Rat Shack dB meters- how good?

[colterphoto1]

I had my Radio Shack dB meter out checking some of the lower ranges of my Cornwalls hooked up to new Yamaha RXV2400 (whose 'optimizer' microphone/para eq only goes down to like 200 HZ- what a GYP!) and noticed the following.

With my new receiver in two channel mode, presumably about 120 watts per channel, and it cranked up pretty loud into the Cornwalls (efficiency 98 db/watt/meter) my radio shack meter measured a paltry 94 decibels just a few feet in front of the speakers. I take it that the Yamaha probably puts out close to rated wattage, and that my Klipsch speakers shouldnt' be too far off from rated efficiency, so why did it measure so poorly? Is the Radio Shack meter good only for comparison tests, and not as a pure measure of loudness? Should (and can) it be calibrated for a reasonable sum? Have others noticed this or am I measuring the wrong thing in the wrong way (per PWK)?

Thanks, this is perplexing.

[3dzapper]

The RatShack meter is an OK general knowledge unit. I've had one for thirty years. Back when I was in radio.

94Db Ave is loud. I doubt your amp is even putting out a watt steady state at that level. Do you have VOM? If you do set it on AC and turn up the volume until it reads 2.6V. That is nominally 1 watt. Now what is your SPL? Let us know, I'm interested even if no one else is.

Rick

[WMcD]

I've played with an RS meter and then went on to a better test system. It could be off by a few dB, even according to the instruction sheet.

I'm in agreement with zapper overall. You will need a multimeter to set the amp output level to 2.828 volts (the square root of 8) with a steady sine wave tone. Of course the volt meter may be off a bit too. This will give you the nominal 1 watt reference.

The real issue may be that you have to realize that 101 dB is very, very loud. This what you should be getting at 1 meter, or 39 inches distance. It will drive you from the room.

If you apply 0.89 volts (square root of O.8) you should get 91 dB. This is 0.1 watt and thus 10 dB down.

If you apply 0.282 volts (square root of 0.08) you should get 81 dB. This is 0.01 watt and thus 20 dB down.

Gil

[michael hurd]

What weighting did you have the unit on, A or C?

[formica]

What do the peaks look like? Set it on "fast" and post them with your impression of how loud it is.

I'd say something's is a miss with the meter, if it doesn't go much higher than that. The RS SPL meter aren't pieces of laboratory equipment, but they are "relatively" accurate with overall SPL... esp within the lower frequency ranges.

With Cornwalls and 100W, you should easily pass 110db peaks in room with a music source.

For example, with a similar setup and my sub playing, I get over 115db in room. That is very loud by the way.

Later...

Rob

[michael hurd]

My own analog rat shack meter has seen the high side of 115 db a few times. Very loud! Since I sit only 6-7 feet awaw, a quick turn on the volume knob can be violent. When I was at NOZ's place with his stacked Lascala's, at 1m we were hitting 126 db peaks and sustained 120 db! Even at the listening position, we were still pulling 112 db. I am thinking that somehow your meter is out of whack.

[michael hurd]

I don't know which meter you have, but there is a compensation chart for the Radio Shack analog spl meter. It is not quite linear in the low frequencies but Sv subwoofers have tested several meters and found them to be all similar in response, so they have a chart on how much to add to the reading to make it correct.

http://www.svsubwoofers.com/faq_rscomp.htm

[colterphoto1]

I was using the C weighting, fast and slow (slow is easier to read the peaks, but I realize the needle probably doesn't reach top of peaks). Maybe I just don't understand the linearity (?) of the volume knob, like what does -??dB mean in Yamaha-speak? I will try the aforementioned test with VOM, so I check the speaker leads for 2.6 volts and at that volume position I am putting out one watt, right? Would this be volts DC? SHould this test be conducted with white/pink noise, 1 kHz test tone or something not so 'peaky'? I have a couple of test CD's that would have these available. Is there any danger to amp to playing with no speaker hooked up to this lead?

