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post #1 of 651 Old 12-27-2013, 12:55 AM - Thread Starter
 
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Hi everyone,

 

Recently bought myself the new B&W CM10 speakers. I want to bi-amp these speakers to get the most out of them. Some people say that I need maximum power. I think just for peace of mind I want to give them all the juice I can.

 

I have a Yamaha 5ch 1010 receiver and a Rotel RMB-1075 5ch power amp. The 1075 is 120 watts x 5. Bi-amping the front two channels will give me 240 watts.

What do you think of my setup?

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post #2 of 651 Old 12-27-2013, 01:17 AM
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Hi everyone,

Recently bought myself the new B&W CM10 speakers. I want to bi-amp these speakers to get the most out of them. Some people say that I need maximum power. I think just for peace of mind I want to give them all the juice I can.

I have a Yamaha 5ch 1010 receiver and a Rotel RMB-1075 5ch power amp. The 1075 is 120 watts x 5. Bi-amping the front two channels will give me 240 watts.


What do you think of my setup?

why? what do you think passive biamping does for you? hint, it doesn't give you 240 watts per channel.

you should read through this thread before continuing.

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post #3 of 651 Old 12-27-2013, 01:58 AM
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Bi-amping is a waste of time.

That power amplifier will drive them nicely with no need for bi-amping. With their 90 db per watt sensitivity, 100 watts is all they need or can handle.

Just make sure you use 12-gauge speaker wire for minimum resistance.

Monoprice #2789 is a 100-foot roll of 12-gauge pure copper speaker wire for only $30.
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post #4 of 651 Old 12-27-2013, 02:26 AM - Thread Starter
 
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why? what do you think passive biamping from does for you? hint, it doesn't give you 240 watts per channel.

you should read through this thread before continuing.

 

Why it not give double the power? I just looked at the thread but its 34 pages! I can't read through all that. Can someone perhaps give me an explanation here?

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post #5 of 651 Old 12-27-2013, 02:31 AM - Thread Starter
 
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The intended method of connection is as follows:

 

1. FR and FL will be driven by 1075 in biamp/biwire mode. To achieve this the FR and FL each will have one RCA out from the AVR pre-outs and split in two. This will then be connected to the respective front and rear inputs for each side of the 1075. In this way I can supply max power to the CM10's (in excess of 200w bi-amped vs 120w single amp).

 

2. The center channel pre-out from AVR will be connected to center channel input of the 1075.
3. The RR and RL will be driven by the AVR directly.

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post #6 of 651 Old 12-27-2013, 02:34 AM - Thread Starter
 
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why? what do you think passive biamping does for you? hint, it doesn't give you 240 watts per channel.

you should read through this thread before continuing.


Why does it not give 240 watts? I just clicked on the link and the thread is 34 pages long! Can someone please explain why it does not double the power?

 

Some people say I need ample power for these speakers. Bi-amping seems like a good idea and I have the power amp, so I don't see the harm in taking advantage of it.

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post #7 of 651 Old 12-27-2013, 02:56 AM
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Originally Posted by Mekail View Post

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Originally Posted by 67jason View Post

why? what do you think passive biamping does for you? hint, it doesn't give you 240 watts per channel.


you should read through this thread before continuing.


Why does it not give 240 watts? I just clicked on the link and the thread is 34 pages long! Can someone please explain why it does not double the power?

Some people say I need ample power for these speakers. Bi-amping seems like a good idea and I have the power amp, so I don't see the harm in taking advantage of it.

read the thread i linked.

its your time to waste, biamp if you want, but you should understand what it is you are doing and what you will get out of it. i don't want to repeat or rehash the linked thread, but the info in it is current and relevant to this threads question. please check it out.

or follow advice of whoever the "some people" are that you mentioned.

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post #8 of 651 Old 12-27-2013, 03:08 AM
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As I said before, 100 watts is PLENTY OF POWER for those speakers.

You obviously do not understand that your speakers are quite SENSiTIVE (90 db per watt) and that bi-amping will just make more power available than they will ever actually USE.

