On Wednesday, October 14, 2015 at 11:11:32 PM UTC-4, Phil Allison wrote:
wrote:



OK - a few basics on speakers - at least as they were sold in the
US under FTC regulations (sit on your fingers, Phil!):


** The are simply no FTC rules for published speaker power ratings. The rules you seem to be alluding to are for *amplifers* used in home entertainment.

Let's clarify, then. US speaker manufacturers very rapidly adapted to the FTC rules when publishing their ratings. Prior to these rules, IPP was the way amp makers would fool their buyers, and speaker makers would do their ratings similarly. As things equalized, their ratings became much more realistic.


c) Low cost, low-wattage amplifiers are much more likely to cause speaker damage than large amplifiers.


** Depends a lot who is using the amplifer - but in general the risk of speaker damage goes up with more amp power.


What can happen with some solid-state designs is that when the
amplifier clips (called to produce more power than it can),
it may send straight DC into the speaker

** Absurd.

Clipping does not cause DC, the main effect is to compress the dynamic range of the music so there is more average power going to the speaker - which eventually overheats the voice coil.

If you can, next time you are out on the street, see if you can borrow either of a Dynaco ST80, ST120, AR amplifier, any of several Scott/Fisher/Sherwood solid-state designs, any any of many pacific-rim solid-state designs that used discrete output transistors, a Revox B722 - the list goes on. Drive it to clipping. At clipping you will see serious DC at the outputs. This will 'freeze' the VC(s) in one position with lots-O-energy at the same time. Not generally a good idea.


This issue is far less so from a tube amp - the simplistic explanation is that it is harder for a transformer to pass DC,


** Impossible in fact, but clipping wave peaks is just what tube guitar amps do most of all the time and blown speakers are very common - due again to high average power levels. Instrument amps blow speakers for many different reasons - and even a transformer will transfer chopped DC. Hence the term "simplistic". But instrument amps are a balance of many things. I have always wondered why the makers do not use much heavier speakers than they do - I guess it is a cost/benefit thing. But musicians using such devices seldom care much about fidelity - being more interested in noise and effects. And they generally operate at the bleeding edge.

A well-designed amplifier not driven to clipping into well-designed speakers not driven at ear-bleed levels will generally be safe forever, or at least until the one or the other device fails for other reasons than being over-driven. But I betcha I could do more damage to my AR3a or Maggie speakers with the 40-watt solid state amp than with the 17-watt or 75-watt tube amp - these representing my most rugged speakers being rated at 100 and 200 watts respectively.

Point being that not all devices are safe across the board. And many legacy/vintage devices are flatly unsafe if abused. The typical user these days believes that decent sound can come from a highly compressed source into computer speakers and/or earbuds, and have probably never heard a decent system under decent conditions with decent signal. Nor do they have a clue about Clipping, and what it actually means, nor its relationship to perceived volume and power requirements to achieve it. So, off they go trying to shake the floor or rattle the windows with a 4" speaker...

Peter Wieck
Melrose Park, PA