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Topic: Audible symptoms of amplifier clipping (Read 50972 times) previous topic - next topic
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Audible symptoms of amplifier clipping

Hi,

I have a friend of mine who is experiencing an issue with his system, so I thought I might ask you guys some questions.

My friend has a pair of B&W 704 speakers. And he is running a Marantz 5 ch power amp, bridged into 2 channels he gets 150W.

But he "feels" like the speakers need more power. Now I want to know what possible symptoms are of amp clipping so that I can ask him. Maybe his amp isn't underpowered.

He says they hold back a little at low volumes and only open up at higher volumes, but feels that they aren't opening up enough, so he suspects the speakers are a bit too much for his amp.

What symptoms can one expect to hear if his/her amp is clipping while listening to music? Apparently the 704's dip down to 3 ohms, so it's possible his amp is the culprit, but I thought I would ask you guys first for advice.

Audible symptoms of amplifier clipping

Reply #1 –
Quote from: Rich B on
He says they hold back a little at low volumes and only open up at higher volumes, but feels that they aren't opening up enough, so he suspects the speakers are a bit too much for his amp.


Just to clarify, isn't he saying that he thinks the speakers sound better when played loud compared to playing at lower volume?

Quote
What symptoms can one expect to hear if his/her amp is clipping while listening to music?


Distortion. But until it gets really bad, it can actually sound subjectively pleasing.

Quote
Apparently the 704's dip down to 3 ohms, so it's possible his amp is the culprit, but I thought I would ask you guys first for advice.


3 ohms shouldn't be a problem for a normal amp, but something that is bridged could be struggling - but I don't see any correlation between that and the description of the symptoms.

Do you have an oscilloscope?

Audible symptoms of amplifier clipping

Reply #2 –
Quote from: julf on
Quote from: Rich B on
He says they hold back a little at low volumes and only open up at higher volumes, but feels that they aren't opening up enough, so he suspects the speakers are a bit too much for his amp.


Just to clarify, isn't he saying that he thinks the speakers sound better when played loud compared to playing at lower volume?


He thinks that B&W speakers sound a bit lifeless at low volumes and demand to be played at higher volumes so they can open up more. He seems to think that something is holding the sound back, so suspects his amplifier is underpowered or that the speakers are demanding too much from his amp.

Quote
What symptoms can one expect to hear if his/her amp is clipping while listening to music?

Distortion. But until it gets really bad, it can actually sound subjectively pleasing.


So if the sound is distorting it could sound nice to the ears? I should clipping distortion was bad distortion, not like tube distortion? Am I right/wrong?

Quote
Apparently the 704's dip down to 3 ohms, so it's possible his amp is the culprit, but I thought I would ask you guys first for advice.

3 ohms shouldn't be a problem for a normal amp, but something that is bridged could be struggling - but I don't see any correlation between that and the description of the symptoms.


It is being bridged. He has not mentioned hearing any gross audible distortion or anything. Which makes me think that maybe the amp he is using isn't at fault.

Quote
Do you have an oscilloscope?


Unfortunately not. I wouldn't know how to use one or how to interpret the results if I did.

Audible symptoms of amplifier clipping

Reply #3 –
Quote from: Rich B on
He thinks that B&W speakers sound a bit lifeless at low volumes and demand to be played at higher volumes so they can open up more. He seems to think that something is holding the sound back, so suspects his amplifier is underpowered or that the speakers are demanding too much from his amp.

This might be the cause: http://en.wikipedia.org/wiki/Loudness and http://en.wikipedia.org/wiki/Loudness_compensation

edit: in other words, this is 'normal', music sounding thin on low volumes.
Music: sounds arranged such that they construct feelings.

Audible symptoms of amplifier clipping

Reply #4 –
Quote from: Rich B on
Now I want to know what possible symptoms are of amp clipping so that I can ask him.


The sound of clipping is like so many things in audio - how it sounds depends on the circumstances.

