Bi-wiring for 2ohm?

[str8dwn]

I've scoured the internet and found lots on the benefits of bi-wiring home audio, but very little details on car audio.

 

I have a new set of PVF-216 Quarts on the way that I'd like to bi-wire via the front two channels on my HiFonics amp to achieve a 2ohm stero load. My question is: Is there a difference between bi-wiring on two channels vs just running the crossovers normally via a single wire? Will bi-wiring yield a near 2ohm stereo load? I see the crossovers have a jumper used in normal wiring, which gets removed when bi-wiring.

 

I guess I am not seeing the difference in running 4 pairs of wires from the amp's front two channels to the crossover's inputs vs the normal 2 pairs. I am of course running two pairs to each door on the output side of the crossover to each speaker.

[NSFW]

Bi-amplification: use an active crossover, so separate amplifier channels power the mids and tweets (I assume you're talking about mid/tweet component speakers here)

 

Bridging: combine two amplifier channels to drive a single speaker (or, if using passive crossovers, to drive a set of speakers).

 

Bi-wiring: Help me out here.

 

Bridging two amp channels will leave each channel "seeing" half the actual impedance (4 ohm speakers look like a 2-ohm load). It also combines the left and right signals, so this only makes sense if you have four channels that will be bridged into two.

 

Bi-amping will leave each channel seeing the same impedance as before.

I think this is what you're talking about. If you've got 4-ohm speakers, the amp channels will still see 4-ohm loads. Opinions differ about bi-amping, but IMO the main benefit to bi-amping components is that (with most crossovers) it's a lot easier to experiment with different crossover frequencies and tweeter levels.

[str8dwn]

NSFW,

From what I read, bi-wiring is the same concept as bi-amplification but using one amplifier either with 4 or 2 channels. In bi-amping, you often need an active crossover (though the quarts can also do this if you want to use their specific point).

 

To achieve a 2ohm stereo load, I believe you place each speaker in parallel on that specific channel (4+4=2), w/o the need to mono the signals. You could do the same I believe with a single component set in the front (4ohms) and another in the rear while still maintaining a stereo signal.

 

I am trying to understand what happens to the impedence when you bi-wire and the effects of using a 2ohm stereo load.

 

I found this great resource on bi-wiring - but for home audio: http://www.audioasylum.com/audio/cables/messages/4953.html

[laz]

I always only heard of bi-wiring subs that are made for it (dual voice coil) attached to same class amps but never component speakers. You may be better off running independent amps since I am not sure if all amps that are not Class D can run 2 OHM's.

 

X

[112 dB]

As I understand it, bi wiring is different than wiring a dual voice coil sub. It looks the same, but the purposes and goals are different.

 

Hang on a second while I pull out my trusty . There we go .

 

With a Sub, dual voice coils allow you flexibility in your installation. For example, I have a 10 inch sub with dual 2 ohm voice coils. My 2 channel amp is 2 ohm stable when bridged mono, so the lowest load I can set on that bridged channel is 4 ohms (each channel sees effectively 2 ohms). I wired my sub's voice coils in series (AmpL+ to VC1+) (VC1- to VC2+) (VC2- to AmpR-) (2+2 = 4, 4/2 = 2).

 

I could have also bought a single voice coil 4 ohm sub or a pair of 8 inch 8 ohm subs - but the sub I wanted only came with dual 4 ohm or dual 2 ohm configurations.

 

Now if I had an amp that was 1 ohm stable, I would have bought the dual 4 ohm voice coil version and wired these in parallel, (product/sum), so [(4x4)/(4+4) = 16/8, reduces to 2/1], 2 ohm load, and each amp channel would see 1 ohm. Basically.

 

[Please forgive me if I'm not explaining this clearly, or if you get a sense that I am I talking down to you. I'm not. It's been a long day...]

