Re: [Phys-l] Advertising bad physics!

["John Clement" <clement@hal-pc.org>]

There was a very interesting test of consumer perception of distortion.
They put a knob on an amplifier marked "bass", but it only increased the
harmonic distortion.  They asked various people to adjust the bass to their
liking.  Most people including audiophiles turned it up, but as I recall
audiophiles turned it less than the general public.  The one exception was
audio engineers who said the bass did not increase, but they noticed the
increase in distortion.  So one might conclude that people like harmonic
distortion.

The BOSE tactic was in its own way disingenuous.  If you rate amplifiers at
higher distortion they all have higher power ratings.  While Amar Bose was a
very clever designer, his company is very predatory.  And tube amplifiers
generally produce higher harmonic distortion at all power levels, which may
contribute to a slightly "warmer" sound.

But to bring it back to physics education, can anyone identify common
misconceptions about either physics and/or technology in the examples?  I
already mentioned the prevalence of worrying about 3rd order effects, which
relates to accuracy and precision.

An example of this is putting isolators under speakers to prevent coloration
due to interactions.  But most of the interactions are mediated by the air
which carries far more energy, so it is a 3rd order effect.  And interaction
through the floor is impossible on a concrete slab floor.  Also imaging is
conveyed by the first signal to arrive at the ear and the interaction
through the floor will be a delayed signal which contributes nothing to
imaging.  So isolators are worthless under speakers!  But raising speakers
slightly can dramatically change the sound and reduce some room resonances
so using cheap wooden shims would probably produce the same effect but would
not look as nice.  Technobabble is used to sell a cheap fix at an expensive
price.

John M. Clement
Houston, TX

> Audiophile equipment has always been a focus for 'cost of diminishing
> returns' analyses.  I suspect most of these claims have some physical
> basis.
> For example, tube amplifiers DO sound different than transistor
> amplifiers--at clipping.  This is measurable--at least the waveforms
> are--and 'golden eared' audiophiles claim to hear the difference.  OTOH,
> many double blind tests have been done that indicate that basically no one
> can tell the difference in most electronics (speakers are another matter).
> [However, BOSE once tried to market an amplifier that had up to 3%
> Harmonic
> Distortion claiming no one could discern it at that level and the unit
> could
> be more powerful for the money with that compromise.  No one would buy it
> when other amps advertised .1% distortion.]