Axiom Home Page Forums General Discussion Home Theater How much power do I need - m60 measurements

Gena,

This was an interesting test and it certainly continues to show how at average to moderately high volumes, consumers still only require relatively small amounts of power. However something is still missing from the equation (in practice) which may only be tested at the risk of damaging your system, something a friend of mine tried some time ago.
If i understand your measuring correctly, you hooked up a single M60 to test the power consumption at limited frequencies, then turned on all other speakers plus a sub and set the speakers back to 'small' before testing music (some inherent holes in the measuring by doing this, but easily rectified). Ayway, with all channels running, the amount of power consumed will actually be x times the wattage per each speaker. In your example of peaks ( and assuming the setup consisted of 4-M60s), 12W peaks times a 4 speaker setup brings the total consumption into a 48W range, well below the rated output for a receiver but about 50% of its rating, not 10% (and these numbers use the subwoofer "on", mains set to "small" power values).
Next take that 4 speaker setup and turn the receiver up to 100% (or maybe even less) and measure the output as it drives the speakers once distortion begins.
You may find that the total wattage consumed is still not beyond the rated output of the receiver (a guy i knew tested something similar). So if this is the case, how is it possible that distortion is present if the measured consumption 'should' be under the rated receiver power output?
Here's where capacitors and power supplies (size, quality) comes into play for energy storage/flow during sound playback and power consumption (rates vs. capacity). This is usually where receivers fall short of separate components...but again only at higher SPL, varying with room size, amount of low frequency energy being played, speaker size, impedance or the other usual suspects as to why a receiver drops out before separate SS amps.

I wish i could provide more details on the experiment but it was done quite some time ago and my memory is faded. I don't know the guy anymore.
Food for thought.

Incidentally, my listening preference for movies is often lower than for music. When i'm playing pool in the room next to the media room, my Axiom system can average 94-98dB at the seating location (about 11'). I only have a receiver at this point but will likely add an external amp for the mains to give me a bit more overhead as the 100dB point is approached, distortion can begin (on my system).
My larger Tannoys upstairs typically average 104dB (also at about 11') when i'm listening to them while cooking in the kitchen. I'm planning on getting a larger amp since the one driving them is incapable of overdriving them. I would rather have an overpowered rather than an underpowered amp for those pricey dickens.

A WATT is a mathematical sum of voltage and current.

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Power=Voltage x Current. Using the Ohms low U=IR that can be written as W=U*I=U^2/R=I^2R.

In your example, 1W into 4 Ohms requires only 0.5 A. That is an easy task for your amp. However, if you want to drive a 100W into 4 Ohms that would require 5A and may be your amp was not rated for that, I don't know. May be it was hitting the rail voltage limit.

These numbers are the power into the load. The power from the wall can be higher, by a factor of 2, so the amp was trying to draw a high current from the wall and was hitting the fuse limit. It's hard to say.

But, again, 1 W into 4Ohm requires only 0.5A of current and it should be a peace of cake for any decent amplifier.

...brings the total consumption into a 48W range, well below the rated output for a receiver but about 50% of its rating...

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Small correction. The receiver is rated 100W+100W, 2 channels driven, so it's at worst 25% . Plus there there is power in all other channels as well, may be 50Wpc, so over all the figure would be closer to 48W/300W = 16%. Still plenty of headroom

In reply to:

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12W peaks times a 4 speaker setup brings the total consumption into a 48W range, well below the rated output for a receiver but about 50% of its rating, not 10%

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You make some good points, but typical amps are rated at X Watts per channel, not total. Certainly depends on the amp. There are many different ways of expressing the ratings that can me misleading to some.

A decent amp usually denotes the Watts per channel rating with "all channels driven simultaneously into 8 Ohms at 20Hz-20kHz". Less desirable is the "driven with 1 kHz".

The other thing I've seen recently is an amp rated at 110 WPC driven into only 6 Ohms, which works out to be about 80 WPC into 8 Ohms. I think it is the manufacturers way of inflating their specs to the consumer.

