HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Some thoughts from my reading around on this subject.

*Doping mostly near the centre of the cone (and over the dust cap) can smooth out the spiky high frequency output of the woofer and attenuate these frequencies.
*The obvious T&S parameter that is changed is the increased mass of the cone (Mms)
*The resonant frequency (Fs) is lowered as a result of adding more mass. For a woofer that is considered good.
*As a result of lowering Fs, the efficiency is lowered - can be good or bad depending on what you want to do (but mostly bad)
*A change in Fs has an effect on Qes and Qms and therefore Qts. Decreasing Fs (by adding mass) increase Qes & Qms. This in turn leads to Qts increasing (via equations i won't mention here).

There may be other things affected that i have not found yet.

What don’t manufactures ‘dope’ them themselves ??

I think some do have doped models but it is usually a very thin coat over the whole cone. Nothing like as extreme as what we like to do here.

Doping is an expensive buisness and labour intensive.

Thanks both... never knew.

There are a number of companies who use the bass driver directly coupled to the amp. Of these epos es11 are the most famous.

Many manufacturers approach the problem by using other materials and thus try to maintain efficiency. My only experience of NVA doped speakers was with a pair of cubettes. I was quite surprised how much I had to crank up the volume to get the stereo image to come good.

Well the drivers the doc used were lowish efficiency to start with- about 84 dB for the 5" and 86 dB for the 12" before they were doped. Can't remember what the others are.

Starting with a much more efficient driver would help.

Hemmo1969 wrote: ↑Thu Oct 17, 2019 1:24 pm What don’t manufactures ‘dope’ them themselves ??

Goodmans did it to woofers in the early 70s (e.g. those in the Magisters and Goodwoods).
My understanding is it was the job of one old lady in their Wembley factory (can’t remember her name, nor exactly what she used. It’s something that took years (decades?) to dry out completely).

Nana magic