Still confused about speaker power handling...

[audio]

Can anyone explain this to me in more detail? The thermal power rating of my Tannoys is 30 watts. The Fisher X-202-B that I am getting is supposedly 40 wpc. Is this a bad idea? Forgive me if I seem ignorant about this, but I guess I am. Should I be looking at a lower powered tube amp to use with vintage Tannoys or other high efficiency speakers?

[tomcat]

Never combine a weak amplifier with high power handling speakers: you may kill them with distorsions! At least for transistor amplifiers it is always better to have a stronger amp than the speaker's limit...
Happy listening
Thomas

[fjhuerta]

I think the rule of thumb here is that your speakers will be happy with an amplifier rated at twice their RMS power ratings.

I heard it has something to do with the amp never clipping the signal, and the speakers being able to handle the extra power for transients.

Always remember - a clipping signal is WAY worse than clean RMS power. :)

[PMC7027]

The main problem you must worry about with solid state (SS) amplifiers is clipping. When many SS amplifiers clip they put out higher order harmonics (3rd, 5th, 7th, etc.). These higher order harmonics can fry tweeters very easily.

Because of this it is dangerous to have too SMALL an amplifier because you may drive it into clipping and damage your speakers.

Also, the thermal power rating refers to continuous power. Very rarely with high efficiency speakers does the amplifier have to put out more than a watt or two continuously. Transient peaks can easily get into the hundreds of watts, but rarely does continuous power get very large.

You should be fine power wise, in my opinion, with the combination you described.

[Metralla]

I know this argument, and have repeated it myself when asked, as it appeared to have a ring of truth. But is it really true?

I think it may have been true in the old days of paper cone tweeters, and dome tweeters with very low power handling capacity, and low powered (transistor) amplifiers that really did clip badly with lots of nasty harmonics.

But these days with ferro-fluid tweeters and quality diaphragm materials - I somehow don't think so. And modern amps have plenty of power - try to find a sand amp these days under 50 watts; and these are really clean and mostly honest watts.

Let's say I am driving my 50w amp into 6dB of clipping. If I get a 100w amp and run the system at the same volume I'll be running at 3dB of clipping - it's still clipping, but there is way more power. Will that be good for the tweeter? Is it better?

Tweeters cannot take much power - they'd be lucky to be able to take 8 watts or so. When a loudspeaker system is said to have a power handling capacity of 100w, it's almost all bass. I think tweeters can be damaged if they are driven too hard - and that's it.

Who here has personal experience of exactly this - ruining a tweeter by over-driving it with a low powered amp that was clipping?

I've only destroyed one driver in my life, and that was a woofer on a Celestion SL6 that was massaged into oblivion by my 100w pure Class A Metaxas amp. No distortion - but the massive current at full volume melted the voice coil. When I showed the dealer he was pretty impressed. (Party situation, dual mono pre-amp, incompetents at the switch).

There are many factors that define the amplifier-speaker interface, but I'm not sure that the power rating of the loudspeaker as a whole is one of them.

Regards,
Geoff

[AudioEnz]

Originally posted by Metralla
Who here has personal experience of exactly this - ruining a tweeter by over-driving it with a low powered amp that was clipping?

i'm involve with the hi-fi industry here in New Zealand and have a lot of contact with hi-fi dealers. I can assure you that the #1 speaker problem that hi-fi dealers see are blown tweeters, caused by smaller amplifiers driven into clipping.

"But the speaker has 100w power rating" the tweeterless customer says, having driven their amp well into clipping by playing music too loud, plus turning the bass up full. 100w of clean power, no problem. Smaller amps driven into clipping, big problems.

[Cliff]

I think you'll be just fine, prix :) The manufacturer of my speakers, Legacy Audio, has said it doesn't matter how much extra power the speakers are fed (above their RMS rating), assuming it's clean, quality power. I've always felt this way anyway, but it was nice to hear it from a "professional". I think mine are rated around 100-150 RMS. I am driving them with around 185 Watts continuous. Mine are nothing special, so the same should apply to yours. BTW, my rear surround speakers are 'ittle-bitty Infinitys. I'm feeding them with the same 185wpc, and I think they were rated at 30w RMS or so :) Still going strong after 7 or 8 years.

[Tony Plachy]

Prix, your just fine, do not worry. As everyone else has sad clipping on SS amps is the big problem. Also if you take your 30 watt speakers and hook them up to a 300 watt amp and turn it up all the way, you might fry something, but that is not your situation.

[audio]

Well, my initial concern was that I had been using a 70 wpc solid state amp with these speakers, but from Metrallas earlier reply to another thread I posted, I guess I was okay. I turned them up pretty loud, but I wouldn't say I was blasting them.....well maybe I got close, but I didn't do it for very long. Do you think they are okay?

[-=Rudy=-]

Originally posted by Metralla
Who here has personal experience of exactly this - ruining a tweeter by over-driving it with a low powered amp that was clipping?

