Is WinISD correct?

[mazeroth]

I purchased 32 of these drivers about 6 months ago because they were a Buyout from Parts Express for $8 each. Very nice woofer for the money. I am throwing around ideas for my line array project and modeled one of these woofers in WinISD. Here's what it recommends:

Sealed: 1.215 cubic feet (34.4 liters) Qtc: 0.71 (-3db @ 56 hz)
Vented: 2.384 cubic feet (67.5 liters) Tuning Frequency 31.62hz

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-493

It measures out physically to be a 6.5" driver, but PE calls it a 7" due to it's larger mounting area. I'm having a hard time imagining a line array, or even a regular speaker with a box as big as they're recommending. Is WinISD telling me the truth, or is it playing games with me? Can I use a smaller sealed box and maybe tune its -3d to around 70ish? I could still easily integrate a sub at that frequency, or do you guys have a better idea?

I'm thinking of using these tweeters from Parts Express, and if I buy them in quantity I get a pretty good price. They say to cross them over between 2500 and 3000 but after looking at the response graphs I was wondering if you guys think they could be crossed a little lower? Maybe compare them with the Vifas I have and see what you think.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=275-085

I REALLY appreciate any feedback you guys can give me. Jim, I would have e-mailed you personally but I think I've bombarded you with enough questions for the time being!

Thanks!!!

EDIT: If these woofers aren't ideal in you minds and it would save me a lot of trouble, I could just Ebay them and get different ones, although for the money, I think they're a good deal. Thanks!

 

[BillFitzmaurice]

WinISD speaks the truth; look at the Qts. Your best bet for these puppies is a TL/LA, which is happy with high Qts drivers and will allow you to keep the size reasonable, should be good to 35Hz easily in a seven foot line.

You can safely cross the Pt2s at 2kHz with a 4th order HP filter, especially with a bunch of them.

 

[RJ]

I used WinISD to model my Line Array.
10 5.25" Aluminums 295-330 and 6 PT2's
I tried 3000, 2500, & 2000 4th order crossover on the tweets.
I liked 2500. In fact I could'nt tell the difference between 2k & 2.5K...
Also, I could bring down the slope better at 2.5 k to match the Woof's...
This line array can Slam!!!
The bass is really tight & punchy. You can hear the fingers stroke the bass guitar on Diana Krall's "East Of the Sun" & punch you in the chest on NiN's" Down In It"
So the size of the box came out right. I ended up going Sealed.
I didn't like extraneous noise coming out of the ports....
Go For It!!!

 

[mazeroth]

Fiddled with WinISD some more and started to adjust the closed box volume. Here's what I came up with...

Box is 12x12x70. Internal volume = 4.37 cubic feet. This yields a Qtc of 0.88. The 0.707 Qtc used a 9.722 cubic foot box. WinISD shows the F3 going up by 3 (to 58.5 hz) and there's a small hump of +0.5 db from 90-120 hz. If that's all it's going to do to the frequency response, and WinISD is correct, I think that's a VERY fair tradeoff. It's almost tempting to make it a little bit smaller. A sub can easily integrate into a 60hz -3 db point in my opinion. Is there more to this than I can see? What exactly does Qtc effect?

Thanks guys!

(oh ya, I'm using 8 of the drivers in this config)

 

[BillFitzmaurice]

Qtc effects the bass response and cabinet size; you get more bass but need a larger cabinet volume. When you build your pipe leave one end open and fully stuff it with poly fill; see how you like it, then seal the end and try again. Mount the woofers frame to frame, starting tight to the closed end (top) of the pipe. The open end version well may extend the bass response another 20 Hz or so, and with room lift a sub may not be necessary. You may want to use 9 drivers to keep impedance at 8 ohms instead of 4.

 

[tiroth]

I used these recently. I started with a (boomy as heck) empty box and then really packed it with fiberglass...uncompressed near the driver but progressively heavier. The end result was quite tight and listenable...I think the Q was near 0.8. These were long thin enclosures so they probably aren't classic sealed boxes.

I think the final volume was only 15-20L.

I'm at work and the measurements are at home, but if you want I could give you more details. I think these drivers sound good overall but they aren't as coherent as a more expensive cast chassis driver like SS or the Audax HM series.

 

[mazeroth]

Bill, good call. At work a few weeks ago I had drawn up plans to use 9 woofers but forgot about it. Thanks for reminding me.

Tiroth, what kind of speakers were these? Were they some form of line array or just a regular floorstander? If my memory serves me right I think 15 liters is only about 0.5 cubic feet, so I guess those were just regular speakers. Also, I'd much appreciate any info you could post about your project. Pics too if you're feeling crazy I have 32 of these to put to use if I don't sell them so I'm up for any options.

Thanks!

 

[tiroth]

Correct, floorstander. ~16L per woofer. Not bad response really...if you have a midrange. Pretty unusable in a 2-way.

 

[tiroth]

Unstuffed Q predicted .85 (BOOM!) stuffed Q 0.63. Fb=63Hz.

 

[richie00boy]

Or you may well be able to just stick them in the (sealed) box size you desire and use a Linkwitz Transform to get the Q (and F3) to a value you prefer.