Newbie question about dome tweeter construction

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Dear all,

I've seen and worked with a few (inexpensive) dome tweeters, and I'm confused: do they need an enclosure at all?

Basically, some of the tweeters I've seen have no hole on the rear plate. The rear appears to be a thick, heavy metal disk. The terminals are on one side. Assuming that the dome's membrane is actually 25mm, as is often the spec, does this mean that only the 25mm dome in the centre, visible from the front, vibrates? If yes, and if there's no hole at the back, does this mean that the dome is sealed at the back, hence there's no difference between mounting it on an open baffle and mounting it in a closed chamber?

And if there's a hole in the centre of the rear plate, is this what they call "vented pole piece"?

Request patience dealing with my newbie questions...

Thanks and regards,
Tarun

[SY]

Most tweeters do have sealed backs. The back of the dome normally vents back into a wee chamber built into the driver. When they do anything different, the spec sheet usually idicates this.

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Originally posted by SY
Most tweeters do have sealed backs. The back of the dome normally vents back into a wee chamber built into the driver. When they do anything different, the spec sheet usually idicates this.

OK, and thanks for replying. And really sorry if I'm slow on the uptake , but can you please clarify the following?

1. If dome tweeter backs are sealed, will they be exactly the same, accoustics-wise, if they are mounted on a box or on a flat plate (ignore baffle step effects and box dimension differences.) If they are exactly the same, why don't more speaker designers fit them on a cute-looking flat plate on top of the mid or bass driver? Is this just a convenience and aesthetics issue then?

2. I have one tweeter (made by Peerless India) which has a hole on the rear plate? What is this for? Is this "normal"?

3. Is the B&W treatment of tapered pipes for their tweeters in the Nautilus range an example of tweeters with open backs?

Tarun