How Does One Determine a Volume Limit Setting for an Amp to Avoid Damaging Speakers if the Amp's Wattage Rating is Higher than the Speakers?

[GoSounders]

I have 4 Ohm speakers. The manufacturer's specs say the recommended power is 20 - 100 watts and maximum SPL is 105 @ 1 m. I'm using a Sonos Amp, and Sonos says it provides 250 watts per channel for 4 Ohm speakers. The Sonos app has a volume limit setting, which is a slider control that lets me set the limit to a value in the range 0 to 100%.

Recently I had the volume turned up to a "pretty loud" level, subjectively, relative to how loud I usually play music with this setup. I thought--uh-no this seems loud, am I going to damage my expensive speakers? Should I set a volume limit so I don't ever do that? If my amp is rated for 250 watts, and my speakers are rated for 100 watts, that seems like a big difference. Does it matter? If do set a volume limit, how do I figure out where to set it?

I imagine that I want to set the volume limit to some percentage of total volume that prevents the amp from damaging my speakers. Does that even make sense? I don't really understand what the relationship is between wattage and volume is here. Also, I'm guessing that the "volume limit" setting's relationship to sound level and to wattage is probably non-linear, So, I suspect that a simple 100/250 ratio (40%) isn't necessarily the right answer. Maybe it is, but at 40% total volume, my speakers don't sound as loud as I would want them to be if I want to listen to loud music.

Does it make more sense to just set the limit to essentially the loudest sounding level I feel sounds good to me without feeling "way too loud" or distorted? I did a test tonight using a volume meter app on my iPhone--how good this app (Decibel X) is, I have no idea, but it at least showed me some db numbers while I was playing music. I found that at my usual listening position, if I turned up the volume so it was about the loudest as I feel I'd usually want, the app showed sound was peaking about 65-70 db on average, At this level, if I held my phone about 1m from the speaker the app showed sound spiking at about 75-79 db. Since this level is below the 105 db maximum SPL rating for the speaker--should I just stop worrying about this?

Thank you in advance for help answering my newbie questions. I hope I found the right forum.

 

[kemmler3D]

Hey, welcome to ASR!

Also, I'm guessing that the "volume limit" setting's relationship to sound level and to wattage is probably non-linear, So, I suspect that a simple 100/250 ratio (40%) isn't necessarily the right answer.

Yep, If your amp's volume setting was linear with power, the 40% setting would make sense, but this is unlikely. Usually it's steps in dB and dB are logarithmic.

Does it make more sense to just set the limit to essentially the loudest sounding level I feel sounds good to me without feeling "way too loud" or distorted? I did a test tonight using a volume meter app on my iPhone--how good this app (Decibel X) is, I have no idea, but it at least showed me some db numbers while I was playing music. I found that at my usual listening position, if I turned up the volume so it was about the loudest as I feel I'd usually want, the app showed sound was peaking about 65-70 db on average, At this level, if I held my phone about 1m from the speaker the app showed sound spiking at about 75-79 db. Since this level is below the 105 db maximum SPL rating for the speaker--should I just stop worrying about this?

Probably this is good enough.

If you want to get closer to the real maximum, I'd say a reading of 95-100dB @ 1m is still probably safe for your speaker, even assuming the app is not totally accurate. This would mean you're actually still at less than half the maximum power. (2x watts = +3dB output).

Since it seems like you're happy listening at normal / safe levels, setting the volume limit around there would give you the ability to turn it up if you're listening to music with a lot of dynamic range.

One thing I would note is you might want to set the volume using pink noise instead of music, it will tend to be more accurate in terms of SPL / wattage this way.

 

[GoSounders]

Thanks for the response.

 

[Laika2]

Normally you can hear the audio fall apart before damage. Just don't crank it up fast.

 

[A Surfer]

Normally you can hear the audio fall apart before damage. Just don't crank it up fast.

Absolutely, great information and advice. That has been my experience as well.

 

[Beave]

This is actually a very difficult question to answer, because there are several complexities involved:

1. Speaker power handling can't be described by a single number. Power handling depends not only on frequency but also on duration. Speakers can be damaged by heat buildup when sustained tones are played at modest levels. Speakers can also be damaged by short bursts of high power content.

2. Music or home theater content can't be described easily either. It's constantly changing in amplitude and in spectral content.

3. Power from an amp into a speaker varies with the content being played, with the volume settings on the amp, and with the speaker's impedance.

So it's really hard to make a simple rule, other than to say that if you are hearing strain or distortion - whether it's from your amp or from your speakers - then turn it down.

 

[skankhobag]

If the speaker is audibly distorting, you’re pushing it too hard.

Also, if the amp is causing the distortion, you run the risk of burning out the tweeter due to the distortion causing much more power going to its range.

