# roundovers on hlcd ?



## scoott (Feb 22, 2013)

I am putting roundovers on my usd waveguides to go in my Dodge Ram. 

Question I have is what happens if you put the pvc on 3 sides, with mitered corners? The top pvc could be cut back to match the dash, then stretch grill cloth over the whole affair. Seems like the more effort to smooth transitions the better.


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## Patrick Bateman (Sep 11, 2006)

scoott said:


> I am putting roundovers on my usd waveguides to go in my Dodge Ram.
> 
> Question I have is what happens if you put the pvc on 3 sides, with mitered corners? The top pvc could be cut back to match the dash, then stretch grill cloth over the whole affair. Seems like the more effort to smooth transitions the better.


Basically do this:
1) look at the shape of the horn at the mouth
2) look at the shape of what's next to the mouth. (The dash, the doors, the center console)
3) make a curve that creates a smooth transition from one curve to the other. 

I used PVC in the Homster article because it's quick and easy. You could also use wood; for instance the Danley Synergy horns use the same trick, but with wood. (If you look at the mouth, it flares out in the last third of the horn)









If you're willing to add an additional baffle to your horns, you could do what Peavey did. Basically the mouth of the horn is made of closed cell foam. But that'll take some work, as you have to match the curve carefully. You can't just stuff closed cell foam into the horn, because it'll be too thick. It basically has to create a seamless surface with the horn walls. 

For more info on this, check out the quadratic throat waveguide paper from Peavey, and also Google 'diyaudio roundover Homs"


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## thehatedguy (May 4, 2007)

You only really need to concentrate on the sides that are not touching the dash- the bottom and inside edge. Those would be the areas most needing help with the termination.


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## thehatedguy (May 4, 2007)

The swoop is a major problem and design flaw.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> so basically, you could cut the peavey horn right at the point where the upper edge foam rolls into the throat, and stick that directly to the bottom of the dash?
> 
> except, with the USD the horn is already somewhat deep, but on a deep dash install it may be possible to extend the bottom edge forward following the same horn flare..
> 
> ...


All of the comments above assume that the wavefront is going down the center of the horn. *And there's just no way that's possible.* When I stuffed the USD horn with reticulated foam, the SPL levels dropped *significantly.* (Check out the Homster thread at diyaudio for measurements.)

My interpretation of the data is that the wavefront from the USD horns is reflecting and diffracting at multiple points along the pathlength.










The easiest way to visualize this is a water hose. Basically the water comes out of the hose, hits an obstruction, then 'fans out' into a cone. IMHO, the USD horn does the same thing.

Great Waveguide List - diyAudio

Now before you take the USD horns and throw them in the trash, take a look at the polar plots above ^^^

In that list of horns, you'll see that A LOT of horns do the same thing. *There is basically a point along the pathlength that the wavefront just 'detaches' and now the horn isn't doing anything at all.* I have some 18Sound xt1086s that do this. There's a point where the walls of the horn are actually wider than the wave that's travelling down the horn; the wave has 'detached' from the waveguide.



I hope all of that makes sense 


Anyways, instead of tweaking the USD Horn, what I'd try is to simply use a plain ol' conical. Literally take a couple sheets of 1/4" plywood, cut out a triangular mouth, and bolt the compression driver to that.

From the top it would look like this:










Obviously, it would be angled so that the HLCDs can be cross fired.

Anyone could build this in less than an hour using a $40 jigsaw and a $10 round file. The compression driver would mount horizontally, just like I did in my Paralines:










^^^ see how the driver fires UP into the horn, and the mouth is flared with PVC pipe? The actual horn body is only 1/4" tall.


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## thehatedguy (May 4, 2007)

The problem is that sound waves doesn't necessarily travel as a fluid in a pipe. If the dimensions of the pipe is larger than the wavelength, then the sound wave does not flow as a liquid bending around the curves without turbulence. This is the problem with the USD horns- you have a large (in relation to the size of wavelengths) bend in there. They are (the USD horns)sort of a swooping conical expansion, and there is no way for the affected frequencies to properly realign for a singular wavefront exiting the horn. You can't fix that with some simple glue in piece. It would mean a total redesign of the horn.

