Reduce mouth resonance in horn

this YouTube song (I use a CD) on my Klipschorns (despite the rather small K400) has that big - easy old school theater sound with lots of vibrancy in the singer's voice. In contrast with the 2nd Eminence B102 + Morel Cat37-8, the sound on the voice is dry -dull - (as if recorded in a dry - damped booth) - I want good exciting sound - not realism (if the latter really is representative - lol)
 
The tweak bug has bitten again. I recently trashed the "plug" of polyfill in my horns. I had bought some 30 ppi foam but apparently it's too thick when entirely filling the horn...I miss the two upper octaves :) so removed it. I can re-add it in 1" depths. I "upgraded" from a ratty white towel to a black towel for two towel cowls. So now I'm experimenting to see (er, listen) if I actually can hear any differences.
 
Yeah, my Altec 511 horns have three different density, thickness foam throat inserts to flatten them out in lieu of using mass quantities of CD horn EQ, with one working best rolled up into a tube placed longitudinally across the abrupt conical throat to expo horn transition, i.e, once you move away from Dr. Geddes' whole horn insert the solution can get really complicated/long time to get right.

GM
 
One could try magic trickery that Dave Gunnes has been doing, FIR filters. Basically when acoustic impedance changes in the horn some of the sound is reflected back to the compression driver. Reflected sound is counteracted (by FIR filters) in the compression driver effectively preventing them reflecting back to the horn and to the listener. The compression driver is made a towel by FIR filters, how cool is that :)

Never heard such system, and know almost nothing about it, but I think this would reduce "reverb" mentioned in the OP.

Temporal EQ (TQ™) | Fulcrum Acoustic
YouTube
 
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Yeah, sometime in January I've been invited to a serious tweaking session of a horn loaded MTM stereo system where the latest DSP full tilt boogie processors will be the 'guests of honor', so health permitting I aim to become intimately familiar with these as they 'sound' too good to be true, so prepared to be disappointed. Looks good in theory though if I understand the basic concept.

GM
 
Minor tweakery, some yes, some no...

One advantage (?) of having made my "plug" from 1" thick sections is this: the full plug was too much attenuation, so I can try smaller ones (e.g. just 3" at throat). I also have some felt (probably synthetic) on hand, so I cut two equal rectangular pieces and have it placed along walls near throat. I can't tell any difference. With much music, however, I seem to be able to identify where the sound arrives from (the speakers). So I tried this next:


Since my 1" foam absorbs too much when used as a plug, why not try it to absorb along some of the horn's wall? I have two 15" circles cut, so I cut them in half and loose stuffed them in, so they fit between mouth (towel cowl) and perhaps half in, towards the throat. Of course, not full coverage, but...


I am quite sure that just this has improved imaging; I like it better with the latest foam treatment than without. Could this be something as simple (and non-HOM) as narrowing the HF dispersion? I can still see fully to the throat and CD with no obstruction, so it must be at most a narrowing of the 60 degree horn profile?
 
Back to full foam plug...wow

After about 1 1/2 years of mostly open horn (but partially lined with felt), I gave the 1" foam discs another try. This time, I made a few attempts to snugly pack them bottom to top (throat to top) for best effect (by ear, no measurements). I also added a bit of upper end EQ. Wow, what a difference! A very audible improvement; no easy way to A/B with no plug.



I finally can hear why Dr. Geddes patented his foam plug.
 
I've worked with a variety of methods of termination. It all matters, for your traditional diyer "standalone" horn commercial cabinet-mount horn sitting on top of a bass cab, the towel is a great call. Open cell foam is easier than people think to shape- get a hot knife or a compress/cut solution to shape it into a decent looking "collar" that follows the horn profile but extends it. I haven't had a horn yet that wasn't helped by this method. I hoard open cell shipping foam for this application. The best part about foam in this app is you just cut a slit into it and press-fit. A thin thread can tie it to the mounting holes.

An alternative is to use a fabric bag made of grill cloth, then you can use whatever ugly absorbtive material you want and have it look decent, so long as you can work the fabric effectively. This is what I do for the "bottom" lip of my midbass horns, a bag with fugly foam inside.

For larger horns, where lower frequencies are more the concern, simply adding a (strong) baffle whose face is tangentially aligned to the exit of the flare can be huge. While a larger horn designed for the space is always a better solution, "wings" are a great way to add a little more LF capability to a horn and reduce some sources of ripple (again, designing it as a single horn is superior but not always an option). I use wings on both sides both to extend the midbass loading ever so slightly, but more importantly, to limit reflections from my sidewall. I have a basement space with 2 foundation walls forming a corner, one end open, and one end built-in shelves. To give enough listening distance and make the small space usable with huge speakers, the horns are mounted into the shelves. This leads to the left side of left horn mouth only being 2' from one foundation wall (w/drywall and acoustic treatments), and the right mouth has open space to the right (they both "use" the display as a mouth extender on their respective "inside" edges). By adding big wings, the room gets less noticeable. A bigger space, using proper corner horns, would be better still, but I haven't got that space just yet. Maybe I can diy a listening lodge.
 
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There was a version of the duelund horns that had "wings" on piano hinges so that they could be folded out of the way when not in use. I think they folded to the front so each wing was 1/2 the with of the front. Having wings folding backwards should enable wings as wide as the cabinet is deep.

Regarding mouth refection: I recall an article in HFN & RR back in the 80s that described a patent by Technics that had a thin plastic membrane streached across the horn opening and at intervalls parallell membranes further back in the horn.
 
A bit dark and harsh analog to towels and wings and stuff:
Going to doctors, they would often prescribe something for the symptoms but not cure the cause. Not that they couldn't but because often the "customer" doesn't want it, because curing the cause might mean changing eating habits and doing exercise. Many people just do not seem to want to take responsibility for their own health but instead externalize the responsibility to society and doctors, take the medicine so that they can continue their habits and do nothing about it except whine about costs. Got many relatives doing this, despite trying to get them wake up. A lucrative business, so there is not much intent to help people to change habits and give useful advice for better health, because that would reduce customers and not bring any money in. Starting from government, schools, so on, at least here in Finland things seem to go south, while costs of healthcare go up and service availaility goes down so soon there is nothing else left than everyone taking care about them selves, which might be a good wake up call for some. Allright, sorry about the vent.

Anyway, one can use a towel, or wings, anything, to change symptoms of a horn, but why not just make a better device and cure the cause? It's free and accessible stuff in year 2024 after all, see ATH thread. https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/ no need to use archaic devices with slap-ons. Well, takes some work and courage to deviate from long established norms, but I think it's worth it. If your device needs a towel, perhaps consider replacing it with better one. Have fun!:)
 
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