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Old 29th January 2011, 04:53 PM   #1
steevo is offline steevo  United Kingdom
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Default converting passive speakers to active

Hi I have a pair of passive PMC FB1+ transmission line speakers and am thinking of convertering them to actives using amplifiers i have and building a linkwitz riley 2 way crossover from elliot sounds. But I am not sure if it is straight forward as this to get decent flat response and sound that is better than the original. Would I need some sort of eq circuit too for the speakers???.

Has anyone had any exerience converting existing passive speakers to actives with any success.

Cheers
Steevo
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Old 29th January 2011, 05:13 PM   #2
Helmuth is offline Helmuth  Netherlands
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Quote:
Originally Posted by steevo View Post
Hi I have a pair of passive PMC FB1+ transmission line speakers and am thinking of convertering them to actives using amplifiers i have and building a linkwitz riley 2 way crossover from elliot sounds. But I am not sure if it is straight forward as this to get decent flat response and sound that is better than the original. Would I need some sort of eq circuit too for the speakers???.

Has anyone had any exerience converting existing passive speakers to actives with any success.

Cheers
Steevo
It would be easy to make some equalizing in a active filter, but to you that is a question this means your not into creating your own circuit.

But no worry here many use mini-dsp. With basic knowledge of filter and speakers you can create your best solution with the program.

Mini dsp film
http://www.youtube.com/watch?v=6uptQHSU9TY

And a good amp with four outputs.
http://cgi.ebay.com/4-100W-4O-Tripat...-/370293320597
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Last edited by Helmuth; 29th January 2011 at 05:17 PM.
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Old 29th January 2011, 05:59 PM   #3
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You are right it is not that easy, unless you have good data of the driver responses and know what you are doing, then it is unlikely you will get a result that is equal to let alone better than the dedicated crossover.

A classic mistake a lot of people make is to just take the published crossover frequency and make that in an active version.
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Old 29th January 2011, 06:22 PM   #4
Helmuth is offline Helmuth  Netherlands
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And you have to use a MLS measurement to check the result.
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Old 29th January 2011, 06:34 PM   #5
steevo is offline steevo  United Kingdom
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Quote:
Originally Posted by Helmuth View Post
It would be easy to make some equalizing in a active filter, but to you that is a question this means your not into creating your own circuit.

But no worry here many use mini-dsp. With basic knowledge of filter and speakers you can create your best solution with the program.

Mini dsp film
YouTube - miniDSP 2.1 Advanced Plug-in

And a good amp with four outputs.
4*100W @4O Tripath TK2050 D-class Audio Amplifier Board - eBay (item 370293320597 end time Feb-12-11 04:56:12 PST)
I do have a UV box and etching tank so i can etch my own PCBs and have done so in the past but not for years, I have tended to build and buy circuit boards from the likes of Signal transfer designed by doug self as these amps give fantastic peformance, although i have started to design my own high performance feed forward current dumping amplifier, this will take me a while to do. I find that PCB layout has been difficult in the past to give the best SNR performance although i was never able to really measure properly so that is partly why i have opted to buy other peoples designs and circuit boards. I have only recently been able to measure amplifier performance after buying the excellent TRUE RTA sprectrum analyzser from TRUE AUDIO.

Anyway yes i think without knowing the driver characterisitcs it is going to be diffucult to come up with something better than the passive version.
The bass unit is a VIFA driver but the tweeter is bespoke soft dome PMC
unit i think, so getting the data sheet for the tweeter my prove difficult.

I did read an article about the possibility of sweeping throught frequency rage
and measuring the voltage at the passive crossover outputs and then
reproducing the response using active network, but i am not sure if this would
be successfull. Any comment on this idea??.
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Old 31st January 2011, 06:37 AM   #6
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Is this one of their models that is available in an active version as well ? If yes, try to get the circuit diagram of the active one.

Regards

Charles
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Old 31st January 2011, 07:41 PM   #7
steevo is offline steevo  United Kingdom
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Originally Posted by phase_accurate View Post
Is this one of their models that is available in an active version as well ? If yes, try to get the circuit diagram of the active one.

Regards

Charles
The origianl FB1 could be made into active speaker using a Bryston power amplifier pack, not sure if this included the EQ and active crossover circuits, it
must have done, but they removed the active option with the FB1+ and FB1i version, so i am not sure how to approch it now.

cheers
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Old 31st January 2011, 07:51 PM   #8
Davey is offline Davey  United States
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steevo,

Assuming you want to create the same transfer function as the passive filters, you could take a differential measurement from crossover input to each of the driver terminals and save those as "target" filter responses. You can then try to realize/match those with some sort of active design (either analog or digital.)

No acoustic measurements are required.

Cheers,

Dave.
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Old 1st February 2011, 12:35 PM   #9
steevo is offline steevo  United Kingdom
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Originally Posted by Davey View Post
steevo,

Assuming you want to create the same transfer function as the passive filters, you could take a differential measurement from crossover input to each of the driver terminals and save those as "target" filter responses. You can then try to realize/match those with some sort of active design (either analog or digital.)

No acoustic measurements are required.

Cheers,

Dave.
I did think of that but I think the enclosure is tuned to the response of the drivers when combined with passive crossover, when using a active crossover
the transient response of the drivers will be improved so their response will
change drastically. It will sound a bit crap i think. The only option is to use a
mic to measure the response and correct it with eq. What do you think.

Cheers
Steevo
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Old 1st February 2011, 02:04 PM   #10
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Quote:
Originally Posted by steevo View Post
The origianl FB1 could be made into active speaker using a Bryston power amplifier pack, not sure if this included the EQ and active crossover circuits, it
must have done, but they removed the active option with the FB1+ and FB1i version, so i am not sure how to approch it now.

cheers
Not sure if it is pertinent to this model but PMC used to offer active and what they called 'activated' speakers.
The 'activated' speakers got a single Bryston amp in form of a so called power pac. This did not include a line level crossover and they thus retained the passive one.
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