Box Design For Radio Shack 18" Subwoofer

Discussion in 'Speakers & Subwoofers' started by Richard Sherman, Nov 6, 2003.

  1. Richard Sherman

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    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
     
  2. Jason_Me

    Jason_Me Stunt Coordinator

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    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.
     
  3. Geoff L

    Geoff L Screenwriter

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    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
     
  4. Richard Sherman

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    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
     
  5. Geoff L

    Geoff L Screenwriter

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    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....
     
  6. Kenneth Harden

    Kenneth Harden Screenwriter

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

    Aaron Gilbert Second Unit

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    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. [​IMG]

    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
     
  8. Aaron Gilbert

    Aaron Gilbert Second Unit

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    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. [​IMG] 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
     
  9. Richard Sherman

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    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
     
  10. Chet Wilson

    Chet Wilson Stunt Coordinator

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    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!!
     
  11. Ron Gugel

    Ron Gugel Auditioning

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    i know this is a very old thread....but i was needing some opinions on same drivers - i have a pair of these 18" drivers that i did some trading for 12yrs ago or so - they have never even been hooked up....still in original packaging...they have been in storage since i got them years ago i always planned on building some cabinets for them for a home audio system using the recommended box designs that came with the woofers...i can see that everyone seems to be in agreement that these woofers are not desirable....but i have them and would like to, at the very least, give them a shot before i move on to other drivers....most of the negativity regarding using these appears to the finished box size and the overall performance even within a suitable box -- i was wondering if anyone had an opininion on using them in an IB configuration.....ive never built an infinite baffle system...but this is what i want to do with the system i am putting together - these drivers are advertised as "free air" but i know that the actual parameters of the speakers are what speak volumes as far as this is concerned...and the original post has these listed so i wont re-list them - all of my expierience is involved with DIY car audio in the past....but IB seems to be pretty simple - i'm planning on a manifold design so that i dont have to cut mounting holes in the wall so that if im not happy with these i can just replace the manifold and use the same opening if i want to try different woofers in the future -- i guess im just asking if anyone has any strong opinions about these drivers in this application -- these woofers look really impressive and i am truly curious about how they will perform.....i will be using a Marantz ME-500 to drive them...one for each...and i do have an EQ to put inline of these "sub" amps to try to help correct areas that may need help.....any thoughts??
     
  12. Cranky

    Cranky Auditioning

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    Wow!
    Just stumbled across this old thread while digging up info on some new 18" woofers. I too, bought two of these 18" Radio Shack woofers back in the '90s. Only paid around $50.00 for each of them as the local RS's here were clearing them out.
    I can both agree and disagree with the remarks I've read. Despite their obvious shortcomings I have actually had great success with mine. From the very beginning my plan was to build two transmission lines for a set of 18s. These had decent power handling and a very low Fs. Just what I wanted, and cheap. I built two boxes according to designs I learned building trannnys for 18" & 24" Hartleys back in the '80s. Paralleled them for a 4 ohm load on an Adcom GFA 555 Mk II, bridged. They're being driven with around 850 watts of headroom. An important thing that a lot of folks forget nowadays, loads of power combined with high damping factor will help avoid losing control of a woofer. My mains are a pair of Martin Logan Prodigys in the main floor family room.
    The subs are located in a wide open basement, around 2,400 sq ft.
    They CAN be over driven but don't need to be to get unbelievable low bass. 16hz pipe organ is astonishing. The Telarc 1812 Overture with REAL canons make me consider having to do major repairs to my house!
    Only lately I've noticed that certain dynamic bass overtones are accompanied by some rattling. Well, time to buy new woofers. 10+ years with these was money well spent. Looks like the best bang for the buck are the Dayton Classics.
    Thanks all.
     
  13. Cranky

    Cranky Auditioning

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    Well, forget the Dayton Classics. Not enough power handling. Found a pair of Pyle PL1890BL woofers on Amazon. These bad boys are wicked. Now, when the Adcom clips I'm not worrying about the drivers. One problem though, my wife is complaining more now... about drywall nails backing out.
     
  14. Cranky

    Cranky Auditioning

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    Another thing. I mentioned that my subs are in my basement. How many of you do this, or something akin to it, also?

    Cranky
     
  15. Robert_J

    Robert_J Lead Actor

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    A lot of people with basement theaters do this. Did you install your new Pyle drivers in the original transmission line sub? How are your getting the sound into your first floor listening room? Most people in your situation would have installed an infinite baffle sub.

    -Robert
     
  16. Cranky

    Cranky Auditioning

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    Yes, I did install the Pyle drivers in the same enclosures.

    The reason I place my subs in the basement is to allow the low frequency waves to develop better. Basically, these subs are just used for "foundation" bass. There's no in-your-face mid bass coming from them.

    I listen to a wide variety of music. It's important that my system be as flat as possible, and I don't use an equalizer.

    Cranky
     
  17. Robert_J

    Robert_J Lead Actor

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    Unless your entire house is the size of a full sized theater, then you really aren't getting the full impact of the better developed bass waves. You are just using your sub as a sort-of bass shaker and a real shaker from Aura or the dozen of other tactile transducer companies will work better. In your face bass will pressurize the room and give you a much better response.

    I've measured the response of my room and it is + or - 6db over the entire frequency range from 20,000hz to 15hz. I use the 3 band EQ built into my Pioneer receiver and MCACC auto calibration plus the parametric EQ of the Behringer Feedback Destroyer for flattening out the in-room response of my dual subs. I did a little work on my quad 18" subs today. Once they are installed I expect usable output down to 5hz.

    -Robert
     
  18. Cranky

    Cranky Auditioning

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    Hey, I hear what you're saying, but I just can't convince the wife to let me put two refrigerator size speakers in the family room. I'll may end up using a couple of 12" drivers I have to build another sub that will fit into the listening room. Either way, the two behemoths provide considerable bottom end.

    Cranky
     
  19. goodolbiggin

    goodolbiggin Auditioning

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    That's just nonsense. I've got two of the Radio Shack 18's and here's your box. If you want one sub per box, make the box 12" x 12" x 36". You'll be very happy with the results. If you want two subs per box, just make the height 72" instead of 36". You might as well say the volume is 3 sq. ft. You can resize it any way you want as long as it remains 3 sq ft. If you want it to destroy your house, make it into a folded horn design. If you design it properly, it will crack your sheetrock and pop your light bulbs if you put more than 200 watts into it. I play bass through a 18" folded horn with 300 watts that will fill a stadium. If you're just wanting to make a great home theater sub, just put about 100 to 200 watts into it and you won't be sorry.
     
  20. goodolbiggin

    goodolbiggin Auditioning

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    Sorry, was incorrect. Box size is 24" x 24" x 36". Box is actually 12 sq ft. 24 sq. ft. for 2 drivers. Good luck.
     

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