There have been questions about the high frequency response of the Sonos Amp. User hodgeal posted a very interesting plot showing the frequency response of the Sonos Amp using the software REW. It didn't show excessive high frequencies in that single test.
I had the opportunity to compare the Sonos amp to my Peachtree amp using the same software (which is very useful and easy to use - thanks hodgeal), and this provides a comparative test of the Sonos Amp frequency response.
The Peachtree Nova 125 SE amp is well-respected in the audio community. It is a class D digital amp, same as the Sonos Amp, but as far as I can tell uses different chips. The test uses Duntech Marquis speakers and a Studio Projects C1 microphone. The mic is setup on-axis at a distance of 120cm, which is pretty standard. But none of the details should matter because this is a comparison under identical conditions - I simply swapped amps and repeated the test.
And the results?
As you can see, the amps are almost identical. Ignore low frequencies - they vary from test to test even with the same amp below about 30Hz. At high frequencies, above about 4kHz, the Peachtree gets gradually brighter, ending up being about 1.5dB louder at 20kHz. This would be imperceptible to pretty much everyone.
Note that there is a slight increase in high frequencies above about 7kHz for both amps, so this could be the speakers. However, I think this is due to the frequency response of the microphone - the specifications show a similar slight increase.
Amp freq response: Sonos vs Peachtree
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Yes I think I agree with this. Some might want to use the main speakers full range, though, and set the sub filter within the sub controls. The only want to do this, as I understand it, is to connect to the sub with speaker level input.
You can prove to yourself that even a cheap amp is not affected by the presence of the low frequencies. In Audacity, import a clip with a good range of frequencies. Filter out the low end. Then listen to the filtered and unfiltered clips. The mids and highs will be played at the same level for both clips.
None of this is incorrect, but nor does it refute what I stated. The Amp's gain is under software control, and the software can raise the gain for a given volume setting when there is no requirement to produce low frequencies.
Yes. And there is someone struggling to achieve just this without a hum! See:
Correct, I think it's intentional. The Amp has more headroom for gain when not required to produce low frequencies, so the Amp's software takes advantage of this. Amplifiers with simple manual controls typically cannot be run at 100% of dial volume without distortion, so one tends to assess by ear how loud they can be run, and one can increase the maximum volume setting if low frequencies aren't required. The Amp can be run at its 100% volume setting without distortion, so it makes sense to recalibrate via software control when the gain available increases.
Correct, I think it's intentional. .
Do you mean that removing the low end is likely to result in a significantly lower peak amplitude in the output to the main speakers? I suppose that could be why they bump the gain. I'm not sure if that reasoning would hold true or not, I would think it would be dependent on what music is playing.
Yes, that's the gist of it.
My guess is that there is a bug in the DSP part of the Amp. The fact that the boost is exactly 3 dB suggests a coding error in the filtering software. It can be very easy to leave out a factor of 2. And a 3 dB boost is exactly double the power.
Like kumar and lahey, I don't know what the point would be in deliberately boosting the non-filtered frequencies by 3 dB.
Presumably, since the Amp's gain is entirely under software control, Sonos can calibrate it however they wish for different volume settings.
Agreed. They could have no boost at low volumes and larger boost at high volumes. Although, it is a bit of a coincidence that both hodgeal (in the original LS50 thread) and I found an exact 3 dB boost at whatever volume we tested (I was at 30%, I don't know about hodgeal).
3 dB is a doubling of power, but it takes 10 dB to achieve a perceived doubling of loudness.
So 3 dB changes are noticeable but not big.
The Sonos Amp becomes 250 wpc into 8 ohms?!
p.s. The Amp plus powered sub combo might now be 250W.
p.s. The Amp plus powered sub combo might now be 250W.
Why is it wrong to say it is 250W into 8 ohms for a 80-20k measurement? Isn't that what the p.s. also conveys, if the Sub delivers 250 wpc from 20 to 80 hz, that the combination is 250 wpc from 20-20k?
Suppose the same Sub was to be attached to the Sub out of a traditional HiFi stereo amp of the same power spec of the Sonos amp, 125 wpc into 8 ohms across 20-20k.
1. Would that combo now be 250 wpc also?
2. The 3dB boost seen here, isn't typical for such amps, as far as I know. So how does this ability to drive the 80-20k to higher sound levels than before achieved? And if it never gets achieved, with unused headroom even with amp volume at 100%, does it mean that the combo is NOT 250 wpc, but 125 wpc as it was minus the Sub?
Given an 8 ohm impedance, I think the Amp can only put out 125W - this would be determined by the design of the amp, in particular its ability to push current through an 8 ohm load. If that power (ability to push current) is spread over 20-20k, you get a certain sound level. If that power is limited to 80-20k, then frequencies above 80 Hz can have a 3dB increased sound level (i.e. more current), but the total power is still 125W. The power saved from not having to reproduce the low frequencies is now able to be utilised for frequencies above 80 Hz. But the total available power is fixed at 125W by design.
I think this is correct. It is demonstrated by the measurements hodgeal and I made.
What I was doing with audacity was just filtering a music file, nothing really specific to the amp. I was just trying to see if high-pass filtering creates enough headroom to justify bumping gain with a sub crossover. I'd be interested to see what others find.