ohms questions

[Big Daddy]

Originally Posted by srrndhound

In a typical biamp case, where the crossovers are inside the speakers, it is not advisable to use an amp with a lower power rating for the mid/tweet than the woofer, since both amps are driven from the identical full range signal, and we would not want the mid/tweet amp to clip before the other--that will give you less output capability than if you used the sub's amp for the whole system.

One can only play the different power rating game when the crossovers precede the amplifiers.

The majority of members who use bi-amping use their receivers' rear channels to bi-amp their front speakers. A smaller group have purchased external multi-channel amplifiers (mostly Emotiva) and use the channels of that amplifier to bi-amp their speakers. To the best of my knowledge, almost all the members use passive bi-amping and I don't believe too many people are using different amplifiers to bi-amp their speakers or are using active bi-amping.

In my opinion, passive bi-amping (where two amplifiers are used with the existing crossover network of the speaker) is probably a waste of money. Although there may be some moderate sonic benefits, they are not worth the expense of the extra amplifier. Real bi-amping requires an active electronic crossover and disconnecting part of the existing passive crossover of the speaker. Generally speaking, the mid to high section needs to be retained since in a typical bi-amp setup, we only need to eliminate the bass from the mid+high frequencies, unless we are tri-amping the speaker.

The following table shows the approximate power distribution at different crossover frequencies for typical music applications:

PowerDistribution.jpg

Note that according to this table, the equal power point is 350Hz. As can be seen, the power requirement falls quite rapidly after 1,200Hz. The table assumes equal efficiencies for the bass and mid+high drivers. Should they be different, then a correction factor must be added in. For example, if the bass driver were to be 3dB less efficient than the mid+high drivers, then the bass power must be doubled (or vice versa).

Most speakers are rated for a continuous power and an instantaneous power. The voice coil and to a lesser degree the suspension can withstand short bursts of higher powers without damage. However, this does not imply that such power will be reproduced cleanly, and it will definitely increasew the level of distortion.

It is true that the two amplifiers in a passive bi-amping application receive full-range frequencies (assuming the speakers are set to large), but the lower frequencies use a larger percentage of their allocated power. As an example let's assume a two-way speaker with a single woofer/midrange driver and a tweeter. Furthermore, let's assume that the crossover is around 3,000Hz and the peak power rating of the tweeter is 100 Watts.

From the above power distribution table, we can see that 85% of the power is used in the low frequency range below 3kHz, and only 15% in the high frequencies above this point. It is not difficult to calculate from this that the peak power to the tweeter will be around 15 Watts at full power from the amplifier. The average power will be significantly less.

[srrndhound]

Originally Posted by Big Daddy

The majority of members who use bi-amping use their receivers' rear channels to bi-amp their front speakers. A smaller group have purchased external multi-channel amplifiers (mostly Emotiva) and use the channels of that amplifier to bi-amp their speakers. To the best of my knowledge, almost all the members use passive bi-amping...

Yes, that is why I injected a clarifying comment relevant to most "bi-ampers" on this Forum.

...and I don't believe too many people are using different amplifiers to bi-amp their speakers or are using active bi-amping.

Thankfully not. But you stated >>it makes sense to use the more powerful amplifier to power the woofer<< and that's not a good idea due to reduced peak level capability for the system. One would think using more amps would not reduce the max drive capability of the system, but here's a case where that's the unfortunate result.

In my opinion, passive bi-amping (where two amplifiers are used with the existing crossover network of the speaker) is probably a waste of money.

I agree completely, but that's a separate issue from the matter at hand.

It is true that the two amplifiers in a passive bi-amping application receive full-range frequencies (assuming the speakers are set to large), but the lower frequencies use a larger percentage of their allocated power.

Allow me to clarify what I meant when I stated "full range" before. I meant the entire range of signals being fed to that multi-way speaker system--as opposed to the case where crossovers are used ahead of the amps to subdivide the spectrum.

It's irrelevant whether the bass management is set to large or small. It's also irrelevant how much power each amp delivers to their respective loads. It only matters that both amplifiers are driven from the same signal--as is the case with passive in-speaker crossovers. The only way to get the full performance of one of the two amps in such a bi-amped system is to use two amps with equal power rating.

[Big Daddy]

Originally Posted by srrndhound

Yes, that is why I injected a clarifying comment relevant to most "bi-ampers" on this Forum.

Thankfully not. But you stated >>it makes sense to use the more powerful amplifier to power the woofer<< and that's not a good idea due to reduced peak level capability for the system. One would think using more amps would not reduce the max drive capability of the system, but here's a case where that's the unfortunate result.

I am not sure I fully understand what you are saying. Let’s forget about hypotheticals and bring it down to a level that people can understand.

