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If I know the effieciency of my speakers, their average impedance, and the power out of my amp + my room size? Do I need more information? I know this is a rough calculation, but I am way-overpowered!
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This measurement gets my vote, especially if the distance to your nearest neighbor is measured in miles/kilometers......and there is no ordinance concerning noise in the town.
My system is rated at three squad car power. That includes the seargent's car. Harry
n
... as "ordnance concerning noise" would be a whole different ballgame....
DevillEars
. . .and possibly more fun too!
... there is an equation that goes something like this:Where factor definitions are:
x = sensitivity rating of speakers in dB
y = amplifier power in dBW (not simple Watts)
z = distance from speaker in metresThe dB peak listening level = (x+y)-5(z-1)
(Remember that the ‘5’ comes from the 5dB loss for every metre moved away from the speaker and the ‘-1’ allows for the fact that the speaker’s dB sensitivity was measured at a distance of 1m).
Then there is a table that helps to convert Watts (RMS values) to dBW:
10 = 10
20 = 13
50 = 17
63 = 18
79 = 19
100 = 20
126 = 21
156 = 22
200 = 23
251 = 24
316 = 25
400 = 26Now, by way of example, here is the calculation I used for my set-up:
a) Speakers : Tannoy D700
- Nominal Impedance : 6 ohms
- Quoted Sensitivity: 93dB at 1m
- Listening Distance: ~3 metresb) Amplifier: Jeff Rowland Model 201 monoblocks (x2)
- Output into 8ohms : 250 watts per channel
- Output into 4ohms : 500 watts per channel
- Output into 6ohms : 375 watts per channel (interpolated)c) Calculation as per the formula:
- From Amp Power Table: 25dB
- Speaker Sensitivity : 93dB
- Maximum SPL (1metre): 118dB (ie: 25 + 18)
- Distance Attenuation: ((3-1) x -5) = (2 x -5) = -10 dB
- Peak Listening Level: 108dB (ie: 118 - 10)Where "Peak Listening Level" is at 3 metres from the plane of the speakers.
.......I have an amp rated at 200w/channel into 8 ohms & another rated at 70w/channel into 8 ohms.Why does the 70w/channel amp sound & measure much louder than the higher rated amp?
Isn’t the conversion from RMS watts to dBW only a VERY rough guide?
Smile
Sox
Howdy stranger! I assume at the start that your question "Why does the 70w/channel amp sound & measure much louder than the higher rated amp?" is based on retaining the balance of the system as a constant in the two listening experiences?Firstly, the Watts to dBW conversion is accurate in electrical terms provided the input power rating is accurate to start with...
Amplifier manufacturers are guilty of, shall we just call it "loose interpretation", of the definitions of "output power" and "watts".
Similarly, speaker manufacturers can also sometimes quote misleading specs for their speakers - particularly that lovely term "nominal impedance" and also sensitivity.
The amplifier-related anomalies can be seen - using extremes - between the following "usages":
a) Continuous output power in Watts into an 8 ohm load, all channels driven, and measured across a frequency spectrum of 20Hz to 20KHz.
b) Peak Music Power Output (sic)
Now, a) is how power ratings SHOULD be quoted - by inclusion of parameters such as:
- a specified duration (in this example = "continuous")
- a specified speaker load (impedance in ohms)
- a specified number of active channels sharing the power supply
- a specified frequency range (in this case, the full audio spectrum)On the other hand, b) omits all of these parameters and, as a result, it is virtually impossible to verify/disprove the claimed rating. Judging by some the numbers they come up with, I'd hazard a guess at some of the values to the parameters above as used for PMPO derivation:
- a specified duration = <1 millisecond (to save the power supply from exploding)
- a specified speaker load = somewhere between 2-4 ohms
- only a single channel active
- a specified frequency range = an interval of approximately 5HzUsing these blatantly bullshit parameters allows these boombox manufacturers to quote PMPO outputs somewhere in the "Bevawatt" regions... :-)
Now, that comparison was based on hyperbole and looked at two extremes. Coming back to your question, I would check out the parameters mentioned above for each of the two amps - and using the first case example:
1) a specified duration (in this example = "continuous")
2) a specified range of speaker loads (impedance in ohms) (eg 8/4/2)
3) a specified number of active channels sharing the power supply
4) a specified frequency range (in this case, the full audio spectrum)These parameters will provide a fairly good guide to the quality and reserves of the power supply(ies) used, while other information (if available) will help to assess the psycho-acoustic aspects (such as frequency-linked responses with peaks/troughs that might sound subjectively louder on one amp vs t'other), etc.