Bi-amping them is silly, but maybe it will make you feel warm and fuzzy.
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post #9 of 651 Old 12-27-2013, 04:35 AM
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Originally Posted by Mekail View Post

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Originally Posted by 67jason View Post

why? what do you think passive biamping does for you? hint, it doesn't give you 240 watts per channel.


you should read through this thread before continuing.


Why does it not give 240 watts? I just clicked on the link and the thread is 34 pages long! Can someone please explain why it does not double the power?

Essentially passive biamping cuts the load presented by the speaker into two pieces, and hooks each piece to a different identical amplifier. The maximum amount of power that can be delivered to each part is essentially the same whether the halves are connected to one amplifier or two.

Not the best example, but let's take a car and hook the left wheel to one drive train including engine, and the right wheel to another drive train including another engine. If you don't change the gearing, the car's top speed will remain pretty much the same. Most modern cars have rev limiters in the engine computer which limits the top speed of the car, and that and the gearing that turns revs into speed isn't changed. Therefore the top speed of your car is unchanged even though it has twice the horsepower. What really happens is that each engine works a little less harder but it still has to rev as high.
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Some people say I need ample power for these speakers. Bi-amping seems like a good idea and I have the power amp, so I don't see the harm in taking advantage of it.

The problem is that there is so little to take advantage of. If you screw up your biamping experiment you could fry your amplifier. No joke! In passive biamping you end up connecting two amps to the same speaker, and if there is any unseen or accidental connecting of the amplifiers to each other, well its not a good thiing at all!

You can estimate how much power you need without a lot of work or a big investment.

Obtain a sound level meter that has a fast response and peak hold feature such as the az 8928 sound level meter http://www.ebay.com/itm/8928-Decibel-Meter-Digital-Accurate-Sound-noise-pressure-Level-tester-40-130-db-/271167212819?pt=LH_DefaultDomain_0&hash=item3f22d34d13

Set it up for C weighting, fast response, and peak hold. When you power it on press the peak hold button to disable auto shutoff. Put it where you listen and listen as loud as you usually do. Note the SPL meter's reading after your listening session.

Now go online and pull up this SPL calculator, http://myhometheater.homestead.com/splcalculator.html . Plug in the numbers for your system and see whether the number you get for max SPL is more or less than what you measured. If its more, you have more than enough power.
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post #10 of 651 Old 12-27-2013, 04:43 AM
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As I said before, 100 watts is PLENTY OF POWER for those speakers.

You obviously do not understand that your speakers are quite SENSiTIVE (90 db per watt) and that bi-amping will just make more power available than they will ever actually USE.

Bi-amping them is silly, but maybe it will make you feel warm and fuzzy.

+1

If one plugs his system;s numbers into the SPL calculator at http://myhometheater.homestead.com/splcalculator.html and assume two speakers and a 9 foot listening distance one obtains 107.2 dB which is 2.2 dB over THX peak levels and also pretty loud and approaching or in ear damage territory depending how long you listen.
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post #11 of 651 Old 12-27-2013, 05:29 AM - Thread Starter
 
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Essentially passive biamping cuts the load presented by the speaker into two pieces, and hooks each piece to a different identical amplifier. The maximum amount of power that can be delivered to each part is essentially the same whether the halves are connected to one amplifier or two.


So instead of  1 x 120 watt going to each speaker, I will have 2 x 120 watt - 120 for the tweeter section and 120 for the woofers. Is that what you are saying? So the available power does double then.

 

It would seem to have more reserve available for the woofers. I would assume that would be a good thing.

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post #12 of 651 Old 12-27-2013, 05:33 AM - Thread Starter
 
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If one plugs his system;s numbers into the SPL calculator at http://myhometheater.homestead.com/splcalculator.html and assume two speakers and a 9 foot listening distance one obtains 107.2 dB which is 2.2 dB over THX peak levels and also pretty loud and approaching or in ear damage territory depending how long you listen.

How accurate are those SPL calculators? What if I had a sudden change in loudness at a low frequency, like 40 Hz. Would the SPL calculator and wattage still apply?

