Lousy woofer choice? help!

[14G-Dutch^]

Hi guys, this is my first post. (nubiusMaximus) Make Me feel at home! =)


I bought some 6.5" Audax woofers from Partsexpress several years ago. The model # is AT170M0 (Partsexpress# was 296-082 Discontinued.)

The specs that I am able to get are:
Vas 36.2 liters(huge!)
Fs 48 Spl 90db (2.83V)
Qts .69
Response 48-6000Hz
50 watts Xmax 3.5 mm

Has anyone used, or seen this woofer used before? I am getting lousy preliminary results (maybe because I am such a noob) The specs suggest the requirement of a huge enclosure. PeBox from Partsexpress calculates a vented box of 7.51 cf, OR a Sealed enclosure of 17.93 cf for a Qtc of .707 Instead of these huge boxes I tried another route: A U-frame enclosure. Which is a tube roughly twice the length of the woofer diameter, and is about 7 inches in diameter.

This produces practically no bass. None. It is listed as a woofer but performs more like a midrange. I also have the woofer in enclosure that I use for my home theater Center channel. It is sealed .75 cf. Same basic result.

I may be just missing the boat by not building a traditional enclosure, but I don't see much promise in these drivers to push me forward.

Any ideas? Or any reference to previous projects, either failed or successful.

I think I wasted some money here. Thanks for any help

Jon King

[planet10]

High Q makes it a bit problematic... its not likely to work at all well in a vented box. I wonder if this was designed to go in car doors? Except for limited swept volume it is ideal for an open baffle.

You could try an alphaTL http://homepage.mac.com/tlinespeaker...TL-article.pdf

Or model a sealed enclosire with a Q of ~1.1 and then make it aperiodic...

dave

[sreten]

Hi,

Audax do not usually produce drivers with poor specs.

Your problem is not a huge Vas - its a high Qts.

Simply put I don't believe the specs, I think Qts is lower.

Fs and SPL sound typical of a paper Audax driver.

But with Vas of 36L (= lightweight cone when Fs =48hz)
I'd expect Qts to be around ~ 0.3.

Your experiments with a sealed box also suggest this.

WinISD suggests BL = 4.3 = a very wimpy magnet.

If the magnet looks fairly reasonable i'd say specs are wrong.

If they are right it should boom away in any box around 0.75cuft.

Not much point in Q less 1.

/sreten.

[BobEllis]

I bought those drivers for my first return to speaker building project a long time ago. The specs are correct, unfortunately. Even ignoring that it has a bucking magnet, the magnet is small...

I used about 2 cubic feet heavily stuffed in a tower MTM, and it wasn't to bad for the time it took to save up for my next drivers in a HT setup. OK for kid's speakers or garage use. Now they are used for my son's bass guitar practice amp.

[RJ]

Interesting formula in that alphaTL article;
http://homepage.mac.com/tlinespeaker...TL-article.pdf

Fo=Fs/Qts.
My Goldwoods that I used in my Aperiodic TL came out to be 112" approximately;


And using the above formula it comes out to 105"
The 112" line was calculated using MJK's MLTL worksheet.
The box size was 20"Hx19"Dx9"W....with 5 internal baffles slightly tapered and fully stuffed with a 4"x 3/4" port/terminus.
The Goldwoods were not designed for bass, since the Xmax is only 2mm. The Fs/Qts on these drivers are 85/.81 = 105"...
The box's real purpose is for a very smooth midrange since a TL box is the closest enclosure to an Infinite Baffle.

The Audax comes out to 69.5" So the box could even be smaller than mine. I would still probably use MJK's worksheet to find out for sure, and it's simulated bass response...

[planet10]

Originally posted by RJ
I would still probably use MJK's worksheet to find out for sure, and it's simulated bass response...

seconded... the alphaTL is just a no effort design for high Qts drivers that works OK...

dave

[14G-Dutch^]

Thanks for the replies guys.

I guess I should have mentioned this earlier, but I am using these for HT and music too. I don't have room for 5 fairly large enclosures......at least according to my wife =)

I did some calulations using the article u recomended. I had decided on an fO of 80 Hz for my calculations. Which nets a lenth of 32 inches, with a cross section of 127 sq inches. So a sample size might be: 10x12.7x32. This also makes for a rather large enclosure. I am aiming for something small if possible.

I miss-guessed my enclosure size for that sealed center channel I am using now. It is .27 cu ft, which should yield a really hi Qtc of 1.65. Even so, bass is very lacking. Surprisingly it is not muddled or thumpy, just sort of non existant. I realize iI am not going to get a large output from a 6.5 inch driver but.....

So, with the Alpha TL, I am likely to net an additional 2-3 db, and if I remember corectly that sounds like twice the outpout for each 3db increase? Even so, I think I may end up dissapointed. I have a Sub with 2 Dayton Series 2 Drivers (no I haven't set the Xo point for certain yet) =)

My hope was to use these as sort of Mid bass/midrange drivers. It looks like maybe I should use them as Midrange only. Or should I make the effort of building the Alpha TL to try it out? I think if I am going with that large of an enclosure, I would rather have something that performs better in the bass range.

Thanks so much for you opinions. Keep em coming. =)


Jon King

[planet10]

If you only need 80 Hz, i'd throw some aperiodic boxes togther... you could even just try it with your existing centre... it will bring the Q down at least a bit...

Try something like Dynaco used on the A 25 (maybe best to put it out of the way on the back of the box)

http://www.t-linespeakers.org/classics/dynaco.html

dave

[14G-Dutch^]

I guess I don't really know WHAT I need =)

I have no experience with the aperiotic type design. I will look into the forum for info on this.

Thanks for stickin with me Dave.

Jon King

[planet10]

Originally posted by 14G-Dutch^
have no experience with the aperiotic type design. I will look into the forum for info on this.

Thanks for stickin with me Dave.

Aperiodic design is still a black art... (i'm sure with some port stuffing data it could be modeled in MJK)... my receipe is to build a big a box as you can live with (but Q no lower than 1.0-1.1) and then add an aperiodic port. My experiments have lead me to the Dynaco style port as the easiest to actually implement... a long skinny port, with a rebate. You put a piece of plastic gutter mesh on the bottom of the rebate, add 1-3" of suitably shaped fiberglass insulation, and then squish it down flat (the Dynas have a 3/8" rebate -- a convienient size for 3/4" material) using another piece of gutter mesh.

The variables in your control are the size of the vent, the depth of the rebate, and how thick the fiberglass you are squishing. Unless you build a bunch of boxes or a removable port panel, the first two become more or less fixed at build time.

GM has described a click test, or you can use repeated impedance measures (you are aiming to just kill the bottom impedance peak of the BR saddle that happens when you put a hole in the box), but you can get pretty close by ear.

dave