Bridging / bi amp - bi wire

CWK

I bought a set of LSi 15's and have not used the bi-wire hookup. My Yamaha HTR5790 receiver has 7 speaker outputs (7x110Watts). I'm only going to use 4 of them. Is it possible to bridge some of the receiver channels to gain twice the power?

If not, can I simply hook surround front channel to the top (mid/high freq) biwire posts and hook surround rear channel to the bottom (low freq) posts and then adjust the output from the amp with the graphic eq to send only the appropriate frequencies to each? That would theoretically give me double the Wattage into the same speaker with one channel driving the bass and one channel driving the mid/highs.

Will need to check the resulting impedances of course.

F1nut

Can't wait to see the answers to this one.:D

CWK

I would like to hear it even if you're making fun of my ignorance. I've been out of hi fi for 20 years and am trying to get back into it. There's not much info in either the Polk manual or the Yamaha manual.

VR3

No, you cant bridge channels on a receiver, unless the manual says u can - some higher end models do..

Bi-amping only helps you if you have a second amp...

Bi-Wiring...I dont believe in it, but if you want to try it...give it a shot...money better spent elsewhere though, IMO

jdhdiggs

Just picked an open fight on this topic over in the electronics forum. Waiting for people to stew for a while before answering...

My thoughts: Bi-amping is only just "cool" It doesn't help you in anyway. In fact, since both amps are drawing from the same power supply, you are probably hurting yourself.

Bridging? Only if you need the low end bass help. If you are X-overing to a sub, don't bother since bridging typically comes with a THD penalty.

CWK

You said,

My thoughts: Bi-amping is only just "cool" It doesn't help you in anyway. In fact, since both amps are drawing from the same power supply, you are probably hurting yourself

What do you mean drawing from the same power supply?

The Yamaha is a 7 channel receiver, 7x110W, and I'm only using 4. If it's the same power supply, are you saying that if those 3 extra 110W channels aren't being used, then does that free up a bunch of extra current for the channels that I am using? Would'nt that be nice.

jdhdiggs

By same power supply, I mean the transformer taking the "wall" power into the reciever. Every load you introduce is going to feed back a little into that transformer and cause the noise floor to raise and/or THD to raise.

Essentially, your pulling the same power twice from the transformer, adding that noise to the system (and other channels) for no power gain. Not a good tradoff in my book.

billbillw

The only way to get the exact same output from more than one channel of your amplifier is to use the external inputs and have them connected using a Y-cable.
In otherwords, from your source (cd) to your 5.1 external input, have the stereo split into 4 channels instead of two. This would obviously cause problems if you wanted to play multichannel SACD or DVD-A and would also cause you to give up your surrounds. It just really isn't feasible.

In addition, I believe that JHDiggs is right. The power supply inside most receivers is not enough to drive all channels simultaneously at the rated power. Your reciever could easily drive 2x110 simultaneously, but not 5x110 or even 4x110. I've seen numerous tests over at Sound and Vision Mag that verify this. For example, my Denon 2802 is rated at 90x6. Testing found that it was capable of 108W in stereo before clipping, but only 61W in 6 channels all driven mode before clipping.

The sonic benefit you might gain by bi-amping would be negated by the suffering performance of the amplifiers.

Some will say they can hear improvments with Bi-wiring, but I think the easiest thing is to just change out the jumper plates with some decent speaker wire. Many have reported noticable improvement with this simple fix and it doesn't cost you much, especially compared to a good set of bi-wire cables.

Edit: I should also mention, that you will already be pushing your amp hard due to the 4 ohm impedence of the LSi. Running multiple channel into this kind of low impedence load will probably cause frequent overheats. The receiver is only designed for 6 or 8 ohm loads.

F1nut

Originally posted by CWK
I would like to hear it even if you're making fun of my ignorance.

I wasn't making fun of you, not at all. I don't know the answer either, but I expected that the answers could be interesting.

marker

Does the Yamaha receiver in question have this feature like the Pioneer 1014?

If so, I say go for it! If the channels are being unused anyway, it would still be more total power going into the mains than not doing it regardless, but it probably won't actually be double the power though.

unc2701

Don't forget that a good number of multichannel amps have more than one power supply... 5 channel usually splits it mains/ center&surround. Not sure about 7 channel, but that would impact the discussion.... In some newer amps which let you switch rear channels over to a zone 2, I believe that the rear surrounds have their own power supply, so it's not necessarily pulling from the same pool.

Of course, the story you will almost always end up with is that passive Biamping and Biwiring gains are minimal, but knock yourself out if you want to try.

