How quiet is your listening room?

[Chris A]

When I'm unmastering music with lots of quiet passages or dynamics, I wait until the conditions are right--such as not during meal preparation time, etc.  This shortens CD unmastering efforts by about 2-3 hours/day.  I'm about 75% complete in unmastering my two-channel library of >15K tracks (>1300 CDs). I'm expecting to be complete after the beginning of the year.

 

Of course, that ETC depends on how much K-402-MEH fabrication success I achieve...and at which time I can no longer call it a "K-402-MEH" since they will not be made from modified K-402 horns. 

 

Chris

[derrickdj1]

Nothing wrong with a little reverb.  It makes the sound more expansive within limits.  We live in a world with reveb all around us: some of that needs to be in the listening room.

[Quiet_Hollow]

"Can silence actually drive you crazy?"

 

City slickers....

[Woofers and Tweeters]

I have one basement room that's ~ 8'x20'x24' with the sound coming from the wide wall. Carpet floor, acoustic ceiling tile and, among other smaller furniture, a big cloth covered couch soaks most tramp sounds. Another basement room that's only had that square area, same carpet, very little furniture, painted concrete walls and drywall ceiling. Fails the clap test and fails to sound good regardless of what speakers I have in there (tried everything from Heresy to Khorn). That room all get treated, some day. Both rooms are under ground, so no outside noises to deal with.

 

Sound deadening has been worth the efforts.

 

I'm working on a bedroom that's ~ 12'x20'x20'.. I have read that a square room is the worst shape room to try have as a sound room.  

[Quiet_Hollow]

On 9/23/2016 at 3:10 AM, Weber said:

I'm working on a bedroom that's ~ 12'x20'x20'.. I have read that a square room is the worst shape room to try have as a sound room.  

Perhaps...but really when it's only too small. 12 foot ceiling is a BIG plus, and 20X20 won't hurt so bad as long as your not digging around 40 Hz or so.

 

With a big enough room, the shape becomes much less of a factor.

[Woofers and Tweeters]

2 hours ago, Quiet_Hollow said:

Perhaps...but really when it's only too small. 12 foot ceiling is a BIG plus, and 20X20 won't hurt so bad as long as your not digging around 40 Hz or so.

 

With a big enough room, the shape becomes much less of a factor.

I hope it keeps getting better. I keep trying to do more to arrest the tramp sounds. Area rugs and curtains are next. It has a octagon shape, double step tray ceiling that helps break the sound up. 

[Paducah Home Theater]

I measured mine the other day by running a sweep but not plugging in the heaphone jack, most frequencies was about 25 db.  About 70 hz as well as 15 kHz or so it actually got up to 40 db.  Tried to listen real close to see what was going on and there seemed to be a coal truck way down the road which may be the 70 hz, plus my laptop was on and the fan isn't totally quiet.  The upper end dropped just by throwing a blanket over it so that had to be what it was.  I have no idea how an otherwise dead silent room out in the middle of nowhere could have a noise floor of 25 db.  Walls are 6" insulation, I have like 168 square feet of insulation on the walls, double insulation in ceilings, no washing machine was on or anything... where would that come from?  I do have a UPS that buzzes a little but it's in the rack and I can't hear it on the other side of the room.  

[dirtmudd]

It's much better now

[DrWho]

On 10/3/2016 at 5:55 PM, MetropolisLakeOutfitters said:

I measured mine the other day by running a sweep but not plugging in the heaphone jack, most frequencies was about 25 db.  About 70 hz as well as 15 kHz or so it actually got up to 40 db.  Tried to listen real close to see what was going on and there seemed to be a coal truck way down the road which may be the 70 hz, plus my laptop was on and the fan isn't totally quiet.  The upper end dropped just by throwing a blanket over it so that had to be what it was.  I have no idea how an otherwise dead silent room out in the middle of nowhere could have a noise floor of 25 db.  Walls are 6" insulation, I have like 168 square feet of insulation on the walls, double insulation in ceilings, no washing machine was on or anything... where would that come from?  I do have a UPS that buzzes a little but it's in the rack and I can't hear it on the other side of the room.  

 

Nerdy engineering talk for a second, but if you're looking at the frequency response of the noise floor, then your total noise energy needs to be integrated over frequency....

 

In other words, if you have a flat noise floor showing up at 25dB on a frequency response or FFT, then the actual RMS measured noise will be 43dB higher for a noise floor of 68dB SPL.

 

Basically, add 43dB to the response you're seeing in your plots....if your noise floor is flat. If your noise floor isn't flight (usually there's a lot more LF energy), then you should add 43dB to the level measured at 20kHz. You'll usually be within a few dB of the actual unless things are crazy.

 

 

 

 

 

[Paducah Home Theater]

22 minutes ago, DrWho said:

 

Nerdy engineering talk for a second, but if you're looking at the frequency response of the noise floor, then your total noise energy needs to be integrated over frequency....

 

In other words, if you have a flat noise floor showing up at 25dB on a frequency response or FFT, then the actual RMS measured noise will be 43dB higher for a noise floor of 68dB SPL.

 

Basically, add 43dB to the response you're seeing in your plots....if your noise floor is flat. If your noise floor isn't flight (usually there's a lot more LF energy), then you should add 43dB to the level measured at 20kHz. You'll usually be within a few dB of the actual unless things are crazy.

