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Eilex PRISM EQ Interview With Yoshi Asahi

by October 13, 2014
PRISM EQ isnt a conventional room EQ system, but instead takes a series of near field measurements to correct loudspeaker response.

PRISM EQ isn't a conventional room EQ system, but instead takes a series of near field measurements to correct loudspeaker response.

If you’re a regular reader of Audioholics, you might have noticed our recent interview with Chris Kyriakakis on Audyssey MultEQ. This time around, we were able to get in touch with Yoshi Asahi of Eilex to discuss the company’s PRISM EQ system. It should be noted that Eilex PRISM is not a conventional room EQ. Instead, it is an APVD (Acoustic Power Volume Density) measurement and equalization system.  PRISM measures the acoustic energy emitted to the frontal volume of speakers and tunes it to any desired characteristics. Eilex claims that a speaker corrected by PRISM performs as a perfect transducer, reproducing true-to-source acoustic power (energy). Their belief is that if the room changes the sound in an unfavorable way, you should fix the room rather than making your speakers perform pre-equalized. However, Eilex PRISM can be used as a room acoustics EQ tool very successfully for the subwoofer range.   

Audioholics: What kind of filters do your products use, and at what resolution (i.e. 1/3 octave, 1/12 octave, etc)?
Yoshi Asahi: VIR filters with 1/20 octave resolution.

Equalized Response

Graph showing the before measurement, applied EQ, and target response.

Audioholics: What is the maximum boost / cut your products will apply? Is it possible for users to set a limit in this respect (i.e. no more than 3dB of boost)?

Yoshi Asahi: The maximum range is 20dB boost and 30dB cut. The range can be adjusted by the installer to any level.

Audioholics: How do your products help to address the typical issues a room causes (resonances, modal peaks/nulls, etc)? Does room correction largely negate the need for room treatments for consumers, or would you suggest using both room correction and physical treatments?

Yoshi Asahi:
Eilex PRISM is not intended for use as a room acoustics correction tool.  Only when you make measurements at the listening point, after equalizing the speakers, you may see the room acoustic characteristics.  If you see unusual peaks and they are audible, you want to use physical treatment to flatten it.  Nulls are normally ignored unless they are wide.  

Audioholics: Do your products utilize multi-point measurements? Why or why not? If so, how many measurement points are available?

Yoshi Asahi: Eilex PRISM typically uses a few hundred measurement points in each speaker’s frontal space. We make measurements of a speaker along the frontal hemisphere of at least 100 points about 2’ away from the speaker, then repeat the measurement a couple more times along different hemispheres by increasing the distance from the speaker.  The result leads to a complete frontal space measurement.  Around 300-500 measurement points are used, thus we can say PRISM measurement is still a near-field APVD measurement.  

Do your products correct subwoofer response? How do your products calibrate and correct the response of multiple subwoofers? Please describe the benefits of your method.

Yoshi Asahi:
Yes, Eilex PRISM corrects subwoofer response.  Near-field measurement corrects subwoofer’s response itself.  If the bass in the room need to be corrected, measure the room by walking around the room and equalizing it.  In the case of multiple subwoofers, activate them all and measure the response.
 Eilex PRISM typically uses a few hundred measurement points in each speaker’s frontal space


Audioholics: What is the default frequency range corrections are applied to? In other words, is there a frequency ceiling or floor above/below which correction isn't applied? If correction isn't applied full band, please explain.

Yoshi Asahi: Eilex PRISM can correct the frequency response in the range from 10Hz to 24KHz or 48KHz (depending on the selected sweep).


Audioholics: The typical top frequency for correction is 24kHz, implying that PRISM is functioning at a 48kHz sample rate. Does this mean that high resolution content (for example 192kHz or 96kHz sample rate PCM) will be downmixed?

Yoshi Asahi: The top correction frequency of 24KHz is in the case of 48KHz sampling.  PRISM can EQ 96KHz, if the system runs at 192KHz. However, the actual measurement data ends around 30-40KHz depending on the microphone to be used. It is meaningless to EQ in the ultrasonic range. In the case of playing back 192KHz-24bit materials PRISM can EQ only the meaningful range while passing the rest untouched.  (If you really need to EQ the ultrasonic range, for example giving a slow LPF, you can do so by assigning the EQ range accordingly.)

 Measurement 2

Sample APVD measurement graph.

Audioholics: Does your room correction software show users "before", "target", and "after" response curves? Is it possible for end users to adjust the final response curve such that they can flavor the sound to taste?
Yoshi Asahi: Yes, Eilex PRISM shows original APVD, target curve and expected APVD result. The target curve can be modified in real-time while listening to the sound.


Audioholics: What do you feel are the important differentiators between your room correction solution and competitors?

Yoshi Asahi: We believe the speakers should reproduce true-to-source sound at the speaker position.  The sound changes depending on the listener’s location, but that is normal.  The same thing happens at a concert hall. The best seat at the concert hall does not have a flat frequency response. Again, if your room sounds bad, you have to physically fix that, instead of relying on electronics. If your room has minor irregularities, you are compensating for them while tuning the sound by Eilex PRISM.  That level of room correction is performed by Eilex PRISM.


Audioholics: Does your room correction software run on an AVR/Pre-Pro or require an external computer for processing?  If it requires an extra computer, what platform(s) does it run on?

Yoshi Asahi: Eilex PRISM runs on a PC running Windows 7 or Windows 8.

 if your room sounds bad, you have to physically fix that, instead of relying on electronics


Audioholics: Can consumers purchase your solution as a stand-alone product/solution or only bundled as part of an AVR/pre-pro?

Yoshi Asahi: The PRISM processor EP-1 (to be announced 2014 Fall) is installed only by certified installers. 


Audioholics: Do users have the ability to set multiple profiles—for example, setting a separate "music" and "movie" room correction profile where one can be tailored for a different frequency response range, bass response, different crossovers, etc?

Yoshi Asahi: EP-1 has 5 presets (memories) to store preferred EQ curves.


We'd like to thank to Yoshi Asahi for sharing his insights on Eilex PRISM EQ with us.


About the author:
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Steve Munz is a “different” addition to Audioholics’ stable of contributors in that he is neither an engineer like Gene, nor has he worked in the industry like Cliff. In fact, Steve’s day job is network administration and accounting.

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