ohms questions

[Steve]

Originally Posted by Deelow537

I have a Onkyo HT-RC180 which give me the option of 4 ohms or 6 ohms @ 110 watts per speaker... My JBL speakers are rated at 8ohms @ 100 watts per speaker! I also have a 300 watt sub woofer.... Which ohm setting would be better for me?

Leave it on the 6 Ohm setting, which I'm guessing is actually 6-16 Ohms. I'm reading now that a receiver like this should not be switched to the 4 Ohm mode even if you're driving 4 Ohm speakers. Here it is if you want to read it for yourself. (Jomari posted the link on the first page.)

NOTE: Some Receivers have an impedance selector switch. DON'T USE THEM! The manufacturer puts them there for UL approvals as well as easing consumer concerns about driving low impedance loads. These switches step down voltage feed to the power sections which will limit dynamics and overall fidelity. Keep the switch set for 8 ohms regardless of the impedance of your speakers and ensure proper ventilation of the Receiver.

Full Article

[Deelow537]

Thanks I will give that a shot when I get home tonight!

[jomari]

my linkies never get any love...

thanks for the repost steve (i still remember you as the fireman )

[Deelow537]

I thank u both...truly

[Steve]

Originally Posted by jomari

my linkies never get any love...

thanks for the repost steve (i still remember you as the fireman )

Always try to give credit where it's due.

[jomari]

Originally Posted by Steve

Always try to give credit where it's due.

thanks fireman, appreciate the gesture..

[srrndhound]

Originally Posted by Steve

Leave it on the 6 Ohm setting, which I'm guessing is actually 6-16 Ohms. I'm reading now that a receiver like this should not be switched to the 4 Ohm mode even if you're driving 4 Ohm speakers. Here it is if you want to read it for yourself. (Jomari posted the link on the first page.)

Full Article

Gene may be right is saying the impedance switch is there to help pass UL. But he is incorrect in that:

a) If UL were interested in checking worst case heating of an amplifier, they surely wouldn't be testing it at some rated distortion that required pushing into clipping. It would be at 1/3d the max rating--as that generates the most heat, and is actually much closer to actual use conditions, since no unclipped audio signal can heat an amplifier like a sine wave.

b) Below clip, the sound quality, fidelity, dynamics are totally unaffected. Only the max output is reduced.

The switch is there because folks like to put AVRs inside cabinets with less than ideal air circulation, and this is an easy way to avoid them shutting down unnecessarily, or worse.

Based on the above, their advice to avoid using those switches is misguided.

[srrndhound]

Originally Posted by BLUTRIG

I have 10 channels at 140 watts each and I bi-amp all speakers so all speakers would receive up to 280 watts max or peak

That's not how bi-amping works. By driving two amps @ 140w into your speakers, you still have only 140w available. The voltage at the speaker terminals is not increased by biamping.

[richteer]

Originally Posted by srrndhound

a) If UL were interested in checking worst case heating of an amplifier, they surely wouldn't be testing it at some rated distortion that required pushing into clipping. It would be at 1/3d the max rating--as that generates the most heat, and is actually much closer to actual use conditions, since no unclipped audio signal can heat an amplifier like a sine wave.

I'm confused. Why do you assert that most AVR's generate the most heat when running at 1/3 their maximum rating?

[richteer]

Originally Posted by srrndhound

That's not how bi-amping works. By driving two amps @ 140w into your speakers, you still have only 140w available. The voltage at the speaker terminals is not increased by biamping.

Yeah, but each driver could theoretically draw 140 W, so the speaker as a whole could (in that case) draw up to 280 W.

[srrndhound]

Originally Posted by richteer

Yeah, but each driver could theoretically draw 140 W, so the speaker as a whole could (in that case) draw up to 280 W.

No, not really. The total current the high and low drivers draw is identical whether there are two amplifiers used or one.

[srrndhound]

Originally Posted by richteer

I'm confused. Why do you assert that most AVR's generate the most heat when running at 1/3 their maximum rating?

Consider what causes heat in the output devices--the product of current times voltage. Both must be present.

