How much power is "enough"?

rbbert

rbbert

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Based on some info posted in the Pass INT60 thread, I began to wonder how much power actually is "enough", for me or anyone. Many different pieces of information will factor into this (and note that some of my assumptions and calculations are probably in error, I'm looking for help here)

First, what volume levels should we be hoping to achieve? I've read that a typical symphony orchestra at the 10th-15th row in the audience will reach peaks of 105-110 dB when average levels are around 80 dB. I well remember a Grateful Dead concert in a theater in 1976 where I was in the sound booth and the sound man was checking his sound level meter: peaks of about 112-114 dB, average about 90 dB (I'm assuming that's louder than any of us want to achieve at home? It's certainly louder than I want).

So if a typical 2,3, or 4 way dynamic speaker has an efficiency of about 90 dB/W/m, in a typical listening room with a mix of reflection, absorption and diffusion, what power per channel (remember there are 2 speakers, so we're really talking about 93 dB/(W x 2)/m) do we need to reproduce the symphony orchestra or the Grateful Dead concert? How do we know how much the room reinforcement will amount to, and therefore how much volume will fall off with distance from the speakers to the listening position?
 
I'm cross-posting this response from Duke Lejeune:

AudiogoN Forums: Help with a system for a guy into electronic music


5-18-13: Audiokinesis
"...just wish I understood all the math & logic behind this stuff."

Sorry for laying down a math smokescreen!

Let's walk through an example: The Coincident Super Triumph speaker (and for those who know their way around specs and marketing departments, I'll be making some simplifying assumptions along the way). Here's the webpage:

www.coincidentspeaker

The relevant specs are:

- 3 dB @ 45 Hz
- 8 ohms
- 94 dB @ 1 meter with 1 watt
- 300 watts maximum power
- 16" x 9" x 12.5" enclosure (from which I estimate .70 cubic feet internal volume)

I'm going to make a semi-educated guess and assume this speaker's RMS power handling is about 100 watts, but it can handle 300 watt peaks. So I'm going to make my projections based on 100 watts RMS.

Okay first question is, how loud will these speakers go with the 340i's 100 watts? We get a 3 dB increase in SPL for each doubling of power, and a 10-fold increase in SPL for each 10-fold increase in power. So if we start out with 94 dB from 1 watt, we can expect a 10-fold increase going from there to 10 watts, and another 10-fold increase going from 10 watts to 100 watts. So 94 + 10 + 10 = 114 dB! That is very loud.

By contrast, let's look back at the Dynaudio Focus 160. I am assuming its efficiency to be 83 dB / 1 watt, but the 340i puts out 200 watts into its 4 ohm load, so we get 83 + 10 + 10 + 3 dB, = 106 dB. This is still quite loud, but on paper at least, this speaker falls well short of the Coincident in SPL capability.

Now I'm going to muddy the waters a bit. I do not believe Coincident's claim of -3 dB at 45 Hz from a 94 dB efficient, .70 cubic foot box UNLESS the speaker is assumed to get generous reinforcement from room reflections, particularly in the bass region. I don't expect this to be obvious to anyone who hasn't dug into the math side a bit, but in this case I don't think my misgivings about the yardstick used have much bearing on whether or not this speaker would be a better match SPL-wise with a pair of high-output subs. You see, we really don't care whether the speaker gets down anywhere near 45 Hz, because you'll have two powerful subs to cover the low end. And even if the broadband efficiency spec assumes a 3 dB contribution from room reflections, we're still in much better shape as far as dynamic headroom goes.

Why does all this matter, if you're not going to listen at 106 dB, let alone 114 dB?? Well, you might be listening at 90 dB average SPL, and along comes a 20 dB peak (not at all uncommon). That would be 110 dB. If you want your system to convey the feeling the artist intended, then you want it to deliver that full 20 dB peak, or at least come as close as possible. (Note to the old timers: Yes, I've left out the effects of thermal compression for the sake of clarity; in my own home audio systems, I shoot for another 10 dB of power-handling headroom on top of the anticipated max peak SPL to mitigate the effects of thermal compression.)

The logic involved, which is the driving force behind doing the math, is this: It doesn't make sense to pay a premium for capabilities that you cannot use. Like, you'll never come close to using the capabilities of a pair of F113 subs when your main speaker became the limiting factor 14 dB before your subs!

