Please explain amplifier output impedance

Tvad,

If you accept solid state amplifier technology and you do not desire to tweak the sound and wish for a tight controlled bass and wish to simplify it to a damping factor then I would say 80 is adequate and perhaps an ideal number.... i.e. for an 8 ohm load the amp should have an output impedance of of around 0.1 ohms. There is very little to be gained with even lower impedance and probably not audible anyway unless the speaker impedance drops very low.

BTW: This discussion applies to equipment input impedance too.....ideally you want a high input impedance (nominally around 10K Ohm) on all equipment prior to your speakers or headphones. This reduces the effect of interconnects and coupling of equipment in your system to almost negligible levels.

Damping factor has less effect on a speaker than most might imagine. Keep in mind that any waveform will cause an amplifier to produce power (and incidently, it is *power* that drives all speakers- voltage cannot be produced in the absence of current and current cannot be produced in the absence of voltage...). That power will cause a voice coil (or other motive mechanism) to obtain a particular location with respect to rest. As the power level changes, the VC will follow it- in effect power driven to excursion and back again. Damping factor only plays a minor role.

What is really happening is that we are able to hear what negative feedback does to sound. Too much (more "damping") and the sound dries up, too little and with *some* speakers you loose flat frequency response.

In general tube amps have less feedback and many have none. This is not because it is not somehow available (this is the 21st century after all and we *do* have the technology). The problem is that feedack is a failed concept and many designers recognize that.

IOW having a 'constant voltage' output characteristic is a thought model and does not have a basis in the real world where our ears exist. As humans we are often looking for ways to place things in neat cubbyholes but Life itself does not care what we think- it exists in spite of our thought. Feedback and constant voltage are examples of cubbyholes that are thus not actually real.

What is really happening is that we are able to hear what negative feedback does to sound

negative feedback just ensures linearity - it makes sure that the output matches the input. An electrical circuit operates at close to the speed of light...I doubt anyone can hear negative feedback in modern circuitry. Slew rates of good amps are typically 50 volts per micro second or enough to accurately reproduce a signal of well over 100 KHZ without distorting the signal. Since it is accepted that people rarely are able to hear anything above 20 KHZ then it is extremely doubtful that any slight anomalies of this kind of order are actually audible.

Speaker cones will try to keep moving because of inertia, the suspension pulls them back and as they move they induce current (EMF) in the coil which the amp will sense and will dampen by driving the output to match with the input. Provided the drivers have low mass, a high Xmax and a strong magnet then a powerful low output impedance amp should be able to control the driver well. If the driver is low quality, with a weak magnet and a low Xmax then it doesn't matter as much if the high powered amp has a high damping factor as the cones become harder to control as they travel well outside the linear range of the magnetic field...in this case, ultimately, the suspension pulls them back in but unfortunately at this point you have large amounts of audible distortion).