BillFitzmaurice.info

My mate is studying this course. he sent me the lecture powerpoint slides, since I have an interest in such things. Includes this:

Danger Low Power

If an amplifier is over driven:
harmonic distortion increases
more high frequency energy than usual
tweeters may be underrated
DC signal generated
inductive reactance plummets
high currents destroy voice coils

Section on speakers:

Colouration
A loudspeaker enclosure will:
Add panel resonances
Produce standing waves
Inflict it’s own frequency response

To reduce this, the construction must be:
Rigid
Heavy

Under bass reflex enclosures:

Tends to “hoot” and “chuff”

This is like, all the classic wrong info found on DIY forums, but its part of a degree and I assume the exams match up.

Mr. foxen wrote:My mate is studying this course. he sent me the lecture powerpoint slides, since I have an interest in such things. Includes this:

Danger Low Power

If an amplifier is over driven:
harmonic distortion increases
more high frequency energy than usual
tweeters may be underrated
DC signal generated
inductive reactance plummets
high currents destroy voice coils

Section on speakers:

Colouration
A loudspeaker enclosure will:
Add panel resonances
Produce standing waves
Inflict it’s own frequency response

To reduce this, the construction must be:
Rigid
Heavy

Under bass reflex enclosures:

Tends to “hoot” and “chuff”

This is like, all the classic wrong info found on DIY forums, but its part of a degree and I assume the exams match up.

In some instances: an example of myth being perpetuated in a formal setting leading to a qualification.

I wonder if a pre requisite to the course was a hearing test?

I'm just dabbling in doing my first amp repair and there is DC generated in amps.
Step one after making sure no smoke gets out is to measure DC at the output and then correct DC offset (from my amp service manual)

Also, in the same manual, it says when adjusting Short circuit detector:
The desired AC voltage is superimposed on a DC voltage of 9V, so the CRO or millvoltmeter will need to be AC coupled.

I guess the argument from Bill would be that bracing ensures rigidity...

Mr. foxen wrote: This is like, all the classic wrong info found on DIY forums, but its part of a degree and I assume the exams match up.

It just shows that even some sources that should know better don't. The usual reason is that they relied on information from others that was incorrect. One does have to rely on sources, you can't research everything personally, but one also can't assume that everything found in a reference is correct. That's why you have to fact check with multiple sources.

The JBL thing about power and speakers was cited at the end, which is some of the underpowering stuff, but I read it ages ago and it was for saving tweeters.

Mr. foxen wrote:The JBL thing about power and speakers was cited at the end, which is some of the underpowering stuff, but I read it ages ago and it was for saving tweeters.

+1. Unfortunately the story deviated further and further from the truth with each retelling of the tale, until the myth was all that remained.