transmission line woofer question

[marlboro]

Does the end of the transmission line have to terminate in the same space that the speaker does?

If you are using a woofer transmission line and you want nine feet but your ceiling is only 7.5 feet, but decide to terminate the top of the open tube in the inside of the drop ceiling, is that OK or does it have to be terminated in the room itself.

Marlboro

[Pete Schumacher]

Re: transmission line woofer question


> Does the end of the transmission line have
> to terminate in the same space that the
> speaker does?

> If you are using a woofer transmission line
> and you want nine feet but your ceiling is
> only 7.5 feet, but decide to terminate the
> top of the open tube in the inside of the
> drop ceiling, is that OK or does it have to
> be terminated in the room itself.

> Marlboro

An open ended TL must terminate in the same room or your system response will hardly be smooth. The open end contributes the bulk of the SPL at the low end.

[marlboro]

what if?


So what if it goes into the ceiling and then comes back out of the ceiling again, about three feet away? Will that work?

> An open ended TL must terminate in the same
> room or your system response will hardly be
> smooth. The open end contributes the bulk of
> the SPL at the low end.

[johnddaugherty]

Re: what if?


> So what if it goes into the ceiling and then
> comes back out of the ceiling again, about
> three feet away? Will that work?

Yes.

[johnddaugherty]

Re: what if?


> So what if it goes into the ceiling and then
> comes back out of the ceiling again, about
> three feet away? Will that work?

Opps! I didn't get finished. Why go to the trouble of putting it through the ceiling, adding a 90 degree joint, three feet of tube, then another joint, then through the ceiling again when you can leave your ceiling alone and meke the "U" totally inside the room and exiting behind or beside the upright?

[ccochran]

Re: transmission line woofer question


Depending on the properties of the drop ceiling, you have just created an infinite baffle design. If the drop ceiling will relatively limit the sound from transmitting through (have it insulated) and there is sufficient air volume above it, the design could work well.

You could just locate the woofer in the ceiling then and forget the pipe up to it. That design would probably take you 15 minutes to rig up and test out, and see if you like it.

> Does the end of the transmission line have
> to terminate in the same space that the
> speaker does?

> If you are using a woofer transmission line
> and you want nine feet but your ceiling is
> only 7.5 feet, but decide to terminate the
> top of the open tube in the inside of the
> drop ceiling, is that OK or does it have to
> be terminated in the room itself.

> Marlboro

[johnddaugherty]

Re: transmission line woofer question


> Depending on the properties of the drop
> ceiling, you have just created an infinite
> baffle design. If the drop ceiling will
> relatively limit the sound from transmitting
> through (have it insulated) and there is
> sufficient air volume above it, the design
> could work well.

> You could just locate the woofer in the
> ceiling then and forget the pipe up to it.
> That design would probably take you 15
> minutes to rig up and test out, and see if
> you like it.

If he took your option #1, the enclosure would behave as a terminated line, probably with characteristics somewhat different than an infinite baffle, although I certainly don't know in what way they might differ or even if the differences are all that audible; by taking option #2, he could just use an 8-incher with a whizzer cone and pretend to be in a department store or an elevator, unless his drop ceiling is a lot more airtight than any I've ever seen.

[Pete Schumacher]

You are correct and then some.


> If he took your option #1, the enclosure
> would behave as a terminated line, probably
> with characteristics somewhat different than
> an infinite baffle, although I certainly
> don't know in what way they might differ or
> even if the differences are all that
> audible; by taking option #2, he could just
> use an 8-incher with a whizzer cone and
> pretend to be in a department store or an
> elevator, unless his drop ceiling is a lot
> more airtight than any I've ever seen.

The line properties will cause vlarge response anomolies, with a very large loss of output near tuning, far less than what the infinite baffle would produce. Remember, an open line will have it's maximum SPL contribution at the fundamental resonance, which means that the action of the line is greatly reducing the driver's contribution to the overall SPL. Just look a the excursion plot which can actually drop off as tuning is approached.

So if you don't feed the line back into the room, you're far better off getting it out of the line and into IB.