Axiom Home Page Forums General Discussion Technical Questions Amplifiers

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Do we agree with it?

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Actually, went through and read that after my last post - didn't want Rane's theory clouding mine. Compression IS a better explanation than the harmonic theory, but I would add one more piece to the puzzle - the fact that pop/rock albums are recorded and mastered with hideous amounts of compression already, so the dynamics between the low amplitude and high amplitude (quiet and loud) portions of the sound are already falsely narrowed (that "wall of sound" *twitch*)... would explain why even with "soft clipping" amps (call a spade a spade - they're soft limiters - there is no "soft clipping" really!) and better THD+n ratings on amps... we can still blow tweeters.

Bren R.

Not really, John; probably the best analysis available online of why tweeters can sometimes be damaged when amplifiers are driven into clipping by very high level low frequency signals is found at the St. Andrews University site . Both the "harmonics" and "compression" hypotheses are analysed and other possible contributing factors are briefly discussed. Apparently a combination of factors may be responsible.

Doug(bug), on your original question, as was said, the power rating of a speaker is nearly meaningless for use in the home; theoretically it would be the maximum power that could be applied continuously without the speaker going up in smoke. Nothing remotely like that happens in listening using about 1 watt most of the time with possible split second peaks of 100 watts or more. Don't be overly concerned with power, voltage and current; we can get all we need(Ohm's Law hasn't been repealed)quite inexpensively these days.

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Ohm's Law hasn't been repealed

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Though some audio boutiques are looking to take it to the Supreme Court.

Bren R.

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probably the best analysis available online of why tweeters can sometimes be damaged when amplifiers are driven into clipping by very high level low frequency signals is found at the St. Andrews University site . Both the "harmonics" and "compression" hypotheses are analysed and other possible contributing factors are briefly discussed. Apparently a combination of factors may be responsible.

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I have to admit... as soon as the crazy equations come out, I have to force myself to keep reading. There's really not much "new" that I didn't touch on in my two posts. The main theories are a combination of:
-HF creation by clipping of the LF (ie: harmonics)
-Rise in the HF level of the original signal which – although limited by clipping by an amount similar to that which occurs at LF – rises to a high level. (compression - though his tests show that highs don't run off as bad as one would think)
-Leakage of LF power. (that really depends on the crossover type - and I think you'd see some real differences in which manufacturers' tweeters go "sizzle" if this were a major factor, but... bundled with the other reasons - it can only hurt!)
-Non-themal effects due to an increase in the peak displacement or accelerations. (actual physical driver excursion and acceleration aggrevating the other causes - though tweeters now are cooled much better than they used to be, I haven't seen a tweeter give off a little puff of smoke in... 15 years?)

Bren R.

Yeah Bren, I like the words better than the numbers myself; they sometimes revive bad memories of all that calculus in undergrad.

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Yeah Bren, I like the words better than the numbers myself; they sometimes revive bad memories of all that calculus in undergrad.

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Math was never my strong point. I majored in Power Mechanics with a double minor in Biology and Computer Science.

I'd rather have it explained as "okay start with your impedance in ohms, now divide by..." and do my "gunzintas" than try to determine what (Vss - {{Rqa}} ^2) is driving at.

Bren R.

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Let me ask a question like this: would my m60s (rated at 250 watts) peform better with a 200 wpc or 130 wpc? I am not talking about deafening listening levels, just normal.>>


This was the question I was trying to ask. And It seems the answer is that in a clean lab environment yes, at home no. Too many variables. So I don't see an Outlaw in my future. So spend the money on 80s.

I wasn’t so much referring to Watts, but current. You can see my evaluation on the Stereo board of what my impressions were when I fired up the Rotels.

In summery, I did notice a difference in overall SQ. Not a slap in the face kind of difference, but definitely an improvement. And that was going from a HK rated at 100 wpc to the Rotel at 200 wpc. I suspect that the HK is closer to 150 wpc though, so the difference in actual wattage was not significant. I attribute most of the gains were related to the pre-amp and not just power, but who knows for certain.

I have also seen numerous posts where folks went with separate high current power amps and noticed SQ improvements. I do not know the workings of tube amps, but they appear to be high in current, but with relatively low wattage. If you can, I’d suggest finding out what your amp’s current is for comparative analysis, and not put as much weight on the wattage.

OK. I'm not disputing that you hear a change in SQ. Measure current. How do I do that? Maybe I can find a loaner amp. Running my 60's, a 200 wpc amp?

Either the spec sheet or a phone call to the tech dept will tell you what current capacity the amps in question have.

When I was looking into all this, I found some interesting trends with different manufactures. Many claim high wattage ratings, but when I started looking at current, I found that there was a pretty big disparity. That’s why Axiom suggests Nad, HK and Dennon when running the M80’s……they all have robust power supplies with plenty of current, at reasonable costs. Other brands like Parasound, Krell, Sunfire, Rotel, Mcintosh, etc have plenty of current as well, but are more expensive than the other three. I’m sure there’s a few dozen other high end amps as well, but all out of my price range, so I didn’t even bother looking at them.