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Post by MartinT on Jul 22, 2014 8:58:13 GMT
It was Musical Fidelity who started promoting the idea that far more amplifier power is required for real-life dynamics and natural music reproduction, without clipping or limiting, than had been standard practice up until then. I'm sure the big American muscle brands did something similar in the US, but I remember it being all over the British press at the time. This was the time when a 40Wpc amplifier was a fairly standard offering. It's a sobering exercise analysing your real requirements using the standardised formula for amplifier power calculation, so I knocked up an Excel spreadsheet to demonstrate the idea. The only variables you need in order to perform the calculation are: - Distance between the plane of your speakers and the plane of your listening position
- Your speakers' sensitivity
- The required maximum SPL loudness at your seating position
The first two are simple measurements, the last one is subjective, but easily verifiable with a sound pressure meter, such as the Radio Shack one that I use (shown below). Set it to C weighting, peak reading, and read the peaks when you are playing at the loudest volume you normally listen to. For me, orchestral peaks often give a higher reading than anything in rock music, but it will depend on your preferred listening.
The formula is Power = 10^((SPL - Lsens - 20 Log (1 / Dist)) / 10)
If the resultant amplifier power reading at 0dB (= near clipping) or 3dB is greater than your real amplifier's specification, then you do not have adequate power for your speakers, listening distance and preferred loudness. This happens more often than is realised! I would suggest that 6dB gives a safe headroom, 10dB gives total peace of mind.
Here is an example for my system. 100dB is extremely loud, but just the odd peak is getting there. Remember, the more dynamic your system's performance, the more headroom you need for those highest peaks if you are not to be limiting them. My total peace of mind figure is 625W, which I only just have. As I said, sobering! |
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Post by danielquinn on Jul 22, 2014 9:12:54 GMT
Interesting , but I am struggling what to make of M/F position .
100 db is to loud for comfortable listening . My screaming baby hits 105 [ I have a phone app ] . I would not want to listen to genesis at 100db, unless I was at Madison square garden .
Given that 95% of people must listen 2.5 m and have speakers at or below 90db and less than 1% will have power amps at 625watts , I am confused as the efficacy of this test . Especially as you say "real requirements" thereby inferring that less than 625 watts will lead to loss of fidelity .
And anyway , surely room size if far more important that distance from speakers ?
It sounds like m/f makers of big amps , hit on means of making audiophiles paranoid  { lack of them surely } Not enough watts get a musical fidelity
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Post by Deleted on Jul 22, 2014 9:50:52 GMT
The problem is that most listening actually uses only a few watts. In normal rooms with say 90db plus speakers were you sit no more than 2m away, 40/50w is sufficient in practice. You won't want concert hall levels if you don't want to upset the neighbours. MF were promoting those mega watt amps at the same time as selling a low powered class A model. They also marketed some high efficiency speakers at one time suggesting you needed these plus 100s of watts. I regard it as mostly a marketing move by AM to promote his more expensive products. Admittedly at the time you got a lot of watts per £. Their current mega class A amps are firmly high end pricing. A brand that has strangely gone out of fashion and received a lot of brickbats.
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Post by danielquinn on Jul 22, 2014 9:53:55 GMT
Brickbat by Billy Bragg is mine and my missus song , I just thought it was a daft word , didn't know it meant something - ]
ta for that .
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Post by pinkie on Jul 22, 2014 9:56:10 GMT
What's really interesting, and I think few people appreciate is that db is a log scale and small changes in value have a big impact. So running the calculations for probably my typical situation - same sensitivity, 90db listening level (peak) 2m speaker distance and allowing 3db headroom gives 8 watts. The numbers I ran for Wonky were 2m distance 90db sensitivity 4db headroom and required 100watts. But I think his speakers are nominal 85db/w (and manufacturers usually err on the optimistic side) so taking the headroom back down to 3db would give 318 watts. A perhaps more normal (for me) 95db peak, say 85db average (I line up with Peter Walker on this one) would give Wonky a need for 85w. You sure those 25w monoblocks of yours are going to do it Wonky?  |
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Post by danielquinn on Jul 22, 2014 10:01:50 GMT
I would suspect most people on here know db is a log scale , I bloody hate them , I want them abolished ,what's wrong with scales with equal increments !!!!!!!!!! If something is twice a loud , it should have twice the db , !!!!
