hakanson@orstcs.UUCP (06/03/83)
#R:rabbit:-150500:orstcs:2900003:000:750
orstcs!hakanson Jun 2 17:03:00 1983
My wife is a speech pathologist, with some audiology background,
and she brought home one of those sound-level meters. We tried
it out with my stereo, and were able to easily get a reading
of 70db with an indicated amplifier output of less than 10 watts/channel
(maybe closer to 5 watts/channel, but I don't recall for sure).
All this through my Infinity RSa loudspeakers, which I never
thought to be particularly efficient. Now maybe we weren't operating
things properly, etc., but I suspect it may have something
to do with the small size (8'x16') of the room. Any theories?
Sorry about my earlier comments about cow colleges. Some of
my co-graduates took offense. We get by.
Marion Hakanson
{tekcad,teklabs,hp-pcd}!orstcs!hakansonray@utcsrgv.UUCP (Raymond Allen) (06/07/83)
Actually, your speakers must not be very efficient. If you were to try to reproduce a symphony orchestra recording at concert hall volume levels (where the musical peaks could exceed 100dB) then, on these peaks, your amplifier would have to produce instantaneous power on the order of 5000 to 10000 watts!!! Although there is little likelyhood that an attempt to produce such power would destroy your amplifier (since the transients are of very short duration) some simple mathematics would indicate that to produce 5000 watts across 8 ohms requires 200 volts. Very few commercial amplifiers use a power supply of this high of a voltage (dare i say none?). The result? Your amplifier will simply clip, and thus distort the output. To be perfectly fair, it is important to note that i have never seen an audio power amp which has power meters which actually give a true indication of the power that the amplifier is producing. All the amps that i see just use a voltmeter on the output with a scale that is calibrated for watts which assumes that the amp is driving an 8 ohm resistive load. Most real-world speakers are quite reactive and, thus, this type of meter is less than useless. The only thing that you can be sure of is that the actual power is less than or equal to (if the load is a pure resistance) the reading on the meter.
gregr@tekid.UUCP (06/08/83)
If you were only getting 70dB SPL from 5 watts this would actually be very inefficient. I suspect that 70 dB only requires one or two watts. This depends on the room size, furnishings, speaker efficiences,etc. For the sake of arguement lets assume 2 watts gives you 70 dB. Since the SPL changes by 3 dB each time you double the power it would take 256 watts to produce 91 dB. Assuming I can still multiply without a calculator. An SPL of 91 dB is very reasonable for home listening except of course for rock music.
caf@cdi.UUCP (06/08/83)
I recently heard Orff's "Carmina Burana" at the Oregon Sympnony. Based on past observations with my sound meter, I rather suspect that the bass drum peaked at over 100 db in one place near the end of the piece. Now, if very much of that number had been that loud I would have had to put my fingers into my ears to attenuate it, but in this case the whump was musically and emotionally very proper and effective. If you are getting only 70db from 1 watt, you'll need 1000 watts to get 100 db. Perhaps you will want to work very hard at making your listening environment very quiet before you get serious about CD's and/or DBX records as reproduction of deep bass at 1000 watt levels would entail considerable expense. BTW, does anyone know the comparative effect of 100 db of low bass compared with the same power level (no weighting) in the midrange (re hearing loss, etc.)? -- Chuck Forsberg, Chief Engr, Computer Development Inc. 6700 S. W. 105th, Beaverton OR 97005 (503) 646-1599 cdi!caf