Recently I was playing a bit with speaker measurements so I've measured the quasi-anechoic on-axis response of my pair of Revel M16s. Since there are two independent sets of spins available for it (ASR and Revel's own), I found this exercise interesting as it's possible to validate the data quite nicely.
The methodology (gated far-field HF response spliced/blended with baffle-step-compensated nearfield LF response) is based on the
whitepaper by Jeff Bagby and
this blog post by Archimago.
Let me start with a question to those more experienced with speaker measurements and design. When attempting to scale the port nearfield measurement level to appropriately match the woofer level, there is a need to calculate the effective radiating surface for both the woofer and the port, and scale the response based on their ratio. If both the woofer and port are round, we can calculate the approximate radiating surfaces by using the generic circle area formula, as long as we have the appropriate diameters.
- For the woofer we measure the approximate effective radiating diameter using middle-of-surround as start and end point
- For a simple cylindrical port it is trivial to measure the effective radiating diameter (i.e. same as port diameter)
My question is what do we use for effective radiating port diameter if it is a flared port - is it the port 'throat' (narrowest point) or 'mouth' (widest point / exit) diameter?
My assumption (based on some experimentation) is that it should be port 'mouth' (widest point / exit) diameter, and this is what I used in the measurements below - but would love to have some references (or better argumentation) for this.
Anyway, these are my results:
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Here the responses are separated, so the detail visibility is improved:
View attachment 95241
As far as differences go, vendor measurement shows a bit lower-Q bass hump (and approx. 1dB lower peak), while ASR measurement shows a drop in response above 10kHz. Also, in my measurements there is some loss of fine details in the ~300Hz-2kHz range. This is due to the nature of in-room gated HF measurements.
But as you see, overall there is pretty good agreement with both ASR and Revel/vendor measurements. So it seems that unit-to-unit response consistency of Revel M16 is quite good.
A note that I don't have full confidence in the absolute level (or slope) of LF response in my measurement for now - mainly due to the above question on flared port effective radiating surface estimation.
Here's a diagram showing (scaled) nearfield measured components vs full on-axis response:
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In-room distortion measurements (these are definitely not reliable in an absolute sense due to room influence). We see the same slight rise in distortion before the crossover. Absolute level:
View attachment 95245
Normalized to fundamental:
View attachment 95246
Anyway, hope this might be interesting to some - if nothing else, it is one more independent dataset