View Full Version : bi amp from passive filter

11-11-2004, 06:15 AM
Question : I do not know anything about filter .

If I want to bi amp from the filter I have :
1. just connect the bass connection to first amp and other hp connection ( med hf -uhf) to 2nd amp ?

2. keep actual filter , disconnect bass Hp and make an additionnal filter only for bass with just a 7 mh and 56uf component for a 270 hz cut ?

Thank in advance for the info ?????

Earl K
11-11-2004, 10:23 AM

I don't think I understand your question,,, but just in case this is what you meant ;

You cannot take your existing passive speaker filters that are situated after your existing amplifier and put them infront of any amp - and get useful results. These speaker (LC) passives must do their filtering just before the speaker components. Their values are determined by the impedances ( usually 4 to 24 ogms ) of the speaker components that they filter .

You can not reuse/recycle those passive speaker filters as Passive Line Level Filters situated in front of 2 amplifiers . The reason you can't is because the component values are all wrong for the filter ranges you'd be after. They are just soooo wrong that they are in a completely different range . Amplifiers have working ( AC ) impedances ranging from 5,000 to 100,000 ohms. Useful inductor values for "inlines" end up being in the "Henrys" not millihenrys range while capacitor values are in the (.xx or .0xx)uf range, not the (xx.)uf range that one finds in Speaker Level Passives.

Since ( as you've stated ) you don't understand passives- but think you want to biamp using Passive Line Level Filters,,, check out the XM46 from Marchand Electronics (http://www.marchandelec.com/xm46.html) . Two cards loaded with the components necessary to give you the slopes of your choice will be a minimum of $ 360.00 ( shipping not included ).

Here are prices $$$ for Marchands' kits (http://www.marchandelec.com/pricelst.html)

regards <. Earl K

- below is a single 24db/octave card ( HiPass & LowPass ). These only exist with unbalanced "ins" & "outs" .

11-11-2004, 11:06 AM
If i understand right he wants to biamp his passive network.
He has to divide his network in low-and highpass and put them to the speaker terminals of his amps.


11-11-2004, 12:37 PM
Well yes that is what I ask .

I have 4 speakers ( bass - low medium - Hf - UHF ) and one filter .

I want to do the following :

i connect one amp directly to go thru 7mh and 52uf and coming out to the bass speaker and the other amp to the wire going thru the filter to the other speakers .

Don't know if I am clear enough i am not so good in english for this type of explanation !

Or what should I do to bi amp ?

gerard .

Mr. Widget
11-11-2004, 01:14 PM
I don't think there would be any real benefit in doing this. Of course I don't think there is any real benefit in bi-wiring either and there are many who have bought the extra wire and felt quite proud of their "improved" sound.

If you want to get the benefits of using two amps you should use a proper active or passive crossover/filter between your preamp and amps.


Earl K
11-11-2004, 02:10 PM
Okay Gerard

i connect one amp directly to go thru 7mh and 52uf and coming out to the bass speaker and the other amp to the wire going thru the filter to the other speakers .

Don't know if I am clear enough i am not so good in english for this type of explanation !

Yes, now you are clear enough .

Yes, you can drive a separate amplifier through a 7mh (coil) & 52uf (cap) into the woofer. You need to make sure the new LowPass circuit is completely separate / & electrically isolated from the existing speakers' crossover network. .
The reason ? You really don't want two amps to "share" a common ground that effectively bonds the minus side of their respective output drivers/transistors.

If you go this 2 amp route, you should buy 2 new ( better quality ) 7mh inductors and 2 new 52uf capacitors. ( Remember, a 52uf capacitor can be created by wiring a 12uf & 40uf in parallel to each other.) Wire each new inductor and capacitor according to the JBL schematic for your speakers. ( What speakers are they and do you have the schematic ?)

Put these new lowpass filters on individual small perforated boards ( 1 per channel ) . Small individual boards will allow for easy placement inside or outside of your existing speakers.

Placement of these new low-pass filters. They can go inside the enclosures - just make sure they are firmly affixed to something , like a side-wall. Keep inductors away from magnets - they induce hum. If you go this route you'll need to wire inputs & outputs onto the crossover cards. You could buy 2 more binding posts & put them onto the existing backplate of the speaker - if there's enough room.
On the other-hand, you can just run wire to these lowpass filters through the woofer tuning port and back to the amplifier outputs. You might want to go this route if this is more of an experiment .

