# 250 - A Sweet Front Stage On The Cheap.



## Patrick Bateman (Sep 11, 2006)

In this thread I'll detail a new system I'm working on for my car. The goals of this design are a system with world class imaging, that's also dynamic.

First off, *how does imaging work?*

The way that we perceive a stereo image is that we hear a sound from the loudspeaker, and the sound arrives at our ears at the same time, with equal intensity, across the frequency spectrum.

There are many things that can distort the location of an image:

1) if the speakers are not equivalent in intensity, the image will shift towards the LOUDER speaker. IE, the frequency response must match from left to right. A difference of even three decibels will cause the soundstage to collapse.

2) if the sound from one speaker arrives before the other, the image will shift in that direction.

That's about all there is to it. Make the speakers equidistant, and make them have the same frequency response. Of course, the devil is in the details, because in a car we can't do that easily.









A wide range driver like the Fountek FR89EX can image well. This is because all of the sound is radiating from a 3" point in space. There's no interactions between a midrange and tweeter, because a single driver is doing everything.









In this polar measurement from Erin's site, we see the main problem with wide range drivers. First, the driver begins to beam. In this measurement, we see that the on-axis and off-axis response begins to diverge around 4khz. *This is due to the size of the driver.* A 7.62cm driver will do that, beginning at 4,461hz. (speed of sound / diameter = 34,000cm per second / 7.62cm)

The other problem with wide range drivers is a lack of dynamics. Small drivers have low efficiency and small voice coils. The FR89EX is running out of steam at an SPL in the 90s. That's barely 20dB over the noise floor of some cars. This kills your dynamics.

In summary : the FR89EX is quite good. But imaging cues above 4khz will be problematic, because it is not possible to make the left speaker match the right, unless you EQ them so that they're asymmetric. Which introduces another can of worms.

But it's still a good speaker. But it would be a better speaker if it was smaller. But if you made it smaller, you would make the dynamics worse. And that's why it's the size that it is. It's not so big that it will have no image, and it's not so small that it will sound anemic. It is right in between those two goals.

































Here's some pics of a waveguide I built. The idea is to get something like that Fountek FR89, but louder, more dynamic, and without the 'beaming' problem that it has above 4khz.
The first two pics show the 3D model, designed in Autodesk Design 123D.
The next pics show the 3D printed result.









There are three drivers on the waveguide. First, there's a tweeter. Or a compression driver, to be more accurate. I am using the Celestion CDX1-1445. In the measured polar response above, *we see that the on and off-axis response is basically the same, all the way to 10khz.* Things get a little ragged in the last octave from 10-20khz. But this is a significant improvement over the Fountek, which starts to beam at 4khz. The waveguide gives us even response to 10khz, and the Celestion is much MUCH louder than the Fountek.









Here's the response with the midranges on, and with them off. *We see that the midranges on the waveguide extend the response by about an octave and a half.* Our F3 goes from 2khz to 700hz.









Here's the money shot. This is the polar response of the waveguide, with all three drivers working in Synergy. (Get it? Synergy Horn.)

To the microphone, the three drivers basically act like a single wide range unit, with a bandwidth of five octaves, from 700hz to 20khz. Now it's true that there are wide-range drivers that can cover the same bandwidth. But the wide range units fail at two tests:
1) Their directivity isn't this good
2) Their output isn't this good

The reason for this is the waveguide. Waveguides are basically The Gold Standard for directivity control. Yes, you can do it with an array, but you can't do it as seamlessly as a waveguide can. The other thing that the waveguide does is increase output. In this measurement, we see that the output of the Peerless 830970 has risen by about ten decibels. If you used the 830970 as a 'direct radiator' you'd be lucky to get 95dB out of it. But on a waveguide our output goes up to around 110dB. The reason that we get such an efficiency bump is that it doesn't take much of a horn to horn-load a small driver. For instance, if you want to horn load a driver down to 500hz, you only need a horn that's 17cm deep:
(speed of sound / frequency / 4) =
(34,000 cm per sec / 500hz / 4) =
17cm.

In the horn above, part of the pathlength is in those funky crayon shaped things hanging off the side. I'll get to that shortly.


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## Patrick Bateman (Sep 11, 2006)

https://www.youtube.com/watch?v=MFhq4MId9Wo

Here's a video of the waveguide being printed. I am using a Printrbot Simple Metal. About $600 from Amazon. You can have the waveguide printed by Shapeways, shouldn't cost much. I used up five dollars worth of plastic. In fact, the epoxy and carbon fiber that I used to glue the waveguide to that piece of wood probably cost more.

I'll post the STL file at some point, in case someone wants to have one printed for themselves.


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## Patrick Bateman (Sep 11, 2006)

One 'neat' thing about Synergy horns is that it's actually possible to get the drivers to blend, *with no crossover.* John Hasquin over at diyaudio was the one that clued me into this; basically if you tweak the distance from midrange to tweeter, and you tweak the size of the phase plug, *poof*:

Full range response, no xover.

That's pretty wild. I am not aware of any other speaker that can do that. I've seen some two-ways that could do it if you kept the mic at *exactly* the right spot. But check out my polars, the response doesn't change (much) as you move the mic.

