Need help with ported boxes.

[slayer]

I'm using these Truaudio in CP-8 ceiling speakers for a covered patio I just built. The ceiling has exposed rafters and is roofed above that. I want to build some enclosures that will fit between the 2x6 rafters that are spaced 16 on center to improve the bass performance of them. I am a dealer for them and have several sets of speakers just sitting around so I plan on using them. I just put a set of rock speakers in the yard. I have a set of surface mount outdoor speakers I could use here but would like to use the ceiling speakers mounted in ported enclosures to help put out some bass in the area. Not sure if I will be able to get the Theil parameters for these, will I need them? Or can I just worry about the tuning of the port? Thanks for the help. Here is a link to the site to see the speakers. They are the 8" CP-8's.

Forum rules prohibit hotlink to products someone sells, so I cut and pasted the info

• 2 way in-ceiling design
• Frame and grill can be painted to match rooms décor
• High-grade crossover design and components
• 8" woofer provides a great amount of bass
• Large 1" swivel tweeter for custom installations

Speaker Specifications
Speaker Type: In-ceiling, 2 way
Woofer: 8” polypropylene
Tweeter: 1” silk, swivel
Power: 5 - 100 watts
Impedance: 8 ohm
Frequency Response: 42 - 20k Hz.
Sensitivity: 90 dB
Grill: Micromesh
Finish dimensions: 11 1/8” diameter, 3 1/2” deep
Cutout dimensions: 9 3/4” diameter

[ThomasW]

The factory can't provide this info?

It would cost $150 to buy the Woofer Tester, that would allow you to measure the T/S parameters.

Looking at the surround I would port them around 45Hz or so. You could go lower but the ambient noise outside would probably drown it out.

[slayer]

So how would I port them at that frequency?

[ThomasW]

A ported box is tuned via the port, like blowing over a bottle. The size of the box combined with the diameter and length of the port create the tuning, this can be independent of the specifics of the driver.

The space for your box is 14.5"X4.75"(subtracting .75" from the joist height to allow for a baffle) by what length?

With that info a generic box can be designed with a given tuning.

[slayer]

I called and it does not look like I will be getting the specs needed from them. Their tech guy is out for at least a week and the feeling I got about getting this info was not too good.
You are correct on the measurments. 14.5" wide, 5.5" deep, length?
I would like to use a back plate as well. I want to build the enclosure to be able to just fit into the bay flush and just screw it in from the side bays. I have unlimited length on the enclosures as the bays are 15 feet long. So I guess all I need is the internal volume of the enclosure and the port width and length. I can figure out the enclosure as soon as I know what volume it needs to be. Thanks for the help Thomas.
BTW, sorry for the link. This was not an attemp to sell product. It was only mentioned to establish why I'm using these speakers for the project.

[ThomasW]

It's okay I understood the link, it's just against policy so I posted the data instead having an admin come in and delete it.

It's the cart before the horse, there is no fixed number for the length. But here's what you do.

Go to this link (it's an archived website so slow loading)

http://web.archive.org/web/20010409192051/xsspl.tripod.com/Audio/VentCal1.htm

Fill out the following

Port round
Number of ports 1
Enter desired tuning frequency use 42
Enter desired port diameter enter 2

Now enter different box volumes and hit the Calculate Length button

1.5 cu ft gives a 1.74" port
1 cu ft gives a 3.34 " port

Decide the volume you want for the box, it's not all that critical. Too small and the port length goes up, to big and the length drops for the same tuning.

You can lower the tuning and see what that does, I wouldn't go lower than 35-38Hz. Since we have no T/S parameters we're sort of guessing.
As I'm sure you know the outdoors sucks up bass like a sponge. So you can't expect much output under any circumstances. But using the port will protect the driver by allowing it to play louder before it runs out of excursion.

[slayer]

It's more so for playing at lower volumes. They are going right over a patio table/sitting area and will be used for background music. I want them to sound full at a comfortable level so we can still talk normal and not have to yell. I was thinking that by putting them in a ported enclosure, it would boost the bass performance even at low volumes. Thanks again for the help.