response?
> 
> Also, wouldn't a parabolic section be required to properly focus parallel paths into a point source (like a solar cooker in reverse)?


I'm only speculating here, but keep in mind that only a fraction of the radiation is combined by the lens.









In a conventional waveguide, basically 100% of the radiation is controlled by the waveguide. (Because 100% of the sound radiated by the driver radiates into the waveguide.)









In the SAW lens, only a fraction of the radiation is reflected. To be exact, about 50%. (Watch the animation, half of the radiation goes to the front, half goes to the back.)

So, yes, you're right. A fraction of the radiation is out-of-phase. But it's just a fraction, so the impact on the frequency and phase response isn't as significant as if it was 100%, like you get in waveguide.


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> The SAW waveguide is a circular rotation of an ellipse according to the patent: US5615176 A
> 
> Interestingly enough the inventors recently sold the patent to B&O. They have continued development of a similar waveguide, see patent application US20140119588 A1
> 
> -David


That patent inspired me to combine the SAW lens with a waveguide.









Here's a pic of it coming along










When it's done it will look fairly similar to the Image Dynamics HLCDs, except it will be loaded with a dome tweeter not a compression driver.


----------



## Kevmoso (Jun 4, 2013)

Patrick Bateman said:


> When it's done it will look fairly similar to the Image Dynamics HLCDs, except it will be loaded with a dome tweeter not a compression driver.


And have room to add synergy mids?


----------



## deeppinkdiver (Feb 4, 2011)

This keeps getting more and more interesting


----------



## depthsounder (May 19, 2008)

I don't want to speak for anyone else, but the appeal of the original proposal to me was mostly aesthetic. I am looking for a way to reduce some of the late multi path reflections which are inherent in the stock dash placement of my tweeters. I could enjoy a nice shape protruding from the OEM speaker location, it would even be somewhat of a conversation piece ("this is the same tweeter design as in the Audi A8"). 

The latter waveguide, while it interests the acoustics nerd in me and would probably yield superior results in the right installation, doesn't have the same aesthetic appeal or ease of integration that made the original proposal so enticing. I wouldn't mind seeing more of it though as a separate project (on your dash not mine!) :laugh:


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> I don't want to speak for anyone else, but the appeal of the original proposal to me was mostly aesthetic. I am looking for a way to reduce some of the late multi path reflections which are inherent in the stock dash placement of my tweeters. I could enjoy a nice shape protruding from the OEM speaker location, it would even be somewhat of a conversation piece ("this is the same tweeter design as in the Audi A8").
> 
> The latter waveguide, while it interests the acoustics nerd in me and would probably yield superior results in the right installation, doesn't have the same aesthetic appeal or ease of integration that made the original proposal so enticing. I wouldn't mind seeing more of it though as a separate project (on your dash not mine!) :laugh:


I'll return to the regularly scheduled programming on Monday 

There's a big show here in CA on Saturday, and it would be great to get something working for my car by this weekend. (Odds are long, but...)


----------



## Patrick Bateman (Sep 11, 2006)

I've noticed that flat surfaces sound worse than curved surfaces. For instance, if you use a spline to join two surfaces, you lower diffraction and make things sound better. Basically the last thing you want near a tweeter is a sharp edge.

So I redesigned the waveguide from post 60 and replaced the straight walls with curved walls.


----------



## hot9dog (Mar 23, 2013)

This thread constantly give me a geek hard on! I love reading this thread as it develops. Very cool stuff!


----------



## Patrick Bateman (Sep 11, 2006)

I'm not 100% sure how to list the model on shapeways.

Here's a link: https://www.shapeways.com/product/H6T2WAM65/sawlens-6?li=shop-inventory

I'm "PatrickBateman" at SHapeways


----------



## Guest (Jun 19, 2015)

Patrick, are you still planning to model a standard SAW LENS ?


----------



## Patrick Bateman (Sep 11, 2006)

SQ_TSX said:


> Patrick, are you still planning to model a standard SAW LENS ?


Yes, I'll do it on Monday. Focusing on the waveguide option because of the sound-off on Saturday.


----------



## Patrick Bateman (Sep 11, 2006)

depthsounder said:


> The SAW waveguide is a circular rotation of an ellipse according to the patent: US5615176 A
> 
> Interestingly enough the inventors recently sold the patent to B&O. They have continued development of a similar waveguide, see patent application US20140119588 A1
> 
> -David





















Here's my take on what the inventor proposed in that patent. It basically takes the original SAW lens and grafts it onto a waveguide.

