[rollei_list] Re: Completely OT- Loudspeaker info

  • From: Frank Dernie <Frank.Dernie@xxxxxxxxxxxxxx>
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Wed, 16 Feb 2005 08:09:08 +0000

It is interesting to study the audibility of phase distortion. I have 
listened to  a square wave through a loudspeaker and can barely tell 
the difference caused by a level of phase distortion which makes the 
wave visibly unrecognisable as a square wave on an oscilloscope. One's 
eyes are much more phase sensitive than ones ears! In order to do this 
one must find a phase coherent loudspeaker and listen in the nearfield, 
before the room interactions have had their effect. Very few speakers 
on the market are phase coherent.
If phase accuracy was extremely important multi miked recordings mixed 
using a conventional desk would sound even worse than they do!
An electrostatic is fairly phase coherent in the first 3 to 4 feet in 
front of the speaker. By the time the back reflection is heard (and the 
extra stereo "depth" thus created enjoyed) there is no phase coherence 
whatever.
A friend of mine designs dipole speakers which sound great. I have some 
of his prototype units at home just now. The biggest benefit is the 
cost savings associated with the box. Producing an effective closed box 
speaker where a considerable proportion of the sound being heard is not 
cabinet vibrations is spectacularly expensive, and rarely achieved. 
Creating an effective baffle to effectively separate front and rear 
waves needs a good understanding of the physics but then can be done 
relatively inexpensively. They have to be positioned very precisely 
within the room to achieve bass evenness and extension.
The Celestion 6000 system was AFAIK the first to exploit this acoustic 
characteristic, the bass module was positioned  and orientated 
correctly then the main speaker put on top. The position of the bass 
units was calculated for each customer by Celestion using the listening 
room plan. They are spectacularly effective when thus positioned, but 
probably had a tiny market because, as you so rightly write, most 
people have to put their speakers where they go!
Frank


On 16 Feb, 2005, at 06:23, A. Lal wrote:

> The ear's sensitivty to group delay (or waveform integrity as you put
> it) is well beyond what most xovers produce.


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