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Thread: JBL GTO sub bass project

  1. #1
    JBL 4645
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    JBL GTO sub bass project

    Well after the chit chat on the (stereo sub bass) I looked at two nominees at Halfords which is the nearest placed to buy some JBL car audio. Well it’s not going in to be used for (vroom, vroom car) its going in, my living room, end of story.

    I’ll try it out later to see how it fairs (yes in the Eltax enclosure) I’ll run a few frequency response sweeps to see where it stands.

    I’ll have to start buy buying as many and at £49.00 I’m not complaining.

    pdf brief description on the GTO series
    http://www.convoy.com.au/downloads/p...1002D_a9d2.pdf

    I plan to get as many as possible within reasonable limits. I don’t want to have to climb over speaker enclosures to get to the sofa.
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  2. #2
    JBL 4645
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    Sooty was sniffing the new JBL for 5 paw approval. Maybe he should be sniffer cat at airport security.
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  3. #3
    JBL 4645
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    (It won’t fit) the basket is the wrong shape no mater, I’ll wait and wait and get few more, and get some boxes knocked up. I flipped it upside down it’s slightly wider by a few extra (mm) millimetres.

    Well I have the specifications

    12"(305mm)

    Cut-out diameter
    11-3/16” (284mm)

    Outer diameter
    12-7/16” (316mm)
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  4. #4
    JBL 4645
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    I kinder cheated with towel (looks like something out of Total Recall “wrap wet towel around your head”) LOL and (few dust cloths) tucked around the inside of the basket to give it a near close sealing with the enclosure. A bit impractical and risky but I managed to get this frequency response at the front of the room.

    Similar issues of nulls at seating location it’s the right front that is good for certain frequencies and lousy for other frequencies.

    If I had placed it on left side of the room it would be different and same goes for rear right corner or along the rear wall it beefs up the 50Hz to 60Hz range

    If I get few boxes made to size to give optimum maximum performance I’d be happy with that.

    I did notice the slight rise in the 40 to 50Hz range as well 90 to 100Hz range. I guess if the seal is 100% it would be bit tighter in the lower 20 to 40Hz range. Well I can hang on there’s no rush.
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  5. #5
    JBL 4645
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    Well the “nulls” can be seen (or gaps between) the in-room frequency response (SPL db metre placed on the sofa) a scene from Star Trek “Balance of Terror” where the space station gets blown to “kingdom come” has few good lows. The lows shown here is left and right front sent to sub though the mixer the centre low end is less on the Dolby5.1 mix. The LFE.1 track doesn’t cut in till later on in the show and is only used now and then to add extended low end jolt.


    I could plot the room out with the Eltax loaded back in its enclosure and test each and ever single 15” square box size along the sidewalls front and rear wall to get a rough guess where the strongest areas are and weaker spots. Wow that will take up whole day of testing.
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  6. #6
    JBL 4645
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    I’ll pick up another GTO1202D tomorrow and store it till I have around x16 of them, to start the project next year.

  7. #7
    JBL 4645
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    I’ve just momentarily picked up a second JBL GTO1202D only x14 more to go now.

    The guy in the store told me they need to order more in. “How many do you need?” (About x14 more) “16!”
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  8. #8
    Senior Member pos's Avatar
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    Crazy project you have here! 16 subs!
    How are you going to amplify them?
    With so many woofers, and the EQ gears you have, I would not worry too much about box tuning, and just put them in small sealed boxes spread around the room (and also at different heighs) to counter room modes problems (that clearly show in your measuremets)

    With that many subs (and providing you have enough amplifier power), you do not even need to have separate eq per sub: the frequency response is likely to be quite smooth. Just make sure everything is wired as it should (global Re, and polarity), measure, eq, and you are good to go!

    But are you really planning on installing 16 of these subs?

  9. #9
    JBL 4645
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    Quote Originally Posted by pos View Post
    Crazy project you have here! 16 subs!
    How are you going to amplify them?
    With so many woofers, and the EQ gears you have, I would not worry too much about box tuning, and just put them in small sealed boxes spread around the room (and also at different heighs) to counter room modes problems (that clearly show in your measuremets)

    With that many subs (and providing you have enough amplifier power), you do not even need to have separate eq per sub: the frequency response is likely to be quite smooth. Just make sure everything is wired as it should (global Re, and polarity), measure, eq, and you are good to go!

    But are you really planning on installing 16 of these subs?
    Evening pos

    What can I say the room is bitch! LOL She is life sucking frequency null in certain spots and I just want to cut around that once and for all without ever having to hump sub boxes around.

    No they will get a stereo amp for each few pairs per side left and right stereo channel of the amp.

    So hopefully I get away with four stereo amps.

    Yes, it is crazy LOL but I’d sooner have a sane smooth frequency response rather than going crazy mucking around with a single sub to find the best place in the room.

    So you would say (sealed) rather than ported then!

    Can you enter the T-S-P into the Win program because there is some parts of the specifications that are not listed on the link here that was required and I think I might have miscalculated the data entered.

    Stuff the link I can’t find the specifications! Here’s the T-S-P from the spec sheet I have.

