Amp freq response: Sonos vs Peachtree

Forum|Forum|7 years ago
April 11, 2019
84 replies
6698 views

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.

Cheers, Peter.

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K

Kumar

Exactly. Manually, since in the case of a third-party sub, the Amp has no idea of its power output.

But then once that is done, the 3dB boost the Peter refers to becomes a non issue. And no reason for a brighter sound.

L

lahey

Trending Lyricist II

Isn't this just the Amp being able to deliver more power to the frequencies above the crossover, now that it doesn't also have to serve the frequencies below it?

Ideally, an amplifier's output is simply the input signal multiplied by a gain factor. The output should not sag by having to provide the low end. That would mean it is a poor piece of equipment.

pwt

Virtuoso

Exactly. Manually, since in the case of a third-party sub, the Amp has no idea of its power output.

But then once that is done, the 3dB boost the Peter refers to becomes a non issue. And no reason for a brighter sound.

To be clear, I don't think it's an issue, nor does it indicate a brighter sound profile. I was just explaining why the Amp's volume at frequencies above crossover would be increased in the presence of a sub.

4 x P:5 | Sub | 4 x P:1 | 3 x Connect | 2 x Boost | Connect:Amp | 2 x One | Amp | Move | Port | Era 300

K

Kumar

To be clear, I don't think it's an issue, nor does it indicate a brighter sound profile.

Right; over to Peter if he disagrees.

pwt

Virtuoso

Isn't this just the Amp being able to deliver more power to the frequencies above the crossover, now that it doesn't also have to serve the frequencies below it?

Ideally, an amplifier's output is simply the input signal multiplied by a gain factor. The output should not sag by having to provide the low end. That would mean it is a poor piece of equipment.

No-one said that the Amp 'sags'. It has to operate within a total power envelope with a gain that it can deliver across the required frequency range while meeting its target distortion values. Remove the requirement to amplify signals below the crossover and that total power envelope can be applied to a smaller frequency range, hence the remaining frequencies can benefit from higher gain.

4 x P:5 | Sub | 4 x P:1 | 3 x Connect | 2 x Boost | Connect:Amp | 2 x One | Amp | Move | Port | Era 300

L

lahey

Trending Lyricist II

No-one said that the Amp 'sags'. It has to operate within a total power envelope with a gain that it can deliver across the required frequency range while meeting its target distortion values. Remove the requirement to amplify signals below the crossover and that total power envelope can be applied to a smaller frequency range, hence the remaining frequencies can benefit from higher gain.

The Sonos Amp output voltage should just be input signal * gain, until clipping. If you remove low frequencies the amp's output in the pass-band should not change if the crossover filter has unity gain for the pass-band.

L

lahey

Trending Lyricist II

But what Peter found (I think) is that the sub crossover does change the gain. So it is not a unity gain implementation.

L

lahey

Trending Lyricist II

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.

K

Kumar

As I said earlier, I don't know enough about amp design to opine. But if the across the board uniform boost to frequencies - as Peter suggests is present when a Sub is in play - that are directed towards the speaker terminals of the amp is a design intent, what is the point of doing that?

L

lahey

Trending Lyricist II

As I said earlier, I don't know enough about amp design to opine. But if the across the board uniform boost to frequencies - as Peter suggests is present when a Sub is in play - that are directed towards the speaker terminals of the amp is a design intent, what is the point of doing that?

I don't know what the point would be. Maybe it is just a result of the signal processing that they do for the crossover, and they did not bother to correct for this.

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