Understanding Frequency Response Specs

[hylaphone]

Hi folks -- can anyone explain or point to a link explaining how Frequency Response specs are derived?
General frequency response seems like -3dB points lo and hi? For example 20Hz to 16KHz, or a variance spec +/- 3dB

I'm unsure how manufacturers choose specs for tone controls -- example: +15dB, - 10dB@ 3Khz - is that frequency chosen for measurement because it provides the greatest dB variance?
How does corner frequency of a tone filter come into play with this spec?
Thank you in advance.

[nickb]

+15dB, - 10dB@ 3Khz means +15dB gain at 3KHz with the control at max and -10dB at 3KHz with the control at min. The spec tells you nothing else other than that.

[hylaphone]

Right, but I see a spec like this and wonder what gain is at 4KHz?
The missing piece for me is why a manufacture chooses the 3K to represent the spec.

[nickb]

Unless they give you a plot of gain vs frequency for different control settings you simply don't know at anything other than the given point. Do you have a specific manufacturer and model in mind?

[hylaphone]

Well, here's an example:


Are 40Hz, 500Hz, and 4KHz chosen because they represent the widest +/- of gain per control? Or just because the are useful reference points for a bassist?

[Old Tele man]

Well, 40Hz does just happen to be the frequency of an open bass E string. And 500Hz is just above the sq-root mid-point between 40Hz and 4KHz.

And, those ±dB numbers are the gain & cut values for that control, centered on their respective Hz value.

[vintagekiki]

...

Data (+/-) ..dB expresses the relationship between the two sizes in relation to the agreed reference value.
Data - 3dB (if it is about power) indicates which frequencies a 50% power decrease in relation to the reference value (power at 1kHz)

https://en.wikipedia.org/wiki/Decibel

http://www.sengpielaudio.com/calculator-gainloss.htm

Are 40Hz, 500Hz, and 4KHz chosen because they represent the widest +/- of gain per control? Or just because the are useful reference points for a bassist?

Each manufacturer according to his taste, selects the frequencies of tone controls, depending on the type of instrument and type of music.
At the beginning of the amplifier there was only a (treble) cut control.
The bass and treble tone control has spread over time to the low / high (bass) (middle) (treble) tone controls.
With the emergence of the third generation amplifiers and the modern production, classical tone control evolved into resonant color tone regulation (graphic eq, parametric eq etc)

https://translate.google.com/

[pdf64]

...And, those ±dB numbers are the gain & cut values for that control, centered on their respective Hz value.

ie at different frequencies, the degree of cut / boost available is likely to be reduced; 40Hz is likely to be somewhat lower than the bass control lower corner freq, 4kHz is likely to be somewhat above the treble control upper corner frequency.
As the corner frequencies are by definition 3dB closer to the nominal reference level, compared to the shelf max/min levels.

[hylaphone]

ie at different frequencies, the degree of cut / boost available is likely to be reduced; 40Hz is likely to be somewhat lower than the bass control lower corner freq, 4kHz is likely to be somewhat above the treble control upper corner frequency.
As the corner frequencies are by definition 3dB closer to the nominal reference level, compared to the shelf max/min levels.

Wouldn't a shelf max/min level be a more useful spec?
Ampeg shows 4KHz +16/-15, but what if the shelf peaks at 5KHZ +18/-16?

Sorry to go in circles with this, without an industry "standard" I'm having a tough time understanding how manufacturers choose these specs.

[Enzo]

Standard?

These are guitar amps, never forget that. They are not hifi amps, and are not intended to be hifi. So a lot of specsmanship is pointless in describing them. Guitar amps are intended to color the sound and add (or subtract) their own character to the sound.

A 5kHz tone spec might be of little value when the speaker rolls off at about 3kHz or 3500Hz.

Some circuits more than others, but in many the tone controls are interactive, in other words there are no center frequencies. As you change the bass or treble control the mid peak moves up and down the scale.

Go to Duncanamps and download his excellent tone stack calculator. it shows graphically what happens to the freq response as you change controls.

[Tom Phillips]

For a guitar amp the marketing department / spec sheet numbers are not of much value. The important test is to play the amp and listen to the sound. Close your eyes and adjust the controls. It is of no importance if the knob is at 10% rotation or 90% rotation when you are satisfied with the resulting sound. As long as there is a setting that gives you the sound you like then you have success. It does not mater if the settings of one amp are drastically different than those of another amp as long as it is possible to achieve a result that you like. There is an age old comparison where one person says "my amp on 2 is louder than your amp on 4" but that is of no significance as long as either amp can be adjusted, at any setting, to give the performance the user requires.

[J M Fahey]

FWIW many respected Musical stuff manufacturers never ever published Tech specs, yet had such a distinctive and recognizable sound that everybody knows what are they talking about.

Celestion even today publishes very scarce data on their speakers ... but everybody knows what "Celestion sound" or "Marshall sound" means.

Does anybody know Thiele Small data for old Jensen or Celestion speakers?
Nope, and it´s sort of useless anyway, doubly so if you end up stuffing them in an open back cabinet or at best a closed back one, but where dimensions are not calculated at all, just "the proper size so they fit in a car trunk or back seat"
Groundbreaking Tweed Bassman or Marshall 4 x 12" are not much more than: "some wood wrapped around 4 tightly clustered 10" or 12" speakers"

Even behemoth Ampeg 8x10" is again "as compact and movable as can be" ... for *eight* 10" speakers in a single cabinet that is.

Regular Bass lowest frequency reaches about 40 Hz, yet this most respected Ampeg cabinet drops like a brick below 100 Hz

To avoid retyping, read it here: http://music-electronics-forum.com/t37915/#post364337

There is also a latent danger lurking around: modern speaker data ***looks*** way better on paper, in fact *is* better in a Lab environment, than old tired classic speakers, and today people "read too much online" and "listen with their eyes" so based on that only old stuff would be junked ... yet as you know it´s not the case.

One example: Jensen speakers are currently made in a state of the art, highly automatized Italian factory, with modern equipment, instead of the mostly handmade Chicago ones from the 50´s and 60´s.

They profit from better adhesives, consistent magnets (and powerful capacitive discharge magnetizers instead of the old brute force ones which never *fully* charged them), computer run quality control, of course they measure each speaker and publish full TS data, specs in every aspect are "better" than the old ones ... yet almost nobody likes them

"Too trebly/loud/analytical/annoying/cold", in fact they are more efficient, but more important, they are "too Hi Fi" for a guitar ... not surprising considering the 50/60 year gap in Technology.

Same applies to most other stuff.

Only area where "advancement" and better specs are a Godsend is that modern amps are way more careful with buzz and hum.