 

Dual voice coil subs allow you to get more performance from a situation where you have limited room or if you have what's known as a high-current amp (lower impedances require more current) and it makes sense to hook it up to a lower impedance.

 

Bi-wiring looks a lot like the same thing, but it isnt because the speakers you are wiring only present a load to the amp through the frequencies they reproduce.

 

Take a simple 2 way crossover for example. I can use a 4 ohm woofer, and wire it in parallel with 2 8-ohm tweeters. Properly crossed over, the amp will see this as a 4 ohm load - the 4 ohm driver below the crossover point and a 4 ohm load (product/sum) [(8x8)/(8+8) = 64/16 = 4] of the two 8 ohm tweeters above the crossover point.

 

Look at it this way. Take one channel from an amplifier. You have a speaker with a two sets of inputs, one for highs and the other for lows, and the right and left channels are connected with a buss bar or a jumper between the Low+ and the High+ and the negatives are similarily connected. You have the option of keeping the buss bars in place and running one set of cables (+ and -) to the (usually low) one set of inputs. Or you, can get rid of the jumpers/buss bars and run 2 sets of cable [2x (+and-)] from one amp channel, one set for the highs and another set for the lows.

 

I remember seeing this setup for the first time and laughing my ass off. Because, it does not make a difference in this case whether or not the bars are there, the amp will see the same load (basically). The low and high inputs will still be wired in parallel, they will share a common point either where the cable and and buss bar come together (using one set of wires), or at the amps outputs (when using 2 sets of cables). My friend and I joked that this was the preferred wiring method of all wire salesman, because from an electrical point of view, the amp is seeing (almost) the same load.

 

I thought more about that experience when I saw this thread. I thought maybe that bi-wiring was put forth as a way to counter the skin effect. See an explanation of that here:

 

http://www.st-andrews.ac.uk/~jcgl/Scots_Guide/audio/skineffect/page1.html

 

But when I read a bit more about bi-wiring, I found that apparently it has more to do with the impedances of the cables themselves, see

 

http://www.st-andrews.ac.uk/~jcgl/Scots_Guide/audio/biwire/Page1.html

 

I think the only difference you'll notice between running 1 set of cables vs 2 is going to be the size of the hole in your wallet.

[NSFW]

If you mean this...

http://www.davidmannaudio.com/faq/faq3.html

...then it's snake oil, don't waste your time.

[str8dwn]

112db and NSFW,

You are very likely correct. I wonder though why every high-end manufacturer now makes bi-wire capable crossovers including our favorite resident guru from JL.

 

As a marketing guy, I know sometimes in business it's monkey-see monkey-do. If your competition has some 'sexy' feature, you may need to have it too. But JL is not that type of company IMO, so maybe there is something to this.

 

Since I plan to have my crossovers in the trunk tray near my amp, and I already ran two pairs of cable to the doors anyway, the most it would take is a few feet to test this. I am planning part of my install this weekend, though not sure it'll be complete.

[NSFW]

It would be interesting hear MSmith's take on this. He's been pretty up-front in the past about where his personal preferences don't align with those of the mass market market or of audiophiles.

 

I don't believe this bi-wiring idea is worth anything for the same reasons that whats-his-name's amplifier challenge money still hasn't been claimed, except that this is actually far less likely to make an audible difference - bi-wiring is electrically identical to normal wiring. I guess the effective resistance of the wiring is halved, but it was negligible in the first place.

 

I would only be slightly surprised if somebody was able to consistently discriminate between a decent consumer amp and a high-dollar amp, but I would be shocked if somebody was able to consistently discriminate between a conventionally-wired and bi-wired system.

 

If you're going do some experimenting, see if you can arrange things so that a friend can switch the wiring around for you. Try it both ways, then have your friend toss a coin, tweak the wiring without telling you which way they're doing it, and get your opinion. See if you can tell them apart reliably. Don't worry if you can't - the two system are electrically equivalent, so they should be audibly equivalent as well.