Higher wattage amp or Cab?

[KohanMike]

A little less than a year ago I bought a Carvin MB15 combo 200/250w with their matching MBE115 extension cabinet (for the 250w) and had them install neo speakers, which are rated at 400w. I assume they decided on that wattage speaker because having headroom is important.

 

[Passinwind]

Never seen those spectral diagrams for transients. Would be really nice to see some sub Harmonics "transient" content which is settled down way below a distinct played note 1st Harmonic.
Although I know those transient sub Harmonics do really appear but unhappily I didn't further researches on it.

I originally posted this waterfall plot many years ago, taken from a direct recording of my Travis Bean fretless playing a low F (F1, 43.64Hz), in the "waterfall" thread linked in the Amps FAQ here:

I found similar artifacts in plots for a couple of other basses, and none at all for one. It was something I wanted to look at in greater depth eventually but somehow never got back to.

 

[megafiddle]

I originally posted this waterfall plot taken from my Travis Bean fretless playing a low F (F1, 43.64Hz), many years ago in the "waterfall" thread linked in the Amps FAQ here:

I found similar artifacts in plots for a couple of other basses, and none at all for one. It was something I wanted to look at in greater depth eventually but somehow never got back to.

That could be a subhamonic there at about 21.8 Hz, but none of those sub fundamental frequencies are transient in nature. Their sustain envelopes are very similar to the fundamental and 2nd harmonic.

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[BadExample]

That doesn't work.

Instead of removing every bottom half of the sine wave, remove every other bottom half. In other words remove the 1st bottom half, leave the second bottom half, remove the 3rd bottom half, leave the 4th bottom half, etc.

That will produce a 1/2 subharmonic.

Remove every third bottom half, and it produce 1/3 subharmonic.

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Interesting. Thanks for explaining that.

On the waterfall plot above, there are four "notes" coming out under the fundamental freq. Are you saying they are not sub harmonics of the fundamental frequency because they are not the mathematically correct frequency to be a sub harmonic?

 

[agedhorse]

I think will find those "sub-harmonics" to be mechanical artifacts rather than true harmonics.

 

[BadExample]

I'm pretty sure that's the case with old upright pianos. There are a lot of parts inside old pianos that shouldn't vibrate, yet they do.

 

[Passinwind]

I think will find those "sub-harmonics" to be mechanical artifacts rather than true harmonics.

That was my assumption at the time I did those plots, and also that they were probably something to look at removing, not embrace.

 

[BadExample]

That was my assumption at the time I did those plots, and also that they were probably something to look at removing, not embrace.

Old church basement pianos would go all but silent if you chased down all the loose screws.

 

[honeyiscool]

On the flipside, countless guitarists will run their 22W Fender Deluxe Reverb with their 15W Celestions and max it out and be fine. I myself run an 18W into the 15W Celestion Blue. I ran it with all the volume knobs at 10 at a house punk show through a few different bands, some with pedals in front even, and the speaker never sounded better.

(Although everybody knows that the Blue is no 15W speaker since the AC30 it's made for puts out well over 15W per speaker.)

 

[ThisBass]

Hope you all know that I'm (mostly) more interested in discussing rather than trolling or talking something about pipe dreams.

Many years ago I experienced randomly excessive driver excursion and also "chuffing" coming out of the cab's port.
Interstingly these artifacts had (nearly) nothing to do with a played note itself but, obviously appeard by distinct damping of strings or some distinct kind of touching/hiding a string just to play a note.

The touch or "hit" of a string with finger can produce nothing but a very short spike. It's a "spike" that roughly comes close a Dirac Impulse or a Gaussian function.
The spectrum of a Dirac impulse starts at DC and spreads to infinitely by steady level. There is no more discret spectrum present like it is known for periodic signals.
I think that's the reason why it can't be captured with waterfall diagraming software tools.

Of course it's impossible to generate a perfect Dirac impulse with a bass guitar but, I think it's a good idea to take the Dirac impulse as kind of "getting started" just to consider (roughly) all the things that also may happen besides a "bare" played note.
In most of all cases we are clearly more interseted in spectrum of attack, followed by decay and sustain and also it's very distinct levels.

Touching or damping a string with the finger generates a short spike and the generated spike is clearly audible (hope you all agree on this statement).
The spike isn't identical with a Dirac and as well isn't identical with Gaussian function.
The spectrum of a Dirac starts at DC and is infinitely, the spectrum of Gaussian function is identical to the Gaussian function itself.
I'd suppose the spike that can be generated with bass guitar is something like a mixture of Dirac and Gaussian spectrum.

