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88 dB Ambient?????

heeman

heeman

PRETTY HAPPY.........
Famous
Broke out the old Radio Shack SPL Meter yesterday after work, just to do some sanity checks in the HT.

Check the battery on the meter, put the range to 80 and move to the sweet spot........WTF, the needle swings almost all the way to the right. Move out of the sweet spot an drops almost to the bottom of the scale.

So, what is going on???? I still haven't had to much to drink???

I take the meter out of the HT, and it is working fine................ :angry-banghead:

Time to trouble shoot.

I go back into the HT move to the sweet spot...........needle almost pegs!!! :angry-tappingfoot:

I unplug the HT Seat's figuring maybe there is some kind of interference.....NOPE!!

The Air Conditioning was on, so I went and turned that off.................NOPE!!

Grabbed a flash light and turned of the recessed lights (pot lights).......THAT'S IT!!! Needle drops. :happy-smileygiantred:

My guess is that the lights were giving off some very High Frequency sound, because it was nothing the I could hear. The interesting thing, besides this, was it was primarily in the sweet spot. Move from the sweet spot and it would drop to almost nothing........

Anyone else experience and ultra-high frequency interference when measuring SPL????
 
704_2.jpg
 
^ :laughing:

heeman, if you don't already have one, download the free version RTA from http://www.trueaudio.com/ or similar programs available online. Set it up with your SPL meter (I suppose it's compatible?) and see what the frequency is.
 
Even though you can't hear it, can ultra high frequencies contribute to listening fatigue? I've been curious about that.
 
Place about five layers off tissue or toilet paper over the mic on the SPL meter and run the test again. If you still get the pegged signal, then it is subsonic bass, not ultra-high frequency. I encourage the test because the mic on the RS SPL meter starts rolling off at 15kHz, so if you are measuring 88dB at some frequency above 22kHz that noise could much higher, perhaps as loud as 100dB SPL. That is possible, but very unusually loud.

I almost want to believe there is some RF signal interfering with electronics rather than an acoustic noise above 20k at 100dB.

As for ultra-high frequency noise causing problems, it depends on the frequency and the intensity.
 
Flint said:
Place about five layers off tissue or toilet paper over the mic on the SPL meter and run the test again. If you still get the pegged signal, then it is subsonic bass, not ultra-high frequency. I encourage the test because the mic on the RS SPL meter starts rolling off at 15kHz, so if you are measuring 88dB at some frequency above 22kHz that noise could much higher, perhaps as loud as 100dB SPL. That is possible, but very unusually loud.

I almost want to believe there is some RF signal interfering with electronics rather than an acoustic noise above 20k at 100dB.

As for ultra-high frequency noise causing problems, it depends on the frequency and the intensity.
Click to expand...

A couple of things.......

The tissue paper had no effect, however, either did turning off the lights???

So I unplugged the chairs, and that reduced it significantly. I also observed that when the chairs are plugged in and I have the Meter lying on the top of the chair, and I touch the meter, it swings even higher???

There is some kind of interference from the chairs..................

Test data from last nighted is bogus, I must have had the chairs unplugged with the lights off????

Will go try again.
 
More Data.

There are spots in the room reading over 90dB. This is with nothing on, no equipment on nada!!! There are areas, well under 70dB.

I put on Rubber Flip Flops thinking that maybe my bare feet on the carpet was somehow doing something. No effect.

Stepping on the power cord going to the chairs pegs the meter. So some kind of Conductive and/or radiated emissions going on here and maybe in the so call "loud spots" in the room, even though it is dead quit.

"Loud Spots" in the room are there even when the lights are off and the chairs are not plugged in............

Last night I was able to make measurements of all 5 speakers and the sub, and the system is well tuned/balance. Confirmation with Movies and Music confirmed the proper balance, however what else is going on...............

WHO KNOWS!!!!
 
More.................

So, let's take the meter and put it on the 80dB scale and slowly walk around the dead quit house.........

There are a few area's that actually peg the meter in other area's of the house, and other area's were there is zero reading on the 80 dB scale..........

Time to move...................

Maybe Botch is right!!
 
Swap out the battery (again) and make certain the connections are secure. If that delivers no relief, as Towen suggests, new meter.

Rope
 
Any utility power lines & their transformers near your house?

Any of those capacitive "touch" on/off lamps in the house?

Any electronic lamp dimmers in the house?

You might try shutting off circuit breakers one at a time to see if it's coming from one of the house circuits....

Also, as DIY said, a test with TrueRTA or REW would be very revealing - to see if you can identify the frequency - especially with a better/different mic
 
Switch the meter between A-Weighted and C-Weighted and let me know the results.

Most houses and buildings have lots of bass noise in them, the hot spots are often nodes and the quiet spots null, just like any room response. In my HT, which is on the 2nd floor, I get an ambient rumble at 20Hz of over 70dB. Due to how humans hear frequency, as denoted in the equal loudness curve, we cannot typically hear low bass below 70dB and usually don't fully recognize until it is over 90dB SPL. That's why OSHA safe noise level regulations are all made with an A-Weighted measurement.

If the tissue had no affect on the measurements, then you are not getting a reading on ultra-high treble.

If you live relatively near a freeway, that could be the source of the subsonic noise. Recording studios actually build their recording rooms as buildings inside buildings with the inside room suspended from the foundation with rubber, sorbothane, or springs.
 
With the meter switched to "A" Weighted................no sound is measured, anywhere!

It is really interesting that once again when on "C" Weighted and I step on the power cord going to the chairs, the meter spikes?

It has been years since I have performed and understood the FCC Standards for Conductive and Radiated Emissions, however I do remember the principles and filtering/shielding and the effects.

T7 - No I do not have another meter.

Orbison - non of the items you mentioned.

Nearest highway is about 3/4 miles by the way a crow flies......
 
That's pretty close for a highway.

Try wrapping the meter in aluminum foil and grounding the foil with a spare speaker cable.
 
I'm leaning towards Towen's post. Maybe get another meter. You could always return it or keep it as a spare.
 
Flint said:
Try wrapping the meter in aluminum foil and grounding the foil with a spare speaker cable.
Click to expand...

When Flint starts telling you to raise your left leg a bit higher, please shoot/post video. :happy-smileygiantred:

I'm being brought back 5 decades, when we attached tinfoil to our rabbit ears and jiggled the channel knob... :laughing:
 
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