Are most amps clipping and most speakers strained or destroyed with home theater? - AVS Forum
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post #1 of 10 Old 01-02-2014, 04:54 AM - Thread Starter
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I don't get how they survive some soundtracks. Our least efficient speaker (surround) is 96 dB at 1 watt at i meter. Each speaker is fed by one channel of a set of 2 channel audiophile power amps. The RMS power of each channel of each amp is 120 watts rated conservatively (the manufacturer says 150 watts), with all channels operating. The surround speakers have a continuous rating of 100 watts, with peaks acceptable at 400 watts.

An efficiency rating I see a lot in HT is 90 dB @ 1W @1M. Our conservatively rated 120 watt amps into our least efficient 96 dB sensitive speaker should produce SPL in the room equal to a hardy 90 dB speaker receiving 480 watts, wouldn't it? Who has 480 watts of power or more through each of their channels? Yet when we play certain films (Star Trek Into Darkness, Loopers, The Grey) at Audyssey/THX reference level we really worry about our speakers. They sound quite clean and undistorted, but we worry that the next explosion, crash, clang or scrape may take them out. We start out most films at Audyssey determined reference level, and end up turning down the main volume control anywhere from 1 or 2 dB to 5 dB for Star Trek Into darkness, and we still found it overwhelming. We love loud sound, particularly when artistically done, but worry about the equipment -- ours and that of everybody else.
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post #2 of 10 Old 01-02-2014, 05:19 AM
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Quote:
Originally Posted by garygarrison View Post

I don't get how they survive some soundtracks. Our least efficient speaker (surround) is 96 dB at 1 watt at i meter. Each speaker is fed by one channel of a set of 2 channel audiophile power amps. The RMS power of each channel of each amp is 120 watts rated conservatively (the manufacturer says 150 watts), with all channels operating. The surround speakers have a continuous rating of 100 watts, with peaks acceptable at 400 watts.

Where is the problem?

Your audiophile power amps are in the same power range as the amps in a good AVR.
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An efficiency rating I see a lot in HT is 90 dB @ 1W @1M. Our conservatively rated 120 watt amps into our least efficient 96 dB sensitive speaker should produce SPL in the room equal to a hardy 90 dB speaker receiving 480 watts, wouldn't it? Who has 480 watts of power or more through each of their channels?

The obvious flaw in the above discussion is that it seems to ignore the fact that people only turn their systems up as loud as they want to hear. Most normal people don't listen at arbitrarily high levels.

The THX standards for SPL are reference level = 85 dB, and peak level - 105 dB. 85 dB happens to be close to the level at which most undamanged ears are the most sensitive to small details. 105 dB corresponds to a 20 dB peak-to-average level which covers 95%+ of all real world musical and dramatic recorfdings.

Here is a typical calculation of expected max SPL in a typical home system:


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Yet when we play certain films (Star Trek Into Darkness, Loopers, The Grey) at Audyssey/THX reference level we really worry about our speakers.

Is this about audio nervosa or a technical problem? ;-)
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They sound quite clean and undistorted, but we worry that the next explosion, crash, clang or scrape may take them out. We start out most films at Audyssey determined reference level, and end up turning down the main volume control anywhere from 1 or 2 dB to 5 dB for Star Trek Into darkness, and we still found it overwhelming. We love loud sound, particularly when artistically done, but worry about the equipment -- ours and that of everybody else.

Maybe you are worrying about your speakers because its just too loud for your preferences. Just a thought.
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post #3 of 10 Old 01-02-2014, 06:04 PM - Thread Starter
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Originally Posted by arnyk View Post

Where is the problem?
...
Is this about audio nervosa or a technical problem? ;-)
Maybe you are worrying about your speakers because its just too loud for your preferences. Just a thought.

