Axiom Home Page Forums General Discussion Technical Questions Underpowered receiver? How loud can I go?

I have just bought a pair of M22's and a VP150, and have a "modest" receiver. It's a Yamaha HTR-5240, and it's rated at 70W into 8 ohm. I occasionally like to listen at quite loud levels, but because the VP150 is 6 ohm, I have to put the receiver into its low impedance mode which even further limits its power. At levels above 96dB at the listening position, I notice high frequency crackling especially when the tweeters are being pushed hard. I assume the amp has begun clipping at this point, because in high impedance mode during two channel listening I can obtain slightly higher levels before the crackling sets in.

Someday I will invest in separates to alleviate this, and I know that the speakers are rated for 200W, so I'm wondering how loud in terms of dB the speakers can comfortably go. In other words, what is "reference level"? I'm not planning to hit ear-damaging levels, but on the other hand I've never had speakers with power ratings as high as these. I'd like to know mostly so that I don't buy an amp with the capability to damage the speakers. Also it would be good to know because this weekend I will be taking the speakers to my dad's, and hook them up to his dual 300W Parasound amps to see what they can really do :-)

Thanks!

-tim

Hello Waveman,

First, a warning. Amplifiers approach clipping in different ways, and with different audible results, but in all amps, as you increase the level, distortion begins to rise as the amplifier's output section works harder and runs hotter. Some amps may have a sudden increase in distortion and begin clipping immediately as they reach their output limits; others may increase distortion rather gradually.

In either case, don't run your amp and speakers to the point where you're hearing audible articacts of either amp clipping or speaker distortion. The side effects of the clipped waveform may produce all sorts of garbage that will overheat and burn out the tweeter and/or the woofer voice coils.

Another fact: the M22ti's are not bulletproof studio monitors meant to play at deafening levels (which some engineers seem to prefer, Lord only knows why). Subjectively, 96 dB Sound Pressure Level (SPL) at your listening seat is termed "very loud" on conventional scales of loudness. The M22Ti's can certainly go louder on peaks--but remember that all relatively compact speakers using fairly modest drivers will begin to sound strained or "edgy" when they are driven into the 96-to-100 dB SPL region without a subwoofer. That's because driver distortion begins to escalate quite rapidly at high volumes. So that edgy, strained sound is a signal to you to TURN DOWN THE VOLUME! By comparison to amplifiers, speakers generate quite high levels of distortion when they are pushed--often in whole percentages, and we can all hear it.

The maximum power ratings of speakers are not intended to encourage driving speakers to absurdly high SPL levels. They are a very rough indication of what the speaker can accept on a very brief, instantaneous basis with CLEAN amplfier power--not distorted.

There are, of course, very large horn-loaded speakers that are used for large auditoriums, movie theaters, rock concerts, and the like, and they are capable of levels well above 100 dB SPL at very low distortion. However, they are comparatively low fidelity, the horn loading requires complex equalization to get decent sound, they are incapable of really deep bass, and they're not necessary in a domestic living room to create a reasonable facsimile of real-life SPL levels.

In conclusion, be careful with the M22ti's with your Dad's big Parasound amps, particularly if you're running them alone without a subwoofer. If they sound stressed, turn down the volume!

Regards,

You pose some interesting questions about the relationship between (rated) amplifier power and sound pressure levels from speakers. If you want/need to understand the basics about the relationships, try visiting this address: http://www.modrec.com/about/MRT_decibel.pdf
This is a .pdf file and you need Adobe Acrobat reader to view it (it's a free program) This simplifies the information somewhat, but you can see that in order to hear a noticible change in volume (3db) you have to double your amplifier output (i.e. from 5 watts to 10 watts) To increase the volume to what is generally percieved as twice as loud (10db), you have to increase your amplifier output by a facttor of 10 (i.e. from 5 watts to 50 watts). And to double the loudness again you would need 500 watts! Most of us can't afford 500 watt amps, so a good solution is to find more effecient speakers, which reduce the need for bigger amps. In normal listening environments (home use) - the real difference between a 70W amp and say a 100W amp translates to about 1.5db increase in speaker loudness. (all else being equal) What a bigger amp WILL give you is increased dynamic headroom and that WILL contribute to better/cleaner sound (unless you drive that amp into clipping) A speakers power input rating (i.e.200W) has nothing to do with its sound pressure output level. I too, would be curious to know how "loud" the speakers can play before they start to break up the sound - but I doubt that this can stated as matter-of -factly, since there are so many variables.

