Reduce mouth resonance in horn

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Joined 2012
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I was lying in bed last night and it occurred to me: the stub/Helmholtz won't solve our problem! Yes, it would be good to reduce (say) a 1000 Hz peak. But the mouth reflection issue is one of delay (time) of the entire signal leaving the horn. Per Bouska and others, the distortion is a low-passed and multiply time delayed alternately inverted/not inverted delay of the signal.

One of the most popular ways of dealing with the mouth impedance discontinuity reflections is to put the driver about 1/3 from the closed end of the horn - in effect, forming a stub to help cancel the big first reflection peak. So, it still works and works down to low frequencies even, not just kHz (which is a tiny distance).
 
If the horn is going to be infinite, just give it a 10Hz flair rate.

Hi William,

That is a great idea, but why settle for just 10Hz?

Let's pull out all the stops, and make it a 1Hz flare cutoff infinite exponential horn - ruler flat down to 5Hz... :).

Kind regards,

David
 

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Eh... What does infinite mean? I know the option in Hornresp, but have not understood what type of loading that means.

As the word suggests, infinite means that the horn is infinite in size :). It is a theoretical concept only - you cannot actually build one physically. Infinite horns are usually the starting point for any discussion on acoustic horns in the standard reference textbooks because they have simpler mathematical models than those of finite horns, and can give reasonably useful indicative results in simulations. This aspect is somewhat less important these days though, because computing power is now such that finite horns can be simulated almost as easily and as quickly as infinite horns.

The attachment compares the throat impedance of an infinite 100Hz exponential horn to that of a relatively large finite 100Hz exponential horn. As the horn length and mouth size are increased while maintaining the same flare rate, the ripples reduce in amplitude, disappearing completely in the limiting case of an infinite horn.
 

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Eh... What does infinite mean? I know the option in Hornresp, but have not understood what type of loading that means.

It's a thought exercise. Positive and negative infinity are used in mathematics to establish one or both ends of a continuum. All horns are compromised and being able to see what an infinite horn looks like demonstrates the magnitude of the compromise. It's an interesting feature but not one I've used often. I've never attempted to build one :cheeky:
 
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Since this thread has perished faster than resonances in a treated Geddes waveguide :) I thought I would post a helpful hint. Of cheap tweaks I've discovered, only the towel tweak seems to be effective. Yet it suffers from poor appearance. Here, then, is a substitute that is much more elegant. Too, it should win acceptance from the spouse, at least during the holidays.
 

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As the word suggests, infinite means that the horn is infinite in size :). It is a theoretical concept only - you cannot actually build one physically.

It's a thought exercise. Positive and negative infinity are used in mathematics to establish one or both ends of a continuum. All horns are compromised and being able to see what an infinite horn looks like demonstrates the magnitude of the compromise. It's an interesting feature but not one I've used often. I've never attempted to build one :cheeky:

Thank you, gentlemen!
 
Since this thread has perished faster than resonances in a treated Geddes waveguide :) I thought I would post a helpful hint. Of cheap tweaks I've discovered, only the towel tweak seems to be effective. Yet it suffers from poor appearance. Here, then, is a substitute that is much more elegant. Too, it should win acceptance from the spouse, at least during the holidays.

Ho-ho-ho! ......... Try sandpaper.

Shape pieces of say, 400 grit wet and dry sandpaper to fit around the lips of the mouth, using double sided adhesive tape.

I am very interested in the idea that turbulence created in the throat and amplified by the horn, can be attenuated (or ameliorated) by a textured surface. I am thinking a lot about this to factor in for my next build.

If needs be, you can always remove the sandpaper by running a drop of naphtha (zippo type lighter fuel) along the edges of the sandpaper, leave for a minute, and it should lift off without much sticky residue left behind.

ToS
 
I thought the reference was intended for a physical obstruction (hump) at the horn mouth rather than damping material. This would also generate the turbulence mentioned earlier like the sandpaper although in a different way. Is the towel intended to act as a damping material or an obstruction or both? I’m open to being educated!
 
Crude terminus damper. I've been posting about using foam mouth extensions/false baffles to deal with the various reflections of finite horns/WGs since the '90s basslist to mostly deaf ears even after me n' others pointing out various proven applications, not to mention Dr. Geddes' decorative 'shotgun' solution via stuffing it.