I *did* use two components in my crossover, but they're basically there to reduce the output on the compression driver, and to compensate for the high-frequency rolloff that's introduced when you put a driver on a constant directivity waveguide.

Anyways, here's the parts list at this point:









Celestion CDX1-1445 Ferrite 1" Compression Driver 20W
Celestion CDX1-1445. A rather awesome compression driver, at a great price ($45)









https://www.madisoundspeakerstore.com/approx-2-fullrange/peerless-830970-2-full-range-4-ohm/
Peerless 830970. I'm kind of amazed more people don't use this driver. There are plenty of cheap 2" drivers made for television sets. The Peerless isn't one of them. It has a copper cap to extend high frequency response and lower distortion. The really killer part is the absurdly large voice coil. And inch in diameter. I've seen 6" woofers that didn't have a 1" voice coil. The 830970 is built like a tiny subwoofer. I've been using Dayton ND91s for a lot of my projects, but I think the 830970 gives them a run for their money, in a smaller package, with better build quality. They're under twenty bucks.

The waveguide costs about five bucks, depending on how you print it.

At this point, the crossover is two components. There's a 10ohm resistor in series with the compression driver, to reduce it's output and to extend the high frequency response. And there's a 1.5mfd cap that goes between the resistor and the positive output of the amplifier.

So the crossover looks like this:

positive on amp -------> 1.5mfd cap -------> 10ohm resistor -------> positive terminal on Celestion CDX1-1445

There's no crossover on the midranges. The midranges are wired in series. Yes, you read that right, I had to wire them in series because they were too loud in parallel(!) Gotta love horns.

That's a total of less than $100 to build one waveguide, including the drivers and all the xover parts.


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## Victor_inox (Apr 27, 2012)

Interesting in car implementation, subscibed.
Synergy horns could sound terrific, this one does.


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## thirdman (Jan 23, 2015)

:bowdown: That is awesome. How long did it take to print the waveguide? ooh, and how does it sound?


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## Orion525iT (Mar 6, 2011)

Gee Patrick, you had to get all fancy on us with the 3D printer. I was a bit worried that I would not be able to identify your contraptions on sight based on their construction. But now I see that at least you are still cobbling things together somewhat. 

I was making plans for something similar with a pair of aura whispers using a conjoined phase plug mated to a wave guide. The goal was the same as you have posted here. But, the idea of the conjoined plug was to see how high up in frequency I could play the whispers alone. Two drivers would allow for my desired ohm and power handling. The wave guide would be tiny 

Is this suitable for a two seat set up, or is it best reserved for one seat only?


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## thehatedguy (May 4, 2007)

Why would you not go to the kick panel for something like this? You would have much more horn area if you counted the floor and the bottom of the dash as an extension of the horn.

And it would make packaging it easier...especially when driving. It might be me, but that driver hanging down like that where it is at would annoy the living hell out of me.


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## Patrick Bateman (Sep 11, 2006)

thirdman said:


> :bowdown: That is awesome. How long did it take to print the waveguide? ooh, and how does it sound?


Thanks!

It took 3.5 hours to print the waveguide.

The sound is a revelation. If you look at all the polars that I've posted of my various Synergy horn projects, there's ALWAYS a dip in the midrange. The dip might be three decibels, or it might be ten decibels. But it's ALWAYS there.

It sucks, because the last place you want a dip or a peak is between one and two kHz. Our ears are insanely sensitive at those frequencies, so even a small problem will grow fatiguing.

But check out those polars from this waveguide; they're completely seamless.

If anything, it has me re-thinking my 'Black Mirror' project, my home speaker project which I was actually quite happy with.

Now, obviously, I'm being a bit hyperbolic here. Black Mirror is an awesome sounding speaker, and tossing it in the trash over a minor dip in the midrange is kinda OCD. But this waveguide does sound really really good.

I think there's a couple of keys to this:

1) Those peerless midranges are awesome. Lots of output, wide bandwidth, low distortion

2) I think using a proper phase plug improved the roll off of the midrange, and that smoothed things out at the xover point


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> Gee Patrick, you had to get all fancy on us with the 3D printer. I was a bit worried that I would not be able to identify your contraptions on sight based on their construction. But now I see that at least you are still cobbling things together somewhat.
> 
> I was making plans for something similar with a pair of aura whispers using a conjoined phase plug mated to a wave guide. The goal was the same as you have posted here. But, the idea of the conjoined plug was to see how high up in frequency I could play the whispers alone. Two drivers would allow for my desired ohm and power handling. The wave guide would be tiny
> 
> Is this suitable for a two seat set up, or is it best reserved for one seat only?


The main thing that sucks with these 2" drivers is that their efficiency bandwidth product is too low. Even with a fairly elaborate phase plug on the 830970s, I'm only getting them to play to about 2khz.

