Another Goodmans Magnum project

[Toontrev]

Thanks for the directional tip doc, totally slipped my mind but checked and its OK. Baffles sprayed up and look good.

[Toontrev]

I decided to finish the baffles off with black and they look great. The plasti-coat does some odd things with the rubber surrounds so I may wait until tomorrow to give then the a first listen,the wrinkling calms down the next day. Its been a very informative project so far.
cheers

[Dr Bunsen Honeydew]

I have never seen those surrounds not wrinkled, it make no difference. Listen.

[Daniel Quinn]

Looking good they are.

I have a few of those maplin capacitors indeed yesterday I got two 3.3uf . They are good. I could not tell the difference from clarity caps at 4 times the price.

I am keen to try oil in paper and copper foil capacitors but price puts me off. when I've got nothing left to buy maybe.

[Dr Bunsen Honeydew]

Capacitors, the different sound, confusing and small can be. (in Yoda mode )

[Toontrev]

Well first listen today and generally I'm fairly pleased. Tonal balance is just about spot on, cant see any need to make an alteration. The overall impression is that they are very smooth, more so than I expected so I tried female vocals which are always a good test and the result was excellent. The amp is a £20 1970's Sanyo job off ebay but its getting a lot of headphone use at the moment and I'm enjoying it.
Amazing to think these are over 50 years old.

[Dr Bunsen Honeydew]

Must be on stands up to max 18 inches high. You should do the wall dance and toe in dance to find the right balance. All newly doped drivers need a run in time for the doping to settle.

[Toontrev]

Cheers doc thanks for all the advice its been invaluable. very enjoyable project, I'd like to think there is another 50 years out of these, they do look great.
There is one question that I cant find in the searches or anywhere on goggle come to that, which has me very curious since I joined the forum. Take out the crossover, bass driver now receives a high frequency signal, doping or making the cones heavier means it doesn't or can't respond. Is it simple as that ?

[Dr Bunsen Honeydew]

You have to understand the physical characteristics of materials and construction. A large cone driver transmits HF from close to the edge of the coil / dustcap. Progressively lower frequencies are transmitted out to the edge of the cone. Complicated by the way the paper is laid and the cone formed and what termination is applied, corrugated paper or rubber / foam roll. Interestingly I was trying to explain this to DSJR last Saturday. JBL / Altec got it off to a fine art (then lost it or wont pay for it as the skill involved to do it is bloody expensive). Goodmans weren't bad at it, Tannoy ballsed it up.

So to tame HF propagation you damp the inner part of the cone with the most doping (worms of Bison) helped by coats of Plastidip on the whole cone. As a side benefit the cone behaves more predictably with less cone resonance standing waves which creates distortion. The doping damps it. To be honest I am completely dumbfounded to find no one else I have found has even talked about this. It has just become an industry given that a multi drive unit speaker must have crossovers either passive or active - they don't.

Lightly doped paper as used in production by some makers is purely to create cone production consistency.

[Dr Bunsen Honeydew]

Some more inf.

Lets talk about doing paper cones properly so doping is not needed. If I was faced with *properly* made paper cones like old JBL and Altec I would not dope, and probably Lyndsays big buggers as well, they looked like it when I saw them but you have to look at the driver out of the cab.

It was a very skillful job as the cone had to be thicker with coarser paper pulp near the centre, thining and going to finer pulp towards the edge, and to work really well a well made corrugated paper surround. The cone would then act as a whip to project the sound and the corrugated surround would then damp it. When they moved to cheaper cones they had to go to rubber / plastic / foam half roll cone termination = compromise!

Now we come to cabinet design. The roll surround was developed by Acoustic Research as they did things very differently to the likes of JBL. With AR the cabinets were integral with the driver in the design and *had* to be airtight so the driver *sat* on the sealed air in the enclosure so the surround had to be very compliant and the driver didn't act as the JBL whip it acted as a piston. So the JBL type design would not do. Modern speaker have *all* copied and followed the AR way unless they have been fecked up by adding a port to get artificial bass extension - yuk !

The likes of Tannoy and others copied the roll surround for big drivers for all the wrong reasons i.e. cost and ignorance, which is why the corrugated surround Tannoys are far better than the more modern ones with roll surround. But none of them are very good in reality compared with JBL and Altec.

Do you now see how much shit AVi (and Harbeth) talk

Drive unit design can be thought of as a black art that has been commercialised away from excellence to simplicity and price and profit. So to get back to near the origins work has to be done to them by adding mass and damping and making it progress across the cone.

If you had to have an old JBL or Altec 12 or 15 inch drivers built today to the standards of those days they would cost over £500 to build in labour and material costs alone so would cost well over £1000 even at a trade price.