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More DIY Sub stuff........

Discussion in 'Home Cinema Building DIY' started by theritz, Jul 5, 2004.

  1. theritz

    theritz
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    OK, I know I'm going to regret this but......................

    Any suggestions for a replacement for the BSB12-100 while retaining the BSB 100w plate amp ??

    I've run the Avia sweep and find it rolls off fairly quickly from about 35 - 30hz. I was pleased enough with the overall response, there's a couple of dips in the overall system, but nothing dramatic. On Saturday while trying to improve its set-up, I also noticed that the driver makes a fairly pronounced "buzzing" noise during the sweep - while watching movies it's only really noticeable during the opening scene of AOTC (when that blooming huge silver spaceship make its approach to Coruscant,) I checked out everthing - whether the wire was vibrating in the enclosure, air escaping, driver vibrating against the baffle - all to no avail. The driver and the amp are sealed using weather strip stuff. I ran the sub with the driver out face down on the floor (not at high volume, needless to say,) and the noise is clearly coming from the driver itself - It looked to me as though it's running out of excursion (like it's hitting the capability of its travel). I was a bit disappointed, TBH, because the thing hadn't been running for more than about 3 - 4 hours overall, and I didn't have the "gain" on the amp up more than a little bit past 12 o'clock. I don't run my sound system very loud in any event. Turning the gain up sees the driver moving quite a lot - looking very "odd" to me (like its "flapping"), but then I don't have a lot of experience to rely on.......... :confused:

    Watching stuff today, (the Fast and the Furious Superbit - the DTS track was brill - I could feel the exhaust noise and the air pressure form the cars whizzing past against my chest...... :D I haven't tried U571 or K19 yet......) I didn't notice the same noise, but I didn't run the sweep again - I'm anxious not to do any damage. It's a bit of a bummer because BKelec are on hols until 19 July - Has anyone got experience of how good they are at sorting things out when there's a fault ?

    As I indicated in my other thread, I'm not a fan of over-powering bass, and if it performs OK over the next week or so I'll probably let things as they are..... but if it niggles me I know I'll want to do something about it.


    As ever, all and any advice would be appreciated............... As far as a possible alternative speaker is concerned, I'd like to keep the enclosure and plate amp............ and would prefer not to graduate to anything exotic (read expensive.....)

    Thanks...............


    Sean.
     
  2. GaryG

    GaryG
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    Sean

    If you are not careful you will end up spending more money by swapping components than buying something more substantial in the first place.

    Understandably you want to keep costs down and make use of your existing amp, however, 100W is not a lot for a sub. The most likely scenario is that when you replace your driver the next obstacle we be the amp 'clipping' as it runs out of power.

    You're welcome to borrow my 12" Shiva to see if it solves your problem.

    EDIT
    Just noticed you're in Ireland, not a practical proposition with the cost of postage.
     
  3. theritz

    theritz
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    Gary,

    I know what you mean about the component swapping, but in a room 13' x 8' the sub is quite sufficient as it is........ if it's turned up at all it completely overpowers the rest of the soundbalance in the room. I very much appreciate the offer of the Shiva and you're right, the slight obstacle of the Irish Sea is a bit of a bummer !!

    I'm curious though...... the Shiva (and the Lab12) are rated at something like 600w, would a 100w amp drive them ok ? I had originally thought of both of these drivers as an upgrade path. Alternatively as a low cost replacement if there was damage to the driver I had considered this one from Farnell as a replacement - it's sourced from MCM in the States, and the only specs I can find are Magnet weight 42oz, Qts 0.42, Vas 7.2 cu ft, fs 28hz, specs which aren't a million miles away from the BSB12.

    I watched some more stuff last night without any problems, and having read some more (particularly over on diyAudio) I think that the noise I heard was distortion so I'm probably going to stick with it for the moment. If I'm niggled by the end of next week, I'll talk to BK about a replacement.

    I hadn't intended getting on a merry-go-round, and tbh I'm delighted with the way it fits into the sound in my movie room as well as having "thumps and whooses" at the appropriate times during action movies. I was watching Eric Clapton last night and the definition in the bass was brill.

    Thanks for the response - I had begun to think that the diy sub community had gone on holidays with BK !!!


    Thanks,

    Sean.
     
  4. GaryG

    GaryG
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    Sean

    Can't comment on the Farnell, but the Shiva and Lab 12 are good drivers, the Shiva has dual 8 ohm voice coils which you could wire in parallel to get the most from your amp. The higher power rating will give you flexibility to upgrade your plate amp at some point in the future.
     
  5. slingshot

    slingshot
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    Wiring in the Shiva Parrallel gives a 4 ohm load ? I thought the BK bass panel was recommended for only 8 ohm or greater loads, I know it works because I've used a IP acoustics 100w panel (which I believe is basically the same as the BK electronics) but there is a warning about it reducing the life expectancy of the panel.

    theritz, I maybe asking silly questions but have you checked that the driver is screwed in tightly, this can cause some buzzing.
     
  6. theritz

    theritz
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    slingshot - yep all screwed down nice and tight. Afaik, the BSB 100 panel puts 120W into a 4ohm load..........