Clipping is more audio mystery meat - there is AFAIK no formally defined way to quantify it.

For example, clipping can be easily quantified in terms of either the percentage of the wave that is cut off, or the percentage of the time the wave is cut off. 

A little clipping of music that has a lot of variation in its level is pretty much inaudible.

The same amount of clipping in terms of the percentage cut off, of a wave that lacks dynamics, can be very audible. They can differ greatly in terms of the percentage of the time that the wave is cut off.

However the measure based on the percentage of time the wave is clipped does not necessarily give any weight to the difference between a wave that has only its very highest peaks cut off, and one that is most cut off.

A little clipping - inaudible

A little more clipping - perhaps the perception of an increase in brightness

A lot more clipping - the music sounds like mud.

Quote
Maybe his amp isn't underpowered.


The best way to shed light on these concerns for people without test equipment or a clue how to use it is to try to estmate the actuall power required based on SPL, speaker efficiency, and listening distance.

Quote
He says they hold back a little at low volumes and only open up at higher volumes, but feels that they aren't opening up enough, so he suspects the speakers are a bit too much for his amp.


That sounds like the usual effects of low SPLs - as others have correctly observed in this thread the Fletcher Munson curves say that we don't hear deep bass and extended treble very well at low SPLs, and so we perceive that they aren't there.

The effect of higher SPLs is that we start hearing the sounds at the frequency extremes and the sound "Opens Up".

However, indefinite increases in SPL do not provide ever-increasing improved sound quality - at higher SPLs the ears themselves become more nonlinear.  The ears have their maximum sensitivity to small details when the average levels are around 75-85 dB SPL. Of course depending on the music's dynamics, the peaks may be much higher.

Quote
Apparently the 704's dip down to 3 ohms, so it's possible his amp is the culprit, but I thought I would ask you guys first for advice.


Remember that simply not running an amp at such a high wattage dramatically improves its ability to power low impedance loads.

Reducing the SPL by 6 dB roughly doubles the ability of an amp to drive low impedance loads.  IOW an amp that can drive a 6 ohm speaker to a certain peak voltage can drive a 3 ohm speaker to half that voltage. This is important because very few people actually push their equipment anywhere near its maximum capacity, and if they do most  only do so very infrequently.

As a rule speakers have highly variable impedance curves so whether the amp actually sees the low impedance segments of the speaker's impedance curve critically depends on the distribution of frequencies versus power in the music.

Audible symptoms of amplifier clipping

Reply #5 –
Do you have more details on the amp? How he bridged it?
Do you also happen to know the source?

Does it go loud enough for him, regardless of "opening up"?
"I hear it when I see it."

Audible symptoms of amplifier clipping

Reply #6 –
B&W's own data claims minimum 4.1 ohms:

http://www.bowers-wilkins.com/Downloads/Pr..._info_sheet.pdf

By bridging a pair of amps, each will "see" half the speaker's impedance. In this case that's just over 2 ohms at minimum and that could cause a problem for the amp if sufficient power is demanded. Typically, amps are rated for 8 or 4 ohms for single-ended and 8 ohms minimum for bridged. Check the amp's specs to see if that's the case for this one.

B&W claim 90dB spl @ 1m/2.83V (i.e. 1W @ nominal 8 ohms) so they aren't excessively insensitive. The problem your friend describes, however, doesn't sit well with lack of power since he's complaining about lower levels.

Audible symptoms of amplifier clipping

Reply #7 –
Quote from: antz on
B&W's own data claims minimum 4.1 ohms:

http://www.bowers-wilkins.com/Downloads/Pr..._info_sheet.pdf

By bridging a pair of amps, each will "see" half the speaker's impedance. In this case that's just over 2 ohms at minimum and that could cause a problem for the amp if sufficient power is demanded. Typically, amps are rated for 8 or 4 ohms for single-ended and 8 ohms minimum for bridged. Check the amp's specs to see if that's the case for this one.

