[sdiy] Harmonic bandwidth

[Magnus Danielson]

From: Donald Tillman <don at till.com>
Subject: Re: [sdiy] Harmonic bandwidth
Date: Wed, 09 Jan 2008 14:30:17 -0800
Message-ID: <m2sl168wee.fsf at till.com>

>    > Date: Wed, 09 Jan 2008 09:45:33 -0700
>    > From: Ian Fritz <ijfritz at comcast.net>
>    > 
>    > Speaker dynamics: If you put a perfect sawtooth into a speaker
>    > you would be asking for its displacement to change
>    > instantaneously.  If you rephased the harmonics then you would no
>    > longer have this step.  Of course you never have exactly this
>    > situation, but the transient mechanical response of the speaker
>    > to a step should be kept in mind.  For this reason I think the
>    > sawtooth does not make a very good test.
> 
> Hey Ian,
> 
> Not exactly; a speaker cone's acceleration is proportional to the
> input signal voltage.

No, it ain't. The current flowing through the coil might be it, but it is not
totally correct either. The electrical side of the coil is that it is both
resistive and inductive. The element itself experience mechanical issues due to
weight, resistance and there's resonance modes in the cones to help confuse
things. Then the speaker assembly creates various forms of nodes.

There are no simple model to use. If you look at the evolvingly more complex
models used in Thiel-Small and followers models and the way speakers have been
modeled and then it becomes clear that these things work backwards into the
electronic side of things, since the speaker after all is reciprocal.

So, the exact electrical condition is not accuratly described in that way.

A sawtooth is not very good test signal, but the step responce can to some
degree be found this way. Impulse responce is beast measured using the MLS
method. The classical MLS using MLSSA was quite nice, but a bit limited.
I have a MLSSA card sitting in the basement... got to check it out I guess.

There where a number of things to improve on the MLSSA software application.

Cheers,
Magnus