 

I looked at the SPL calculator and I have not checked my peak SPL levels yet, but I messed around with the calculator. It tells me that if I want 98 dB, I need about 30 watts at a 10 feet. I assume you would double that into 4 ohms, so 60 watts. These speakers have a minimum impedance of 3.1 ohms. So I assume 90 watts?

 

How would these calculations change if low frequencies were thrown into the mix, or do they already factor that in? I've read that it takes a lot more power to handle low frequencies than it does mid-range and highs.

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post #13 of 651 Old 12-27-2013, 05:37 AM - Thread Starter
 
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If one plugs his system;s numbers into the SPL calculator and assume two speakers and a 9 foot listening distance one obtains 107.2 dB which is 2.2 dB over THX peak levels and also pretty loud and approaching or in ear damage territory depending how long you listen.
 

I messed around with the calculator. It tells me that if I listen at 98 dB I would need about 30 watts at a 10 foot distance. I assume double that into 4 ohms, so 60 watts. My speakers have a minimum impedance of 3.1 ohms, so about 90 watts.

 

How would these calculations factor in low frequencies? It takes more power to handle lower frequencies than mids or highs, so if there is a sudden change in volume at 30-40 Hz, would these calculations still apply, or does it simply not include those things? I haven't tested what my peak SPL is in my room. Don't have an SPL meter at the moment but I plan on buying one later.

 

I also don't know how accurate these calculators are. Thoughts?

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post #14 of 651 Old 12-27-2013, 05:49 AM
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Essentially passive biamping cuts the load presented by the speaker into two pieces, and hooks each piece to a different identical amplifier. The maximum amount of power that can be delivered to each part is essentially the same whether the halves are connected to one amplifier or two.


So instead of  1 x 120 watt going to each speaker, I will have 2 x 120 watt - 120 for the tweeter section and 120 for the woofers. Is that what you are saying? So the available power does double then.

It would seem to have more reserve available for the woofers. I would assume that would be a good thing.

if you only read the other thread.....

tell me can the woofer in a biamped connection scheme use the watts going to the tweeter? will the tweeter ever use anywhere near the 120 watts available to it? hint the answer to both is no.

there is no doubling of power because the power hungry woofer only has 120 watts available to it regardless of what is available to the tweeter.

the much more efficient and less power hungry tweeter while having 120 watts available to will likely never ever need more then a small fraction of that even at insane volume levels. everything unused by the tweeter is left at the amp and the woofer may demand more then its available power on certain peaks and not be able to touch the power left on the table for the tweeter.

the only thing that sees a doubling of power in a passive biamp scheme is your av rack. your speakers don't, not now and not ever.
read the other thread!

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post #15 of 651 Old 12-27-2013, 06:07 AM
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If one plugs his system;s numbers into the SPL calculator and assume two speakers and a 9 foot listening distance one obtains 107.2 dB which is 2.2 dB over THX peak levels and also pretty loud and approaching or in ear damage territory depending how long you listen.

 

I messed around with the calculator. It tells me that if I listen at 98 dB I would need about 30 watts at a 10 foot distance.

???

I used 2 speakers with 90 dB sensitivity. 9 foot lisening distance and 98 dB takes 12 watts.
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I assume double that into 4 ohms, so 60 watts. My speakers have a minimum impedance of 3.1 ohms, so about 90 watts.

Not exactly. When the impedance goes down your amp's max music power output goes up. Sine wave testing does not show this well, but testing with waves that are more like music show more power as the impedance goes down. Therefore the speaker's impedance is not part of the calculation.

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How would these calculations factor in low frequencies?

If the speaker has resonably flat response, there's no difference because flat response = constant efficiency.

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It takes more power to handle lower frequencies than mids or highs,

In the real world most speakers don't have flat response down to 20 Hz, not even most floor standers. So you are right in the sense that real world speakers take more power to handle lower frequencies. Another influence is that the ear's sensitivity falls off a cliff at low frequencies so we want even more power at bass frequencies.

The counterpoint is that powered subwoofers are the standard tool for dealing with this situation and they therefore take a big load off of the amps. Remarkably good subs are being sold for attractive prices.

Even if you have impressive floor standers and monster amps, mere modest powered subs can clean up the sound of your system.
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I also don't know how accurate these calculators are. Thoughts?