Two of my speakers have 15" inch woofers/subwoofers in the bottom and MTM drivers on top. My receiver is rated 140 watts x 7 into 8 ohms (20-20,000 Hz) at 0.05% THD. I have several vintage amplifiers that are still in pretty good shape that I can use for passive bi-amping.

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SCENARIO I:

Let’s assume I want to bi-amp the speakers by using the front channels of the receiver and the following amplifier.:

Carver TFM 45 Amplifier
8-ohm power/ch: 375W
4-ohm power/ch: 500W
2-ohm dynamic power/ch: 560 W
Bridged mono power: 1000 W, 4/8-ohm @ THD 0.5 %

Question 1: According to your posts, I should connect the receiver to the woofer/subwoofer and the Carver TFM amp to the midrange/tweeter. Is that correct? How would you do the bi-amping and why?

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO II:

I have a second spare amplifier and prefer to use this one instead of the receiver in passive bi-amping. The specifications are as follows:

Carver M-1.0t Amplifier
8-ohm power/ch: 200W
4-ohm power/ch: 500W
Bridged mono power: 1000W, 4/8-ohm @ THD 0.15%

Question 2: Which Carver amplifier would you connect to the woofer/subwoofer and which one to the midrange/tweeter and why?

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO III:

My speakers actually allow for tri-amping and have separate speaker inputs for the woofer, mid-range, and tweeters. Let’s assume we want to use the receiver and the two Carver amplifiers to do passive tri-amping.

Question 3. How would you connect the amplifiers and why?


If you think this is tough, wait for the midterm exam.

[crazyBLUE]

Originally Posted by Big Daddy

I am not sure I fully understand what you are saying. Let’s forget about hypotheticals and bring it down to a level that people can understand.

Two of my speakers have 15" inch woofers/subwoofers in the bottom and MTM drivers on top. My receiver is rated 140 watts x 7 into 8 ohms (20-20,000 Hz) at 0.05% THD. I have several vintage amplifiers that are still in pretty good shape that I can use for passive bi-amping.

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO I:

Let’s assume I want to bi-amp the speakers by using the front channels of the receiver and the following amplifier.:

Carver TFM 45 Amplifier
8-ohm power/ch: 375W
4-ohm power/ch: 500W
2-ohm dynamic power/ch: 560 W
Bridged mono power: 1000 W, 4/8-ohm @ THD 0.5 %

Question 1: According to your posts, I should connect the receiver to the woofer/subwoofer and the Carver TFM amp to the midrange/tweeter. Is that correct? How would you do the bi-amping and why?

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO II:

I have a second spare amplifier and prefer to use this one instead of the receiver in passive bi-amping. The specifications are as follows:

Carver M-1.0t Amplifier
8-ohm power/ch: 200W
4-ohm power/ch: 500W
Bridged mono power: 1000W, 4/8-ohm @ THD 0.15%

Question 2: Which Carver amplifier would you connect to the woofer/subwoofer and which one to the midrange/tweeter and why?

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO III:

My speakers actually allow for tri-amping and have separate speaker inputs for the woofer, mid-range, and tweeters. Let’s assume we want to use the receiver and the two Carver amplifiers to do passive tri-amping.

Question 3. How would you connect the amplifiers and why?


If you think this is tough, wait for the midterm exam.

scenario ~ 1

No . the carver to the woofer because it takes more to drive it !

scenario ~ 2

The carver TFM 45 to the MTM & the carver M-1 to the Woofer , The TFM 45 has A higher 8 Ohm rating .

scenario ~ 3

Receiver ~ tweeters
TFM 45 ~ Mids
M-1 ~ Woofer

Why not

[Big Daddy]

Originally Posted by crazyBLUE

scenario ~ 1

No . the carver to the woofer because it takes more to drive it !

scenario ~ 2

The carver TFM 45 to the MTM & the carver M-1 to the Woofer , The TFM 45 has A higher 8 Ohm rating .

scenario ~ 3

Receiver ~ tweeters
TFM 45 ~ Mids
M-1 ~ Woofer

Why not

I accuse you of copying your answers from the attractive girl sitting next to you in the classroom and banish you to spend the next 24 hours with her in the same room before I report both of you to your parents.

[crazyBLUE]

Originally Posted by Big Daddy

I accuse you of copying your answers from the attractive girl sitting next to you in the classroom and banish you to spend the next 24 hours with her in the same room before I report both of you to your parents.

Good ~

You are A Great Teacher

[srrndhound]

Originally Posted by Big Daddy

I am not sure I fully understand what you are saying. Let’s forget about hypotheticals and bring it down to a level that people can understand.

