Understanding Electric Guitar Amp wattage/dB and Speaker Efficiency

[RedJoker]

Originally Posted by jonfields45

Another anecdote... A friend was buying a high end dishwasher and wanted advice if she should spend quite a bit more for a couple dB less noise. I set up a demo where she listened to 1, 2, 3, 4, 5, 6 db volume jumps (1.25, 1.6, 2, 2.5, 3.2, 4 times the power respectively). Only 6 dB was clearly noticeable as louder and no amount of money bought a Bosch dishwasher that much quieter than the cheaper one she had originally chosen. Jon

As a side note, those acoustic ratings came from a lab that uses some data acquisition software that I wrote as a consultant. I then got hired on full time but I've since moved on.

The whole logarithmic dB is always confusing. We see a number that is clearly and measurably different but are surprised that we can't actually hear a difference.

[mc1]

Originally Posted by RedJoker

As a side note, those acoustic ratings came from a lab that uses some data acquisition software that I wrote as a consultant. I then got hired on full time but I've since moved on.

The whole logarithmic dB is always confusing. We see a number that is clearly and measurably different but are surprised that we can't actually hear a difference.

that's cool about the software you wrote.

are all decibels created equally? is a 3 dB change more noticiable for louder or quiter sounds? i thought i read last night that for really quiet sounds 6 dB was required to hear a difference for for loud noises 0.5 dBs could be perceived.

[RedJoker]

Originally Posted by mc1

that's cool about the software you wrote.

are all decibels created equally? is a 3 dB change more noticiable for louder or quiter sounds? i thought i read last night that for really quiet sounds 6 dB was required to hear a difference for for loud noises 0.5 dBs could be perceived.

There are all kinds of things that effect perceived loudness, including frequency content. That's where the weighting systems come in (A, B, C). Then there's the whole sound quality field and things get complicated quick.

[jricc]

Good subject. Thanks Dru for starting this thread. This has always confused me. Can someone tell me if I replace my Blues Jr speaker with a speaker with more sensitivity, it would be louder than its 15 watts? In addition to sounding better?
thanks
jricc

[Rodger Knox]

Originally Posted by jricc

Good subject. Thanks Dru for starting this thread. This has always confused me. Can someone tell me if I replace my Blues Jr speaker with a speaker with more sensitivity, it would be louder than its 15 watts? In addition to sounding better?
thanks
jricc

No, it would not be louder than it's 15 watts, but it would be louder than it was with the less sensitive speaker.

Sensitivity is the correct parameter, efficiency is something completely different.

[Rodger Knox]

Originally Posted by mc1

that's cool about the software you wrote.

are all decibels created equally? is a 3 dB change more noticiable for louder or quiter sounds? i thought i read last night that for really quiet sounds 6 dB was required to hear a difference for for loud noises 0.5 dBs could be perceived.

Well, that's a yes and no question. A 3dB change is a noticeable difference, 6dB is twice as loud, so from the perspective of what you hear, they are the same as the level increases.

From another perspective, there's significantly more power per decibel as the level increases.

[Dru Edwards]

Originally Posted by jricc

Good subject. Thanks Dru for starting this thread. This has always confused me. Can someone tell me if I replace my Blues Jr speaker with a speaker with more sensitivity, it would be louder than its 15 watts? In addition to sounding better?
thanks
jricc

Hi JR. Rodger answered you and my thoughts are the same as his. The amp is pushing 15w to the speaker, regardless of what the speaker is, but a more efficient speaker will translate more of that 15w into sound, so a speaker with an efficiency rating of 100 will be louder than one with a rating of 97.

You should be able to look up the efficiency of your speaker in your Blues Jr and that will let you know.

[Rodger Knox]

Originally Posted by Dru Edwards

Hi JR. Rodger answered you and my thoughts are the same as his. The amp is pushing 15w to the speaker, regardless of what the speaker is, but a more efficient speaker will translate more of that 15w into sound, so a speaker with an efficiency rating of 100 will be louder than one with a rating of 97.

You should be able to look up the efficiency of your speaker in your Blues Jr and that will let you know.

Once again, the correct parameter is sensitivity, usually expressed as dB/watt@1meter.

The efficiency of a speaker is the sound power output divided by the electrical power input, and is usually expressed as a percentage.

[Dru Edwards]

Originally Posted by Rodger Knox

Once again, the correct parameter is sensitivity, usually expressed as dB/watt@1meter.

The efficiency of a speaker is the sound power output divided by the electrical power input, and is usually expressed as a percentage.

Thanks Rodger. I guess I'm one of the people who use the terms efficiency and sensitivity interchangeably, which in incorrect.

[jonfields45]

High single digit percentage efficiency is roughly typical for pro sound and guitar speakers. If you measure the DC resistance of a typical 8 ohm speaker, it is north of 7 ohms. Most of the power heats up that resistance. I love QSC speakers, but when they rate them at 1 KW you know it is not the same kind of watts Marshall is selling. Jon

[mc1]

Originally Posted by Dru Edwards

Thanks Rodger. I guess I'm one of the people who use the terms efficiency and sensitivity interchangeably, which in incorrect.

i'm sure rodger is correct, but efficiency seems like it should be the right word to a lay person. sensitivity seems like it should be on the input side, like a microphone.

edit: i just searched and there is a relationship between the two:

Sensitivity in dB = 112 + 10 log (efficiency)

Efficiency = 10 to the power of (Sensitivity in dB – 112)/10

online conversion here:
http://www.sengpielaudio.com/calculator-efficiency.htm

[Rodger Knox]

Originally Posted by mc1

i'm sure rodger is correct, but efficiency seems like it should be the right word to a lay person. sensitivity seems like it should be on the input side, like a microphone.

edit: i just searched and there is a relationship between the two:

Sensitivity in dB = 112 + 10 log (efficiency)

Efficiency = 10 to the power of (Sensitivity in dB – 112)/10

online conversion here:
http://www.sengpielaudio.com/calculator-efficiency.htm

Good link! Once, many years ago, I discovered that all speakers were not created equal. Naturally, I wanted louder, so I started reading spec sheets to find the most efficient speakers. Efficiency was not usually included, but sensitivity was. It's also much more useful for matching a speaker and amplifer to get a desired output level.
Want twice as loud from the same amp? Get a speaker with 6dB higher sensitivity. Values run from about 95 to 103.

[Steve DeRosa]

Originally Posted by Steve DeRosa

...while I own/have owned a few higher-powered combos, my favorite is a Bugera V22 outfitted with an Eminence Swamp Thang (rated @ 102dB vs. the OEM Celestion G12-75 clone @ ~97 dB) that serves as my go-to amp, and which can go toe-to-toe with my '65 Super RI and Frontman 212R (@ 45W and 100W respectively) right up to its useful limit - as a 22-watter it admittedly lacks the ultimate headroom of the big boys, but by the time I've reached that point my ears are ringing anyway...

Originally Posted by Rodger Knox

...Want twice as loud from the same amp? Get a speaker with 6dB higher sensitivity. Values run from about 95 to 103...

My point exactly - now to swap a set of Swamp Thangs into the Frontman...