Now the MOST IMPORTANT question has been left out of all of this, because it is unanswerable on an internet forum: How do you like the sound?? You may prefer the sound of the Dynaudios over the Coincidents by a wide enough margin that the max SPL difference doesn't matter... but if your preference is based on the Dynaudio having better low end, remember that your subs will be providing the low end, and will leave any small stand-mount speaker in the dust. While I'm one of those little guys who sells direct (as are most of the high efficiency manufacturers I'm aware of), I certainly understand and approve of your desire to only consider speakers you can audition.

I hope some of that was helpful.

Duke
Audiokinesis (Threads | Answers | This Thread)
 
Power is like money or horsepower. More is better. :)

For 4 ohm speakers, I prefer 1200W/ch. I found with 800W/ch I was clipping. Of course, I have also found with 1200W that while there was no clipping, speaker damage can occur if too loud. Choose your poison, as the saying goes.
 
KeithR said:
I'm cross-posting this response from Duke Lejeune:

AudiogoN Forums: Help with a system for a guy into electronic music


5-18-13: Audiokinesis
"...just wish I understood all the math & logic behind this stuff."

Sorry for laying down a math smokescreen!

Let's walk through an example: The Coincident Super Triumph speaker (and for those who know their way around specs and marketing departments, I'll be making some simplifying assumptions along the way). Here's the webpage:

www.coincidentspeaker

The relevant specs are:

- 3 dB @ 45 Hz
- 8 ohms
- 94 dB @ 1 meter with 1 watt
- 300 watts maximum power
- 16" x 9" x 12.5" enclosure (from which I estimate .70 cubic feet internal volume)

I'm going to make a semi-educated guess and assume this speaker's RMS power handling is about 100 watts, but it can handle 300 watt peaks. So I'm going to make my projections based on 100 watts RMS.

Okay first question is, how loud will these speakers go with the 340i's 100 watts? We get a 3 dB increase in SPL for each doubling of power, and a 10-fold increase in SPL for each 10-fold increase in power. So if we start out with 94 dB from 1 watt, we can expect a 10-fold increase going from there to 10 watts, and another 10-fold increase going from 10 watts to 100 watts. So 94 + 10 + 10 = 114 dB! That is very loud.

By contrast, let's look back at the Dynaudio Focus 160. I am assuming its efficiency to be 83 dB / 1 watt, but the 340i puts out 200 watts into its 4 ohm load, so we get 83 + 10 + 10 + 3 dB, = 106 dB. This is still quite loud, but on paper at least, this speaker falls well short of the Coincident in SPL capability.

Now I'm going to muddy the waters a bit. I do not believe Coincident's claim of -3 dB at 45 Hz from a 94 dB efficient, .70 cubic foot box UNLESS the speaker is assumed to get generous reinforcement from room reflections, particularly in the bass region. I don't expect this to be obvious to anyone who hasn't dug into the math side a bit, but in this case I don't think my misgivings about the yardstick used have much bearing on whether or not this speaker would be a better match SPL-wise with a pair of high-output subs. You see, we really don't care whether the speaker gets down anywhere near 45 Hz, because you'll have two powerful subs to cover the low end. And even if the broadband efficiency spec assumes a 3 dB contribution from room reflections, we're still in much better shape as far as dynamic headroom goes.

Why does all this matter, if you're not going to listen at 106 dB, let alone 114 dB?? Well, you might be listening at 90 dB average SPL, and along comes a 20 dB peak (not at all uncommon). That would be 110 dB. If you want your system to convey the feeling the artist intended, then you want it to deliver that full 20 dB peak, or at least come as close as possible. (Note to the old timers: Yes, I've left out the effects of thermal compression for the sake of clarity; in my own home audio systems, I shoot for another 10 dB of power-handling headroom on top of the anticipated max peak SPL to mitigate the effects of thermal compression.)

The logic involved, which is the driving force behind doing the math, is this: It doesn't make sense to pay a premium for capabilities that you cannot use. Like, you'll never come close to using the capabilities of a pair of F113 subs when your main speaker became the limiting factor 14 dB before your subs!