I'm not talking about hypotheticals, but the real world advice you gave.

Let's look at it another way. A 2-way speaker with internal crossover. It has woofer/tweeter terminals with an option to remove the strapping jumpers. A big amp is available to drive it.

Case 1) the jumpers are in place. One amplifier channel drives both inputs. As the big amp approaches full output--near clipping, both sets of terminals have the identical, high voltage signal from the amp.

Case 2) Remove the jumpers. Leave the big amp connected to the woofer input. Add a smaller amp (say, half the power of the big one) to drive the tweeter input. Both amps are driven from the identical signal, and both amps have the same gain. As the input signal rises, the small amp approaches its max output first--and once it reaches clipping, you must stop. But the big amp is not yet delivering its full output.

Conclusion: The addition of the lower power amp has forced the total output from the speaker system to be limited to that of the smaller amp. The system could play louder with just the big amp used alone.

Two of my speakers have 15" inch woofers/subwoofers in the bottom and MTM drivers on top. My receiver is rated 140 watts x 7 into 8 ohms (20-20,000 Hz) at 0.05% THD. I have several vintage amplifiers that are still in pretty good shape that I can use for passive bi-amping.

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO I:

Let’s assume I want to bi-amp the speakers by using the front channels of the receiver and the following amplifier.:

Carver TFM 45 Amplifier
8-ohm power/ch: 375W
4-ohm power/ch: 500W
2-ohm dynamic power/ch: 560 W
Bridged mono power: 1000 W, 4/8-ohm @ THD 0.5 %

Question 1: According to your posts, I should connect the receiver to the woofer/subwoofer and the Carver TFM amp to the midrange/tweeter. Is that correct? How would you do the bi-amping and why?

No. Not according to my posts.

SCENARIO II:

I have a second spare amplifier and prefer to use this one instead of the receiver in passive bi-amping. The specifications are as follows:

Carver M-1.0t Amplifier
8-ohm power/ch: 200W
4-ohm power/ch: 500W
Bridged mono power: 1000W, 4/8-ohm @ THD 0.15%

Question 2: Which Carver amplifier would you connect to the woofer/subwoofer and which one to the midrange/tweeter and why?

---------------------------------------------------------------------------------------------------------------------------------------

SCENARIO III:

My speakers actually allow for tri-amping and have separate speaker inputs for the woofer, mid-range, and tweeters. Let’s assume we want to use the receiver and the two Carver amplifiers to do passive tri-amping.

Question 3. How would you connect the amplifiers and why?

1) I don't believe in biamping with dissimilar rated amplifiers, for the reason stated above.

2) I'd also be concerned about this scenario because we have not established that the AVR and external amps have identical gains. It can easily be checked, but if they do not match, some means would be needed to fix that.

3) Lastly, I'd never want to add another amplifier to bi-amp a system that had higher distortion than the amp I was using before to drive the whole speaker.

[crazyBLUE]

Originally Posted by srrndhound

2) I'd also be concerned about this scenario because we have not established that the AVR and external amps have identical gains. It can easily be checked, but if they do not match, some means would be needed to fix that.

This makes no sense at all . Why would it matter if the gain is different from the AVR compared to the amp . One set of binding posts is getting one signal & the other set of binding posts is getting another signal

[srrndhound]

Originally Posted by crazyBLUE

This makes no sense at all . Why would it matter if the gain is different from the AVR compared to the amp . One set of binding posts is getting one signal & the other set of binding posts is getting another signal

It will result in a shelved frequency response, the shelf size being that of the gain difference between the amps. That would matter to me.

[Big Daddy]

Originally Posted by crazyBLUE

This makes no sense at all . Why would it matter if the gain is different from the AVR compared to the amp . One set of binding posts is getting one signal & the other set of binding posts is getting another signal

It does matter because we don't want the woofer to play louder than the mid-range/tweeter or vice versa. but that is not relevant to the main questions that I asked. Several of my amplifiers, including the 6-channel Cinepro amplifier, have level controls for all the channels. Even without level controls, I can easily add L-Pads.


srrndhound,

Unfortunately, you avoided answering my questions and kept talking about clipping. First of all, the main reason you do bi-amping is not to avoid clipping. Secondly, with amplifiers that powerful, the last thing I worry about is clipping, particularly when you turn the volume to a reasonable level in a home theater application. I have a Proton amplifier that I purchased in early 1980's for a lot of money back then. Its RMS rating is only 100 watts per channel, but its dynamic power is 1,000 watts per channel. In more than 25 years of use and abuse, the amplifier has never clipped and still works without a problem.

