Photos of my system

[Reid Malenfant]

Oh dear oh dear

Please don't think i'm a simpleton Yes i understand that an acoustic suspension speaker is near as damn it governed by the enclosure volume & it is more important than the drivers VAS, it swamps it - hence the acoustic suspension thing! It relies on the restoring force of the air in the enclosure to swamp the driver parameters so the enclosure takes control.

However, as i said previously if the whole new assembly with new suspension etc weighs more it'll have a lower free air resonance frequency & on top of that a higher driver Q. In the same enclosure this will result in slightly lower efficiency & & higher closed box Q (Qcb) & the end result will be different from what the manufacturer intended.

That's not even going into what a stiffer or more relaxed foam surround would add or take from the mix

[Dr Bunsen Honeydew]

Sorry but within accepted parameters it will make no damn difference, the surround is rejected, you would have to be a lot out in weight and compliance of surround to make any difference. Anyway the guys who make these surrounds stateside used to supply then to AR and Allison and Jensen and others.

Perhaps you haven't seen that I used to work for AR (uk) for about 5 years in the 1970's. I know this type of drivers backwards. I even replaced foams on the speaker production line at Houghton Regis when the assembly girls tore them.

[Reid Malenfant]

Sorry but within accepted parameters it will make no damn difference, the surround is rejected, you would have to be a lot out in weight and compliance of surround to make any difference. Anyway the guys who make these surrounds stateside used to supply then to AR and Allison and Jensen and others.

Perhaps you haven't seen that I used to work for AR (uk) for about 5 years in the 1970's. I know this type of drivers backwards. I even replaced foams on the speaker production line at Houghton Regis when the assembly girls tore them.

Name dropper

Frankly i'm not interested in who you worked for...

You make a driver cone heavier with the same suspension compliance & the driver Qts increases! So does the Vas & in the same enclosure it'll result in an increased output but at a lower efficiency at low frequencies.

You may well know your stuff with amplifiers etc, but i have been designing speakers since the early 80s.

I really don't want to get into too deep a discussion with you as this is the wrong thread & i hate threadcrapping, but all the driver parameters are vitally important.

That glue you use to stick the new surround, the weight of the surround, it's compliance etc.

If you can keep it all the same when fixing it then yes you should get what the manufacturer intended. Get it wrong & you'll either get more or less bass than was intended... Along with a slower or faster rolloff

[Dr Bunsen Honeydew]

Then we will just have to agree to disagree, Trio Leo can decide which advice to take and which has more validity.

BTW I also design and build speakers and I rebuild the bass drivers for the speakers I currently make, and they are acoustic suspension like the Allisons.

[Reid Malenfant]

I'm pleased you are interested in the electronic/acoustic interface Richard

If there are any other comments i'll attempt to get some kind of coherent reply together tomorrow as i'm off to enjoy the music, & a few more beers

[Marco]

Hi Alan,

Please see further discussion of your system (and some other stuff) here: http://theartofsound.net/forum/showt...092#post220092



Marco.

[Beobloke]

Apologies for prolonging somewhat of a thread drift but I'M going to have to jump in here and agree with Richard.

The fact is that only around half of the surround roll contributes to the moving mass of the cone assembly and in the case of the drivers used by the Allisons, the size of the cone will form the majority of the mass in question. Hence the mass of the surround can vary to a surprisingly large degree before it has a noticeable effect. Also, it is true that in most drive units (certainly ones designed for use in sealed enclosures) the free air resonance and thus the overall parameters of the drive unit are governed by the suspension rather than the surround, thus demoting the importance of the surround parameters further.

Hence, whilst aware that a drive unit will generally sound different, I would say that re-foaming for a good but rotten driver is always worthwhile, particualrly as the effects will be less pronounced than replacing the whole driver with a modern 'equivalent' to the long-discontinued original.Equally, a re-foamed driver that sounds a bit different is still going to sound better than one with knackered foam!

The only other thing I would say is that I personally would NEVER re-foam a driver without removing the dust cap and shimming it. It can be done without, but it's far more hit and miss, espeically with drivers that have small magnet gaps.

[Dr Bunsen Honeydew]

With the Allison drive unit the OP is talking about there is no need to shim. Remove the surround and shake the driver, the cone wont move it is held rigidly in place in the horizontal mode by the spider. Most large bass driver designed for acoustic suspension are the same. You would have to be really stupid and physically pull the cone off centre when gluing the new surround to cock it up.