Some quick questions about plugging ports in speakers

[JonW]

I’ve got to place my rear speakers nearly right up against a wall. These will be Modula MT’s used for rear speakers in a 5.1 system, with a sub. Perhaps I should plug the ports. This compromise doesn’t really bother me because it’s just for rear speakers- it’s not the main speakers for music. And I wanted to build ported speakers in case I like them enough to use as mains sometime down the road. And also for the challenge of incorporating the port into the cabinet design.

What do you use for plugs? Just some rolled up cloth (“put a sock in it”)? An option in my particular case is also to put a thin board or something between the rear baffle and the inside port, as shown below in the photo below. (That’s my first attempt at making a cabinet. The second and third ones look a little better.)

In general, what are the disadvantages of plugging the ports? (Other than reduced bass extension) Say, versus just making a sealed cabinet?

Thanks.



Image not available

[chasw98]

Thomas told me to use a nerf football from Walmart.

[JonW]

Thomas told me to use a nerf football from Walmart.

Serious? Cut down to size?

People always tell me things like that. But they're seldom referring to speakers.

[chasw98]

Serious, and I don't think you have to cut down the tiny ones for M/T's. You do want it to stuff in there and block.

[JonW]

Thanks. And now that you mention it, there are some small Nerf footballs- not regular football size but much smaller. OK, easy to try out.

Any significant difference versus just building a sealed speaker in the first place?

[dlneubec]

Thanks. And now that you mention it, there are some small Nerf footballs- not regular football size but much smaller. OK, easy to try out.

Any significant difference versus just building a sealed speaker in the first place?

The main difference can be seen when modeling in Unibox.

For example, I just checked the RS180S-8 in Unibox. For a single driver, QTC of .707 for an 8.8L box, walls covered, you get an F3 of 72.4hz and 25w is about the max power you can apply before the driver is over-driven at about 30hz, with a max SPL of about 100.6 db.

Now, if your optimum size for ported is say 20L for a ported, and you plug that into a sealed box arrangement, you get quite different results. In a 20L box, walls covered, you get an F3 of 75.9hz, a QTC of .572 and at 12w the driver is over-driven at about 30hz, with a max SPL of about 97.3 db.

[SteveCallas]

25w is about the max power you can apply before the driver is over-driven at about 30hz, with a max SPL of about 100.6 db

He mentioned these are for surround use - I would assume a 4th order highpass at 80hz.

[JonW]

OK, back to thinking about plugging ports...

Thanks for the calculations, Dan:

The main difference can be seen when modeling in Unibox.

For example, I just checked the RS180S-8 in Unibox. For a single driver, QTC of .707 for an 8.8L box, walls covered, you get an F3 of 72.4hz and 25w is about the max power you can apply before the driver is over-driven at about 30hz, with a max SPL of about 100.6 db.

Now, if your optimum size for ported is say 20L for a ported, and you plug that into a sealed box arrangement, you get quite different results. In a 20L box, walls covered, you get an F3 of 75.9hz, a QTC of .572 and at 12w the driver is over-driven at about 30hz, with a max SPL of about 97.3 db.

I don't have much feel for how those numbers translate to actual sound. But the numbers seem quite far off each other. So I guess that it all comes down to cabinet volume. Interesting. When my speakers are done, I'll fool around with them ported versus plugged and see what it's like. I'm curious. I'll use the speakers mostly for surrounds. But I want to try them as mains for a while.

(Some day I want to be able to do these calculation myself, to better understand things. But I only have Macs around and Unibox doesn't work on Macs. :cry: )