Was not talking about tube amps AT ALL in that post - just quoting real world
typical solid state amp behaviour relating to linearity of power output v load impedance - BECAUSE You said:
"Solid state amps in general are less sensitive to load variations because the source impedance is usually order of magnitude lower."
They may be
less sensitive than tube amps but they are still very sensitive - as shown by the
typical amplifier power output v load specs quoted
OK - constant voltage accepted within the limits of the SS amplifier electronics and power supply capability but power equals voltage squared over load. It follows that for any given amplifier and at any given output voltage, a 2, 4, 8 or 16 Ohm load will draw different levels of power from the SS amplifier - the lower the load the greater the power.
Another way of explaining it is that the amplifier can deliver a certain value of Current (Amps)
Power equals current squared times load, so for whatever maximum power the amplifier can deliver, the value of the current will be square root of the power divided by the load. So the greater the load the lesser the current.
As you know, maximum prospective power occurs when the load equals the source impedance of the circuit. So acknowledging your comment re source impedance, it is the case that in a conventional SS amplifier the lower the load the higher the power output as the load approaches the amplifier source impedance. But not every SS amp delivers proportional power output to varying loads and many will not handle nominal 2 Ohm loads at all - any amplifier manufacturer's User Manuals tells the story for each specific product.
As we have seen from discussion re MI waveforms, the actual load at any instant in time is a mish-mash of a myriad of fundamental and harmonic frequencies, so will be a composite value. But in the LF fundamental bass range between 40 and 320 Hz the actual load will be much higher than with say a guitar
The purpose of my post was to show the relationship between
typical speaker ratings and their electro/acoustic performance v
typical amplifier power output ratings and performance. Not everyone has a shed full of test equipment so must rely upon what the manufacturers say
The average bass player buys an amp and buys a speaker - each having published ratings. If it is a combo amp/speaker the user will only have an amp power rating. That's all he or she gets. Since the object is more or less "better" bass, the tendency is to turn up the bass tone control, the LF EQ and volume/gain control to offset loss of bass response which is built into the system via speaker impedance characteristics interacting with the amplifier. The easy solution is to simply use a more powerful amplifier but heavily damped speaker drivers can show little cone movement even at low frequencies so drivers can be easily cooked - every component has a limit.
Therefore a basic understanding of what actually happens should be beneficial to those bass players concerned about their equipment and how to get the sound they want. That was my purpose.
Given the physics involved as described above, in my experience it is more likely better bass improvement can be achieved by either more speakers, larger speakers or a better designed cabinet. It is unlikely a change in power amplifier will make much difference - unless the amp has built in effects such as EQ at 40 Hz
Still don't believe me ?
Check this one out -
Frequency Response of a Marshall 4x12 Cabinet
Now I am confused. Before the global economy, most speaker manufacturers used to say they test raw drivers for frequency response by mounting them in a wall - ie in an infinite baffle and with specified power source characteristics - according to recognised standards.
Here is a speaker of high repute from JBL tested in a sealed enclosure. It can be seen the result is much the same as in the previous post for a speaker mounted in an infinite baffle
View attachment 2898808
But nowadays some manufacturers do not declare how they test at all - check their websites for yourself.
The natural rolloff of low frequencies is a function of cone characteristics, suspensions characteristics and the power of the motor as driven by the amplifier - speaker design is science in its own right but so far they all suffer similar general characteristics.
So a uniform or standard test method is important to enable purchasers to compare optional designs and make informed choices
It is well established that various enclosure designs will produce similarly variable impedance characteristics, but the basic rules remain
It is true that the power handling capacity of raw drivers is tested in free air because that is simply a thermal test - see
Loudspeaker power handling | Eminence Speaker
but without simultaneously comparing frequency response and SPL a power rating of itself does not tell the whole story
For example - it is often the case that in the frequency range of interest to bass, a speaker with a 2 or 3 inch VC is actually louder than a similar sized speaker with a 4 inch VC requiring more driving power for the same SPL
So the question is why, in an electro-dynamic speaker, does the impedance rise from the nominal rated with reducing or increasing frequency ? To my mind it's been that way for at least 80 years , is just the way it is and we have to live with it.
But regardless of the cause, the effect is that the actual load on the SS amplifier changes increasingly with frequency and that affects power output DOWNWARDS because the amplifier power DECREASES with increasing load impedance
And that was the point of my post and is the challenge bass players face
An undamped driver will bottom out in free air at resonance at a very low power level - because the cone is unconstrained
But in a correctly designed cabinet the resonance effects can be damped electronically by the amplifier damping factor effect and the acoustic loading on the driver by the cabinet
As far as I know SS amplifiers respond directly to the load presented - therefore a rise in impedance will cause a loss of power and therefore SPL and therefore damping - but a smart designer would not utilise the range at or below resonance
So for a 4 string bass the ideal speaker resonance would be around 30-35 Hz. Below that life becomes difficult because the speaker suspension needs to be free, requiring careful acoustic loading to prevent over-travel.
Guitar amplifiers, which operate from about 80 Hz upwards, typically use open backed cabinets because they are adequate for the frequency range covered and use speakers designed for the purpose. But instal a bass woofer in an open backed cabinet and it will not work so well in the LF range and may be easily damaged.
Have to limit it at that for now because enclosure design is also an art form in its own right.
From Day One I have given you great respect based upon your declared qualifications and long experience but respect, of itself, does not bestow a right to "guru" or "oracle" status above or beyond disagreement or challenge by others - we are all mortal
"Respect" is clearly important to you and has been a recurring theme, so to gain the respect that you desire from your audience it might help to explain more fully the technical reasoning to support the claims you make - rather than simply "because I say so"
"Respect", like "power", is granted - and is not a right. It should work in both directions - to the bestower and the bestowed.
In public life, respect may be given to an "office" but not to the incumbent. Most people gain respect for what they do and how they do it - not who they are
Talk Bass is a forum where people can discuss and explore - it is not a university lecture room where enquiring students are required to accept without question all the teacher delivers to them
