Speaker resonance

[Leevi]

This is most probably depending on the speaker/cabinet and the used frequency?


Are there any good recommendations for the amp in order to minimize the resonance?


/Leevi

[jjasilli]

My understanding is that resonance is actually desirable for guitar speaker cabs.  This is the opposite of hi-fi.  For hi-fi ideally, speaker (driver) resonance should be damped, and cabs should not resonate.  The driver (what we call a speaker) will have its own free air resonant frequency; and so will the cab.  The 2 together is the "system" resonant frequency - system = driver + cab combination.  Reducing the size (volume) of the cab raises the combined resonant frequency.  Any frequency that is not part of the input signal is undesirable.  But this pertains to sound re-production. 

For guitar we have sound production.  Different rules apply.  Subjective tonal preferences prevail over strict adherence to fidelity to the input waveform.  For el guitar sound production, the "pure" waveform is what?  The original waveform is from the strings in combination with overall string length (neck scale); the type of material comprising the nut, saddle, guitar woods, & metals, etc.  From there the PU's are a "lens with filters" -- humbuckers, single coils, resistance value, etc > amp > speaker cab.  Waveform production is tampered with from start to finish.

A hi-fi cab should have a 1 1/2" thick baffle board.  Guitar cab baffle boards are in the 1/2" range.  Guitar cabs are lively, often made of solid pine.   They ring if you rap them with your knuckles.  Quality hi-fi cabs sound dead and lifeless.  Vive la différence!

[Leevi]

I'm not meaning a mechanical resonance of a speaker cab. Speakers have a defined parameter
Resonance frequency like 100Hz or lower. I have understood that the speaker starts to resonate on
the frequencies below that value even in free air?

/Leevi

[shooter]

try JBL design labs if you can't sleep 

for fun and boredom you can even do your own simple tests

http://hyperphysics.phy-astr.gsu.edu/hbase/Class/PhSciLab/speakerres.html

[jjasilli]

I'm not meaning a mechanical resonance of a speaker cab. Speakers have a defined parameter
Resonance frequency like 100Hz or lower. I have understood that the speaker starts to resonate on
the frequencies below that value even in free air?

/Leevi

Yes, every speaker (driver) has a free air resonance. It, itself, is a mechanical system analogous to a rubber band or a spring hanging vertically with a weight at the bottom.  If you start it moving it will settle-in to bounce at its own resonant frequency.  A speaker, obviously, can produce many frequencies at once.  Once it starts emanating the signal frequency(ies) you feed it, it will also emanate it's own resonant frequency. 


In terms of the amp, speaker resonance is damped electrically through the use of negative feedback.  Because the speaker freely vibrates at its resonant frequency, it acts like an el generator & produces a back EMF voltage at that frequency which it sends back into the amp.  This is less of an issue with Triode or SS power amps, because they have a low output impedance.  This works to substantially short-out the back EMF.  IOW, they have a large damping factor.  Pentode power tubes have a hi output impedance; hence a lo damping factor.  Negative feedback may be used to compensate.


Manufactures state the Thiele parameters of their speakers.  These are a number of factors including the free air resonance, designated Fs.  Fc= resonance of speaker in the box.  See, https://www.diyaudio.com/forums/multi-way/1417-resonant-frequency-enclosure.html  Checkout any speaker on the Eminence site, e.g., and its Fs and other parameters will be stated. 

A speaker may also be damped physically by the cab. If you put the speaker in an enclosure which restricts its movement compared to being in open air, then its resonant frequency will become higher. 

It's not clear what you're trying to accomplish.  E.g., Vox's sound great without NFB. 

[PRR]

A speaker only covers a limited range. At the bottom of that range, one of several somethings causes a fall-off. Speaker cone mass, stiffness, size. Box size and openess. Amplifier response. We usually contrive the several parameters for some "useful" response. There is a mathematical notion of "maximally flat". In musical systems, we may prefer a shaved bass, a boomy bass, or a smaller box (accepting less-full bass).

Guitar speakers are often limited by maximum clean (or somewhat dirty) output on low notes. This means CONE AREA is your first goal. You can't make a big wave with a small paddle. Next is the idea that guitar goes to 82Hz and anything lower is useless. (This is not-untrue even for dropped tuning, which gets flavor from working the speaker below its limit.) In an open-back box this suggests a natural resonance at 80Hz-100Hz. In a sealed box it suggests a lower natural resonance then raised to the 80-100Hz zone by box size. With resonance at 80-100Hz the Q should be 0.8 to 1.4 for good output; lower is shave-bass and higher is boomy.

If you truly hate the rapid change of response through resonance, you get a theater-tune 15 (Altec 415, JBL 2220) with Fs near 45hz and Q about 0.5, in a large box. All guitar will be above resonance.

[Ritchie200]

jjsilli, don't you dare go there again!!!! (cryogenically frozen camel turds) 

Here: https://el34world.com/Forum/index.php?topic=22718.0

For those who are wondering why I am laughing hysterically.....

Jim