 

 

 

I don't see how a dead silent room out in the middle of nowhere has a noise floor of 68 db.  That's louder than a normal face to face conversation which is typically said to be between 60 and 65 db, and probably louder than my system usually is during normal scenes since we usually listen at -25 db.  Does that make sense to you?  We're talking about a room whose 21 decibel projector fan is the loudest thing by far, and it wasn't even on.  I had to use rack fans that are like 7 db or else I can hear them from 10 feet away.  I don't know if my initial technique was legit or not but 68 db sounds WAYYYY high.  

[Chris A]

I believe Mike is talking about "standard loudness level" - like you measure with a hand-held SPL meter on slow response and without weighting (A, B, C).  That's not difficult to do...especially if you take some handheld SPL measurements and average them.

 

The plots that I posted above work for me since it is the result of integrating over time--by frequency ("RTA" or real time analysis) rather than integrating everything again into one number--like a handheld meter.  "Ergodicity" is the principle employed.

 

Understanding background SPL vs. frequency is useful--at least to me--and that's why I posted it above.  The RTA function in REW or TrueRTA works pretty well for that. If you use the built-in calibration function within either application using a hand-held SPL meter, you're very close.

 

YMMV.

 

Chris

[DrWho]

10 minutes ago, MetropolisLakeOutfitters said:

 

 

I don't see how a dead silent room out in the middle of nowhere has a noise floor of 68 db.  That's louder than a normal face to face conversation which is typically said to be between 60 and 65 db, and probably louder than my system usually is during normal scenes since we usually listen at -25 db.  Does that make sense to you?  We're talking about a room whose 21 decibel projector fan is the loudest thing by far, and it wasn't even on.  I had to use rack fans that are like 7 db or else I can hear them from 10 feet away.  I don't know if my initial technique was legit or not but 68 db sounds WAYYYY high.  

How did you calibrate the SPL of your signal path?

 

There's no way your room is sitting at 68dB SPL, so your electronics are dominating the noise floor of your measurement. Are you sure that 70Hz wasn't actually 60Hz? The 60Hz of the grid shows up all the time in acoustic and electronic measurements.

 

Since we're already geeking out.....

 

The Behringer ECM8000 capsule is rated for -39dBV per 94dB SPL:

http://www.cross-spectrum.com/cslmics/001_mic_report.pdf

This means that a 94dB SPL tone results in a voltage waveform with an amplitude of -39dBV.

 

20dB SPL is 74dB lower than 94dB, so the voltage level coming out of the microphone would be -113dBV if you were playing a 20dBSPL sine wave. The voltage level at each frequency for a flat noise floor would be even lower....more like -156dBV at each frequency. That's really really quiet.

 

On your SPL chart, this would correlate to -23dBSPL for the noise floor frequency response amplitude. This is in order for your system to resolve down to 20dB SPL ambient noise. It's doable, but you gotta be careful with your gain structure and all that.

[dBspl]

According to that Behringer spec, the noise floor of the microphone is 32 dBA.  That's pretty high for background noise measurements.  It will probably be difficult to resolve noise levels below that.

 

Kerry

[DrWho]

 

 

Going back to this plot....the noise floor isn't flat over frequency, but let's take the levels at 20kHz (extrapolated looks like -12dB for inside and 3dB for outside). Adding 43dB gets you to 31dB SPL inside and 46dB SPL outside. These numbers aren't too far off. The way noise energy works, you can have a tilted line where 20Hz is 31dB higher than 20kHz and it only adds 3dB to the integrated total. This is because higher frequencies have more energy that lower frequencies (they're wiggling faster).

 

In this plot, the energy at 20Hz is 50dB higher than at 20kHz, which means the average noise floor is actually 20dB higher. However, our ears don't hear LF energy very well - especially this low in amplitude, which is where A weighting comes into play and ignores some of the LF energy. It also ignores the extreme HF energy as well because 20kHz is really hard to hear. If we go to the 1kHz number, then 1kHz can be 13dB louder for the same effect as the 20Hz. The 1kHz number is at 12dB SPL, so subtract 13, add 3, and then add 43 and you're at 45dB SPL equivalent if the noise floor were actually flat. In other words, the Awtd noise floor with 20kHz bandwidth here is somewhere between 35dB and 45dB SPL.

 

Just thinking about studios for a second - it's hard to get below 30dB SPL. I would be extremely surprised if an untreated room (even in the middle of nowhere) was getting below 40dB SPL.

 

Anyways, my only point is that it's hard to tell from plots like these. Knowing the spectral content is helpful, but a straight up RMS average is how it's really measured (using the meters on your equipment). One could certainly integrate these plots by hand, but my question is why go down this road? Are we trying to prove to the world that our room is quiet? Or are we trying to identify problems that need resolution?

 

 

 

 

[DrWho]

1 hour ago, dBspl said:

According to that Behringer spec, the noise floor of the microphone is 32 dBA.  That's pretty high for background noise measurements.  It will probably be difficult to resolve noise levels below that.

 

Kerry

Ya, it's not low noise at all. We use the KSM44A in omnidirectional mode for measuring ambient noise of acoustic spaces at work. 6dB SPL self noise.....requires a preamp with -135dBV EIN to not add more than 0.1dB of noise to the measurement.

[jacksonbart]

shhhh, I can't hear my pulse

[RoboKlipsch]

37 lowest typically 43 to 47