Thanks for the reply Alan.

I did say that I like to listen at such high levels "occasionally", lest anyone think that I'm on a collision course with bleeding ear syndrome :-) When I did my test, 96db was "peak" level as measured by the analog Radio Shack SPL meter on its "slow" setting. The overall level was around 90db nominal, which I know for a fact is considered to be within normal listening levels by many people, though certainly not the majority. For example, calibration with Avia is done at 85dB, which provides several dB of headroom for normal listening material at "reference" level.

Also, I should have added that I do run the M22's set to "small" on the receiver, and they are coupled with a subwoofer. This may explain why the amp seems to fizzle out on the high frequencies first(?) But I still wonder whether its the speaker which is distorting, or the amp. How can I tell which it is? That is why I want to run the same test with more than adequate power. I will be careful with the levels so as not to explose the speakers to peak output for very long.

I was not aware that bookshelves cannot attain levels above 100dB, as you mention. Kind of a blanket statement don't you think? From what distance was this number obtained? Just curious because any SPL measurement certainly must take into account distance, room size, etc.

Thanks again for the helpful reply!

Hi,

Thanks, Anonymous, for posting the explanation of subjective loudness and the logarithmic relationship of decibels and amplifier power requirements.

Waveman, I didn't say that bookshelf speakers can't attain SPL levels greater than 100 dB. I said (to elaborate a bit) that they often begin to sound strained or edgy when they get into this region. Also, on maximum power ratings, I should have said that these are a rough indication of how many watts of CLEAN amplifer power the speaker will accept WITHOUT INCURRING DAMAGE to the drivers. It does not mean that the speaker distortion at those power levels won't be audible--it likely will.

Listening distances for many of these tests are "average", about six to 10 feet, and that's my experience (and those of my former listening panel colleagues, Dr. Floyd Toole and Ian G. Masters) doing speaker comparisons in the National Research Council IEC listening room, which approximates in its dimensions, furnishings, and shape, a typical living room.

Other variables that come into play are individual tolerance for speaker distortion levels and overall loudness. For example, during double-blind tests with colleagues on the panel, we always agreed in our written comments when small speakers began to sound strained or edgy. On the other hand, I preferred SPL levels about 3 dB less than Ian or Floyd.

By the way, I haven't heard all compact speakers; there may be some that are capable of much higher SPL levels without signs of edginess. But I suspect these will be horn-loaded systems with compromised fidelity. So far, in speaker design, there's no free lunch.

Regards,

Alan,

Some of this advice seems a little different from the information conveyed to me by Ian in an earlier thread. He said that the M22s handled even more than 200 watts in the lab. I have a pair of M22s and I drive them with a NAD C350 rated at 60 watts/channel. I occasionally play acoustic jazz at very loud levels for a group of jazz enthusiasts in a very large room (perhaps 50ft X 50 ft). Floor-standing models are too big for me to transport for this purpose, so I'm stuck with the M22s. I notice very annoying distortion in the bass range when I move the C350 volume past 2 o'clock---and by 12 o'clock for some CDs. That seems a little early for the NAD to be clipping, and I get the same problem with soft clipping engaged. Am I reaching the sound-pressure limits of the M22 or do I just need a more powerful amplifier?

Roger

PS The M22s sound fantastic at lower volumes that do not induce the distortion.