I'm curious how it will measure; the ability to use a dome tweeter with a waveguide is attractive.

My version is admittedly kinda ugly, due to the midrange ports and the bevy of screw holes required to mount the drivers. Acoustically, they don't make a difference, but they definitely hurt the aesthetics.


----------



## depthsounder (May 19, 2008)

That looks like a very interesting design, and with the unity-horn-esque features is very "you". Rock those bad boys on your dash this weekend and let us know how it goes! 
epper:

Then please make something that isn't so gosh awful ugly for the rest of us! :laugh:


----------



## Patrick Bateman (Sep 11, 2006)

Well I measured it this morning, and lo and behold, it actually seems to work!

I'm actually a bit surprised really! I've built a bunch of these out of wood over the last few years, and I generally found that it was really hard to get them up to 20khz.

Here's some measurements to show you why I'm kinda stoked.









First off, this is a measurement of a Paraline built by Nate Hansen over at diyaudio. In Nate's measurement you'll notice a long series of peaks and dips across the entire bandwidth of the device. I think that I understand horns pretty well, and I believe that the reason that we see the peaks and the dips is because the horn is too small.

















Here's a measurement I made of some car audio HLCDs from the 90s. See the pattern? The peaks and dips aren't as severe, but they're there. (On the upside, I think that can be reduced quite a bit, check out the "Homster" thread at diyaudio. You can definitely make these horns sound quite good with some tweaks.

















Here's a quick and dirty measurement of the device from post 70. As soon as I hooked it up, I noticed that it sounded "smoother" than my Paralines, and I think you can see the reason why; from 2khz to 20khz there are no major peaks or dips. There's a 5dB dip at 10khz, but it doesn't seem to be offensive. I'd much rather have a dip at 10khz then a peak at 3khz. Or even worse, a peak *and* a dip, like the other two devices exhibit. (Brightness cranked up so you can see the lens better. Tweeter is Dayton RS28.)

















I'm still not out of the woods completely; a really high quality waveguide like the one in my Summas measured like this. But it's impractically large for the car. So getting something close to that kind of performance, from a dome tweeter, is pretty cool.


----------



## Patrick Bateman (Sep 11, 2006)

If a 2" driver is all you can fit, I don't think you can do much better than the Peerless 830970. It's as smooth as a Scanspeak in the midrange and it can take some abuse.

But the stupid frame is flimsy. This is partially unavoidable; in order to squeeze so much output from such a small driver, they made the cone stretch from edge to edge, and it has a lot of excursion too. The Aurasound Whisper suffers from the same fault.



















So I made the back chamber in such a way that it basically "clamps down" on the driver; when it's on the waveguide the woofer is basically sandwiched from BOTH sides. This is just to secure the driver, it's also to avoid cracking the stupid frame. (I've ruined a couple of these by over-tightening the bolts, which cracks the woofer frame.)
By clamping down on the entire circumference of the frame, the stress of tightening the bolts should be spread out.


----------



## Patrick Bateman (Sep 11, 2006)

Going back to post 72, this is pretty close to "ideal" waveguide behavior. This is a measurement of a Gedlee Summa, from the "great waveguide list" over at diyaudio. There are about five or six waveguides in the world that measure this well.









Here's a measurement of the DIY SAW waveguide I made. This time around *I measured it on a flat table, and added some EQ to offset the high frequency rolloff.* (All constant directivity waveguides require this, and the Gedlee measurement includes it.)

Putting it on a table top smooths out the midrange a great deal, but at the expense of hurting the high frequency response. I can live with that; I'd rather see peaks in the ultra HF response than see them at 2khz or 3khz.









My modest measurement technique. Basically placed it flat on a table. This is fairly close to how it would behave on top of a car dash, or underneath it. The measurement from post 72 was done with the device in "free air".

All in all, I think this is quite good response, especially for such a small device.


----------



## cajunner (Apr 13, 2007)

I'd fill in those Synergy holes, smooth those top/bottom plates with filler, stuff it with some reticulated foam and add a diffraction rollover to the top and bottom.

oh, and I'd elongate one side, so as to "throw" the image to the car's center, that "guide the wave" thing.

on-dash, it might prove to be the sweet spot where the old reflector in a car audio old style horn is gutted and the Sausalito is special fitment.


