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#187657 - 12/12/07 03:33 PM Re: Understanding dB - How much do you need? [Re: Khan Motorsport]
Murph Offline
axiomite

Registered: 10/05/06
Posts: 6884
Loc: PEI, Canada
Well, as you stated by mentioning it "subsonic", most people can't actually hear below 20hz but what it does do is add to the impressive vibrational effect you feel in your clothing or furniture or even body when thinks are cranked. Let me you that the EP500 does this very well.

Your second question kind of asks a couple of questions. First to give you an idea of what the 80db is all about, think of it this way. A lot of movie theaters are designed to present the movie so that the sound is hitting you at an 'average' of 85db. Just like in real life, sometimes things are much quieter and sometimes things get much louder. You might break lightly over 100db at the loudest parts of a movie.

Many receivers are calibrated so that in average conditions, seting the volume at zero will produce sounds at an average of 85 db. Some receivers may have zero set to 75 or 80, but you get the picture. This is what is referred to as a reference level.

Even if you were to leave it at zero, just like real life, many movies while have much quieter moments and much louder moments. Also, one CD or DVD can be very different from another. Between the differences in speakers, sitting rooms, and source material, 'zero' very rarely gives you the actual reference level.

In my case, my HT room is not overly big and kind of bright, I think. My receiver's reference level is 85db at zero. In my case, this works out wayyyy too loud for me. When set my volume to zero, test tones can be calibrate to exactly 85 but when I actually play a movie, most of the movie hits me at a very loud 90db or more. Peaks are hitting way too high over a hundred for my liking.

I usually find I'm set to -25 or so for regular TV and non-intense movies. For an action movie it might go anywheres from -20 up to -15. I have a couple of HD-DVDs that are inherently lower volumed as that seems to be the way the new HD audio tracks are being done. I think I hit an all time high of -10 when I showed off the Transformers HD-DVD to friends. I cranked the HD-version of my Nine Inch Nails concert to -10 as well. It just HAD to be loud!!!

Damn, long winded again. An editor would hate me.

To answer your second question, If a soundtrack was telling a sub to produce a sound at 10hz but the sub is only cable of going down to 50hz....

- Best case scenario is that the sub might be rated for 50hz but is actually capable of going somewhat lower, just it does so at continually weakening volume levels. In this case, there might still be some acceptable LFE but it might get masked altogether by other loud noises in the higher range.

-- Worst case scenario is that the sub will be totally unable to produce anything below 50hz so you will simply lose out. Most likely, it would try to do it's best but what you would end up with was a very bad, rattly noise that would be both distracting and very unpleasant. When this happens, the result probably will actually be much higher than 50hz because you are hearing the rattle and not the actual LFE that should be creating.
_________________________
With great power comes Awesome irresponsibility.

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#187676 - 12/12/07 05:08 PM Re: Understanding dB - How much do you need? [Re: Murph]
Khan Motorsport Offline
old hand

Registered: 11/10/07
Posts: 61
Loc: Toronto, Canada
^ thanks for the write up \:\)

i find I have the same habits..around -25 to -30 for TV...around -25 for normal dvd's and then for gangster surround dvd's i'll bump it to -10 or so.

what reciever do you have?

i guess i gotta call axiom and find out if i can come pick up an EP500...i want a sub this week lol.
_________________________
-Omar
Team Mischief

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#187679 - 12/12/07 05:13 PM Re: Understanding dB - How much do you need? [Re: Khan Motorsport]
BrenR Offline
connoisseur

Registered: 12/10/03
Posts: 3602
Loc: Winnipeg MB Canada
 Originally Posted By: Khan Motorsport
P.S. - That Junk Jiggle reference was PRICELESS.
Only the first time.. only the first time.

Bren R.

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#187680 - 12/12/07 05:17 PM Re: Understanding dB - How much do you need? [Re: Khan Motorsport]
jakewash Offline
shareholder in the making

Registered: 12/26/03
Posts: 10400
Loc: Calgary, Alberta
My sub(not Axiom), when I play test tones will not produce anything untill the signal is high enough for it to work 20-25hz. At this point it is about 20 db lower than the solid response I get at 50 hz, 75db. All subs roll off the frequency at either end, so if the sub can make a noise at 10 it will but it won't be loud compared to the 50hz it is rated for as in your question.
_________________________
Jason
-----------------
TTTHHHPPPPPTTTT!

My HT

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#187743 - 12/12/07 11:21 PM Re: Understanding dB - How much do you need? [Re: Khan Motorsport]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10412
Omar, you might find it interesting to study the "audible threshold" at very low frequencies used in the Ulimate AV sub tests . They don't describe how it was constructed, but it's apparently from equal audibility curve research conducted following Fletcher and Munson. Note that this is just for barely being audible. As a practical matter we're not likely to be hearing 20Hz(or for that matter, 20KHz)at normal levels used in home listening.
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