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Old 3rd November 2012, 12:32 PM   #1
PsychoM is offline PsychoM  Belgium
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Default Subwoofer: filtering line out

Hi,
I have a pair of active Tascam VL-A5 monitor speakers and I really like them. But they are quite small and their bass response isn't really good (the frequency curve drops from about 100Hz).
That's why I would like to add a subwoofer to my system.
I need an active sub with a line in and (filtered) line out, like the Tascam LF-S8.
My sound source will be connected to the sub, and the line out of the sub will be connected to my monitors.

But I recently found a very cheap Sony SA-W505. It has some nice specs, and it has a line in and line out. However, the line out is not filtered. It just passes the input signal.

Will it sound bad if I use the sub without filtering the line out (so both the sub AND the monitors will put out the low frequencies)?
Is there an easy way to filter the line out? I think it is a buffered line out with an opamp, so if just add some caps, will that do the trick?

Thanks,
Psycho
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Old 3rd November 2012, 01:20 PM   #2
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You could consider something like this: Parts-Express.com ? Harrison Lab ? In-Line Crossovers, Line-Level Attenuators, High Pass Crossovers, Low Pass Crossovers

Most of the plate amps PE sells have a first order 125Hz filter on the lineout. Perhaps those more readily available to you have similar characteristics.

Quote:
Originally Posted by PsychoM View Post
Hi,
I have a pair of active Tascam VL-A5 monitor speakers and I really like them. But they are quite small and their bass response isn't really good (the frequency curve drops from about 100Hz).
That's why I would like to add a subwoofer to my system.
I need an active sub with a line in and (filtered) line out, like the Tascam LF-S8.
My sound source will be connected to the sub, and the line out of the sub will be connected to my monitors.

But I recently found a very cheap Sony SA-W505. It has some nice specs, and it has a line in and line out. However, the line out is not filtered. It just passes the input signal.

Will it sound bad if I use the sub without filtering the line out (so both the sub AND the monitors will put out the low frequencies)?
Is there an easy way to filter the line out? I think it is a buffered line out with an opamp, so if just add some caps, will that do the trick?

Thanks,
Psycho
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Old 3rd November 2012, 05:59 PM   #3
PsychoM is offline PsychoM  Belgium
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Thank you for your reply! Those seem really interesting!
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Old 3rd November 2012, 09:58 PM   #4
tvrgeek is offline tvrgeek  United States
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This seems to be a real budget problem, so the answers I will give is in consideration of ultra low budget.

First: Just add a sub and run the monitors full range. I would do this first and see what the result is. You are running them full range now.

Second: Buy a real crossover. Something like the analog Bheringer. Yes, it works fine at line level. Then any old sub will do as long as you can bypass or turn higher the crossover.

Third option: Considering this is the DIY forum. BUILD your own analog crossover. It is easy. If you are creative it can be cheaper than even a used Bheringer.

Fourth option: Many of the car crossovers are not that bad. Most are only third order, but so are most plate amps. So a car crossover feeding the monitors and the plate/crossover feeding the sub.

I would not just add a cap to the input of the monitors. A first order won't do much and if it is not buffered, can cause considerable distortion. If you add an op-amp, that means a power supply, and you might as well add a couple more caps and you are doing option three anyway!
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Old 4th November 2012, 01:35 PM   #5
djk is offline djk
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"A first order won't do much and if it is not buffered, can cause considerable distortion."

Really?

The JBL BX63, Dahlquist DQ-LP1, etc. are all passive high-pass.

" The Dahlquist unit wiped out all the competition...no grain, no audible distortions or colorations" (review by Absolute Sound)

Click the image to open in full size.

https://sites.google.com/site/mpbarn...hlquist-dq-lp1



Click the image to open in full size.

http://www.jblproservice.com/pdf/Vin...BX63A%20ts.pdf

And of course Nelson Pass:

http://www.passdiy.com/pdf/phasecrx.pdf
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Last edited by djk; 4th November 2012 at 01:57 PM.
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Old 4th November 2012, 08:14 PM   #6
PsychoM is offline PsychoM  Belgium
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Quote:
Originally Posted by tvrgeek View Post
This seems to be a real budget problem, so the answers I will give is in consideration of ultra low budget.

First: Just add a sub and run the monitors full range. I would do this first and see what the result is. You are running them full range now.

Second: Buy a real crossover. Something like the analog Bheringer. Yes, it works fine at line level. Then any old sub will do as long as you can bypass or turn higher the crossover.

Third option: Considering this is the DIY forum. BUILD your own analog crossover. It is easy. If you are creative it can be cheaper than even a used Bheringer.

Fourth option: Many of the car crossovers are not that bad. Most are only third order, but so are most plate amps. So a car crossover feeding the monitors and the plate/crossover feeding the sub.

I would not just add a cap to the input of the monitors. A first order won't do much and if it is not buffered, can cause considerable distortion. If you add an op-amp, that means a power supply, and you might as well add a couple more caps and you are doing option three anyway!
You're right about the low budget
I was thinking about building a crossover myself. But I don't have the tools to make a proper circuit board, so I guess I will need a kit, I'll search some more for that.
The Behringer crossover is a good option too but it's quite hard to find a used one here, and I'm not gonna buy it new: for that money I'd better buy a more expensive sub...

I'm not gonna get involved in the passive filter discussion

But I was thinking more about modifying the subwoofer electronics: If the sub has buffered line out stage (opamp?), isn't it just possible to add some parts to the output stage like in a real active crossover circuit? Active filters are just opamp stages with some caps around them. So just adapting the subwoofer line out from a full range stage to a filtered stage, would that be possible?
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Old 4th November 2012, 09:32 PM   #7
djk is offline djk
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Look at the schematics for the DQ=LP1 and the JBL, you could easily duplicate that in the line out of your monitors.
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Old 5th November 2012, 04:36 PM   #8
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Quote:
Originally Posted by PsychoM View Post
You're right about the low budget
SNIP...

But I was thinking more about modifying the subwoofer electronics: If the sub has buffered line out stage (opamp?), isn't it just possible to add some parts to the output stage like in a real active crossover circuit? Active filters are just opamp stages with some caps around them. So just adapting the subwoofer line out from a full range stage to a filtered stage, would that be possible?
The "Active Filter Cookbook" by Don Lancaster is a good resource.
It is all over the net in .pdf form now.
My copy is all worn out.
.
Years ago I built a State Variable filter using TL082's (actually TL084 quad Op-amp) and it worked great.

Dave
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Old 6th November 2012, 02:15 PM   #9
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Quote:
Originally Posted by PsychoM View Post
So just adapting the subwoofer line out from a full range stage to a filtered stage, would that be possible?
Anything is possible with enough time, knowledge and money.
With crossovers going for as little as $25 used at places like Music Go Round and on Craig's list, spending hours figuring out how to DIY, locating and purchasing the various parts does not seem so cost effective.
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Old 6th November 2012, 06:00 PM   #10
PsychoM is offline PsychoM  Belgium
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Okay guys, thanks for all the tips!
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