Rest assured, I'm not trying to test the output of my COrnwalls to destruction, just interested in what level I'm generally listening to and how many watts are being utilized. I'm suspecting that the 10-15 watts you tube and SET guys use is more than adequate. Why then do we have such enormous overhead in our HT receivers? Must movie watching be so much more visceral than the sensation when listening to pure music?

These new motor-driven volume knobs also don't give one the kind of tactile response that old pots do. Seems like they gear them so that the remote-control moron has better control from his position than the user who turns the knob on the unit. If I'm at rack position and want to turn it up, it's like three major cranks on the knob, not a simple twist like in the old days.

[michael hurd]

-db is a reference to maximum, at least that is the way it should be, 0db meaning full output. Leave the speaker hooked up, do not disconnect fom amp and connect meter leads. You would play a steady state sine wave, and set the meter for AC volts, and increase the volume measure 2.83 volts at the speaker terminals. You now have one watt of power from the amp. The meter should read 98 db or very close to, when placed 1m from the speaker on axis.

"Why then do we have such enormous overhead in our HT receivers?" Dynamic range eats up power fast! The difference in sounds from the softest to the loudest is expressed in decibels.

[michael hurd]

Here is a chart that shows how much power is required to produce related sound pressure levels, with differing sensitivity loudspeakers. This does not take into account power compression from low sensitivity loud speakers. Aren't you glad you own LOUDspeakers?

http://home.new.rr.com/trumpetb/audio/dBexamp.html

[colterphoto1]

Hi Michael, another sleepless one, I see! I'll try it out tomorrow with 1 kHz sine wave, VOM set to AC, and meter @ 1 meter on axis. Luckily it looks like my average listening volume is much lower than I thought. Hope to preserve the hearing for years of listening enjoyment to come. I'd wonder what the range of average listening levels is for Klipsch owners. Do we listen to music louder because we can? Or do we just appreciate the power we own and use it judisciously?

[michael hurd]

Compact disc has a thoretical maximum dynamic range of 65 db. This is why to maximize the dynamic range, you need: sensitive speakers, fairly powerful amp, and a quiet background. If we said that your background noise was 40 db, and the minimum queitest sound you wanted to hear 20 db above the noise floor, that would bring us to 60 db. To preserve the dynamic range of 65 db, we would need a maximum of 125 db for peaks.

Now in practice, the dynamic range on a media is rarely ever utilized. It seems nowdays, most cd's use such insane amounts of compression, the average power is very close to the peak power. This means that you can get away with a little less power requirement. So before rushing out to try out these " magical "low wattage amps, regardless of brand or topology, see what the outcome is.

Restricting yourself to 16 watts, would produce 110 db( 98+3^4) on peaks@ 1m, with no extra power for reserve. Assuming you sat 4m from the speakers, you would net 110 - 6= 104 db at absolute wide open. Again, assuming that the noise floor is 40 db, and the quietest sound at 60 db, this would give you a 44 db dynamic range.

Moving to a 1.8 screaming watt amplifier would net you 93 db wide open at the listening position, with a 33 db dynamic range.

[ygmn]

Also remember the room has an effect on the speaker output.....versus what they list in tech specs for speaker....

[3dzapper]

Mike,

My average SPL when I listen, really listen to the Khorns is between 85-90 Db and maybe 95 with a tail wind. I have burried the RS meter with high power SS.

The Heresys seem to peter out over 85Db but I found myself listening to The Dead at 90Db this morning. Those are average SPLs.

At night while I visit the forum, read headlines and do my crosswords, I usually have Music Choice Jazz channel on at around 75-80Db on whichever system is on.

I dfon't like low background music. I find myself straining to hear the music rather than concentrating on what I am supposed to be doing.

[formica]

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On 9/24/2004 2:50:35 AM colterphoto1 wrote:

Maybe I just don't understand the linearity (?) of the volume knob, like what does -??dB mean in Yamaha-speak?

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Many modern volume knobs are based on having "0db" representing "reference" level at the 12o'clock position. If I recall, in the THX standard, this is supposed to represent 105db to 110db peaks. Obviously with high efficiency speakers, the SPL is a lot louder... so you are supposed to calibrate it back down when adjusting each channel level.