Sorry I wasn't very clear. I have two different concerns:
  • My only worry with my own system is that the three movies I cited seem to have some ultra loud, high impact, sounds -- in both the bass and also in the midrange where my front speakers are operating. Even though (at Reference) the regular channels are restricted to 105 dB at the listening position (12.5 feet from the screen for us), and the subwoofer bass goes no higher than 115 dB, I'm guessing that these three movies, and ones like them, have a great number of sounds pushed up to just below the upper limit (105/115) by the mixers turning up the sliders and using a limiter to, well, limit. Another, but surprising, example of the loudness wars. The dialog seems fine, by the way, but those special effects are clustered at the top. We like running at Reference, but can't without attacks of the audio nervosa you mention, with a few films, such as these.
  • I do wonder how people with less efficient speakers supply enough non-clipped power (90 dB efficient speakers would require 480 watts to reach the same SPL that we have with 96 dB sensitive speakers at 120 watts, at reference level, unless my calculations are way off). I like the SPL calculator you included in your post, but it produces much different results than the Crown/Harmon calculator ... which is right?
  • Reference level is just right for us for most movies except for a few like the ones cited, and, as I said, the dialog in these three is at a pleasing level at Reference, even though the sound effects are scary.
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post #4 of 10 Old 01-02-2014, 06:40 PM
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Most ppl don't listen @ reference level. I'd be bleeding in my ears in that level. My movie listening level is at -20db. TVs are -25db. Most modern receivers have room corrections that also calibrates audio level at the listening position to remove the relevance of the efficiency of the speakers. So, when I listen to -20db, it will be -20db below reference level using the test tone. Of course efficiency of the speakers still matters to AMP so that it won't have to work as hard.
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post #5 of 10 Old 01-02-2014, 07:44 PM
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Same here, even sitting ~15 feet from my TV in my home theater setup I've never had to kick it up above -15 db during a movie. If you feel like you may have to, you may be losing your hearing. In that case the best case of action may be to turn on subtitles and to keep the volume down.
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post #6 of 10 Old 01-03-2014, 12:24 AM - Thread Starter
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Originally Posted by Foxbat121 View Post

Most ppl don't listen @ reference level. I'd be bleeding in my ears in that level. My movie listening level is at -20db. TVs are -25db. Most modern receivers have room corrections that also calibrates audio level at the listening position to remove the relevance of the efficiency of the speakers. So, when I listen to -20db, it will be -20db below reference level using the test tone. Of course efficiency of the speakers still matters to AMP so that it won't have to work as hard.

With our Audyssey XT, supposedly everything gets calibrated, based on the listening area microphone positions and full band frequency pings, so when setting the volume control to reference, the loudness (SPL) is set to the level the mixing engineers heard it, when they were carrying out the filmmakers' intentions. At least that's what several sources, including Chris K of Audyssey says (all bets are off with TV, since it is not standardized, at least by the time it reaches us). In most cases, that's what we want to hear, what the filmmakers intended. smile.gif Subjectively, it sounds about like what we hear in the better commercial cinema houses. Tellingly, in Star Trek into darkness the orchestra sounds just about like the SPL I'd expect from an orchestra in a concert hall from about the 10th row, or so. The dialog is also quite plausible in level. It's just the special effects that seem to be pushed up against the top of the permissible SPL range that cause concern. I agree with you that speaker efficiency still matters to the AMP, and I'm guessing that people with 60 to 200 w.p.c. receivers (unfortunately, often spec'd with only two channels straining the power supply) and speakers with the typical 90 dB/1w/1M sensitivity simply don't turn their volume up to near reference, because the regular distortion -- and even the sound of clipping (?) -- sounds too bad at that level, and that saves their bacon.
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Originally Posted by astrallite View Post

Same here, even sitting ~15 feet from my TV in my home theater setup I've never had to kick it up above -15 db during a movie. If you feel like you may have to, you may be losing your hearing. In that case the best case of action may be to turn on subtitles and to keep the volume down.

The reason we run most movies at reference is that we want to hear what the filmmakers intended, rather than feeling that we need that volume in order to hear the film articulated well enough (or even with the appropriate, if attenuated, emotional response). In most cases, with most movies, that works well for us, with very clean and pure sounding reproduction. Our hearing is fine. As to future damage, the usual highly transient peaks in most movies we run are thought to be less damaging than more or less steady level Rock at a lower SPL. Paul Klipsch used to say something like to reproduce the "blood stirring" levels of a live symphony orchestra from fairly close up you need "115 dB at your ears." I believe that, and I've seen even higher figures. Of course, these are the leading edges of very brief peaks.
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post #7 of 10 Old 01-03-2014, 12:40 AM
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It's going to be very hard to hear what the filmmakers heard as everyone uses different set ups biggrin.gif and of course room treatments and such. I personally just turn the volume up to where dialogue sounds "natural" and not too loud nor to quiet. In my room thats about -15 to -10 and at times -8 or -6 (IE Elysium)

No subwoofer I've heard has been able to produce the bass I've experienced in the Corps!