If you want to get something to play past 2khz, you'll have to start looking at compression drivers, or something with a higher EBP

Basically there's a reason that people spend $500 on beryllium diaphragms; the only way to get a driver to play to ten or twenty kilohertz is to lower the mass, because EBP dictates the upper limit of the driver on a horn or waveguide


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Why would you not go to the kick panel for something like this? You would have much more horn area if you counted the floor and the bottom of the dash as an extension of the horn.
> 
> And it would make packaging it easier...especially when driving. It might be me, but that driver hanging down like that where it is at would annoy the living hell out of me.


To get a boundary to extend a waveguide, you need a seamless transition from the mouth of the waveguide to the boundary.

If there's a brief gap, it ****s things up, because you get diffraction at the gap

That's what sucks about putting horns in the kick panels; you have to push the horn all of the way into the corner. And that's not possible unless you use a dome tweeter.

Which WOULD work by the way. I use a Vifa XT25 for my Monster Massive project and it worked fine. But for this project I'm using a compression driver, so that necessitates that it goes under the dash.


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## thirdman (Jan 23, 2015)

"One 'neat' thing about Synergy horns is that it's actually possible to get the drivers to blend, with no crossover. John Hasquin over at diyaudio was the one that clued me into this; basically if you tweak the distance from midrange to tweeter, and you tweak the size of the phase plug, *poof*:

Full range response, no xover."

This is one sahweet trick, thought it was worth quoting. I just need to get may hands on a 3d printer that can do about a 3ft square..:laughfor home us of course)


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## Patrick Bateman (Sep 11, 2006)

Right now the midranges are hanging off of the side of the horn. It looks a lil' weird, admittedly.









Here's the predicted response of the waveguide, with two drivers, and 10 watts for each driver. 20 watts total. Due to the wonders of horn loading, we're getting close to 105 decibels of output with 20 watts. To put that in perspective, that's about ten decibels more output than the Fountek can muster.









It occurred to me that you could wrap a tapped horn around the waveguide. The advantage of doing this is that you can use a much longer horn. And a longer horn will "load" the driver to a much lower frequency. Basically more SPL and a lower F3, at the expense of a larger enclosure.









Here's the predicted response of a *tapped* horn, using the same woofer. This time around, there's one woofer instead of two. Because there just isn't space for two tapped horns under the dash.









Here's the two, side-by-side. We see that one driver in a tapped horn plays lower and about as loud as *two* drivers in a front loaded horn.










It would basically look like an ID HLCD, but with a tapped horn wrapped around it. Forgive my crappy drawing, I'm in Vegas and I should be outside having fun, not here in the hotel on my work laptop


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## Kevmoso (Jun 4, 2013)

Patrick Bateman said:


>


Wait. What? That response and output from a single $20 midrange? That would be amazing!
Some time ago you did a tapped horn sub with 3 8" woofers. Could that type of approach be used here instead of having two separate tapped horn paths? 
I guess not given how the mids synergy entrance to the waveguide is...


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## Patrick Bateman (Sep 11, 2006)

Kevmoso said:


> Wait. What? That response and output from a single $20 midrange? That would be amazing!
> Some time ago you did a tapped horn sub with 3 8" woofers. Could that type of approach be used here instead of having two separate tapped horn paths?
> I guess not given how the mids synergy entrance to the waveguide is...


Thanks!

Yeah, you can get about ten decibels of gain by horn loading. So a 2" midrange with an efficiency of 82dB winds up being about as efficient as an 8" prosound direct radiator.

Displacement winds up being the thing that will limit you, so you have to be careful about the F3. I can run a 2" midrange to 150hz in a sealed box, but on a horn I need to set the F3 about an octave or two higher, around 300hz-600hz.

I tinkered with the tapped horn idea for a bit, but I think I'm going to stick with a plain ol' front loaded horn. *But I'm leaning towards doing a three way on the horn, instead of a two-way.*









If you look at this pic of the current waveguide, you can see there's a lot of wasted space there. The enclosure for the mids is just hanging off the side there, and there's all that wasted space around it.









A few years ago, I tried something similar. Here's a pic from then. I never built this because the size got to be too large. But I didn't have a 3D printer back then.


















Here's a couple of pics. Basically this waveguide would be a three way, with a 2" midrange, a 3" woofer, and a tweeter. *All on a single waveguide.*

The other design that I posted was asymmetrical, which means that I had to make a seperate model for the left and right side of the car. I may go with a symmetrical design this time around, just to make things a bit easier.

At this point I'm not sure if I have room for dual midranges. Hopefully I do, but if I don't, it's not the end of the world. Even a single midrange should be able to hit 100dB.


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## Orion525iT (Mar 6, 2011)

So what is the calculation for EBP in relation to upper frequency response? 

You can use a proper phase plug to get better polar response from a large cone, but as soon as you try to horn load it, the upper frequencies are limited? 

If going with a dome tweeter, what do you want to look for given that your midrange will crap out before 2000hz. I am only thinking about domes because of the smaller footprint.

Have you considered a 2x3" speaker like the Tang Band W23-1287SI? Phase plug might be a bit funky to design, but that 2x3" is a good bit more sensitive off the bat, and has nearly twice the cone area of a 2". Plus it will fit the dimensions of the horn.


