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Old 6th September 2010, 11:08 PM   #1
dcathro is offline dcathro  Australia
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Default Help Please for simple active Xover project

Hi All,

Background:

I have built what I was hoping would be an elegant (simple) speaker, based around a Supravox 215 2000 full range.

This is mounted in a fairly small open baffle giving an acoustic high pass around 250 Hz. Supporting this is a tweeter above 10K, and a 15" woofer in a sealed 130L box.

They are running passive at the moment, with the bass (Re 8.9 ohms) on the end of a 5 MH inductor, with an impedance correction accross the drivers. The Tweeter has a single capacitor, and the Supravox has an broad notch filter for baffle correction.

My biggest problem is the efficiency difference between the full range, tweeter and the bass. The Supravox is rated at around 99 db, the tweeter at 94 db, and the bass (JBL K145 variant) at 96 db. In practice however, I have had to pad both the full range and the tweeter down by close to 6db in order to get a flat response.

Proposed Solution:

I like to keep things simple, and what I was thinking of doing (at least initially) was:
  • keep the bass impedance correction, full range baffle correction, and tweeter hi pass as passive;
  • double up my amps as a biamp setup, with one amplifier on the bass, and one on the full range and tweeter;
  • boost the bass by 6 db relative to the full range/tweeter (or cut the other by 6 db);
  • put the 1st order lo pass before the bass amp;
  • maybe put something before the full range amp to cut the lowest bass.

Questions:

Sorry if some of these questions are niave, or if this has all been asked before!
  • Can I do the above passively before the 2 power amps - i.e. split the signal from my preamp and use a resistor pad to lower the full range amp output, and an inductor to do the bass 1st order lo pass?
  • Am I much better to add gain? Why?
  • Do I need to use buffering - to isolate the two signals?
  • Is there a really simple solution for thsi that even a novice like me can apply?

Thanks for your time and thoughts

David
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Old 8th September 2010, 04:35 AM   #2
dcathro is offline dcathro  Australia
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Seems like I have asked for too much, I will rephrase my question.

Can I integrate a simple active crossover into a twin power amp.

I am thinking of running the preamp output into a OPA627 (at unity gain) with a 1st order roll of below 80 Hz to drive my OB full range & tweeter, and a OPA637 with 6 db (or possibly variable) gain and a 1st order roll off above 250 Hz.

As I am looking to put these within the twin power amp box, I am looking to do this without any buffering.

Thanks

David
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Old 8th September 2010, 09:43 AM   #3
just another
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Hi Decathro, you may get a better response in the multiway forum, but do a search on PLLXO (passive line level crossover) and I think you should get the answers to at least some of your questions.

Not something I have done but certainly something that has been done by others successfully check out Passive Line-Level Crossover

Tony.
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Old 8th September 2010, 11:38 PM   #4
dcathro is offline dcathro  Australia
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Hi Tony,

Thanks for the information - I didn't know what to look for.

Seems like the passive approach will probably be best for my requirements

Regards

David
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Old 9th September 2010, 06:47 AM   #5
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Hi David,

glad it helped I first saw the term pllxo when I was looking for something else, wondered what it was (phase locked loop is the first thing I associate with pll) certainly for what you were talking about it seemed to fit the bill.

regards,

Tony.
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