The old inductors on the lowpass section of the existing crossover will need to be disconnected to remove any possibility of them interacting/effecting the remaining HighPass circuit components .

Some Challenges

(i)You need to get signal into 2 amplifiers. Most people will simply create a "Y" split cable. This has a good chance of working ( having no problems ) with 2 identical amplifiers. Paralleling the inputs of two amplifiers will also drop the input impedance below that of the lowest of the two amps. This is not usually a problem with Solid State amps with input impedances above 5K.

(ii) I'm assuming you're running single-ended ( or unbalanced ). If I'm correct about this being unbalanced, then this means you've just tied the signal grounds of the two amps together. A hum problem , may or may not occur - it's completely unpredictable . If a hum problem develops that you can't eliminate, you'll need to invest in fairly pricey Audio Isolation Transformers.

(iii) Balancing; Both amplifiers should have volume controls to facilitate obtaining a decent balance between top & bottom.


I'm not sure they will outweigh the hassles of the above challenges.

But, assuming you are using typical voltage-souce amplifiers that actually take their delivery cues from the reflected impedances downstream - then - the Top End amplifier will have a Power Supply that devotes just about all of its' current dumping capacity to reproducing Midrange and Up. Conversely, the Low Frequency amplifier will concentrate on delivering Low Frequencies. This separation of "Church & State" should be noticable ( at some point ).

hope this helps <. Earl K

11-11-2004, 02:19 PM
Ok Earl K .

Now I understand this is clear to me .
Thank you for your thread !



11-12-2004, 08:37 AM
Is there any "effect" to biamp or biwire a speaker ?
I think there is only a min. change against drive it with one amp.


Mr. Widget
11-12-2004, 10:22 AM
Is there any "effect" to biamp or biwire a speaker ?
I think there is only a min. change against drive it with one amp.

Using a proper active or passive crossover at line level between your preamp and amps will be better than a single amp driving a passive crossover after the amp. The range of improvement depends on many variables. It can be subtle or quite dramatic.

If you use an inexpensive or poorly designed active crossover you will hear it's sound too though. If you are using high quality electronics and throw in a cheap PA quality active crossover it will degrade the signal and diminish many of the improvements that are achieved by multi-amping. In fact since multi-amping will in general reveal more detail the poor sound quality of the electronics will be even easier to hear. A properly designed passive filter at line level like the one that Earl posted above will be about the cleanest possible solution. The draw back is insertion loss. You will need a preamp capable of putting out fairly high voltage (greater than the usual 3V) to fully drive your amps. This is especially true if they are not pro amps which typically are designed with a higher input sensitivity.

In my opinion Bi-wiring is pure BS from the tweak files. It seems there is more snake oil in the audio business than real innovation.


scott fitlin
11-12-2004, 10:56 AM
We have done this here in my place, mostly on subwoofer runs, because I have some 50 ft + runs! I use 10ga speaker wire, and to tell you the truth, we didnt hear any difference from single 10ga runs to double 10ga runs! Im told that because I effectively increased the wire size to 5ga I get better damping, and less power loss in the wire itself, but Ill be damned If I actually heard a difference!

Once the wire was run, and tiewrapped in place through the ceiling, I was not about to take it down, so I stay with Bi Wired subs, and larger wire size makes sense electrically, but I dont hear a dramatic improvement. maybe its subtle, and actually gets a couple of watts more to the woofers terminals, but ????????


Mr. Widget
11-12-2004, 11:15 AM
Scott, that is not bi-wiring. You are simply adding a second wire in parallel and for long runs it absolutely makes sense especially for the huge current draw of your subs.

Bi-wiring is running two wires from one amp with one wire going to the LF part of the crossover and another wire going to the HF portion of the crossover. Many contemporary home speakers are designed to allow the user to do it. It requires this type of binding post arrangement. I just grabbed this image off eBay.


scott fitlin
11-12-2004, 11:29 AM
I see what your saying, I thought that double runs are Bi wiring as well!

From my point of veiw, double wire runs, or Bi wiring may or may not make a serious audible improvement, but it cant hurt anything either, so if they like doing it, let them have fun!