Depends on the pass-band, the different expansions cause varying degrees of throat and mouth distortion over an increasing BW with decreasing M factor that's easily audible in our acute hearing BW and why some folks put a lot of effort into how the throat mates to the driver and the mouth to the surrounding air.
Once this is done, so much of the horn's length is already accounted for, so in this case the M factor becomes mostly moot and it's not uncommon to just connect them with a straight line, i.e. a waveguide (WG). 😉
GM
Once this is done, so much of the horn's length is already accounted for, so in this case the M factor becomes mostly moot and it's not uncommon to just connect them with a straight line, i.e. a waveguide (WG). 😉
GM
Thanks for the reply. Whats the M factor? Expansion rate?
Given a 2" throat Le-Cleach/tractrix horn, would it be a bad idea to adapt the throat to a 1" like shown in the drawing below? The black line is the horn with a 2" throat and the red lines are with adapter.
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You're welcome!
Right, Prof. Leach uses 'M' in lieu of the 'T' factor of days gone by where 0.5 = Hyperbolic, 1.0 = exponential and hypex for anything in between.
Assuming it's an accurate representation, then in theory the discontinuity at the splice point will cause reflections back to the throat and why the adapter is normally attached at the throat, but this increases HF beaming/throat distortion due to the low M(T) factor.
Seems to me that 'best' in this case would be to use one of the 'new' duplex compression drivers to ~ 'have your cake and eat it too'.
GM
Right, Prof. Leach uses 'M' in lieu of the 'T' factor of days gone by where 0.5 = Hyperbolic, 1.0 = exponential and hypex for anything in between.
Assuming it's an accurate representation, then in theory the discontinuity at the splice point will cause reflections back to the throat and why the adapter is normally attached at the throat, but this increases HF beaming/throat distortion due to the low M(T) factor.
Seems to me that 'best' in this case would be to use one of the 'new' duplex compression drivers to ~ 'have your cake and eat it too'.
GM
Wouldnt this mean spherical horns have less HF beaming/throat distortion due to a higher M(T) factor then say... tractrix? Why is tractrix horns more common? Is throat distortion the same thing as higher order modes? (HOM's)
Would a cone shaped "phase plug" like in the picture below reduse HF beaming in such horns?
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Correct. My understanding is that HOMs are reflections generated within the horn that resonate like a 'horn within a horn' which if massive enough can modulate the driver, so I don't view them as horn 'honk' generators per se, though they can exacerbate them if throat distortion due to an acoustically poor transition between driver/horn is present.
Consider the old Altec 311, 511, 811 sectoral horns, they match the horn to the driver and gradually transition it to a conic radial to get good HF directivity - so far, so good - then abruptly neck it down as required to create an expo radial to make it load with some degree of directivity over a wide BW which causes massive reflections back to the driver's phase plug that its tiny filter chamber can't cushion enough.
Factor in a relatively poor mouth termination that adds a second layer of reflections back to the transition and on back to the throat to create a delayed three stage 'horn within a horn' and little wonder that it 'honks' with a slow decay rate long after the signal stops, though bell/mouth damping and an XO point slope that rolls off the 'honk' portion of its LF BW reduces it to a fairly benign expo WG and a throat foam insert that extends past the conic/expo transition will damp down the worst of the HOMs, though most folks don't feel the need for the latter once the other two 'fixes' are done.
Folks like how its low distortion mouth sounds, but to take max advantage of it requires it be fairly limited in gain BW to keep excessive beaming of its otherwise hypex flare to a minimum.
IME it can certainly help with a point source driver, but haven't tried it with a compression driver nor do I recall seeing one other than as part of the driver. Seems like there wouldn't be enough room for one considering the small throats typically used though.
GM
Consider the old Altec 311, 511, 811 sectoral horns, they match the horn to the driver and gradually transition it to a conic radial to get good HF directivity - so far, so good - then abruptly neck it down as required to create an expo radial to make it load with some degree of directivity over a wide BW which causes massive reflections back to the driver's phase plug that its tiny filter chamber can't cushion enough.
