Woofer rear pole piece vent foam

[profiguy]

I'm rebuilding some Dynaudio 30W54 woofers and need to replace the rear vent foam due to deterioration.

Does anyone know the specs of this foam ie. CPI (cells per inch) count? The density of the foam is important to get right as it effects driver TSPs.

 

[profiguy]

I ordered some 20 CPI reticulating foam so we'll see how it goes. That density is about the same as in wall AC filters. It should barely restrict any flow.

 

[Robh3606]

Just use window screen that's what they did before the foam kis

Rob 🙂

 

[profiguy]

That's a good option but Dynaudio drivers use foam for a reason. It has some dampening characteristics which screen doesn't.

 

[profiguy]

The 20 CPI filtration foam appears to have the right properties. I'd recommend it for all Dynaudio and Morel driver rebuilds.

 

[Robh3606]

That's a good option but Dynaudio drivers use foam for a reason. It has some dampening characteristics which screen doesn't.

A thin 1/8 layer of foam with minimal air resistance? If the foam was a plug that filled the vent maybe. It's there to protect the gap from foreign material. JBL used it too and it could be a nightmare. When deteriorated it can get sucked in and end up in the gap and in some cases actually jam the coil.

At the very least should have screen under when replaced because the foam will just fall apart again over time.

Rob 🙂

 

[profiguy]

@Robh3606 Yes, the original foam filled the entire depth of the opening. I agree using a screen under the foam is a smart idea to avoid contaminating the VC gap in case of foam disintegration. JBL had this issue on their 2213s.