The HOMster! (or How I Learned How to Fix a Horn)

[JLH]

I used a pair of mono Audio Control EQTs back in the day. I really loved those things.

Rgs, JLH

[winslow]

The ID EQs were not Rane. USD were Rane. Don't know about Crossfire. I'm using a converted Rane RPM88 in my car for all of my processing needs.

Eric at ID does have a copy of Dr. Geddes's book. I am supposed to have sent him some foam a few months back. I need to do that.

Interesting results. I have been trying to scheme a way to make a curve for the bottom of the horn to the floor for critical listening and judging. The problem I am having would be it would completely obscure the midbasses in the floors. Might give this treatment a go when I get the horns installed in the new car.

[Patrick Bateman]

Originally Posted by winslow

The ID EQs were not Rane. USD were Rane. Don't know about Crossfire. I'm using a converted Rane RPM88 in my car for all of my processing needs.

Eric at ID does have a copy of Dr. Geddes's book. I am supposed to have sent him some foam a few months back. I need to do that.

Interesting results. I have been trying to scheme a way to make a curve for the bottom of the horn to the floor for critical listening and judging. The problem I am having would be it would completely obscure the midbasses in the floors. Might give this treatment a go when I get the horns installed in the new car.

A horn or waveguide that's fourteen inches wide will lose directivity control around 1khz. The USD horns are a bit wider than that, but they're far, FAR too short to work properly.

Or at least, that's what the theory tells us.

But if you look at the measurements again, you can see that the treated horn has quite remarkable polar response down to 2khz. It gets a bit wonky after that, but all things considered, these are excellent plots.

Of course, we can't even get a proper anechoic measurement, because these horns depend on the car itself to bring up the low end. My measurements are gated. IIRC, it's 12ms long, to capture three wavelengths at 250hz. In a room they wouldn't go this low.

Dare I say it, I think the curve you mentioned would be overkill. Just add some foam, a roundover, and be done with it.

What compression driver are you using? I believe the USD uses a Radian 450PB, which can't play much below 1khz.

[winslow]

Yeah, probably will do the roundover. Tried the foam already.

At first I modded the horns to work with BMS 4591s and was going to use a Fane ST5022 on the top end. But I got a smoking deal on some Beyma CP755nDs from Duke. So I got some 1.4" to 2" adapters and put them on the horn so I can use the Beymas.

I have to mention my ID horns are straight entry horns. The adapter I think made the horns sound better. Why? Because the first 1.5" is round vs. normally angular. Though it is an exponential adapter I think it helped. I want to eventually make an OS adapter. I know these horns are diffraction slots, but I figure the first couple of inches are very crucial for HOM and diffraction artifact development.

Was that too rambling? Have a 3 month old little girl that has me zapped already...lol.

[gedlee]

Originally Posted by winslow

I figure the first couple of inches are very crucial for HOM and diffraction artifact development.

This has been debated extensively and I don't think that there are any conclusions. Its not clear that its true although it does appear to be logical. But "logical" is not proof of fact, and, in fact, in acoustics, its often misleading.

[winslow]

Here's my straight entry ID horns with the large format drivers on adapters.

Excuse the grill cloth coming off of the edges.

[mwmkravchenko]

Hi Winslow

Good application of constrained layer dampening!

I notice the Dynamat layered over with fiber glass cloth. I kind of thought that applied on the exterior of the horn it may work to dampen the resonances. I'm guessing as a slightly viscous layer in between two rigid layers it would really dampen well. Does it work well?

I personally use what is called ice and water shield up here. ( not much use for ice shield in California ) It is used for the first layer on roofing underneath the shingles. It is pretty much the same as Dynamat but has aggregate loading on one side like standard shingles and the most unforgiving sticky glued side on the other. It is not cheap but $85 will get you 3 feet by 60 feet.

Mark

[winslow]

The production horn bodies are urethane and could use a layer or two of damping materials to help tame body resonances. These particular horn bodies are fiberglass as they were custom made for me by Image Dynamics to be a straight entry horn rather than having the driver enter at an angle.

But the plan was to use a 2" compression driver and a super tweeter...so I could play the horns really low. So, knowing the flare rate of the horn I found the area progression where the flare went to a 2" entrance. Then I cut the horns there. The glass was used to hold a new 2" mounting flange. I just spread the chopped fiber until it was smooth and even from the cut part ..like icing a cake. There really wasn't a plan to do any additional damping via the glass...but I guess it worked to some degree. The most resonant part is the mouth, the shape and need for thinner material makes it ring some- though nowhere near as bad as the aluminum bodies from Veritas did.

So, I scrapped the idea of the 2" driver and got a smoking deal on the 1.4" Beymas and rolled with them on adapters. The Beymas sound really really good. Hopefully once I get them in the car I will have them crossed a little below 500 hertz on a 72 dB/octave slope.

[Patrick Bateman]

Originally Posted by winslow

Here's my straight entry ID horns with the large format drivers on adapters.

Excuse the grill cloth coming off of the edges.

In my current project I've turned the waveguides on the dash into Unities, extending their response about an octave and a half. Prior to the Unity treatment they played to about 1khz; with the Unity midranges they're going well below 500hz.

Without a doubt, my favorite part about the unities is their intelligibility. There is something about getting the entire midrange on a single waveguide that's breathtaking. For instance, when I listen to a song on the Unities where two singers are harmonizing, the Unity is able to delineate the two singers in the mix with ease, whereas conventional speakers do not.

The reason that I bring this up is that I think part of the unity magic has to do with covering the whole midrange on a single waveguide or horn. You would think that a full range could pull of the same trick, but it doesn't. They don't have the same clarity as a Unity. I think this is because early reflections are reduced by the waveguide or horn.

My Summas at home sound similar, but you need to sit at least two meters back. I'm guessing this is due to the center-to-center spacing of fifteen inches.

Anyways, long story short, I'll bet the Beymas will sound particularly good in the nearfield.

[Pano]

I'm with you on that! Getting most of the midrange into a good horn or waveguide lends great results. I have had that "hey! who are all those back-up singers?" moment. =) Where were they hiding before?

Nice work! Amazing for a car. (my car has 6 speakers - only 1 works)