Axiom Home Page Forums General Discussion Technical Questions Understanding dB - How much do you need?

I noticed that most of my audio gear measures in negative db when i play with the volume. Why does it to this? Example: my reciever is usually listened to around -26db or less..-28 lets say. But i can crank it up to positive numbers. What does that mean? why don't they just count from 0-MAX like most thing lol (take it to 11? )

Also, how much dB do you actually need in a sub to be able to hear the frequencies, and how does that work with sub20hz stuff that you can't even hear. Is 50dB enough? is 80dB the minimum?

and lastly, anyone have a response graph on the new EP3503

cheers

The negative numbers are "relative to" a reference level... 0.

Like, some set up their receivers so when the volume control is set to 0, the program audio will be at, say, 85dB SPL at the listening position... thus, when the receiver reads -20, sound pressure levels at the listening position would be down 20dB from the reference of 85dB, or 65dB.

Of course, that assumes all program material is recorded at the same levels, all equipment outputs the same line levels, etc...

As for the sub stuff... set your sub to approximately the same levels as your other speakers (taking into account the lowered sensitivity of most SPL meters in the low range) and it will be balanced with your system... and then if you're most people, throw away that setting and turn the sub up until your junk jiggles during either the famous "depth charge" or "tank tap" scenes in various movies.

Bren R.

Woo - Hoo!

It's official, Ladies and Gentleman!

Bren has used the term "junk jiggles" for the One Thousandth Time!!!!

Jack, do you have any celebratory icons you can lend to the celebration?

I was gonna go with . But then, I figured he'd reply with . Then I'd call him a , and he'd call me a . Hard to argue with that, so his term for me being more accurate than my term for him would mean .

So I decided to tone it down and just go with

Those aren't signs of old age, but they sure are signs.

But Mark... at least on here you don't get to see the hand motions that go with it.

Bren R.

But I've been imagining them all along......

As to how many hz you can actually hear from the subwoofer, I think the more important issue is the visceral feel you get from the sub. At the lower octaves you can feel the pressure more than hear it, if that makes any sense...

Oh it does, absolutely.

with regards to this point, i think the axiom subs produce sub 20hz frequencies (as do the SVS's for that matter), at around 50-60dB.

Is this a usable level or is it just a technical spec so that we can say "our subs do make subsonic levels". Also, what happens when i'm listening at say...80dB or so (or -13...whatever the hell that means haha) and the movie has a sound recorded at 10hz but the sub can only produce that sound at 50dB, does it just go haywire and not render it at all, or does it just render at at a lower level.


P.S. - That Junk Jiggle reference was PRICELESS.

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.

^ 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.

Only the first time.. only the first time.

Bren R.

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.

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.