Just a couple of minutes before I did a little measurement to my Spector NS-2.
On board EQ set to "flat", volume at full, blend pot at center position
The (moderate) touch of the E-string with the fingers like damping generates a spike peak Voltage of around 0.2 Volt
Playing E1 (moderate) generates a max "transient" level of around 0.45 Volt peak
Average rms of the "total" signal around 0.1 Volt (which is the thing that makes actually loudness if the signal should be "directly" compared to steady sine wave)

 

[agedhorse]

Touching or slapping a string is not the same as free oscillation, which is why the transient noise is not harmonically related (other than the tension and moving mass that's initially displaced).

 

[ThisBass]

That doesn't work.

Instead of removing every bottom half of the sine wave, remove every other bottom half. In other words remove the 1st bottom half, leave the second bottom half, remove the 3rd bottom half, leave the 4th bottom half, etc.

That will produce a 1/2 subharmonic.

Remove every third bottom half, and it produce 1/3 subharmonic.

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That's an idea that is already implemented on the Rocktron Voodovalve where the tube stage does nothing but half wave rectifying to the signal.
The generated Harmonics are of even and odd order in this case.

 

[ThisBass]

Touching or slapping a string is not the same as free oscillation, which is why the transient noise is not harmonically related (other than the tension and moving mass that's initially displaced).

Absolutely right and, of course I have to apologise the wrong usage of the term Harmonic on this topic.
The idea was to explain with "more easy understanding" words that there is something involved below the fundamental when a bass guitar is played in practice.

edit:
I have got no idea the way how we shall call a transient noise by name that is capable to underrun Fundamental of a played note.
BTW I think I'd get similar problems anyway if I'd try to explain this tricky stuff in my 1st languguage to the crowed.

 

[agedhorse]

Yes, there is transient noise generated and this noise can certainly be well below the fundamental (ie. slowly moving a string within the magnetic field) which is exactly the reason why I have been including fairly comprehensive high pass filters in all of the products I have designed over close to 20 years now. Since this signal is not musically related, it's more of an artifact.

 

[ThisBass]

Lot's of DIY cab design engineers like it to keep a firm consideration on 1st/2nd Harmonic of lowest tuning of the instrument. Shoudn't they keep more respect to transient noise that depends on playing style technique and something else?
Just a thought but, all of my personal designs were ruled by transient noise.

 

[agedhorse]

I do not want such noise reproduced (or attempted to be), IMO it gets in the way of the important musical content.

 

[Spoono Ghiefardi]

So just an update, i went with a hartke ak410. Seemed like a good fit. Cheers all.

 

[Bob Lee (QSC)]

subharmonics are a fraction of the original fundamental freq. I believe they come from a mechanical dampening of some sort resulting in a fraction of the fundamental. Like you don't get a 40 Hz subharmonic from a 50 Hz vibration (tone). The frequency is divided by and even integer. So the 50 Hz vibration can produce 25 Hz, 16.6 Hz, 12.5 Hz, and so on. That is my recollection from long ago. I believe they may also come from reflected sound waves, but not sure. I remember when my dad was doing the tuning, on the two and three stringed keys, he had to must the other wires with rubber wedges so only one string vibrated when striking the key.

But again, where do they come from? What would produce them? There does not seem to be any mechanism that would produce these subharmonics, and they do not appear in a Fourier analysis of a vibrating string, either.

 

[ThisBass]

In post #115 I tried to refere to the capability of excessive cone excursion with ported cabs that can be caused by transient noise rather than a Fundamental.
Of course those considerations are of no concern if a HPF protects the drivers from lowish transient noise.

The playing of "death" notes and tight damping of strings is very common with lots of different music genres.
Although it is of more noise character than a vibrating string this generated "noise" is very common as part of musical expression.
I agree that sometimes, depending on the players ability, generated noise appears rather unpleasant than really "musical".

"How much power can I push savely to cabinit xy ?"

Questions like this are asked frequently. I think the answer has (sometimes) something to with the players playing technique which of course is very personal.
If there is NO HPF that protects the woofers then generated transient noise can underrun the cabinets tuning frequency and threaten the woofers.

 

[Rick James]

But again, where do they come from? What would produce them? There does not seem to be any mechanism that would produce these subharmonics, and they do not appear in a Fourier analysis of a vibrating string, either.

+1. No doubt there's something there, but they're not 'subharmonics'. The term 'subharmonic' has been concocted to plausibly explain what's in the signal below the fundamental instead of identifying the actual source.