Now the MOST IMPORTANT question has been left out of all of this, because it is unanswerable on an internet forum: How do you like the sound?? You may prefer the sound of the Dynaudios over the Coincidents by a wide enough margin that the max SPL difference doesn't matter... but if your preference is based on the Dynaudio having better low end, remember that your subs will be providing the low end, and will leave any small stand-mount speaker in the dust. While I'm one of those little guys who sells direct (as are most of the high efficiency manufacturers I'm aware of), I certainly understand and approve of your desire to only consider speakers you can audition.

I hope some of that was helpful.

Duke
Audiokinesis (Threads | Answers | This Thread)
Click to expand...


@ Keith,

There's alot of conjecture and error's in that quote , this is only going to mislead other members,
I'm sure Duke would love to have that one back,

@Rob,

Could you please change the word efficiency to sensitivity, you are discussing speaker sensitivity when saying 90db@1w/m , speaker efficiency is a totally different can of worms .. :)
 
Clipping damage speakers too........ :)

BlueFox said:
Power is like money or horsepower. More is better.

For 4 ohm speakers, I prefer 1200W/ch. I found with 800W/ch I was clipping. Of course, I have also found with 1200W that while there was no clipping, speaker damage can occur if too loud. Choose your poison, as the saying goes.
Click to expand...
 
Yes it does, but a good amp design will reduce the output and soft clip (for lack of a better term), which provides a warning to back off ASAP.
 
OK, let's try this:

If the listening distance is 3 meters, and the level falls off in inverse square (it wouldn't in an anechoic space, but perhaps room reinforcement will allow this?), then to get that 93 dB at 3 meters, you need 8x the power, or put another way the volume at the listening position will be about 84 dB with 1 Watt. Then 100 W would give 104 dB peaks, 200 W 107 dB peaks. That's assuming an average volume of 84 dB, which believe me is very loud, as I said louder than the average volume of a typical symphony orchestra in a prime listening position. Also, virtually every recording is at least a little bit compressed simply because each piece of hardware in the recording chain will resultin some compression (especially the microphones)
 
rbbert said:
First, what volume levels should we be hoping to achieve? I've read that a typical symphony orchestra at the 10th-15th row in the audience will reach peaks of 105-110 dB when average levels are around 80 dB. I well remember a Grateful Dead concert in a theater in 1976 where I was in the sound booth and the sound man was checking his sound level meter: peaks of about 112-114 dB, average about 90 dB (I'm assuming that's louder than any of us want to achieve at home? It's certainly louder than I want).

So if a typical 2,3, or 4 way dynamic speaker has an efficiency of about 90 dB/W/m, in a typical listening room with a mix of reflection, absorption and diffusion, what power per channel (remember there are 2 speakers, so we're really talking about 93 dB/(W x 2)/m) do we need to reproduce the symphony orchestra or the Grateful Dead concert? How do we know how much the room reinforcement will amount to, and therefore how much volume will fall off with distance from the speakers to the listening position?
Click to expand...

You lose 6db for every doubling of distance with a point source speaker, so at 3-4M typical listening distance , you will have to subtract up to 12 db. It's best in discussion to leave out the variable of room gain. Basically it's not how loud, but how loud can you go to reproduce faithfully all of the dynamics of the recording , an unclipped peak of 110 db will not phase you if distortion is low.

All recordings have to have added compression if not it will sound like crap on 99.9% of all systems, Hi-Fidelity ..?


Regards
 
BlueFox said:
Yes it does, but a good amp design will reduce the output and soft clip (for lack of a better term), which provides a warning to back off ASAP.
Click to expand...


Safety kills dynamics, the most alive and dynamic of amplifiers will have no such limiters, I tend to stay away from big amps loaded down with gizmo's ...
 
rbbert said:
OK, let's try this:

If the listening distance is 3 meters, and the level falls off in inverse square (it wouldn't in an anechoic space, but perhaps room reinforcement will allow this?), then to get that 93 dB at 3 meters, you need 8x the power, or put another way the volume at the listening position will be about 84 dB with 1 Watt. Then 100 W would give 104 dB peaks, 200 W 107 dB peaks. That's assuming an average volume of 84 dB, which believe me is very loud, as I said louder than the average volume of a typical symphony orchestra in a prime listening position. Also, virtually every recording is at least a little bit compressed simply because each piece of hardware in the recording chain will resultin some compression (especially the microphones)
Click to expand...

