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ulf wrote:

One advantage of the use of a phase plug in a midbass horn is that it will beam less at higher frequenzies than a horn without phase plug. If the phase plug is designed for the specific horn and driver it will help "steer" the HF. Me and a friend designed (and built) a 100Hz Tractrix midbass horn for a TAD1201H driver and we used a phase plug that was about 15cm long. It followed the tractrix curve all the way to the diaphragm. The basic idea was to get a horn that would have a wide distribution at it's upper region. Practical tests have shown that it works rather well. Compared to a similar horn without a phaseplug it beams much less. Ulf

Your midbass horn philosophy sounds very interesting (I’d like to build one having a 80/100-800/1000 Hz range).

I agree -as it was said in "midbass horn: the problems"- that seeking a speaker/horn/room combination response without significant irregularities in the two octaves beyond the intended crossover with the midrange horn is a necessary design constraint, allowing use of 1st order crossover.

As I understand it and in order to achieve this, one would look for a speaker having among other characteristics a high efficiency-bandwidth product, a limited voice coil inductance, a diaphragm sufficiently rigid and airtight to withstand a moderate to medium (3 to 5) compression ratio and a smooth response up to 4-5 kHz. I selected a few 8 to 12 inches models sharing such characteristics: Electro Voice Dl 10X, B & C (10 MD 26, 8PE 21), Beyma (102 Nd), Mc Cauley 2326, PHL Audio 3860, RCF L10/750 YK, Precision Devices (PD 107, PDN.10 MH 25), Supravox Alnico 285-2000 (interesting but Fs may be a bit low for this application), TAD TM 1201 H.

But as you mentioned, this won’t be sufficient to predict accurately the sound of the driver once loaded by the horn. The Fane studio 8M you mentioned is out of production and old models not easy to find here.

Ulf, I would really appreciate to know which drivers you tested before selecting the TAD 1201 H (real tests? with different or identical compression ratios?). May you please detail your findings and listening impressions, as it might be very educative? May you also describe more accurately your rectangular tractrix midbass horns: flare rate, length, mouth and throat cross section area, mouth width and height, measured response you mentioned? As well as the integration of the midbass with the rest of the system?

I thought it may be interesting to load the back of the driver with a progressively damped (stuffed) quarter or even half-wave pipe, tuned to (say) 30 or 40 Hz and having cross section area equal to throat area, having enough place to play with it. This may be another way to cancel throat reactance at Fc; it would also provide a resistive load down in the LF region and may allow use of interesting drivers having in other respects limited Xmax and higher Fs, such as the Mc Cauley 2326. I would appreciate your comments about these suppositions.

Thanks for your answers,

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