    Diameter: 12” (305mm)
    Sensitivity: 93db
    Power handling: 300wRMS 1200Wpeak
    Frequency response: 23 – 400 Hz
    Normal impedance: 1 or 4 ohms
    Voice-coil diameter: 2.0” (51.0mm)

    Dimensions:
    Mounting depth 5-1/6” (129mm)

    Cut-out diameter
    11-3/16” (284mm)

    Outer diameter
    12-7/16” (316mm)


    Voice coil Dc Resistance Revc: (ohms) 1.00
    Voice coil inductance: @1 kHz: Levc (mH) 0.71
    Driver radiator area: Sd (in2) 82.46
    Sd (M2) 532.00

    Motor force factor: Bl (tm) 7.71
    Compliance volume: Vas (FT3) 3.45
    Vas (litters) 97.80

    Suspension complianc: Cms (um/N) 242.00
    Moving mass, air load: Mms (grams) 189.00
    Moving mass, diaphragm Mmd (grams) 182.00

    Free-air resonance: Fs (Hz) 23.50
    Mechanical Q: Qms 7.14
    Electrical Q: Qes 0.47
    Total Q: Qts 0.44

    Magnet-gap height: Hag (in) 3/8
    Hag (mm) 9.00

    Voice-coil height: Hvc (mm) 9.00
    Hvc (in) 1-5/16
    Hvc (mm)34

    Maximum excursion Xmax (in) 1/2
    Xmax (mm) 12.50


    I’ve looked and looked I just can’t find where the specification sheet is hiding?

    Cheers pos

  10. #10
    Senior Member pos's Avatar
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    something between 40L (Qtc 0.8) and 60L (Qtc 0.7) will be good. You will have to eq anyway.

    with 18mm walls a 40L box could measure 59x38x25cm (winISD's optimum ratio, but any ratio will do for such a small box used as a sub)

    Will 16 of these fit into your room?
    That's almost 1 cu meter in total with exterior dimensions!

  11. #11
    JBL 4645
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    Quote Originally Posted by pos View Post
    something between 40L (Qtc 0.8) and 60L (Qtc 0.7) will be good. You will have to eq anyway.

    with 18mm walls a 40L box could measure 59x38x25cm (winISD's optimum ratio, but any ratio will do for such a small box used as a sub)

    Will 16 of these fit into your room?
    That's almost 1 cu meter in total with exterior dimensions!
    Cheers on the feedback pos

    LOL I guess that now depends on the size of the enclosures doesn’t it!?

    Yeah I’ve kinder over looked that fact! LOL The smaller Eltax A12R sub is 15” square and if a box of that size will suit these JBL GTO 1202D, then so be it 15” square I can get 16 in easily along the sidewalls front and back walls.

    I’m not looking for high over the top SPL db that ruptures the ear drum! I’m just after an even-smooth frequency response that can play at sensible SPL db levels.

    Oh, bugger cm you guys work in cm I need to convert that to inches?

    I’ll go to a calculator conversion for the size-up.

    I was going to buy car Hi-Fi box today and the JBL GTO1202D didn’t fit it was out by at least 5mm on the cut-out hole on the box. No I don’t fancy sanding it down LOL.

  12. #12
    JBL 4645
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    pos

    I assume that is the order for height length and depth?

    H 59 centimeter = 23.228 346 457 inch
    W 38 centimeter = 14.960 629 921 inch
    D 25 centimeter = 9.842 519 685 inch

    I don’t want to mess this up!

    So you strongly think that sealed will be the best option here as I read in the owners manual JBL advised that sealed will be good without too much trade offs in the lower octave below 40Hz.

    How many enclosures can I get out of a 4x8 18”mm sheet of MDF?

    So go for rectangular shape that sounds good because the depth will take up less floor space, it’s the height that I’d have to get used to.

    Room size is
    15 feet length
    10 feet 4” wide
    7 feet 8” high

  13. #13
    Senior Member pos's Avatar
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    15"x15"x15" is 40L with 18mm walls (don't know how many quarter of which finger that will end up to be in your strange unit system ).

    I am not sure this dirver will be ok if facing down, like your eltax sub.

  14. #14
    Senior Member pos's Avatar
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    Sealed is the best option here.
    Any shape will be ok, as long as it is 40L, or around 55L exterior with 18mm walls.

    Are you going to build the boxes yourself?
    With that many subs calculating the dimensions to maximize your MDF sheets is a good idea indeed!

  15. #15
    JBL 4645
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    pos

    Oh, I’ll ask the chap at the timber yard how many sheets I can get out of it. As long as I have rough size that’s good enough.

    (I’m guessing I can get x2 boxes out of 4x8 sheet of MFD at specific cut size.)

    I think it was 2 sheets for the other JBL diy box, 13 years ago. The cost was around £45.00 for the MDF. V.A.T might have gone up a few bob since the budget this year!

    The Etax sub is, on its side it fires outwards into the room. So the JBL will be facing front and forwards!

    Can I take the size up a few litters and how badly will that affect the performance?

    You know I have “Images” JMJ playing only on the L/R stereo only no sub bass turned on and I can hear the engine of the bus across the road at 35Hz! It smoothly blends in with humming, humming sound!

    Anyway what of taking the litter size up a tiny notch is your formula sound!

    I might just play it by ear and see how it progresses over the time if I can see a rapid improvement in frequency response smoothness and can do it for less than x16 then so be it, x2 won’t get near x4 might start to see some progress, maybe? It’s an odd room to sort out!

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