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Thread: W15GTI MkII & W12GTI MkII

  1. #1
    Senior Member Hoerninger's Avatar
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    W15GTI MkII & W12GTI MkII

    W15GTi MKII
    http://www.jbl.com/car/products/prod...TIDifferential

    Drive« Design (DDD) motor
    Die-cast vented basket
    Kevlar«-impregnated paper woofer cone
    Nitrile-butylene surround
    ----------------------------------------------------
    AVS-Forum by Andy Wehmeier:
    ... I have something to add about the Klippel test and the determination of Xmax.

    The motor uses two coils and two gaps. When excusrion is low, both coils operate in the gaps for reduced distortion (gaps and coils are in opposing polarity). At high excursion, one cil drives the woofer forward and the other drives the woofer rearward. as soon as one coil leaves its gap, the BL falls, but the other coil is in its gap. This is one speaker for which the XMAX can't be accurately determined by measuriing BL.
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    Senior Member Hoerninger's Avatar
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    W12GTI MkII


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    If you've ever heard one, it's a fantastic driver in the right application. It has unbelievable output.

    It's hilarious that JBL used such a dopey representation of the driver in the document. The real W12GTi looks like this:
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    Out.

  4. #4
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    Ti,

    It looks like the W12GTI has a flat frequency response when it is in a vented 2 1/4 foot box and it's 'out of the car'. I imagine it's still in the box either way, but being 'in the car' reinforces the bass heavily, especially at the 30 hz peak. Correct me if I'm wrong on that theory.

    BTW, please educate this fool on how many watts 2.3 v works out to, to get 91 db. Must be Ohms law or VxC=W (Volts x Curr = Watts). Would a pair of these in a vented box perform well for home audio use?

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    That's a standard method for comparing sensitivity measured at one meter from the front of the driver. Usually it's described as 1 Watt at 1 meter at 2.83v, but this is in fact only accurate for 8 Ohm speakers. A 4 Ohm speaker driven by 2.83v is gonna be at 2 Watts.

    I wrote that bass-ackwards, but hopefully you get the point that speaker impedance is a variable that impacts Wattage. So 2.83V is used as a constant, as is the distance, while W and dB will change.

    The LE14H-3 will produce 91dB, 2.83v @ 1m. The LE14H-4 will produce 92.5dB, 2.83v @ 1m. So, we'd commonly say the LE14H-4 is more efficient.

    Yeah, it's a bit more complicated than that, but hopefully it illustrates the issue.
    Out.

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    Sorry, should have continued that the W15GTi puts out 92db and the W12GTi puts out 91dB at 2.83v @ 1m. Looking at the graphs, you can see that this is not a static figure and it varies with frequency for each driver. Usually a central frequency or frequency range relative to the drive is chosen to measure sensitivity.

    What is not immediately apparent is how much a driver can handle power-wise. The LE14H-4 is slightly more efficient than the W15GTi, but the W15GTi can endure greater environmental and power extremes, with peaks up to an insane 5000W. Say good-bye to your LE14H-1, -3, or -4 if you try that. :shock:
    Out.

  7. #7
    Senior Member sourceoneaudio's Avatar
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    Here is a link to my usage. Mine are in half what they really need to get down really low. But they do sound killer, and I'm contemplating a correct size cabinet. But I have to get the 8+cuft end tables past the wife, not sure if she would notice a difference..... hee hee

    http://www.audioheritage.org/vbullet...ghlight=W15GTI
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    Jeff-S1A

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    Quote Originally Posted by sourceoneaudio View Post
    Here is a link to my usage. Mine are in half what they really need to get down really low. But they do sound killer, and I'm contemplating a correct size cabinet. But I have to get the 10cuft end tables past the wife, not sure if she would notice a difference..... hee hee
    That's a great thread, and I remember a question I had at the time but never posted. What happened to all that stuff you had on the enclosure when you really turned things up? I would think the figurines, lamp, and candle would end up on the floor.
    Out.

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    Senior Member sourceoneaudio's Avatar
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    Quote Originally Posted by Titanium Dome View Post
    That's a great thread, and I remember a question I had at the time but never posted. What happened to all that stuff you had on the enclosure when you really turned things up? I would think the figurines, lamp, and candle would end up on the floor.
    Hello T-Dome,
    Things do tend to move around a bit. With the added bracing across the top that did reduce the top plate flexing. The biggest problem I have is, and it's hard to believe. The end tables are spaced 6" from the wall and the active drivers face the wall, during high volume listening the end tables lift up/tilt from the air pressure/movement created coming off of the woofer. One would think that with the weight of the driver being on that end and the cabinets constructed out of 1" MDF that this would not happen. These are no light units, it's a two man operation to move them around.
    Jeff-S1A

  10. #10
    Senior Member Hoerninger's Avatar
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    For comparison some calculations.
    (Closed box, straight forward, no losses and stuffing considered)
    ___________
    Peter
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    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by 4313B View Post
    Please say it isn't so!
    Closed Box calculation was simply much quicker than bass reflex design, I would not go that closed route.