Bottom line: at any sane volume level, it’s rather doubtful that you’ll cause damage to your speaker or amplifier.

If you’re trying to recreate PA concert levels, you’re asking a Yugo to go 300mph.

 

[Keith_W]

Welcome to ASR! Some simple points should help you understand the problem.

1. Power (Watts) = Voltage (V) * Current (I)
When you turn up the volume, the amplifier increases the voltage differential between + and - terminals. The loudspeaker then draws the current it needs from the amplifier.

2. Maximum speaker power handling is determined by testing a speaker under sustained power for a set duration to find the maximum continuous power before permanent thermal or mechanical damage occurs. This "set duration" is not standardized and varies between manufacturers, so a published spec is virtually meaningless. Having said that, if you have a 100W amp and 100W speakers, and the amp's clipping indicator is coming on constantly, you are likely to damage your speakers very soon if you don't turn it down. Sustained power is not the same as instantaneous power, for e.g. it is possible for loud transients to exceed maximum speaker power handling without causing damage.

3. It is more common for lower powered amps to damage speakers than high powered amps. When an amplifier is unable to supply more current than the speaker demands (see point 1), it clips. Clipping squares off the waveform - mathematically, this is the same as producing a lot of high order harmonics. These are sent to the tweeter, and since tweeters are less robust than woofers, they are more easily damaged.

The easiest way to determine if you are asking too much of your system is to simply listen. As voice coils start to overheat, music will start to compress. As amplifiers distort, the spray of high order harmonics makes the sound harsh in the treble region. As speakers distort, the sound becomes "dirty" - at some point you might hear buzzing or flapping as the driver reaches its limits and starts smacking against its suspension. Turn it down and listen at sensible levels, and you won't have a problem.

 

[Vincent Kars]

You might try a hard limiter.

 

[DanielT]

He he. Creative with those screws.

Speaking of feeding too much power into speaker drivers and blow them up. It's easy to do, see here:

 

[ZolaIII]

100 to 250W is 3.75 dB, then there is rated and mesured and sustained and burst for an amplifier and so is for speakers. When enough is enough you will be able to hear compressing on both from either the amplifier soft clipping or woffer that simply had enough and then it's time to take a brake and let it cool down. Diffusion entropy can accumulate and then you pop a tweeter or demage amplifier (V collapse) on the long run.
Best practice is limiting on amplifier it self if you have gain settings to sensible calibration point to listening position (white noise 85/88 dB mono/stereo) of course being sure bout speakers and amplifier can follow by not being over pressured by it. From there it's to implementing ELC and I assure you you can have all there is there even at moderate SPL and if ELC is particularly good implemented even on levels of normal speach (low 60).

 

[DVDdoug]

So it's really hard to make a simple rule, other than to say that if you are hearing strain or distortion - whether it's from your amp or from your speakers - then turn it down.

I agree. I'm pretty sure I have enough power to blow my speakers but I have nearby neighbors and I don't listen at "live" or "disco" levels.

In the real world speakers usually get blown when a drunk person or teenager is in charge of the volume control... or when "testing" to see how loud you can go.

The best way to be safe is probably to use an amplifier less than the rating of the speaker. This old JBL paper says that in applications like guitar speakers where the amp is frequently driven into distortion the speaker should be rated for twice the power of the amp.

3. It is more common for lower powered amps to damage speakers than high powered amps.

That's a popular myth. You can fry a speaker either way. But for example, 6dB of more "real power" (4 times the power) is worse than 6dB of clipping. And when you over-drive and amplifier you are more likely to hear distortion and turn it down.

Most of the power is in the lower frequencies which means that the strongest harmonics don't extend to the tweeter. The harmonics extend to infinity but they get weaker as you go higher. In fact if you clip badly the sound tends to get a little "muffled" with relatively reduced highs. The highs are increased but not as much as the lower & mid frequencies.

But as you increase the volume beyond clipping the peaks are clipped/limited, the average power continues to go up, depending on how dynamic the program material is. On top of that, if you clip a sine wave to the point that it becomes a square wave, that's twice the power, with the additional power being harmonics. (Assuming the amplifier can sustain it twice the power.)

 

[Hayabusa]

There is so much level difference in source material that thus is an impossible task without peak meters

 

[AcousticTheory]

I have used "1200W" Icepower Class-D amplifiers to drive a pair of Neumi Silk 4 speakers while I was testing the amps to make sure everything was good before hooking up something more expensive. The speakers are nothing special in terms of power handling, rated 80W max. Even though I played things at a spirited level through the Silk 4, nothing blew or caught fire. Why?

