Soundproofing—How much and in which frequency range

How much sound proofing a person needs depends on many thing, not the least of which is the cost. Independent of cost there still are some important soundproofing facts a person needs to know. Let’s begin with the concept that you certainly don’t need to reduce the intruding noise any lower than your threshold of hearing for that noise. The Fletcher Munson curve is spectrum graph of equally loud sounds. It ranges in frequency 20 to 20k and in loudness between 0 and 100 dB.

Look at the lowest curve. It is the threshold of audibility. It is the least loud sound a person can hear. This is what a hearing test measures. Notice that at 50 Hz, the threshold of hearing detection is about 50 dB while at 500 Hz or 5000 Hz the lowest level of audibility is about 0 dB. This means that in general, we do not need to reduce the bass range of noise as many dB as we need to reduce the treble range of sound.

Look at the loudest curve, it is at 100 dB regardless of which frequency. Very loud sounds all have the same loudness level regardless of frequency. When you need a noise control project you want a spectrum analysis done on the noise so you know how loud the bass is that is leaking through the walls and how loud the treble is. Plot those levels on the Fletcher Munson curve and scale off how many more dB of soundproofing are needed to reduce the intruding noise to the threshold of detect ability, which is actually very, very, very quiet.

When we work on your project, we record how loud the noise is, that is bothering you. We send you a small pro audio DAT recorder and all you do is press RECORD, then send it back to us.

Copyright 2010 Acoustic Sciences Corp.