Some apps for sound level meters and reverberation times…

Marshall Chasin
August 9, 2011

Dr. Joe Smaldino put me on to some apps that can be downloaded onto your iPhone, iPod touch, or iPad.  For those of you who don’t know Joe, think “room acoustics”.  He, along with Drs. Carol Flexer and Carl Crandell wrote the seminal book on room acoustics for hard of hearing children. Normally I would simply reach up and pull it off my bookshelf, but alas, someone has “permanently borrowed” my copy.  So, I can’t give you the full title, but trust me, it’s a great book… I guess that’s why someone permanently borrowed it?

But back to Joe….  Joe gave a talk at last year’s American Academy of Audiology conference in Chicago where he compared some of the inexpensive apps (or is it aps?) that can be downloaded onto your iphone or ipad against expensive sound level meters and devices to measure the reverberation time in a room.  It seemed that these apps did as well as the very expensive ones and were obviously more portable, and accessible.  In most cases, the sound level meter app was within 1 dB of the more expensive type II sound level meter.  The same thing was found for reverberation time.  Just go to the apple app store or to to see what they have.  Similar apps are available from other suppliers but by in large, are quite similar.

Sound level meters and reverberation time measures are not just useful in classrooms, but in a wide variety of musical and music settings.  This can be your home studio/garage, a high school band room, or a professional venue.  Having a reverberation time that is too long will muddy up the sound and this would call for absorptive curtains, floor and ceiling coverings to reduce the echoes.  Too short of a reverberation time and the room sounds sterile- time to pull back the curtains and remove some rugs.

Reverberation time is the amount of time (in seconds) for a sound to die off to a point that is 60 dB below the initial time.  Reverberation times have been used since 1900 with the construction of the Boston Symphony Hall.  In the app world, this measure is frequently referred to as the Energy Time Curve because it shows the energy drop off as a function of time (in seconds).

Here are some optimal or preferred reverberation times (in seconds) for various types of music and speech.

Symphonic music 1.8 – 2.1
Chamber music 1.6 – 1.8
Opera 1.3 – 1.6
Modern music 1.1 – 1.7
Live theatre 0.9 – 1.4
Lecture or conference 0.6 – 1.1
Broadcasting / recording 0.3 – 0.7

As can be seen, when speech is involved, the reverberation time needs to be less.  When music is played with a lot of sustained notes, then longer reverberation times are required.  But not too long- underground car garages have a reverberation time of about 4 – 5 seconds and are lousy for everything except parking your car (and a few other illegal things but I wouldn’t know about that)…

And imagine having a sound level meter at your finger tips- or iPad tips… setting or checking the level on a recording or a playback of a song can be done inexpensively.

I know that this sounds like an ad (or add?) but it’s not…. well, it is, but that’s not the intention.  This is the dawn of an entirely new technology that promises access to tools that were once only owned by the rich (or technical).  Your home studio can now be “tuned” to near perfection.  Your garage will still be your garage, but may be slightly better if you know something about the sound levels and the reverberation times.  And who knows, a rarely used hallway may be the perfect acoustic environment for your needs.

Experiment and enjoy the technology that we now have access to.  And stay out of underground garages.

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