Gena and Others:

This has been a most interesting and stimulating thread and has stimulated me to do some "deep" thinking!!

Let me try to make a case for requiring more than 100 Watts of Peak Power. This may answer, at least in part, why some folks report better sounding music with the higher power amps.

Lets use some of Gina's data (and maybe I will take a little liberty with an "assumption" or two).

1. 5 Watts for 85 dB SPL (some board members report listening at 90 -100 dB SPL)

2. Factor of 24 between Peak and Average (.5 W average versus 12 W peak)

3. Speaker impedance is not fixed across the spectrum (may dip from 8 ohms to 4 ohms or lower)

Ok, lets take some of you folks who like to listen at 85 dB SPL, no louder. That's 5 watts. Multiply that by 24 is 120 watts (consider just a single channel). Lets "assume" that the impedance dips, at the same time to 4 ohms, then we have 240 W of peak power.

Now, if you want to listen at 95 dB SPL, that equates to 2400 Watts of peak power.

I don't know how realistic this hypothetical case is, but it does demonstrate that you may need much, much more than 100 W of peak power to accurately reproduce your music at moderate to loud listening levels.

I think that this analysis would apply to fronts and center channels. Rears and surrounds probably an order of magnitude or two less.

Alright, what say the tribe?

Ratpack,

I am not really an expert in loud listening:)

You have shown very convincingly that by applying certain numbers and assumptions one can arrive to an absurdly high number - 2400 W per channel. That's the SuperDome class acoustic.

I see you have the same Onkyo 703 as I do. I think it's a very capable and powerful receiver. However it might be not so for you.

Here's what I would suggest. Pick an inexpensive multi-meter and measure the average power coming into your speaker. You can measure the voltage if you connect it to the speaker's posts or the current if you connect it in series with the speaker. Then you will have an idea how much power the receiver puts out into the speaker at your listening level.

Now, granted it will be the average power. If you have a scope, you can make the same measurements for the instantaneous power. If not, well, you can apply some reasonable multipliers. At the end, I believe, it will make the decision of whether upgrade just a bit more sound

Secrets of Amplifier and Speaker Power Requirements Revealed

Lots of points raised, I'll make some brief comments.

Larry, blind listening tests have shown that THD has to be more than about 1% to be detectible when listening to music rather than pure test tones. The THD numbers for any of the units which we would seriously consider are far below audibility when operated within their designed limits.

Speakerchooser, the 120 watts of your Yamaha are measured according to the FTC regulations with two channels simultaneously driven at full rated power for at least five consecutive minutes. The three front speakers don't "share" this. The difference between 120 watts and 200 watts is 2.22dB in maximum sound output; e.g. if a peak could be played at 110dB with 120 watts, it could be played at 112.22dB with 200 watts. Both figures are higher than likely to be needed for home use.

Mike, the controlling element is voltage, not current. For 1 watt into 8 ohms a bit under 3 volts is required(V[squared]/R)and about a third of an ampere(P/V)rather than 60 amperes.

Bernard, the calculation of power required has to take into account both the reverberent and direct sound fields. This is as was described in the Voelker and Linkwitz material that was linked in my first reply here. They should be studied carefully(especially the Linkwitz power calculation) to understand why less power is used than is sometimes thought.

Gena: I'm not really interested in doing any experiments. I think that you did an excellent job.

My point was that you could take a lot of liberty with my numbers and still come up with peak power requirements of more than 100 Watts.

One other thing to consider is that solid state amplifiers are not very forgiving to peaks (spikes) that exceed their maximum ratings. They can be destroyed very easily by fast spikes containig very little energy.

In the course of all of this discussion, I think that I have convinced myself that if I get a seperate amplifier, I want at least a 3 channel unit (RCL).

This is a most interesting thread.

By the way, what color is your 703? I bought silver.

Wid: an interesting article by Alan. In so many words, I think that he agrees to my analysis.