So, come back with the results of the comparison and research and then there might be enough information to answer the question. (You made no mention of brand/model references for the two amps).
I trust you are both well and have quaffed the first frothy of the day?
DevillEars
......Over Xmas I was toying with my system as I wanted to integrate my 2 channel and main HT setup.The amps I was using to see how they would perform in two channel mode with my main speakers are.
• Musical Fidelity A300 integrated 150w x 2
• Musical Fidelity A308 integrated 150w x 2
• Pioneer VSX-AX10AiG receiver 200w X 7
• Denon AVR 3805 120w X 7
• Yamaha RX-V2400 Receiver 120w X 7
• Opera Audio Consonance Cyber-800 mono blocks 70w X 2I am pretty sure ( no I haven’t looked at the manuals) all the amps, except the Cybers, are rated 20Hz – 20KHz into 8 ohms. The Cybers are rated <10Hz – 100KHz into 8 ohms.
Now in order of performance (which coincidentally correlated to how loud they would play as well)
1 The Cyber mono blocks were far superior in every way.
2 The A308 (just over the A300)
3 The A300
4 The Pioneer AX 10
5 The Yamaha 2400
6 The Denon 3805Now the Cybers can play at concert levels continuously and sound way better than anything else I have. The MF gear can not quite reach the loudness of the Cybers and get VERY hot when pushed hard for 30 – 40 mins but I did live with them for a while before the Cybers.
All the receivers simply can’t play at concert levels and the auto overload/heat circuit trips when they are pushed (That is in two channel mode – load em up with 5 speakers and they run out of puff real quick)My speakers are full range and rated at 90db 1w @ 1 metre and between 5 to 6 ohms. ( I’m on a new PC and currently can’t access my old data to give the measured details I have on the exercise)
I also have auditioned a Audio Aero Capitol Power amp with the same speakers etc ( 12 months ago though) and it is rated at 50 w and it also could play at concert levels continually. ( I was a tight-wad and passed on the purchase even though I was very impressed)
So DE I reckon the rated wattage of a lot of gear is a load of bollocks. ( I know receivers are notoriously over rated )
PMPO ratings are meaningless for musical applications. My powered PC speakers are rated at 480w PMPO and I reckon they are about 8 to 10 w in realistic ratings.
IMHO most speakers will sound wayyyyyyyy louder in room than out in the paddock. ( I have tried that with Paradigm Studio 100’s - they can play very loud in room but are no good in the paddock)
Um, yes, I am having a frothy one & we are all very well here indeed thank you.
Cheers to you and your three lovely ladies.
Smile
Sox
After seeing your first post and before seeing this one, the first thing that came to mind was that the 70-watter was likely a tube amp and the 150-watter was solid state. I see that initial thought was right. From experience with both SS and Tube amps, I have come to this rule of thumb: a tubed amp sounds about equal in volume to a SS amp at about half the wattage of the SS amp. I have found this rule of thumb to be pretty true. The question becomes why is it so. My guess is that tubes can be pushed into higher power before sounding stressed (i.e. before the generated distortion becomes objectionable). It is the fundamental nature of the difference between tubes and SS. It also explains why I like the dynamics of tube amps much better than SS. Tubes respond dynamically more musically than SS. This explanation is independant of the pure electrical calculations found in this thread. If you follow those calculations, the 70-watt tube amp is less capable of generating SPL's than the 150 watt SS samp. But I'll bet the 70-watter sounds better and more dynamic.
Mark
... of those amps...I'd be prepared to put money on it that the "order of performance" shown would correlate very closely with the various amps' ability to come close to "doubling wattage into halving load" - with the Cyber monoblocks a definite winner (separate power supplies are "finestkind" in audio).
What would also make interesting reading would be a comparative set of frequency response curves (dB at frequency) to identify any potential culprits for the "psycho-acoustic loudness prize" (some amps have peaks in the midrange (usually upper mids) that tend to create a false impression of high playback levels because the human brain perceives this band more clearly than the balance.
Having compared integrated stereo amps with stereo power amps and with monoblocks - I'm convinced that the more "dynamic headroom" there is in the power supply coupled with less need for "power sharing", the better the end sound quality will be.
Interesting note: I've always found that a high quality and neutral sounding system will not sound as "loud" as one of lower sound quality and a lack of neutrality to the sound. By "loud" in this context, I mean that the sound results in me wanting to get up turn down the volume (or, in really extreme cases, leave the neighbourhood entirely...)
