Slot ported version of The Tango

[HumbleDeer]

Anna,

Looking at your figures above, I believe you have it correct: shelf port 0.45" high by 7" long. My best guess is that this should work just fine. (although you should remember what Ben Franklin said: Free Advice, worth every penny you paid for it.)

Changing from round to slot will have some effect--greater surface area means more friction with the air slug in the port. Dave Dlugos (P-10) uses this feature in his Fonken and related designs to good effect.

If you want to compensate for the internal volume lost to the thickness of the slot plate, you might add 0.3" to the height of the cabinet. If you want to do a round-over on the ends of the slot plate, then add a fraction of an inch to the length to compensate; exact length depends on the radius of the round-over.

Cheers, Jim

hey thanks, really useful! Do I need a roundover, actually?

Otherwise, does the thickness of the wood back panel count as a part of the port too? Then I just have to subtract that right?

What would I pick: Small long or high shorter port?

I'll write that down though.

I like your cheapness....haha!

Why go out of your way to buy a piece of plastic that will only make it more expensive and more difficult and less attractive?

Anyway, i'm gonna draw this in Solid Edge now.

 

[scottjoplin]

Oh yes, show us your artwork...... You asked about phase, I'm not familiar with this design, I'll go have a look...

 

[HumbleDeer]

I need at least three feet behind boxes that are read ported right?

 

[Jim Shearer]

I wouldn't do the round-over myself, but others may feel differently. It would affect the appearance slightly. Not sure it would change the performance, but then I don't know the velocity of air in the port to have any idea if chuffing is possible.

Total length of the port is 7.75". Measure from the exterior end of the port to the interior end; The wall thickness of the cabinet is included in the port's length.

Cheers, Jim

 

[HumbleDeer]

nono. The port is the length of the one Chris said. If I subtract the thickness of the back wall from the measurement I know how long to make the internal piece to total it.

Also, I'm making it metric.

 

[scottjoplin]

Total length of the port is 7.75".

Oops, sorry, didn't spot that

 

[HumbleDeer]

Oops, sorry, didn't spot that

Well the port's total with the back wall is indeed 7.75. Do you need to recalculate things?

 

[scottjoplin]

Chris said 7.75 in post 6. That's the internal length including thickness of panel I presume?

 

[Jim Shearer]

You probably don't need to have 3 feet between the wall & the back of a rear ported speaker; so distance for sure, but it will depend on the tuning of the speaker and how it interacts with the room, as well as your personal preference. Closer to the wall will tend to increase bass, further away will decrease bass.

I didn't check the dimensions of the cabinet, but perhaps there is room to place the port on the front of the speaker? would not work for the round port, but the slot might. Not sure how this would affect the sound--might be better, might be worse. Maybe others have experience in this?

Cheers, Jim

 

[scottjoplin]

It will change things slightly because we've changed the area of the port. You have a go, I need a rest.....I'm old haha!

 

[Jim Shearer]

Just noticed above, someone suggested a higher slot dimension, but wanted to keep the volume the same by shortening the port.

Noooooo!

If you increase the cross-sectional area of the port, then it needs to be LONGER to maintain the same tuning. If you enlarge the area of the port, you will need to re-calc the length--and be sure you can accommodate the greater length in the cabinet.

Cheers, Jim

 

[scottjoplin]

So sorry, I thought the volume of the port had to remain the same, that was what gave the tuning? Have I created confusion?

 

[Jim Shearer]

Scottjoplin,

The air slug is resonating in the port. If you maintain the same volume (equal mass), but shorten the length, then the resonant frequency increases.

Cheers, Jim

 

[HumbleDeer]

gmm that's actually what I thought but I thought I was wrong. So.. what do I go for now for port, and added height? I don't want to have a blunder happen here.

Jim if you could explain:: If I made the port 50% higher, how many % longer would it need to be?

 

[Jim Shearer]

I would be reluctant to change the port height. I'm pretty sure that if you make it 50% greater, then it will not fit into the cabinet.

This may not be much help, but if you want to try variations without wasting a ton of lumber, you can build prototypes from foam core board or rigid foam insulation and hot melt glue--look in the full range section for examples of folks doing foam core builds.

Cheers, Jim

 

[HumbleDeer]

It was just hypothetical haha. So, I make the port the original height and width, and depth? I'm not sure anymore of the depth with all this confusion, sorry.

We have a ton of scrap mdf at school I'll be able to use. I'm making them for a school project.

I just make sure the total depth from the mount outside to the inside edge is 7.75?

 

[HumbleDeer]

and just to be sure: when the box's 7 inches wide whats the height of the port again?

http://www.diysoundgroup.com/media/...5d08d6e5fb8d27136e95/t/h/thetango_drawing.jpg

 

[scottjoplin]

0.45 inches as Jim confirmed in post 58. Sorry I confused the issue for you.

 

[Jim Shearer]

Yes. 0.45" high by 7.75" total length; length includes thickness of the cabinet wall; if the wall is 0.75" thick, then the port shelf extends 7" inside the cabinet.

 

[HumbleDeer]

Yes. 0.45" high by 7.75" total length; length includes thickness of the cabinet wall; if the wall is 0.75" thick, then the port shelf extends 7" inside the cabinet.

Then if my back wall and the other walls become 18mm instead of 3/4" (19.05mm I believe) I just extend the internal piece byva milometer?

You both, and others, have been a great help to me. I'm thankful for that c: