Thursday, 18 March 2010

Nobody Understands Bass

Actually most do, especially if their music collection includes Acoustic instruments which are an excellent reference with which to judge the quality of reproduction and the amount of bass extension their system is capable of in their room.

Bass varies enormously from recording to recording (possibly by as much as + or - 10 dB), from room to room and much modern popular music is mixed harsh and bright to make it appear loud and exciting even on cheap systems. It gets more bass as well, but treble is dominant.

Active speakers have very much better control of low frequencies (all frequencies actually) and so, to the uninitiated, may appear to have less bass, but they haven't, so in this blog I'm going to attempt to show all the different factors that effect the amount that you hear.

Most music has a spectral content that covers an area a little over an octave each side of Middle C. Typically bass rolls out quite steeply from about 80 Hz and in classical music about 1 kHz.

The image above is of the opening bars of Mahler's Symphony of a 1000 or number eight. The peaks at 80 Hz are from the Organ. Note that there is a 10 dB drop at 1 kHz which is typical of acoustic music of all types. It's not as bright as pop.

This next spectral plot shows modern commercial rock music, which is not much different at the low end from the Mahler, so equally dependent on strong bass for its message, but what should be noted is the massive additional treble extending by another octave before slowly rolling out. This is typical modern music and is mixed to sound loud, exciting or good on anything. The extra treble benefits a cheap system by improving perceived clarity but can be a problem on an accurate one, especially to a younger listener who will have a massive 10 dB extra sensitivity in the 3 kHz region compared to an over 35 year old.
Our ears don't have a flat amplitude response, they peak at 3 kHz and the slowly roll out again

Now consider the amplitude response of a typical AVI 6" Two way speaker:

Measured anechoically the amplitude response is within plus or minus 1.5 dB and the minus 6 dB point is 50 Hz, so more than enough extension for all music, given that an untreated listening room tends to add bass as the frequency lowers. This is called Room Gain.

Rooms have a profound effect at low frequencies and they vary as you move or your speakers move.

The above image shows the same speaker measure in a typical listening room. Notice that the amplitude response is profoundly affected and also that this measurement would be completely different if the mike or the speakers were moved. Most enthusiasts realise this and juggle with their speakers and their listening position to achieve an acceptable result.

We're finding that about 90% of listeners do not want or need a Sub, but as you can see from the above measurement, it is quite conceivable that some might, especially if their preference is for particularly bright modern rock or large scale Classical Music, Big Bands and most important of all, with Movies where the greater scale is almost essential.

Passive speakers boom because passive crossovers prevent amplifiers from properly controlling them and cheap speakers also boom because they come with smaller magnets and less linear travel. When a cone is driven beyond the point where the magnet can control it, distortion goes up very quickly and the subjective effect is boom. ADM9.1s have expensive high performance drivers with lots of linear travel and they are active so definitely don't boom and may not have enough "bass" for some, which is not a problem because a dedicated Sub with an almost infinite variety of adjustment has been designed to provide exactly what may be required.

The option of our special Subwoofer means that ADMs are firmly in three way floor standing territory, but with the substantial advantage of being fully adjustable to suit taste, music and room acoustics, not to mention the enormous benefit it brings to movies, which just wouldn't be the same without a Subwoofer.


1 comment:

  1. Excellent stuff. Some good material here on an often poorly-explained subject.