B&W claim 90dB spl @ 1m/2.83V (i.e. 1W @ nominal 8 ohms) so they aren't excessively insensitive. The problem your friend describes, however, doesn't sit well with lack of power since he's complaining about lower levels.


I agree that bridging his amps might be a backwards move.

Whether it actually matters depends on what his listening levels are. It sounds like his preferred listening level might be low enough that he is getting noticeable loss of audible response to to Fletcher and Munson effects, which is to say that they are probably modest. So, even though this bridging may be a step backwards, he is probably not demanding enough from his amps for it to cause an audible problem.

Step one is to obtain a SPL meter and find out what his preferred listening peak SPLs actually are.

Audible symptoms of amplifier clipping

Reply #8 –
Quote from: antz on
B&W's own data claims minimum 4.1 ohms:

http://www.bowers-wilkins.com/Downloads/Pr..._info_sheet.pdf

By bridging a pair of amps, each will "see" half the speaker's impedance. In this case that's just over 2 ohms at minimum and that could cause a problem for the amp if sufficient power is demanded. Typically, amps are rated for 8 or 4 ohms for single-ended and 8 ohms minimum for bridged. Check the amp's specs to see if that's the case for this one.

B&W claim 90dB spl @ 1m/2.83V (i.e. 1W @ nominal 8 ohms) so they aren't excessively insensitive. The problem your friend describes, however, doesn't sit well with lack of power since he's complaining about lower levels.


He suspects the sound is not as "open" as it should be with his Rotel. Now I didn't know that bridging caused his amps to see half the speaker impedance. So this can potentially be very problematic?

I'm not sure how loud he listens to his music, but I'll ask him and I will report back, preferably with an SPL figure.

Audible symptoms of amplifier clipping

Reply #9 –
Quote from: Rich B on
Quote from: antz on
B&W's own data claims minimum 4.1 ohms:

http://www.bowers-wilkins.com/Downloads/Pr..._info_sheet.pdf

By bridging a pair of amps, each will "see" half the speaker's impedance. In this case that's just over 2 ohms at minimum and that could cause a problem for the amp if sufficient power is demanded. Typically, amps are rated for 8 or 4 ohms for single-ended and 8 ohms minimum for bridged. Check the amp's specs to see if that's the case for this one.

B&W claim 90dB spl @ 1m/2.83V (i.e. 1W @ nominal 8 ohms) so they aren't excessively insensitive. The problem your friend describes, however, doesn't sit well with lack of power since he's complaining about lower levels.


He suspects the sound is not as "open" as it should be with his Rotel.


Two words: sighted evaluation.

Quote
Now I didn't know that bridging caused his amps to see half the speaker impedance. So this can potentially be very problematic?

I'm not sure how loud he listens to his music, but I'll ask him and I will report back, preferably with an SPL figure.


I suspect that we will find that he isn't stressing either amplifier, despite the probable configuration error (bridging that is potentially dysfunctional).

let's see where the cards fall... ;-)

Audible symptoms of amplifier clipping

Reply #10 –
Quote from: Rich B on
He suspects the sound is not as "open" as it should be with his Rotel. Now I didn't know that bridging caused his amps to see half the speaker impedance. So this can potentially be very problematic?

I'm not sure how loud he listens to his music, but I'll ask him and I will report back, preferably with an SPL figure.

As with so many things in audio, the answer is "it depends". If the amp is designed to run a 2 ohm load, it shouldn't be an issue. If it's not turned up too loud, likewise. The main, potential problem is if the amp is not designed to cope with a 2 ohm load, the bridged pairs will run into the current-limited region and are likely to distort earlier than expected. That may also be compounded when both channels hit a transient and all four amps demand high current from the power supply, simultaneously, which it may not be designed to cope with. Note the use of "may" a few times in the preceeding and that the effects may or may not reach audibility anyway.

