OB alpha15a with HF tratrix horn questions

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i am going to go with 2 alpha15a's per side OB... similar to MJK OB article.

HF will come in at around 500Hz.

Thought about the audax PR170M0 but maybe go with some compression drivers in a tratrix horn.

Radian 7 series or the 950.

Looking for a pre-made horn or instructions (basic or detailed) on how to do this.

have no experience with horns... and maybe need some intro advice and links to info.

any comments or advice is welcome!
OB w/horn


In order to cross at 500 Hz, your horn should probably be a design of ~ 400 Hz cut-off, along with a driver that will also be capable of undistorted output below the crossover point. This will limit your options.

There aren't many good drivers to choose from at a reasonable price with the bandwidth you desire, and all will require a fairly large horn to support the low end. Hardly any large tractrix flares are to be found in the usual commercial market.

Pro audio sources for these products will be familiar with the large format 1.4" and 2" JBL, Altec, EV and TAD drivers that may work in this application, but almost all will require an additional HF horn to aid output above a certain point (few extend beyond 10K Hz), so you end up with a three-way anyway.

The TAD 4001/2 are exceptions, but costly ones. Some of the older JBL 1" will also come close.

BMS and B&C both make a coaxial drivers for this purpose, and the Radians look good on paper, but I would verify through a dealer with good return policies. Parts Express carries them now, and they can probably steer you in the right direction.

In the long run, it may be easier to use the Audax PR170MO for the midrange, and a 1" driver/waveguide above that.

Some, even here, have also used the old Altec 511 1" horn for this purpose, which can go down to 500 Hz, but driver selection again gets difficult. Even then it is a good idea to thoroughly damp and baffle mount the horn to reduce the ringing.

Good luck!

According to John Hasquin's posts on the subject, the lowest usable range of a tractrix id flare rate x SQRT2, do fo 500Hz, a FR of 340Hz is required. This matches my experience with the 4590's and 270Hz flare for a 400Hz xover.

I don't know of a 1" driver that is going to do 500Hz on a tractrix well. The BMS is the only one I could recommend here (and I don't like it that low), unless you go to a JBL2440 and cross it out to something else higher like the Fane or Fostex drivers Bruce Edgar recommends.
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