----------



## Patrick Bateman (Sep 11, 2006)

cajunner said:


> I'd fill in those Synergy holes, smooth those top/bottom plates with filler, stuff it with some reticulated foam and add a diffraction rollover to the top and bottom.
> 
> oh, and I'd elongate one side, so as to "throw" the image to the car's center, that "guide the wave" thing.
> 
> on-dash, it might prove to be the sweet spot where the old reflector in a car audio old style horn is gutted and the Sausalito is special fitment.


I'm going to fill in those "holes" with a couple of midranges 

The back chambers have finished printing and I'm off to Home Depot to get some 3" bolts to mount them.

Should be interesting to see if I can cover five and a half octaves with a $30 Dayton tweeter and a couple of $15 Peerless midranges. We're talking about a $100 point source with wide directivity.


----------



## Kevmoso (Jun 4, 2013)

These are looking pretty amazing! Would the DQ25 be an easy change from the Dayton?
And where are you getting those peerless's (or would that be peerli?) for $15???


----------



## Patrick Bateman (Sep 11, 2006)

Kevmoso said:


> These are looking pretty amazing! Would the DQ25 be an easy change from the Dayton?
> And where are you getting those peerless's (or would that be peerli?) for $15???


Thanks!









If you look at the response of the RS28, from the last page, you'll notice that's it's only down about 12dB at 500hz.

So, oddly enough, it's a bigger tweeter than you'd really need.

IE, one of those little neodymium tweets wouldn't just work, *they'd work better.*

I'd use them myself if I had some on hand, but I don't.

I'm thinking a 1" neo tweeter would be just about perfect.

The RS28 is 1.25" in diameter (hence the name, 28 = 28mm)

And I was honestly surprised that it was capable of reaching 20khz on one of these lenses. Even *without* the lens it's hard to get a tweeter that big to 20khz.


As for the Peerless 830970, I paid $6 for mine a few years back : Peerless 830970 2" Full Range Driver 4 Ohm
They're $15 now : Peerless 830970 2" Full Range Woofer


The $6 drivers appear to be from the Creative "Gigaworks" system:








More than likely, they're the exact same drivers, but they didn't anodize the cones. You see this a lot; Creative uses Peerless and I've seen some Logitech speakers that appear to use Tangband


----------



## Patrick Bateman (Sep 11, 2006)

The Dayton RS28 has some neat features in it that make it sound great.
It has a copper shorting ring to lower distortion, and IIRC, it's largely a clone of a Scanspeak tweeter that costs something like $300 a pair. The Dayton is manufactured by Usher, who largely made a business out of copying Scanspeak.

To my ears, the RS28 sounds "cleaner" than this Celestion compression driver that I have sitting here.

But compression drivers are DESIGNED to be placed on waveguides. And call it what you will, the SAW lens is undoubtedly a waveguide.


















Here's the polar response of the waveguide from the last page, when equalized (fairly) flat and loaded with a Dayton RS28.









In order to do a head-to-head comparison of the Celestion versus the Dayton, I mounted each on the waveguide, added a simple passive filter, then measured the frequency response and distortion. I made the output level about the same. (It's not fair to compare a compression driver at one watt versus the Dayton at one watt, because the compression driver will have much MUCH more output.)

Looking at this graph, I see that the total harmonic distortion of the Dayton (in blue) is noticeably lower than the Celestion. In fact, the distortion in the Celestion is about 0-20dB below the fundamental in the octave from 1-2khz.

Both the dome and the compression driver exhibit a dip at 10khz. This is likely due to the geometry of the waveguide. (If it was inherent to one driver, we would only see the dip in one measurement.)

I think this measurement is also an interesting example of why it's A Very Bad Idea to run compression drivers down to 1500hz or even 1000hz. Although their diaphragms are larger than a conventional dome tweeter, their displacement is often lower because their suspensions don't allow for much xmax. If you look at the RS28, it has a fairly beefy suspension. The Celestion basically has no suspension at all. The reason that Celestion has done this is because the additional weight of a suspension would lower the sensitivity, and in prosound the limiting factor in a loudspeaker is typically the tweeter. So compression drivers usually have insanely high efficiencies (108dB+) but surprisingly high crossover points (2000hz+) The high crossover points are required to minimize distortion; compression drivers are designed for massive output, not wide bandwidth.

