How much amplifier power is required?

[Sal1950]

I can see it now. Frank with his head down the horn, symphony level volume, listening for hiss and the cat jumps on the remote...

 

[restorer-john]

It may be a myth that too little power blows tweeters, but as the article shows very well, it's excessive level that blows tweeters (and woofers). This comes earlier on a low powered amplifier as the amp clips and the average level goes up.

It's not quite a myth. People can do all the maths they like on the power, but they forget that some amplifiers often burst into momentary (or extended) bouts of oscillation on a clipping event, sometimes supersonic, uncontrolled and it is that high powered multiple cycle content which the tweeters cannot tolerate. In these cases, it is not the harmonic decaying energy from a clipped sine wave- that model is simplistic.

The failure mode is not a cooked tweeter voice coil from typical long term overpower events, it is a fuse like failure of the lead in wires to the voice coil or the connection to the voice coil where it is exposed across the suspension. There is no thermal mass to absorb the transient current event, like there is in the VC itself.

I was tasked back in the day with post-mortems of warranty speakers to determine abuse or factory failures and cut open a lot of drivers...

I personally believe the above failure mode is more common than people realize and I base it on the number of very esoteric tweeters I have been able to repair simply by either unwinding a single turn to bypass the vaporised lead wire or very carefully creating a new link to the VC itself. Those tweeters show absolutely no heating damage to the VC itself, so "overpower" was rapid and transient in nature.

 

[sergeauckland]

It's not quite a myth. People can do all the maths they like on the power, but they forget that some amplifiers often burst into momentary (or extended) bouts of oscillation on a clipping event, sometimes supersonic, uncontrolled and it is that high powered multiple cycle content which the tweeters cannot tolerate. In these cases, it is not the harmonic decaying energy from a clipped sine wave- that model is simplistic.

The failure mode is not a cooked tweeter voice coil from typical long term overpower events, it is a fuse like failure of the lead in wires to the voice coil or the connection to the voice coil where it is exposed across the suspension. There is no thermal mass to absorb the transient current event, like there is in the VC itself.

I was tasked back in the day with post-mortems of warranty speakers to determine abuse or factory failures and cut open a lot of drivers...

Yes, I'd forgotten about amplifiers of marginal stability that do all sorts of crazy things when clipped.

And then the manufacturers make a virtue of the amp's 'purity' .........

S

 

[RichB]

Yes, I'd forgotten about amplifiers of marginal stability that do all sorts of crazy things when clipped.

And then the manufacturers make a virtue of the amp's 'purity' .........

S

Hell hath no fury like an amplifier clipped.

- Rich

 

[HifiLove]

The ceiling of the "recommended power" is basically meaningless.

The general rule of thumb is to err on the high side -- get as much as you can afford. For a very detailed explanation of how to estimate the amount of power you need, take a look at part 3 of Dr. Toole's "How to design a home theater".
https://routledgetextbooks.com/textbooks/9781138921368/home-theatre.php

I looked into it and just for fun , estimated the power requirements for the +20db peak, over reference level(85db), for my listening distance and speaker sensitivity of 91.5dB...and the required power estimate of 70.7w for speaker with 8 Ohm nominal impedence and 141.5w for speaker with 4 ohm minimal impedence

is not very different from my calculations from my earlier post

"For eg, I get 0.7W power requirement for reference level(85db) listening and 64w for 20db peak(105db). This is for an 8 ohm nominal impedence and double this (1.4W at avg spl, 128W at peak spl ) when it dips into 4 ohms ]"

So its not about calculations..we know whats needed.

But not sure how I jump from this to "the ceiling of the "recommended power" is basically meaningless. The general rule of thumb is to err on the high side -- get as much as you can afford."

esp given the quoted article on https://sound-au.com/tweeters.htm concludes with

"A persistent myth in the audio industry is that clipping damages tweeters, so you should use a bigger amp to ensure more headroom so the amp won't clip. This claim is simply bollocks!
It is simply nonsense to imagine that the loudspeaker drivers in a 100W speaker can survive an average power of over 250W and peak power of up to 1.6kW. "

This is where , I think I'm trying to get a sense of how much is too much, when procuring the amp. and may be thats where the ceiling in the speaker manufacturer spec 'recommended amplifer power' helps ?

My original question still remains...

 

[HifiLove]

I am in the process of upgrading and renovating the game room system. The Revel M20's have been replaced by Revel M126Be's.
I measured the Oppo UDP-205 at 2.829 volts so basically 1 watt at 8 ohms and played some music.
Even at 2 watts, it is amazing how loud this is and emphasizes the importance of the 1'st watt.

