Acceptable ambient noise level?

[ats]

Hi,

I have just acquired some office space. There is one large room that I hope to use as a sound studio for recording. The building is very quiet, but I can occasionally hear low frequency sounds from a truck driving by, etc.

How do I determine if those sounds are quiet enough for acceptable use of the room for recording? I would like to be able to record acoustic instruments as well as other louder sources.

One SPL meter I looked at goes down to 50dB SPL and I think I recall that ambient noise in a studio should be considerably less than that. Is the rule that if my ear can hear it it's going to be a problem on the recording? Or do you have acceptable studios where some outside noise is detectable if you listen carefully?

Is an SPL meter useful for measuring ambient noise in a studio, or is there another technique I should use?

Thanks!

Mark

[the dreamer]

According to Philip Newell ambient noise in pro studios should be 20 db and never more than 25.

[knightfly]

I agree; and from research I've done on SLM's, it would be much cheaper if you can find one to rent for this particular purpose. To find one sensitive enough to tell you what NC curve you have would cost several thousand dollars. For $40-50 you get 50 dB sensitivity, for $400-1000 you get 35 dB sensitivity, and for about $2000 and up you can get 20 dB sensitivity.

If your ear can hear it, almost any decent condenser mic will record it - then, if someone wants to listen to your acoustic guitar part "larger than life", he'll get free truck noises.

If you check the very top link in this section, it leads to some useful info on isolation - if nothing there seems to relate to your specific conditions, feel free to post more detail and ask about your particular situation... Steve

[ats]

Thanks guys. It's remarkable that our ears are so sensitive.

I went ahead and ordered the RS $50 50db SPL meter which will be useful with the ETF software later. I know it won't tell me anything about the low-level ambient noise but it will be useful for experimenting as below.

For my own education I think I will simulate a recording situation with a sound source (CD player maybe) at various SPL levels and a condenser mic to see what kind of truck noises I can hear when played back "larger than life" as you said. I suppose just recording the room with no sound source and playing that back at high gain would be instructive.

Perhaps I'll have my employee drive his camaro by the building and record those passes for comparison after doing some isolation treatments.

If I can semi-objectively measure the ambient noise this way then I hope I can tell how well my isolation efforts are working (for example after treating the front windows), and if nothing else I should learn something along the way.

After that amateur experimentation I'll probably have to go looking for a place to rent a sensitive instrument from.

Thanks again.

Mark

[Eric_Desart]

Just a thought,

I'm not a recording engineer.
But one tries to get S/N as high as possible.
With nowadays means S/N 90 dB is possible.

Your mic and gear shows a floor noise which will limit this S/N.

If your background noise is higher than then the noise floor of the mic and gear, the background noise will become defining for the S/N of the recording.
One just can't increase S in the S/N just like that because otherwise one's deaf.

As such the theoretical optimum is that the mic and gear can't pick up any background noise.
That explains Philip Newell's 20 dB (good mics will be between 15 and 20 dB).
In theory the background noise should not increase (or be audible) the most silent level the equipment can record.

With ventilation and gear this becomes difficult.
And depending on the type of music this optimum S/N can be more or less important. If the background noise is masked by the recording (during most silent passages) it hardly matters which level it is.

And as Steve said: measurement equipment for such low levels is expensive.

Just thoughts, nothing more.

[ats]

Thanks for that post, it seems very sensible. I will let you know how my testing goes. I am looking into some used SLM's that can measure low levels.

Perhaps it is more of an educational tool than an absolute necessity, but i love the idea of being able to objectively measure how well my isolation techniques are working.

If I buy one do you think anyone here would be interested in renting it?

Mark

[Eric_Desart]

If I buy one do you think anyone here would be interested in renting it?

Mark

That shouldn't be a wise decision in function of responsibility and insurance. It's an easy way to get a lot of trouble (and packing, shipping, testing etc. Was this fealure present, who did it?)

If you want it, check if you can rent it yourself.
Such companies are organized to do so.

As I understood on Ebay there are regularly from those old but good beasts at a fraction of the original cost. The question is how and when do you know?
A calibrator to check it (when it's maybe too late) may cost more than the budget you intent to spend.
My personal opinion: this is typical equipment to buy second hand from somebody or from an organisation one knows and/or trusts.

[drfrankencopter]

You don't need a sensitive meter to determine how well your isolation is working. You can do this with a cheap 50 dB meter no problem. All you need is speakers that can get you to around 110 dB SPL! Crank em up in your room and go outside and measure the dB loss. The same loss will apply for sounds getting into the room.

If you want to measure your noise floor, well thats a different story. Maybe take a very sensitive mic (with a know, or at least published sensitivity) and put it into a mic preamp of a known, accurate gain level. Measure the voltage level at the output, compensate by subtracting the preamp gain to determine what level of signal was present at the input. Use the mic's sensitivity to determine the Pa (pressure) or SPL level.

All that said, I'm happy I have access to an old (but good) B&K SPL meter and calibrator. Measured 35 dB SPL in my basement before the drywall goes up. I wouldn't buy one myself though.....

Cheers,

Kris

[ninjakyle]

that is a good point. sounds like fun
i think i will give it a try