We see a couple of unexpected things in the graph:
1) Even though the Dayton is smaller, it has MORE output in the midrange. This is similar to how car subs are designed; they're small but they have a lot of LF output. This comes at the expense of efficiency.
2) Even thought the Celestion is larger, it has MORE output above 20khz. This is likely due to it's phaseplug and it's higher efficiency bandwidth product.

TLDR: in the very important midrange octave of 1-2khz, the $50 Dayton RS28 exceeds the performance of the Celestion compression driver.


----------



## thehatedguy (May 4, 2007)

Which RS28 is that- the A or the F?


----------



## Patrick Bateman (Sep 11, 2006)

Dayton Audio RS28AS-4 1-1/8" Aluminum Dome Shielded Tweeter

^^ shielded version of the RS28A. Was on sale for about 30% less than the unshielded one a few years back.

This is a very nice tweeter.


----------



## thehatedguy (May 4, 2007)

Yeah, they are on my list of tweeters I would like to try...they can play stupid low and are supposed to sound really good.

The DQ25 is a nice little tweeter. The phase shield may or may not be an issue depending on how close you need to get the waveguide to the edge of the dome. It's a really nice inexpensive metal dome tweeter. I used them for a bit. The only thing that annoyed me was a very slight resonance in the 6-7k range...and that took a while to hear and decide if it was really there, and if I could live with it.


----------



## Guest (Jun 27, 2015)

Patrick... any further progress on this project ?


----------



## Patrick Bateman (Sep 11, 2006)

SQ_TSX said:


> Patrick... any further progress on this project ?


Yeah I've made a couple more and about to print a third.

Most of them are on this page:

http://www.diymobileaudio.com/forum...iscussion/180497-28-weeks-later-new-post.html

I went that route because 2/3rds of these are some kind of "variation" on the SAW lens, not a "pure" copy of the B&O design.

I literally have a dozen of these on my computer now, so if anyone wants me to upload anything to shapeways, LMK

I've noticed that Shapeways is quite pricey, so if there's a cheaper option LMK

For instance, what costs me about five bucks to print at home costs about $60 to print at Shapeways.


----------



## Guest (Jun 28, 2015)

Would it be possible to apply one of your designs to my Sinfoni tweeters ?


----------



## cajunner (Apr 13, 2007)

what I think people need, is the tweeter on the dash, not to sound like a tweeter on the dash.

I think the use of a lens, makes perfect sense here, and if that lens could actually create some compression, or at least, added gain in the lower registers of the tweeter while also spraying the interior with that ~100 degrees of beamwidth, that would be great.

I wonder if you just added a hat to a compression driver's exit hole, with the funny little side wings giving you 1/4 pie, or half of the 180 degrees of the Sausalito, it could not only reduce vertical splash off the windshield early reflection, it could also keep the door window bounce down as well?

sort of like focusing a flashlight from flood to a narrowed beam, so that everything that comes from the dash is also not boundary-diffracted?


----------



## Patrick Bateman (Sep 11, 2006)

I owe you guys a lens.

Someone tell me which style you would prefer. There are a bunch of different ways to do this; here are three. The first style has a beamwidth of about 270 degrees - it's close to omnipolar.

The second style radiates into 180 degrees. On the plus side, it will be more efficient, and it will play louder. But it will also take up more space.

The last style is the smallest by far. The downside is that it depends on the boundary behind it. (That's why it's so small.) So if you wanted to do the last style, you would need to figure out some way to get it up on your A-Pillar. If you want the last style, you'll probably need to know how to do some fiberglass work to integrate it into the car.

Also, all of these styles can be inverted; for instance if you wanted to use a big beefy tweeter you could put the tweeter on top and have the device fire upside down. That's what I'm doing with my Mazda.


----------



## deeppinkdiver (Feb 4, 2011)

I personally would be interested in #2 to use on the dash as far into the corners as possible. I do love the idea of the A-pillar design but would that still have glass reflections as a *180deg* set up?


----------



## req (Aug 4, 2007)

thank you for the shout out pat :'(

http://www.diymobileaudio.com/forum/hlcd/113901-bang-olufsen-tweeter-lens-idea.html


----------



## gijoe (Mar 25, 2008)

I also like the first one. It would be easier to install if you could easily have it flush mounted to the flat surface of the dash. The last B&O lens is cool, but if you can fit that lens, you can just as easily fit a tweeter on axis, it would look cool, but there's no reason to over engineer it.


