Amplifier power and efficient speakers, Is more power better?

Russell Dawkins · « **Reply #20 on:** 25 Nov 2009, 10:59 pm »

I don't think the power available from the wall is the issue - I think it's the amplifier and speaker limitations.
10 gauge back to the breaker box would be nice - I have that - but I don't see it as the crux of the issue.

GDeering · « **Reply #21 on:** 25 Nov 2009, 11:06 pm »

I'm having to face the fact that I like more power and better dynamics - but more power does not equal better musical reproduction, I totally agree that any audio system is a study in trade offs.

Perhaps one of the benefits of the low-watt crowd moving up the power chain is that their attitude toward sound will help to lessen the number of hi-fi non-musical muscle amps that seem to dominate the landscape.

Gregg

werd · « **Reply #22 on:** 25 Nov 2009, 11:14 pm »

I think it plays a big part. I installed 240volt Torus and now have to be very careful now how i use my volume. The Dynamic passages stress my speaks, where they never used to in 120volt. It was only at first and an adjustment i had to make, not turn up as high. I get the same volume sensation but not so high on the attenuator.

i used to try and simulate that by overpowering my speakers with rated amp output. I am more inclined to believe it's the power retrieval than the gear.

AmpDesigner333 · « **Reply #23 on:** 28 Nov 2009, 04:57 am »

Let's consider the limitations of microphones in this discussion, and the DNR of the recording as well.

The human ear is an amazing device. It allows huge dynamics to come through with a running compensation for the SPL of the perceived sound at hand.

Another analogy... With a system capable of 120dB dynamic range (DNR) or more, add a variable input range that allows sounds to be pre-compensated before they are processed with more than 1000x (another 60dB) pre-amplification. This is only an example, but you might see the point...

AmpDesigner333 · « **Reply #24 on:** 28 Nov 2009, 05:00 am »

By the way, I have made many recordings or thunder, mostly as a teenager! What I really loved was hearing the lightning come through the microphone before the thunder erputed, and sometimes upsetting the compression system of the mic-pre...

NewBuyer · « **Reply #25 on:** 28 Nov 2009, 11:58 am »

Benchmark Media's own Applications Engineer, Elias Gwinn, advises the following:

Quote from Elias Gwinn: "Avoid using amplifiers that are too powerful for your system! You'll get best results when using 75-95% of the amps total power."

I believe that his argument is to maximize a system's signal-to-noise ratio (and dynamic range), by minimizing any required source-signal attenuation.

This is most certainly at odds with Musical Fidelity's advice on the matter!

konut · « **Reply #26 on:** 29 Nov 2009, 12:37 am »

IMHO this is one of the most misunderstood aspects of the hobby ie. amplifier power requirements. Having worked in live sound, I can attest to the fact that microsecond transients can cause overload of even massive amplifiers. This is why most record labels place limits on the dynamic range of their CDs, but others, like Telarc, permit a wide dynamic range, but warn you to take care as to not damage your speakers. Most people severely underestimate the wattage required for even moderate dynamic range reproduction. As AmpDesigner333 so rightly points out, the power supply is the key to providing clean peaks as its there, rather than the outlet, where the reserve for transients is kept.
It used to be that the audio mags printed graphs of the power delivery specs of amps. One graph tracked where the distortion was as as wattage increased, so one could get an idea of how much continuous power the amp could produce, and how much headroom the amp had. Another graph showed the level of distortion along a frequency curve for a given wattage, usually rated output. With these 2 graphs one could see how an amp would mate with a speaker of a certain efficiency, and not get into trouble WRT the Elias Gwinn quote from the previous post, which should only be taken as a general guideline. Not all amps have a "power envelope" to which Mr. Gwinns' rule applies. Most amps, like the ones Mr. Gwinn has in mind,have distortion at relatively high levels with even low power, then drop significantly as rated power is achieved, and then rise again. Some amps, though, have low distortion at even low power,only rising when rated power is approached. And then there is transient intermodulation distortion. With all the parameters to consider its enough to make your head spin. Suffice to say, in most cases, the more power the better.

JoshK · « **Reply #27 on:** 29 Nov 2009, 01:41 am »

To me this debate is proof that power compression is real and important to deal with. Solution? Get higher efficiency speakers. You can throw more and more watts at it, but that is driving a nail with a sledge hammer. Low efficiency speakers just use the extra watts to heat the voice coil.

Russell Dawkins · « **Reply #28 on:** 29 Nov 2009, 02:32 am »

Quote from: AmpDesigner333 on 28 Nov 2009, 04:57 am

Let's consider the limitations of microphones in this discussion, and the DNR of the recording as well.