I encourage you to determine your desired listening level and estimate your power requirements.

- Rich

Pls see my earlier posts...I've done all the power estimates , through multiple means and they are in the ball park. Its not about how much I need.

Its about how high I can safely go, when buying the amp ( no I am not talking about cranking the volume to max and listening at 120db..,but for a reference level listening of 85db with 20db peak).

My questions were around , what does the 'recommended amplifier power' high value , from manufacturer mean (is it average, peak , at nominal impedence or minimal impedence etc) , how to incorporate that into buying decision. So for eg, can I safely drive a speaker with this guidance

with this amp
Output Power: 300 RMS watts/channel into 8 Ohms, 450 watts/channel RMS into 4 Ohms
?

 

[RayDunzl]

Mine:

Rated as 4 ohm, though they dip to 1.2ohm at 20kHz

Recommended power 20 - 500W

Amp in use: 350/700/1400 (rating) into 8/4/2 ohms

Just be judicious with the volume knob.

They will happily play with 110dB peaks at the listening position, about my limit, and have, many times.

 

[HifiLove]

It may be a myth that too little power blows tweeters, but as the article shows very well, it's excessive level that blows tweeters (and woofers). This comes earlier on a low powered amplifier as the amp clips and the average level goes up.

Unfortunately 'loud' when measured subjectively depends greatly on the distortion present so using a higher powered amplifier that doesn't clip i.e distort as easily means that the volume can go up higher, damaging the drivers more easily.
S

Thanks @peanuts for the article. Very informative.

@sergeauckland , thanks., think you got my original intention behind asking the questions. How high can I go safely without damanging the speakers. I'm not worried about under powering, I will ensure I buy an amp with enough power, based on the calculators and Floyd Toole's 'How much Power is Needed' article.

I'm worried about over powering(accidentally) and frying the tweeters. There should be a reason manufacturer has a 'recommended amplifier power' in their spec sheets ? Why people are not factoring that in their amp buying decisions ?

Its simple really. Calculator shows I need 142w peak power , when speaker dips into 4 Ohms. Speaker manufacturer's recommended amplifier power is 40-250W. What happens if I drive this speaker with an amp that outputs 300W into 8 Ohms and 450W into 4 Ohms ....and keep to normal listening levels(~80db avg, 100db peak) ?

Or am I better off , buying an amp , thats limited to 200W Max at 8 ohms/300w @4 Ohms
Or even lower ...150W @8 ohms , 200W @4 Ohms ?

I thought I'd just buy a big enough amp with lots of headroom (like 400w/500w) and be done with it.... but now the article puts a dent to that idea!

 

[RayDunzl]

My questions were around , what does the 'recommended amplifier power' high value , from manufacturer mean (is it average, peak , at nominal impedence or minimal impedence etc) , how to incorporate that into buying decision.

Amps are rated at RMS (typically), so to keep things easy, I suppose that is what the speaker makers quote.

 

[RayDunzl]

So for eg, can I safely drive a speaker with this guidance

with this amp
Output Power: 300 RMS watts/channel into 8 Ohms, 450 watts/channel RMS into 4 Ohms
?

I wouldn't be concerned.

 

[restorer-john]

I've said it before, buy twice as much power as you think you ever need or want. At least 200W/ch@8R, 350W@4R and be satisfied you have enough power on tap for any number of speakers, listening levels and speaker efficiencies.

I use pairs of power amps which in mono BTL do 600W@8R, 900W+@4R and use them with any speakers, small bookshelves whatever- just be sensible with the volume knob.

 

[RayDunzl]

With music, not test tones, the tweeter will typically receive less power than the mid or woofer, due to the declining power (voltage swings) in music as the frequencies increase.

A Steely Dan track:

At 3kHz, the power peak is 1/10 the midrange peak.

That 142W you calculated might become 14.2W at that frequency.

 

[HifiLove]

Mine:

Rated as 4 ohm, though they dip to 1.2ohm at 20kHz

Recommended power 20 - 500W

Amp in use: 350/700/1400 (rating) into 8/4/2 ohms

Just be judicious with the volume knob.

They will happily play with 110dB peaks at the listening position, about my limit, and have, many times.

Thanks, what I was looking for.., so seems the "recommended power" ceiling doesnt come into play at all ... just an insurance policy for manufacturer to say 'we warned you...its on you"

 

[sergeauckland]

Thanks @peanuts for the article. Very informative.

@sergeauckland , thanks., think you got my original intention behind asking the questions. How high can I go safely without damanging the speakers. I'm not worried about under powering, I will ensure I buy an amp with enough power, based on the calculators and Floyd Toole's 'How much Power is Needed' article.

