Reflection free (or minimised) mic setup

[Dave Bullet]

I'd never really paid much attention to mic placement and the boom and clip that holds the microphone. When Andrew Jones suspected I had some mic related ripple in my response, I switched to a long pole boom in line with the microphone. Voila!, ripple greatly reduced. A small pointer for those who want to continuously improve their measurement capabilities. For this, I just used a piece of 32mm OD "repair" conduit. IT comes in handy 1m lengths here in good old New Zealand and split down the middle (so you can squeeze a UMIK-1 down the middle). A bit of dodgy chamferring of the end and electrical tape to hold everything securely and we have a marked improvement.

Top set = mic with clip
Bottom set = mic with long PVC boom (length > the measurement window)

Driver in question is a SB Acoustics SB26ADC in a Visaton WG148R waveguide with stepped felt in an attempt to smooth waveguide throat to tweeter surround.



And here is the PVC boom in question:
Prior mic setup:

[Reet]

I should do the same for my setup, as my mic is even slightly worse than the average measurement mic. I haven't been that motivated however, as I would make the same choices for crossover design with either set of measurement data above.

[Dave Bullet]

I should do the same for my setup, as my mic is even slightly worse than the average measurement mic. I haven't been that motivated however, as I would make the same choices for crossover design with either set of measurement data above.

Good point about not changing the "macro" choices on a crossover, however I feel some may resort to smoothing to remove the noise created by reflection ripples and therefore mask other tuning opportunities. My goal is to get as clean a setup as possible (given environment constraints) and not use smoothed data at all in my designs (and I am not implying you do).

[tktran]

Thanks for sharing Dave.

i first learnt about this issue from Troels:

http://www.troelsgravesen.dk/measurements.htm

and although Reid is correct in saying that it doesn’t really affect your crossover design choices, I did what you did, to help me understand ”why do my measurement look funky?”

Another thing you may also be interested in:

http://www.troelsgravesen.dk/chamfer.htm

Recently I had a go at building a small speaker (3L ie. 1/8 cu ft internal volume ). I had a measurement headache trying to figure out why I had an anomaly at ~500Hz.

Turns out- my baffle was too narrow. Note to self- don’t try to cram a driver with 125mm OD frame into a box only 130mm wide.

[Reet]

Early reflections are real!