Whats the reference Sensitivity ....?


There are other factors involved than just amp power, VC induced distortion and speaker compression itself are other limiting factor. If one listens to a lot of recordings of live musicals , they require tremendous amt of power and large speakers to sound "real" , the human voice is tremendously demanding to reproduce, much more than any Symphony.

There is also the issue of amp recovery and stability when driven to near peak power, IMO, it's best to have an amp 3 times the calculated power requirement for best sonic' s...
 
Challenges in Faithful Reproduction of Musical Peaks: A Power Amplifier Designer's Perspective Article By Simon Thacher Ph.D. Of Spectron Audio

Real Life Speaker Loads
The ability of an amplifier to produce undistorted dynamic passages of music is frequently mistaken as its continuous (rms) power output rating. However, this specification is useful only to approximate the amplifier's ability to reach the desired loudness of the sound at the listening position — and no more. Alan Lofft from Axiom Audio has shown in Enjoy the Music.com [SUP](1)[/SUP] that if you want to reproduce the illusion in your living room of standing next to a grand piano, then peaks of 109dB would be required. To reproduce realistically a peak loudness of 109dB using the speaker with a sensitivity of 88dB to 89dB located 12 feet from the listening chair, the amplifier must produce about 400 watts peak power. To reproduce realistic peaks of a rock band, the amplifier must produce 4000 watts of peak power. Nearly the same power capabilities are needed to approximate the realistic experience of a symphonic conductor at the podium.
These projections are accurate only if the speaker in question has purely resistive impedance. However, loudspeaker loads comprise complex impedances with both resistive and reactive (capacitive and inductive) components. Such impedance can be depicted as a vector with its magnitude (modulus) and angle (phase), and both vary with frequency. In general, the voltage and current waveforms, in complex impedance load, are out of phase with each other and therefore, to characterize accurately a speaker's load impedance, both modulus versus frequency and phase versus frequency plots must be known. Frequently, the phase angle is much more crucial to the speaker load than the modulus alone. Their peaks and dips, as a rule, do not coincide with each other. Because of those disparities, the resulting actual load can be very severe at frequencies that would not be intuitively obvious from looking at the separate plots.
To deal with this phenomenon, Keith Howard [SUP](2)[/SUP] introduced the figure of merit he has labeled Equivalent Peak Dissipation Resistance (EPDR). This is, simply, the resistive load that would give rise to the same peak power device dissipation as the speaker itself. Using EPDR as a figure of merit, the speakers can be compared directly with each other. It is an excellent idea, and John Atkinson of Stereophile has supported its use [SUP](3)[/SUP]. However, speaker manufacturers are not utilizing it, and amplifier manufacturers are not demanding it.
Using the B&W 805 speaker, with 87.5dB/W/m sensitivity, and the powerful Music Fidelity amplifier, Howard did a number of measurements of produced peak SPL from a few recorded classical pieces. He found that peak SPL can be as high as 120dB at 10 feet from the speakers. The measured peak power at this peak was 3.4 kW. While this output is extremely difficult to achieve we still should remember that B&W 805 is only a bookshelf speaker (albeit an excellent one) and the comparison with more difficult-to-drive speakers would be most instructive. For example, the estimate for B&W 803D for the same recordings is that its peak power requirement would be as high as 7 kW. Many speakers have even more reactive loads making truly enormous demands of the amplifier power delivery.






Regards ...



 
To understand speaker spl in relation to undistorted power, the sensitivity across the entire frequency range and phase angles from reactive loads must be considered for any given speaker.

IMO total and instantaneous current are very key. In this regard, power can be extremely misleading on its own. Without immediate current available for transients and current reserves available for low impedance conditions (with reactive loads causing, bad phase angles etc.) you lose dynamics and get distortion. Rated Power derived from high voltage is a paper tiger. Some amps with a couple hundred watts can punch much harder and sound much better than ones with much higher rated watts rms.
 
FlexibleAudio said:
To understand speaker spl in relation to undistorted power, the sensitivity across the entire frequency range and phase angles from reactive loads must be considered for any given speaker.