I'm worried about over powering(accidentally) and frying the tweeters. There should be a reason manufacturer has a 'recommended amplifier power' in their spec sheets ? Why people are not factoring that in their amp buying decisions ?

Its simple really. Calculator shows I need 142w peak power , when speaker dips into 4 Ohms. Speaker manufacturer's recommended amplifier power is 40-250W. What happens if I drive this speaker with an amp that outputs 300W into 8 Ohms and 450W into 4 Ohms ....and keep to normal listening levels(~80db avg, 100db peak) ?

Or am I better off , buying an amp , thats limited to 200W Max at 8 ohms/300w @4 Ohms
Or even lower ...150W @8 ohms , 200W @4 Ohms ?

I thought I'd just a big enough amp with lots of headroom (like 400w/500w) and be done with it.... but now the article puts a dent to that idea!

I think Restorer John is right in his suggestion, to get about twice the power you're ever likely to need. This is only a 3dB increase, so really not a lot. A loudspeaker's recommended amplifier power is really just a guide, and there's no harm in going higher provided you're sensible with volume and you're not in the habit of giving parties, where a limiter can be really useful!

Going too low in power can firstly just not be satisfying in that distortion will set in early, but there's the risk of damage as mentioned due to average power rising when clipping, and thirdly, it will limit any future choice of loudspeakers. Clean power is cheap enough these days, so there's no real benefit in skimping.

S

 

[restorer-john]

That 142W you calculated might become 14.2W at that frequency.

Typical tweeters cannot even absorb 14W, letalone 100s of watts when the amplifiers oscillate. Most tweeters in three way systems are rated 5-10W and that is sitting behind their crossover.

Plenty of excess power for any conceivable transient and an amplifier that is kind to tweeters at the onset of transient induced clipping/oscillation.

From experience, I can tell you a superb measuring power amplifier instantly vaporized the lead-in wire to two very expensive tweeters of mine on a benign transient event many years ago. Tracked it down to oscillation and yes, I was able to repair the tweeters, but not before Sony kindly already sent me a pair under warranty direct from Japan. They were vapor deposited alumina crystal dome tweeters and around $400 at the time. I still have the spare original pair.

 

[HifiLove]

I've said it before, buy twice as much power as you think you ever need or want. At least 200W/ch@8R, 350W@4R and be satisfied you have enough power on tap for any number of speakers, listening levels and speaker efficiencies.

I use pairs of power amps which in mono BTL do 600W@8R, 900W+@4R and use them with any speakers, small bookshelves whatever- just be sensible with the volume knob.

thanks , thats reassuring. So I'm going ahead with my original thought of buying 300W@8Ohm/450W@4ohm Amp , to drive the speaker with max recommended amp power of 40-250W .

As a follow-up , are there power amps , that can enforce hard limits on o/p power, if say the Volume control on DAC/Preamp , gets accidentally turned all the way ? Is that the same as gain controls on the amp ?

Thanks

 

[HifiLove]

With music, not test tones, the tweeter will typically receive less power than the mid or woofer, due to the declining power (voltage swings) in music as the frequencies increase.

That 142W you calculated might become 14.2W at that frequency.

Oh K, didnt think about it..Thanks

 

[restorer-john]

As a follow-up , are there power amps , that can enforce hard limits on o/p power, if say the Volume control on DAC/Preamp , gets accidentally turned all the way ? Is that the same as gain controls on the amp ?

Yes, there are and there have been in the past. You would need to investigate and make enquiries as to what amplifiers outside of the pro scene can do that.

Gain controls will only act as a limit if your input signal is capped.

 

[HifiLove]

I think Restorer John is right in his suggestion, to get about twice the power you're ever likely to need. This is only a 3dB increase, so really not a lot. A loudspeaker's recommended amplifier power is really just a guide, and there's no harm in going higher provided you're sensible with volume and you're not in the habit of giving parties, where a limiter can be really useful!

Going too low in power can firstly just not be satisfying in that distortion will set in early, but there's the risk of damage as mentioned due to average power rising when clipping, and thirdly, it will limit any future choice of loudspeakers. Clean power is cheap enough these days, so there's no real benefit in skimping.

S

thanks again.. Yes I agree.., I want to buy something that has ton of juice and be done with it. Right , twice the power is only +3db..,so the 142 will double into 284w for the addl headroom...and now that 300W@8Ohm amp sounds perfect.

Can you talk more on the volume limiters ?

 

[RayDunzl]

Can you talk more on the volume limiters ?

I am the volume limiter here.