I just leave the L&R mains at ±0db and adjust the other channels... but this isn't technically correct. Actually I may rethink this... because even with the volume turned all the way down, I still get some sound out of my speakers.

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Should this test be conducted with white/pink noise, 1 kHz test tone or something not so 'peaky'?

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I'd go with pink noise. BTW, pink noise is quite annoying at high volumes in room... and white noise is unbearable.

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I'm suspecting that the 10-15 watts you tube and SET guys use is more than adequate. Why then do we have such enormous overhead in our HT receivers? Must movie watching be so much more visceral than the sensation when listening to pure music?

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I agree with Michael, the extra wattage helps recreate a more dynamic experience. Given the compression already included in the recording, I rather not restrict it even further.

One important difference between SS and tube is they way they behave when overdriven, as tubes remain much more graceful (pleasant sounding). So pushing a tube amp near (into) clipping is nowhere as annoying as pushing a SS to a similar point. SS needs the extra headroom even more, given this limitation.

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On 9/24/2004 4:19:45 AM colterphoto1 wrote:

Do we listen to music louder because we can? Or do we just appreciate the power we own and use it judisciously?

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I just listen to it louder.

Rob

[D-MAN]

The only source that I know of that actually exercises the available dynamic range is a DVD soundtrack. Their dynamics are specifically expanded (or at least highly-exagerated) rather than compressed.

They go from 3mW to 300Watts on my amp in the blink of a cannonade. That is the only source material that I am concerned for the speakers frying...

DM

[DrWho]

Just a passing though, how is the battery in your meter doing? I was once mixing a live concert and the guys on stage kept complaining that the monitors needed to be louder and I was like heck no, your stage volume is already deafening. They didn't believe me so I busted out the old Rat Shack meter, hoping to show them their stage volume was around 115dB. Well when I busted out the meter, it was showing around 90dB on the peaks! For a second there, I couldn't believe my eyes and the guys on stage were like ya ok, stupid kid go turn the monitors up. I then put the meter onto the battery setting and noticed that the battery was basically dead. I went back to the board, turned the monitors down and put a new battery in the meter (it's funny when you do the opposite of what the band asks and then they think it sounds better and thank you for doing what they asked, lol). I went back up on stage and was measuring volumes of 118dB solid! I was peaking out above 126dB everytime the drummer smashed his snare...man it was deafening. I then told the band that I had turned down the monitors when I went back and I told them that FOH needs to be at least 20dB louder than the monitor overflow...I usually mix FOH around to be around 110dB on the loudest passages (peaking at 115dB) up front in the first row...Assuming that 10dB of the stage volume wasn't making it into FOH, I turned their monitors down to a 95dB stage volume (this also involved turning down everyone's amps). I was later thanked by the lead singer for having the best monitor mix he's ever had (and he had been playing pro for like 15 years).

Anyways, sorry to get carried away there with a story, lol. Michael Hurd mentioned being 20dB above the noise floor and I was thinking that maybe your battery was low if you were measuring such a low volume when you felt it was loud.

I also wanted to mention that you would be surprised how loud sounds can get. I personally don't like listening to music much louder than 90dB, otherwise i'll notice that my ears start to get plugged up (aka earwax build up cuz it's too loud). Also, there is a difference between loud and shrill (i use the term shrill loosely). Two tones could be the same volume, but one can sound louder than the other. Part of this is due to the fact that our ears are more sensitive around the 3kHz region and also that certain tonalities sound louder as well (we can tell when someone is talking loud and talking quiet, even if we measure both voices to be the same dB).