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## Patrick Bateman (Sep 11, 2006)

Orion525iT said:


> So what is the calculation for EBP in relation to upper frequency response?
> 
> You can use a proper phase plug to get better polar response from a large cone, but as soon as you try to horn load it, the upper frequencies are limited?


The efficiency bandwidth product tells you how high your driver will play. EBP is FS/QES. The upper limit for your driver on a waveguide or a horn will be about twice that. (2 * fs/qes)

Here's an example:









The EBP of the Peerless 830970 = (2 * FS / QES) = (2 * 148 / 0.7) = *423 hz*









Here's an actual measurement of the 830970 on my waveguide. We see a couple of things. First, it's playing to almost 2khz, a couple of octaves higher than expected. Second, it's not playing down to 350hz, which is what the F3 should be. The lack of output at 350hz is simply because the enclosure sucks. I wasn't prepared to glue the back caps onto the midranges, so I sealed it up with saran wrap. The output to 2khz is mostly due to the use of a phase plug and due to the use of a very small midrange.

Getting drivers to play past their EBP is a bit of an art I think. In 2009 I used the TangBand W2-852SH. That driver has a higher EBP than the Peerless. The reason I switched to the Peerless is that I found that you can massage another octave or two of output out of a driver if you use a decent phase plug, and I found that the smaller the diaphragm is, the easier it is to exceed the EBP.

IE, there are 8" drivers that have an EBP of 400hz, but I can get more extended response out of a 2" driver with an EBP of 200hz because the diaphragm is smaller.









A great deal of this stuff hinges on pathlength. Equalize the pathlengths, and you get more high frequency output. I think that's why JBL is using ring radiators for a lot of their speakers now; a ring equalizes the pathlength and equalizing the pathlength solves a lot of problems.

If you look at the layout of the drivers in a Synergy horn, you'll notice it's a ring.




Orion525iT said:


> If going with a dome tweeter, what do you want to look for given that your midrange will crap out before 2000hz. I am only thinking about domes because of the smaller footprint.


Any tweeter will work on a waveguide. The problem with domes is that the tip of the dome has a different pathlength than the edge of the dome. It's only a fraction of an inch closer, but at 20khz, a fraction of a inch matters.

So if you use a dome, the response above 10khz is going to be ugly.

The solution is to use a compression driver, or use a ring. JBL uses domes successfully, but they use a phase plug to 'mask' off the tip of the dome. This will work too.

If you don't want to use a compression driver, the ring radiators from Vifa are the obvious choice.



Orion525iT said:


> Have you considered a 2x3" speaker like the Tang Band W23-1287SI? Phase plug might be a bit funky to design, but that 2x3" is a good bit more sensitive off the bat, and has nearly twice the cone area of a 2". Plus it will fit the dimensions of the horn.


I kinda have a thing for big voice coils. Peerless claims their 830970 has a power handling of six watts IIRC. But their driver has a 1" voice coil, while the TB has a 0.75" voice coil. Due to the fact that area goes up exponentially, the Peerless has 79% more surface area on the voice coil. 

Not saying the TB is bad, just saying that I'd be willing to bet that the Peerless will exceed it's power handling.


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## thehatedguy (May 4, 2007)

The small back chamber will help with the power handling too.


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## Kevmoso (Jun 4, 2013)

Would a higher EBP be desired here?
1" coil, fs 160, Qes 0.29. EBP 1103 if I'm not mistaken?
Tang Band W2-800SL 2" Aluminum/Mg Full Range Speaker Driver


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## Patrick Bateman (Sep 11, 2006)

Kevmoso said:


> Would a higher EBP be desired here?
> 1" coil, fs 160, Qes 0.29. EBP 1103 if I'm not mistaken?
> Tang Band W2-800SL 2" Aluminum/Mg Full Range Speaker Driver


You got a winner there. That would work really well.


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## Patrick Bateman (Sep 11, 2006)

Here's the new waveguide.

















It took some juggling, but I think I can squeeze two midranges onto the waveguide. That's dual 2" mids, with a combined surface area that's basically the same as a 3" driver.









I reduced the depth of the midrange phase plug, and went from one phase plug to two. Dual phase plugs should smooth out the frequency response a little bit. (Basically you get a dip in the frequency response from reflections off of those holes, so if you use two small holes instead of one big hole, you 'push' the dip higher in frequency.)


I also added an 'access panel' for the midrange.


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## thehatedguy (May 4, 2007)

Now you are talking.

If you are enclosing the mids in the horn/shell/enclosure, you could do something even more Danley-like and port/tap the back side of the mids in the horn. That may or may not do the same thing as a dedicated midbass.


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## Patrick Bateman (Sep 11, 2006)

The design in post 20 looked cool, but didn't work. When adding the second midrange and the woofer, it just got huge in a hurry. The sheer size of the woofer basket becomes a problem quickly.

I made about three more designs, and finally settled on one that has the following improvements:

1) It's similar to the waveguide from the first post, but the midranges aren't "hanging" off the side so far. This makes the overall footprint much smaller, which is important when you're putting the waveguide under a dash.

