Oh well... it's approaching 16h00 here, so I suppose you're already in the arms of Morpheus and will only see this in the morning -
"What would also make interesting reading would be a comparative set of frequency response curves (dB at frequency) to identify any potential culprits for the "psycho-acoustic loudness prize" (some amps have peaks in the midrange (usually upper mids) that tend to create a false impression of high playback levels because the human brain perceives this band more clearly than the balance."
Well, you got that right, look at huge lift in the midrange (into a real speaker load as a result of ohms), there are many others where that came from.
> The dB peak listening level = (x+y)-5(z-1)This is completely wrong
1) You're listening in a reverberant space and probably far beyond the critical distance at which direct and reverberant sound field presures equal.
For typical speakers in a typical room this happens at 2-4'. Going farther does not result in an appreciable volume decrease.
2) If you were in an open field, sound presure from point sources drops with the square of distance which is to say output decrease in decibels is 20 log distance in meters compared to the output at 1 meter. Going from 1 meter to 2 is 6dB, 1 meter to 4 12dB, etc.
Line source loss is proportional distance so the number would be 10 log distance.
You need to work with room volume and Rt60 to get a meaningful number.
You're partially right...That was an oversimplification - and the full unsimplified version that takes into consideration room modes, etc is unnecessarily complex in the context of the question posed.
There is an axiom that goes something like this:
"It is better to be approximately right as soon as possible than to be 100% accurate six months too late!"
In the same vein, the slightly more accurate version - still ignoring room modes - would be a four-step calculation:
a) Speaker Sensitivity PLUS
b) 10 x Log 10 Watts LESS
c) 20 x Log 10 Distance in Metres PLUS
d) Delta in SPL for a Stereo Speaker Pair (doubling) = 3dBSo, for a 90dB speaker pair and 100 wpc at 3m:
90 + 20 - 10 = 100dB for 1 speaker and 103dB for a pair
Versus originally posted formula:
90 + 20 - ((3-1)x5) = 100dB for 1 speaker (and 103dB for a pair)
The answers appear to be the same.... Hmmm....
> That was an oversimplification - and the full unsimplified version that takes into consideration room modes, etc is unnecessarily complex in the context of the question posed.If you want a useable simplification in typical rooms the best thing to do is to throw out the distance. Otherwise you're going to end up with an answer that's off by 6-10+ dB (implying you need 4-10X the amplifier you actually do).
I got curious about this once and measured my center channel (left and right speakers were actively tri-amplified dipoles which were too messy to make sense of). It took .88 VRMS to produce pink noise at 75dB SPL at my listening position 9' distant, which is the same thing as 75 + 20 log (2.83/.88) + 20 log 2.74 meters = 93.9dB/2.83V/1 meter sensitivity.
Since actual sensitivity is 90-91dB/2.83V/1 meter, the SPL at my listening position is what it would be at .6 - .7 meters distant.
This is in a not atypical 13x19x8' room with some openings to the rest of the house, the center channel on a short stand a couple feet out from the screen wall and no room treatments, just carpet, window treatments, furniture, and other stuff. The center channel was high-passed at 80Hz so most of the gain from front wall + floor proximity was outside the speaker's pass-band.
If you want an actual calculation that's meaningful, you need to start with room volume and Rt60.
Actually, you also need to include the speakers directivity index. Both directivity index and reverberation time (Rt60) are functions of frequency. And even then, the appropriate formula gives a statistical probability, not a precise prediction. And the statistics inslude the assumption there are many overlapping room modes - which is not true below a few hundred Hz in most listening rooms.Given all those complexities, I generally assume the 1-meter anechoic sensitivity or efficiency applies to the listening position,. All the variations get lumped in with the listener's preferences for loudness, preferred music, variations in how compressed recordings may be, etc. etc. Usually if you can make 102dB at full power at 1 meter, you will be happy with the available loudness - though you are probably listening at 82dB on the sound level meter with "slow" response. This does not apply to those who want a rock cencert in the home - they will need another 10 to 20dB, and a good otolaryngologist to fit their hearing aids later. :^)
Also, I would guess your 5 dB falloff for a doubling of distance is an approximation. Theoretically it's 6 dB per doubling of distance under anechoic conditions, so I presume that 5 dB is taking room reverberation into account. Actually room reverbertion would add less than 1 dB at 1 meter but progressively more as you moved farther back. Still, your answer is definitely in the ballpark.Overall nice job, pointy-eared one.
... and it looks something this:dBW = 10 x Log 10 (Watts RMS)
Example: 75 watts RMS
10 x Log 10 (75) = 10 x 1.875 = 18.75 dBW
It helps confirm what I thought.
... if you want...
I got your result. Send it to my email: famcallaway@mail.tele.dkThanks again.
.
DevillEars
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