building a slot port enclosure

[bmccord]

Hello all, changed my design again. I am going to attempt to build a box for my titanic using a slot port. Does anyone know of any sites to aide me in designing a proper slot port. My idea was to something like the following...



This is a rough drawing of what i was shooting to do. Can I get good sound from something like this with treated corners and edges? I am basically shooting to not having to go out and pick up a new hole saw, tubing, elbows...etc...

Brett

 

[bmccord]

haha, sorry for the huge pic, don't have photoshop att he office...

 

[Lee Batchelor]

Hey Brett,

Looks like your new design resembles more of a labrynth enclosure, if that's how you spell it. Didn't you post your T/S parameters, box size and desired F3 cut-off on a previous post? If so, supply me with this info and I'll try modelling the enclosure; although, I'm sure there are people on this site that are equally qualified..........Lee

 

[bmccord]

specs are as follows:

Power handling: 400 watts RMS/565 watts max
Impedance: 4 ohms
Fs: 28 Hz
Xmax 18.7 mm
Sensitivity 87.7 dB 2.83V/1m
Vas: .95 cu. ft.
Qts: .39

Box size open, doens't matter. Main purpose is music but needs to do ok for movies (building a dedicated HT twin 12" sub in a few months). Basically, I have come down to 1.65 TOTAL interior volume. That includes amp and sub as well as ports. I was going to do a 1.65 ft^3 box with a 4" 40" long tube port (a series of bends within a secondary enclosure). Now i am pondering the idea of maybe seeing if i can get the same output from a 2"x12"x35 or so inch long slot port. That basically would make it rediculously easy to build. To sum it up, this sub is going for MAX SPL within reasonable freq range (high 20's to low 30's tune)

Brett

 

[Lee Batchelor]

Hi Brett!

Finally got around to modelling your sub. To my best abilities I find that a box 14" high, 14" wide and 16" deep (inside dimensions) would give you an F3 of 35 Hz with an SPL of 105 db. This is just the box as I can't include the volume that the amp occupies. (It should be possible to add a section on, to house the amp). I modelled it being driven at 200 watts, with damping material on all walls, a port with the mouth flared. The port would be 2 inches inside diameter and 6 inches long. At 200 watts, you're pushing the envelope for port flutter. My model shows a port air velocity of 25 m/sec. (33 m/sec is max but 15 would be best.)

As someone mentioned, speakers are all about trade-offs. In your case, I would think that 200 watts with this speaker would give you adequate but not enormous bass. We could achieve a higher SPL but porting would become an issue. I would stay conservative on wattage in favour of frequency response. If anyone else can come up with another model, please feel free to chime in. Hope this helps.......Lee

 

[windowrattler]

That design is a ported box. You can get WINisd to model ported boxes. It is freeware I believe. A port has two measurements length and opening size. The bigger the opening (with out changing length) the higher the tuning frequency and the smaller the opening the lower the tuning frequency. The same holds true for the length. The longer the port the lower the tune, and the shorter the port the higher tune. If the net volume of the box is increased the tuning will be lowered, decreased raised.

I'm more familar in custom making car audio boxes, but generally for increased output the larger the port opening the better. The port "acts" like speaker. You can also increase enclosure size to increase output. Winisd will give you frequency response graphs so you can choose the type of output and range. Good starting points are: 10 inch 1cf - 1.5cf with 15-25 sq inchs of port: 12 inch 1.5-3cf with 25-40 sq inchs of port: 15 inch 3cf-4cf with 30-60 sq inchs of port. Building boxes is one of my favorite things.

 

[Lee Batchelor]

How true Windowrattler! I've seen real pro designs which utilize realtively cheap drivers. If they get the box right, it's amazing what kind of sound you can get out of a speaker. What do you think of my comments/design?..........Lee

 

[bmccord]

Well, I built the enclosure this weekend. I went with a 1.85 ft^3 gross volume enclosure (after amp, driver and port takin into account, its 1.5) and a 37" long 4" dia port. I will post up my CAD drawings and pictures when I get a chance but it sounds amazing. Basically, its a 14x15.5x18 box with another 8" tall section above it to house the port. Its front firing as well as front ported. I ran a few test tracks, and its make the house shake in ways I have never heard at 16Hz... The last box made nothing at that freq. Overall SPL is not as much as I had hoped but it is amazingly flat. My goal has been met. A kick drum feels like a kick to the chest...I will have some normal size pictures up tomarrow (I took them at 6 megapixels so they need to be photoshoped down).

Brett

 

[Sheep]

Well, I built the enclosure this weekend. I went with a 1.85 ft^3 gross volume enclosure (after amp, driver and port takin into account, its 1.5) and a 37" long 4" dia port. I will post up my CAD drawings and pictures when I get a chance but it sounds amazing. Basically, its a 14x15.5x18 box with another 8" tall section above it to house the port. Its front firing as well as front ported. I ran a few test tracks, and its make the house shake in ways I have never heard at 16Hz... The last box made nothing at that freq. Overall SPL is not as much as I had hoped but it is amazingly flat. My goal has been met. A kick drum feels like a kick to the chest...I will have some normal size pictures up tomarrow (I took them at 6 megapixels so they need to be photoshoped down).

Brett

Cool! Now update that Sig!

SheepStar

 

[MacManNM]

See, I told you it would sound good.