Recorded music is usually compressed enough that when you play the signal at a sane volume level, around 80-85dB, even though you may have momentary peaks of 95dB or more, they are not "that" much higher than the signal. If they are, their duration is so short that the voice coil of the speaker doesn't heat up meaningfully. There is a phenomenon called thermal time constant, which is the time it takes the voice coil to heat up by a certain amount with a certain power input. This time constant is shorter for tweeters that have lightweight voice coils, and longer for woofers that have heavier voice coils, because this time constant is based mainly on mass and current, with the amount of current being dependent on the drive voltage and the load impedance. Then the time for the voice coil to recover to a certain temperature is based on the mass and the surface area exposed to air and other materials. If you only need to listen at a certain level, then no matter how much output the amp is capable of, you only need a certain amount of power to maintain your comfortable average listening level. A high power amplifier, when running at a typical listening level, is not delivering more average power than a lower powered amplifier, provided that both amplifiers are able to supply the necessary power to support the dynamics of music without clipping.

Why bother with high wattage amps, then? Dynamic headroom - every time you increase the level of sound output by 3dB, you double the input power in watts. With a less dynamically compressed signal, the transient power demands of music may be 10-20 times what the continuous power demands are. Lower power amps with lower rail voltage either compress or clip the output. These transients are so short in duration that the amount of voice coil heating is reduced, and the power to midrange and treble speakers is also reduced by limiting the amount of the spectrum they cover. Pink noise is used to measure speakers because it has equal energy per octave, but it also sounds more balanced, like music. The spectral balance of pink noise is a line trending downward at a rate of 1/f, but when plotted on a logarithmic scale with FFT bin widths defined as fractions of an octave, the FFT bin widths result in a FFT plot that looks flat, which we know as the target 'flat' frequency response. The spectral balance of music is similar. So tweeters and midrange speakers handle considerably less power when playing music than woofers. And woofers, because of their larger thermal mass, can handle more power for brief durations than tweeters.

The danger in amplifier clipping is that the crest factor of the signal - the ratio between peak and RMS level - approaches 1:1, that of a square wave, the more severely the amplifier is clipped. Also, this screws up the spectral balance of the music, because the square wave contains much more high frequency content than the original music signal did, in the form of harmonic distortion. These two things working together can nuke your tweeters, because the assumptions that let tweeters be built with small and lightweight voice coils (that handle less RMS power broadband) start to break down. It is still better to avoid amplifier clipping by using an amplifier that can supply 1.5-2x the rated power of your speakers, then don't drive the amplifier into clipping; using an over-spec amplifier doesn't do any good if you're just going to turn the signal up louder and clip the amp anyway.

 

[mhardy6647]

re: clipping and tweeters....

Digital clipping or square waves damaging tweeters over time. Myth or real?

Can digital clipping damage speakers? I have heard both sides on many forums. Don’t know what side is speaking the truth. What do you experts think ?

www.audiosciencereview.com

That whole thread is worth a look.

 

[Barrelhouse Solly]

I'm glad that several members who know more about the electronic side than I do say that at "normal" listening levels you're probably safe. I rarely go over 80 Db and mostly listen in the 70s. I'm almost in the Klipsch "good 1 watt amp" group.

 

[jmdesignz2]

Welcome to ASR! Some simple points should help you understand the problem.

1. Power (Watts) = Voltage (V) * Current (I)
When you turn up the volume, the amplifier increases the voltage differential between + and - terminals. The loudspeaker then draws the current it needs from the amplifier.

2. Maximum speaker power handling is determined by testing a speaker under sustained power for a set duration to find the maximum continuous power before permanent thermal or mechanical damage occurs. This "set duration" is not standardized and varies between manufacturers, so a published spec is virtually meaningless. Having said that, if you have a 100W amp and 100W speakers, and the amp's clipping indicator is coming on constantly, you are likely to damage your speakers very soon if you don't turn it down. Sustained power is not the same as instantaneous power, for e.g. it is possible for loud transients to exceed maximum speaker power handling without causing damage.

3. It is more common for lower powered amps to damage speakers than high powered amps. When an amplifier is unable to supply more current than the speaker demands (see point 1), it clips. Clipping squares off the waveform - mathematically, this is the same as producing a lot of high order harmonics. These are sent to the tweeter, and since tweeters are less robust than woofers, they are more easily damaged.

The easiest way to determine if you are asking too much of your system is to simply listen. As voice coils start to overheat, music will start to compress. As amplifiers distort, the spray of high order harmonics makes the sound harsh in the treble region. As speakers distort, the sound becomes "dirty" - at some point you might hear buzzing or flapping as the driver reaches its limits and starts smacking against its suspension. Turn it down and listen at sensible levels, and you won't have a problem.

All true

In the benchmark ABH2 thread I argued this same thing and got dog piled with "lower powered amps can't damage speakers" with some semantic gymnastics following