I think if microphones and mic preamplifiers and, consequently, the DNR of the recording were so big a factor in this discussion the advantages of having more dynamic capability in the replay system would not be so readily apparent, but having more efficient speakers and more power shows its advantages with almost any recording - even one that has been pretty compressed as most popular recordings are.

Quote

Another analogy... With a system capable of 120dB dynamic range (DNR) or more, add a variable input range that allows sounds to be pre-compensated before they are processed with more than 1000x (another 60dB) pre-amplification. This is only an example, but you might see the point...

isn't 1000X amplification equal to 30dB?

*Scotty* · « **Reply #29 on:** 29 Nov 2009, 03:17 am »

As quoted Benchmark Media's recommendation regarding amplifier power does not make any sense to me. If the you are operating at 75 to 95 percent of the amplifiers rated power on a continuous basis you have only 25 to 15% of the amplifiers remaining reserve power for peaks. It makes more sense to be operating at 75 to 95% on the worst case peaks thereby hopefully minimizing the possibility of clipping. I think if you have a choice, purchasing an amplifier with a relatively flat distortion vs power curve would be very desirable. For a SS amp, an amplifier with .0022%THD at 1 watt and .0044THD at 100watts @ 8ohms 1kHz with a rated power of 110watts at clipping would be an example an amplifier with a fairly flat distortion curve across its power envelope. It would also be nice if the high frequency distortion didn't go to pieces when the power output goes to near maximum. Virtually every amplifier will show a rise in distortion as the frequency increases because the negative feedback is increasingly ineffective as the frequency rises. For the aforementioned amp, .05%THD at 10kHz at 100watts would be pretty acceptable performance. The usual assumptions apply to the this "amplifier",its measured performance should be achieved without excessive negative feedback and the amplifier should have excellent sonic performance,otherwise why bother. Another desirable aspect of amplifier design to look for is adequate slewrate and slew symmetry. Slew symmetry is the ability of the amp to follow the positive and negative swings of incoming signal accurately. Many amplifiers will turn on fast enough to follow the positive swing but they are unable to turn off fast enough as the waveform heads down towards zero. This results in smearing,loss of focus and higher distortion. This is a problem frequently seen in amplifiers with bipolar outputs but slew asymmetry can be a problem with any amplifier,tube or solid state.
If your amplifier meets the criteria of the "amplifier" used as an example it should be easier build a good sounding system because your amplifier isn't bringing undesirable characteristics with it to add to your problems. To add to what Josh said the cheapest and most effective power you can buy is found in more efficient loudspeakers.
Scotty

konut · « **Reply #30 on:** 29 Nov 2009, 03:23 am »

Were that it was so easy. High efficiency drivers, typically, are less linear that lower efficiency drivers. Not all lower efficiency drivers compress. Its easy to make generalisations, but knowing how to evaluate individual components goes a long way towards putting together a system that will satisfy the end user.

JoshK · « **Reply #31 on:** 29 Nov 2009, 04:21 am »

Quote from: konut on 29 Nov 2009, 03:23 am

Were that it was so easy. High efficiency drivers, typically, are less linear that lower efficiency drivers. Not all lower efficiency drivers compress. Its easy to make generalisations, but knowing how to evaluate individual components goes a long way towards putting together a system that will satisfy the end user.

I don't have any desire to get into a debate on the issue, but I am not so sure I buy the less linear statement. If you mean as in less flat FR, well sometimes that is true but many modern HE drivers don't fit that generalization. There are more and more HE drivers meant for other application than ultimate SPL that measure quite flat, as good as many low eff drivers.

"Not all lower efficiency drivers compress." I haven't seen one that doesn't. Even the best of the bunch ScanSpeak revelators compress when asked to produce peaks over 100db. There just can't be enough copper in the motor to not heat up, and if there were, they'd have so much inductance there would be no top end. There is no replacement for 10db of sensitivity.

Well that is my opinion anyway.

*Scotty* · « **Reply #32 on:** 29 Nov 2009, 05:03 am »

We kind of have to specify what we mean by efficient. I would consider 96dB at 1 meter as pretty efficient. If you get to this figure by using multiple drivers you avoid the compression problem. If you use two drivers you cut the power per driver in half as well as the heating and the potential compression. You also cut the excursion in half and this can reduce your THD by as much as 75% compared to the THD a single driver exhibits. If you accept this as efficient enough you can chose drivers with linear behavior and have a very satisfactory sounding loudspeaker with low coloration and low compression characteristics.
Scotty

konut · « **Reply #33 on:** 29 Nov 2009, 01:50 pm »

Quote from: JoshK on 29 Nov 2009, 04:21 am

Quote from: konut on 29 Nov 2009, 03:23 am
Were that it was so easy. High efficiency drivers, typically, are less linear that lower efficiency drivers. Not all lower efficiency drivers compress. Its easy to make generalisations, but knowing how to evaluate individual components goes a long way towards putting together a system that will satisfy the end user.

