how much power do you need?

[ratso]

That calculator does not say anything about peaks. Please keep in mind that any decent 100W rated AVR such as those by Yamaha and Denon will give you much more for peaks, as well they will also do better into 4 ohms and even 2 ohms, but again we are talking peaks. For example, the RX-A830 is rated for 100W, but it's dynamic power is specified as:


Front L/R (8/6/4/2 ohms)..........140/180/210/250W. Another thing, for those who always listen to 2.1 or 2.2 such as ADTG, they will get a lot of help from the sub to bump up the SPL.

the calculator is labeled the peak spl calculator?

 

[fuzz092888]

So I have a 5.1 system. All of the speakers have a 92dB sensitivity rating. The factory spec is 8 ohm however the DefTech support tech recommended I run them at 6 ohm. The tech indicated I may get a little more db by setting them to 6 ohm. So how much of a difference does the ohm setting make in relation to the spl calculator? Also, how do I relate the calculator results with the actual volume knob setting on my receiver? I rarely get past -10dB as indicated on my AVR display before it is really loud. I can go to -0dB only on a few recordings like Pink Floyd or classical. From the results below, does this mean my system will hit 113.8 dB when the volume knob is set to +21.5dB? If not +21dB, then where would I expect to see the volume setting at 113.8 dB?

That's a theoretical peak value. There are a lot of obstacles between you and that number, mainly content. Plus, because very little to no content will require full power to all 5 channels at once, the power requirements to get there will be a lot different for your front channels/subwoofer than your side surrounds and rears.

 

[lsiberian]

I only need about a watt for maximum peak dynamics in my theater. I have very sensitive ears though. Though I've been told my movies are too loud by family members.

 

[PENG]

the calculator is labeled the peak spl calculator?

I don't think so, not the one you linked. It specifically says if the spl calculated will be rms if the amplifier power is rms. So yes if your amplifier's 100W rating is peak then the spl will be peak, but most of the time when people say 100W amplifier they typically mean 100W rms. Now if you want to be technically correct then it is not even rms but average. Technically speaking there is no such thing as rms power, when manufacturer (some/most?) use that term they meant average, but that's any topic, sorry.

FWIW, Average power = Voltage (V)rms X Current (I) X power factor (pf=cosine of the phase angle between V and I).
For a Sine wave, Vpeak = square root 2 X VrmsX Irms

Again, that's a different topic but we are still talking peak vs rms so I thought I could throw that in.

mplifier rated power per channel, expressed in watts. The calculated SPL will be RMS if amplifier power is RMS2. The amplifier rated power per channel, expressed in watts. The calculated SPL will be RMS if amplifier power

 

[AcuDefTechGuy]

How much power do you need?

More than the minimum recommended and less than what everyone else says.

 

[RichB]

This is an interesting topic.
I wonder if this can be determined with measurements.

From the AH article on Loudspeaker Sensitivity:

Loudspeaker Sensitivity: a measure of Sound Pressure Level (SPL) at a specified distance for a specified input signal. This is usually specified for a loudspeaker in a non-reverberant environment, in dB SPL and referenced to 1 meter on the reference axis with an input of 2.83 volts RMS, typically at one or more specified frequencies (often 300, 400, 500, 600Hz or the average of these). Sensitivity should always be accompanied by an impedance specification.
Loudspeaker Impedance: is the sum of DC resistance and complex AC reactance comprising inductance and capacitance, the value of which changes with frequency.

So if I do this experiment:

- Play a tone at which I know my speakers impedance (say 4 ohms)
- Use a multi-meter and adjust the volume until I measure 2.83 volts
- Measure the SPL at my seating position.

Does this give me a bases upon which compute the actual power needed in my room to produce different SPLs?

- Rich

 

[PENG]

This is an interesting topic.
I wonder if this can be determined with measurements.

From the AH article on Loudspeaker Sensitivity:



So if I do this experiment:

- Play a tone at which I know my speakers impedance (say 4 ohms)
- Use a multi-meter and adjust the volume until I measure 2.83 volts
- Measure the SPL at my seating position.

Does this give me a bases upon which compute the actual power needed in my room to produce different SPLs?

