To seal or not to seal...that is the question!

[jberger]

I have a set of Bose 901 II's that I'm bringing back to life (mostly cosmetic). These have the Bose drivers with cloth surrounds, so I don't have "foam rot" on 18 drivers. However, I've noticed that (to my eyes, at least) that the doping on the cloth may not be providing a good seal. I have some of the cloth-surround sealer liquid from vintage-ar.

If this were a single-driver system, I'd push in the woofer, and see if it springs back slow (good) or fast (bad seal).
How would I do this (test for seal) with a multi-driver (or passive radiator system)? If I push in one, the other eight pop out, and I'm not an octopus, so I can't push all eight at once.

Or do I just bite the bullet, seal all of them, and re-do the putty behind the drivers? I mean, it's not like refoaming all 18 drivers....

 

[gbroot]

I'm not real familiar with the early 901's. As you can see in my signature I am used to much higher end gear! If your 901's are a sealed design, I'd definitely retreat the surrounds. I have used the Vintage-AR sealer on several sets of KLH's and while a bit pricey it is the right way to go. They must be early 901's cause I have read re-foaming is very time consuming and an expensive ordeal.

 

[jberger]

The Series I & II used treated cloth surrounds. Series III used crumbling foam, and I think that by Series V they switched again to a more stable foam. I wouldn't want to refoam a set of these.

But the larger question remains: how to test for an airtight seal on a multidriver box.

 

[mech986]

You may have to consider using some weights on the cones or probably tape or screw down covers with spacers holding the cone down so they don't move. IMO, that's probably a lot more work than needed.

Personally, IF one assumes this should be a completely sealed system, I would just use the surround seal, caulk all cabinet joints, and then redo all the driver seals, and call it a day.

 

[GoldSounds]

I don't know that a perfect seal is necessary on these particular speakers. The vintageAR sealant is designed for AR and KLH cloth surrounds, but these are more essential since they are acoustic suspention designs. Aren't all of the 901's ported? As long as they aren't too leaky such that the port(s) is the primary path for air entering and leaving the speaker I would think that they should be okay. I'm not sure that there's an effective way to test the airtightness of a box with 9 drivers anyhow.

 

[jberger]

Bose switched from acoustic suspension to ported between Series II and Series III; mine are sealed.

 

[GoldSounds]

Well, since they are sealed boxes then put me in the "use vintageAR sealer" camp. It may be expensive and time consuming but I think that you are on to something by trying it.

 

[jberger]

Sealer is on order, even though the drivers don't look as bad as I remembered. Next, to order the caps and a couple of transistors, as there is no output from one channel. Bose lists their part number as 1024357-2. Any cross reference suggestions?

The part number on the transistor is BC 239C, which shows as obsolete. It looks like it was replaced with a BC 239CG, which is also obsolete, and there's an NTE47 that claims to be a substitute. Suggestions?