[Bent]

I have a length of 14.5" OD poly tube, approx 7'
and I have approx 6' of 12.5" OD poly tube.

I've roughly calculated approx 24 sq inches of "port area" between the two cylinders if they were nested. 5.5 in diameter is what I'm guessing is the equivalent in tube size if I was to calculate this area as a port.

anyone wish to discuss using a 10" driver of some kind for a multi-media subwoofer with these materials?

 

[Mike P.]

Interesting design. Got a budget for the sub and amp?

 

[Bent]

no budget yet, I need to find out how the tubes will interact, how much shorter the inside tube needs to be than the outer tube, what to use as an endcap, feet, baseplate (if needed) etc.

The driver will be chosen based on enclosure size - the amp chosen to match the the driver.

 

[Mike P.]

6' of 12.5" would be about 4.5 cu.ft. That's lots of room for a ported 10".

 

[Bent]

keep in mind this "port" won't infringe on any interior volume.

 

[Bent]

I just checked, the length of 12" tubing I have is 26" - the rest is unusable.

This gives me 1.7 cubic feet of interior space, but I'm not sure how the space between the 14" piece and the 12" piece will interact with each other. Will the enclosure consider the space as "enclosure", or will it consider it as "port area"? Note, the 1.7 ft^3 spec isn't realistic either, it only indicates the smaller tube's interior volume, once the smaller tube is inserted into the larger tube the total sum of volumes should be higher than the single 1.7 ft^3

As an aside, my calcs say @ 5.5 inches of port area interacting with 1.7 ft^3 results in huge port length for tuning around 20 hz.

If I insert the 12 inch into any length of the 14 inch tube longer than 26 length then the apparent volume will include the addition of the 14" length, and as a side benefit, the port length will drop.

 

[Bent]

I re-calcualted, and 3.5 inches looks closer to the realistic equivalent radius of a port, so port diameter = approx 7 inches. (note, this is only a 1" gap between the two tubes...

tube/enclosure length is getting too large to tune in the 20Hz neighborhood - a 56" tall tube is a tad big for a computer subwoofer....

 

[collo]

You will need to ease the air into and out of the "port" to avoid chuffing.

I did some experiments with a concentric port some time back, which might give you a few ideas.....

 

[Mike P.]

5.5 inches of port area

Are you sure the calculations are right? A round port 2.3 inches in diameter has a port area of 5.5 inches.

 

[Bent]

Creating any transition within is going to be difficult,
Do you think that chuffing might be an issue even if equivalent port area is as high as my "esticulations" show? (my most recent calculations are getting closer to the equivalent of a 5" diameter port)

 

[Bent]

Are you sure the calculations are right? A round port 2.3 inches in diameter has a port area of 5.5 inches.

My calcs are prolly right... it's my terminology that's off. I meant 5.5" of equivalent diameter, not area.
Sorry about that.

 

[Mike P.]

Gotcha.

 

[Bent]

I guess I can't call mine the Sadhara - but I named it that on my desktop.

at 48" of outer tube, and 26" of inner tube, I get 0.2062 ft^3 of equivalent vent area according to Sketchup's area calculator - which translates into 29.69 inches^2 of vent area, or the approx equivalent of a 6" diameter port.

the 48" outer tube and 26" inner tube also give a combined volume of 3.38 ft^3.
3.38 ft^3 interacts with 26" of 6" diameter port to achieve a tuning freq. of 26 hz.

My port dimensions can't change, so to achieve lower tuning I need to lengthen my 14" diameter tube.

extending the 14" tube to 56" long brings my tuning down to 25 Hz.

 

[collo]

Creating any transition within is going to be difficult,
Do you think that chuffing might be an issue even if equivalent port area is as high as ....

The CSA should be fine, but its the terminations that might cause noise.

Some MDF plugs can make flares for you...

 

[Bent]

I ran this through Unibox,
Drive Unit Parameters
CSS SDX-10
Fs 26.00 Hz
Re 3.50 Ohm
Qms 4.00
Qes 0.42
Sd 330.0 cm2
Vas 53.0 l
Xmax peak 18.40 mm
(Le) 1.42 mH
(Le2) 0.00 mH
(Re2) 0.00 Ohm
Nominal Power 300.0 W


I re-measured my tubes, and get an equivalent area of a 5" diameter port.
The port would be 26" long - as dictated by the length of the smaller tube.

inside tube is 26" long, outside tube is 48" long,
total sum of volumes of each tube = 3.38 ft^3

it shows, when using a Creative Sound 300 watt Bash amp.

(Note, I'm just moderately under ported here).

This has grown to be larger than a computer monitor subwoofer though.

 

[Owen Bartley]

Heh, I was going to ask if this had gotten bigger than you thought it would. It looks like a very cool project though. Are you intent on using the concentric design? If you're OK with the bigger size, it would make a very nice sub. As you saw in my thread, my SDX10 is going into about 1.5 cubes in a ported box, and the response rolls off a lot earlier than yours does in the big tube. I think my F3 is about 28Hz.

Now my only question is... how are you going to mount that BASH amp if most of your tube is port??

 

[Bent]

Well, I don't actually have the SDX-10, nor the BASH amp yet. All I do have are the tubes and Unibox.
(and the tools).

I'd stick with the concentric design because it is unusual - but not original. I really like the idea of not having a port open to the top, in fact, I think there might be some acoustical gain in keeping it low to the floor.

The amp, I'd think, would mount in a cut-out a few inches above the top of the inside tube, it would take ome tests, but I have lots of 14" to practice with in trying to integrate a flat amp into a rounded surface (I'd need to fabricate a mount of some type).

I found the concept of designing the enclosure to match the port dimensions kinda backwards - but unique itself.