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Max Sub Output Level

Discussion in 'Subwoofers' started by spuddler, May 18, 2005.

  1. spuddler

    spuddler
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    Hi,can anyone tell me how you tell when you are reaching the safe Max output level of your sub?Sound distortion,driver hitting stop's,spl level etc,i have the SA-WX900 supposidly long throw driver,i have seen it move about 0.75inch(it is very stiff)what would you think the max movement would be?when do you stop turning your sub's gain up?Any advise would be appreciated.
    BOB
     
  2. Mroizouk

    Mroizouk
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    If you're hearing any untoward noises (distortion, rattling, clacking) you must turn the gain down immediately.
    If you find yourself turning the sub up but you're not getting any increase in volume, then either the sub has some limiting circuitry which is coming into play or the driver is encountering thermal compression. in this state, it becomes too hot to be efficient so you should turn it down.

    There's no specified max movement you should expect to see from the driver because all subs are different. As long as you're getting a clean sound you can increase the volume.
     
  3. eviljohn2

    eviljohn2
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    If you can find the T/S specifications of the driver then the maximum excursion will be given as Xmax. Even if you exceed that though the driver will just hit the endstops which won't do it any harm as long as you don't do it regularly and it will be very audible so you'll know when this is happening. :)
     
  4. spuddler

    spuddler
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    Hi,thank's for the reply's.Played part's of LOTR at high gain(measured 116db at listening point at loudest part's)speaker cone moving like the clapper's at time's,1inch displacement prob max,cone making a bit of a noise but don't think it was hitting the stop's or distorting.Plenty of air movement and multiple noise's coming from lot's of thing's in room,even one of the wall's.Frequency's must be low as you can feel it more, rather then hear it when turning gain up.Just trying to find a safe max level,so i know what to watch out for in the future.Ethier that or i'm getting subsonic fever!!!.Have not been able to find much about this sub(only what's in SA-WX900 thread,and bit's more),don't have much spec on driver ect.
    Cheer's BOB
     
  5. Chris Bellamy

    Chris Bellamy
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    You can do what I think are called power curves, plotting curves showing freq vs dB output for stepped increases of input; the lines should be parallel, horizontal, and equally separated. but when fixed dB incremental increases of input signal amplitude start giving successively reduced dB increments of sub output, then the sub is maxing out and compressing dynamic range. It starts a lower levels than you might think, particularly for the lower frequencies which the sub struggles with relatively more. Once dynamic range goes, its time to stop turning the dial up, not so much for safety reasons, as for quality of reproduction.

    Chris
     
  6. eviljohn2

    eviljohn2
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    To be perfectly honest, I don't understand what you're trying to find out and why?

    If your sub starts behaving or sounding erratic then you're pushing it too hard, there's no general rule you can apply since different media will have a different effect on it.
     
  7. spuddler

    spuddler
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    Hi,Eviljohn2 just trying to see what the Sub will do,also to see the point were i don't want to go ie distortion and risking damage to SUB.So during normal operation over prolonged period's i can play it loud if i want to and be OK.
    I understand what you mean Chris,seem's logical etc,will try this when i have some time.I have done SPL test's but cannot upload them at the moment as i have only a Interactive Set Top Box(freeview box with which you can browse web).Prob try and do this with my mate's computer or my own computer ie hoping to get one shortly.My room response was'nt very good,a big peak at 45hz and a big trough at 95hz,i don't think i can BFD these out that well.Don't want to move my Sub yet as i have equipment all over floor and my rear's stacked up on box's,so not really a good place to put it yet.Did some test's 2 to 2.5ft away from Sub,to try an eliminate room effect as much as possible,result's were better,will try and upload these when i can.Any advise then will be welcome.
    Cheer's BOB
     
  8. bilba

    bilba
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    I've been down this road and found that there is quite a variation in the max levels for different DVDs. Luckily, I have an amp that has a dB readout for the level of each channel.

    To find the max level for a particular title, I turn all speakers except the sub down as low as I can (-10dB with my amp) and turn the sub feed up to the max (+10dB) and set the master volume to 10db quieter than my normal listening level.
    This gives the sub at normal level and everything else 20dB down.