The maximum power into the load would be a square wave going from +rail to -rail. All current, no voltage across the output transistors (or high voltage when there's no current). No heat in the amp, all the heat in the speaker.

It has been standard practice to use 1/3 power as the heat stress point. Here's a quote I found in my first search:
>>If a manufacturer chooses to quote a power rating at 4 ohms in their advertising, the amp must be capable of delivering this much power after a 'warmup' period of operation at 1/3 power (which level actually dissipates more heat in the output stage than full-power operation).<<

Here's an even better article. See Fig. 4 which shows dissipation in a class AB amplifier--which I am assuming is the type we are discussing in typical AVRs.

[Big Daddy]

Originally Posted by richteer

Yeah, but each driver could theoretically draw 140 W, so the speaker as a whole could (in that case) draw up to 280 W.

Originally Posted by srrndhound

No, not really. The total current the high and low drivers draw is identical whether there are two amplifiers used or one.

Allow me to dazzle and confuse you with a little math.

When you use two 100 Watt sources to bi-amp a speaker, there will be some MAGIC involved. You will not get 200 Watts. You will get 400 Watts. This is Big Daddy's new math:

100 Watts + 100 Watts = 400 Watts

First of all, you cannot add power or Watts. Power and work do not exist until some action takes place. In the case of speakers/amplifiers, you will need to add voltages.

Assume we are bi-amping a speaker by sending 28.3 volts to the mid-rage/tweeter and 28.3 volts to the woofer. Furthermore, we assume the impedances of all the components are equal to 8 Ohms.

The relationship between power and voltage is as follows:

Power = Voltage^2 / Resistance

Therefore, 28.3 volts is equal to 100 Watts for an 8 Ohm speaker..

Power = (28.3^2) / 8 = 100 Watts

When we bi-amp a speaker by sending 28.3 volts to the woofer and 28.3 volts to the mi-range/tweeter, the total voltage will be 56.6 volts.

Total volts = 28.3 + 28.3 = 56.6 Volts


Total Power = (56.6^2) / 8 = 400 Watts

It is all magic.

[DangeRuss]

Originally Posted by Big Daddy

Allow me to dazzle and confuse you with a little math.

When you use two 100 Watt sources to bi-amp a speaker, there will be some MAGIC involved. You will not get 200 Watts. You will get 400 Watts. This is Big Daddy's new math:

100 Watts + 100 Watts = 400 Watts

First of all, you cannot add power or Watts. Power and work do not exist until some action takes place. In the case of speakers/amplifiers, you will need to add voltages.

Assume we are bi-amping a speaker by sending 28.3 volts to the mid-rage/tweeter and 28.3 volts to the woofer. Furthermore, we assume the impedances of all the components are equal to 8 Ohms.

The relationship between power and voltage is as follows:

Power = Voltage^2 / Resistance

Therefore, 28.3 volts is equal to 100 Watts for an 8 Ohm speaker..

Power = (28.3^2) / 8 = 100 Watts

When we bi-amp a speaker by sending 28.3 volts to the woofer and 28.3 volts to the mi-range/tweeter, the total voltage will be 56.6 volts.

Total volts = 28.3 + 28.3 = 56.6 Volts


Total Power = (56.6^2) / 8 = 400 Watts

It is all magic.

Maybe you could help me with a little math problem.

I realize impedance ratings for a system (speakers) is just an average because the ohm's fluctuate with a given frequency . How does this in turn effect the load on an amplifier when bi-amping or does it ?

[Big Daddy]

Originally Posted by DangeRuss

Maybe you could help me with a little math problem.

I realize impedance ratings for a system (speakers) is just an average because the ohm's fluctuate with a given frequency . How does this in turn effect the load on an amplifier when bi-amping or does it ?

Normally, with bi-amping, there are no major concerns about impedance as one amplifier will power the mid-range/tweeter and the other amplifier powers the woofers. We are assuming that the amplifiers can handle the loads of the speaker’s drivers. Since woofers require more power, it makes sense to use the more powerful amplifier to power the woofer.

If you are using the rear channel amplifiers of a receiver to bi-amp the front speakers, it really doesn't make any difference as the receiver still assumes that they are connected to two different speakers. However, if the individual drivers have impedances that go below the capability of the receiver, you may have a problem.

