Help with porting of new Shiva enclosure PLEASE (1 Viewer)

[Matt D K]

My enclosure is just about finished. I am in need of some help with the port size/frequency.

The net volume(not counting port or speaker displacement) is 6522 cu inches/106.876 liters. I am using the PE 250 watt amp. My main speakers are Polk LSi15's which have an 8" woofer and play nicely down to about 50hz or so. My room is about 16' x 17' with 10' ceilings that vault to about 14', there is no rear wall. I primarily want it for home theater use, but still want it to play music well (mostly classic rock / modern jazz / and country) I THINK i want to tune it to around 18 - 20hz, unless someone tells me why I shouldnt. I will be using the 4" flared port firind down onto a base plate mounted about 4" from the bottom of the cabinet.

Thanks for any and all help!
Matt

 

[Chris Carswell]

Everything sounds good but......
If you are using the PE flared port you won't be able to tune it lower than 22Hz. The reason for this (IIRC) is that port is only 17" long. To tune it lower (19Hz) it would have to be something like 22" long (maybe you can splice in some standard 4" PVC). I don't think there will be a major noticeable, night & day difference between the two. If you want I can run some #'s later & give you exact figures.

 

[Matt D K]

Chris,
That would be great if you could run some #'s for me! My box has 23" of total depth where I'm installing the port. I am using the PE tubing.

What part of FL are you in? I'm near Tampa

Thanks again
Matt

 

[Brian Bunge]

Chris is in the part of Florida where gators wear ugly orange sweaters with a big 'F' on the front!

 

[Chris Carswell]

Yah that's right
What's up Brian, how ya been? Cold.... Not me, FL is nice. Don't even need those sexy orange sweaters the girls love to see on us . I was in ATL for New Years. I wanted to check out some more of your stuff but didn't have the time. I want to go back up soon to visit some other friends so maybe then I'll have more time.
Matt,
I ran some quick sims of your box tuned to 21.4Hz. With this tunning you use the entire length of your 4" port (which is 17"). F3 is 23.4Hz, F10 is 16.8Hz. If you tuned it lower (say 18Hz) your port would need to be 25.25" long. F3 would be 26.2Hz & F10 at 15.4Hz. I'd say just stick with the 17" port. Maybe even throw in 2-3 lbs of fill if you want. You'll be fine.

 

[Stephen Hopkins]

You have to remember that using a flared port changes the length of your port's center piece. If WinISD or similar software gave you a STRAIT port length of 17" for your tuning point, then the length of your center piece of the port should be about 12".
Also, your enclosure is fairly close in size to the 95L SBB4 enclosure, which uses a tuning point between 20 and 21 hz, so going below 22hz should be ok, but you probably wouldn't want to go any lower than 20hz.
This can all be found in the vented enclosure application guide for the Shiva available for download from the Adire website.
Hope this helps

 

[Jack Gilvey]

Didn't run the sim, but going with Chris' Fb of ~21.5Hz for the full-length port kit I'd say it's just about perfect to use with that amp. Assuming it's the 300-794 (?) the rumble filter is set for -3dB @ ~19Hz and so should mate extremely well with that box for great output and protection from bottoming below Fb. Tuning lower wouldn't really be worth it I'd say. Go for it!

 

[Matt D K]

Thanks to all for your help. It looks as tho this set-up is going to sound great. I should know in a day or two. I will post pics when I am finished. I built it to look like my LSi 15's.

Chris: One last question. is you port lenth measurements taking into account the flared port as Stephen indicates?

Thanks again
Matt

 

[Chris Carswell]

Nope, that's just the straight section. I would have no idea how long the flare would be with your particular port so that is something you are going to measure. I make my own flared ports so my flare depth varies. I assume Stephen has worked with the PE flared port so he would know how much to compensate (I hope ). If you don't want to extend the length of your port by splicing in some PVC I would just add some pollyfill. Either way you'll be fine (F3 23Hz). Like Jack so correctly stated: Tuning lower wouldn't really be worth it. Go for it!

