SPL Meter observation

[pauln]

Anyone ever notice that the meter swings really hard to the right at points in the music where nothing seems that loud? Moody Blues comes to mind.

Other times a loud passage does not seem to swing the meter much at all. Also, I've noticed that my "Hot Rocks" Stones album has more swing on the meter than just about anything else. Incredible dynamics - the engineer must have been asleep at the wheel, or they just had great folks on the board, or was it a musical accident like so much I like about the old Rolling Stones?

Paul

[ben.]

Ballistics of the meter itself, speed of the circuit, and frequency response of the measurement mic are probably all at work here.

[Scp53]

I have found that "hidden" peaks in music and ht can only be seen if

the meter is set to "max". not sure if the old analog one has that

function or if its just on the new rs digital ones.my meter might be

reading around 100db for the avg per second reading but put it on max

and it hits 110db plus. not sure if that helps...

scp53

[pauln]

PWK said that the analog meter on "Peak" is 13dB below the actual true peak dB level. They were made and timed for voice. But it bugs me that the peaks don't correspond to the apparent volume in the music sometimes. The punch in most music is mostly packed in the 200-500Hz range. Maybe the real low stuff in pushing the meter, but its not as audible?

Paul

[colterphoto1]

Are you using the RS meter Paul? Make certain to use the C weighting and I perfer SLOW for test tones. The meter should be at RIGHT ANGLES to the source of sound (it's in the manual). One or more of those points might alleviate the apparent lag in response. I don't think it looks very accurate on the FAST reading either. Good observation. I wonder how crazy it is trying to read the new digital one!

Michael

[3dzapper]

I use The Moody Blues "In Search of the Lost Chord" and "Threshold Of A Dream"as two of my amplifier test records because of the high level of low bass energy from the combination of the bass guitar and Moog Synthesizer. Properly reproduced, the tunes rise from a very "dark" background.

Although your LaScalas can't make noise at twenty or thirty hertz, the woofer is still vibrating and producing those subsonic waves much like my Khorns will do at 20. I can feel them but the horn is incapable of forming the proper wave.

Rick

[sfogg]

"Anyone ever notice that the meter swings really hard to the right at points in the music where nothing seems that loud?"

If you are hand holding the meter sometimes that happens if you move the meter or change your position somewhat.

It could be low frequency information, esp. if the note his a resonance point in your room which will throw off your measurments. If you want to mostly avoid the effects of the bass on the measured SPL set to meter to 'A' weighting to further roll off the bass response of the meter. That will make it give you a more accurate reading for the midranges SPL level.

Shawn

[crazytubepower]

I have a rat shack digital, when i c wight I get 126 on some parts on

songs when the going rate is 90. I've gotten 126 dba!!!!!! I was

wearing hearing protection however. Your hearing is to golden to kill

[WMcD]

I thought the the rule of thumb was 18 dB peaks over average, but I may be wrong.

This headroom thing arose in the days when there were live feeds down telephone wires. You can probably still find a statement on meters that 0 dB = 1 mW at 600 ohms. That is to say that the meter was set up so that a constant tone would put 1 mW into a phone line which had a 600 ohm impedance. We could do the math to figure the voltage. What ever that voltage was, was set at 0 dB, which was about 75% of full scale. The so called ""VU" meter is in fact a sensitive volt meter.

The amplifiers down the line were designed with that 18 dB of headroom over that voltage reference.

So the wire transmission system would be set up (calibrated) with a constant tone at 0 dB. Remember the dB scale is relative. In sound pressure level, 0 dB is the least loud sound we can perceive. But in the VU meters, it is bottom of "red", when the real "red" for the system was 18 dB above.

As mentioned above, the issue was the "balllistics" of the meter needle, or its mass . . . and how quick it gets up to the highest altitude, in a way. The needle just can not be moved fast enough to track the fast peaks. Of course now we have systems with LED which do track and hold at the peaks.

The problem came to the fore for hi-fi nuts with the advent of home tape recorders. There we needed the same type of meters to make sure the record level did not saturate the tape.

In all events that translated to letting the "bouncing around meter" only get to 0 dB. It was assumed that actual, not indicated short peaks were actually a lot more powerful.

Getting back to the original subject. The problem is that the meter is under reporting what is loud to our ears, such as drum impacts. But then when there are relatively long term signals such as long term notes, they are accurately reported. That may explain what you're seeing.

Gil.