40hz ratings/speaker response

Hi, Joe: The frequency range quoted for a speaker is normally stated to some frequency at which point the response is down by 3db. Hence, the speaker has usuable output below that point, but it will be increasingly weak. If you looked at a graph of the frequency response, it would show how rapidly the frequency response drops -- if it is a severe drop, then the speaker's low frequency (or high frequency) response will very rapidly become almost too weak to hear.

If you have a speaker that is reasonably flat (+ or - 3db at 40 Hz), you will still get decent output for the lower frequencies of the acoustic bass and piano. The lowest note on an acoustic/string bass is about 32 Hz, and a Steinway Grand piano has a low note of about 28-29 Hz. Your speakers will probably reproduce the lowest notes of the bass and piano, but their volume will be diminished relative to the upper bass and lower midrange.

If the loss of full output at the lowest frequencies concerns you -- for example, if you want to reproduce the pedal tones of an organ -- then you will need to add a good subwoofer to your system. Subwoofers actually do more than just reproduce the bottom 1-2 octaves -- due to the crossover, they also relieve the woofer or mid-range of reproducing the deepest frequencies, which reduces their IM distortion levels. This often results in much cleaner, more transparent, and more dynamic sound reproduction by the main speaker.

There have quite a few threads lately on subwoofers, their pros and cons, and the better brands/models, so you may want to do some digging in the Audiogon archives for these threads.

A lower limit of 40 Hz is not that bad. The trouble is we only speak of fundamental tones and not the harmonics. A lot of instruments have second or third harmonic energy below 40 Hz. If it is a ported alignment, roll off below the 40 Hz FS will be 12 db per octave while a sealed alignment will be at 6 db. Trying to equalize the bass below the FS is tricky since it requires a great amount of power on the part of the amp and the ability to handle it on the part of the woofer. Only try moderate boost of about 4db. That will require over double the amp output than the non boost.

Many would make a good argument that these speaker ratings are largely meaningless. But assuming they are at all meaningful, a rating will include a low end frequency and a tolerance. So it won't just say "40hz", but instead, it will say "40hz +/- 3dB". If you look at a frequency response curve of a speaker, it shows the output in decibels for the range of frequencies at a given signal strength. Ideally, a curve will be completely flat from 0 to infinity, meaning that all frequencies are equally represented. the 40hz +/- 3dB means that the curve is flat within 3db of the vertical center of the curve. In almost all cases, the curve deviates from flat at the low end and you can pretty much assume that that's where the greatest fall off is. So, for a given signal strength, you should hear the music pretty much as recorded, but as you approach the lower frequencies, frequencies of 40hz and less will be 3db or more "quieter" than they should be.

If you at all rely on this spec at all, remember that it is completely meaningless without the tolerance number. For instance, there are many speakers around for under $100 a pair that have a frequency response from 20hz to 30Khz!! (20hz at -18dB, that is!)

A speaker rated down to 40hz will play below the frequency, just rolled off. The amount of rolloff depends on the type of low freq. system. Bass reflex rolls off at twice rate of acoustic suspension below the low frequency resononce. But with room gain, a speaker rated down to 40hz ("faithfully" i.e. +/-2db etc.) would still reproduce down through the 30's and even some of the 20's depending on the room. Small rooms can offer 9db of gain at 20hz. You turn it up, and like with any driver, distortion will go up.