    What about sixth-order vented-box loudspeaker system alignment with two speakers caring mutual conductance?
    (I do not have an easy to use software at hand.)
    ____________
    Peter

  12. #12
    Senior Member Hoerninger's Avatar
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    Food for thought

    As said "I do not have an easy to use software at hand." but the idea is as followes and there is an estimation without a programm (but relying on an existing example).
    It is about using two woofers.
    Quote Originally Posted by 4313B View Post
    ... Maybe you would prefer to place each 2245H in a decent B4 alignment and then give yourself the option to add an external 20 Hz second order high pass filter with a Q of 2 which effectively turns the system into a B6 alignment. The 3 dB downpoint will be roughly 20 Hz.

    In other words, you build an enclosure of roughly 10 cubic feet per transducer (280 liters) and tune the box to 28 Hz. This is roughly a B4 alignment (4th order Butterworth). To turn it into a B6 alignment (6th order Butterworth) you simply retune the enclosure to 20 Hz and apply a 20 Hz high pass filter with Q = 2. This extends the VLF by roughly 10 to 15 Hz. We used to build the enclosure and then use two duct/port configurations. One port/duct would tune the volume to 28 Hz and the other port/duct would tune the same volume to 20 Hz. We would cover whichever port wasn't in use.

    If you want further information on what I am talking about look up "A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments" by D.B. Keele Jr. - Journal of the Audio Engineering Society June 1975, Volume 23, Number 5....
    With the mentioned retuned B4 alignment there is a roll off with about 6dB/oct for the lows. You can compensate for that with a filter (Q=2). Or you take a second filtered speaker placed close together.

    1. By mutual conductance the sound pressure for the lows will increase by 6 dB. You can omit the high pass filter (Q=2) but insert a 12 dB/oct low pass for the second speaker. Due to the alignment the frequency response will fall with only 6 dB/oct for the second speaker.
    2. Combined with the first speaker with an increase of 6 dB/oct both speakers sum up to a flat response. (The whole can be seen as a 6dB/oct high/low filter.)

    Care should be taken for the cut off frequency of the 12 dB/oct low pass filter, the summed up frequency response should be flat. JBL has given a working example, long term readers will know what I mean.
    ___________
    Peter

    Literature:
    http://www.xlrtechs.com/dbkeele.com/...Alignments.pdf
    http://sound.westhost.com/articles/cscaling.htm (Compliance Scaling and Other Techniques)

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    Thanks for doing the search for those references and reposting them. The references Rod Elliot cites are very nice and are the same references Mark Gander cited back when they were first published. Mark eventually tied everything up into anthologies.

    We've talked about these higher order alignments versus lower order alignments before and it boils down to personal choice. I personally prefer the lower order 2nd and 3rd order alignments but the higher order alignments offer extended response with increased efficiency and they work fine as subs for movie playback.

    I think it's interesting that Rod examples a quasi-fifth order design; B380 and B460 deja vu (I could be mistaken but I think the 1500 Array is also QB5). Note that the 2235H and 2245H are lower Q designs while the W12GTi and W15GTi automotive transducers are higher Q designs.

    With the mentioned retuned B4 alignment there is a roll off with about 6dB/oct for the lows.
    B4 alignments roll off at ~ 24 dB/octave, B6 alignments roll off at ~ 36 dB/octave.

    Because the automotive transducers are already higher Q, and well suited for sealed boxes, by venting them you can easily get that thump that is so important in competition automotive sound systems (a home hifi example would be the old L100 with the high Q transducer in the vented box resulting in some good old thump). The drivers are designed for extreme competition and provide enhanced low frequency performance in small enclosures and listening spaces.

    One should very carefully examine the above enclosure volumes, response curves, excursion and efficiencies shown in the JBL product sheets and note the interrelationships. Keep in mind that "room rise" plays an important roll. Automobiles tend to start the 12 dB/octave rise around 50 Hz while typical living rooms start closer to ~ 30 Hz. This "room rise" effectively EQ's the VLF response of a loudspeaker system. If one has a loudspeaker system that exhibits flat response to 20 Hz in an anechoic environment it is going to have a pronounced low frequency response in a typical listening room. Some people like that.

  14. #14
    Senior Member grumpy's Avatar
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    Thanks Hoerninger and 4313B, I appreciate the thought/time that went into those posts.
    Should be useful as reference if questions regarding the use of these drivers come up
    again (they will).

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