[Kim Schultz]

Hi.

I´m working on an OB with an Eminence BETA 12CX with a BMS 4524 driver.

Both drivers have been modified. The BETA 12CX to smooth out the horn to cone transition, and the BMS 4524 to be able to screw it into the back of the BETA 12CX.

The BETA 12CX was modified by cutting off the dustcap and the excess voicecoil former. Then I made a small paper cone out of cardstock and glue it to the cone and the voicecoil former.

The BMS 4245 is normal bolt-on driver but as I needed it to fit the BETA 12CX, I turned it down on the lathe.
This also made it possible to make a better fit for the BETA 12 CX horn throat which is NOT 1 inch, but more like 23mm.

The plan is to cross the two drivers passive, and then use either one or two A&D Audio 1524 15" drivers below this, crossed active.

Here are some pictures of the modifications, and the improvement seen in the frequency response.
Measurement taken with the driver laying on the floor pointing up.

Regards
Kim

[AJinFLA]

Very nice Kim, color me impressed.
Look forward to more details, but looking very good so far. Narrow notches are difficult to hear, but you've definitely smoothed things out on axis. Would be nice to see some off axis as well.
What's the plan for the rest of system?

cheers

AJ

[Kim Schultz]

I have spent some time playing around with different crossovers, and it seems a simple first order on the BMS 4524, and a third order on the BETA 12CX sounds pretty good.
Both drivers have impedance correction though.

I also hooked up an old Zomax P1565 15" in a experimental H-baffle and crossed it actively to provide som bass under 200hz, and it made me wonder if I should just use one 15" per speaker, as I could play pretty loud this way.

These speakers are being made for HT duty, because after having lived with my Hawthorne Sterling Duets in the living room for a few years, I miss the uncoloured sound whenever I use box speakers.

What is your opinion on one vs two 15" bass drivers for HT use ?

Regards
Kim

[Kim Schultz]

I tried making an animated gif with 0-15-30-45 degrees measurements, of the unmodified cone, and the modified cone, but it would not show here.
So here are the two measurements on its own.

These were done in a very narrow box, and not the OB.

Regards
Kim

[Russtafarian]

Impressive work on those drivers.  I get the impression you've done cone driver modification before.

Russ

[AJinFLA]

In the original on axis graph, is the blue - stock, red - modded?

[Kim Schultz]

In the original on axis graph, is the blue - stock, red - modded?

Yes, I think it is a worthwhile improvement.

[Kim Schultz]

I have tried several crossovers, different orders and with or without corrections, and today I build this one out of parts from the parts drawer.

It uses impedance correction to get the phase and impedance nice and flat, for an easier amplifier load.

I think it sounds pretty good, but it might need a bit of tweaking.

Measurement taken at 1 meter in room, not calibrated to show actual db/w.

EDIT 09/03: Changed a bit in the crossover to be able to try some Obbligato 3,3 uF in the tweeter crossover, and lower the parallel resistor.
It sounds more balanced and sweeter now.

[bladesmith]

That is impressive.