The actual performance of a loudspeaker design in terms of power handling is that they are designed to handle bursts of power for short timeframes. If you were to feed a speaker rated at 200 watts with a sound frequency (say a single 750hz tone) played at 200 watts for a sustained period, you would cause severe damage. That is what I believe Ian alluded to, that they could withstand that power level for music - which is usually made of short timestamps of certain frequencies at the levels mentioned.

Something to keep in mind regarding amplifiers and volume controls - they are not designed as linear devives. This means that Amp A can have a rating of 20wpc and stop delivering power and start clipping when the control is turned to 4o'clock, and Amp B rated at 100wpc can reach this point with the control at 10o'clock.

Your NAD is of solid design, and I would say it is entering clipping and gone beyond producing clean sound at the points you mention. It will react differently to different frequencies it is asked to amplify. Even with 'soft clipping" enabled, the amp WILL clip, as this does not stop that phenomena.

Hi,
BBIBH is correct. And Roger, that is a huge room (50 x 50 ft.) to try and fill with a 60-watt-per-channel amplifier, with or without "soft clipping." There's no question your amp is clipping or distortion has risen to audible levels.

Besides, as BBIBH mentions, don't use the volume control as a guide to how much power the amp section is delivering. The non-linearity of volume controls (it's called the taper of the control) is such that some "open up" quickly, i.e. by the mid-position of the control, the amp may be delivering all the power it can and could, on some models, be already clipping, or nearly so.

You should pair a subwoofer with the M22ti's, and use an amp with 175 watts/channel or more. Maximum power ratings are difficult to measure in practical terms because music is so diverse in frequency content. If you make measurements using a constant-state pink-noise signal, you may get a huge figure but it won't necessarily bare any relation to how the speaker handles music at high power levels.

Ian is currently doing some experimentation in the lab to determine some real-world method of getting practical maximum power ratings for speaker reproduction of music and typical soundtrack content.

Regards,

Thanks Alan and BBIBH for some very useful information. Although the room we're in is huge, the group occupies only a portion of the room, so I don't have to fill the whole room with loud music. Nevertheless, such an open space robs us of much of our music. It is very nice to know that it is the amp that is giving up and not the speakers. I'll try moving to the NAD C370 with double the rated power.

I have tried using a fairly large subwoofer and I frankly didn't hear enough of a difference to make it worthwhile. Is it possible that there just isn't much musical information in the acoustic jazz I play that is below the M22s range? If that's true, then wouldn't another set of M22s (and another amp) be a better solution than a subwoofer? With proper placement, it seems that music would have to travel less distance to get to everyone from 4 speakers instead of 2, so that we could actually run at lower volumes. And it would probably improve the off-axis performance too, right?

Roger

Hi Roger,

Adding an extra set of M22ti's will only increase Sound Pressure Level by 3 dB, a "just nicely noticeable increase in volume". It will improve the overall bass energy by 3 dB as well. If you place them in an arc closer to your listening group, you'll be doing a quasi-distributed array of speakers, which is an approach some professionals use in theater sound reinforcement, only they use many, many speakers. On the other hand, remember that even though you're not sitting that far away, you are still asking the amp and the four speakers to pressurize or fill a huge space. That's what the speakers "see".

And using an amplifier with twice the rated power output will only increase acoustical output by 3 dB, which you'll perceive as "somewhat louder". To subjectively "double the volume"--an increase of 10 decibels--you'll need an amp with 10 times the rated power of your existing amp, or 600 watts per channel!

Yes, it will improve off-axis performance to use four M22tis. And re your query about the frequency content of jazz, the bottom string on an electric or acoustic stand-up bass is at 40 Hz, but the bottom keys on a standard piano extend to 28 Hz. Keep in mind as well that bass response in most speakers gradually tapers off, so while the M22ti still has good output at 40 Hz, and will accept a few dB of bass boost quite gracefully, a properly set up subwoofer should reinforce the bass energy in your large room significantly.

Regards,