 

[Stephen Hopkins]

Like i said before, the best thing to do is to read the Vented Shiva Application white paper available at the Adire Audio web-site, or by following this link:
http://www.adireaudio.com/Files/Vent...plications.PDF
It clearly states that to compensate for the lack of flares (I.E. Strait Port) you would add 5" to the recommended length of the flared port. This will work in reverse as well. Just take what ever strait port length you have found for your tuning point and subtract 5" to compensate for the flares. The PE 4" Flared port is exactly the same as the Adire 4" Flared port, so that is a non-concern.
More than anything, I would highly recommend reading the Shiva Vented Application white paper (link above) even if you don't plan on using on of the reference designs. It is very informative on how venter enclosures work, especially in relation to the Shiva.
You're on your way to building a great sub. When i built my Shiva, I opted for around 140L, dual 2" ports, and a tuning point of right at 20hz, which in my room yields -3db sound as low as 14hz. I'm really amazed at my Shiva... to think I was considering paying $600 for an SVS!
Good luck on your project and tell us how it turns out

 

[Matt D K]

Stephen and Chris, THANKS ALOT for all you input.

Stephen, I read the Shiva white paper briefly when I was deciding on which driver I was going to use. I should probaqbly take the time to read it more thouroughly tho. I think I'm pretty clear on how to port my enclosure now.
I'm expecting my Shiva to arrive (from Kyle) tommorrow. In the mean tim I'm putting the finishing touches on my box. Going to finish laminating it tonite and tommorrow. I think it's going to look pretty good. I'll let you all know how it turns out.

Thanks again
Matt

 

[Chris Carswell]

Wow, didn't know that their flare takes up 5" total (2.5" per side). That's a lot. I usually use a 3/4" roundover (when using 4" PVC) which has a depth of 1" so I add 2" to the total length when cutting the PVC. You learn something new everyday . Thanks Definitely a good idea to re-read those white paper.
Stephen, why did you use 2x2" ports? Could you not fit a 4" one in there? It would only need to be ~14.5", unflared length that is . Volume wise you are looking at 44in^3 (.03ft^3) for the 2x2" ports vs. 176in^3 (.1ft^3) for the 4" port so I wouldn't see it effecting the Vb that much. Do you get any chuffing? 2x2" ports have almost 1/2 the area of a 4" port.

 

[Stephen Hopkins]

I had the 2" PVC around, the vent match was in the green on WinISD, and the lengths didn't take up much internal volume, so I went ahead w/ the dual 2" ports knowing that I could always cut them out and replace them w/ dual 3" ports on down the line if I started hearing port noise. So far (after about 2 weeks) I haven't heard the slightest bit of port noise, even at insane SPLS (above 115 db). But like I said, if I ever do hear any noise, i can always cut the 2" ports out and put a couple of 3" ports in their place (still only 9" long each) that would be a vent match around .06 (the dual 2" ports were about .14, but still in the green).
Cost was a big part of my entire project. My 3/4" MDF, Driver, ports, and trim pieces (white pine stained golden oak) all came in at about $105. When I get my PE 250W plate amp ($120, free shipping), I'll have only $225 invested in what has proved to be a truly amazing sub. Add another $11 for the inset glass top I added yesterday ($8.50 for glass, $1.50 for rubber feet, $0.75 tax) and the grand total is still a mere $235. My paint (Black Satin Acrylic), Stain (Golden Oak), and all of my screws were left over from the construction of my parent's house. My binding posts came out of an old car-sub box that's been in my basement for a few years. Thee feet are made from 2.5" x 2.5" table legs that were scrap from a TV stand I built. I'm currently externally using a 200W plate amp out of a RCA sub. It gets the job done, but I think there are some boosts that are keeping me from getting real flat response. My PE amp and spikes for the feet should ship on the 20th, so hopefully by the end of the month my sub will be complete. When I get it out from it's current placement (acting as a corner table and blocked in by a couch and chair) to swap the amps and install the spikes, I'll take some pictures to post. I'm really proud of my sub (sound AND looks), so I guess I'll get to show it off then

 

[Chris Carswell]

That sounds like a cool looking sub. I can't wait to see it. That goes for yours too Matt