Factor in a relatively poor mouth termination that adds a second layer of reflections back to the transition and on back to the throat to create a delayed three stage 'horn within a horn' and little wonder that it 'honks' with a slow decay rate long after the signal stops, though bell/mouth damping and an XO point slope that rolls off the 'honk' portion of its LF BW reduces it to a fairly benign expo WG and a throat foam insert that extends past the conic/expo transition will damp down the worst of the HOMs, though most folks don't feel the need for the latter once the other two 'fixes' are done.
Folks like how its low distortion mouth sounds, but to take max advantage of it requires it be fairly limited in gain BW to keep excessive beaming of its otherwise hypex flare to a minimum.
IME it can certainly help with a point source driver, but haven't tried it with a compression driver nor do I recall seeing one other than as part of the driver. Seems like there wouldn't be enough room for one considering the small throats typically used though.
GM
HOM are basically as you say, but because they are delayed in time relative to the main wave - they travel a longer path - they can be quite audible long before they are a significant acoustic effect.
The minimization of HOM has been shown to reduce (elliminate) horn honk and since the coutour has a major effect on HOM's we must assume that the contour also has an audible effect.
There are, of course, other considerations.
Hello Defo,
I don't like the presentation of the different profiles on the graph you shown.
See in atatched file a comparison of different profiles of horns having the same acoustiacla cut-off.
Best regards from Paris, France
Jean-Michel Le Cléac'h
I don't like the presentation of the different profiles on the graph you shown.
See in atatched file a comparison of different profiles of horns having the same acoustiacla cut-off.
Best regards from Paris, France
Jean-Michel Le Cléac'h
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Hi Jmmlc,
I'm surprised that the two Tractrix profiles are so much smaller (240/270radius) than the three other profiles (370/380radius) that are very similar in diameter (@ the mouth or @ the 90degree diameter).
I'm surprised that the two Tractrix profiles are so much smaller (240/270radius) than the three other profiles (370/380radius) that are very similar in diameter (@ the mouth or @ the 90degree diameter).
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Hello Andrew,
This is easily understandable when we consider the main hypothesis on which is based the tractrix :
tractrix = propagation of cap spherical wavefronts having a radius :
radius = c / (2 . pi. Fc)
with c = speed of sound
and Fc = the acoustical cut-off frequency of the tractrix horn
As we can see Voigt choose empirically a mouth perimeter equal to one wavelenth at the cut-off frequency. (This is probably related to the common idea that's there is no need for a horn to have a mouth over a wavelength of the lowest frequency to cover.)
Then if you take the Kugelwellen horn which also uses an hypothesis of cap spherical wavefronts, that radius is 2 time the radius of the Tractrix.
No hypothesis about the shape of wavefronts is made for the Le Cléac'h but we can see that the profile of the Kugelwellen horn is very much similar on a large part of the profile.
Best regards rom Paris, France
Jean-Michel Le Cléac'h
This is easily understandable when we consider the main hypothesis on which is based the tractrix :
tractrix = propagation of cap spherical wavefronts having a radius :
radius = c / (2 . pi. Fc)
with c = speed of sound
and Fc = the acoustical cut-off frequency of the tractrix horn
As we can see Voigt choose empirically a mouth perimeter equal to one wavelenth at the cut-off frequency. (This is probably related to the common idea that's there is no need for a horn to have a mouth over a wavelength of the lowest frequency to cover.)
Then if you take the Kugelwellen horn which also uses an hypothesis of cap spherical wavefronts, that radius is 2 time the radius of the Tractrix.
No hypothesis about the shape of wavefronts is made for the Le Cléac'h but we can see that the profile of the Kugelwellen horn is very much similar on a large part of the profile.
Best regards rom Paris, France
Jean-Michel Le Cléac'h
On the one hand we seem to disagree on what the main cause of horn 'honk' is since I can line some horns and treat its termination to audibly remove HOMs (don't know about measurably) and still have audible ('cupped hands', 'choked') throat induced distortion and on the other hand we seem to agree that it is, so your response seems ambiguous to me.
I thought my definition of horn 'honk' and its core cause was ~universal, but apparently not, so what's the prevailing definition?
