"I have done a few recording rooms before"
This mus be one of the most things we hear when we start talking with a construction contractor about building a dyno room.
Even though recording rooms are loud, trust me dyno testing is even louder on a different scale!
Before we get to that, to make sure you understand the scale of loudness, we would like to recap on the 'loud scale' below.
Level, and Intensity of sound.
Sound is measured in bel (B), but since it is a too rough scale we would normally see decebel (dB).
1 decibel (dB) = 1/10 bel (B)
bel and decibel both are unit of the power of sound in logarithmic scale. Such that 1 dB difference in sound unit is equal to 10 to the power of 1/10 in power.
So we see that every +1 dB sound has 1.25 times the power, but it's amplitude (loudness) is 1.12 times.
This means that every 10 dB difference we hear 4 times louder.
Still can't think of 'hearing' the difference between +1 dB and +10 dB?
Here we put common things on dB scale as a reference:
60 dB - Normal ambient voice in a resturant 70 dB - Vacuum cleaner 80 dB - Telephone rings 90 dB - Hair dryer 100 dB - Pneumatic torque gun 110 dB - Wall drilling 120 dB - Ambulance siren 130 dB - Jet takeoff at 100 meters
Jet take off? Like this :
Was it loud? That was 130 dB !
Ok, now we're on the same page on the sound level scale.
How loud is the dyno testing?
We're here at our main office which we have our own dyno cell.
We're using BMW E36 328i with M52B28 2.8L Straight piped, no CAT, no muffler as a test subject.
Let's find out how loud would it be.
From the video, the loudest record was at 129 dB(A) only 1 dB away from a Jet plane take off, OR only 12% difference
How hard would it be to conceal the noise level?
Since we now understands how loud the dyno test is,
Let us take back this calculation:
Loudness in a restaurant is 70 dB
From an engine in dyno cell was 129 dB
129 dB - 70 dB = 59 dB
The difference is 59 dB , or
59 dB = (10) ^ (59/10) = 794,328.23
795,000 times the power of sound than a restaurant'
Yes, almost 800k times the power, or 890 times the loudness.
What if we want to make it only sound as loud as a restaurant?
We have to reduce the loudness by 890 times.
So what? How it it harder than a recording room?
Okay, we take some information from this research (click the link)
This research looks at the loudness of each instrument groups practicing in a music practice room.
From the research, Table 4 has the loudest group, Bass instrument. The maximum recorded was 98.5 dB(A).
So if we take the difference from a restaurant:
98.5 dB - 70 dB = 29.5 dB 28.5 dB = (10) ^ (28.5/10) = 707.95
From calculation, power difference was 700 times or loudness difference of 26.6 times when compared to 70 dB in a restaurant.
Clearly we see that dyno testing and musical practice is on a different level of sound!
This is what we currently have in our dyno cell, a lot of sound proofing materials and frame.
This is the same dyno test 1 foot away from the door, and recorded 1 meter away from the other side of the door.
The sound was maxed at 102 dB or just a pneumatic gun level
129 dB - 102 dB = 27 dB -27 dB = - 10 ^ (27/10) = 501.18
If we measure 1 meter away from the door, the sound power has been reduced by 500 times and loudness reduced by 22 times
Since the sound proofing door's manufacturer claimed that it is about - 30 dB noise reduction, it is very close.
How about at the front?
Similarly measured at 1 meter away from the door, maximum recorded was 99.7 dB(A) or reduced by 29.3 dB
The same as the door inside the office, it was designed to reduce 30 dB of sound, it came out very close.
Is this the best we can do?
NO. Noise cancelling is something can spend a lot of money in and still doesn't get good enough results.
It is all down to the very first foundation of the room that should be designed for noise cancelling. Given that, how much you will need to do is totally depend on your surroundings.
If there is a dense residential area near to your dyno room, it will be challenging to make a good noise cancelling room not to disturb them.
There are a lot of factors to consider when it comes to making the dyno room to be as quiet as having a restaurant next door. However, it is not impossible, just not with a budget.