Active crossover for ZaphAudio BAMTM?

[sharpi31]

A year or so ago I built a pair of John "Zaph" Krutke's BAMTM (Bargain Aluminium MTM) speakers and have been very happy with the sound. I recently completed a full passive transformer output mod on my Behringer DCX2496and would like to try using this as an active crossover for the BAMTM.

The original passive crossover for the BAMTM is detailed on Zaph's page: Zaph|Audio - Bargain Aluminum MTM

My understanding is that the crossover is 2nd order at 1450Hz with some tweeter padding. With the natural rolloff of the drivers, the resulting slopes approximate to LR4.

I'd appreciate some guidance on how to set up the DCX. I have the option of Butterworth, Bessel or LR 2nd order slopes - which would be most appropriate for the BAMTM?

My plan is to apply the correct slopes at 1450Hz then attenuate the tweeter outputs as required to flatten the response.

I have a pair of 200uF film caps that I may use to protect the tweeters - will check amplifier turn-on thump and apply if required.

Any advice would be gratefully received.

[Boden]

To mimic the passive filters of the BATMT is unfortunately not as easy as you might think. What has to be done is making an exact replica of the so called transfer functions of the passive crossover legs.
You have to know these first. This can be done by plugging the component values of the passive filter legs into a simulation program. The hard part is getting the DCX to "do" exactly the same transfer functions.

I have not used the DCX, but it is my understanding that the Beringer software cannot copy transfer functions, that are not in the software library. Maybe I am wrong here.

With Soundeasy or LspCad 6.1 it is somewhat easier done: measure the output of woofer and tweeter separately, when fed through the passive filter.
Subsequentely use these measurements as "target functions" in SE or LspCad .

After optimization the program will have calculated the correct filter coefficients for active emulation on the DCX. Feed these into the Beringer.

Simply flatting the SPL curve by manipulating the DCX will not do the job: you will end up with a different speaker system, and not an active copy of the original.

Good Luck,

Eelco de Bode

[sreten]

Hi,



The above are the two transfer functions you need.

rgds, sreten.

[sharpi31]

Many thanks both - extremely helpful advice. Will finish the required four channel amp (this weekend?) then test and report back.

Thanks again.

[sreten]

Hi, FWIW you will need far less power for the treble amplifiers than mid/bass, rgds, sreten.