[colterphoto1]

WOW, this is FUN, didn't do the whole test (reference 1 watt to 2.6 volts AC with pink noise), but I did put fresh AA in meter, measured one metre from Cornwall, positioned mic carefully, set to C weight fast response and let some tunes rip. Seems the Yamaha -??db on volume knob must be pretty close to calibrated, cause at about 0db on Yammie, I was at about 98 db on meter. I'll check tomorrow with VOM and see if that is truly 1 watt. GOD ITS LOUD inside the house. I used to mix rock bands, but always work ear protection and mixed from a distance. Anyway, I kept monitoring woofer movement (didn't want to blow up) and got her up to about 120 db before it started breaking up a bit. YYYEEEOOOWWW can't take that for to long, but nice to know it's there. WIth the 'double wattage to gain 3 db rule' I figure that was about max output with maybe some clipping, as the Yamaha is rated at 120watts which with the Corns 98 db rating would equal exactly 120 db max by my elementary calculations.

[wheelman]

This is cool. I had to break out my rat shack meter now thanks to Yendor for that good deal I might add. I put it on a radio station and that really isn't as loud as cd. But in my listening position about 9-10 from my mains. I have and use sf-2's with a 70 watt deon. I was getting a steady 106 steady decibel reading with Hearts barracuda tune with the denon on 10 which it even goes louder, but it's pretty late. I will have to try a cd tomorrow or better yet a dts dvd rock concert. I had my settings at: range 100 with it peaking and staying at around +6, weighting on c, response on slow.

[WMcD]

Hmm, I thought that a CD had a 96 dB dymanmic range. 16 bits 2^16 different levels of voltage. We should crank the math.

Using a meter to measure the level of "music" is actually a very crude measurement. In the old days with orchestral music the rule of thumb was that instantaneous peaks were 18 dB above what a VU meter would indicate. Therefore, the whole recording and playback system had to have 18 dB of additional headroom.

That is almost 20 dB and 20 dB is a power increase of 100.

My guess is that the RS meter is doing about the same. Modern pop music may, I think, not quite have the same 18 dB peaks simply because so much of it is compressed. But some recordings, particularly drums, may well have an even greater dynamic range.

You can see some of the dynamics in more sophisticated metering systems which measure a peak and then hold it. You see this on some LED type meters and Real Time Analyzers (RTA).

I see that the Windows Media Player in XP has what looks like an RTA with peak and hold. Unfortunately, it does not show what the frequency bands are or the levels. Still it is fun, and instructional to look at. The price is right if you've already paid Mr. Gates for the software.

What you see is the instantaneous level in a dozen frequency bands of whatever you're listening to . . . and a little marker holds the peaks before settling down.

What we can do is play a CD on the computer using Media Player, feed the output to the audio system, and then look at the measured output on the RS meter.

The issue will be . . . what are we measuring? There is a wealth of fairly accurate data on the computer screen which is constantly changing in time to the music. And the RS meter will show an average of it. It just shows how crude the RS meter (or any single averaging meter) really is.

We're not even talking about room acoustics when the mike is moved around. That is another issue. And we're not talking about it being off by 2 or 3 dB.

Suffice to say that if we feed a sine wave which is a single frequency, we have a single level at a single frequency. Music is much more complex. The meter is giving us one number and it gives little of the entire story.

- - - -

I cringe a bit at people playing music at home, or on stage, as loud as they are reporting. Hearing damage is one issue. But also, to me, the ear overloads and things get mushy-distorted-loud. It happens to me in rock concerts and even the Chicago Symphony Orchestra. Creshendos in live, non amplified music, up close, with a large orchestra are hard on the ear.

Please join me in an experiment. The next time you go to a rock concert and things sound distorted, fashion some earplugs from paper and saliva. In my experience, the music becomes more clear. This is, I think, because the output runs our ears into distortion.

This may be the reason for a lower level on stage sounding better.

- - - -

We can look at some numbers based on that 18 dB principle. Let's appreciate that PWK said that 1% distortion is his limit, and the K-Horn puts out 104 dB for one watt at 1% distortion.

The bottom line seems to be that if an averaging meter at one meter (39 inches), on music, is showing 86 dB, peaks (not registered even on a fast setting) go up another 18 dB to 104 dB, which is his limit for distortion.

You can see where I'm going. 86 dB on the RS meter for music is pretty darn loud. Anything more may well be annoying for even young ears. Perhaps this is simply because even the K-Horn is being driven into distortion with a nominal reading of 86 dB.

Best,

Gil