----------



## thehatedguy (May 4, 2007)

120 degrees would be a good coverage angle.


----------



## subwoofery (Nov 9, 2008)

What would it take to create a 90° coverage SAW? 

The car is mostly a cube, right? So a 90° coverage would reduce windshield and side windows reflections... 

Kelvin


----------



## deeppinkdiver (Feb 4, 2011)

^ but would that create more reflections...


----------



## Guest (Jul 2, 2015)

I'm thinking a 90 degree SAW lens would be very good for a vehicle dash... roughly the same dispersion area for an on-axis install.


----------



## Patrick Bateman (Sep 11, 2006)

Looks like a Beolab 9 style lens will be the first one up









Here's some pics of it coming together. Now that I've built a bunch of these, I've learned a few tricks, and I'm applying them here. For instance, in the top right corner you'll see a teardrop shape. That's going to become a waveguide for the tweeter. 


Basically we want to create a slooooow transition from the tweeter diaphragm to the edge of the sphere. That reduces diffraction, makes it sound smoother, makes it harder to tell where the loudspeaker is (aurally), and smooths out the frequency response. If you look at the new patent from the original inventors, they figured this out too. Once it's done it will look a bit like the waveguide pictured above, only much smaller.









I sat in the car for a bit, trying to figure out how to mount these things. The problem is that our lenses won't retract into the dash. The solution I came up with is basically what JAMO does here. Put the speaker on a little circular stand. The reason that we have to do this is because of the curvature of the dash. If you just sit the speaker on the dash, it won't sit right. It will lean to one side. (Unless you happen to have a perfectly flat dash, which nobody does.)


----------



## thehatedguy (May 4, 2007)

Will 90 get both seats equally?


----------



## Patrick Bateman (Sep 11, 2006)

SQ_TSX said:


> I'm thinking a 90 degree SAW lens would be very good for a vehicle dash... roughly the same dispersion area for an on-axis install.


Yeah I thought that narrowing the dispersion was a good idea too. That's why I made this:










Unfortunately I got a rude surprise when I actually measured it in a corner. There was a small gap between the waveguide and the corner, about 1" on each side. And that gap just completely wrecked the frequency response. Sucks.


----------



## Patrick Bateman (Sep 11, 2006)

subwoofery said:


> What would it take to create a 90° coverage SAW?
> 
> The car is mostly a cube, right? So a 90° coverage would reduce windshield and side windows reflections...
> 
> Kelvin











The coverage angle is dictated by the vertical and horizontal angle of the walls. For instance, in the pic above, the horizontal angle is 180 degrees. To get 90 degrees you'd bring the walls in closer, forming a 90 degree angle.

The vertical angle is dictated by the angle of the top and bottom wall. In the pic above, that's zero degrees.

In the real world, it gets more complex. For instance, the lens above should have a vertical coverage of zero degrees, but in the real world it's more like 30 degrees.


----------



## Guest (Jul 2, 2015)

You know your right... 120 might be better....


----------



## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Will 90 get both seats equally?


If you can see the lens, the volume doesn't change. (For the most part.) That's basically the idea behind this thing. If you're in it's beam, the response shape is the same.

So if you have 90 degrees and it's crossfired, it will basically be the same for passenger and driver. (There will be a little bit of a drop due to the unequal distance.)

If you have 180 degrees, same story.

I scrapped the 90 degree unit because the response went to hell when I stuck it in a corner.


----------



## Patrick Bateman (Sep 11, 2006)

Coming along nicely...









the real deal


----------



## Guest (Jul 2, 2015)

Very interested in this design, Patrick. ... Looking good


----------



## Guest (Jul 6, 2015)

Anything new ?


----------



## MDubYa (Feb 17, 2011)

Sub'd... Very intriguing


----------



## Patrick Bateman (Sep 11, 2006)

I'm finding some problems with the SAW lens.

But I think there's a potential solution.

In order to test my hypothesis, I've ordered some 3/4" tweeters from Meniscus. (SB Acoustics SB19ST )

















^^ This is a SAW waveguide I built two weeks ago. I scrapped it because the high end was totally rolled off.

At 10khz it's down about fifteen dB. To put that in perspective, it means that if I wanted it to play flat and I gave it ten watts at 1khz, *I'd have to give it about three HUNDRED watts at 10khz!* Obviously, this is impractical.

