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Does impedance of a speaker change when one bi-amps?

I'm fairly new to the audiophile arena and i have seen this question asked before, but not answered.
rickytickytwo
ramtubes's avatar
ramtubes
460 posts
 
@rickytickytwo  

Yes for speakers with complex impedance dips and peaks there can be a significant change when you biamp. We dont care about the peaks, its the dips that bother the amplifier. Drivers themselves do not dip below their DC resistance. However when combined with inductors and capacitors this is no longer true (unless its 1st order). 

When you separate the high and low crossovers (unstrap them) the impedance of each will improve because it no longer sees the other. 


erik_squires
16,041 posts
 
Sorry, erik. BDP24 is correct. Individual drivers have rather smooth impedance curves because they are mass loaded drivers and thats what mass loaded drivers do.. The wild impedance variations we see in complete speakers are due entirely to the passive crossover which we want to eliminate.

You’d be correct if we were talking about active bi-amping AND removing existing filter sections which I did not believe we were.

WIth passive bi-amping we remove only the connection between the two filter sections while leaving the filters in place. In that context I was not incorrect.

I apologize if this wasn't clear from the blog posts I pointed to.

Best,
E
bdp24's avatar
bdp24
9,788 posts
 

Being able to get rid of the speaker-level crossover parts is one of the two reasons for bi-amping (doing so has at least the potential for producing a worthwhile improvement in the sound quality of a loudspeaker). The other is, as Roger Modjeski said above, to separate the low frequencies from the mids/highs in the amplification (giving each it’s own amp, of course), thereby decreasing the potential for the creation of IM distortion in the amp(s).

Bi-amping need not be complicated and difficult. And, it can be cheaper than replacing stock speaker-level x/o parts with those pricey boutique ones. Not only that, you can use a brute-force amp on the woofers if you want, with a nice tube amp for the mids and highs. I first bi-amped with a pair of Magneplanar Tympani T-I loudspeakers in 1973, using the ARC passive x/o designed specifically for that task. Nelson Pass makes a great electronic x/o, but it’s not cheap. Fortunately he also makes (or made, it has just been discontinued) a modestly-priced 2-way x/o, the First Watt B4. It provides 1st/2nd/3rd/and 4th order filters in 25Hz increments from 25Hz to 3200Hz. All discrete (no opamps, no ic’s), retail price $1500. Reno Hi-Fi may have one left, I don’t know. For DIY’ers, it will soon be available as a kit.

erik_squires
16,041 posts
 
Bi-amping need not be complicated and difficult. And, it can be cheaper than replacing stock speaker-level x/o parts with those pricey boutique ones.

Really the only one’s who should engage in this are those who have speakers specifically designed with active crossover in mind (pro speakers), or who can build their own speakers anyway.

Everyone else is probably going to do it wrong and is far better off with a single amp solution.

Best,
E
ramtubes's avatar
ramtubes
460 posts
 
@erik_squires 

bdp24 said..  Beside the advantage of a bi-amped speaker presenting an impedance of less variation to each of the two power amps than one amp sees from a non-bi-amped speaker

This is what I think he is saying. 

The advantage of a bi-amped speaker is that is presents an impedance of less variation to the individual power amps than what one amplifier has to deal with when the high and low drivers are strapped together. 

I think this is easy to confirm. Just think of capacitors and inductors hooked together vs them not. 

I dont see why you say this statement is not true. Seems true to me. I believe bdp is saying that the high and low terminals driven together are a much more difficult load than the high and low terminals strapped together. 

Really the only one’s who should engage in this are those who have speakers specifically designed with active crossover in mind (pro speakers), or who can build their own speakers anyway.

Everyone else is probably going to do it wrong and is far better off with a single amp solution
.
Well they have my permission and I am willing to help. Ye of little faith. 

Is it soooooooo hard to buy a woofer and a tweeter, divide the signal before the amps, choose appropriate amps. 

As far as I am concerned, speaker level crossovers where an ok solution when one had only one amplifier. Now we have lots of ampifiers. A 6,12,18 db/octave analog crossover is childs play. 
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