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Is this clipping or just high SPL?

Hey everyone,

A question arose today during a listening session. I have a Yamaha M40 120wpc amp driving GMA C1's with a passive pre-amp. I usually run both my pre-amp and amp at about 12... but on rare occasions I will turn my pre-amp up all the way and boost my amp to about 2 or 3 o'clock. I do this on recordings that seem to be mastered lower than usual...

Anyways, today I was listening at the higher play levels and a particularly abrupt loud passage came... specifically, it was 'Dark Side of the Moon' when the bells come in on the beginning of the third track (that everyone has heard at least 40 times).

I didn't hear any clipping, and never have on this system... but things just sounded more congested with less separation and clarity than I'm used to. Given, it only lasted about 10 seconds during that one sequence... but it sparked the question of whether it was likely that the amp was clipping or that it was just loud beyond my comfortable listening level. I am in a small room about 8 feet from the speakers, btw...

Thanks.
djembeplay
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shadorne
7,333 posts
 
Do you have an SPL meter? How loud was it? If it was above 100 db SPL then you might be "pushing" your speakers too much.

See this article Unreasonably large distortion in midrange drivers. You can see that it gets bad above 105 db SPL.

The main issue in the midrange and tweeter is excursion outside the non-linear range of the driver rather than amplifier power. This is why many studios use horns and why most speakers for sound reinforcement uses horns. The fact is that most normal speakers (even good ones) compress and distort above 100 db SPL (at the listening position - which can be 110 db SPL for the speaker).
rodman99999
3,557 posts
 
DJ- To answer your question: YES, reflected sound/loud mush at the listening position. As an experiment: find two or three large, thick comforters and drape them on the wall, behind your listening position. That should let you know if slap echo is the problem. Of course- it's also possible that the side walls can contribute as well, but the front and back walls are generally the main offenders.
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shadorne
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As Linkwitz states, in the article I referred to,"the large low frequency voice coil displacements can cause large amounts of intermodulation distortion products near the high frequency signal due to the large low frequency variation of Le(x)."

A bell or chime is percussive and contains loads of low AND high frequencies all at once - just like a Cymbal...so it is a tough to impossible test for most speakers to generate at high SPL levels without some audible distortion or congestion...
djembeplay OP
169 posts
 
Gotcha - thanks guys.

I just listened again at a slightly lower volume and worked my way back up... because this was driving me nuts.

It sounds fine, actually... I think I'm just not used to playing at higher SPL's than what I'm used to... in fact I'm really impressed with these old Yamaha amps. I think what I was hearing was a combination of room reflection and having sensitive ears... (which seems to vary from day to day for me... some days loud sounds are less tolerable than others... anyone else experience this?).

Incidentally, I would like to measure the DB to get a sense of proportion.

Out of curiosity, if a speaker does have some audible distortion / congestion in a loud passage, but not to the point of obvious clipping... is this going to damage a speaker or just be annoying? Will high end speakers on high end amps all pretty much start to congest at these 100-105 DB ranges?

I doubt I'm up that high in this small room... I hope.
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shadorne
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Will high end speakers on high end amps all pretty much start to congest at these 100-105 DB ranges?

At 2 meters from the speaker - yes absolutely. Soundstage will not even test speakers at 100 db SPL as most would get damaged - see quote below from soundstage:

As volume increases, all frequencies should rise at the same rate. However, as a speaker is stressed, compression will occur at certain frequencies. The stress may be mechanical, thermal or otherwise. This test shows those frequencies at which deviation occurs as a result of compression. Many speakers show slight deviations at 90dB. Most speakers start to show serious deviations at 95dB. Very few speakers can be tested at 100dB without damage.

Furthermore remember that soundstage are NOT making IMD tests - so their results look artificially good (when a speaker plays simultaneously high and low frequencies you get MORE distortion).
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