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Re: Leach throat size vs. Keele/Edgar size

Hi

I am not familiar with hornresp although I have heard of it.
I don’t know if it can show the electrical impedance or radiator motion but if so, the difference between the Keele and Leach alignments is clear.

A quick physical model of your driver and horn (Keele alignment) shows that while the output goes up above 900 Hz, the electrical impedance shows that the efficient range of operation is below ~ 350Hz
The Leach alignment shows a somewhat lower efficiency (predicted to be about 30%) based on the impedance but the acoustic loading is present on the motor to above 500Hz.
Also, as a result of a smaller throat, one finds the cone motion is significantly less than the Keele alignment for a given SPL. Since motor non-linearity is the primary source of distortion in a LF / MF horn, one could expect that the Leach alignment with the same driver will have less harmonic distortion at that given SPL.
If driven by a passive xover or tube amplifier, having a broader range of acoustic loading means there is also less SPL variation due to a changing load impedance.

In each case, the horn is a little too small (for 80Hz) and in both cases, an increase in front volume (over the computer calc for an ideal horn) lowers the hf corner acoustically down to the crossover region, such a move also lowers the distortion as it acts as an acoustic low pass filter.
To be accurate here, one needs the real Le .

I am not clear on a few things though.
Do you have a horn built which is 81 cm long ? (in which case the best bet would be to try to find the best driver for your horn based on its physical size)
Or, are you wanting to build an 80Hz horn for your EV drivers?
Or want to know what the response will be with your drivers on that horn?

So far as what Leach’s math predicts, it is FAR better at scaling the acoustic load to suit the driver and bandwidth than the “folk lore math” as I have called it a few times over the years.
This is why Leach’s paper IS in the AES loudspeaker anthology and Keele’s approach is NOT.
Understand, the math is a “starting place”, nearly always (at least for bass) a practical horn is usually considerably smaller than the theory assumes. Being able to model the real thing is the best way to further “adjust”, based on predicted response.
Cheers,

Tom Danley


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