By the way, that's a new measurement there. I re-did the measurement, for a reason I'll explain shortly...

















Over the past week I built what amounts to a "clone" of the SAW lens from the Beolab 9. Once again, I used a nice dome tweeter, the Dayton RS28. In the measurement above, *I've EQ'd the polars to about as close to flat as I can get.*

The polars look good. It doesn't matter if you're seated in front of the speaker, or 45 degrees off axis, *the response is basically the same.* That's the magic of the SAW lens, and it is doing it's job.

But I'm seeing and hearing a problem in the response. There's is a dip in the frequency response at 3600hz, 7200hz, and 14400hz. *The thing that has me particularly annoyed about the dip is that the dip is harmonic.* IE, those numbers are a multiple of each other. The reason that sucks is that it "sounds" like distortion. IE, when I measure the loudspeaker, the distortion is about what you'd expect from a dome tweeter. But it SOUNDS distorted, because distortion is harmonic. You could use the cleanest tweeter in the world, and if you put some peaks or dips in the response that are multiples of each other, it's going to sound "grungey" there's just no way to get around that.

I didn't notice this "grunginess" with the SAW lens from two weeks ago. It definitely needed more "sparkle" but it didn't sound distorted.

So we're at a fork in the road here:
We have one lens that won't play to 20khz, but sounds clean.
We have another lens that will play to 20khz, but sounds "grungey."

Rather than go with either option, I think I have a solution. I believe that the harmonic dips in the response are caused by the fact that the geometry of the lens is symmetrical.









Siegfried Linkwitz* demonstrates on his web page that a circular baffle will exhibit these harmonic dips. I think we're running into the same problem with the SAW lens, particularly when done the way that B&O is doing it in the Beolab 9. If you'd like to learn more about this phenomenon, read this: Diffraction from baffle edges

I know that Linkwitz basically dismisses the audibility of these artifacts, but I couldn't disagree more strongly. Perhaps it's due to owning Gedlee Summas for so long, but I find diffraction to be horrendously audible. I hear it a lot in car stereos and I can't stand it.

I believe that I can create an improved version of the SAW lens, by doing the following:
1) breaking up the symmetry of the lens, which I believe is causing the harmonic dips in the response
2) using a smaller tweeter, which allows the use of a smaller lens, which pushes the dips higher in frequency where they're less audible

The bad news here is that my solution might mean that all of those nice 1" tweeters that everyone uses won't be good candidates for a SAW lens. You're welcome to use the lens I finished last week, it will work fine with a multitude of 1" tweeters. But I personally feel like we can do better than that.



* On a side note, it hit me the other day that Siegfried and I might work at the same place. I looked him up in the corporate directory, looks like he retired a while back. But it's still neat to have the same place on my resume!


----------



## Patrick Bateman (Sep 11, 2006)

Some more reading on diffraction:

https://www.trueaudio.com/st_diff1.htm










_"The worst case appears to be placing the driver at the center of a circular baffle so that it is the same distance from all diffracting edges."_

^^ There's another article on the phenomenon, from John Murphy, designer of the Dayton woofer tester. If you look at the SAW lens from overhead, you'll realize that it's basically a worst case scenario. The solution would be to get rid of the symmetry that's causing the diffraction in the first place.


----------



## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> Yeah I thought that narrowing the dispersion was a good idea too. That's why I made this:
> 
> 
> 
> ...




On page eight of this thread, I posted some pics of this waveguide that I printed. The waveguide worked really nice anechoically, but once I stuck it in a corner, the response got nasty.

I've been unsatisfied with many of these SAW lenses that I've built. The ones that used the Dayton RS28 dome suffered from a dip in the response, sometimes many of them.

I believe the dip is caused by a reflection inside of the lens. Due to that, I figured that using a smaller tweeter would improve on things.









Luckily, I was correct. Here's the polar response of that same waveguide, but this time loaded with a 3/4" tweeter instead of a compression driver. It took a lot of power to get to this level, probably something like fifty watts. *But you can see the polars are about as good as it gets, and the distortion is very low too.*









That measurement used EQ to flatten out the response. This is something that you have to do with all constant directivity waveguides, it is unavoidable. Here's the completely "un-eqd" response. You can see the distortion is still low, but it needs a lot of EQ to bring up the top end. The good thing about this tweeter is that the EQ actually WORKS; with the Dayton RS28 the EQ didn't have much of an effect. This is because the large diaphragm of the RS28 is struggling to hit 15000hz, much less 20khz. (The surface area of the RS28 is almost four times as large.)