Any math model is based on assumptions. If I tried to list all of the assumptions in the model we're talking about, I'd still be typing at noon EST and its not even 9am. ;-)

However even in its ignorance of all that, the model is good within a few dB for most situations, and right now that kind of accuracy beats whatever is in second place by a country mile.

For example if memory serves, that model predicts that my home system peaks out at 109 dB, and actual measurements which have some limits of their own, find like 108 dB.
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post #16 of 651 Old 12-27-2013, 06:10 AM
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So instead of  1 x 120 watt going to each speaker, I will have 2 x 120 watt - 120 for the tweeter section and 120 for the woofers. Is that what you are saying? So the available power does double then.

It would seem to have more reserve available for the woofers. I would assume that would be a good thing.

No, that's not the way it works.

(Disclaimer: Experts, yeah, I know, but gimme a break here....)

The internal crossover of the speaker routes a certain percentage of the incoming signal to the woofer and the tweeter. There are many factors that are involved so for simple sake of discussion let's just say 75% goes to the woofer and 25% goes to the tweeter.

So, in the case of connecting a single amp of (in your case) 120W, roughly 90W goes to the woofer and 30W goes to the tweeter.

If you split the crossover to biamp the speaker, the split of the crossover doesn't change so a 120W amp connected to the woofer input still gives only 90W to the woofer and a 120W amp connected to the tweeter input still gives only 30W to the tweeter. And, headroom/reseve power is not increased because the max power available to any part of the speaker hasn't changed. Regardless if there is just one amp or two amps, no part of the speaker can see more than 120W nor will the woofer and tweeter both see 120W simultaeously because both amps are being fed the same signal and the crossover split mentioned previously is still the same.

Now, some have made credible claims that despite not the power increase many think happens, there can still be benefits if (for example) the woofer section is exceptionally hard to drive and the amp has very poor performance at low impedance. However, that sort of case is the exception, not the rule.

Just because there is a knob doesn't mean you should turn it.
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post #17 of 651 Old 12-27-2013, 06:23 AM
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Essentially passive biamping cuts the load presented by the speaker into two pieces, and hooks each piece to a different identical amplifier. The maximum amount of power that can be delivered to each part is essentially the same whether the halves are connected to one amplifier or two.


So instead of  1 x 120 watt going to each speaker, I will have 2 x 120 watt - 120 for the tweeter section and 120 for the woofers. Is that what you are saying? So the available power does double then.

Kinda sorta. The crossover keeps each amp from delivering its full power with musical waves by cutting into the frequency range over which the amp can actually get its power to the speaker. In the end its power that can actually be delivered that matters more.
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It would seem to have more reserve available for the woofers. I would assume that would be a good thing.

That particular reserve gets cut into very significantly by the fact that both amps have to amplify the full music waveform, even if they can't deliver all of it to any speaker due to the crossover. At this point a competent speaker designer would remove the passive crossover in the speaker and replace it with an active crossover hooked in front of the amplifiers. This would trigger another cascade of engineering but done right this can be very effective.

We call this "active biamping" and it can be a wonderful thing, done right.

BTW please note that we are well into launching another 240 pages of debate. ;-)
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post #18 of 651 Old 12-27-2013, 06:27 AM - Thread Starter
 
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[quote=arnyk"???]I used 2 speakers with 90 dB sensitivity. 9 foot lisening distance and 98 dB takes 12 watts.[/quote]

 

Not sure how you ended up with that calculation. I used 90 dB, 10 foot (2 speakers), away from the walls and I got 30 watts to hit 98 dB. 10 watts would give me 93 dB.

 

Quote:
Not exactly. When the impedance goes down your amp's max music power output goes up. Sine wave testing does not show this well, but testing with waves that are more like music show more power as the impedance goes down. Therefore the speaker's impedance is not part of the calculation.

 

What are you talking about? If the impedance goes down then the power goes up. Which is what I said. So if I need 30 watts to hit 98 dB into 8 ohms, then I would need 60 watts into 4 ohms. Halving of impedance means double the power. So my speakers have a minimum impedance down to 3.1 ohms, which means even more power -90 watts. Not sure why you think this is incorrect.