Printing in 3D is a learning experience. I've learned that at least half the time, you wind up making a bad print. One way to improve the reliability of the prints is to "fight" the issues that cause bad prints. For me, one of the biggest problems has been that it's basically impossible to make a large flat surface. For instance, in the pics above, you can see that the surface is convex. I think the reason that it's convex is that the plastic shrinks a little bit as it cools. It might be just 5%, but it's enough to cause flat shapes to 'bow.'

When the shape 'bows', it fails to print. Basically the print head hits the part. And when that happens even once, your print is ruined. It's seriously annoying, considering some of these parts take eight hours to print.










I thought about this for a couple weeks, and I think the best solution is to use some type of matrix. At the moment I am using honeycomb. The advantage of a honeycomb matrix is that it's strong, but it also *substantially* reduces the amount of plastic for a wall. About 80%. And since there's less plastic in the wall, the shrinkage is practically nil. Or at least that's the theory.









I'm also using a radial phase plug on both midranges. The radial phase plug isn't used much, because it's a p.i.t.a. to manufacture. But in 3D, it's fairly easy to construct and print.









Here's an overhead pic. The depth is very shallow. I actually have plenty of space under the dash, but you have to keep it shallow to get good vertical coverage without a diffraction slot. (The Image Dynamics and the USD horns have a diffraction slot in the horn body.)


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## thehatedguy (May 4, 2007)

The pressures are lower in the corners, so wouldn't that be a better place to put the taps for the mids?

How are the ID horns diffraction horns?


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> The pressures are lower in the corners, so wouldn't that be a better place to put the taps for the mids?
> 
> Yep. But if I moved the midranges into the corners, it would have doubled the height of the horn. That would have made it about 6" tall and it wouldn't have fit well under the dash
> 
> ...


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## thehatedguy (May 4, 2007)

I thought a diffraction slot was where you fired a driver through a slot that was smaller than the size of the driver. Eric's horns are essentially exponential in profile. I wouldn't personally call them diffraction horns since the height of the throat is the same as the driver's exit.

But I might need to re-read on diffraction horns...


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> I thought a diffraction slot was where you fired a driver through a slot that was smaller than the size of the driver. Eric's horns are essentially exponential in profile. I wouldn't personally call them diffraction horns since the height of the throat is the same as the driver's exit.
> 
> But I might need to re-read on diffraction horns...


This is about to get really technical, so if people are reading this and wondering WTF I'm talking about, please ask questions. I studied, and re-read, and studied some more, and it took about five or ten years to make sense of all this.










First, *what is a diffraction slot?*
A diffraction slot is where you put a sudden change in angle in a waveguide or a horn. These old ElectroVoice designs are the most obvious example, because the slot is really abrupt and obvious. It's that tall vertical slot in the horn.

Next, *why would anyone do this?*
The reason that it's done is that it allows us to change the coverage angle. When you use a diffraction slot, you basically get a coverage angle that's like a ribbon. You know how people love ribbons? Yeah, a lot of that has to do with the narrow vertical coverage. It reduces reflections off of the floor and the ceiling, and that contributes to that 'ribbon sound', that x-ray quality they have. There's nothing particularly special about ribbons themselves (which is why I rarely use them.) But they *do* have a special coverage pattern.









Traditional car audio horns have a pattern that's a lot like a ribbon, except flipped on it's side. There's wide *vertical* coverage, to compensate for the fact that they're playing at knee level. And there's *narrow* horizontal coverage, to reduce reflections off the side of the car. Combine those two things, and you get that 'x-ray' sound that's so lovely. When looking at a car audio horn, like the one pictured above, try to picture the dash as an extension of the horn. Once you understand that, you'll "get" that this horn is a lot like the EV horn, but flipped on it's side. The dash of the car is an integral part of the horn; the car audio horn depends on the dash.

The thing that sucks about car audio horns is diffraction and pattern flip. Diffraction causes that 'horn honk' that everyone who's owned horns is familiar with. That 'nasal' quality. Pattern flip is that 'sound' you hear with car audio horns, where it's really tough to get them to mate with a direct radiator. IMHO, a lot of people blame that problem on the low efficiency of the midranges. But I don't believe that's the case. IMHO, the problem is pattern flip.

These waveguides I'm working on are designed to solve both problems.
First, I solve the diffraction problem by eliminating the diffraction slot.
Second, I solve the pattern flip problem by putting the midranges on the same waveguide as the tweeter.


Having said all that, it *is* possible to dramatically reduce the diffraction problem by stuffing the horn with polyester fiberfill or reticulated foam, a la Geddes. You can hear the improvement, and the measurements show it. (Check out my 'homster' thread at diyaudio.)

I've *definitely* been tempted to go that route, because a diffraction slot *is* very useful. The reason that my new waveguides are so insanely shallow is because I'm not using a diffraction slot. If I were using one, I could make them 8" or even 12" deep. But the only way to make them that deep is to use a diffraction slot.


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## thehatedguy (May 4, 2007)

Other than possible pattern flip, what was wrong with the horns that you had tucked in the corners under your dash?


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Other than possible pattern flip, what was wrong with the horns that you had tucked in the corners under your dash?


Pattern flip isn't a problem on the top of the dash; if you push everything into the corners the windshield and the waveguide are basically the same thing.

