Cold Iron

[Bob Womack]

This weekend the air handler that serves my studio is getting its first major service since 1979. Temperatures are expected to rise. In order to protect the gear, the A/C mechanics have asked me to turn off most of the heat-generating devices in the suite. That means amplifiers, mixing consoles, self-powered monitors, computers, etc., many important systems in both the machine room and the studio. That rarely occurs in my room. Long ago we learned from experience that startup, before power supplies are stabilized and when stray voltage spikes can occur, is the time when component failures occur.

This is a quiet suite, isolated from the rest of the complex by floated flors and multi-layered walls with dead spaces. The high volume low velocity A/C is fed through labyrinthine boxes that quiet it down to where it isn't perceptible. Well anyway, it has been years since I last powered the room down, and whenever I do a total power down on my studio one thing that strikes me is how much quieter a shut down room is than the measured 38db operational floor the room normal exhibits. I mean, you can hear your own body at the usual operating level, but with everything off, the the room is positively DEAD silent, probably more quiet than a tomb, and it is a profoundly eerie feeling.

Bob

[AcousticDreams]

Originally Posted by Bob Womack

I mean, you can hear your own body at the usual operating level, but with everything off, the the room is positively DEAD silent, probably more quiet than a tomb, and it is a profoundly eerie feeling.

Bob

In the 70's my good friend worked at Marantz Superscope in San Fernando Valley, California. Only a few miles from where I lived. I got a chance to go inside their anechoic chamber. Yes, " eerie " is a good description.

[Rudy4]

The perception of quietness is interesting as we perceive it in different circumstances.

We live out in a rural area that occasionally has total power outages lasting several hours. It's interesting how we grow accustomed to a variety of sounds and don't notice their presence until they are absent.

I used to have a PC at my mixing desk / recording area and moved the entire PC to an adjoining room by passing all the cables through a wall mounted "poke through". I recorded the "room" before and after moving the PC and was amazed at how quiet the room was!

[Chipotle]

Originally Posted by AcousticDreams

In the 70's my good friend worked at Marantz Superscope in San Fernando Valley, California. Only a few miles from where I lived. I got a chance to go inside their anechoic chamber. Yes, " eerie " is a good description.

I have been in an anechoic chamber a few times as well. It's decidedly unsettling, as even in open air there are usually surfaces--the ground at a minimum--to reflect some amount of sound back to you. In the chamber, there is none.

That's a bit different than having extreme (even if just relative) quiet. But there is always some kind of background you are tuning out, and you definitely miss it if it stops.

What's interesting is that it occurs to me that that's how we often want to apply effects to our mixes--subtle so that it's not obvious, but if you bypass it you definitely miss it.

[b1j]

Originally Posted by Bob Womack

... the measured 38db operational floor the room normal exhibits.

Bob

Bob, I read this with great interest. First let me say I use the (free) Decibel X app on my iPhone, and I have no idea if it is accurate or reliable.

With that out of the way, I was curious how my (still untreated) room measures up. I first measured my quiet bathroom at 11 PM with the HVAC off: 25 dB, A weighted ("Threshold of hearing," according to Decibel X). It was really quiet in there.

I moved into my music room. By then the heat blower was revving up. I snagged a measurement at about half blower speed: 33 dB ("Rustling leaves"). Once the heat came all the way up I got 39 dB (still "Rustling leaves," but 40 seems to be the beginning of "Quiet whisper").

At that level it seemed really loud in here, too loud to record. Am I really just 1 dB louder than your studio? Seems hard to believe.

Then I took another reading in the music room when the heat was done. The most prominent sound is the Xfinity gateway, which seems annoyingly loud. Measurement: 28.6 dB (still called "Threshold of hearing"). A world away from your 38.

Am I missing something? Or, if Decibel X is reliable, should I stop worrying about the gateway noise? Or even the HVAC? Or do I need a better sound meter? Or will my music be so many orders of magnitude louder that it won't matter?

__________

Finally, I tried C weighting in the music room: 50 dB HVAC on, 36 dB HVAC off. Is this relevant?

[Bob Womack]

Originally Posted by b1j

Bob, I read this with great interest. First let me say I use the (free) Decibel X app on my iPhone, and I have no idea if it is accurate or reliable.

With that out of the way, I was curious how my (still untreated) room measures up. I first measured my quiet bathroom at 11 PM with the HVAC off: 25 dB, A weighted ("Threshold of hearing," according to Decibel X). It was really quiet in there.

I moved into my music room. By then the heat blower was revving up. I snagged a measurement at about half blower speed: 33 dB ("Rustling leaves"). Once the heat came all the way up I got 39 dB (still "Rustling leaves," but 40 seems to be the beginning of "Quiet whisper").