Most people use passive bi-amping and rely on the internal crossover of the speaker. The benefit of passive bi-amping is limited. The most beneficial type of bi-amping is to use an external active crossover network as demonstrated in the following diagram.

As you mentioned in your post, it is true that a speaker or driver’s impedance is not constant and varies with frequency. For example, a speaker with a nominal 8 Ohm rating can fall below 4 Ohms at certain frequencies. If the current reserves of the amplifier are not sufficient to sustain its output wattage into low impedances, the amplifier will run out of juice, at the time when the extra power is needed most. This can explain why some very high quality 50 watt per channel amplifier may sound less strained than another unit rated at 200 watts per channel.

When you are connecting two speakers to the same amplifier, then impedance becomes a major concern. For example, if the two 8 ohm speakers are connected in parallel, the impedance will drop to 4 ohms. If they are connected in series, the impedance will rise to 16 ohms. When the impedance drops, more current will flow into the speakers. When the impedance rises, the current going to the speakers will drop

You can add two amplifiers to the same speaker in two different ways:

1. Bridging two channels of a stereo amplifier or bridging two mono amplifiers. Bridging an amplifier is a procedure to generate more output voltage by inverting the second channel (or the second mono amplifier) and connecting it to one speaker. Think of it as connecting two mono channels in series. The impedance implication will be the opposite of series speakers. In the case of series speakers, the impedance will rise. When you bridge two channels of an amplifier, you will be cutting the effective load impedance in half. For example, if a bridged amplifier is connected to a 4 ohm speaker, it will make the effective impedance 2 ohms. This is why an amplifier can quadruple the rated power of a single channel when bridged. Many people believe that if their amplifier stable for 4 loads, then they can bridge it to a 4 ohm speaker load. This is not the case as a bridged amplifier will see the 4 ohm speaker as a 2 ohm speaker load and the amplifier may fail. I did this recently and damaged my amplifier.
   
2. Connecting two mono amplifiers in parallel to the same speaker. When two amplifiers are connected in parallel, the effect on impedance will be the opposite of parallel speakers. If you connect two speakers in parallel, the impedance will drop. With parallel amplifiers, the impedance will rise. For example, if two identical amplifiers, each rated for 4 ohms, are connected to a 4 ohm speaker, each amplifier will see an equivalent of 8 ohm and each amplifier will supply half the current that it provide before. With this type of setup, the two amplifiers must be identical because they see other as loads. If the amplifiers are different, the stronger one will try to drive the other one and you run into all sorts of problem. Furthermore, the gains for the two amplifiers must be exactly the same.

Some amplifiers have connectors for two pairs of speakers and have an A/B switch on the front panel. Most of these amplifiers connect speakers in parallel when both speakers are selected. It is common for these amplifiers to require 8 ohm speakers only, because they are usually built to drive either 4 or 8 ohms, and two sets of 8 ohm speakers in parallel will result in 4 ohms. If you connect two set of 6 ohm or 4 ohm speakers to these type of amplifier, they may overheat and fail.


Sorry about the long post. Most probably, I got off the subject. It is your fault for asking tough questions. I am tired now and need to rest.

[DangeRuss]

Originally Posted by Big Daddy

Normally, with bi-amping, there are no major concerns about impedance as one amplifier will power the mid-range/tweeter and the other amplifier powers the woofers. We are assuming that the amplifiers can handle the loads of the speaker’s drivers. Since woofers require more power, it makes sense to use the more powerful amplifier to power the woofer.

If you are using the rear channel amplifiers of a receiver to bi-amp the front speakers, it really doesn't make any difference as the receiver still assumes that they are connected to two different speakers. However, if the individual drivers have impedances that go below the capability of the receiver, you may have a problem.

Most people use passive bi-amping and rely on the internal crossover of the speaker. The benefit of passive bi-amping is limited. The most beneficial type of bi-amping is to use an external active crossover network as demonstrated in the following diagram.

