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Old 24th February 2009, 00:22   #1
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Hi Gurus.
Was just thinking about my ICE when this thought came to my mind.
Why is it that when i was doing my dB test after keeping the sub ON for 15-20 mins produce lesser dB rating than when i tried it after not playing the sub for 1 hour or so.

Also does dB rating depend on the song and the bitrate of the song?

Abhinav
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Old 24th February 2009, 00:50   #2
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Electronics,bro! The amp heats up and starts losing its efficiency.
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Old 24th February 2009, 00:55   #3
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Electronics,bro! The amp heats up and starts losing its efficiency.
Yep yep!

If you run the testones for too long or stress the voice coils too much you might end up blowing them up.

SPL test need to be done with precaution if serious SPL figure's are anticipated.
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Old 24th February 2009, 01:24   #4
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Very simple. Sub woofer if played hard even with undistorted signal will tend to get heat up becasue the energy given by the amp has to end up in some place. In a sub woofer it goes majorly in three places...
  • Sound output
  • Heating of the Voice coil
  • Mechanical movement of the Voice coil, Spider etc...
In a SPL setup a lot of power is given to the sub so the VC gets heated up. And a conductor when heat its resistance increases. The same thing happens here. If played hard even for few mins the VC resistance increases and the SPL output decreases. Sad but true. Thats why when ever going for a SPL test keep your setup cool.
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Old 24th February 2009, 10:24   #5
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Quote:
Originally Posted by low_bass_makker View Post
In a SPL setup a lot of power is given to the sub so the VC gets heated up.
using aluminum formers a voice coil can be kept pretty cool. anodised aluminum is great becuse the anodised layer does not transfer electricity but is a transfers heat well.
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Old 24th February 2009, 10:28   #6
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using aluminum formers a voice coil can be kept pretty cool. anodised aluminum is great becuse the anodised layer does not transfer electricity but is a transfers heat well.
Yes. Also the SPL subs have bigger Voice coils so that there thermal rating is improved and we have larger surface area to disipate heat. Like few SPL subs I have seen have 4 inch VC and that is quite massive one. 2 inch would be a normal sub.
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Old 24th February 2009, 15:30   #7
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Quote:
Originally Posted by low_bass_makker View Post
Yes. Also the SPL subs have bigger Voice coils so that there thermal rating is improved and we have larger surface area to disipate heat. Like few SPL subs I have seen have 4 inch VC and that is quite massive one. 2 inch would be a normal sub.
these subs also have a vented pole piece to help disappate the heat.
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Old 24th February 2009, 17:02   #8
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these subs also have a vented pole piece to help disappate the heat.
Sorry I forgot that part.
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Old 24th February 2009, 20:38   #9
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So what would be the range of drop in dB levels if suppose i continuesly play sub for 10-15 mins ( mix of full and medium bass) and then immediately do a dB test.

P.S Thanks for the explanations guys.
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Old 25th February 2009, 00:46   #10
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Quote:
Originally Posted by abhinav.gupta88 View Post
So what would be the range of drop in dB levels if suppose i continuesly play sub for 10-15 mins ( mix of full and medium bass) and then immediately do a dB test.

P.S Thanks for the explanations guys.
1 or 2 db can be more...
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Old 25th February 2009, 11:04   #11
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Quote:
Originally Posted by low_bass_makker View Post
1 or 2 db can be more...
more than 3db is considered a bad design. most of the stuff I've used limit loss to 1db or so.
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