If it turns out that he really needs 150W of power (which is rather a lot in a domestic scenario) then a higher-powered, single-ended amp is likely to perform better in that it should not run into current-limit issues. Bear in mind also that 150W is only 3dB louder than 75W, all other things being equal, whilst single-ending the exisiting amps will reduce significantly the load on the amp's power supply, not to mention lowering voice-coil heating on the speakers etc.

Audible symptoms of amplifier clipping

Reply #11 –
You didn't mention which amp? Only a 5ch from Marantz?

If it doesn't have more than a single power supply, then that may be constraining.  The simple test is to try it without bridging. Many 2ch amps can deliver way more than half the power in a single channel.

Audible symptoms of amplifier clipping

Reply #12 –
Quote from: Porcus on
You didn't mention which amp? Only a 5ch from Marantz?

If it doesn't have more than a single power supply, then that may be constraining.  The simple test is to try it without bridging. Many 2ch amps can deliver way more than half the power in a single channel.


The first place that most multichannel amps and AVRs become power supply constrained is usually the test bench and not the listening room.

The impression that they are power supply constrained is a consequence of All Channel Driven (ACD) tests which are highly asymmetric with actual use.

Audible symptoms of amplifier clipping

Reply #13 –
Doesn't the same go for the transistors' ability to deliver voltage - the "constraint" the OP's buddy fixed by bridging?

Audible symptoms of amplifier clipping

Reply #14 –
Quote from: Porcus on
Doesn't the same go for the transistors' ability to deliver voltage - the "constraint" the OP's buddy fixed by bridging?



Probably. Still awaiting information about preferrred peak SPLs and listening distance.

Audible symptoms of amplifier clipping

Reply #15 –
Sorry to keep you guys, but the amp in question is not a Marantz, it is a Rotel RMB-1066 5 channel power amp. My apologies for the error.

No word on his SPL levels, but hopefully I'll have some information soon.

Audible symptoms of amplifier clipping

Reply #16 –
Too bad - and slightly off topic - But I was thinking of the same question: How does an underpowered amp sound? But in this case, for headphones. I can calculate estimated voltage and current requirements, but that means nothing if I have no specs on the amp, like pretty much every single motherboard's onboard amp. So it's tricky to figure out when somebody needs an amp, especially if the symptoms of clipping can be less than flat out annoying (like clipping in a very bad master like Imagine Dragon's "Radioactive") 

Audible symptoms of amplifier clipping

Reply #17 –
(On topic) I think we need to determine whether the problem isn't related to expectation bias (first) or Fletcher-Munson (second).

The sound of running out of headroom really isn't subtle once enough of the signal clips. Also, it isn't like the onset of clipping is a large window of tone nirvana in hi-fi systems. If you think you're at the onset, bump the gain up a tad and you'll easily go into audible clipping.

If the volume is too loud, insert a series resistor or replace your speaker with a dummy load and feed the output to an appropriate monitor.

It seems like there's a group of people who are treating clipping like some mysterious thing, attributing to it all sorts of silly qualities and using it as a reason why amp a sounds better than amp b.

Before anyone chimes in about the euphonic effect of second order harmonics, please be prepared to provide some audio clips.

Audible symptoms of amplifier clipping

Reply #18 –
Quote from: Dark_wizzie on
Too bad - and slightly off topic - But I was thinking of the same question: How does an underpowered amp sound?


It depends. Most likely the underpowered amp starts clipping. A little clipping might not be noticed. More clipping may sound like a slight brightening. Lots of clipping sounds like mud.

If you want clipping to really stand out, use test tones. Take a 100 Hz or a 1 KHz tone. When you start clipping it even a little, its character changes dramatically, and its a far more sensitive indicator than music.

Quote
But in this case, for headphones. I can calculate estimated voltage and current requirements, but that means nothing if I have no specs on the amp, like pretty much every single motherboard's onboard amp.