TIA,
GM
Interesting! Thanks for the comparison. Don't recall ever reading about the Kugellwellen termination, but it looks 'close enough' like what I arrived at empirically. Back when you first posted about yours on the basslist, I remember thinking that since it ~mirrored mine up to a point that it was at least somewhat smaller and that since it was arrived at mathematically it might be audibly as good or even superior, but haven't yet been able to compare them, so have you and if there is an audible difference is the 'K' worth the extra size/effort?
TIA
GM
What I think "honl" is due to and what others think are usually different and indeed so in this case. I completely discount any form of nonlinearity as being the culprit and have offered up evidence that HOMs alone can create this kind of effect. My data in this regard is all in AES publications and I know of no other data in this regard that has been per reviewed. "Cupped hand" experiments are not "data".
Hello GM,
I just wrote something about the cupped hand test in another thread.
see
http://www.diyaudio.com/forums/multi-way/154447-how-build-large-round-front-horns-3.html#post2095658
This test is IMHO useless...
there is also a recently started thread onthe topic:
http://www.diyaudio.com/forums/multi-way/161627-horn-honk-wanted.html
Best regards from Paris, France
Jean-Michel Le Cléac'h
I just wrote something about the cupped hand test in another thread.
see
http://www.diyaudio.com/forums/multi-way/154447-how-build-large-round-front-horns-3.html#post2095658
This test is IMHO useless...
there is also a recently started thread onthe topic:
http://www.diyaudio.com/forums/multi-way/161627-horn-honk-wanted.html
Best regards from Paris, France
Jean-Michel Le Cléac'h
Hello GM,
I used to listen to one Kugelwellen horn and it was pretty much the same "no horn sound" that a le Cléac'h horn.
On the other hand, there is a small difference in the sound between a tractrix horn and a Le Cléac'h horn and this may be due to the way the mouth is (rapidly) stopped with the tractrix (even for the "tractrix modified" horns).
Best regards from Paris, France
Jean-Michel Le Cléac'h
I used to listen to one Kugelwellen horn and it was pretty much the same "no horn sound" that a le Cléac'h horn.
On the other hand, there is a small difference in the sound between a tractrix horn and a Le Cléac'h horn and this may be due to the way the mouth is (rapidly) stopped with the tractrix (even for the "tractrix modified" horns).
Best regards from Paris, France
Jean-Michel Le Cléac'h
The differences seem smaller than they are on that scale. Overall, I think of round horns as a continuum, and different features blend together in different designs.
Better CD or less EQ? Size vs. mouth roundovers? etc.
I'm working on mine with a resin layup... if I had it to do over, I'd just make wood horns. They're months in and are just finally getting close to 'ready'. I wanted an exceedingly smooth surface, which was the major part. One-offs are just hell.
Better CD or less EQ? Size vs. mouth roundovers? etc.
I'm working on mine with a resin layup... if I had it to do over, I'd just make wood horns. They're months in and are just finally getting close to 'ready'. I wanted an exceedingly smooth surface, which was the major part. One-offs are just hell.
Indeed we do. I haven't read all your AES papers, but if you've ~proved that HOMs can cause horn 'honk' in a linear driver/throat transition horn, then that makes two ways to cause it based on my own listening experiments that has included others. I guess I've never experimented with a bad enough mouth termination to induce it enough in an otherwise linear enough expansion horn.
Agreed and didn't offer it as such, merely as one of several descriptions for what 'honk' can sound like. Or do you disagree with this too?
GM
Greets!
OK, thanks, the title didn't interest me, so haven't browsed it.
Agreed and have said as much on occasion which in one case netted me a pretty severe 'reprimand' from a self proclaimed horn design guru with a strong suggestion I not post on any horn design threads until I got properly educated. This 'proof' is about as relevant as the speaker cab 'knuckle' rap test to prove it's non-resonant.
Oops, forgot about this one, thanks!
GM
Greets, part deux!
Good to know, thanks!
Agreed, this combined with Olson's work on baffle step diffraction is what caused me to experiment with increasingly larger round-overs, though even the most keen hearing of us could hear any difference on rearward tapers > ~238 deg, so didn't bother with completing the 'teardrop' shape, instead just curling it around as you've done.
GM
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