Jean Michel on LeCleac'h horns

[green heron]

Originally Posted by green heron

Does anyone have any thoughts on the T coefficient for a 115 Hz horn using the "gramophone-style" JMLC horn spreadsheet? Jean-Michael Le Cléac'h posted about potential advantages of a lower T for larger horns, but what about an upperbass horn? I'd want to keep it horn-loaded as much as possible down to cutoff. I'm planning to use a Fane Studio 8M driving into a 4" throat.

I haven't heard any thoughts on the T Coefficient. Looking at the AudioXpress Horn article http://www.audioamateur.com/media/kolbrek2884.pdf
I'm leaning toward a T Coefficient value between .4 and .6, which seems to be a good balance of loading and SPL output at cutoff. But I still feel the need to do more investigating. Any opinions?

[GM]

Not familiar with this horn calculator, but IME, down in the hyperbolic range, there's too much throat distortion, so I personally would only use them well below 80 Hz as even a truncated 70 Hz expo with its minimally 'pinched' presentation through a 500 Hz XO's BW has proven unacceptable over time, so I'm at the point now where only conical WGs are acceptable since I no longer need the extra acoustical loading.

That said, I've seen a number of postings over time where 0.7 - 0.8 has been an acceptable trade-off.

GM

[green heron]

Originally Posted by GM

Not familiar with this horn calculator, but IME, down in the hyperbolic range, there's too much throat distortion, so I personally would only use them well below 80 Hz as even a truncated 70 Hz expo with its minimally 'pinched' presentation through a 500 Hz XO's BW has proven unacceptable over time, so I'm at the point now where only conical WGs are acceptable since I no longer need the extra acoustical loading.

That said, I've seen a number of postings over time where 0.7 - 0.8 has been an acceptable trade-off.

GM

Thanks GM - I'm currently running a pair of conical upper bass horns with 15" woofers, but I'd like to try a pair of Fane Studio 8Ms and get up to 109 db through horn loading to put them on par with my 110 db round midrange horns. Do you have any idea how hypex in the 0.7 - 0.8 range would compare to tractrix?

[green heron]

Originally Posted by green heron

Thanks GM - I'm currently running a pair of conical upper bass horns with 15" woofers, but I'd like to try a pair of Fane Studio 8Ms and get up to 109 db through horn loading to put them on par with my 110 db round midrange horns. Do you have any idea how hypex in the 0.7 - 0.8 range would compare to tractrix?

After re-reading Edgar's Show Horn article, he goes into much more detail than the AudioXPress article and includes many more values of T (I believe the article refers to it as "M"). His assessment leads to a value between .5 and .6 to give the best response down to the flare frequency. In the article, he gives a formula to determine "M" based on the driver parameters at a point which benefits from reactance annulling.

[Jmmlc]

Hello,

I tend to disagree somewhat!

Throat distortion being due to the non linearity of the air itself is generally less harmful (H2 based distortion) than distortion due to large displacement of the membrane (H3).

and for the same input signal the loudspeaker loaded by a conical horn will provide -10dB to -20dB SPL compared to the same loudspeaker loaded by the hyperbolic horn (e.g. T = 0) at the same test frequency taken near the cut-off of the hyperbolic.

Equalizing the response of the loudspeaker loaded by a conical horn will result for the same SPL acoustical output in a very large displacement and therefore to a distortion much more audible (H3 based distortion ) than for .
the hyperbolic horn (and the + 10dB to + 20dB equalization will result in a pressure at the throat of the conical horn in the same range as the hyperbolic.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Originally Posted by GM

Not familiar with this horn calculator, but IME, down in the hyperbolic range, there's too much throat distortion, so I personally would only use them well below 80 Hz as even a truncated 70 Hz expo with its minimally 'pinched' presentation through a 500 Hz XO's BW has proven unacceptable over time, so I'm at the point now where only conical WGs are acceptable since I no longer need the extra acoustical loading.

That said, I've seen a number of postings over time where 0.7 - 0.8 has been an acceptable trade-off.

GM

[mwmkravchenko]

Yep. EQ being a requirement on a horn means you did not do your design work well enough, or that you might want to look for another driver.

[GM]

Originally Posted by green heron

Thanks GM - I'm currently running a pair of conical upper bass horns with 15" woofers, but I'd like to try a pair of Fane Studio 8Ms and get up to 109 db through horn loading to put them on par with my 110 db round midrange horns. Do you have any idea how hypex in the 0.7 - 0.8 range would compare to tractrix?

After re-reading Edgar's Show Horn article, he goes into much more detail than the AudioXPress article and includes many more values of T (I believe the article refers to it as "M"). His assessment leads to a value between .5 and .6 to give the best response down to the flare frequency. In the article, he gives a formula to determine "M" based on the driver parameters at a point which benefits from reactance annulling.

You’re welcome!

Yeah, don't know why T became M over time. Maybe Prof. Leach decided to personalize his T/S compression horn design routine.

Yes, I recall you having some low throat distortion horns, hence my response suggesting you might not want to insert a high throat distortion horn into the ‘mix’, instead implying building a different alignment to get the desired gain BW at low distortion.

Assuming you built a typical tractrix that unloads at ~1.4x above its F0, then the hypex would theoretically need to be tuned similarly, which will cause the excursion issues cited if you don’t oversize it enough for the XO to attenuate it. This will also lower efficiency a little due to it having a wider gain BW. Not many ‘free lunches’ in audio design.

If max efficiency to Fc is the prime design requirement though, then use one of the horn calculators to find the optimum flare frequency, factor that causes it to ‘ring’ at the desired Fc once all the series resistance is factored in.

GM

[pengesluk]

Will a horn with Le Cleach profile display any advantages in the 100 - 500 Hz region compared to other profiles?

[Esperado]

Originally Posted by Jmmlc

I tend to disagree somewhat!...

Just tend ? ;-)
I would add that a good tool to evaluate the linearity of a horn is to compare the impedance curve of the driver on it test tube with the one of the same driver charged with his horn.
It talk a lot in one sight.

[whgeiger]

... the overall dimensions of the horn. [T] and [m] address horn behavior at the lower frequency bound of the horn as well; however, this is true only so long as the horn overall dimensions remain larger than wave length of the low frequency energy passing through it. When wave length becomes larger, [T] & [m] become acoustically transparent and horn length and mouth perimeter become the principal determinants of horn low frequency performance. So, the order of the questions to be answered is:

1) Is the horn acoustically big enough to pass, unscathed, the lowest frequency of interest?

2) Have [T] & [m] be set appropriately for this size horn and the driver to be used with it.

Regards,
WHG