The ID horn is an exponential flare. That's how the math says it should flare. It's not too fast for the Fc of the horn. But by the time the wave front reaches down there, it is getting acoustically large for the horn, and the wavefront may not "see" small changes. That's the reason the synergy/unity horns don't have FR problems with the drivers before the exit holes for the mids/midbasses- the previous wave front doesn't "see" the holes as they have gotten acoustically larger than the hole. 




cajunner said:


> I agree. I don't know how bad it would be to replace the swoop side of the horn with a progressive rate, positive flare, and just epoxy in place, but I can't see it being worse sonics-wise as long as you could get a decent finish and transition.
> 
> I don't find the Roto-mount part to be that bad, but the swoop is hard to leave alone.
> 
> I'd like to see a Veritas with a circular flare like the ID bodies, but only going into the horn an inch deeper than the way they are stock. I think the expansion rate is too fast right at the very end of the throat, it's too abrupt in the transition area, and would sound better with a more gradual, controlled expansion.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> The problem is that sound waves doesn't necessarily travel as a fluid in a pipe. If the dimensions of the pipe is larger than the wavelength, then the sound wave does not flow as a liquid bending around the curves without turbulence. This is the problem with the USD horns- you have a large (in relation to the size of wavelengths) bend in there. They are (the USD horns)sort of a swooping conical expansion, and there is no way for the affected frequencies to properly realign for a singular wavefront exiting the horn. You can't fix that with some simple glue in piece. It would mean a total redesign of the horn.
> 
> The ID horn is an exponential flare. That's how the math says it should flare. It's not too fast for the Fc of the horn. But by the time the wave front reaches down there, it is getting acoustically large for the horn, and the wavefront may not "see" small changes. That's the reason the synergy/unity horns don't have FR problems with the drivers before the exit holes for the mids/midbasses- the previous wave front doesn't "see" the holes as they have gotten acoustically larger than the hole.


^^^ I agree with all of this. And it's the reason that all of the underdash horns I've done in the last two years have a very short vertical dimension. Basically by keeping one dimension extremely small the wavefront basically can't form until the air exits the horn, so the air is basically traveling through the horn the way that water travels through a pipe.

The wavefront *will* form once the duct is large enough; and when that happens you'll have to deal with diffraction, reflections, HOMs, all that nasty stuff.

For this reason, mounting the compression driver at a ninety degree angle actually has some advantages, particularly if you add a cone to the throat to reduce the volume all the way down to the diaphragm of the compression driver. (Check out the pics of the Paraline to see what I'm talking about)


Unfortunately, there's no free lunch, and the down side to these ultra short horns is peaks and dips in the frequency response.

BUT - 

There's a solution to that too.

Basically the peaks and dips in the frequency response of a horn occur because a horn is an impedance matching transformer. And when the volume of air in the horn doesn't provide a smooth transition from the room to the diaphragm, you get peaks. That's a byzantine way of saying:

*Everything else being equal, big horns have smoother response than small horns.*

But everything ISN'T equal; you can offset the peaks and dips by using a very light diaphragm, a very powerful motor, or both. Basically a big motor and a light diaphragm 'motor' through the dips and peaks in the response.

Jason and JLH had good results with paper cone tweeters, and I think that's one of the reasons why. It's almost like using a ribbon at the apex, due to near weightlessness of the paper cone.


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## Eric Stevens (Dec 29, 2007)

thehatedguy said:


> The swoop is a major problem and design flaw.


It has more issues than just that. Run an impedeance curve on it and you can see the other problems rather easily. 

