Art's Blog: Buy Subwoofers instead of Soundproofing

Dec 2014, comments submitted to Audiophile Review supporting Brent Butterworth’s article about multiple subs. 

Good work Brent…

There are other reasons to have multiple subs than just to minimize mode coupling…….more subs can also mean quieter modes, less power delivering the same sound level, noticeably improved musical clarity and reduced bass boom next door.  

With one subwoofer you will set the volume for a satisfactory sound level. 

With 2 subs, say in the front two corners of the room, you will turn the sound power down 3 dB (in half) because two speakers deliver twice as much power as one speaker if the volume remains in the original position.  So far, the second sub only improved mode decoupling.  

This time put the two subs in asymmetrical different parts of the room and in such a way that they are opposite each other and equal distant from your listening position. Now, the asymmetry further reduces mode decoupling and opposite positioning brings a second benefit into play…….Phase Add.  

When the subs are opposite each other along a straight line that runs through your listening position and equal distant from you, the two wave fronts arrive at the listening position in phase.  This means we have a sonic boost of 3 dB due to the Phase Add effect.  And again, we turn the volume control down, half power setting again and still have the same sub sound level at the listening position.  

Now we are actually injecting half the sound power into the room and getting the same sound level as before.  Less bass power into the room means more available dynamic head room for more explosive bass transients, or the possibility that we don’t need such an expensive amp…..  It also means we are not bothering the neighbors as much.  It also means that what ever modes we do couple to, we are only injecting half the sound power into them, so they are quieter.  

For reference….half power is – 3 dB.  Threshold for hearing sound level differences is 1 dB.  Anyone can hear sound level differences of 3 dB.  

If 2 subs are good, are 4 subs better?  4 subs set up the same way in an X pattern means you turn the volume down again 3 dB because we doubled the number of subs in the room and then down another 3 dB because of Phase Add effect again of the second pair.  Now you are delivering 1/4th the amount of electrical power (-6 dB) into the room and maintaining the same sound level you originally had.  

When you reduced the bass sound power level by 6 dB that is equivalent to doing a soundproofing job that doubled the weight of the walls, doors, windows, ceiling, etc…. (mass law is – 6 dB per doubling of wall weight) of your room.  Now your neighbor is happier.  

Just think, buy 3 subs and save money because now you don’t have to do the soundproofing remodel project you have been planning for….. Then spend your savings on good bass traps, which are put into all the corners of the room, so the acoustic build and sustain of bass in your room gets out of the way faster of the next attack transient. That means you now hear more low level musical detail in the attack transients, which improves the musical clarity of your system….Who’d have guessed? ….

Art Noxon
​Acoustic Engineer
​President of ASC/TubeTraps

Art Noxon is a fully accredited Acoustical Engineer with Master of Science degrees in Mechanical Engineering/Acoustics and Physics. A Professional Engineer since 1982, he is licensed in Oregon to practice engineering in the public domain with the specialty area of acoustics. A prolific inventor, he developed and patented the iconic TubeTrap, the original corner-loaded bass trap/treble diffuser, 150 other acoustic devices, and counting. Lecturer, writer, and teacher of acoustics, he has presented 7 AES papers, numerous magazine articles, white papers and blogs. He is president of Acoustic Sciences Corporation, the company he founded in 1984.

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