Richard Sherman

Ok, I have been watching this board for a long time and you guys know your stuff, so can you guys recommend a good enclosure for the following driver

Radio Shack Cat, No. 40-1309 (18" Subwoofer)

Nominal Impedance........................... 8 ohms
DC Resistance (RE)............................ 6.83 ohms
Free Air Response............................. 16.5 hz
Equivalent Air Volume(VAS)............... 41 Ft3
Moving Mass (Mms)........................... 192.6 Grams
Mechanical Q (QMS)........................... 1.986
Electrical Q (QES)............................... 0.225
Total Q (QTS)..................................... 0.20
Peak Power Handling........................ 200 Watts
Peak-to-Peak Linear Excursion(XD)... 6.1 mm
Gap Flux Density(BG)......................... 7850 Gauss (+/- 200 Gauss)

Thanks for your help

Richard

Jason_Me

That is not a very good woofer. I do not recommend a sealed box. In a 174 liter sealed box, with a Q of .577 you have a -3 db point of 62 hz and a -10 db of 30 hz.

If you go the ported route you'll need a huge enclosure. A 300 liter box tuned to 25 hz would be the minimum ( -3 db at 32 hz). A more ideal box is 550 liters tuned to 20 hz. This gives you a very shallow roll-off from -3 db at 55 hz to -4 db at 23 hz.

The incredibly low excursion of the woofer shows it bottoming out with more then 20 watts when you get below 40 hz.

Geoff L

In short, not a good choice. Low power handeling, along with a huge cabinet is required.

The effort involved to build the encloser to get optimal performance would be a waste of your time and money.
A different driver selction would be a very good idea, unless you want a refrigerator in your room that dosn't make much bass considering it's "MASSIVE" size!

Cheers

Richard Sherman

Well that sucks, especially sense I just bought 2 of them for $75 dollars a piece.

Anyway I can make these work for a little while anyway?

Richard

Geoff L

If they have not been used you should be able to return them with out a problem..

If your stuck with them, they could possibly be used in an Isobarik Clamshell design, but this type design is not a simple one to model and build. Unless your pretty experienced in sub DIY, I would not recommend this as a starter project at all!

For the money you have into the Radio Shack drivers you easily could find a much better driver that would out perform the both of them and in a much less complicated design....

Can you say Tempest-15"... Get rid of them and go to the DIY for help in selecting a driver and design to suit your budget, experience, and bass needs....

Kenneth Harden

Yeah, try to return them, you can get killer stuff for $150.

Aaron Gilbert

I hate to say it, but I think the other folks are right. This is not a good choice for a subwoofer. It would work for for a pro-sound reinforcement type woofer in a medium sealed box. The lowest sealed box F3 would be around 57 Hz, with a box Q of 0.7. That's not hideous (would work great in a car), but hardly a subwoofer. The box size doesn't look bad to me though, at only 3.64 cubic feet per woofer.

Nevertheless, the simple fact that you have two 18" gives you a LOT of cone area, so the low excursion isn't so much an issue. I am using a single 15" with 20mm of linear peak-to-peak excursion. Your extra cone area brings you to just 12% less swept volume (cone area times excursion) than what I have. So, assuming you can't return these suckers, you do have enough air moving capability to get some serious low end output, if you can electronically equalize the bottom end. I would tend to boost it by 6-12 dB per octave below 55 Hz or so. And, your box would still be smaller than my 10 cubic foot monster.

Now if you cannot boost the low end electronically, your best bet would be the giant size ported box. I would strongly recommend against the isobaric configuration, because you are simply throwing away half of your output capability and efficiency, just to get a slightly smaller box size and reduce odd order distortions.

Good luck!


Aaron Gilbert

Aaron Gilbert

If you just want to make them work for a little while, that certainly is doable. To minimize box size, you can shoot for a slightly high Q and put a lot of stuffing in the box. A sealed box of two cubic feet per woofer would give you a Qtc of 0.9, which I personally have used and don't find it too objectionable. Then, what I would suggest is to get a cheap 10 band graphic EQ (preferably used as they still can be pricey new) and boost the 31 Hz band by 10-15 dB. That still won't get you very much output at 20 Hz, but 30Hz and up should really rock.

The first pair of speakers I ever built were a sealed box using an 8", which admittedly had an F3 of around 48-50Hz rather than closer to 60Hz. I ran the system with the aforementioned EQ with 31Hz boosted 15dB, and never wanted for a subwoofer. This was in the pre-DVD days, of course.


Aaron Gilbert

Richard Sherman

Yeah I bought these off ebay so I am stuck with them, what size sealed box would be best, size is not a big deal to me, or would the ported be that much better?

Live and Learn, my lesson for the day, I am slowly understanding all this...

Richard

Richard

Chet Wilson

I would say relist them on ebay. As everyone stated above there are better choices. I think the 15 or 20 dollars it costs you to unload them is offset by the performance gains from another route. Plus after reading what has been said it would be hard to invest the money in this effort and feel right about it.

Good luck!!