I don't have any desire to get into a debate on the issue, but I am not so sure I buy the less linear statement. If you mean as in less flat FR, well sometimes that is true but many modern HE drivers don't fit that generalization. There are more and more HE drivers meant for other application than ultimate SPL that measure quite flat, as good as many low eff drivers.

"Not all lower efficiency drivers compress." I haven't seen one that doesn't. Even the best of the bunch ScanSpeak revelators compress when asked to produce peaks over 100db. There just can't be enough copper in the motor to not heat up, and if there were, they'd have so much inductance there would be no top end. There is no replacement for 10db of sensitivity.

Well that is my opinion anyway.

No debate here, just a friendly discussion.

The main point I'm trying to make is that while generally what you assert is true, there are cases where its not. Your example of high efficiency drivers that are linear,(have flat frequency response) usually, are extremely expensive. Also if one has a design where the Scanspeak revelator is used within a certain bandwidth, less compression will occur. Its possible to design around deficiencies. Bob Smiths' Timepiece models are just such a design.

macrojack · « **Reply #34 on:** 29 Nov 2009, 02:41 pm »

Firstly, when discussing this topic, it might be useful to outline the parameters. Bandwidth is a consideration, as is the type of driver. You could be talking about reproduction at a single frequency point or a full 20 to 20K range. These are very different goals and should lead us in different directions theoretically. Single drivers would be viewed differently as would speakers which power each driver with an dedicated amplifier. All drivers compress the signal at some point. Are we talking about 100 db or 130 db as the point where compression becomes audible?

I use pretty big horns with compression drivers. The manufacturer rates these at 108 db/1watt/1meter. Ultimate SPL is 130 db, so he says. Since I seldom listen above 90 db, and since I use a very controlled 100 watt per channel solid state amp on these horns, I never think about headroom at all. These horns reproduce a spectrum from 400 hz to 14,000 hz so nearly everything is handled there.

Since my drivers are only 2 inches in diameter cones, I have to assume that the horns are what make this performance possible. Mechanical amplification. SPL, after all, results from the movement of air, and only so much air can be moved by a small cone. The only way the small cone can move more air is by moving further in its pistonic excursion. But there is a limit to how far it can travel. At this limit, it will compress before it tears its spider.

If you want high SPLs and extreme dynamics, you have to use products that were designed for that purpose. Don't send a boy to do a man's job. Multiple small cones move more air but their spontaneous excursion range does not increase simply because you use more of them.
20 or 30 or more violins playing in unison cannot be made to sound like a cello.

Those who wish to play loud and lifelike should look to pro gear. For that kind of performance you need tools, not toys.

*Scotty* · « **Reply #35 on:** 29 Nov 2009, 04:44 pm »

macrojack,I think we if consider the average sized living room and an upper limit of 125 dB our choices are a little broader than just horns. Line arrays are one effective alternative that comes to mind. Here are some links to pro-sound applications utilizing line arrays.
http://www.eaw.com/products/linearray/
http://www.alconsaudio.com/site/line-array/line_array_5.html
http://www.linearray.com/
http://www.slsloudspeakers.com/content/view/265/107/
Scotty

AmpDesigner333 · « **Reply #36 on:** 29 Nov 2009, 05:08 pm »

Quote

isn't 1000X amplification equal to 30dB?

For amplitude, dB is 20 * log10(x).
For power, it is 10 * log10(x).
Although I was referring to amplitude (microphone signal), an offshoot discussion could be about perceived volume versus power output...

AmpDesigner333 · « **Reply #37 on:** 29 Nov 2009, 05:24 pm »