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Post by MartinT on Jul 22, 2014 10:09:19 GMT
Interesting , but I am struggling what to make of M/F position .
100 db is to loud for comfortable listening . My screaming baby hits 105 [ I have a phone app ] . I would not want to listen to genesis at 100db, unless I was at Madison square garden .
Given that 95% of people must listen 2.5 m and have speakers at or below 90db and less than 1% will have power amps at 625watts , I am confused as the efficacy of this test . Especially as you say "real requirements" thereby inferring that less than 625 watts will lead to loss of fidelity .
And anyway , surely room size if far more important that distance from speakers ?
It sounds like m/f makers of big amps , hit on means of making audiophiles paranoid { lack of them surely } Not enough watts get a musical fidelity
There is no doubt that MF had an agenda, as a builder of big butch amplifiers. However, you can't dispute the maths.
I never claimed "100dB makes for comfortable listening", to paraphrase you. I spoke specifically about orchestral peaks. Have you ever heard an orchestra at full pelt from about 6 rows back in the stalls at the Festival Hall? I can tell you that that would be difficult to reproduce in your listening room, but I like my system to have a good bash at it.
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Post by MartinT on Jul 22, 2014 10:10:32 GMT
The problem is that most listening actually uses only a few watts. Agreed, but that's not what we are discussing here. It's the ability of your system to handle peaks without compression or clipping. |
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Post by Deleted on Jul 22, 2014 10:13:02 GMT
My personal take on this is simple:-
A cynical ploy of MF's part to sell you their superchargers from a few years back.
Overall wattage should not be the deciding factor in purchasing an amplifier, it is merely an indicator.
The transient current response is far more realistic way of ascertaining whether an amplifier is suitable for your pair of speakers. Along with the impedance speaker matching. Think torque over horse power.
You can either use very efficient speakers say 96dB + sensitivity and a high quality lower powered amplifier sat 8-12Wrms of SET or class 'a' solid state,(though a lot of guys use a hybrid class 'd' with their horns in the summer)
Or you can use a less sensitive speakers (88-91db) and use a medium to high power quality solid state.
Personally I prefer this approach, we feel it gives a greater sense of being there, however both methods are valid.
For most people who' rooms are between 24 feet long and 14 feet wide, speakers will be between 7 and 12 feet away, genuinely if you listen below 95dB then 120-150Wrms of a high quality will more than be sufficient with lower sensitivity speakers.
For higher sensitively speakers the very most I would suggest around 45Wrms would be able to cope and then some.
Obviously if you listen at higher levels in domestic environment, then I would suggest hiring a PA rig or a PMC / Bryston combo which will scratch that itch!
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Post by welder on Jul 22, 2014 10:14:26 GMT
Calculations such as these are not going to please a lot of audio enthusiasts! Thanks for the spreadsheet Martin. There is this on the net; similar but once again, it doesn’t take into account some quite important variables. myhometheater.homestead.com/splcalculator.htmlI can’t help finding some irony in that info like this is to be found for home theatre systems and pro audio, but not in general on audiophile sites. Of course one gets the ‘well it’s the room that matters’, or ‘my amp doesn’t clip until it’s virtually flat out’ and more reasonably general preferences regarding listening levels. It isn’t in general practicable for many enthusiasts to measure their system to find out where the onset of clipping is for a particular recording, and sure, a lot of the less dynamic stuff isn’t going to stress the system at relatively modest listening levels. We found however that some of us who thought we rarely listened above say 80db were in fact quite far out, especially those who listened off axis a lot. I quite often hit 100 db when I have one of those only a bit of Guns ‘n’ Roses will hit the spot moments and we found this to fairly common with our small group. One of us had a 12m by 5.5m listen space in which 110 db wasn’t that loud. Another interesting discovery was the advertised speaker efficiencies weren’t very accurate, usually quoted higher than measured. It seems that quote the most efficient driver in the array is not uncommon. Loudspeakers like Watts if there are required to produce dynamics; even with all the ifs and buts. I’ve got some more bad news regarding Dac perfomance which I would like to get on the forum when I have more time |
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Post by Deleted on Jul 22, 2014 10:15:29 GMT
Oh I forgot, I use a 120Wrms amplifier which in my room can generate well over 110dB totally distortion free and with no dynamic compression (other than that of the recording being played) should you too, so 0.5Kw is not really required  |
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Post by MartinT on Jul 22, 2014 10:17:26 GMT
I am confused as the efficacy of this test . Especially as you say "real requirements" thereby inferring that less than 625 watts will lead to loss of fidelity .
