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Slot reflex port for bass reflex enclosure?
Slot reflex port for bass reflex enclosure?
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Old 22nd April 2015, 10:12 PM   #1
monty78pig is offline monty78pig  England
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Slot reflex port for bass reflex enclosure?
Default Slot reflex port for bass reflex enclosure?

How would I go about calculating a bottom slot bass reflex port for a speaker design?

Also does anyone else have any experience regarding these. I quite like the aesthetic qualities of them.
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Old 22nd April 2015, 10:22 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

You just need a simulator that applies the correct end corrections,
which yield a different port area / length to a free mounted port.

rgds, sreten.
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Old 22nd April 2015, 11:29 PM   #3
xrk971 is offline xrk971  United States
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Slot reflex port for bass reflex enclosure?
WinISD has option of round or rectangular ports. But basically the cross sectional area needs to be kept the same along with length. In the case of very narrow aspect profile slots there is more skin or surface drag that will be more than just the regular slot pressure losses. This is how an Onken reflex is different.
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Old 22nd April 2015, 11:34 PM   #4
IG81 is offline IG81  Canada
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WinISD apparently does not let users enter arbitrary end correction factors, outside of the 4 presets they have, the highest of which is nowhere near enough for a bottom slot port's value of 2.222, if I'm correct.

Funny you should post this today. Just yesterday, I did a tuning adjustment on large enclosures I have for TD15M, with such a vent scheme.

Slot reflex port for bass reflex enclosure?-td15m-jpg

Slot reflex port for bass reflex enclosure?-td15m_2-jpg

WinISD was little help getting me to where I wanted, but I did it empirically. If you implement a scheme like I did, with a drop-on panel setting vent length, it's easy enough to start too long, measure and adjust until you get it right. Which is basically the boneheaded way to do it lacking proper software or the will to look for it.
Attached Images
File Type: jpg td15m.jpg (174.5 KB, 501 views)
File Type: jpg td15m_2.jpg (205.8 KB, 498 views)
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Old 23rd April 2015, 12:39 AM   #5
GM is offline GM  United States
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This may help: http://www.diyaudio.com/forums/attac...ort-length.jpg

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Old 23rd April 2015, 01:30 AM   #6
googlyone is offline googlyone  Australia
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Slot reflex port for bass reflex enclosure?
The beauty of slot loaded ports is that they are damn easy to tune. My experience with them is that the errors in, for example, winisd, are not "catastrophic" more in the few Hz range.

This is something you can fiddle
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Old 23rd April 2015, 02:00 AM   #7
chrisb is offline chrisb
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excellent link, Greg

My personal experience with slots is that they work very well - particularly if you get a math geek to calculate, there are several methods to fine tune them, and depending on configuration, can add to enclosure bracing.
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Last edited by chrisb; 23rd April 2015 at 02:03 AM.
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Old 23rd April 2015, 02:01 AM   #8
monty78pig is offline monty78pig  England
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Slot reflex port for bass reflex enclosure?
Those TD-15 cabinets look amazing. I like your use of cleats!

If the port is only 20cm wide it's not going to need any extra support?
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Old 23rd April 2015, 12:21 PM   #9
IG81 is offline IG81  Canada
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Quote:
Originally Posted by monty78pig View Post
Those TD-15 cabinets look amazing. I like your use of cleats!

If the port is only 20cm wide it's not going to need any extra support?
Assuming it's built from 18mm BB-ply, it's probably stiff enough not require support at 20cm width. OTOH, it can't hurt to have some and if you don't want the slot itself to be separated, like mine picture above for example, you can use a triangular brace on top that ties it to the front panel. The advantage with my drop-on-cleats-panel scheme (not that I pretend having invented it ) is the ease of adjustment. I'm glad to have implemented it this way as, since I've moved, the new room these are in does not agree with the previous tuning frequency.

Last edited by IG81; 23rd April 2015 at 12:25 PM.
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Old 23rd April 2015, 04:17 PM   #10
GM is offline GM  United States
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Quote:
Originally Posted by chrisb View Post
excellent link, Greg

My personal experience with slots is that they work very well - particularly if you get a math geek to calculate, there are several methods to fine tune them, and depending on configuration, can add to enclosure bracing.
Thanks to bjorno and whoever did the basic one he started with for sharing it with us!

Agreed, the first and earliest date, shelf port I saw was a subdivided slot in a custom undersized Altec 604B cab circa 1948. Unfortunately, the driver was blown, so didn't get to audition it and was too expensive for my meager part time lawn maintenance allowance.

The second was in a 1952 Altec 820A horn where it did double duty as a short horn cum pedestal base, so short of contrary eyes-on proof, I'm assuming Altec pioneered slot/shelf/BVR ports.

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