As for me, I do bi-wire, but I don't bi-amp. I got a good deal on some signal cable Bi-wires and my system certainly didn't sound worse with them. As for Bi-amping, I have two empty channels on my 5 channel amp (and each has its own power supply, ie 5x monoblock) and I saw no real gains when I tried out Biamping my surrounds or my center. The LSi25's are already Biamped and they're not wired for triamping.

CWK

thanks for the input unc2701.

Question - You said:

As for Bi-amping, I have two empty channels on my 5 channel amp (and each has its own power supply, ie 5x monoblock)

It sounds like you already tried what I'm asking about. How did you wire it? Using the front / rear surrounds?

How did you know your Yamaha RX receiver has 5 monoblocks? How do I find out if the HTR-5790 has the same configuration?

Thanks,

W

jdhdiggs

Originally posted by unc2701
Don't forget that a good number of multichannel amps

Key word here is amps, and even then they are typically pulling all the power from a single tranformer.

Does your receiver have monoblocks? Unless you spent about $3K for it, I HIGHLY doubt it. It is extremely expensive to do

unc2701

Uhh, ok I should start over. What you are talking about would only do any good if you had a receiver with more than one power supply and that power supply was underloaded. I _think_ (but I'm not certain) that some receivers that have a powered zone two (that doubles as rear surround) have two power supplies- you'll have to look into this, but it'd probably mention it in the manual, since this would be a major plus. I think some older Onkyos also used to have two power supplies, but you'd have to check me on that, too.

You would not want to mess around with the crossovers like you are talking about because you would have to then bypass the crossovers on your speakers, which you do not want to do.

Speaking about my experience, I have the ideal passive biamping situation- a true 5x monoblock power amp (bryston 9b and yep, it cost me $3k) and my conclusion was that it wasn't worth the trouble to biamp.

fireshoes

There really wouldn't be any benefit since the power supply is the limiting factor here. Grab yourself a nice 2-channel amp and give your speakers what they really need.

CWK

FYI. All who participated in this forum:

I called Yamaha tech support and posed the same question. The answers are:

1. DO NOT BRIDGE OUTPUTS

2. They claim that each channel has it's own amplifier and the current capacity of each channel is independent of the others.

3. Bi-amp / Bi-wire gives no benefit with respect to power or signal quality. It's the same signal either way.

So, I'm stuck with the measley 110 wpc (rms) to run the LSi15's. Adding a subwoofer is a possibility but don't want to muddy up the tight bass of the 15's. Also have to live with the fact that the 3 channels I'm not using are just sort of going to waste.

It just kind of bugs me.

malikarshad

I have a 5.1 setup with my fronts Lsi7 stacked over Rti70's. I have Outlaw 770 7 channel amp and Denon 3803.
I'm using a Y cable to split the fronts preout. One goes to the Front channel that feeds the Lsi7 and the seconds goes
to the Rear Back channel that feeds the Rti70 woofer. This way I'm using all the 7 channel of the amp.
Anything wrong with approach.

F1nut

Originally posted by CWK
So, I'm stuck with the measley 110 wpc (rms) to run the LSi15's. Adding a subwoofer is a possibility but don't want to muddy up the tight bass of the 15's. Also have to live with the fact that the 3 channels I'm not using are just sort of going to waste.

Just to be clear, I'm not picking on you or making fun or any of that stuff.

110 wpc doesn't have to be measley, in fact there are many 100 wpc amps (not receivers) that pack quite a punch. Perhaps you could add a separate power amp to drive the LSi15's, if you feel they need more power.

I found your comment on the tight bass of the 15's interesting. I have yet to hear tight bass out of either the 15's or the 25's, so if you have it then I'd say you're doing well as is.

Look at it this way, the other channels are there in case you want to use them in the future.

CWK

Your quote:

I found your comment on the tight bass of the 15's interesting. I have yet to hear tight bass out of either the 15's or the 25's, so if you have it then I'd say you're doing well as is.

You don't think it's tight bass from the 15's? That's what sold me on mine. I compared them to the RT12's. Love the way the 12 look (6 damn drivers!!). But was a little boomy for me. The 15's are what I consider, in my humble opinion and above average listening experience/knowledge, tight bass response.

It's surprising to hear. What do you power your 15's with? Maybe not enough power?

And your comment about a separate amp: I actually have an old Carver M1.0t 200 wpc that I can dig out to see how they do with some real muscle behind them. Will try and report back.