 

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If the speaker has resonably flat response, there's no difference because flat response = constant efficiency.

 

Many speakers don't have a reasonable flat response.
 

Quote:

In the real world most speakers don't have flat response down to 20 Hz, not even most floor standers. So you are right in the sense that real world speakers take more power to handle lower frequencies. Another influence is that the ear's sensitivity falls off a cliff at low frequencies so we want even more power at bass frequencies.

The counterpoint is that powered subwoofers are the standard tool for dealing with this situation and they therefore take a big load off of the amps. Remarkably good subs are being sold for attractive prices.

 

I might want to use my floor standers for music without a subwoofer. So then the SPL calculations I used earlier are thrown out the window for music that has deep bass? Or is it included in the calculations?

 

Quote:
Even if you have impressive floor standers and monster amps, mere modest powered subs can clean up the sound of your system.

Understood.

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post #19 of 651 Old 12-27-2013, 06:32 AM
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Originally Posted by arnyk"??? 

I used 2 speakers with 90 dB sensitivity. 9 foot lisening distance and 98 dB takes 12 watts.

Not sure how you ended up with that calculation. I used 90 dB, 10 foot (2 speakers), away from the walls and I got 30 watts to hit 98 dB.

I used 2-4 feet from the walls which in my view is anyplace but the middle of the room. Do you really have your speakers that far from the walls? You must have a huge room, in which case you probably need larger speakers.
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Not exactly. When the impedance goes down your amp's max music power output goes up. Sine wave testing does not show this well, but testing with waves that are more like music show more power as the impedance goes down. Therefore the speaker's impedance is not part of the calculation.

What are you talking about? If the impedance goes down then the power goes up. Which is what I said.

I read your comment as indicating power required by the speakers. My comment related to power available from the power amp.

The basic idea is that lower impedances can cause the speaker to demand more power, but that the same lower impedances can make the amp capable of providing more power with low distortion. Sine wave tests tend to understate that.

Quote:
So if I need 30 watts to hit 98 dB into 8 ohms, then I would need 60 watts into 4 ohms. Halving of impedance means double the power. So my speakers have a minimum impedance down to 3.1 ohms, which means even more power -90 watts. Not sure why you think this is incorrect.

Please see the previous paragraph. It is true for SS amps, but not true for power amps with output transformers which includes most tubed amps.
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I might want to use my floor standers for music without a subwoofer. So then the SPL calculations I used earlier are thrown out the window for music that has deep bass? Or is it included in the calculations?

No, the subwoofer makes the above calculations pessimistic. With no subwoofer they stand as is.
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post #20 of 651 Old 12-27-2013, 06:33 AM - Thread Starter
 
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That particular reserve gets cut into very significantly by the fact that both amps have to amplify the full music waveform, even if they can't deliver all of it to any speaker due to the crossover.

 

Are you saying that regardless of how much power there is available, the woofer/tweeter won't "see" it because of the passive crossover?

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I used 2-4 feet from the walls which in my view is anyplace but the middle of the room. Do you really have your speakers that far from the walls? You must have a huge room, in which case you probably need larger speakers.

 

I don't know how far the calculator specifies, I just checked the option where it says away from the walls. My speakers are currently positioned 1 meter away from the walls, so I assume that option applies to me.

 

Also, room size is not calculated for. So if I have a large open-plan room then I assume the calculation is meaningless?

 

Edit : apologies, I checked the wrong box. My bad, you were right.

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post #22 of 651 Old 12-27-2013, 06:40 AM
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Are you saying that regardless of how much power there is available, the woofer/tweeter won't "see" it because of the passive crossover?

With respect to your situation with 1 x 120 or 2 x 120 amps, yes.

But if you use more powerful amp then of course more power could go to the drivers.

If you need or want more power to the speakers you have to buy more powerful amps.

Just because there is a knob doesn't mean you should turn it.
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post #23 of 651 Old 12-27-2013, 06:43 AM
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That particular reserve gets cut into very significantly by the fact that both amps have to amplify the full music waveform, even if they can't deliver all of it to any speaker due to the crossover.