At that level it seemed really loud in here, too loud to record. Am I really just 1 dB louder than your studio? Seems hard to believe.

Then I took another reading in the music room when the heat was done. The most prominent sound is the Xfinity gateway, which seems annoyingly loud. Measurement: 28.6 dB (still called "Threshold of hearing"). A world away from your 38.

Am I missing something? Or, if Decibel X is reliable, should I stop worrying about the gateway noise? Or even the HVAC? Or do I need a better sound meter? Or will my music be so many orders of magnitude louder that it won't matter?
__________

Finally, I tried C weighting in the music room: 50 dB HVAC on, 36 dB HVAC off. Is this relevant?

I can see how this might be confusing. A-weighted measurement is shaped for the Fletcher-Munson curve and is used to rate ear exposure in the workplace. It eliminates some high and low noise bands and thus reports lower numbers overall. Z or Zero weighting is flat, and allows a more realistic idea of the background noise, including low rumbles and high hiss. It My numbers for the studio were taken with Z weighting on DecibelX on an iPhone6. I've just sampled my house here with the heat pump audibly running and myself in a position where I can hear both the pump outside and the heat exchanger box fan and flow noise inside. A-weighting is showing 34.3. When I switch over to Z it shows 48.9. When I go to RTA app at Z weighting the reading is 51!

A-weighting won't show you the level of ambient noise very well.

Bob

[b1j]

Originally Posted by Bob Womack

I can see how this might be confusing. A-weighted measurement is shaped for the Fletcher-Munson curve and is used to rate ear exposure in the workplace. It eliminates some high and low noise bands and thus reports lower numbers overall. Z or Zero weighting is flat, and allows a more realistic idea of the background noise, including low rumbles and high hiss. It My numbers for the studio were taken with Z weighting on DecibelX on an iPhone6. I've just sampled my house here with the heat pump audibly running and myself in a position where I can hear both the pump outside and the heat exchanger box fan and flow noise inside. A-weighting is showing 34.3. When I switch over to Z it shows 48.9. When I go to RTA app at Z weighting the reading is 51!

A-weighting won't show you the level of ambient noise very well.

Bob

Thanks!

Z-weighted: 50 with HVAC on, 38 with HVAC off.

So back to the question: is my room (at 38 dB Z-weighted) really as quiet as your studio when the blower's off here? Seems hard to believe, but it's good news, I guess, if true.

[Bob Womack]

Originally Posted by b1j

Thanks!

Z-weighted: 50 with HVAC on, 38 with HVAC off.

So back to the question: is my room (at 38 dB Z-weighted) really as quiet as your studio when the blower's off here? Seems hard to believe, but it's good news, I guess, if true.

You know, if you live in the country without traffic nearby it is possible to have a really quiet room. My parents' home was on a country road that wasn't frequented by cars and my bedroom was really quiet. I did my first recordings there in the '70s. People don't seem to understand that professional studios usually live in built-up places so bringing down the noise requires a lot of work while rural homes can be quite... quiet. There's a studio in rural Texas that has a cathedral window in the main room that is about fifteen feet tall! David Gilmour of Pink Floyd built a studio on a large houseboat barge near Hampton Court Palace on the Thames because he felt he'd spent his life in dark, musty studios. Every room has many windows. He can do that because the surround area is quiet.

My recording room at work sits about forty feet from a loading dock with a garbage compactor and about seventy feet from the main air handling system for the building. The trash compactor has never intruded. When we built the studio we got it down to one (!) mechanical short between the rest of the building and the studio that was created by a contractor's mistake. You could hear NOTHING from the surrounding building. Ten years later they replaced the chiller in that air handling system with a louder one. On hot days when we are chilling I can barely hear that chiller in the control room through that one mechanical short, but, thankfully, not in the recording rooms.

Bob

[b1j]

From a technical viewpoint, I wonder how much higher the SPL of the quiet parts of the music source needs to be than the SPL of the environment in order to make the background trivial.

[Bob Womack]

Were we to ask the fellow who designed my room he'd probably be able to tell us. I was on the design committee with him and stated my goals and made layout decisions. For instance, implementation of a Live-End-Dead-End control room was my biggest requirement and request. I also asked for the labyrinthine boxes in the air handling system to reduce induction of sound from the outside and transfer between rooms. But, I didn't know the background noise threshold number that was necessary.

I can tell you that the number we ended up with has made recording exactly as you describe - room noise really isn't a factor in recording acoustic instruments, and I've done lots from orchestra strings to qanun* to guitar to doghouse bass.

Bob

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