    I now play what I think is the loudest passage on the DVD with my ear close to the sub ( 1 foot away). By slowly increasing the master volume with each replay of the passage, I can hear when the sub reaches its limit - it is a vented sub and it runs out of excursion. You will hear it topping out with a "smacking" sound.
    I make a note of the master volume setting, subtract 2dB for safety, and then put a sticker on the DVD indicating how much "boost" it can handle.

    I use an SPL meter to set the sub to a standard level.

    This is written up on my site, along with some of the DVDs I have measured with this technique - http://www.users.bigpond.com/bcolliso/SPL-levels.htm
     
  9. spuddler

    spuddler
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    Hi Bilba,thank's for info,will try this,my amp allow's me to +/- 10db on each channel(Yammy 2500)when you say show's db reading's do you mean system overall db output(volume).I did some SPL test's dropping speaker's to - 10db and increasing sub to +10db i think this will be OK for ear to sub test's.But to be on the safe side did SPL test's again with Banana plug's pulled out of speaker's.Glad you tested Star war's 'attack of the clone's' and it being highest output signal level in comparison to other disc's,as it's well recommended on this forum i have ordered it from DVDSOON(Soon,still pending!!!)so prob can use this disc as a max ref point.Picture's dropping off wall's!!!!you are as mad as me?
     
  10. bilba

    bilba
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    GDay spuddler, you are correct, my dB readout indicates the master volume setting. As I adjust the individual channels, the readout indicates the +/- dB departure from the master.
    The Star Wars sequence is loud but doesn't go for very long and the level varies - For calibration, I use the surf sequence at the start of the James Bond "Die another day" it is 15dB below the Star Wars title but it's consistency makes it much easier to measure with the SPL meter!

    BTW make sure your amp can handle open circuits before pulling leads out of speakers. If I want a really good reading, I put my mains face down on the floor and cover the rear ports (with mousemats)
     
  11. spuddler

    spuddler
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    HI Bilba,not another DVD to buy!!!!But i use either my reciever's test tone,some tone's i have downloaded or tone's on the DVD Essential's Disc i bought for general calibration.Use the downloaded test tone's from snapbug to test sub.Did'nt know there was a issue with open circuit's,if you remove ie disconnected speaker's by removing banana plug's!!!!????(the surround back and presence terminal's are open circuit unless you connect some speaker's to them?) hav'nt noticed anything?Won't the reciever's protection circuit's kick in anyway?
    Cheer's BOB
     
  12. bilba

    bilba
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    Come to think about it, the modern amps must have protection - not everyone has a centre speaker connected, and no smoke comes out! I was thinking back to earlier days of solid state amps (30 years ago). Time moves slowly in the colonies. :suicide:
     
  13. micb3rd

    micb3rd
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    Bilba method is interesting but can lead to its own problems.

    It has been discovered by some that some AV receivers can clip there subwoofer output when the main volume is at reference levels (usually 00) and the subwoofer level is at 0db or above.

    This is why to reduce the chance of clipping outputs near reference levels some knock the subwoofer level on the receiver down 1/4 or more and then use a bit more gain on the subwoofer amplifier.

    While bilba method will be a maximum level excursion wise but does not show if the subwoofer amplifier is fed a clipped signal and also it does not show if the driver is near its themal limits.
     
  14. spuddler

    spuddler
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    Hi interesting, i am surprised that the amp would send out a clipped signal at such low signal level compared to a high,high level signal to speaker,with regard's what power the amp is pushing out.Even tho the amp is still varying the low level gain on the low level signal,if you know what i mean?
    BOB
     
  15. bilba

    bilba
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    Indeed it it hard to know when an amp might clip. My standard level of listening is with the amp at -30dB and the sub at between 0dB and +10dB depending on the DVD.
    The main problem with my method is that I eat into the headroom to get the maximum out of my sub. This is why I approach each DVD conservatively and with careful testing, determine what is safe - then add a sticker so I can enjoy it more next time!. The biggest risk is forgetting to turn the sub back down after watching a title that I boost by a fair amount - but hey, on some movies there can be an extra 10dB or more just waiting for you.
     

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