Just caught this bit - you need to read what I've written, DQ 
There is no inferring that <625W would lead to a loss of fidelity. At 10dB headroom, that power level gives me excellent headroom so that I'm nowhere near clipping nor close to any non-linear region of operation. The actual figure for loss of fidelity (depending on how linear the amplifier, what power reserves it has etc.) is between 63 and 125W. |
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Post by MartinT on Jul 22, 2014 10:21:41 GMT
Overall wattage should not be the deciding factor in purchasing an amplifier, it is merely an indicator. Of course not. This is an interesting exercise, nonetheless. I like plenty of headroom as it's one less thing to destroy your ability to reproduce the real dynamics in music. No matter what its other attributes, a low power amplifier is going to give you a more limiting envelope of operation. |
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Post by danielquinn on Jul 22, 2014 10:23:31 GMT
I cant think of anything worse that trying to recreate the real life sound of an orchestra in a room 10% of the normal size.* SPL or dynamic headroom is not all there is to hifi and invariably real life spls' or dynamics are not available on vinyl .
* And this is not because I think all music without lyrics is rubbish , which I do . |
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Post by MartinT on Jul 22, 2014 10:23:43 GMT
should you too, so 0.5Kw is not really required The actual figures from my chart indicate 63 - 125W. So I've got headroom! |
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Post by pinkie on Jul 22, 2014 10:24:03 GMT
I think the possible double count in the MF calculations is to add generous headroom on top of a peak value. A peak is a peak. It's the maximum. So if 85db is normal comfortable average, with a brief peak to 100db, for why how where or when do you need even 3db headroom (twice as loud as your peak)? 10db? - you are having a bubble! Does depend a bit on how "peak" is "peak". But even so, as I remember we agreed before, a lot of people under-amp  |
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Post by Deleted on Jul 22, 2014 10:34:38 GMT
Still adamant you can generate a far more complete and controlled sound in your room will a lesser powered amplifier Martin than you are currently using!
One item no one has mentioned thus far, amplifier bandwidth for a quality sound a minimum of the fifth harmonic is required to generate a truly realistic sound both in total head room and dynamics, yet be able to render tonal textures with correctness and true depth.
Which then starts an interesting debate as human hearing has a max bandwidth (when young) of 23Khz (Though a s/n of close to 130dB is possible) and tails off quite markedly as we progress in years. So why would we need 100Khz bandwidth?
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Post by MartinT on Jul 22, 2014 10:44:47 GMT
I think the possible double count in the MF calculations is to add generous headroom on top of a peak value. A peak is a peak. It's the maximum. So if 85db is normal comfortable average, with a brief peak to 100db, for why how where or when do you need even 3db headroom (twice as loud as your peak)? 10db? - you are having a bubble! Does depend a bit on how "peak" is "peak". But even so, as I remember we agreed before, a lot of people under-amp The numbers speak for themselves. I created the spreadsheet and no-one is saying you *have* to have more than 0dB headroom, it means though that you run the risk of non-linearity in your amp as the peaks will just be touching the clip point. |
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Post by MartinT on Jul 22, 2014 10:47:03 GMT
Still adamant you can generate a far more complete and controlled sound in your room will a lesser powered amplifier Martin than you are currently using! Hah - just wait until I get my Sheffield Lab James Newton Howard and Friends out with the awesome drums! |
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Post by Deleted on Jul 22, 2014 11:15:11 GMT
I know the track well having dealt with many audiophiles over the years.
More than up for the challenge Martin any time.
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{ lack of them surely } Not enough watts get a musical fidelity 