- Rich

No, actual power is a function of voltage, current and the phase angle between voltage and current. Using your 4 ohm example, 2.83V across a 4 ohm pure resistive load would equate to 2W. Likewise the same voltage across an 8 ohm pure resistive load equate to 1W but for a pure resistive load the phase angle will be 0 degree. Applying the same voltage across an inductive or capacitive load will yield different results. Your speaker's impedance can be partially resistive, inductive or capacitive as it varies frequencies, but of course you know that already.

Measuring the output voltage when playing a tone and plotting it against the SPL will give you an idea how close your amp appear to be near its limit when delivering your desired SPL, not much more than that unfortunately.

 

[RichB]

No, actual power is a function of voltage, current and the phase angle between voltage and current. Using your 4 ohm example, 2.83V across a 4 ohm pure resistive load would equate to 2W. Likewise the same voltage across an 8 ohm pure resistive load equate to 1W but for a pure resistive load the phase angle will be 0 degree. Applying the same voltage across an inductive or capacitive load will yield different results. Your speaker's impedance can be partially resistive, inductive or capacitive as it varies frequencies, but of course you know that already.

Measuring the output voltage when playing a tone and plotting it against the SPL will give you an idea how close your amp appear to be near its limit when delivering your desired SPL, not much more than that unfortunately.

Good points.
Is there a way for an "enthusiast" to measure the amplifier power output at the speaker terminals?

- Rich

 

[PENG]

Good points.
Is there a way for an "enthusiast" to measure the amplifier power output at the speaker terminals?

- Rich

You can try one of this:

Fluke 345 Digital Power Quality Clamp Meter

I doubt it would be very accurate for music signal but likely more accurate than those built in ones such as my Marantz or some of the McIntosh amps.

 

[RichB]

You can try one of this:

Fluke 345 Digital Power Quality Clamp Meter

I doubt it would be very accurate for music signal but likely more accurate than those built in ones such as my Marantz or some of the McIntosh amps.

Um, that is almost as much as I paid for my amp.

I think I'll try my experiment, even if it produces an optimistic number.
It will be interesting to see how it matches up with the SPL calculators.

- Rich

 

[PENG]

Um, that is almost as much as I paid for my amp.

I think I'll try my experiment, even if it produces an optimistic number.
It will be interesting to see how it matches up with the SPL calculators.

- Rich

Assuming you use the calculator that allows for room and multiple speaker effects (that means not the Crown Audio one), it will match well if you stick to the formula P=V^2/Z, substitute Z (impedance) with R (resistance) so in your case it will be V square divide by 4 (you said 4 ohms right). I know it will match because I have done it. Just realize that both will not be accurate because the power factor thing is not accounted for in either case; and even if you ignore the power factor (i.e. phase angle) effect, the 4 ohm thing is also only nominal and we all know what they mean.

More sophisticated instruments would be able to tell you the average power and peak power but anything like that will cost a fortune. Again, if your measurements shows you only need say 5W for your spl requirement, then at least you know allowing for say 21 dB peak you will theoretically need 640W. That means your A51 might clip audibly though rarely even if you apply a safety factor of say 1.5 to compensate for phase angle and impedance dip effects. My own measurements tell me I only need fractional watts, less than 0.5 most of the time so none of my amps should theoretically never get close to clipping audibly regardless of the music contents I throw at them. My hifi bottlenecks are still the speakers and the quality of the source media. I think we are off the topic, may be you should start another thread. If you are going to use a good multimeter such as the $500 Fluke I recommended before, be aware that you can select true rms or peak as that will obviously affect your results.

 

[Ampdog]

Folks,

For a long time now I saw no mention of the size/appointments of the room (I am not going to reread - see hour of the morning ....) I also see mention of what folks have; what measurements were actually done to establish that is what you need/cannot-do-without, or are actually listening to? Under what conditions of hearing (including your own auditory capabilities), etc. etc?

As was said right at the beginning this is a most subjective matter. At risk of repeating the well-known: Subjectively a 3db difference is something just audible (on a day-to-day basis, not quoting competions for golden ears). That is a factor 2 in power, other things being equal. Dare I say than that I am unlikely to pay any great money for a 4x figure of difference in output capability (perhaps a drop of the proverbial Scottish blood somewhere: What else could I have bought for that monetary difference?).

 

[AcuDefTechGuy]

What else could I have bought for that monetary difference?).

A lot of goodies.

But some people seem to care more about speakers & amps than houses, automobiles, and a lot of other goodies in life.