Drilling out the motor to create a pole vent

[454Casull]

What are the chances that the chips are going to get stuck inside the motor - namely, in the voice coil gap?

 

[MJL21193]

What are the chances that the chips are going to get stuck inside the motor - namely, in the voice coil gap?

Hi,
Slip a strip of paper in to shape of a tube between the VC and the pole piece then drill, go slowwww and put gobs of axle grease on the drill bit and area to be drilled.
The grease will catch the swarf.

 

[tinitus]

To be effective you would need holes on the back poleplate to make passage to the magnet gap area

Its much easier and really effective to remove the dustcap, and maybe mount a foamplug instead

 

[454Casull]

To be effective you would need holes on the back poleplate to make passage to the magnet gap area

Why?

 

[tinitus]

Sorry, may be a mistake on my part...when they do that it may only be to remove heat...not many do it, but I believe AudioTechnology is one

As said, remove the dustcap, much better...theres a very big risk you will have small metal parts jammed in there

You never mentioned what kind of driver ?

 

[454Casull]

MCM 55-3870

It's got a fairly large conical indentation in the back plate which I assume is centered.

 

[Cal Weldon]

Drill hole in dust cap. Nothing magnetic to worry about.

 

[Cal Weldon]

conical indentation in the back plate which I assume is centered.

It is where the lathe centering pin goes when they machine it circular?

 

[454Casull]

Dunno if they used a lathe for that, but if I were them, that's what I would use it for.

 

[John_E_Janowitz]

Is there a particular reason you're wanting to do this? This driver has a 1" VC. To do anything useful with a pole vent would require probably a 3/8" diameter hole. At that point you'll be taking away enough steel that you are now saturating the pole earlier. That means Bl goes down along with efficiency and your Q goes up. I don't think you'd want to do that with an already low efficiency driver with a .50 Qts.

You can make a hole in the dustcap if you want, but just removing it may be the best idea. The dustcap is always going to create one of the worst issues of resonance on any driver. If you really wanted to go all out you could make a little phase plug to go on the top of the pole with the cap removed.

If it's just for ventilation issues, a couple small holes in the cone underneath the dustcap would vent air from inside the chamber created by the dustcap and coil former.

John

 

[454Casull]

Venting the diaphragm underneath the dust cap is a fantastic idea. Thanks.

 

[tinitus]

The late mr Duelund sometimes made holes in the outer edge of the spider, with a solder iron

 

[Moondog55]

I have used both of those techniques on high "Q" drivers, I didn't at the time notice much difference, but still worth doing.
On the venting option what is the usual ratio of hole to pole diametre.
My little Vifa's have 25 mm VC and 10mm hole the 8inch Vifa woofers 50mm VC 20mm hole
My Cerwin Vega's 3inch VC and 1inch hole, what is the ideal??