Been there, done that, bought the replacements. 20 years ago, a shabby 25wpc integrated amp into my (then) new Grafyx SP10's (which are rated 75 watts each). Fortunately Philips was still in the aftermarket speaker business and I was able to get them cheap enough. Wish I'd bought extras now.

In contrast, I can push a 250wpc amp so the same speakers are almost deafening, and they take all I can dish out.

[Metralla]

Thanks Rudy.

Regards,
Geoff

[fjhuerta]

Tweeters cannot take much power - they'd be lucky to be able to take 8 watts or so.


Actually, tweeters can take a bit more power, Metralla! Most DIY designs I've seen (Focal, Scan-Speak, Vifa, Peerless, etc.) handle between 25-50W RMS. In fact, I've seen tweeters rated @ 100W RMS! :eek:

[michael w]

originally posted by Metralla
I've only destroyed one driver in my life, and that was a woofer on a Celestion SL6 that was massaged into oblivion by my 100w pure Class A Metaxas amp. No distortion - but the massive current at full volume melted the voice coil. When I showed the dealer he was pretty impressed. (Party situation, dual mono pre-amp, incompetents at the switch).


Hi Geoff,

You sure it wasn't that dodgy Metaxas amp ?
:D

Clipping doesn't always result in audible distortion.

I had a pair of SL6 too and it managed to handle everything from a 40wpc Naim to a pair of 200w Plinius monoblocks to a pair of bridged Perreaux ~600wpc.

Not a single meltdown.

:)

[Metralla]

Originally posted by michael w
You sure it wasn't that dodgy Metaxas amp ?
Hah! You could be right.

Actually, my Metaxas is one of his first amps, made in 1982 or so. Originally, the A1 came out as a 50w Class A amp, but a friend of mine from Brisbane had one built with 100w output to drive his big Acoustats. I bought the Metaxas from him to drive my Yamaha NS1000s. At the time, my ears told me it was a far better amp than the Naim 250 in my system. I didn't make many other comparisons. It sure handled the big 12" bass driver on the Yammies - great speakers.

I know Metaxas is criticized as "audio jewelry", but his early amps were quite good. I tried a couple of his preamps, and they were pretty awful, but that A1 is a beast. I was mainly using a hybrid preamp hand made by Russell Woolcock from Melbourne. This has a lot of gain - it supports a moving coil cartridge without a step up device. I also had (and still have) one of Allen Wrights (Vacuum State) all-tube preamps.

After a couple of years with that combo, I went back to Uni (Armidale, NSW) and had to downsize to smaller speakers, and ended up with the SL6s. Good speakers, and I still have them. They are very inefficient and need a surprising amount of power for a little box. Mine are the first ones with the copper tweeter. The woofer replacement was cheap and simple, and I've had no trouble since.

I'm into single ended triodes now, so I don't know what I'll do with the Metaxas when I get back to Oz.

Might be good for a subwoofer amp. :) Or a boat anchor. :laugh:

Regards,
Geoff

[Gerry]

Originally posted by PMC7027
The main problem you must worry about with solid state (SS) amplifiers is clipping. When many SS amplifiers clip they put out higher order harmonics (3rd, 5th, 7th, etc.). These higher order harmonics can fry tweeters very easily.

I'd argue that the tube/ SS differentiation based on THD spectrum doesn't really apply here. The term "clipping" is applied because a clipped sine wave on a scope looks like its extremes have been cut off; the rounded extremes are squared off. The problem is that as the clipping becomes more severe, what was originally a sine wave starts looking more and more like a square wave. Do a Fourier analysis on that wave and you'll find tons of high-frequency information (distortion) has been generated and that it is all odd-order. This is in addition to whatever the amp does to the original wave normally. Tube guitar amps are favored for their distortion characteristics because their even-order signature is still buried in there somewhere and guitar speakers have pretty poor high-frequency response; run a Marshall wide open through a full-range cabinet and it'll take your head off. Point is, clip your amp, tube or SS, too hard and you're likely to find yourself sourcing new tweeters.

[-=Rudy=-]

Originally posted by fjhuerta


Actually, tweeters can take a bit more power, Metralla! Most DIY designs I've seen (Focal, Scan-Speak, Vifa, Peerless, etc.) handle between 25-50W RMS. In fact, I've seen tweeters rated @ 100W RMS! :eek:

To add to that: the power rating is misleading--high frequencies are very low in power, so you will get a lot of loudness out of very little power. (The crossover keeps the lower frequencies out of the tweeter.) If you're pushing your power amp to 100 watts, cut the bass and see how little power the mids and highs use. So there's no real need to be concerned if you see a lower-wattage mid- or high-frequency driver in a higher-wattage speaker system.

The only problem is overdriving an amplifier...where you get high-powered high-frequency spikes that you really can't hear, until it's too late.