Eric


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## Eric Stevens (Dec 29, 2007)

cajunner said:


> I'd like to see a Veritas with a circular flare like the ID bodies, but only going into the horn an inch deeper than the way they are stock. I think the expansion rate is too fast right at the very end of the throat, it's too abrupt in the transition area, and would sound better with a more gradual, controlled expansion.


The super fast flare at the center of the Veritas horn is too try and reduce the output energy/level at that axis of the horn. It sort of works as intended but what controls output at higher frequencies doesnt control output at lower frequencies.

I did some extensive polar response measurements of USD, Veritas and of my horns. Wish I still had this so I could share it with all.

Directivity on simplistic level of midrange frequencies is controlled by the mouth of the horn and the high frequencies are controlled by the intial flare. 

Eric


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## scoott (Feb 22, 2013)

Patrick Bateman said:


> ^^^ I agree with all of this. And it's the reason that all of the underdash horns I've done in the last two years have a very short vertical dimension. Basically by keeping one dimension extremely small the wavefront basically can't form until the air exits the horn, so the air is basically traveling through the horn the way that water travels through a pipe.
> 
> The wavefront *will* form once the duct is large enough; and when that happens you'll have to deal with diffraction, reflections, HOMs, all that nasty stuff.
> 
> ...


 So the question I have is this: should I use the usd roto-mount horns with the foam and a lower roundover of 1 1/2 or 2 inches?

Or should I use the traxxis horns I just purchased from Patrick on ebay with a suitable driver?

Having heard/built both, assuming the traxxis would fit, is there any advantage of one over the other after applying 1/3 octave eq,etc?


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## Patrick Bateman (Sep 11, 2006)

scoott said:


> So the question I have is this: should I use the usd roto-mount horns with the foam and a lower roundover of 1 1/2 or 2 inches?
> 
> Or should I use the traxxis horns I just purchased from Patrick on ebay with a suitable driver?
> 
> Having heard/built both, assuming the traxxis would fit, is there any advantage of one over the other after applying 1/3 octave eq,etc?


Depends on your compression driver. Basically I built those horns to accomodate a low xover point. I bought the USD horns *after* I built those horns, basically to see if my own designs were as good as the commercial designs. And to my ears, my design sounded *better* than the USD.

But oddly enough, the USD measures fairly nice, which made me wonder why it didn't sound so hot. And I think the answer is "diffraction."

Which lead to that Homster thread on Diyaudio, where I was basically trying to figure out how to make the USD sound as good as it measures.

I think the roundover helps a lot, and the foam helps a little. Probably my main grip with the USD is that ninety degree bend. It puts a notch in the response that's pretty ugly. (Basically the sound hits the bend, reflects back, and creates a null.)

Eric's horns have a bend too. IIRC, the reason that's not a problem is because the dimensions of the horn are so small at the bend, the wave can't form. Also, I believe Bruce Edgar contributed to the designs of Eric's horns, and Edgar literally 'wrote the book' on bending sound waves:

http://volvotreter.de/downloads/Edgar-Show-Horn.pdf

As for your question - I think it comes down to this:

1) What compression driver are you using? If you're using a high xover point, the USDs with the roundover and foam might work well. They'll definitely look better than the ones that I made.
2) If you need a low xover point (1000hz or so) I think mine will likely work better
3) Due to the fact that my horns have no bend, there's a possibility that you'll prefer them, even with a small compression driver.


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## scoott (Feb 22, 2013)

Patrick Bateman said:


> Depends on your compression driver. Basically I built those horns to accomodate a low xover point. I bought the USD horns *after* I built those horns, basically to see if my own designs were as good as the commercial designs. And to my ears, my design sounded *better* than the USD.
> 
> But oddly enough, the USD measures fairly nice, which made me wonder why it didn't sound so hot. And I think the answer is "diffraction."
> 
> ...


 I bought a set of BMS 4550's to use with your horns. The USD's came with selenium drivers.

Was thinking of starting out around 800hz and going from there.

8" prv mid-bass in the door, stock position.

Your horns may allow wider positioning without removing the park brake pedal.


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