Sonos Amp LS50 Frequency Response Graphs (brightness, crossover, loudness eq)

  • 21 March 2019
  • 8 replies
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Userlevel 1
I'd like to share my impressions of the new Sonos amp paired with kef LS50, id also like to share the frequency graphs i have recorded using REW to address some of the concerns on the amp being bright and the sub woofer crossover boosting the treble.

Positive:
The pair sounds good, I came from a much larger (older) stereo component setup looking to keep the HiFi sound but also have some of the always on convenience that I have found using the numerous PLAY:1s around the house. I now find myself listening to much more music as the amp is always on ready to go.

It also sounds good for TV/Movies using ARC (with my previous setup I always found the voices too quiet and i didn't want a large AVR) even with just having stereo speakers - I feed the amp Dolby 5.1 from the Apple TV4, the Amp down-mix very well to include a DSP centre channel (this sounds noticeably clearer than feeding stereo), I am looking forward to adding rear surround at a later date.

Hardware is built well, and i think the cost is reasonable - especially compared to over HiFi components.

Negative:
I am having a few issues with the remote, sometimes when changing volume, the sound changes normally but the volume OSD lags and sometimes doesn't move at all. I also checked within the Sonos app, and it does the same. I change volume and it will lag and the slider will jump to the new volume setting.

Requests:
Id prefer to have linear volume control rather than a curve, at the moment my volume is mostly set at 50% to achieve good sound. I have read that most of the power is reserved for after 50%. (Source: theverge) and this is noticeable, with lower efficiency speakers.

Id really like to either see TruePlay or even better a parametric eq/convolution ability on the amp. With everything in one box I cannot add third party room correction, so this would have to be a software add-on. This would really complete the package.

On to the Frequency Response Graphs

(Blue) LS50 + Sonos Amp (Ports Plugged) - fairly flat response, note no treble boost/brightness



(Yellow) Loudness Setting On - taken at 50% volume subtle tapered 2.6db boost to bass and treble frequencies



(Purple)Crossover (80hz)
I've seen some reports that turning on the subwoofer crossover makes the sound overtly bright - i thought id investigate.


The crossover works correctly sloping the output at 80hz however it does boost the overall sound 3db, the response above 80hz is the same just louder, the volume setting wasn't touched between taking the measurements.

(Red)Crossover (80hz Reduced 3db)
I reduced the volume 3db, this was 7 pressed on the volume slider


That's better, as shown the crossover setting doesn't make the sound bright, it just boosts volume. I'm not sure why, perhaps because of the lighter load Sonos is happier to increase the volume.

Thanks for reading, if you have any questions or want me to go into any more detail please let me know.

8 replies

Userlevel 7
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Really enjoyed reading that. Thanks for putting it together.
id also like to share the frequency graphs i have recorded using REW to address some of the concerns on the amp being bright and the sub woofer crossover boosting the treble.


I've seen some reports that turning on the subwoofer crossover makes the sound overtly bright

How is it that those hearing a brighter sound and alleging the amp to be the culprit never post any graphs?!

On the Sub - can the crossover be turned on without anything plugged into the Sub Out jack?
You can turn the sub on in settings/room settings etc. without having a sub connected, but in my limited testing it doesn't seem to change the bass response. I'd be interested to see graphs to confirm this. When I first installed my amp, the sub was turned on but no sub was connected. Confusing huh?
Userlevel 1
On the Sub - can the crossover be turned on without anything plugged into the Sub Out jack?
You can turn the sub on in settings/room settings etc. without having a sub connected, but in my limited testing it doesn't seem to change the bass response.

I agree it is confusing - whilst you can access the crossover settings and turn on without a Subwoofer attached it wont do anything, you need a Subwoofer connected for the crossover to be in effect. Failing that you can just plug in a RCA cable and this will fool the amp into thinking that a sub is connected. I queried this with the Sonos team and my own testing to confirm.
Userlevel 2
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How is it that those hearing a brighter sound and alleging the amp to be the culprit never post any graphs?!


As interesting as the first post is, it is *not* a frequency response test of the amp. It is a frequency response test of the amp + speakers together. (And, if you want to be a stickler, it's measuring the room too.)

I agree it's frustrating that the online reviews (at least the ones that I've read) don't include lab tests of the amp, as they would have in years past, when the major audio magazines had far larger circulations (and presumably larger budgets).

This brightness issue has made me hit pause. I was planning to purchase two Amps, but I'll wait and see now.
Userlevel 1

As interesting as the first post is, it is *not* a frequency response test of the amp. It is a frequency response test of the amp + speakers together. (And, if you want to be a stickler, it's measuring the room too.)

This is correct, if it helps I would consider my room to be a "bright" room - minimal furnishings, laminate flooring (with a thin rug), no acoustic treatment.
That room is a recipe for poor sound quality, so I am surprised you are not hearing its impact more than you say you are. Unless you are listening in/close to near field, before the room has had a chance to play its role. Some natural room deadening that does not mess up with the room aesthetic should be possible, like a thicker/bigger rug, bookshelves with books and the like? At a minimum, you should not hear any echo from a handclap in the room.

I have found that the biggest drivers of sound quality are - given a certain standard of speaker quality that need not cost an arm and leg - where the speakers are placed and the room acoustic - after all, what you hear is a function of how the room interacts with the sound from the speakers.
For the purposes of testing, if the mic is positioned directly in front of one speaker (something like 100-120cm is standard), and the test sweep tone only comes through that speaker, the room will not have much effect except at low frequencies (meaning below around 40Hz). I tested this in a room that is 9m x 4m, with speakers in the middle of one long side, and windows along the opposite long wall. The windows have honeycomb blinds, which should be pretty good at absorbing sound due to their pleated structure. I found having the blinds up or down made no difference above about 40Hz.

Cheers, Peter.

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