Here's some reasons I tried putting them under the dash instead of on top:









1) In order to put waveguides under the dash, you really want to match the angle of the dash. That's hard to do when using a waveguide you buy from Parts Express. Basically you have to saw the waveguide in half, vertically. And even if you do that, the angle is wrong. (Because it needs to be cross fired, like the Image Dynamics horns.) 

The thing is, if you design them in 3D and print them, you can get the right shape, similar to the ID horns

2) Probably the big 'Eureka' moment was driving aroung in Jon's Magic Bus at night. I realized that it sounds way WAY better at night. And I think a lot of that has to do with NOT seeing the speakers.

Basically, when you can see the speakers, your brain tends to tell you that's where the sound is coming from.


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## Patrick Bateman (Sep 11, 2006)

3D printing is kinda maddening.

I spent a solid twelve hours working on an improved waveguide, and babysat my 3D printer for six hours, and this is what I wound up with:



















That's *supposed* to be a rectangular shape. You can see there's massive curling at the edges. It's really really annoying.

I'd say that my first print actually came out better than this one. You may recall that the first print didn't have an enclosure; the midranges were basically just hanging off of the waveguide.

That seems to actually work better. Due to curling, the printer has an easier time making complex shapes than making a simple rectangular box.

Here's that I'm thinking now:

I'd like to try a diffraction horn, just to see if I can improve it. And I think I'll build a simple wooden box to enclose the waveguide, because the printer has such a difficult time making a flat surface.


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## Patrick Bateman (Sep 11, 2006)

Here's how to make a waveguide in 3D.










The first thing we do is figure out our coverage angle. This is similar to making a waveguide for light. We have a vertical coverage angle and a horizontal.

In the pic above, I have two waveguides. Each waveguide has 45 degrees of horizontal coverage. I didn't measure the vertical coverage. I would make it zero, but if I made it zero you'd get a resonance due to the fixed height. (Since a vertical coverage of zero degrees means that the top and the bottom wall are flat.)









The old JBL "Smith Horns" had that problem, and are kinda famous for sounding bad.

So my waveguide uses the golden ration for the height; the throat is 1" and the mouth is 1.6". I do this to reduce resonances.

To make the shape, you start by drawing a polygon, and then you extrude it.

Once you do that, you select the mouth and use the 'tweak' tool to stretch the mouth from 1" tall to 1.6" tall.


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## thehatedguy (May 4, 2007)

I have to admit, I am wanting to do something again...still have 7 working Misco 3s, so I could do 2-3 of them per horn. But I would need some way to get down to 100 or so to blend with the sub.

Actually the PHL 1120 looks really good in a 2 way version, so the B&C 6MD38 should work well too since the parameters are about the same as the PHL.

Gotta get some cardboard to do some templates to mock everything up with.

But to be honest, I've lost all of my data on the Miscos and Goldwoods...it was all on your forum and it went bye-bye.


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## Orion525iT (Mar 6, 2011)

Patrick,

What kind of plastic are you using? I know that some people using abs have had similar issues. The solution was to melt some abs in acetone, and put a light coating on the platform and let the acetone evaporate off. The residual abs adheres to the platform enough were the part does not lift and warp as it cools.

Another thought was to design the part with thicker sections that would not warp and that could be cut off once the part was finished. Might be too mutch waste of material.


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## Patrick Bateman (Sep 11, 2006)

Earlier today I posted a way to build a waveguide.

That method works well for flat walls, and it's what I used for the waveguide from the other posts.

It doesn't work so hot for a diffraction horn, because there's no easy way to 'join' the two parts together.

So try this instead:










Draw a side view of your horn, and then rotate it around it's axis.

In the side view above you see a few things:

1) We have two stages. The first stage is there to define the horizontal coverage angle. It basically gives a wavefront that's like a ribbon, except it's curved.
2) The second stage, where there's a change in slope, defines the vertical coverage. So we have this curved 'ribbon' that then expands vertically.

All of this is very very similar to the ID horns btw.


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## Patrick Bateman (Sep 11, 2006)

Here's how the side profile looks after you rotate it around it's axis, and keep a pie slice that's 45 degrees wide

it's starting to resemble a proper waveguide


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## Patrick Bateman (Sep 11, 2006)

Sliced off a piece of the pie, to get a flat mouth to match the dash of the car


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## Patrick Bateman (Sep 11, 2006)

Honestly, the trickiest part of all these dumb waveguides is the throat. Screw up the throat and the whole design is wrecked. In the pic above, I've used the same process that I used to make the waveguide to make a throat adapter.

There's a few important elements here:

1) The throat has to be square, and measure 1" x 1". The reason it has to be that shape is that I'll filet it later to make it circular. If that throat is off by even two millimeters, the whole thing is wrecked.

2) The horizontal angle on the throat adapter is 20 degrees. That's designed so that we have a gentle transition from the throat (22.5 degrees) to the mouth (45 degrees.)

If you really wanted to go crazy, you'd make a spline from one angle to the other.



















