How important is burst power?

[ex audiophile]

I’m looking to purchase a stereo amp for a 2.1 setup. The Audiophonics purifi based amp that Amir reviewed recently looks ideal except that it has very little power reserve for intermittent peaks in high dynamic range recordings.
In general quality AB amps have substantial power reserves. The STR power amp for example is rated at 400/600 watts into 8/4 ohms and has a kilowatt of burst energy.
Problem is that all of the top rated amps on this site are D class, other than the AHB2 and Topping.
Ignoring price and ergonomics are we better off with superb measuring amps with limited reserve or a solid AB amp with substantial power reserves with a SINAD in the 90’s?
I realize there are crucial variables such as the volume we typically listen at, speaker efficiency, dynamic range in our source material etc. But can we make general recommendations for enthusiasts like myself who don’t understand the technical complexities of modern amps?

 

[Blumlein 88]

Burst power by itself has no inherent advantage. Extreme example. A 30 watt amp with burst power to 100 watts, is no better than 100 watt amp with zero burst power. Both can momentarily put out 100 watts. Question is how much power do you need and does the amp have it?

The Audiophonics had 255 watts of very clean power into 4 ohms, and 367 watts into 4 ohms at 1% THD+N. Do you need more than that? An 86 db rated speaker would be putting out around 112 db at 1 meter from this amp. With 1000 watts it would be 116 db. It is doubtful you need more than that or that most speakers could make use of it.

To give a good answer of course we need to know what speaker you are using. I have some Soundlabs ESL speakers that are terribly inefficient and can handle 1000 watts. But those are unusual. The extra 3-5 db 1000 watts might get me with those might have some use. With most speakers I doubt it. BTW, using a 250 watt class D amp with those Soundlabs is the best I've heard them sound.

 

[ex audiophile]

Burst power by itself has no inherent advantage. Extreme example. A 30 watt amp with burst power to 100 watts, is no better than 100 watt amp with zero burst power. Both can momentarily put out 100 watts. Question is how much power do you need and does the amp have it?

The Audiophonics had 255 watts of very clean power into 4 ohms, and 367 watts into 4 ohms at 1% THD+N. Do you need more than that? An 86 db rated speaker would be putting out around 112 db at 1 meter from this amp. With 1000 watts it would be 116 db. It is doubtful you need more than that or that most speakers could make use of it.

To give a good answer of course we need to know what speaker you are using. I have some Soundlabs ESL speakers that are terribly inefficient and can handle 1000 watts. But those are unusual. The extra 3-5 db 1000 watts might get me with those might have some use. With most speakers I doubt it.

Very helpful, thanks. In my case speakers are Revel M106 bookshelf (around 86db efficient, i believe) and a pair of JLA fathom subs.

 

[Chrispy]

You would consider spending $6500 on such an amp for those speakers? Nice amp no doubt but a bit out of balance with your speaker budget it seems. What is your listening distance and typical/average spl level such that you need that kind of power? Something like this seems a better choice for a fairly powerful amp.... https://www.buckeyeamp.com/shop/p/hypex-nc502mp-amplifier-2-channel

 

[Blumlein 88]

Well Revel says 50-150 wpc for your speakers and nominal 8 ohm impedance. The Audiophonics is rated for 227 wpc at 1% THD @8 ohms. They don't say, but probably good for about 150 wpc at lower distortion levels. Since we know it will put out more into 4 ohms, and 2 ohms it will not be bothered by any impedance variation in your speakers. I doubt you would hear any benefit from the extra burst power. In fact the Audiophonics would appear almost tailor made for the M106 speakers.

 

[Steve Dallas]

Your speaker efficiency, speaker impedance curve, room size, average listening SPL, and listening distance are critical inputs into the equation. The truth is, most people do not need more than 100W continuous unless they employ DRC with aggressive boosting, and even then 100W is often more than enough, considering the limited dynamic range of most recordings.

Most people in home settings consume less than 10W continuous at normal listening levels (80dB or so). Everything above that is "burst power," whether hidden in the power supply or not. Here is a handy calculator.

In this example, you are listening at 80dB average SPL and want to reproduce bursts of up to 95dB, you need 99W "burst power." Even if a 100W class D amp is PS limited, it would still work. And, this assumes 3dB headroom to be sure the amp stays out of clipping. Change that to 1dB, which is more realistic for home audio, and you are at only 62W.

This is for a single speaker. Everything gets ~3dB louder when you add the 2nd speaker of a stereo pair. It also does not account for early reflections nor other room characteristics, so it is a worst case scenario.

Add the 2nd speaker (-3dB) and account for some room gain (-1dB), and we get:

 

[charlielaub]

One thing that you should keep in mind with "burst" power is that (by definition) the amp can only maintina it for a very brief time, typically for less than 10 msec. This is enough time to handle a high frequency peak in the signal at frequencies of 1kH or more. But do not confuse burst power with 20-20k power. Take the amplifiers mentioned in post #2 (quoting):

Burst power by itself has no inherent advantage. Extreme example. A 30 watt amp with burst power to 100 watts, is no better than 100 watt amp with zero burst power. Both can momentarily put out 100 watts. Question is how much power do you need and does the amp have it?

The 100W amp can still deliver 100W at 20Hz while the 30W amp with 100W burst power will not. This is because the duration of low frequencies is longer than the 30W amp can maintain the burst. So which amp is better? I would say the 100W one.

 

[ex audiophile]

One thing that you should keep in mind with "burst" power is that (by definition) the amp can only maintina it for a very brief time, typically for less than 10 msec. This is enough time to handle a high frequency peak in the signal at frequencies of 1kH or more. But do not confuse burst power with 20-20k power. Take the amplifiers mentioned in post #2 (quoting):

The 100W amp can still deliver 100W at 20Hz while the 30W amp with 100W burst power will not. This is because the duration of low frequencies is longer than the 30W amp can maintain the burst. So which amp is better? I would say the 100W one.

Agreed. And while I don’t know for sure I’d bet good money that @amirm doesn’t plan to replace his ML amps with anything of lesser wattage regardless of its measurements lol