Must..stop...buying...every bluray release...
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post #8 of 10 Old 01-03-2014, 07:32 AM
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Quote:
Originally Posted by garygarrison View Post

Quote:
Originally Posted by arnyk View Post

Where is the problem?
...
Is this about audio nervosa or a technical problem? ;-)
Maybe you are worrying about your speakers because its just too loud for your preferences. Just a thought.

Sorry I wasn't very clear. I have two different concerns:
  • My only worry with my own system is that the three movies I cited seem to have some ultra loud, high impact, sounds -- in both the bass and also in the midrange where my front speakers are operating. Even though (at Reference) the regular channels are restricted to 105 dB at the listening position (12.5 feet from the screen for us), and the subwoofer bass goes no higher than 115 dB, I'm guessing that these three movies, and ones like them, have a great number of sounds pushed up to just below the upper limit (105/115) by the mixers turning up the sliders and using a limiter to, well, limit. Another, but surprising, example of the loudness wars. The dialog seems fine, by the way, but those special effects are clustered at the top. We like running at Reference, but can't without attacks of the audio nervosa you mention, with a few films, such as these.
  • I do wonder how people with less efficient speakers supply enough non-clipped power (90 dB efficient speakers would require 480 watts to reach the same SPL that we have with 96 dB sensitive speakers at 120 watts, at reference level, unless my calculations are way off). I like the SPL calculator you included in your post, but it produces much different results than the Crown/Harmon calculator ... which is right?
  • Reference level is just right for us for most movies except for a few like the ones cited, and, as I said, the dialog in these three is at a pleasing level at Reference, even though the sound effects are scary.

I see no evidence that you measured any SPLs or power levels in your listening room which means that you are just speculating on what is happening. That gets me back thinking about audio nervosa. If you have some reliable relevant evidence, then let's see it!
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post #9 of 10 Old 01-03-2014, 03:44 PM - Thread Starter
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Originally Posted by arnyk View Post

I see no evidence that you measured any SPLs or power levels in your listening room which means that you are just speculating on what is happening. That gets me back thinking about audio nervosa. If you have some reliable relevant evidence, then let's see it!

The audio nervosa kicks in -- at reference level -- on very few movies.smile.gif

I guess I'm going on a number of indicators and, yes, some educated speculation:
  • Audyssey claims to set up one's equipment so that when the volume control on the pre/pro (in my case) or the AVR is set for reference level the sound is limited to 105 dB out of each speaker (LF/C/RF/SURRs), except for the sub which is limited to 115 dB, from the microphone positions. Each separate speaker must be able to reach these levels, since movie soundtracks sometimes have a very loud event coming from somewhere other than dead center in the front. If Audyssey is working correctly, the 105 dB level should be possible from any speaker (with the sub topping out at 115) . With all speakers operating at their maximum Audyssey allowable levels, the SPL could get higher, because the SPL can add up. Since some movies with big sound effects, etc. sound much louder than others that also have big effects (with the dialog and the orchestral sound sounding like it moves over a similar SPL range in all movies, despite the sound effects being much louder in some films), I thought the explanation might be that in some movies the sound effects are moved up to the top of the range, with the ceiling limited, just as is done for the loudness war pop music and for TV commercials. Yes, that is a speculation. What do you think the explanation is?
  • I did take some measurements with two different Radio Shack meters (an old one and a new one), "C wt.," "Fast," but I didn't specifically compare the movies I cited to the others in our collection. With various films, transient peaks got to about 110 dB, but, since these are both analog meters one would expect needle ballistics to cause the reading to be up to about 13 dB low for the briefest peaks. Really broad peaks got to 115 dB (not often). Loud passages (not peaks) were in the high 80s and the low 90s, as I recall.
  • My ears told me that the three films I mentioned contained effects that were louder than those on most BDs, with the same VC setting. I might add The Impossible to that list.
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post #10 of 10 Old 01-03-2014, 04:19 PM
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I will agree about "certain" scenes being louder than the majority of the movie. There have been times that I've made it 40 to 60 minutes into a movie, at -20, but once I get a gun fight scene or a gas station explosion....here comes the wife..."I can hear that 3 floors up"..so maybe you are on to something. At first I was going to agree with the majority and just say..turn it down.

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