To get the final waveguide, I smooth out all the rough edges, then subtract one shape from the other to make a shell


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## Patrick Bateman (Sep 11, 2006)

In these pics, I've smoothed out the inside of the waveguide, to reduce diffraction and smooth out the frequency response. I've also added the compression driver mounting plate.

Here's a 'trick' that helped me out:
When cutting the holes for the driver bolts, it helps to calculate the spacing using the pythagoreaon theorem. IE, the holes in the driver are arranged in a square. So instead of measuring the spacing from left to right, I *also* measured it diagonally. This tends to produce really accurate spacing for the holes.

I know that sounds like a small thing, but when you have twelve mounting holes, getting them right makes a big difference.

It just occurred to me that some of the Jericho horns must require close to 500 nuts and bolts :O


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## Patrick Bateman (Sep 11, 2006)

Here's some pics of the printed waveguide, the waveguide described since Sunday

This thing is just comically bad. *This is the worst waveguide I've made since the 90s.* It might even be the worst waveguide I've ever made. It is ****ing terrible.


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## Patrick Bateman (Sep 11, 2006)

Here's a measurement of the frequency response. The response is so terrible, I literally thought my microphone might be broken. As soon as I hooked it up I knew something was wrong because it had more 'horn honk' than I think I've ever heard.

The pic above shows the response with and without stuffing; I tried all the usual tricks to tame higher order modes, as described in my 'homster' thread over at diyaudio.

With waveguides like the USD waveguides, treating the horn makes a big difference. I was seeing improvements with this waveguide also, *but the baseline was just so awful, it was like putting lipstick on a pig.*

The response was so terrible, I seriously tried to figure out if it was literally broken in some way. I tried two different compression drivers, I tried filling any 'leaks' in the waveguide. But there was just no way to avoid a *massive* dip at 2500hz, right where our ears are super-sensitive.









Here are the polars. AWFUL. (by the way, this measurement includes the Synery midranges in the mix; that's why the F3 is lower.)
















I went down to the garage and grabbed a QSC waveguide, to be sure that my amp, mic, or brain hadn't broken down completely. Here's a measurement of the QSC, using the exact same mic and compression driver. (Celestion CDX1-1445)

You can see that it ain't the mic. Everything looks great on that QSC.

















I was starting to think that the culprit was that diffraction slot in the waveguide that I printed. So I measured an 18 Sound XT1086 that I had sitting in the garage. The 18 Sound is similar to the QSC, but it has a modest diffraction slot in the throat. And sure enough, you see a little bit of that dip in the 18 Sound, but it's not NEARLY as bad as the one that I made.


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## thehatedguy (May 4, 2007)

I am not exactly sure how you got measurements of that last one....it doesn't even look like it would function.


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## diy.phil (May 23, 2011)

These are very nice projects Pat! 
But yeah the home printers just aren't going to cut it. Those prints with stray strings and uneven/unwanted surfaces are the same that ive seen on other projects. In the end... we've gotta spend big bucks to send it out to have it printed on those fancy $30K professional printers Something like the Quickparts CJP/Z-Print method is still affordable/reasonable. You can also merge multiple parts into one file and this counts as one order/job. But this CJP/Z-Print material is not flexible like ABS (do not try to flex any Z-Print parts or it'll break! Basically different materials we choose for 3d prints have different characteristics/properties). If we have large enclosed sections in a solid (ie. hollow inside) we need to place a holes for the powder to exit during their cleaning process. Ideally the walls should be around 0.1" thick for durability (less thickness is ok it's just sitting on a desk for a non-critical project, more thickness is ok too but makes it heavier). best wishes to you!


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## Patrick Bateman (Sep 11, 2006)

OK, here's the current status on this project:

1) A conventional waveguide will work really nice. This is demonstrated by the measurements of the QSC and the measurements of my waveguide from page one of this thread.

2) In a car audio scenario, we really need a diffraction slot. *Without a diffraction slot, it's basiclly impossible to get the wide vertical coverage that we need.* IE, without a diffraction slot, when the waveguide is at knee level, the high frequencies won't reach our ears. They're all spraying against our kneecaps.


































JBL has an innovative diffaction device in their flagship loudspeaker, the JBL M2. So let's copy it for the car.

















A happy coincidence is that the 'knuckles' in the M2 waveguide gives us a spot to place the midranges for a Synergy Horn.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> I am not exactly sure how you got measurements of that last one....it doesn't even look like it would function.


I think people would be surprised how little horn you need!

For instance, if you want to load a tweeter down to 2khz, *it only needs to be about 1.75" deep.* (speed of sound / frequency / 4)









This one performed very well, and is about 3" deep.









Here's the polars of that device, from page one of the thread









Here's the polars of the QSC waveguide from Parts Express ($35).
Yes, the QSC is a little smoother, but not a lot. And it's easily 10x as big.

The thing I do with these tiny waveguides is basically get all the drivers crammed into a tiny space, and then use the car itself to load the low frequencies. All the waveguide is there for is to control directivity from about 2khz and up.









This device looks pretty wonky, but it's basically a traditional car audio horn, minus the baffle. (The baffle will smooth out the response a bit, but it won't eliminate that dip at 2500hz.)









