How much do driver properties change over time?

[leadbelly]

I have been running my Tempest for about 2 years now. I am finishing my basement and would like to move to stereo subs in the new bigger space. If I buy another new Tempest now, will it be a good match for the other? I guess this raises the question both of aging of a driver and of the manufacturer's quality control/batching.

[GRollins]

You're opening a can of worms.
Setting aside the question of burn-in and changes in the first 50-100 hours of use, there are changes in drivers. The single worst example the is foam surround, which rots after 5 to 10 years. People think,"Oh, well, then I'm okay for another X years." Not so. The surround doesn't behave like the proverbial one horse shay and come apart all in one 24 hour period--it's a slow, continual deterioration that begins the day it's manufactured. In fact--and this is something a lot of people don't realize--the surround will rot even if the driver is just sitting on a shelf. Ever wonder why you don't see any NOS Advent woofers? Trust me, you won't. They're all gone. I don't care how great a driver is--if it has a foam surround it's a non-starter in my book.
Another problem that's more subtle is heat damage in drivers that are run hard. It's not that difficult to imagine the coil melting, but a more insidious evil rears its ugly head when the magnet loses strength as a result of being exposed to heat.
Moisture can effect paper cones.
The softer glues can harden.
Etc. Etc. Etc.

Grey

[leadbelly]

Wow, Grey, that must be the longest post you've written about a Tempest without slamming it....

Seriously, thanks. I'll have to wait for a good sale on sub drivers and pick up two.

[BassAwdyO]

Ahh foam surrounds rotting, always hurts a speaker. Hasnt some sort of treatment been invented to prevent the rotting of foam surrounds? If not perhaps there is a DIY way to treat a foam surround to prevent it's decay... any ideas?

[mwmkravchenko]

They have been using foam surrounds that are encased in a thin plastic. From the literature that I have read it is foams susceptability to ozone that leads to it's untimely demise. Poor critters. RIP

Mark

[keyser]

why do manufacturers still use foam surrounds? why not just all rubber?

[djQUAN]

simple. foam is cheaper than rubber.

[Ron E]

Originally posted by keyser
why do manufacturers still use foam surrounds? why not just all rubber?

Originally posted by djQUAN
simple. foam is cheaper than rubber.

It's not just economics. Proper surround design doesn't just involve attaching the driver to the frame with something flexible. The mass and stiffness and damping of the material (most significantly for mid and fullrange drivers) are used to terminate the resonances of the cone in order to minimize them. A low mass material is useful for this at high frequencies, and even at low frequencies foam is very easily adjusted in properties.

Rubber can rot and harden and change parameters, so it is not immune to degradation, either.

[cocolino]

originally posted by leadbelly
I guess this raises the question both of aging of a driver and of the manufacturer's quality control/batching.

I wouldn`t rely on consistent manufacturing quality of drivers.
Sometimes it appears that even manufacturers of quality drivers change something in the fabrication process or they use different raw materials.
This means that a driver bought a few years ago do not necessarily have the same (initial) parameters or properties as the same type of driver bought today.
Not rarely these differencies can be quite substantial, sometimes so that it literally could be called another type of driver and also not rarely the "old" specsheet for that driver wasn`t changed according the new parameters or properties.
For customers this is bad thing as they never can be quite sure what they really get.
There is only one way out of this - never rely on manufacturers specs - measure everything by Yourself.

originally posted by BassAwdyO
Hasnt some sort of treatment been invented to prevent the rotting of foam surrounds? If not perhaps there is a DIY way to treat a foam surround to prevent it's decay... any ideas?

Not that I`m aware of. I wouldn`t recommend to treat foam surroundings with anything. The best way to prevent or to delay detoriation of foam surroundings is to avoid exposure to direct sunlight.

originally posted by djQUAN
simple. foam is cheaper than rubber.

Also I partially agree it`s not always that simple.
Or why do You think that manufacturers as Scan-Speak sometimes also use foam surroundings?
I don`t think it is always a cost decision but one based on technical issues as Ron E already pointed out.


And BTW: foam is not foam. I still have Scan-Speak drivers that are 20 years old and the foam surround is in still very good condition. I have seen drivers with completely rotten foam surround after less than 10 years while just sitting around on the shelf most of their lifetime.

[morbo]

I was unde the impression that the foam used these days does not rot as much as it used to. Adire uses foam surrounds on even their most expensive woofers, like the Tumult. This is from the Tempest whitepaper:

3.4 Why a foam surround?
We chose a foam surround based on the requirement for large Xmax. Simply put, available rubber (natural
and synthetic) surrounds did not provide the long Xmax (or Xsus) needed for Tempest. Going with a
rubber surround would have removed several mm from both specifications, and would have run counter to
the concept of Tempest being an extremely long-throw subwoofer.
Additionally, thin and loose surrounds, both foam and rubber, can experience "suck back" at high SPLs
when the negative pressure (relative to ambient outside pressure) inside the box literally pulls the surround
backwards, flipping it inside out and quickly destroying it. To avoid this effect, the surround must be made
thick. However, synthetic and rubber surrounds of sufficient thickness to avoid this problem would have
added dramatically to the stiffness of the suspension, resulting in a much higher Fs. The foam material used
on the Tempest surround allows for sufficient thickness to avoid suckback, but without the negative effects
of a much stiffer suspension.
Some people may be concerned about the reliability/longevity of the foam surround. The foam surround
used in Tempest is fully UV resistant, and should exhibit a lifespan of considerably longer than 10 years.

The Shiva has been around for a pretty long time now, and I have not heard any reports of surround degradation. Not saying it doenst happen, just that if it was a big issue I can't see well regarded companies like Adire not using rubber for a $500 driver like the Tumult.