Khanspire Volume Question

[lcolbur1]

I'm seriously considering building the Khanspires and noticed they come in 2 versions:

Sealed (65 liters @ ~58hz)
Ported (100 liters @ ~24hz)

I was thinking of going with the ported version, but am running into volume constraints. Right now I have ~80 liters and it got me thinking, could I get away with an 80 liter design if I employed 2 passive 8" radiators per tower? What sort of tuning could I expect from using PRs? Not sure if it works this way, but because 80 liters is about halfway between the sealed and ported volume requirements, would that mean that I can expect tuning to be about halfway between 24hz and 58hz, or could I go lower? Could I employ PRs without having to alter the crossover?

[cjd]

You can definitely tune the box differently, but as you go smaller you lose low end extension. You also gain a little wiggle room on power handling below tuning frequency...

I just did a fresh install of the OS on my computer so don't have the software running just now, but finding what 80L wants for a pair of RS225-8 should be pretty straight forward for someone (or me when I get the rest set up.)

[lcolbur1]

Here are the results of parallel RS225-8s with 2x8" prs and 2x10" prs, respectively:

https://scontent.xx.fbcdn.net/hphotos-xaf1/t31.0-8/12185199_10101706399234132_1429490927514539176_o.jpg

https://scontent.xx.fbcdn.net/hphotos-xlf1/t31.0-8/12189185_10101706399089422_6836053246725658327_o.jpg

[sdl2112]

Since the Statements are very similar, I recommend you read Jim Holtz's Statement link. It talks about using the newer RS225 and it appears to work well in a smaller cabinet.

[lcolbur1]

They look pretty similar to the Statements, but your link doesn't mention anything about using radiators instead of a sealed/ported enclosure.

[sdl2112]

Passive radiators won't reduced the required box size for a given tuning frequency. It performs the same function as a port.

[BobEllis]

But a PR allows a smaller box to be tuned lower by replacing the mass of air in an impossibly long port.

[lcolbur1]

Passive radiators won't reduced the required box size for a given tuning frequency. It performs the same function as a port.

But a PR allows a smaller box to be tuned lower by replacing the mass of air in an impossibly long port.

I was under the impression that passive radiators allowed for a compromised design somewhere between the low frequency tuning, high volume requirement of a ported enclosure, and the higher tuning frequency, lower volume requirement of a sealed enclosure.

In the Khanspires' case, if the crossover doesn't need to be adjusted whether using the ported or sealed variation, would it need to be adjusted if using PRs? Would it just be a matter of finding the right tuning frequency that doesn't require crossover changes?

[BobEllis]

Unless you are going to tune it so high that there is a big bump in low end response, the crossover and box tuning are rather independent. The crossover generally impacts frequencies well above box tuning.

Box tuning is determined primarily by box volume and port/PR resonance. Ports are simple, the tuning is determined by length and cross section with a little end correction thrown in. The up side of PRs is that they allow you to have a higher mass/lower tuning frequency for a small box without a super long port. Play with a modeling program and see how long a port it takes to get a 1 cubic foot box tuned to 25 Hz. A heavy enough PR with appropriate compliance could do it with much less impact on total system volume. Way back when, I built a JBL2245H based sub. Two tuning options were presented - 8 cubic feet with a ~9" long 6" diameter port for 24 Hz and 12 cubic feet with an 8" diameter 30" long port. I got a bit of chuffing with the smaller port. PRs don't chuff, but they can bottom out if overdriven.

[---k---]

Sorry, I've been a bit MIA recently.

Bob's got it right. Box tuning and crossover are for the most part independent. You're free to build the box with any tuning you'd like. In the original Khan's thread I suggest the Statement's box for a ported design. The newer RS drivers have change slightly and generally require smaller boxes. I haven't gone back to re-run the numbers. Unibox and the other software is easy enough that I encourage everyone to try it out for themselves. Post the graphs and we'll take a look for obvious mistakes.

I've never done PR. I personally have a hard time justifying the added price over a port. Last time I looked (a long time ago) there weren't a lot of good PR options out their. They are either cheep junk with very low xmax that isn't compatible with the woofers we're using or they are really expensive. They make sense in some cases, but in my opinion generally not.


Just FYI, I think the port in my old sub was like 30" long. That's a long port. Luckily the box was like 50" tall.

[lcolbur1]

Here are the unibox graphs for 2x 8" and 10" Dayton PRs with the RS225s.








It looks like Dayton's 8" PRs have a 9mm xmax, where are the RS225s have 7mm xmax:

http://www.parts-express.com/pedocs/specs/295-492-dayton-audio-sd215-pr-specifications-46183.pdf

http://www.parts-express.com/pedocs/specs/295-356--rs225-8-spec-sheet.pdf