Recording Isolation Booth DB reduction
May 21, 2018 4:38 PM Subscribe
Is my new isolation recording Booth getting the DB reducition it was advertised to get?
I recently bought a very expensive prefabricated isolation booth which was shipped to the states from far over seas. The booth is beautiful and has great dead acoustics inside. The problem is, I'm not sure it's getting the adverstised DB reduction. I've been doing some tests...not sure I'm doing a fair test. The booth was advertised at a 52 DB reducition. So if someone is in the booth playing a saxafone at 80 DB I expect that on the outside of the booth I would get around 30 DB. Is this fair to expect or am I not taking the measurement in a fair way? Right now I'm getting around 80 DB on the inside with a sax and around 50 DB on the outside. This was measured with just an app on my my smartphone. If the lawn guys are right outside my house I'm still able to easily hear the mowers. On the flip side if I'm in the booth and my wife is in the living room just down the hall I can not hear her talking. Also if I play some music on my smart phone at the highest volume and go into the booth I can not hear the music. If someone is outside the booth you can only hear them in a muffled sound. Any thoughts?
I recently bought a very expensive prefabricated isolation booth which was shipped to the states from far over seas. The booth is beautiful and has great dead acoustics inside. The problem is, I'm not sure it's getting the adverstised DB reduction. I've been doing some tests...not sure I'm doing a fair test. The booth was advertised at a 52 DB reducition. So if someone is in the booth playing a saxafone at 80 DB I expect that on the outside of the booth I would get around 30 DB. Is this fair to expect or am I not taking the measurement in a fair way? Right now I'm getting around 80 DB on the inside with a sax and around 50 DB on the outside. This was measured with just an app on my my smartphone. If the lawn guys are right outside my house I'm still able to easily hear the mowers. On the flip side if I'm in the booth and my wife is in the living room just down the hall I can not hear her talking. Also if I play some music on my smart phone at the highest volume and go into the booth I can not hear the music. If someone is outside the booth you can only hear them in a muffled sound. Any thoughts?
The numbers on smartphone decibel meters should be treated as guesses.
You should buy a cheap decibel meter. I have that one, seems to be reasonably accurate compared to another more expensive meter.
posted by gregr at 5:22 PM on May 21, 2018 [1 favorite]
You should buy a cheap decibel meter. I have that one, seems to be reasonably accurate compared to another more expensive meter.
posted by gregr at 5:22 PM on May 21, 2018 [1 favorite]
Measuring dB reductions is very difficult.
I agree you need an actual sound level meter if you want really accurate results.
In order to determine whether the 52 dB reduction is accurate, you would have to use the same measurement metrics as they did when they determined that reduction. That would mean using the same stimulus, frequency integration, levels, and - perhaps most importantly - the same dB weighting and time window. It makes a HUGE difference when you are measuring these things whether you are using peak reduction or some average over some time. It also makes a huge difference whether you are using, e.g., A or C weighting.
In general, reported dB reduction ratings are not very accurate for most real-world situations. The saxophone example you give, with a 30 dB reduction, seems reasonable to me based on a reported 52 dB reduction rating.
posted by Lutoslawski at 5:56 PM on May 21, 2018 [4 favorites]
I agree you need an actual sound level meter if you want really accurate results.
In order to determine whether the 52 dB reduction is accurate, you would have to use the same measurement metrics as they did when they determined that reduction. That would mean using the same stimulus, frequency integration, levels, and - perhaps most importantly - the same dB weighting and time window. It makes a HUGE difference when you are measuring these things whether you are using peak reduction or some average over some time. It also makes a huge difference whether you are using, e.g., A or C weighting.
In general, reported dB reduction ratings are not very accurate for most real-world situations. The saxophone example you give, with a 30 dB reduction, seems reasonable to me based on a reported 52 dB reduction rating.
posted by Lutoslawski at 5:56 PM on May 21, 2018 [4 favorites]
Best answer: These are all helpful answers in a way, but regardless of what the meter tells you, you're only getting part of the necessary measurement. Decibel reduction alone is largely meaningless without dynamic range information. E.g., pitch is at least as important as volume here.
The reduction of your booth happens across a frequency curve. Outside that range, particularly below that range, more sound will get through.
For a sample curve, see the chart on page 4 of this sound booth catalog. Their single walls reduce 500 Hz signals by 43dB. They don't even post measurements below -29dB/125 cycles. For reference, the low Bb on a tenor sax is about 116 cycles.
By contrast, a single-stroke lawnmower emits around 80 dB in the 125 Hz range, and up to 40dB at 31.5 Hz.
Trapping bass frequencies is hard and usually requires a lot of mass. I'm not remotely surprised that mower rumble would get through something that would easily block voice/smartphone speakers.
posted by aspersioncast at 9:17 AM on May 22, 2018 [3 favorites]
The reduction of your booth happens across a frequency curve. Outside that range, particularly below that range, more sound will get through.
For a sample curve, see the chart on page 4 of this sound booth catalog. Their single walls reduce 500 Hz signals by 43dB. They don't even post measurements below -29dB/125 cycles. For reference, the low Bb on a tenor sax is about 116 cycles.
By contrast, a single-stroke lawnmower emits around 80 dB in the 125 Hz range, and up to 40dB at 31.5 Hz.
Trapping bass frequencies is hard and usually requires a lot of mass. I'm not remotely surprised that mower rumble would get through something that would easily block voice/smartphone speakers.
posted by aspersioncast at 9:17 AM on May 22, 2018 [3 favorites]
This thread is closed to new comments.
posted by SaltySalticid at 4:50 PM on May 21, 2018