As you mentioned in your post, it is true that a speaker or driver’s impedance is not constant and varies with frequency. For example, a speaker with a nominal 8 Ohm rating can fall below 4 Ohms at certain frequencies. If the current reserves of the amplifier are not sufficient to sustain its output wattage into low impedances, the amplifier will run out of juice, at the time when the extra power is needed most. This can explain why some very high quality 50 watt per channel amplifier may sound less strained than another unit rated at 200 watts per channel.

When you are connecting two speakers to the same amplifier, then impedance becomes a major concern. For example, if the two 8 ohm speakers are connected in parallel, the impedance will drop to 4 ohms. If they are connected in series, the impedance will rise to 16 ohms. When the impedance drops, more current will flow into the speakers. When the impedance rises, the current going to the speakers will drop

You can add two amplifiers to the same speaker in two different ways:

1. Bridging two channels of a stereo amplifier or bridging two mono amplifiers. Bridging an amplifier is a procedure to generate more output voltage by inverting the second channel (or the second mono amplifier) and connecting it to one speaker. Think of it as connecting two mono channels in series. The impedance implication will be the opposite of series speakers. In the case of series speakers, the impedance will rise. When you bridge two channels of an amplifier, you will be cutting the effective load impedance in half. For example, if a bridged amplifier is connected to a 4 ohm speaker, it will make the effective impedance 2 ohms. This is why an amplifier can quadruple the rated power of a single channel when bridged. Many people believe that if their amplifier stable for 4 loads, then they can bridge it to a 4 ohm speaker load. This is not the case as a bridged amplifier will see the 4 ohm speaker as a 2 ohm speaker load and the amplifier may fail. I did this recently and damaged my amplifier.
   
2. Connecting two mono amplifiers in parallel to the same speaker. When two amplifiers are connected in parallel, the effect on impedance will be the opposite of parallel speakers. If you connect two speakers in parallel, the impedance will drop. With parallel amplifiers, the impedance will rise. For example, if two identical amplifiers, each rated for 4 ohms, are connected to a 4 ohm speaker, each amplifier will see an equivalent of 8 ohm and each amplifier will supply half the current that it provide before. With this type of setup, the two amplifiers must be identical because they see other as loads. If the amplifiers are different, the stronger one will try to drive the other one and you run into all sorts of problem. Furthermore, the gains for the two amplifiers must be exactly the same.

Some amplifiers have connectors for two pairs of speakers and have an A/B switch on the front panel. Most of these amplifiers connect speakers in parallel when both speakers are selected. It is common for these amplifiers to require 8 ohm speakers only, because they are usually built to drive either 4 or 8 ohms, and two sets of 8 ohm speakers in parallel will result in 4 ohms. If you connect two set of of 6 ohm or 4 ohm speakers to these type of amplifier, they may overheat and fail.


Sorry about the long post. Most probably, I got off the subject. It is your fault for asking tough questions. I am tired now and need to rest.

Wow ....I'm diggin all of the info Now here's another question..
My system is connected like the diagram shown (without the electronic crossovers) for the 5 different channels . Is this considered serial or parallel ?

[Big Daddy]

Originally Posted by DangeRuss

Wow ....I'm diggin all of the info Now here's another question..
My system is connected like the diagram shown (without the electronic crossovers) for the 5 different channels . Is this considered serial or parallel ?

Most probably, you are bi-amping your speakers according to the following diagram:

Bi-Amping.jpg

Your connections are neither series nor parallel. Series and parallel apply to connecting two or more speakers to the same power source like one of the following diagrams.


Series Loudspeakers:

This connection would give a final impedance of 8 ohms.

Parallel Loudspeakers:

This connection would give a final impedance of 2 ohms.

[DangeRuss]

I see .....Thanks for the clarification

[FreddieFerric]

Originally Posted by DangeRuss

I see .....Thanks for the clarification

There's a quiz later.

[srrndhound]

Originally Posted by Big Daddy

Normally, with bi-amping, there are no major concerns about impedance as one amplifier will power the mid-range/tweeter and the other amplifier powers the woofers. We are assuming that the amplifiers can handle the loads of the speaker’s drivers. Since woofers require more power, it makes sense to use the more powerful amplifier to power the woofer.

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.