CD versuc Wide dispersion lens

[Bernard Wolf]

Hi Guys

I would like to know what you all might have to think about the Constant Directivity lens versus the normal wide dispersion lens found on most horn speakers. In particular the situation with regards the use of our largish JBL’s in rather smallish rooms. Recently on a posting by Niklas Nord, the necessity of side wall treatment was addressed and mention was also made of direct versus reflected sound. The room that the S9500 is in looks to be about 12’ wide. I happen to own the S3100 and had for a number of years used them in a 12’ x 27’ room. I was able, because of the CD lens, to place them almost touching the side walls with very little side-wall reflected sound. On records with various surface problems I did have that problem on occasion but found that overall it was not of great signifigance with most Lps being fine and CDs of course being no problem at all. I am fortunate in that I now have enlarged my room to over 700 sq.ft. 35’ x 24’ on the long side with a bit of a cut out – a rather irregular room. Because of posts and the like I use the 3100 across a corner 12’ apart and because the room runs away from them I hear no side-wall reflections at all. The imaging that I get is incredible and at times it sounds as if I have surround sound. The bass has also improved. I have no room treatment other than recoreds - 2500 - and books, but at times I do feel that I would not mind a bit more splashy sound that a dome tweeter might give. I guess there are trade offs for everything. But back to my original question : would a CD lens not make more sense for the majority of listeners out there who have small rooms and cannot or will in all probability never do room treatment ?

Thanks for your thoughts. Bernard

[Ian Mackenzie]

Bernard ,

This is a very involved subject and it depends on a lot on many inter related issues.

Constant Directivity lens versus the normal wide dispersion lens found on most horn speakers.

Based on what the CD horns function is, ie flat on axis and power response after Eq I doubt if one has an advantage over the other but this is a very general statement.

CD horns in themselves can be designed for controlled dispersion so that they emit an even coverage over a defined field of view, say 60 degrees horizontal x 30 vertical, or 100 x 100 degrees.

This angle of projection is very useful for controlling the direction /distribution of sound in the acoustic environment which is often a mishmash of reflected and reverberant sound waves interwoven with room modes forming a very complex set of effects in terms of audible sound to the listener.

The virtues of a particular horn also depend on the listener's position in the room, near, mid or far field and this is key to the percentage of reflected versus direct sound rather than the speaker system.

Small rooms are more difficult to deal with in terms of control of low frequency energy without doubt, however large rooms can also present a challenge for control of reflected sound in the mid and Hf bands. More importantly people under estimate the importance of high ceilings if possible and an even distribution of soft and hard furnishings in their listening rooms.

Ian