The other issue that you raised was distortion. Again, this has nothing to do with the main questions. For the sake of argument, assume both amplifiers have exactly the same distortion except one is slightly more powerful than the other. Furthermore, unless we borrow the ears of a bat or a dog, I don't believe human beings can tell the difference between 0.01%, 0.05% or 0.005% distortion.

Let's forget about distortion, clipping, and gains. I also realize that the best option is to use identical amplifiers and active bi-amping is by far the best option. However, let's not avoid the main issue and ask the following basic questions:

1. Does passive bi-amping offer any benefit (simple Yes or No)?
2. In passive bi-amping, if one amplifier is slightly more powerful than the other, which one will you connect to the 15" woofer/subwoofer and which one to the mid-range/tweeter (please forget about clipping, distortion, gain and limit your discussion to sonic benefits)?

[srrndhound]

Originally Posted by Big Daddy

It does matter because we don't want the woofer to play louder than the mid-range/tweeter or vice versa. but that is not relevant to the main questions that I asked. Several of my amplifiers, including the 6-channel Cinepro amplifier, have level controls for all the channels. Even without level controls, I can easily add L-Pads.

This thread is a friendly discussion, not testimony in court. You can expect me to interject what I think are relevant comments even if you did not specifically inquire, so as to more fully inform the readers.

L-pads?

srrndhound,

Unfortunately, you avoided answering my questions and kept talking about clipping. First of all, the main reason you do bi-amping is not to avoid clipping.

But one might not want the total headroom of the system to be reduced--no? Your premise was that a tweeter uses less power than a woofer, so you could get by with a smaller amp for the tweeter. I am merely pointing out the error in that assumption.

The other issue that you raised was distortion. Again, this has nothing to do with the main questions.

I didn't raise it. You included distortion in your amplifier specs, and asked which amp to use for which job. Was I supposed to ignore the information you provided?

By they way--what is the main question, and what are your goals for bi-amping?

For the sake of argument, assume both amplifiers have exactly the same distortion except one is slightly more powerful than the other. Furthermore, unless we borrow the ears of a bat or a dog, I don't believe human beings can tell the difference between 0.01%, 0.05% or 0.005% distortion.

Ok. But how about 0.15%, or 0.5%? Those are the figures you quoted.

Let's forget about distortion, clipping, and gains. I also realize that the best option is to use identical amplifiers and active bi-amping is by far the best option. However, let's not avoid the main issue and ask the following basic questions:
Does passive bi-amping offer any benefit (simple Yes or No)?

Not enough to worry about with decent amplifiers. This is my personal opinion. Others may decide differently.

In passive bi-amping, if one amplifier is slightly more powerful than the other, which one will you connect to the 15" woofer/subwoofer and which one to the mid-range/tweeter (please forget about clipping, distortion, gain and limit your discussion to sonic benefits)?

The one with the higher damping factor.

[DangeRuss]

Originally Posted by BluRayFred

There's a quiz later.

I guess I'll be putting on my thinking cap

BTW..... Here's one for ya http://myhometheater.homestead.com/files/htquiz1.htm

I wonder how you'll do

[crazyBLUE]

Originally Posted by DangeRuss

I guess I'll be putting on my thinking cap

BTW..... Here's one for ya http://myhometheater.homestead.com/files/htquiz1.htm

I wonder how you'll do

I missed 2 out of the 10 Questions

[DangeRuss]

Originally Posted by crazyBLUE

I missed 2 out of the 10 Questions

The questions get tougher the further you go........ It's a blast

[kareface]

Originally Posted by DangeRuss

I guess I'll be putting on my thinking cap

BTW..... Here's one for ya http://myhometheater.homestead.com/files/htquiz1.htm

I wonder how you'll do

Whoever thinks an HTPC is difficult to build and operate fails on many levels. The irony is the answer that is likely less correct is "Match output resolution to display device" as the majority of HTPCs don't output the correct FPS for the average HT display. Someone really needs to rewrite a few of the questions on that site.

[srrndhound]

Originally Posted by kareface

Whoever thinks an HTPC is difficult to build and operate fails on many levels. The irony is the answer that is likely less correct is "Match output resolution to display device" as the majority of HTPCs don't output the correct FPS for the average HT display. Someone really needs to rewrite a few of the questions on that site.

Maybe this is the home theater version of the Kobayashi Maru--you have to give the technically incorrect answer to get it right.

But I agree, some of those "opinion" questions are not useful. It was fun anyway.

[DangeRuss]

Originally Posted by kareface

Whoever thinks an HTPC is difficult to build and operate fails on many levels. The irony is the answer that is likely less correct is "Match output resolution to display device" as the majority of HTPCs don't output the correct FPS for the average HT display. Someone really needs to rewrite a few of the questions on that site.

Point well taken