What are -3dB limits?

JediCowboy

Over the past few months I've really expaneded my knowledge of home audio and home theater, how to read specs, what to look for and what to listen for. Lurking on forums like this one and reading books had certainly helped, but there is one thing I can't seem to find an answer to.

What are -3dB limits and why are they quoted in speaker specificaions? Are they important?

For expample, my RTi70 manual states the speakers are:

Overall Frequency Response: 28Hz - 27kHz
-3dB Limits: 40Hz - 26kHz

I've noticed that the -3dB numbers are smaller in range than the overall frequency response.

I'm guessing that the Overall response is the widest range the speakers are capable of playing and that the -3dB range is what they can play clearly?

Also, why is this called a -3dB Limit? Why not a -5dB Limit or a +3 dB limit or whatever.

Is there something that must be done to adjust equipment to this range?

Thanks for satisfying my curiosity!

hoosier21

It is a standard speaker spec.

speakers strive to reproduce the whole fq range of 20-20k as flat as possible (+/-0 db).

the standard is to specify what the speaker can reproduce within a tolorance of 3 db.

fireshoes

If you were playing a test tone at each frequency, the bottom and top of the range would be 3 db less than the other tones.

The bigger range is what it is physically capable of playing, though there would be even more dropoff in volume at the extremes.

cturner

Imagine if you will a frequency response chart. There is a flat line at 0db that goes from 40Hz to 26KHz. So it's "flat" from 40 to 26K. OK, the speaker can reach down to 28Hz, but the output will be -3db lower than at 40hz. Also it will reach to 27K, but again, the output will be -3db lower at that frequency. Sometimes there will be a +3db rating, but it is unlikely because the output doesn't go up at the extreme ends of the chart. Most commonly you will see manufacturers use somthing like " 28Hz to 27KHz +- 3db". With that statement, you've stated the entire fequency response, but not a flat one. We can get a lot more technical, let me know if this helps your "curiosity"!

cturner

Man! 2 people post while I was getting that one out. You gotta love these guys!

CT

GuitarheadCA

Uh, sorta,

Actually if the speaker are rated as 40-26k +/- 3db, that means that there is no noticable difference in volume between any frequencies in that range. The spectrum will surely not be on the 0db perfectly flat line (just look at the graphs is sound and vision) but it will be within 3 db. 3 db is the standard because that is typically considered the smallest volume difference that is able to be detected. So actually, 40 hz may be -3db, and 26 hz may be +3db. The overally response is going to by much more faded, and the 28 hz "overall" may actually be -10 or 12 db or significantly less.

RuSsMaN

Guitarhead, thats funny.

A 3db increase in sound is DOUBLING the volume...and a 3db decrease would cut said volume in half..... I'd say that's noticeable for most......

Where in the hell did you get that explanation? Go slap whoever it was....

Cheers,
Russ

RuSsMaN

Maybe that read wrong GThead, I simply talking about the +/-3db not being noticeable, I think that would be noticeable....

As far as the reponse, I think everyone is right here, -3db limits were explained, and a +/-3db 'variance' throughout the entire reponse was explained...

Cheers,
Russ

nascarmann

Hell.....get your she-at straight you big heed dumb **** you:D

RuSsMaN

Dude, I'm not wearing my helmet today, sorry, I tipped over and smacked my heed on my desk....

burdette

A 3dB change *is* is considered "just noticeable", on average. Anyone's ability to detect a change in volume of less than 3dB is questionable. It takes a 10dB change for you to think the sound has doubled in volume. Therefore, once your speaker has dropped off by at least 3dB, you'll begin to notice it.. which is why the RATE of drop-off is also important.

It takes DOUBLE the amplifier power to produce a 3dB gain in volume for a given speaker. That is why, in many circumstances, if you're trying to decide between an amp with 80wpc and one with 100wpc, you're better off using other criteria to decide.. because all else equal, you won't be able to play noticably louder.

RuSsMaN

Ed Zachry. Wires crossed big time, and I'm not even drinking.

Thanks Burdette, I gotta run, the short bus is here to take me home...

Cheers,
Russ Gump

TroyD

ever see a big guy moonwalk?? NOW you have....

BDT

RuSsMaN

Thanks a-hole, can't you tell I'm tryin' to back-peddle DISCRETELY....

Effer....

****....

nascarmann

and.....another one gone, and another one gone....another one bits the dust....:D

mantis

3 db is noticable,it's a slight increase or decrease in sound pressure.
If your ears are out of calibration you might not hear ir..nor feel it.:p

JediCowboy

Thanks all.

I my understanding was close, now I got it.

GuitarheadCA

Thanks Mantis and Burdette, I'm glad someone could clear up my post. I'd like to think I wasn't off my rocker when I wrote it and that it was in fact accurate.