What are -3dB limits?

JediCowboy · 08-22-2002, 10:13 AM

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 · 08-22-2002, 10:22 AM

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 · 08-22-2002, 10:22 AM

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 · 08-22-2002, 10:26 AM

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 · 08-22-2002, 10:27 AM

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

CT

GuitarheadCA · 08-22-2002, 02:16 PM

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 · 08-22-2002, 02:21 PM

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 · 08-22-2002, 02:46 PM

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 · 08-22-2002, 02:48 PM

Hell.....get your she-at straight you big heed dumb mofo you

RuSsMaN · 08-22-2002, 03:03 PM

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

burdette · 08-22-2002, 03:16 PM

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 · 08-22-2002, 03:27 PM

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 · 08-22-2002, 04:15 PM

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

BDT

RuSsMaN · 08-22-2002, 04:20 PM

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

Effer....

Fatass....

nascarmann · 08-22-2002, 04:24 PM

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

mantis · 08-22-2002, 06:00 PM

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.

JediCowboy · 08-22-2002, 09:32 PM

Thanks all.

I my understanding was close, now I got it.

GuitarheadCA · 08-23-2002, 01:14 AM

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.

08-22-2002, 10:13 AM	#1
JediCowboy Member Sales Rating: (0) Join Date: Aug 2002 Posts: 56	What are -3dB limits? 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!

08-22-2002, 10:22 AM	#2
hoosier21 Member Sales Rating: (21) Join Date: Jul 2001 Location: Georgia Posts: 4,105	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. __________________ Looking - Preamp Looking - Power amp Sony DVP-NS999ES - SACD player ADS 1230 - Polk SDA 2B DIY Stereo Subwoofer towers w/(4) 12 drivers each Crown K1 - Subwoofer amp Outlaw ICBM - crossover Beringher BFD - sub eq Where is the remote? Where is the $%#$% remote! "I've always been mad, I know I've been mad, like the most of us have...very hard to explain why you're mad, even if you're not mad..."

08-22-2002, 10:22 AM	#3
fireshoes Member Sales Rating: (1) Join Date: Mar 2002 Location: West Des Moines, IA Posts: 3,206	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. __________________ (¯`·._ (¯`·._-=- Fireshoes -=-_.·`¯) _.·`¯)

08-22-2002, 02:21 PM	#7
RuSsMaN Moderator Member Sales Rating: (37) Join Date: Jul 2001 Location: North Texas Posts: 16,652	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 __________________ If you're gonna be dumb, you gotta be tough - when you get knocked down, you gotta get back up - Roger Alan Wade Last edited by RuSsMaN; 08-22-2002 at 02:25 PM..

08-22-2002, 02:48 PM	#9
nascarmann Member Sales Rating: (0) Join Date: Sep 2001 Location: Tennessee Posts: 1,465	Hell.....get your she-at straight you big heed dumb mofo you __________________ Oh, the bottle has been to me, my closes friend, my worse enemy!

08-22-2002, 10:26 AM	#4
cturner Member Sales Rating: (0) Join Date: Apr 2002 Posts: 10	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"!

08-22-2002, 10:27 AM	#5
cturner Member Sales Rating: (0) Join Date: Apr 2002 Posts: 10	Man! 2 people post while I was getting that one out. You gotta love these guys! CT

08-22-2002, 02:16 PM	#6
GuitarheadCA Member Sales Rating: (0) Join Date: Jul 2001 Location: Davis, CA Posts: 400	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.

08-22-2002, 02:46 PM	#8
RuSsMaN Moderator Member Sales Rating: (37) Join Date: Jul 2001 Location: North Texas Posts: 16,652	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

08-22-2002, 03:03 PM	#10
RuSsMaN Moderator Member Sales Rating: (37) Join Date: Jul 2001 Location: North Texas Posts: 16,652	Dude, I'm not wearing my helmet today, sorry, I tipped over and smacked my heed on my desk....

08-22-2002, 03:16 PM	#11
burdette Member Sales Rating: (1) Join Date: Jul 2001 Location: LR, AR Posts: 1,192	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.

08-22-2002, 03:27 PM	#12
RuSsMaN Moderator Member Sales Rating: (37) Join Date: Jul 2001 Location: North Texas Posts: 16,652	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

08-22-2002, 04:15 PM	#13
TroyD Member Sales Rating: (7) Join Date: Jul 2001 Location: lookin' for fava beans and a nice chianti Posts: 11,589	ever see a big guy moonwalk?? NOW you have.... BDT __________________ That statement will probably offend someone. They need to know ahead of time that I don't give a sh*t. -G.B. Grand

08-22-2002, 04:20 PM	#14
RuSsMaN Moderator Member Sales Rating: (37) Join Date: Jul 2001 Location: North Texas Posts: 16,652	Thanks a-hole, can't you tell I'm tryin' to back-peddle DISCRETELY.... Effer.... Fatass....

08-22-2002, 04:24 PM	#15
nascarmann Member Sales Rating: (0) Join Date: Sep 2001 Location: Tennessee Posts: 1,465	and.....another one gone, and another one gone....another one bits the dust....

08-22-2002, 06:00 PM	#16
mantis Member Sales Rating: (14) Join Date: Jul 2001 Location: Pa Posts: 10,119	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. __________________ Dan My personal quest is to save to world of bad audio, one thread at a time.

08-22-2002, 09:32 PM	#17
JediCowboy Member Sales Rating: (0) Join Date: Aug 2002 Posts: 56	Thanks all. I my understanding was close, now I got it. __________________ The Force is with Me -- YEEHAW!!! Denon 3802 Mains -- RTi70s Biwired Center -- CSi40 Biwired Surrounds -- FXi50s

08-23-2002, 01:14 AM	#18
GuitarheadCA Member Sales Rating: (0) Join Date: Jul 2001 Location: Davis, CA Posts: 400	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.

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