MadSci Network: Engineering
Query:

Re: How do small, modern speakers create bass equal to larger, older ones?

Date: Sun Jul 5 18:50:36 1998
Posted By: Matthew Buynoski, Senior Member Technical Staff,Advanced Micro Devices
Area of science: Engineering
ID: 896980055.Eg
Message:

You can get into arguments on whether or not the "new, small" speakers do 
create bass equal to the "old, big" speakers, or not...heated arguments 
among audiophiles.  Your Mad Scientist tends to take the view that the 
newer speakers are not the equal of the older ones, and with that bias 
exposed, explains further.

Bass takes a fair amount of energy. The volume of air to be pushed around 
by the speaker is large relative to midrange and above. This can be accom-
plished in three ways that I can think of:

	a. Large speaker with small excursion of voice coil.
	b. Small speaker with large excursion of voice coil.
	c. Many small speakers acting in concert (mimics larger overall area).

There are also considerations of acoustic isolation. That is, the wave that
comes off the back of the speakers must somehow be prevented from 
interfering with (and thus cancelling, as they are exactly 180 degrees out 
of phase as created) the wave off the front of the speaker. The more power 
and air movement, the harder it becomes to dampen out the back wave. Large
enclosures filled with deadening material (some old speakers even had sand
in them) help here.

Now, the take on how the new, smaller speakers are supposedly able to equal
the older, larger ones is that they choose to make much larger voice coil
excursions. This is allowed mostly because of better and more exotic 
materials.  It was, in olden times, hard to move the voice coil very far
without getting into serious non-linearities and thus considerable 
distortion. Also, the speaker cones were not as "stiff", so that they would
flex instead of moving as a coherent unit if asked to move too far.  Better
materials allow for larger excursions of the speaker without wiping out the 
signal with a lot of  distortion.  The matter of acoustic isolation of
the back wave, however, is not really subject much to these arguments, and
your Mad Scientist is, well, yet to be convinced that it has been fully
taken care of.

As to whether or not the newer, smaller speakers do equal the older, bigger
speakers  insofar as sound quality, is a matter of subjective judgment.  To 
settle the matter, double-blind testing with very exacting control over the 
sound pressure levels is necessary. Otherwise, you end up with an endless 
set of arguments of who thinks what is better. Your Mad Scientist remains
skeptical in this regard. 



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