Allison Six refurb

[kazam]

Doc mod driver in, original tweeter and crossover. Cabinets have had an initial tidy, clearly more work to be done.

I hope to get the other speaker set up with a spare SEAS tweeter this afternoon for comparison (a minor amount of cabinet work is required to facilitate this).

Plating and crossover minimisation will follow, I'm keen to try and learn by exploring the options in turn. All positive sound wise so far..

[_D_S_J_R_]

Do you have both original tweeters still? I'm told these are possibly better than a lot of modern designs, but personally don't know.

[Dr Bunsen Honeydew]

Do you have both original tweeters still? I'm told these are possibly better than a lot of modern designs, but personally don't know.

They are far more musical than most modern tweeters (apart from Doc Mods ones ), but a bit fragile, and fail with age.

[Fretless]

I am really impressed by the quality of Visaton tweeters - Doc will be able to advise which are most suitable for the Allison's and what the best crossover solution is.

The 8" Doc drivers must sound MASSIVE !!!

[Dr Bunsen Honeydew]

Sell the original Allison tweeter on ebay, it will fetch good money as they are looked for as they fail easily. And lots of Allison owners are looking for tweeters. The nipple tweeter is unique and all the *proper* Allison speakers used it, and a similar version was used by Acoustic Research.

[kazam]

DSJR, yes, I also seem to recall reading something positive about the Allison 'nipple' tweeters. Unfortunately, it appears that only one is working, so I will likely do as the Doc suggests.

Before I start fettling with the second speaker, I thought you may all be interested in taking a look at the DM driver, which is on the left. On the right there is a mid bass driver (170mm) taken out of a pair of PMC OB1is, which retailed for just under £5k when they were available. Make of this what you will.

[SteveTheShadow]

The PMC driver will have been designed for use in a quarter wave transmission line, which is what the PMC OB1 is.

The reason for the smaller magnet is not about cheapness, it is that this bass/mid driver has a higher Q factor (Qts);this characteristic governs the driver's behaviour at the line resonance frequency, spreading the resonance over a wide bandwidth, avoiding too rapid a roll off at bass frequencies, keeping the bass reinforcement going down a lot further. These kinds of drivers are one of the reasons a transmission line goes down very low. Of course the rest of the speaker system has to be up to snuff too, in order to get good sound. The damping/absorbtion/length of the line itself provides stiff control of the cone at bass frequencies rather than the use of a big motor.

A driver with a large magnet has a more powerful motor and these are usually found in sealed boxes or in bass reflex types, where tight electrical and mechanical control of cone behaviour is vital to avoid bass boom rather than relying too much on dampling wool, hence the whacking great magnet on the Doc modded driver.

Put a high Q driver in a sealed enclosure or a reflex box and you are just asking for a boom and tizz monster. Different Q drivers are for different purposes and each have their optimum application.

Googling Thiel Small parameters will probably turn up some stuff that will explain this in a more sophisticated manner than I can.

[Dr Bunsen Honeydew]

I take your point Steve, but it is still a crap cheap driver, I looked at it as I helped Kaz change the driver in his speaker. I looked at the speaker construction as well and basically it is an overpriced rip-off (per usual for the British hi-fi industry) that has been built to give perceived value, but it has little real value relative to the price being asked for it.

[kazam]

Steve, thanks for taking the time to explain this to me, I do appreciate it. You have offered just the right level of detail for me to understand at present and when i'm ready for more, I now have an idea of where to look.

[SteveTheShadow]

@Doc
Well I of course have not seen the driver itself, so can't comment on the cheapness or not of said driver; I was just trying to explain the reasoning behind the use of that particular driver type.
You are dead right of course. Some of the drive units I saw in the commercial speakers I used during the time before I started building my own were universally dire. The standards were truly awful. They all used complex crossovers to paper over the cracks; arse about face engineering, designed to make as much money out of the hapless punter as possible.