Basic questions on speaker ports (my post #2)

[jonw]

A continuation in my series of questions on my first speaker project (Modula MT)…

I’ll make the ports from 2” PVC tubing and I’ll add a roundover/flare on either end.

-Is a 1/2” roundover best or should I go 3/4”? (I have to buy a router bit either way.)

-The port is supposed to be 7.5” long, so that includes the flares, correct? (1/2” flare, 6.5” of PVC, then 1/2” flare)

-Where to put the port on the rear of the speaker? Some say anywhere, some say behind the tweeter. Does it matter?

Thanks!

-Jon

[Chris Roemer]

> A continuation in my series of questions on
> my first speaker project (Modula MT)…

> I’ll make the ports from 2” PVC tubing and
> I’ll add a roundover/flare on either end.

> -Is a 1/2” roundover best or should I go
> 3/4”? (I have to buy a router bit either
> way.)

I've found 1/4" to be waaay better than none at all. Diminishing returns I think, plus MOST PVC has about a 1/4" wall, so you can round it over before installing it. If you're going to use a 3/4" r.o. on EACH end, then you'll actually be rounding over the cabinet at the front, and you have to make some kind of big wooden doughnut-thing on the back end so you've got material to round over.

> -The port is supposed to be 7.5” long, so
> that includes the flares, correct? (1/2”
> flare, 6.5” of PVC, then 1/2” flare)

The way I do it is to figure the unflared portion plus ONE flared end (which is like averaging the whole thing - I guess). So . . .

For a port that WinISD (or your plan) says needs to be 7.5" long, I'd make its TOTAL length 7.75 if using a 1/4" r.o., 8" if going with 1/2" r.o., and 8.25" if 3/4" r.o..

With your 1/2" r.o. example, my overall port length would be 8", and my unflaired length would be 7" (8" - 1/2" - 1/2"). That averages out to 7.5 ".

> -Where to put the port on the rear of the
> speaker? Some say anywhere, some say behind
> the tweeter. Does it matter?

> Thanks!

> -Jon

Doesn't really matter. I vent out the top sometimes. I guess behind the tweeter (if rear firing) is suggested because tweeters are sealed so there's no back wave being generated there that could exit the port.

[quietstorm]

Provided Link: Port Tube Installation


I just wanted to add a point about porting: Anywhere is fine EXCEPT directly behind the woofer. That may be obvious to you, but I've seen others make the mistake. So, this is just a heads-up, if you didn't know.

Also, the link below is a short article on port installation that might be helpful. It might seem to be a bit of work, but the finished product is really worth it.

> I've found 1/4" to be waaay better than
> none at all. Diminishing returns I think,
> plus MOST PVC has about a 1/4" wall, so
> you can round it over before installing it.
> If you're going to use a 3/4" r.o. on
> EACH end, then you'll actually be rounding
> over the cabinet at the front, and you have
> to make some kind of big wooden
> doughnut-thing on the back end so you've got
> material to round over.

> The way I do it is to figure the unflared
> portion plus ONE flared end (which is like
> averaging the whole thing - I guess). So . .
> .

> For a port that WinISD (or your plan) says
> needs to be 7.5" long, I'd make its
> TOTAL length 7.75 if using a 1/4" r.o.,
> 8" if going with 1/2" r.o., and
> 8.25" if 3/4" r.o..

> With your 1/2" r.o. example, my overall
> port length would be 8", and my
> unflaired length would be 7" (8" -
> 1/2" - 1/2"). That averages out to
> 7.5 ".

> Doesn't really matter. I vent out the top
> sometimes. I guess behind the tweeter (if
> rear firing) is suggested because tweeters
> are sealed so there's no back wave being
> generated there that could exit the port.

[jonw]

> I've found 1/4" to be waaay better than
> none at all. Diminishing returns I think,
> plus MOST PVC has about a 1/4" wall, so
> you can round it over before installing it.
> If you're going to use a 3/4" r.o. on
> EACH end, then you'll actually be rounding
> over the cabinet at the front, and you have
> to make some kind of big wooden
> doughnut-thing on the back end so you've got
> material to round over.

Right. I was planning on doing the roundover on the back of the actual cabinet. And also add a donut and some sort of support/donut/flare to hold up the inside end of the tube.

> The way I do it is to figure the unflared
> portion plus ONE flared end (which is like
> averaging the whole thing - I guess). So . .
> .

> For a port that WinISD (or your plan) says
> needs to be 7.5" long, I'd make its
> TOTAL length 7.75 if using a 1/4" r.o.,
> 8" if going with 1/2" r.o., and
> 8.25" if 3/4" r.o..

> With your 1/2" r.o. example, my overall
> port length would be 8", and my
> unflaired length would be 7" (8" -
> 1/2" - 1/2"). That averages out to
> 7.5 ".

Got it.

> Doesn't really matter. I vent out the top
> sometimes. I guess behind the tweeter (if
> rear firing) is suggested because tweeters
> are sealed so there's no back wave being
> generated there that could exit the port.

OK, thanks.

[jonw]

> I just wanted to add a point about porting:
> Anywhere is fine EXCEPT directly behind the
> woofer. That may be obvious to you, but I've
> seen others make the mistake. So, this is
> just a heads-up, if you didn't know.

Right. I don't know too much about this, but I kinb of figured what you say to be the case- it just kind of makes sense.

So how far from the direct rear of the woofer is OK? I thought it might be easier to have the port toward the bottom of the cabinet. But that would put it somewhat close to the woofer. Idunno, maybe just a few inches away. Maybe just going in the center, at the tweeter height is the wise thing to do here.

Nice link, thanks.

-Jon

> Also, the link below is a short article on
> port installation that might be helpful. It
> might seem to be a bit of work, but the
> finished product is really worth it.

[quietstorm]

There's a lot of opinions on port placement. To keep things safe, I generally mount the port at the rear of the tweeter.

> Right. I don't know too much about this, but
> I kinb of figured what you say to be the
> case- it just kind of makes sense.

> So how far from the direct rear of the
> woofer is OK? I thought it might be easier
> to have the port toward the bottom of the
> cabinet. But that would put it somewhat
> close to the woofer. Idunno, maybe just a
> few inches away. Maybe just going in the
> center, at the tweeter height is the wise
> thing to do here.

> Nice link, thanks.

> -Jon