Smallest room dimensions for good bass to 20hz

Woundering how small of a room can you build and still get good bass responce to 20 hz.
I am 13 X 17 as of now and I get good measurements.
20 HZ is 56.6 feet long, so I guess the perfect room would be that long or longer. I doubt there are many homes with a stereo room that length, so maybe all of us are compromised?

Maybe Rives or some other acoustics persons has a formula that determine how much less than that still works fine for our needs.
Is there a formula for figuring out how long (in footage) a given frequency is?
I thought a frequency of 20 hertz would be a wave 20 feet long between peaks.
So what does it mean if your SPL gets a good rolled off read when you play that frequency?
8f - high
15f,2" X 11f,2"
However, large room with good dimentions will always sound better then small room with good dimentions becouse: larger the space - more resonance modes which are more closly spaced in frecuency and will have smoother distribiution.
The best-sounding non-large listening rooms should have a length which is 140-230% (139-233% exactly) of their height (which for most of us can be normalized at 8' ±, more precisely 7.5'-9'), and their width should be within 5% (±5%, that is, or 93-110% exactly) of the geo-metric mean of length and height. The venerable 1:1.26:1.6 ratio
For an 8' ceiling, then, ideal length ranges from 11.1'to 18.6' (say 11-19') and width, provided it meets the geometric-mean (which I now dub least-cubes") restriction, from 8.8'to 12.8' (say 9-13').Within these limits, the larger the properly proportioned room, naturally, themore pleasing also its reverberation time below 500Hz-1kHz.

The Boston Audio Society - Vol. 17, Num. 6 May 1990
I get a compensated/corrected reading of 21Hz at -3dB in my 14x13 room at the listening position. That works just fine for me.

If I am not mistaken, even though the dimensions of your room may be shorter than the wavelengths of bass frequencies, a small room can support low frequencies through pressurization and depressurization of the room. I am in a small room and I can hear/feel 20 Hz bass from the calibration curve of my JL Audio subwoofer.

20 Hz = 20 cycles per second. A 20 hz sound wave is 56.6 ft long peak-peak.

Here is a link to a calculator which also list the formula:


Thanks Reubent. Great site.
Thanks for the responces. Looks like as big as i can get would be best. With the right ratio of width length and height to reduce bass nodes.
Uh no. The bigger the room, the (way) more power and the larger the speaker/subwoofer you will need. You don't need a big room to have low frequencies. Actually, most big rooms I have auditioned systems in never sound like they have much bass cause the speakers can't load the room sufficiently. I have friends who have given up big rooms with big amps ($$) and big speakers ($$$) in favor of a little room that gets even more bass extenstion out of a small system. That is my 2 cents. Just didn't want you to only believe part of the answers. Reread my post above. If you want a large room and have a large budget and want subwoofers, then go for it, but you don't need all that for deep bass.

Just because the wavelength of the signal is longer than the room dimensions doesn't mean it isn't generated by the seakers and heard/felt by the listener. If that were the case then my headphones would really sound like crap.
In a small room the bass is there to be felt but care must be taken to keep it under control.
Arthur is right - big rooms need lots of powerful bass reproduction - very expensive as loud accurate bass is exponentially expensive. So the sound is indeed far better in a large room provided you have the resources to fill it with sound at necessary high SPL.

The one downside of a large room is long reverb times in the need plenty of LF absorption on surfaces and soft furnishings to keep this down (wood walls help leak out bass whilst concrete can be bad)....think of how lecture hall or brick gymn sounds awful(this is obviously far to big and too reflective)

My guess is that around 25 to 35 foot dimensions make a good large room with significant improvement over 15 feet. After this improvements diminish and eventually too large is bad....some wall reflections are actually pleasant remember that speakers outside in the open air sound hollow.
Although 20Hz is 56.6 ft long, one needn't 'fit' the whole length in the room, just 1/2 the wave will do nicely, which gives 28.3 ft. Also, the corner to corner (ceiling to floor)distances must be factored in and of course those dimensions are always longer than any one of the three other dimensions.
Aball, I guess more information would help. I have fairly large speakers, Aerial Acoustics model 9s driven by a Parasound Halo A21 amp at 250 watts per channel. At present they are in a L shaped room 7ft high, about 25 feet long on both ends, and 14ft wide. These speakers go down to 30 hz and in this room don't overload the room. In the future I will build a dedicated room for these and don't want to build to small a room for this set up. I wont have the room to build a room thats bigger than 10ft high 25ft long and 16ft wide. I also don't want to build any bigger than need be, but have heard that full range speakers can overload a small room. I also may add a good sub or two to fill out the last octave.
Upper corner front left to lower corner rear right need to be 1/2 of 56.6 ft. That length works out to be the SQUARE ROOT of:
[(square root of: L squared + W squared) SQUARED + H squared]

Of course if your listening room has at least one wall which has (roughly) half its total surface area open to an adjoining room, you need to measure the longest top-to-bottom diagonal of the combined spaces ;-)) Have fun!
If you are going to the expense of building a dedicated room, why not get an acoustical consultant like Rives in to help you out?

Swampwalker offers some good advice. If you are going to the expense of building a dedicated room, get some professional advice. I've never used Rives, but I've checked out their website and their rates seem to be very reasonable. For possibly less than the price of a component upgrade you can get a customized room layout showing size, materials, etc. Heck, if you get it right the first time using professional advice, it could actually save you money in the long run as it might prevent unnecessary upgrades in an attempt to overcome bad room acoustics.

Just my $.02 worth......


If room dimension had to equal wave length in order to reproduce a frequency of sound, what would one hear in a earphone or headphone?????????? nothing at all but very high frequencies?!!!!!
Kanuk, the space between the headphone driver and your eardrum is not the same as the space in a room between the speaker and your ear.

To vibrate your eardrum, the air in a whole room must already be vibrating at (whatever) frequency.

A headphone driver uses the air between itself and your eardrum as a 'fluid coupling', using it to 'grab' your eardrum and shake it back and forth at the same frequency.

Once again: "The longest room dimension has to equal HALF the wavelength of the frequency you want to produce in it. ;-)
Is using a headphone the same as listening to speakers in an anechoic chamber?

This is only anecdotal;I'm not a physicist.

The lowest note a string bass plays is 41hz,which works out to about 29 feet,so the half wave would be about 15 feet.

With the exception of some organ pipes,most reproduction at 20 hz would be difference tones. (A tone at sixty generates a difference tone at thirty,and fifteen,and seven and a half,and so on. This is the ambiance you get in a concert hall,where the reverb is maybe a second. For more,see Carl Seashore's Psychology of Music.)

Keep in mind that the lower the pitch,the less directional it is. A 41hz tone,generating an half wave of fifteen feet,would bounce off a fourteen foot ceiling.

**So my point,and it is only anecdotal,is that deadening the room(including the ceiling) to absorb sound is probably more important than the size of the room.
"Is using a headphone the same as listening to speakers in an anechoic chamber?"

Similar, but the headphones are more efficient. Try listening to speakers outside sometime. You practically have to 'wear' them (like headphones) to get any volume ;-)