Here's the exact same waveguide, but loaded with the Celestion CDX1-1445 compression driver. The Celestion actually has higher distortion! This was unexpected, compression drivers are generally really clean.

This one is a no-brainer - the 3/4" tweeter is less than half the price of the Dayton or the Celestion, it is smaller, and it is cleaner. I know Zaph hates on the 3/4" tweeters, but on waveguides, smaller is often better. The fact that it's smaller makes it easier to hide too.

Dare I say it, I think we (finally) have a winner here. The SB Acoustics 3/4" tweeter.


----------



## cajunner (Apr 13, 2007)

I wonder if you put the baffles in a jagged edge pattern, if it would break up the harmonic plague?

like, broken pie plates for top and bottom baffles. Sort of the Doug Winker JBL 2118 fix, but applied to the Sausalito?

maybe the harmonic ringing is from diffraction caused by comb filtering, with the portion of the signal *not* thrown against the concave/convex elements and dealing with platter rebound?

sort of the HOM of a guide, but in ! 1/4 pi, half steradian... 

yeah. 

like I know what I'm talking about, hahahahahahah..


----------



## mitchyz250f (May 14, 2005)

What about using felt to reduce the edge detraction?


----------



## Patrick Bateman (Sep 11, 2006)

mitchyz250f said:


> What about using felt to reduce the edge detraction?


I'm generally opposed to using damping; I've found that damping absorbs a huge amount of the original sound.

That's great if you have a thousand watts on tap, but I generally use small amps. Damping can seriously cost you ten or twenty decibels of output.

Not saying that I'm 100% opposed to it; I occasionally use it in my midbasses and subs. But at high frequencies I'm trying to extract every last decibel out of my tweeters, because I generally stick to one or two.

And due to that, I avoid any damping at high frequencies.


----------



## cajunner (Apr 13, 2007)

maybe line the top and bottom platters with 1/4" thick Sorbothane in the 25 durometer?

if B&O can cut the platter size down to a little shelf, it could be the wave bounce off the top platter causing the comb filtering with the omni dispersion of the dome.

but part of me thinks that you're trying to go too far down (in frequencies) for the lens with the "in the corner fail" experiment, as those polars looked really good and you shouldn't blame it on your guide to boundary diffraction/mismatch.

let's get back to the thing that worked, there is likely a lower limit at which trying to go lower or get more output at speed, is hitting a physics wall of deconstructive wave formation.

did you try a top platter with semi-permeable membrane yet?

or with screen perforation percentages in the under 20% open ratio?


----------



## Patrick Bateman (Sep 11, 2006)

A few weeks ago I figured out how to make elliptical waveguides with a circular throat. That probably sounds kinda 'meh', but it allows for some really nice waveguide performance. The reason for this is because sound radiates spherically. A lot of waveguides are rectangular, and you're basically trying to push a round peg into a square hole. (Not saying rectangular is the end of the world... but if you really want to get to 20khz, you probably want a really smooth transition, and that's hard to do with a square mouth and a round throat.)

Anyways, figuring out how to do elliptical waveguides was a real breakthrough and it yielded this nicely performing waveguide here:

http://www.diymobileaudio.com/forum.../219681-nice-cheap-waveguide.html#post2941401

Not to get too full of myself, but I've been trying to get this to work for something like ten years now. It's REALLY hard to squeeze a waveguide onto the dash; the size gets huge in a hurry, and it's hard to bend sound 90 degrees at 20khz. This waveguide achieves that.


----------



## 94VG30DE (Nov 28, 2007)

Patrick Bateman said:


> depthsounder said:
> 
> 
> > What frequency range do you estimate the waveguide to have pattern control over?
> ...


----------



## Patrick Bateman (Sep 11, 2006)

If you're copying the B&O style lens, I'd stick with what they did: a 3/4" tweeter. My best results in a B&O style lens used a SB Acoustics SB19.

There's an evolution of the design that puts the lens at the throat of a waveguide. Using that device, you can use a wider variety of drivers. For instance, the Whisper.

The reason is because adding a waveguide raises the on-axis output. By quite a bit, over six decibels.

Without that bump in efficiency, the Whisper is kinda useless because the efficiency is so low.


----------

