PVC Pipe as Port Tubing for Tempest? (1 Viewer)

[EricHM]

Hello, I am trying to design an enclosure for my tempest but I need some help concerning the design and construction of the port.
My enclosure plan is very unique (IMO), it consists of 1 Adire Tempest 15" Driver and 4.75 cubic foot 3/4" MDF enclosure. I plan to have the enclosure Sealed 99% of the time for sound quality purposes, but I would also like to include a 4" wide 1.44" long "pluggable port" tuned to 40hz for SPL burps.
I was wondering if anyone has experience working with PVC and could give me advice on this project.
First, I need to know how I should "flush mount" the end of the PVC tubing to the surface of the MDF. Is there some sort of Flange I need to purchase? If so, what is it called? Does anyone know if having threads inside the PVC pipe will significantly affect the acoustics of the subwoofer? Also, Are there any adverse mechanical affects of having such a short port? As long as it is safe for the driver I am OK, since I will only "unplug" the port for SPL burps where maxium peak SPL below 80hz is desired.
PS: This enclosure is going in a car but that shouldn't really matter.

 

[Dave Poehlman]

I've used pvc in all of my projects. I just cut the hole in the mdf the same size as the pvc so it fits snugly into place and then secure it from the inside with caulk. They aren't subjected to all that much mechanical strain, unless you use them as a lifting handle .
The threads shouldn't be a problem... unless they create some sort of whistling... but it's a short port, that shouldn't be a problem.
A flange might give a nice finished look if you can find one. 4" is pretty wide... good luck. Also... take into account that adding the flange may change the over all length/diameter of your port.
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Dave Poehlman
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It doesn't matter how you get there if you don't know where you're going.

 

[John E Janowitz]

What I do is first recess a hole 1/4" to 1/2" into the material, the size of the outside diameter, depending on the thickness of the piece. I then cut a hole all the way through the same diameter as the inside diameter of the PVC. What this does is gives a lip for the PVC to sit on. It's much easier to align this way than just putting PVC through a hole that goes all the way through. Use a glue that works well for bonding to PVC. I've used some Titebond Melamime glue lately that seems to work pretty good. Then once the glue is fully dried, use a 1/2" or 3/4" roundover bit on the inside of the hole. This will give you a nice flare. Use a little bondo, or equivalent filler if there is any crack between the MDF and PVC, sand and you will have a nice smooth flared port.
You can do the same if you wish to flare the inside of the port. If you use 3" PVC, cut a disc 4 1/2" diameter, with the same recess and hole in the middle. Glue to the PVC, and flare once it is dry.
John

 

[Bob Ahlberg]

There is another person who is doing this with his USAC vehicle. He has already hit 152+ with one tempest and 500 watts in his S-10 extended cab and just switched over to a Maelstrom driver with four ports tuned to 45 hz. He has designed foam plugs to put into the ports to play the sub sealed for the SQ portion of the competition. I think he's hoping for the mid 150's in terms of spl.
I think Kicker did something like this about 5 years back with some little subs they called sub-stations that had removable plugs so they box could be played either ported or sealed.
Have fun!
Bob

 

[Jack Gilvey]

The only problem I see in using a port tuned that high is the danger of unloading it below that point. If you're just going to play 40Hz tones for SPL purposes (burps?), that's fine. If you're going to hit it with music content below 40Hz, you could destroy the woofer pretty quickly.
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[EricHM]

The Foam Plugs sound interesting, But I was planning on using screw on type PVC Endcap Plugs. I wonder if those will give me an airtight seal or not? Maybe I could something that uses an o-ring. Guess I should make a query at home depot.
In any event the box will only play test tones above 40hz when it is in ported mode.......

 

[Hank Frankenberg]

If you use PVC pipe, flush mount it with epoxy, then use a roundover bit in your router to give a "flare" exit for a bit better airflow. The best way, however, as suggested by Dan Wiggins of Adire Audio, is to use a flared port kit with flares on both ends. The effect on airflow capacity is that the port acts as if it were the about the diameter of the flares, which on a 4" flare kit is 6". That will better avoid air flow/port noise.
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"Do you expect me to talk?"
"No Mr. Bond, I expect you to die!"

 

[EricHM]

And oh yeah, another thing....
Will having more port area Give me a Higher SPL?
For instance, If I went with two 4" wide 6.3" long ports I would still be tuned to the same frequency, but I would have drastically more port area than the original single 4" x 1.6" port.
Should the SPL be about the same or would I see a significant difference.
In Winisd, it doesn't seem to make a difference but I've herad people say that it helps to have lots of port volume.

 

[Bob Ahlberg]

Eric...
You will see more spl...now whether it is a "significant" increase depends on your definition of significant. In spl competition every tenth of a db counts.
As a rule of thumb for a 15" driver, start with at least 50 sq.in. of port area per driver. Sizes up to 1/2 sd of the driver work very well. The boys who are doing the extreme classes in db drag are making up to 174db+ for short burps with two 15's and boatloads of power. They are often using boxes in the 25-30 sq.ft. area with port area in the range of 400 sq.in. ! Needless to say, those are spl only setups.
Have fun!
Bob