IMO total and instantaneous current are very key. In this regard, power can be extremely misleading on its own. Without immediate current available for transients and current reserves available for low impedance conditions (with reactive loads causing, bad phase angles etc.) you lose dynamics and get distortion. Rated Power derived from high voltage is a paper tiger. Some amps with a couple hundred watts can punch much harder and sound much better than ones with much higher rated watts rms.
Click to expand...


low impedance current drive is what would seperate them.....

Audioseduction said:
Guys, what weight are we talking about A or C?
Click to expand...


Most likely C- weighted
 
What no love for B and D weighting. :)


There is is no difference between them at the center frequency (1K) used to test sensitivity , in discussion most are referencing "C" .....


When measuring "music" playback always "C" ...........




regards
 
A-weighted decibels are an expression of the relative loudness of sounds in air as perceived by the human ear. In the A-weighted measurement, the decibel values of sounds at low frequencies are reduced, compared with unweighted decibels, in which no correction is made for audio frequency. This correction is made because the human ear is less sensitive at low frequencies below 1000 Hz and high frequencies above 4000 Hz. Our lower sensitivity in the low and high frequency ranges explain why we can tolerate higher volume levels of lower and higher frequencies than we can the midrange frequencies.

C-weighted decibels express the frequency sensitivity of the human ear of sounds in air at very high sound pressure levels. The C-weighted scale is quite flat and includes much more of the low frequency range of sounds than A-weighted or B-weighted measurements. The C-weighted measurement is occasionally used when measuring signal to noise ratios of audio equipment because of the flatter filtering curve that includes the low frequencies of the audio spectrum but more often we see A-weighted measurements for audio testing purposes.


SS4_A-B-C_Weighting_Curves(1).jpg
 
a.wayne said:
Could you please change the word efficiency to sensitivity, you are discussing speaker sensitivity when saying 90db@1w/m , speaker efficiency is a totally different can of worms .. :)
Click to expand...

Actually I find that sensitivity has the greater number of worms per can. Efficiency is a more useful term as it tells you how much power is actually making the sound. Sensitivity does not do that. The former is more useful if you have a tube amplifier, wherein the power is more expensive and the amp generally does not double power as the load impedance is cut in half (which is different than saying it can't behave as a voltage source, many tube amplifiers can). Sensitivity is more useful when dealing with transistor amplifiers as doubling power with half the impedance of the load is more common.

Here is the math on a 90 db loudspeaker:

90 db at 1 watt/1 meter (efficiency) is the same as 90 db 2.83 volts/1 meter (sensitivity) if the speaker is 8 ohms, because 2.83 volts into 8 ohms is one watt.

If the speaker is 4 ohms with 2.83 volts at the input, then the power is 2 watts. So a 4 ohm speaker is thus 3 db more sensitive (93 db instead of 90 db) because it is being driven by twice as much power. Talk about a can of worms! Most people don't realize this at all. In a nutshell, a speaker manufacturer can make the speaker appear easier to drive by reducing the impedance (paralleling drivers) because as the impedance goes down, the sensitivity goes up. However the speaker becomes progressively more difficult to drive; generally speaking speakers with higher efficiency are considered easier to drive!

Its to no-one's advantage to make the speaker harder to drive regardless of the amplifier technology. It simply means that the amp will make more distortion to do its job, and that distortion is audible. For this reason higher impedances and higher efficiencies are desirable. If your goal is high end audio reproduction, there really are not much in the way of good arguments for lower impedance speakers, as they can stress any amplifier (and you can see it in the specs of any amplifier) which results in distortion. IOW a simple way to get any speaker to seem smoother and more detailed is to raise its impedance even if you are running solid state or class D.

Distortion has to be taken into consideration in this discussion. The simple fact is audio gear makes distortion and the ear translates distortion into tonality. Certain distortions (higher ordered harmonics) are also used by the ear to sort out how loud a sound is. So with greater distortion the system can sound considerably louder than it really is. This is why we can stand to sit in front of an orchestra playing peaks of 110db, but doing the same at home will drive us out of the room with peaks of 'only' 100db.

It is thus the mark of a good system that it will not sound loud at almost any volume. That is to say if you are sitting listening to it, it might sound perfectly normal, but you find that in order to be heard by someone right next to you, you have to yell.
 
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