# 1.5 db increase....in my head?

Discussion in 'Amps and Cabs [BG]' started by tallboybass, Jul 25, 2003.

1. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
I just got through changing my Avatar B212 8 ohm cab into a 4 ohm cab with new speakers from Dave. I know on my amp (800RB) that increases the power from 200w to 300w on the low side which is 1.5db I think. 3db is supposed to be the smallest change detectable by humans, right? It seems like more. Also, when I hook up my B210 to the high side and push the bi-amp button, it starts dis-assembling my house. I can't wait to get this thing to a gig!

Alan

2. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
Should the increase from 200 to 300 watts be very noticeable?

3. ### l0calh05t

Oct 14, 2001
Cottbus, Germany
1.) an increase of 200->300W is not equivalent to a 1.5dB increase
2.) No,the increase is most likely barely noticebale
3.)The new speakers are probably simply more efficient

4. ### wneffSupporting Member

May 27, 2003
Woburn, MA
To go from 200 W to 300 W changes the output by
p=10*log(300/200)= 1.76 dB

(sometimes you read 20*log...., this is for voltages, we are talking power here)

The smallest amount you can hear is 1dB, if you double power you add 3 dB, ten times the power is 10 dB more.

As stated before, the difference in power should not be noticable. It is more likely that the speaker is more efficient.

5. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
Thanks wneff, the speakers should be the same efficiency-wise. They are the Delta 12LFs from Dave @ Avatar.

Does this mean that if I saved up and got the new 1001RBII that I want, it would be less than 3db louder than my 800RB? (300+100w vs. 700+50w) Would headroom be dramatically improved?

Thanks to everyone for the advice,
Alan

6. ### brianrostGold Supporting Member

Apr 26, 2000
Boston, Taxachusetts
No, it would be slightly more than 3 dB: 3.68 to be exact.

I wouldn't call that a "dramatic" headroom increase. I advise at least FOUR times the power ( 6 dB) to hear a significant increase.

Own a tape deck? Record something off a CD twice, one time at 3 dB less level than the other, then listen back to hear what a 3 dB difference sounds like.

7. ### wneffSupporting Member

May 27, 2003
Woburn, MA
Good idea.

Just something educational from the ex-physics instructor:
The meter on the tape deck records amplitude (volts), not power.

For voltages you have
dB=20*log(V1/V2), for power you have
dB=10*log(P1/P2)

(this is because P=V^2/R, so comparing two powers is like (V1^2/R)/(V2^2/R)=V1^2/V2^2=(V1/V2)^2. )

Remeber that log(x^2)=2*log(x)

If you double voltage that makes a 6dB change, if you double power 3dB.
BUT: Because the power goes with the square of the voltage, doubeling the voltage gives four times the power: 3dB+3dB=6dB.

You add the dB when you multiply power because
log(a*b)=log(a)+log(b,
so if you increase power by a factor of two you ADD 3dB.

Clever system, isn't it?

8. ### FuzzbassP5 with overdriveSupporting Member

I was told there would be no math.

J/K. Thanks for the details!

9. ### Davidoc

Sep 2, 2000
Northern VA and JMU
This whole science thing is bogus. Even if I run just one side at 8 ohms of my 1100 poweramp, which gives me like, 425? watts, It's a hell of a lot louder than my 160 watt combo using the combo's speaker. I dont' care what science says. The power difference makes a ****ign huge amount.

Screw the science. I believe you.

10. ### geshel

Oct 2, 2001
Seattle
Into the same speaker? if not - doesn't mean much.

If so, louder when? at the exact onset of clipping? make sure that's the power amp clipping you're talking about. How can you tell? Careful, you might need some science to find out.

In all likelihood, you're hearing higher gain, not power.

11. ### Davidoc

Sep 2, 2000
Northern VA and JMU
Yeah, same speaker. I can tell when the poweramp clips from the light, but you have a good point-I'm not sure about the combo, but I can get it to distort easily enough.

Oh yeah, I suppose solid state is superior to tube amps also cause the numbers add up.

12. ### wneffSupporting Member

May 27, 2003
Woburn, MA
Well, 160 to 425 W makes 4.2 dB more. Yes, thats a big difference. Even if you apply science.

Also, keep in mind that combo amp power amps are in most cases designed with cheap components, so the audio quality suffers. The ultimate decision if you like something or not / hear a difference or not is if you like it and hear the difference, independent of what the numbers say.

