401 Plinth

[Dr Bunsen Honeydew]

The only speaker I know that used Aerolam for the cabinet was the Celestion SL600. This was a fine little speaker ruined by the crossover design, which with the usual BBC design (il)logic was far too overcomplicated and seaching for flatness of on-axis amplitude response ahead of time (phase) coherence.

[pre65]

The tip about placing the stylus onto a non moving record is well worth trying !

Try tapping at various places on the plinth and support and see just how much noise comes through. I tried several ways to isolate the armboard on my 401 but they were not very effective.

[Greg]

Hi Phil,

Been there, done that.........however does that mean your TT system is flawed? Probably not. In my view this is a rubbish test and doesn't tell you anything about its performance. What it does when you are listening to music is far more relevant. As ever, bottom line is, if it sounds good and it satisfies you, everything is ok. You may well be able to make improvements, but don't ever stray from the sound satisfaction test.

Regards,

Greg

[Max N]

Why create an artificial situation, it is music you are worrying about not bonks!

Just put your turntable on top of your speaker and place the stylus in a record groove with the platter stationery. Play music though a cd into the speakers and take the lead out from your phono stage to a 'scope. Incease volume of cd until you register a signal then you will see the nodes imposed on the music of the whole TT system not just the plinth. Experiment with design and set up until you get the smallest and least number of nodes and suck outs. You are also reading the nodes of the speaker cabinet but you can null that by always using the same speaker in your tests.

I would advocate fixing an exciter to the test specimen plinth and then try frequency sweeps and or white noise to find the resonances, and maybe some impulse inputs to look at transient decay. In the long run I think you will get a better understanding and make more progress by breaking the system down and studying components in isolation. Testing the whole plinth, motor, arm, cartridge system and speaker cabinet all at once won't be very transparent, and may introduce modes which actually aren't a problem when the deck isn't coupled to the speaker cabinet.

If you want light, stiff and non-resonant, you could try carbon skins with a nomex honeycomb.