    I reckon that the driver is hitting the limit of it's travel at certain frequencies - I'm going to recheck the sealing of the enclosure, but there's no evidence of air escaping that I can find. I'm going to hang with this for a while.......... I might try a smaller enclosure to increase the "air spring" value, or try removing the stuffing. At my normal listening volume it's not a problem.


    Sean.
     
  7. ShinObiWAN

    ShinObiWAN
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    Hi Ritz,

    I had a play with my BSB12/BSB100 combo today.

    Previously I hadn't tried SW:AOTC so I put that on at the beginning using the same bits you described. It sounded aweful, masses of distortion and it was all too much for the cheap driver.
    The strange thing is that it wasn't on very loud, well I say not loud but it was hardly reference level. The amp was on -18dB when it starts to distort.

    Its good for the money and SW:AOTC is one the most demanding DVD's for bass.

    If you something to make the neighbours talk then take a look at a Tempest.
     
  8. theritz

    theritz
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    ShinObiWAN,

    Thanks, mate..................... that's put my mind to rest. I've watched a couple of movies over the last few days and have had no issues with the bass performance, and I'm very pleased overall - there's nothing overwhelming in the soundstage, but LFE stuff pressurises the room - I can "feel" stuff like canonballs (Priates of the Caribbean, Master and Commander) and the bass is nice and "tight", there's no wooliness or lingering overrun in the sound. I have no doubt that it could be improved by a meatier amp and driver.......... a Lab12 as suggested earlier in this thread is a distinct possibility. I just wanted to be sure that I hadn't fecked something up through ignorance (being a DIY sub newbie) or had a damaged driver.

    Thanks again...........

    Sean.
     
  9. IronGiant

    IronGiant
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  10. Mat-Moo

    Mat-Moo
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    I have to admit that upgrading my sub as well is quite tempting (If only I could get the stuff off Gary, but he lives to far and wife is very unsure!!) - so are there any other options to upgrading our BSB combos? The 8ohm panel I guess makes it harder as most subs ar 4ohm - Any advice welcome.
     
  11. slingshot

    slingshot
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    driving a 4 ohm driver with an 8 ohm panel should be OK in the short term, and I'm not sure but I thought I read on the Shiva site you could make a single shiva 8 ohm by shorting out one of it's voice coils. You'll need to check that or maybe someone else has done it.
     
  12. IronGiant

    IronGiant
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    If I recall correctly if you run two speakers in parallel (and a twin voice coil speaker is effectively two speakers as far as the electrics are concerned) that is connecting red to red and black to black and powering them together, you halve the resistance so 2 4 Ohm circuits become 2 Ohms. If you run them in serial ie connect a red and black and power across the pair of them then the resistance is doubled so the 2 4 Ohm circuits become 8 Ohms.

    Dave
     
  13. slingshot

    slingshot
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    I agree with what your saying, however I'm fairly sure drivers like the Shiva are dual 8 ohm, so the same maths say you get either 4 ohm or 16 ohm loads depending on the configuration. The only way to get an 8 ohm load is to power a single coil only.
     
  14. IronGiant

    IronGiant
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    Yes, I just checked their site, you're right, so powering one coil is the way to do it. (I wonder if it matters which one?)
     
  15. theritz

    theritz
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    The BSB 100 panel is rated at 120W into 4 Ohms, so it should be ok to drive a Shiva or a Lab12 ???


    Sean.
     
  16. IronGiant

    IronGiant
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    Not exactly. You needed to specify which version of the panel you wanted when you ordered it:

    "Please note that we now have a 4 ohm version of the sub bass amplifier. Please ensure you order the correct version of the panel to suit the impedance of your loudspeaker drive unit.
    SPECIFICATION
    Output Power
    BSBP 100/8 100W RMS Into 8 Ohms
    BSBP 100/4 120W RMS Into 4 Ohms"

    Two different panels...

    If I've done my homework right, the reason dual voice coil drivers were developed was to get around this problem: so a Shiva can be run at 4 Ohm, 8 Ohm, or 16 Ohm depending on how you wire it up.

    Of possible interest:

    Shiva also suggest you can treat it as an ordinary pair of 8 Ohm speakers and send a full speaker output to the driver and run one coil off the left channel and one off the right.

    Similarly they suggest you can reverse the phases sent to the coils and with a suitable 150k potentiometer (must have massive current handling, surely?) use the second coil as a brake to fine tune the drivers performance (I'm getting completely out of my depth at this point...)

    Pardon me, but I think either of these approaches would make it implode ;)

    But then again I'm not a physicist/dual voice coil manufacturer :D .

    Dave
     
  17. ShinObiWAN

    ShinObiWAN
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    Sorry Dave have to disagree with you here. Although you did admit it would probably destroy the sub :)

    Wiring the voice coils out of phase will make the whole voice coil assembly heat up like mad because they are fighting each others movements, thus generating a lot of heat for it to handle.

    Before long you would toast your coils, especially at high levels.
     
  18. slingshot

    slingshot
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    I've read a similar article on the Adire web site, I think what they are referring to is wiring up one coil out of phase but with a lot lower power, so that rather than relying on drive coming to rest on it's own after going BOOM, the coil is actually slightly powered, didn't really read it that much cause it sounded like a good way to have just one big BOOM, followed by no more output.
     

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