But first, I'm going to try biamping off of my Yamaha by connecting the front A outputs to the top biwire posts (high/mid freq) and connecting one of the surround channels to the bottom (bass) posts. If I put into the receiver into stereo mode, then it's the same signal just a separate channel driving each speaker input. I have an idea that this will boost the wattage to each speaker. Just an idea that I will try. Details soon.

billbillw

Originally posted by CWK
Your quote:

But first, I'm going to try biamping off of my Yamaha by connecting the front A outputs to the top biwire posts (high/mid freq) and connecting one of the surround channels to the bottom (bass) posts. If I put into the receiver into stereo mode, then it's the same signal just a separate channel driving each speaker input. I have an idea that this will boost the wattage to each speaker. Just an idea that I will try. Details soon.

That setup won't work. Stereo mode doesn't output the same signal to all channels. It only feeds the front L and R. If you are talking about some artificial 7(or 5)-channel stereo, beware, the processor creates a slightly different signal for each output to create ambience.

As I state earlier, you will need to use your external inputs and split off your stereo source signal with a Y cable to your front L and R and your unused channels. This is the only way that I am aware of to get the duplicate signals to come out of the rear (or surround) channels. There are directions in your manual on how to increase the normal 5.1 input to 7.1 input.

I think the old carver amp would be your best bet. Plenty of power with low impedance capability.

Edit: I also wanted to mention that bi-amping doesn't really increase the effective power that is going to the speaker. Since the crossover in the speaker controls the flow of current to the speaker, it limits the current from each amp to the frequency range that the crossover specifies. In other words, you will have 110wpc to your highs and 110wpc to your lows. That does not equal 220wpc total. Its still only 110wpc. The benefit comes from the fact that each amp gets to focus on the dedicated frequency range and will usually perform a little better.

CWK

billbillw,

your quote...


[That setup won't work. Stereo mode doesn't output the same signal to all channels. It only feeds the front L and R. If you are talking about some artificial 7(or 5)-channel stereo, beware, the processor creates a slightly different signal for each output to create ambience. ]]

I believe you that the outputs will not be EXACTLY the same. But it will be very close and the bass signal may well be EXACTLY the same for all channels as the ambience will likely be in the form of selectively delayed high/mid's. So if the bass is the same, and I'll be hearing the mid/high freq's on two matched channels, then I figure there will be no degradation in quality.

Further, I can set the sound field program to 2Ch Stereo which is true 2 channel and should defeat all the DSP enhancements.

It's just an idea that I am going to try. I'll let you know if you're right.

I appreciate your idea of y-connecting the inputs, redirecting to a specific output. However, that would require going inside the receiver case and certainly would void the warranty. Even though I'm a degreed EE, I won't consider this.

Also, the Yami receiver has an internal graphic eq which will let me send >160 Hz to the top posts and <160 Hz to the bass posts. This will further add to the power efficiency.

I'm going home tonight to try it. If it blows up, I wont' tell you.

F1nut

Originally posted by CWK
It's surprising to hear. What do you power your 15's with? Maybe not enough power?

I do not own a pair, nor do I expect I ever will, just not my cup of tea. I have demoed them on a average AVR and high tone separates, both times the bass was not to my liking. The 25's I heard at Polk HQ on high tone gear, boomy as hell. As I recall from the reviews I've read, the reviewers found the bass to be sloppy on both also.

As for power around here, trust me, that's not a problem.

unc2701

Ignoring all else, setting the eq like you mention will leave a dead spot from 150-160hz, since the LSi 15 crosses over at 150hz.

On my yamaha, setting it to two channel turns off all but the mains, so I'm not sure how you're going to get it to split the signal & not have the DSP on.

As for what he meant with the y-cable was to go source->y cable->7.1 input (one side of each y to the mains, one side to the surrounds)

Again, knock yourself out, but expect to be disappointed. Most people who do passive biamping have a better setup for it and end up not being impressed.

billbillw

Originally posted by CWK
billbillw,
I appreciate your idea of y-connecting the inputs, redirecting to a specific output. However, that would require going inside the receiver case and certainly would void the warranty. Even though I'm a degreed EE, I won't consider this.

Woa, your not understanding this at all.

I'm not talking about going into the case. I'm talking about using a couple of Y-cable RCA 1 female-2 male to connect 4 channels from two channel output.

On the back of your receiver, you have "external" inputs that correspond to each of the 7 channels of amplification. These analog inputs bypass all the internal processing except for level control. See page 17 and 55 of your owners manual for clarification. These are typically used for external processors like SACD/DVD-A.

