Home Theater Forum and Systems banner
1 - 18 of 18 Posts

·
Registered
Joined
·
207 Posts
Discussion Starter · #1 ·
I am trying to model SI 18D2 in relatively large low tuned enclosure. I would prefer to keep it under 17cu.ft , but can probably go as large as 20cu.ft.

I can get a decent curve at 17cu.ft with 12Hz tune. But I am having difficulties with the port. If WinISD models are to be believed, it appears that at this size/tune I cannot have both low port velocity and first resonance outside the passband.

Is there any way around it?

thank you.

edit: I am going to use Inuke 3000DSP to drive a pair of these. Inuke's filters cannot be set below 20Hz. That's why I am using a combination of HPF and PEQ at 20Hz to simulate 15Hz HPF (last picture)





 

·
Registered
Joined
·
207 Posts
Discussion Starter · #3 ·
Those parameters are not from the Stereo Integrity website so I'm unable to recreate your modeling. You'd gain more output by going 10 cu.ft. tuned to 18 hz with a 20 hz HPF.
Thank you very much

I used specs from Josh Ricci measurements. wdr file is attached.

here is 17cu.ft @12Hz vs 10cu.ft @18Hz.

 

Attachments

·
Registered
Joined
·
207 Posts
Discussion Starter · #8 ·
For some reason I do not get the same output boost with 16Hz tune and 20Hz second order HPF.
The signal is set to 600W for both models.
what can account for the difference?
thank you.



 

·
Registered
Joined
·
207 Posts
Discussion Starter · #10 ·
I modeled with 900 watts and the same EQ as your first model, the driver is under Xmax. One 8" round port 25" long results in a maximum air speed of under 20 m/s at 16 hz.
I am a moron.
For some reason I though the threshold is around 20 ft/s and could not figure out how people can possibly get it to work.

20 m/s is a much easier target ;)

thank you very much, Mike.
 

·
Registered
Joined
·
285 Posts
20 m/s is a much easier target
True, but for high power it needs to be somewhat lower, down to at least 4% mach if very low vent compression is desired.

Out of curiosity, I modeled 17 ft^3 in a ~112.25" i.d. path-length vented TL [aka MLTL] to increase vent loading enough to shorten it and keep vent mach low with a 6" diameter x 10" long vent. 22.5” driver, 6” vent offset from each end.

Folded in half and tuned to ~Fs [or even below], it looks to have some serious potential [2.83 V input sim]

GM
 

Attachments

·
Registered
Joined
·
207 Posts
Discussion Starter · #15 ·
True, but for high power it needs to be somewhat lower, down to at least 4% mach if very low vent compression is desired.

Out of curiosity, I modeled 17 ft^3 in a ~112.25" i.d. path-length vented TL [aka MLTL] to increase vent loading enough to shorten it and keep vent mach low with a 6" diameter x 10" long vent. 22.5” driver, 6” vent offset from each end.

Folded in half and tuned to ~Fs [or even below], it looks to have some serious potential [2.83 V input sim]

GM
Thank you for the suggestion. I am afraid to take anything more complex than a bass-reflex design for my first DIY subwoofer build.
what software do you use to model TL? is there a good primer on MLTL specifically?

thank you
 

·
Registered
Joined
·
285 Posts
You’re welcome!

MJK’s MathCad software, which you can download the MC8 demo program to run, though being a demo you can’t save your work to edit, etc. later, but you can copy/paste it to WORD or similar if desired. There’s also a wealth of knowledge on the theory, design of OBs, the various TLs and he’s now working on BLHs. He also has a yahoo forum.

http://www.quarter-wave.com/
http://www.quarter-wave.com/Back_Door/MathCad_Explorer.zip
http://groups.yahoo.com/group/quarter-wave/join

All the basics of TL, conical horns: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/opecol.html

Anyway, a typical vented alignment [BR] assumes that the trapped air in the cab has a ~uniform particle density, so the driver and vent can be located anywhere on the cab and it shouldn’t affect either the driver loading or cab tuning.

The MLTL is a BR that’s been stretched to a high enough aspect ratio for ¼WL resonant pipe [TL] action to occur, which in turn will increase vent damping, power handling, so there’s no clear cut point where the BR turns into a MLTL, but a gradual morphing.

Now the location of the driver and vent will affect performance as well as vent length, so there’s more tuning flexibility than the simple BR, hence the need for a specialized software.

GM
 

·
Registered
Joined
·
285 Posts
You're welcome!

Indeed, though with MJK's software, AkAbak [which has a fairly steep learning curve to take full advantage of its designing flexibility], one doesn't have to learn it beyond the basics.

GM
 
1 - 18 of 18 Posts
Top