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How close are Shiva's to their rated T/S specs?

Discussion in 'Archived Threads 2001-2004' started by Peter Johnson, May 27, 2001.

  1. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Have you guys found the actual specs to be very close, or are they a little off? Considering I am probably going to build a ported sub, I am a little worried that if they are a little off.....well you know..
    Thanks
     
  2. JohanK

    JohanK Second Unit

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    Even if the specs vary somewhat, if the Fs/Qt ratio is relatively constant, then the box performance should be about the same.
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    " Resistance is FUTILE! " -- The ( HOME THEATER ) BORG
    equipment list
     
  3. Mark Wilcock

    Mark Wilcock Extra

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    I tested my pair using Speaker Workshop
    I got:
    Speaker 1
    qtc = 0.423
    fs = 20.825 hz
    vas = 150.546 litres
    Speaker 2
    qtc = 0.426
    fs = 20.682 hz
    vas = 157.940 litres
    This was just me mucking about with my computer, not a proper lab, but the results are pretty good.
    The slight variations have made the box sizes a bit larger than the alignments in the white papers.
    I don't know whether to tune each enclosure individually, or use the same port length for both.
     
  4. Julian Data

    Julian Data Second Unit

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    Mark,
    Did you make your own jig?
    I have thinking about doing this.
    jd
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  5. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Thanks, good idea Mark.
    What size are you going to make your box now?
     
  6. Julian Data

    Julian Data Second Unit

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    KIM, that the T/S parameters should slightly change after break-in.
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  7. Mark Wilcock

    Mark Wilcock Extra

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    Sorry about the delay, but I couldn't connect to HTF last night (Melbourne time)
    Julian:
    I made the wallin jig 2, I had also made the first version.
    I have also built Eric Wallin's microphone preamp using a Panasonic mic capsule.
    I used a 61 litre sealed box to test the drivers, and broke them in for 24 hours using a 20hz sine wave.
    Peter:
    I'll get back later (got to go to work now) with the box sizes I worked out using Speaker Workshop and WinISD.
    Short version: 127 liters and 19hz (due to size constraints of the room - I'm building two subs and running out of space)
    The full version of LSPCAD would be great, but I spend enough already on HT gear.
     
  8. Julian Data

    Julian Data Second Unit

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    I need to make that jig! [​IMG]
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  9. Mark Wilcock

    Mark Wilcock Extra

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    Peter: I put the various values for shiva drivers into SPSIM, which gives you the Q value for a sealed box.
    To get a Q=0.6 sealed box response using:
    1. Dumax results for Shiva Mk 1 from version 1 white paper
    fs=21.61 hz
    Qts=0.376
    Vas=136.6 litres
    Box volume = 88.5 litres = 3.13cuft (corresponds with white paper)
    2. Results for Shiva Mk 2 from version 2 white paper
    fs=21 hz
    Qts=0.39
    Vas=144 litres
    Box volume = 107.6 litres = 3.8cuft (does not correspond with v2 white paper, they didn't change the box sizes)
    3. Measured results for one of my Shiva Mk 2 drivers
    fs=20.8 hz
    Qts=0.423
    Vas=150.5 litres
    Box volume = 150 litres = 5.3 cuft (heaps bigger than white papers)
    I did notice that the f3 for a q=0.6 response is much lower using the measured parameters.
    After all this playing around, I'm just building a box, tuning the port accurately (I hope) using the measured impedance, and then I'm going to enjoy listening to it.
     
  10. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Thanks Mark.
    Hmm....in other words, the specs cant really be relied on with a 50% difference in box volume....
    Mark, you seem to be very good with all this DIY stuff and you seem to be wanting to end up with the same result as me, with the sub being more orientated towards music.
    It'll be a while before I start anything, my uni exams are like 2 weeks away and I am snowed under with assignments etc.
    BTW, I got all the opamps for the active x-over free from Burr-Brown [​IMG] They even couriered them to me for free, from the US...
     
  11. Mark Wilcock

    Mark Wilcock Extra

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    Peter, I wouldn't say that my measured results are very far off the Version 2 white paper parameters at all. As far as speaker drivers go the results are VERY close. (Way closer than the vifa and nht examples on the speaker workshop page www.audua.com) I'm just using some freeware and a homebuilt jig after all.
    If adire audio used the dumax results to calculate their alignments, then I just don't think that they redid them for the version 2 white paper with the mk2 shiva.
    Even with the measure values I got, the predicted results for a 127 litre/19hz shiva sonosub look REALLY good, way better than any of the jaycar drivers (or any other locally available drivers).
    Free BB opamps - you bastard! - it cost me $60 for the 21 TL072's in my crossover
     
  12. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Not just BB op-amps....Military Grade BB opamps...
    hehe.
    Unfortunately I missed the delivery today, get em tommorrow..
     
  13. DanWiggins

    DanWiggins Second Unit

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    Peter,
    Just wanted to point out that the Mark II Shivas T/S parameters are:
    FS: 21 Hz
    Qts: 0.39
    Vas: 151L
    Mark's measured T/S parameters are quite close to these numbers (average Fs being a bit low, average Qts a bit high, and average Vas a touch high).
    We screen EVERY woofer we sell. We shoot for a 15% tolerance in specs as acceptable (note that the compliance of spiders is VERY tough to get good consistency, and is the main reason the T/S parameters will drift). Overall, I believe our tolerances are at least as tight as other vendors, and in many cases considerably tighter. Many companies consider variances on the order of 25% as acceptable.
    Dan Wiggins
    Adire Audio
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  14. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Thanks Dan.
     

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