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Old 30th September 2011, 10:16 AM   #1
ODougbo is offline ODougbo  United States
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Default Slot Port(s) the easy way

Found this pic and thought some might find this interesting. I’ve built peaty of bass reflex speakers with PVC/Cardboard tubes and came up with a faster/ easier way to tune up a speaker. As some have found out, it’s not easy to pull a PVC tube out a speaker (cardboard is even worse).

The ploy is pretty simple, semi build the box, basically in three parts. (1) side with “rips” top/bottom/back, glued on (2) baffle board with speaker(s) and “L” (3) the 2nd side panel.

It is a dry fit process, it is import to have all the “rips” exactly the same, or air will leak all over the place. Remember to leave plenty of extra material at the top of the baffle board, so it can be slid up and down. Of course sliding the baffle board will change the slot port area/volume.

Once you have it “assembled” hook up to a resistor load and watch the peaks on a volt meter and listen to the bass. You can cut or add to the slot port if needed.

Worried about air leaks anyway, tape them up.

Pics – two different projects, same idea.
Attached Images
File Type: jpg Tuning II.JPG (337.2 KB, 421 views)
File Type: jpg Inside.JPG (581.4 KB, 408 views)

Last edited by ODougbo; 30th September 2011 at 10:21 AM.
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Old 30th September 2011, 10:34 PM   #2
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Do you know that when a slot port aspect ratio gets higher than 1:4 (h:w) that the port starts to detune i.e. the tuning goes up instead of down (~1:8) until it reaches aperiodic friction coefficient (1:14 ) where where the boundary layer takes up the entire volume of the slot at about 90db.

With a high ratio slot port the tuning of the box is dependent on drive level, ie the higher the spl the higher the box tuning shifts.

There are better ways to design a slot port.

Last edited by revboden; 30th September 2011 at 10:42 PM.
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Old 2nd October 2011, 10:54 AM   #3
ODougbo is offline ODougbo  United States
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Thanks for the info on the 1 to 4 ratio. However, I do think a slot ports work better than round tube; a recommendation based on many speaker projects. The wife tells folks, “he builds 19 pairs of speakers, and keeps one pair”.

I do have two (2) of the isobaric “cube” subwoofers (pic on right) in the HT and getting awesome bass; like having my own private orchestra. There may be as simply answer, e.g. the slot is lower close to the floor.

Speaker(s): http://www.mcmelectronics.com/product/55-2421 The height of port is slightly les than 3/4” x 13 1/2” deep, 10”wide.
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Old 2nd October 2011, 11:09 PM   #4
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What you have there is an semi-aperiodic woofer. close to a 'Fonken'. P-10 has good info on them Meet the Fonkens
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Old 3rd October 2011, 06:26 PM   #5
ODougbo is offline ODougbo  United States
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Thanks for the info, I just asked that question on another thread. All I need is a center brace.

I do think the MCM project is a little out of the ordinary, low cost, fairly easy to build and a solid sounding sub. I have other 10s, 12s and always come back to the MCM Isobaric.
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Old 3rd October 2011, 07:36 PM   #6
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Not part of the topic, BUT DAMN! I wish I had those clamps when I was building my box...THOSE THINGS ARE HUGE!
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Old 3rd October 2011, 09:16 PM   #7
ODougbo is offline ODougbo  United States
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Darn clamps………they went up up up $$$

I won’t be buying more anytime soon. Yes the point is, you can dry fit speakers (and side the baffle board to tune).
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Old 4th October 2011, 05:36 PM   #8
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Quote:
Originally Posted by ODougbo View Post
Darn clamps………they went up up up $$$

I won’t be buying more anytime soon. Yes the point is, you can dry fit speakers (and side the baffle board to tune).[/I]
The smaller bar clamps in the photo are about $15 each at the HD. For larger clamps, I use pipe style "pony" clamps.
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