The most claimed reasons for not doing it is cosmetic, i.e. spoils the 'look' of the [vintage] horn or tried it and found it made them sound too 'dry'/'dull'/'uninvolving', i.e. folks preferring [most/all] of these types of distortions and/or wasn't willing/able to find the 'right' amount of density.

Until someone either does the necessary testing or DMB gives us a final horn design section made from open cell foam to calculate surface area, density [depth] it will remain a seldom used tweak.

GM
 
You're welcome! It's ~ part of my response to tapestryofsound's 'turbulence' post.

GM

Hi GM, methinks you and I are on the same wavelength here, only you are a vastly more experienced builder than I am.

My last build was a LeCleach with a 112 degree backwards sweep to the mouths lip, with a satin gloss inside the horn interior. My next build is going to be another LeCleach, this time with a 180 degree backwards sweep and a matt finish interior. Very light weight so as to allow the horn to resonate in sympathy with the music. Or that's the idea. I reckon it depends a lot upon how the horn is suspended, I guess. Maybe I will use the foamed pipe lagging around the lip, it may work or it may not. It is all swirling around inside my imaginarium, and very soon I will get to work.

Reckon I could even make it look nice too :)

ToS
 
I am very interested in the idea that turbulence created in the throat and amplified by the horn, can be attenuated (or ameliorated) by a textured surface.

News to me; how/where did you arrive at this?

I mean 'we' learned way back when from some early pioneer horn designs that 'pinching' the horn at the right point [compression loading] extended its power response via turbulence, so by putting a little lip on an engine's intake, exhaust manifolds to create more back pressure acted as a compression loading device to get a higher density air/fuel charge in/out of the cylinder.

Adding turbulence at the exhaust's or horn's terminus will change its power bandwidth as it's creating a lossy vent, i.e. more compression loading via turbulence, so while it might damp the driver a bit it's going to increase its distortion, so the reality is that the more gradual the flare and more 'slick' the surface the better, i.e. only a point of diminishing returns, which JMLC explored with his 'curley Q' termination [FWIW, in a thought/drafting experiment I 'drew the line' at the 238 deg point when designing carb velocity stacks], manufacturers with internal polymer coatings and DIYers with plenty of sandpaper, compounds, wax, 'elbow grease' and more to polish them to a fare-thee-well.

GM
 
Hi GM, methinks you and I are on the same wavelength here........

Very light weight so as to allow the horn to resonate in sympathy with the music. Or that's the idea. I reckon it depends a lot upon how the horn is suspended, I guess. Maybe I will use the foamed pipe lagging around the lip, it may work or it may not.

Greets!

I'm not so sure.........

Why?! If you want a musical instrument, just attach drivers to a few different types and form a band. ;)

Using open cell foam formed around a horn's lip to damp its various reflections was patented long ago, but can't find it in a general search.

Closed cell foam can attenuate a metal or cheap plastic horn's bell modes, but increases reflections back to the throat, so not a good plan overall.

Regardless, I only provide guidelines, frames-of-reference as I understand them since we all hear the same, yet not so much, so have fun finding your own audio nirvana as lots of folks don't like technically correct speaker systems.

GM
 
If you want a musical instrument, just attach drivers to a few different types and form a band. ;)

Regardless, I only provide guidelines, frames-of-reference as I understand them since we all hear the same, yet not so much, so have fun finding your own audio nirvana as lots of folks don't like technically correct speaker systems.

GM

You've got it in one about my intentions, and respect what you say absolutely.

I have been mapping out a prototype build process whereby I can quickly assemble half a dozen or more horns for modification purposes. My last (and first!) build from start to finish took me eight months. As a technically correct exercise, I did it strictly by the book. It was a lot of work, and it sounds wonderful - a really amazing learning experience. So I do have a very good reference point as a fall back position. Nevertheless, I cheerfully admit to knowing precious little. :p

So, now it is time for me to start breaking all the rules to see what I can come up with. Real crazy stuff......simple and quick to make, hopefully beautiful to look at, and you never know, might even sound good! Whatever, it's worth a try :D

Enjoy the week ahead.

ToS
 
Proposed name for towel mod

I see that there is a project amp called the Babelfish. As noted in the first post here, the towel too has a mention in "Hitch-Hiker's Guide". Therefore, in honor of that novel, rather than the unknown creator of the actual tweak, I propose the towel mod be dubbed the Ravenous Bugblatter Beast Towel Mod. :D