I'm talking about using the Y-cable to duplicate your R/L stereo signal into 2 identical R channels and 2 identical L channels. Understand? Should be basic for an EE.

Using the internal signal processor to create the quasi 7 channel stereo will probably give you very bad results. The bass signal is probably reduced or at the least time altered in the rear channels. Getting signals that are "very close" will result in a poor sound. I would not try this. Y-cables are inexpensive and a guarantee that the highs and lows for each channel will be from identical signals.

unc2701

In response to F1's comments- My 25's took a TON of tweaking before I got them sound right & balanced and if anyone touches those knobs, I'll cut their fingers off!!! Don't trust the stores to put any effort into setting them up right- they probably just cranked them all the way up because people like bass. As for polk HQ... who knows? bad room? Too many people playing w/ them? It takes effort, but you can get smooth response out of them with some work.

malikarshad

Originally posted by billbillw

As I state earlier, you will need to use your external inputs and split off your stereo source signal with a Y cable to your front L and R and your unused channels. This is the only way that I am aware of to get the duplicate signals to come out of the rear (or surround) channels. There are directions in your manual on how to increase the normal 5.1 input to 7.1 input.

That's exactly what I did. I split the Front L & R signal using Y-cable to use the amps 4 channels output to power the my fronts Lsi7 and Rti70's.
However if you don't have external amp then I don't think its possible to split the signal unless you open up the receiver and I personally won't do that.

CWK

Hey billbillw,

Woa, your not understanding this at all.

You are correct. I'm an EE, capable of understanding this but just now digging into it. Please bear with me. I've got a two year old and 10 week old twins so I can only spare 5-10 minutes at a time to research this project.

Looking at p. 17 and 55, I think I see what you're talking about.

So you're suggesting getting some y-split rca cables, connecting the main channel PREAMP outputs into two of the external inputs?

Or coming directly from the cd player with y-split rca's and into the external inputs?

It seems that would accomplish exactly what I had conceptualized. I really appreciate your help.

CWK

Also FYI:

The Denon 3805 apparently can do this bi-amping to double the wattage to a single speaker but specifies 5.1 mode only.

I checked the manual online at denon.com. It appears to be done the same way that I planned originally.

I think billbillw's y-split rca cables make more sense. I'll investigae both.

billbillw

CWK,
I was talking about straight from the CD player to your external inputs with the Y-cable. If you used the preout to the external input, you would get no sound because it would be a closed loop, so to speak. The external inputs have to be selected just like any other input. The pre-outs only pass through the selected input.

Obviously, my suggestion is not very practical for the long run because you wouldn't get correct output from any source other than your cd player. It was just a suggestion to try it out and see how it worked. I still don't think you will get the full effect of having separate 4-channel high current amp with this type of arrangement.

My advice is to just forget about bi-amping for now and enjoy what you have. Sounds like you have your hands full around the house. Maybe someday down the line, you can find a high end dealer to let you demo a nice amp and decide if its worth it to upgrade. It sounds like most around here don't see the sonic benefit of bi-amping.

CWK

Ok. I got my biamping idea to work. Quite impressed with that Yami receiver, very versatile. Used y-split rca cables from the cd player into the external inputs of the 5790. I used Front outputs on the bass posts of the LSi15's and Surr Rear outputs to the top posts. Set the 5790 to use External Inputs and selected MultiChan Input mode. As far as the receiver knows, it's two separate pairs of speakers. According to YEC tech support, it's also two current independent amplifiers at 110 wpc each giving 220 wpc theoretical power to the 15's. I'm running my old Polk RTa11t's from the Front Surr. channel.

Using Multichan Input mode necessarily defeats any signal processing so no effects are added. It's just stereo.

But how does it sound? No real results yet. I finished around 1 am this morning, everyone was asleep and didn't want to chance pi$$in' mama off. So only heard at very low levels. I did verifiy that there was both bass and mid/hi freq's from the 15's. I'll have a chance to turn it up this weekend. I believe you guys that there likely be no perceptible improvement. But I just had to see for myself.

Question for the experts: splitting the source with y-split cables, does that attenuate the signal at all? If so, would that cancel any power improvement as the amplifier gain is only a multiple of the source?

unc2701

The y-cable won't affect the volume- it's based on the voltage, and the voltage should remain constant in the wire (ignoring the resistance of the y-cable which should be negligible).

The reason for the 3db boost people talk about with y-cables and sub amps is that most subs sum the left and right voltages, double voltage=3db boost.