Hi,
I have just such a SW running in Matlab.
I have been publishing EQ suggestions based on Score-optimized EQ:
https://www.audiosciencereview.com/...ctive-speaker-review.13436/page-3#post-432075
https://www.audiosciencereview.com/...tudio-monitor-review.14795/page-5#post-461044
https://www.audiosciencereview.com/...-m16-speaker-review.11884/page-23#post-458542
https://www.audiosciencereview.com/...shelf-speaker-review.14745/page-2#post-458448
I agree with you that the only known/documented model is the Olive score and therefore we should stick with it.
Any deviation from it would need redoing the whole research for validation.
On the other hand my observations are very similar to TimVG's:
- with a speaker with partially constant directivity (i.e flat SPDI at HF, with a waveguide on the HF unit for example, non-coaxial ) the score improves by tilting down the whole response otherwise the PIR HF exhibits too much energy. This is a very important observation I believe.
- the midrange gets boosted to compensate (fill the lack of energy) for the directivity error around the crossover.
The following is based on idealized models so please no nitpicking I am just trying to extract trends…
The preference score Equation is:
PPR_ON = 12.69 - 2.49*NBD_ON - 2.99*NBD_PIR - 4.31*LFX + 2.32*SM_PIR;
If one ignores the LFX to avoid over-stretching the speaker, or latter on add multiple LF sources, then the score driving factor is the PIR.
One should therefore design the speaker with the PIR as priority.
This is linked with the research based on the in-room EQ AND the headphone target curve research both conducted by Harman.
“My” Interpretation:
- 2.49*NBD_ON (100Hz-12000Hz): the score benefits from a flat response with as little deviations from the average value as possible; we want NBD_ON=0.
Even adding a gentle slope would not result asymptotically in NBD_ON=0.
However, having the curve that looks like some stairs on each 1/2 octave band could yield 0 as well; not that I advocate this kind of design it is just a remark…
- 2.99*NBD_PIR (100Hz-12000Hz) same as NBD_ON, we want NBD_PIR=0
- 4.31*LFX: we want 4.31*LFX = 0 which means a 6dB cut-off of the SP to be 1Hz relative to the average of the ON response in the 300-10000Hz range.
If one wanted max Score = 10 (not sure why) then the LFX could be f6dB = 14.5Hz.
+ 2.32*SM_PIR (100-16000Hz) is comprised between 0 and 1, we want SM_PIR = 1.
To calculate this property of the PIR, first, one needs to make a LINEAR regression of the PIR, and then, the SM expresses the validity of this regression.
The more the PIR resembles the LINEAR regression the closer to 1 the SM_PIR will be. The PIR should therefore be a LINE with a slope, ANY slope.
This eliminates the stairs “case” from the NBD, as, in all likelihood, the derived PIR would not resemble a line.
This leads to design considerations on the target one should follow to achieve the best score possible.
- NBD_ON = 0 translates into Flat for ON, OK nothing new there.
- LFX: 14.5Hz, more reasonable that 1Hz… Doable with dedicated SWs stand alone or not and EQ
- SM_PIR = 1 means PIR is a line with with a slope, ANY slope. That is the crux of the matter I believe.
Now, knowing that we also want NBD_PIR = 0 it means that the PIR should therefore be a FLAT line i.e. slope = 0.
- NBD_PIR = 0 translates into Flat for PIR,
Remember PIR = 0.12*LW + 0.44*ER + 0.44*SP
Then a flat PIR also “probably” means
So now we have the “idealized” targets:
- Flat ON: not a surprise
- Flat LW: no variation on the tonal balance across the LW, not a surprise
- Flat ER: no variation on the tonal balance with the ER, not a surprise
- Flat SP: consequence of the rest of the targets, maybe not realistic, the SP contribution is much lower than the ER and LW in the PIR calculation so less critical
Now how does one make such a speaker, at least on the horizontal plan?
- Controlled and constant directivity down to 100Hz via large drivers, waveguides and/or beam forming
https://www.stereophile.com/content/bang-olufsen-beolab-90-loudspeaker-measurements
https://www.stereophile.com/content/dutch-dutch-8c-active-loudspeaker-system-measurements
https://www.stereophile.com/content/kii-audio-three-loudspeaker-measurements
https://www.audiosciencereview.com/forum/index.php?threads/apple-homepod-measurement.8425/
Another good approximation:
https://3.bp.blogspot.com/-OB4hm25dXms/XJVUs8TznTI/AAAAAAAAAEA/r6riUCqhZDgJO61yR8uKzWXbHDYsl_CJgCLcBGAs/s1600/Spin+-+Revel+Performa3Be+F228Be.png
That is also the target for Earl Geddes if I am not mistaken the difference being the DI value more of less high i.e. refection contribution.
- Onmi-directional is a special case of this that might requires multiple HF sources to extend the omni character up to HF
https://www.audiosciencereview.com/...directivity-speaker-review.13982/#post-426504
This is a very old debate that I do not pretend to solve here but that seems to tilt the balance towards constant directivity (Flat SPDI) vs monotonic increasing directivity i.e. a SPDI that increases constantly with frequency.
The latter providing:
- Flat ON, OK for NBD_ON = 0
- Tilted LW with built in issue with NBD_PIR = 0
- Tilted ER with built in issue with NBD_PIR = 0
- Tilted SP that might not be an issue with reasonably directive speakers (high DI)
- Tilted PIR with built in issue with NBD_PIR = 0 but with no reason NOT to achieve SM_PIR = 1 target
Example:
https://speakerdata2034.blogspot.com/2019/03/spinorama-data-kef.html
With all that been said, the score relies on anechoic data that does not include the room influence per definition.
So I guess one way to see things would be to stick to the these anechoic data within the limits of room/speaker dominated domains
Therefore we could restrict the target to the Schroder frequency (which one?) 500Hz as most large speaker Summa, JBL M2 or ?
to get a reasonable approximation of the design targets.
Sorry for the long post but I thought it was the right time to expand on my thoughts.
Cheers
M
