# Low Pass Filter Choices



## Muser (Apr 16, 2011)

Hi:

I purchased a Behringer 1124p with the idea of using it as a low pass filter. However, it appears that it can't actually cut out frequencies, so much as attenuate the volume level. 

My circumstance is this: I have an Onkyo 885(b) that does very nicely as a low pass filter to the subs. Bass sounds quite good through the Onkyho. I bought the Behringer for my highend preamp because the subs (a pair of Acoustic Elegance AV15D4) run straight out of my preamp "ring," and transmit sound well into the vocal range, where things sound horrible through my system. FWIW, the high end preamp sounds great through my two main speakers, and sounded great when I had a Mach 5 IXL15.2.2 with a plate amp so it's not the preamp. I speculate that the aluminum drivers are ringing and that's why they sound horrible through my two channel preamp - the Mach 5 driver was not an aluminum driver.

I want a tool that will function as a low pass between 60 and 80Hz; while equalization is nice, it's secondary to the low pass filter function. 

So, I have a few questions:

1) Am I correct that the Behringer is not really suited for my intended application?

2) It appears that the minidsp would be able to act as a low pass filter and provide equalization, with the purchase of the appropriate plugin. That's the direction I am thinking.

3) Is there another, "better" option than what I've laid out here?

In advance thanks for sharing your thoughts and experience.

Larry


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## natescriven (Jan 12, 2011)

Can you connect the subs directly to the Onkyo? Its internal crossover will cut off everything above your set crossover point. I might be missing something though.


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## Muser (Apr 16, 2011)

Natescriven:

Thanks for your reply. I guess my question was confusing. The Onkyo is doing a great job as a low pass filter. 

The issue I am having is with finding a low pass filter between my 2 channel preamp and the subwoofer amplifier. I bought a BFD 1124p thinking that would be a good low pass filter, but it's probably better used as an equalizer. It seems the better choice would have been a minidsp or a DQX2496 or something like that.


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## WooferHound (Dec 8, 2010)

What you are looking for is called an Active crossover . . .
http://www.newegg.com/Product/Produ...ts+++Accessories-_-Behringer-_-9SIA03V07N1703


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## jackfish (Dec 27, 2006)

Harrison Labs passive low pass crossovers.

http://store.hlabs.com/pk4/store.pl?view_product=9

Two 150Hz with a 3dB attenuator in between becomes a 24dB slope 75Hz low pass filter. $104, no noise.


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## Muser (Apr 16, 2011)

Jackfish:

Very interesting, thanks.

Larry


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## Mark Techer (Jan 17, 2008)

jackfish said:


> Harrison Labs passive low pass crossovers.
> 
> http://store.hlabs.com/pk4/store.pl?view_product=9
> 
> Two 150Hz with a 3dB attenuator in between becomes a 24dB slope 75Hz low pass filter. $104, no noise.


Whilst a passive Low Pass Filter will work, it is not the best route. Reading the OPs first post and he states that he can mids though the subs. 

Adding a LPF is what is needed, but an active one, not a passive one. Here is why.

With no filter the amp output 20~20K and as a result, mids can be heard.

With a passive LPF, the amp still outputs 20~20K and whilst the sub output is now bass only, there is allot wasted power. Having done this myself about 20 years ago, I learned the system just does not play loud.

An active LPF band limits the Amps output from 20~80 (assuming 80Hz is selected) and therefore 100% of the amps power is now used to amplify this section of the audio band.


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## Muser (Apr 16, 2011)

Mark:
Thanks, very helpful information. It makes sense, too.
I had been ready to just give the cheap passive filter a try, but will take the leap to the minidsp. 
Larry


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## Mark Techer (Jan 17, 2008)

Your welcome  

My first active low pass filter was an active car audio crossover. I sourced a 240VAC to 13.8VDC 1 amp transformer, a small switch for the blue lead and away I went. It cost less than $200 from memory and I even had HPF'd Land R. Of course now I just use the BM built into my THX certified AVR.


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## 94vg30de (May 16, 2012)

While I have a miniDSP and love it, I would recommend many of the rack-mount PA active crossovers for this duty. Behringer makes a few that are readily available for really cheap on craigslist. $50-100 gets you active crossover and maybe a little bit of phase/EQ control, without wasting all the processing power that the miniDSP provides. 

See CX3400 and also CS2310.


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