Are you saying that regardless of how much power there is available, the woofer/tweeter won't "see" it because of the passive crossover?

Yes.

The crossover keeps the woofer from seeing a lot of the signal that each amp has to make regardless, and ditto for the tweeter. For example the tweeter amp has to make the same voltage wave as the woofer amp, and it is usually the voltage limits of the amp that are hit first.
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With respect to your situation with 1 x 120 or 2 x 120 amps, yes.

But, of course, if you use more powerful amp then more power could go to the drivers.


I understand the tweeter might not see it.  But the woofers, I don't understand. With 120 watt for the woofers, there would be more power from which to draw from compared to no bi-amping at all. That's how I understand it.

 

So in the event I have a large room, or need the additional power, then it will "see it"? Or have I missed the forest for the trees?

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I understand the tweeter might not see it.  But the woofers, I don't understand. With 120 watt for the woofers, there would be more power from which to draw from compared to no bi-amping at all. That's how I understand it.

Having more power to draw on only helps you if the power can actually get to the woofer. The passive crossover blocks out a lot, up to half of the voltage that the woofer amplifer is making because it was a signal for the tweeter.
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So in the event I have a large room, or need the additional power, then it will "see it"? Or have I missed the forest for the trees?

Only if you switch over to active biamping. That's a lot of work and engineering.
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Yes.

The crossover keeps the woofer from seeing a lot of the signal that each amp has to make regardless, and ditto for the tweeter. For example the tweeter amp has to make the same voltage wave as the woofer amp, and it is usually the voltage limits of the amp that are hit first.


But then what's the difference between having 120 x 2 for both tweeter and woofer - ie no bi-amping? Surely the woofers would still be limited in that case because of the passive crossover. In the bi-amp case, unless I've missed something, the woofers have a dedicated 120 watts from which to draw from. The tweeter has 120 watts too, which most of it won't be seen because of the passive crossover and the distribution of energy for highs, which is a small percentage compared to the lows.

 

It appears that bi-amping can have uses, especially in cases where listening levels are very loud and the room size is big. If the power for the woofers were limited in non bi-amp conditions then it would seem to be advantageous.

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post #27 of 651 Old 12-27-2013, 06:52 AM
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I understand the tweeter might not see it.  But the woofers, I don't understand. With 120 watt for the woofers, there would be more power from which to draw from compared to no bi-amping at all. That's how I understand it.

So in the event I have a large room, or need the additional power, then it will "see it"? Or have I missed the forest for the trees?

Hopefully between Arny and I we are not further confusing you. We're both saying the same thing in slighly different ways.

Bear in mind that you are feeding full range signal to the amp on the woofer. The woofer cannot use the part of the signal/power that is for the tweeter.

Really though, continuing to try to think about it in the box of simply power probably will not lead to the understanding. So, rather than rewrite the many threads that already exist on this topic it may be time for more research of them on your behalf. It's going to take the same amount of your time to receive another personal explanation as it will to read the existing threads.

Just because there is a knob doesn't mean you should turn it.
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Yes.


The crossover keeps the woofer from seeing a lot of the signal that each amp has to make regardless, and ditto for the tweeter. For example the tweeter amp has to make the same voltage wave as the woofer amp, and it is usually the voltage limits of the amp that are hit first.


But then what's the difference between having 120 x 2 for both tweeter and woofer - ie no bi-amping?

Not so much, and now we are back to post 3, and history seems to be repeating itself.

I'm going to visit an art museum in Boston with my family, and fully expect the usual human factors to launch us on another 240 page monsterpiece. Sad for the people who write it and read it but I'm having fun!
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But then what's the difference between having 120 x 2 for both tweeter and woofer - ie no bi-amping?

In many/most cases it amounts to no practial difference, and that's the point.

Just because there is a knob doesn't mean you should turn it.
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Please see the previous paragraph. It is true for SS amps, but not true for power amps with output transformers which includes most tubed amps.

 

I can't seem to quote properly for some reason, unless I quote your entire post, but I only really want to reply to this one point. I assumed amplifiers had to obey Ohms Law and that it was universal. So if the impedance halves the power must double. But you are saying that for tube amps that isn't the case?

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