Here's a Veritas horn, for the people who aren't familiar with these types of devices


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## thehatedguy (May 4, 2007)

Yeah I was thinking it was looking more similar to what is out there.

But that last one looked solid or missing the top.


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## thehatedguy (May 4, 2007)

There was a patent review a few months back in Voice Coil where the applicant used notches in the front (I think) and sides of the baffle to help with diffraction. Some of the guys on DIYA are giving you grief about the JBL stuff...but I will try to post up the patent information on here later tonight. Might relate, be interesting, might not be.


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## Patrick Bateman (Sep 11, 2006)

The JBL waveguide from the M2, which I sorta "cloned", works pretty well.

It's an interesting design. It's frequency response isn't as good as the QSC. And in fact, I think the QSC may be the best waveguide that I've ever measured. (The QSC is so good, it was actually the inspiration for the SEOS waveguide. Basically QSC stopped selling to consumers for a bit, so some people at diysoundgroup made their own.)

If flawless frequency response is what you want, the QSC is the one for you.

But the JBL has a couple advantage for the car:

1) It has the diffraction device that's required to get wide vertical coverage
2) I'm not entire sure why, but it has wider bandwidth than the QSC

Here's some pics of how it came together:

































































If you take the JBL M2 waveguide from post 43, and you tilt it so it's cross fired, this is what you get. (We cross fire it because we're listening off-axis in a car.)


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## Patrick Bateman (Sep 11, 2006)

The $35 QSC waveguide is one of the greats. Here's a pic, along with the frequency response with a Celestion CDX1-1445. We see the response is about as smooth as you'll get with a waveguide, *but the high frequencies are rolling off.* That's the nature of a conical horn.

















Here's the frequency response of a waveguide I made about a week ago, a waveguide based on the 80s technology of traditional constant directivity horns. It's ****ing terrible.

















Here's the frequency response of my JBL M2 type thing. It's not as epically smooth as the QSC. But it's also a fraction of the size of the QSC, literally about 10%. And it has the diffraction device we need for wide vertical coverage.









Here's the frequency response of that waveguide, but filled with polyester fiberfill. Same idea as the reticulated foam in the gedlee waveguide, the polyfill absorbs higher order modes, which improves the frequency and the impulse response.

Again, the QSC is really great. But we need that diffraction slot. The JBL is a reasonable compromise imho.


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## Patrick Bateman (Sep 11, 2006)

Since the M2 type thing worked alright, I'm trying it again. This time I'm going to work on reducing the diffraction.









This time around, I'm using a curve that matches the exit angle of the compression driver. *This should reduce diffraction at the throat and smooth the frequency response.*

















We rotate that shape around it's axis and we wind up with something that looks a lot like the round QSC waveguide









Round QSC waveguide, for comparison


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## Patrick Bateman (Sep 11, 2006)

I did something a little wacky this time around.









Car audio waveguides use the surface of the dash to continue the waveguide.


















My new waveguides 'creep up' the dash. Basically the top lip of the waveguide blends into the dash.

I'm doing this for a few reasons:

1) I find that being able to see the tweeter diaphragm makes a huge difference. If you can't draw a straight line from you're ear to the diaphragm, with nothing in the way, you got problems. True, the steering wheel violates this goal, but at least the steering wheel isn't very reflective. The underside of the dash definitely is, so I'm trying to get it 'out of the equation' as much as possible.

I see a lot of people ditching kick panels and horns and moving to speakers on the dash, and I can see their reasoning, but I think it *might* be possible to make some serious improvements to the whole 'speakers at knee level' paradigm.

2) Using the dash allows us to move the waveguide up and away from the feet. Basically makes the car easier to drive.


Thanks to Mike in AZ for the pic : http://www.diymobileaudio.com/forum/hlcd/96245-install-pics-horns.html


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## Patrick Bateman (Sep 11, 2006)

These things were a real p.i.t.a. to print; it took about three tries before I was successful. It's a good thing that plastic is cheap; I wound up using half a spool before I had a successful print job. (That's only $12, luckily.)

I need to post some pics and some measurements.









In this pic of the waveguide, you can see that it's designed to be pushed up against the dash. So the mouth actually extends beyond the bottom edge of the dash.

That looked good on paper, but when I put it in the car, I found that the compression driver's size makes it hard to get it close to the dash.

IE, the back half of the waveguide is about 2" tall, but the compression driver has a diameter of nearly 4". So the compression driver 'sticks up' and interferes with the bottom of the dash.

Due to that, I'm toying with the idea of re-doing it, but this time with a SAW lens at the throat:










This offers a few advantages for the project:

1) We can use a dome tweeter instead of a compression driver. (You can use a compression driver with a SAW lens, but you don't have to.)
2) Dome tweeters are smaller and cheaper than compression drivers

This is another one of those things where it wouldn't be practical to build it out of wood, but with a 3D printer it's do-able.

On a personal note, I bought a new house, then got laid off the very next day 
So I'm doing my best to avoid the speaker projects for a lil' while, since paying the mortgage is a bit higher priority.


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## Victor_inox (Apr 27, 2012)

Keep up a great work Patrick and good luck with that mortgage!


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