Just a note on the louder tube power amps:
Tube power amps are much more forgiving when driven to the limit than solid state. A solid state amp will go from sounding clean to sounding really bad within a few Watts. Tube power amps are getting increasingly distorted and you have no clear cut-off like in a solid state desing.

That means: The power rating of the Solid state amp is what you cannot exceed. In a well made tube design you can exceed this, at the expense of distortion. Since the distortion of tube power amps sounds very smooth and interesting this may not be a bad thing. But youre really getting something like 1.5 times the rated power out of a well made tube amp.

13. ### brianrostGold Supporting Member

Apr 26, 2000
Boston, Taxachusetts
wneff,

While you are correct about the diffs between measuring voltage and power, you're overlooking that while the meter may indeed be reading voltages it is displaying the results calibrated in dB, not volts. After all, ammeters display amps (current) but do so by reading the voltage across a known resistance...thus they read a voltage but display it calibrated as amps.

In audio metering, a dB is a dB is a dB with ONE exception...what the voltage reference is for 0dB.

So if the level meters on the tape deck indicate a difference of 3 dB, what you get out of the speakers will differ by 3 dB.

14. ### bryan bailey

The esiest way to become louder with out actually increasing in db. would be to get more speakers. Like a 2x12 and a 4x10 would destroy nearly anything. But if you could triamp, a 1x15, a 2x12 and a 2x10 would abolutely pwn everything PWN IT!!

15. ### geshel

Oct 2, 2001
Seattle
Will people never understand????

16. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
Megathanks to all! This has been way more interesting than I would have thought. So, to get a usable increase in headroom I would have to go from 400w to 1600w?

17. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
Sorry to resurrect this old thread, but I finally got the 1001RB-II and the difference in volume is night and day compared to the 800RB. Sure seems like more than 3db......or maybe 3db is a lot more than I thought it would be.

18. ### notanaggieGuest

Sep 30, 2003
Naw, you're Ok.

The "screw the science" reply was the closest to right before.

The deal is that you are NOT using all your power most of the time. So comparing the full power RMS ratings is not real useful unless you play real hard and fast. Someone suggested industrial punk as an example.....

What you need to compare is the PEAK power available. Before you flame me, read on.

You are probably drawing 20% max of your power, average. But every string attack, pop, etc, is a lot bigger than average. If the amp clips trying to put that out, it sounds squashed and lacks "headroom".

Any usual type amp has higher voltages in the power supply when not putting out a signal, or when putting out one well below max. Bigger voltages mean larger potential power output. If you draw that continuously, down come the voltages. But for transients, they stay up, and you get the peak power.

A larger amp has a larger power supply, and is more likely to reproduce a string pop etc without having the supply voltages drop so that it clips. Small amps usually have cheaper supplies, and won't hold up the voltage as long during a peak.

You can probably get quite a bit more than the difference in "RMS" as far as effective transient power is concerned out of a bigger amp. It could add as much as 2dB to the other 3 or 4dB of RMS difference, giving you the "magic" 6dB total, or more.

This isn't usually given in a spec, but it would be called 'dynamic headroom" if it was.

So yeah, you might well find that a "slightly" bigger amp (like 2x power, or 3 dB) gives a lot more difference than "science" says it should be, based on comparing just the "rms" outputs.

19. ### GreyBeard

Sep 5, 2002
BARRACKVILLE WV
If the science says you gain (1.whatever) in head room, meaning it will play barely noticibly louder before farting, then that is what you'll get. Sometimes we confuse more power with where the volume knob is on the dial. For instance, your amp puts out 100 db with the knob on 6 in parallel mono and it puts out the same 100 db with the knob on 3 when bridged. Does this mean that the amp is putting out 10 times the power in bridged? Tough to say. The only real way to figure out what is going on is with a db meter and a scope. That way you can determine how loud each setting actually is before the onset of distortion. Or you can just play the d@mn thing and not worry about it. (jmho)

20. ### tallboybassSupporting MemberSupporting Member

Feb 25, 2003
Tulsa, Oklahoma
Notanaggie, that makes more sense than anything I've heard in a while. However you want to look at it, the 1001 kicks the 800's @\$\$! Certainly it's not as old school sounding, but you can always roll off the highs and lows.