It is possible to measure the performance of motherboard headphone amps. It doesn't take a ton of equipment because all you really need to look at is how much it puts out into your headphones before it starts clipping. 

However if you estimate its maximum output at about 1 volt rms, and can come up with an estimate of its source impedance, you are probably in the ball park.

Audible symptoms of amplifier clipping

Reply #19 –
Quote from: greynol on
(On topic) I think we need to determine whether the problem isn't related to expectation bias (first) or Fletcher-Munson (second).

The sound of running out of headroom really isn't subtle once enough of the signal clips. Also, it isn't like the onset of clipping is a large window of tone nirvana in hi-fi systems. If you think you're at the onset, bump the gain up a tad and you'll easily go into audible clipping.

If the volume is too loud, insert a series resistor or replace your speaker with a dummy load and feed the output to an appropriate monitor.

It seems like there's a group of people who are treating clipping like some mysterious thing, attributing to it all sorts of silly qualities and using it as a reason why amp a sounds better than amp b.

Before anyone chimes in about the euphonic effect of second order harmonics, please be prepared to provide some audio clips.


Thank you for the informative post, and sorry for not responding sooner.

I would find it interesting to know if my own amp was clipping or if it was not clipping. Since I don't have an oscilloscope I can't really measure to see if the signal has or hasn't been clipped, so I'm relying on my hearing to tell if something is wrong.

All that I can tell is that when I listen to music at the sort of volumes I like, I don't hear anything bad happening. I don't hear gross distortion or anything like that. Which makes me think that perhaps I'm not experiencing clipping.


Audible symptoms of amplifier clipping

Reply #20 –
If you don't know what clipping sounds like and don't want to tax your amp (or speakers, whichever comes first) then clip your source signal. There are a number of ways to do this. One easy way is to manipulate a digital file with a wave editor.

PS: I've told you about this before, BTW...
http://www.hydrogenaud.io/forums/index.php...st&p=854375

Audible symptoms of amplifier clipping

Reply #21 –
Quote from: Rich B on
I would find it interesting to know if my own amp was clipping or if it was not clipping. Since I don't have an oscilloscope I can't really measure to see if the signal has or hasn't been clipped, so I'm relying on my hearing to tell if something is wrong.

All that I can tell is that when I listen to music at the sort of volumes I like, I don't hear anything bad happening. I don't hear gross distortion or anything like that. Which makes me think that perhaps I'm not experiencing clipping.


Late in October (around Oct 26)  there were posts to this thread describing a systematic technical way to obtain reliable answers to that question.

Needless to say... :-(

Audible symptoms of amplifier clipping

Reply #22 –
http://www.hydrogenaud.io/forums/index.php...st&p=874772
http://www.hydrogenaud.io/forums/index.php...st&p=879513

Audible symptoms of amplifier clipping

Reply #23 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
I would find it interesting to know if my own amp was clipping or if it was not clipping. Since I don't have an oscilloscope I can't really measure to see if the signal has or hasn't been clipped, so I'm relying on my hearing to tell if something is wrong.

All that I can tell is that when I listen to music at the sort of volumes I like, I don't hear anything bad happening. I don't hear gross distortion or anything like that. Which makes me think that perhaps I'm not experiencing clipping.


Late in October (around Oct 26)  there were posts to this thread describing a systematic technical way to obtain reliable answers to that question.

Needless to say... :-(


Yes, using test tones. But that doesn't tell me what the clipping will sound like using actual music. I don't know about you, but my preferences don't run in the direction of pure tones. I listen to music.

Audible symptoms of amplifier clipping

Reply #24 –
Test tones, real music, going about hearing how they sound clipped is all the same.

You spend more time coming up with excuses than you spend actually trying to learn something.  It's getting very hard for the community to take you seriously.  It's pretty evident by the responses you're getting from members of the forum, some of whom are usually quite patient and charitable with their time.