Quote from: *Scotty* on 29 Nov 2009, 03:17 am

As quoted Benchmark Media's recommendation regarding amplifier power does not make any sense to me. If the you are operating at 75 to 95 percent of the amplifiers rated power on a continuous basis you have only 25 to 15% of the amplifiers remaining reserve power for peaks. It makes more sense to be operating at 75 to 95% on the worst case peaks thereby hopefully minimizing the possibility of clipping. I think if you have a choice, purchasing an amplifier with a relatively flat distortion vs power curve would be very desirable. For a SS amp, an amplifier with .0022%THD at 1 watt and .0044THD at 100watts @ 8ohms 1kHz with a rated power of 110watts at clipping would be an example an amplifier with a fairly flat distortion curve across its power envelope. It would also be nice if the high frequency distortion didn't go to pieces when the power output goes to near maximum. Virtually every amplifier will show a rise in distortion as the frequency increases because the negative feedback is increasingly ineffective as the frequency rises. For the aforementioned amp, .05%THD at 10kHz at 100watts would be pretty acceptable performance. The usual assumptions apply to the this "amplifier",its measured performance should be achieved without excessive negative feedback and the amplifier should have excellent sonic performance,otherwise why bother. Another desirable aspect of amplifier design to look for is adequate slewrate and slew symmetry. Slew symmetry is the ability of the amp to follow the positive and negative swings of incoming signal accurately. Many amplifiers will turn on fast enough to follow the positive swing but they are unable to turn off fast enough as the waveform heads down towards zero. This results in smearing,loss of focus and higher distortion. This is a problem frequently seen in amplifiers with bipolar outputs but slew asymmetry can be a problem with any amplifier,tube or solid state.
If your amplifier meets the criteria of the "amplifier" used as an example it should be easier build a good sounding system because your amplifier isn't bringing undesirable characteristics with it to add to your problems. To add to what Josh said the cheapest and most effective power you can buy is found in more efficient loudspeakers.
Scotty

Some interesting points, but I like the one about symmetry in particular. Slew symmetry is an issue mostly with non-symmetrical amp designs, such as SET. High power amps are almost always symmetrical push-pull designs, valve or SS.

The differences among N-channel and P-channel FETs, for example, can cause minor symmetry issues, but nothing along the magnitude of a single ended design. Consider a BJT based single ended amp, such as the common collector circuit shown here:
http://en.wikipedia.org/wiki/File:NPN_emitter_follower.svg
The load is driven in one direction from the transistor, but the resistor drives the load in the other direction. Let's say the resistor was 8 ohms, which would be the output impedance in one direction. The output impedance in the other direction is close to zero (based on the gain of the transistor and it's other parameters).

This is one factor that attracted me to Class-D amps. They represent a much different way of delivering a varying current to the load (speaker). There is no such thing as a "perfect" amplifier, but if we are debating more or less power, you can never have too much available power. Even if the amp is "perfect" signal quality wise, you have the issues of size, weight, and getting the electricity to the amp from the wall. Well, hope that was interesting to some...

doug s. · « **Reply #38 on:** 29 Nov 2009, 05:43 pm »

Quote from: macrojack on 29 Nov 2009, 02:41 pm

If you want high SPLs and extreme dynamics, you have to use products that were designed for that purpose. Don't send a boy to do a man's job. Multiple small cones move more air but their spontaneous excursion range does not increase simply because you use more of them.
20 or 30 or more violins playing in unison cannot be made to sound like a cello.

Those who wish to play loud and lifelike should look to pro gear. For that kind of performance you need tools, not toys.

macro, while i like horns, your analogy is faulty; line arrays will give similar performance as horns, re: high spl's, as adequately shown in the links to the pro audio tools posted by scotty. (i personally liked the alcons' comparison of distortion w/a pro-audio 2" compression driver compared to their ribbon:

2" c.d:

alcons ribbon:

your analogy is faulty because speaker drivers are neither wiolins or cellos. of course, 30 wiolins won't sound like a cello. but, based on that logic, no speaker, regardless of quantity, will sound like a cello or a wiolin, cuz it's neither - it's a speaker. multi-driver speakers in a line array can more accurately portray either a wiolin or a cello, simply because more drivers will increase efficiency & spl while decreasing distortion.

some day, when i have more room, i will have line arrays, to compare to my horns. (i'd love to try two stacks of the alcons ribbon-based speakers, cuz i love ribbons, but i don't think my budget would allow it; so i give thanks to bill baker of response audio, for prowiding me w/forty quality full-range drivers for cheap.

)

doug s.

AmpDesigner333 · « **Reply #39 on:** 29 Nov 2009, 05:45 pm »

Another few comments about power...

I seem to be drawn to the sound qualities of low efficiency speakers! Maybe this is because it is easier to design a speaker when efficiency is not so high up on the list of concerns --- when you can waste power on better damping or flattening out the response of the drivers.

As far as amps go, give me a 1000W super low noise+distortion amp over a 10W amp any day. If the power output capability of amps had no effect on the other measurable (and unmeasurable) parameters, than there would be no discussion. Coming as close as possible to recreating a live performance is very important to me, and doing so with 10W, even with 120dB/1W speakers is more or less impossible for most music sources, especially if there is any bass.