Calculate output power, and how much is too much for speakers?

[Michiel]

Hi all,

Finally finished my setup and am very happy with it. Chain is as follows:

Windows 10 pc using Tidal Hifi.
usb cable.
Topping D70s DAC in dac mode (output at max volume)
Xlr cables ( Canares star quad from Ghent Audio)
Topping pre90 preamp, input set to xlr, output xlr only.
Xlr cables (Canares star quad from Ghent Audio)
Dual mono Icepower 1200AS1 amplifier. (voltage gain 25.8dB)
Norstone 6mm2 speaker wire.
B&W 802D

I am very happy with this setup, but 2 questions are coming up. Is it possible to calculate the (maximum) output power at a certain volume setting set a the preamp?

And when do you know it is too much for the speakers?

For example, the following track, China Hok-Man Yim: Poems of thunder-percussion, has extreme bass. Even at extreme volumes the sound remains very tight on the 802D’s, not distortion at all. I play the track via Tidal, but this is a Youtube link to the same song

My highest volume setting during this track on the pre90 has been -10dB. The drum slam remained very tight, but was afraid to go any further not to damage the speakers. But how to know you have reached the max?

What would be the output power of the 1200as1 in those heavy drum notes?
Thanks!

 

[NTK]

The maximum voltage output, assuming no inter-sample overs (i.e. source material is not already clipped), from the D70s is 4.0 Vrms.

After a -10 dB attenuation with the Pre90, max input to the ICEpower amps is 4.0 * 10(-10/20) = 1.265 Vrms.

After the 25.8 dB gain of the ICEpower, max input to the 802D speakers is 1.265 * 10^(25.8/20) = 24.66 Vrms.

24.66 Vrms, when driven into an 8 ohm load, is 24.66^2/8 = 76 W.

If we want to be more conservatives and allow a 3 dB headroom for inter-sample overs, then max power into 8 ohm is 76 * 10^(3/10) = 152 W.

 

[Michiel]

Thank you very much for the time taken to answer this! It’s more clear to me how this works.
I believe the D70S output is 5v instead 4v. (The D70 outputs 4v)

Found this calculator http://www.sengpielaudio.com/calculatorVoltagePower.htm and used to recalculate with 5v.

At -10dB the preamp output will be 1.581139V

Then amplified by 25.8dB by the 1200as1 will make 30.829753V

At 8ohm that will be 118.8Watt, and at 3ohm which is about the lowest impedance of the 802D, 316.8Watt. That means i am below the 500Watt @ 8ohm handling power of the speaker.

For the 3dB headroom these will double to 237.6Watt and 633.Watt
Taking this headroom in account means i could be overloading the speaker?

Good thing is the amplifier will probably never reach clipping levels

 

[NTK]

I incorrectly assumed the D70s followed the de-facto standard of 4 Vrms XLR output.

TBH, speaker power handling ratings are quite meaningless. A single number is far from sufficient information to fully describe how much power a speaker can handle. It heavily depends on spectral content (the tweeter can handle a lot less power than the woofers, just compare the driver sizes and imagine the differences in the wire sizes of the voicecoils), amplitude and duration of the signal, etc.

However, with a large top-line speaker such as the 802D, I am very sure your ears will give up long before the speaker drivers. For drum tracks, if you don't hear obvious distress from the woofers, you are more than fine.

 

[Head_Unit]

TBH, speaker power handling ratings are quite meaningless...[etc]

Yes! Oh praise buddah allah yeshua, that is the hidden truth. Pretty much if the speaker sounds fine, it should be fine (barring amplifier DC fault or ultrasonic oscillation or accidents like oops dropping a needle on an LP).

 

[spacevector]

... was afraid to go any further...

But did you want to?

 

[Head_Unit]

Is it possible to calculate the (maximum) output power at a certain volume setting set a the preamp?

Back to this, yes, but no. You can set the volume low, put in like a 400 Hz tone or something, measure with a high quality AC voltmeter across the speaker. Now disconnect the speakers but have the voltmeter still connected (alligator clip leads useful!), crank up the volume settings. You can make a chart, indicated volume on the Topping Pre90 and output voltage. Then you can calculate P=(V^2)/R --> power equals voltage squared divided by resistance. For speakers I use 4; speaker impedance is way more complex but these days even "8 ohm" speakers are more like 4; your 802D are no exception. https://www.stereophile.com/content/bw-802d-loudspeaker-measurements

The interesting question is: what are the voltage rails of that IcePower module? Not the power supply voltage, the audio output rails. Then you can see how that compares versus the volume settings on the Pre90. Calculating the nominal power from the voltage rails will give you the peak possible tailwind output power.

 

[Lambda]

The DAC has + 14dBV RMS output -10dB preamp +25.8dB amp = 29.8dBV RMS. lets call it 30dBV

31.6V RMS in 3Ohm this gives you 333W RMS in 3 Ohm and 125W in 8Ohm
With the +3dB crest this gives you 45Vrms and 675W in 3 Ohm 253.125W in 80hm

For your AMP this is not problem it can provide 100Vp