There is a new AES paper published by Dr. Sean Olive @Sean Olive and Dan Clark @Dan Clark on potential targets for GRAS 45CA and B&K 5128:
A Preferred Headphone Target Curve Defined for the B&K 5128and GRAS 45CA-10 Test Fixtures
ABSTRACT
The Harman around-ear and on-ear headphone target, defined using a GRAS 45CA test fixture with aRA045 (“711”) ear simulator and custom pinna, is often misused with other fixtures, leading to measurement and interpretation errors due to differing acoustic transfer impedances. We compared several headphones on the original fixture and two newer models, specifying calibration and target curves for each to improve accuracy. The purpose was to define Harman target equivalents for these new fixtures that account for differences in their acoustic impedances and produce similar sound quality. Listening tests assessed how similarly headphones sounded when measured and equalized on all three fixtures using these revised targets.
The paper is a bit difficult to follow. But essentially, they measured a number of headphones on three fixtures: the original modified GRAS used by Harman for its listener preference papers. Then on GRAS 45CA with 5000 pinna (what I use). And B&K 5128. Differences were then incorporated as EQ profile and listeners were asked if they thought the translated targets for 5000 and 5128 matched the response of the original research fixture.
The reference itself was in the randomized test, setting the upper bound of similarity at around 90%. Compared to that, GRAS KB5000 single profile for the tested headphone came closest to the reference. B&K 5128 underperformed it some.
Average of 7 headphones reduced similarity to the reference for both fixtures but much more so for B&K 5128 for Noire X headphone. Results are somewhat similar for Noire XO.
In other words, for a specific headphone you can develop a rather accurate target on the new fixtures. But a generalized one based on averages as developed in the original research, does not work that well, and much worse for 5128.
Here are the differences for the 7 headphones under test with each fixture:
Visually, we can see that the reference research fixture matches new GRAS KB5000 (read and green) quite well up to about 3 kHz to 4 kHz. Above that, KB5000 shows higher treble response than the reference. Fortunately, in my testing, I don't put a ton of value on upper treble and at any rate, adjust filters by ear.
B&K 5120 is a different story. Its response varies based on headphone and has a very different shape from bass up to 10+ kHz. This makes it impossible in my opinion, to create a target for it which translates well from the research reference.
It is kind of fascinating that the DCA Corina produced almost identical response in all three fixtures below 1 kHz.
Please note that all of this is my interpretation of the paper. Actual presentation in next week (Friday or is it Saturday) at the AES conference in Newport Beach.
This is the first such formal study and much needed research to inform us of variations we need to consider in these fixtures. I may develop a new target to overlay on the existing one I use in my reviews with GRAS 45-CA/KB5000.
A Preferred Headphone Target Curve Defined for the B&K 5128and GRAS 45CA-10 Test Fixtures
ABSTRACT
The Harman around-ear and on-ear headphone target, defined using a GRAS 45CA test fixture with aRA045 (“711”) ear simulator and custom pinna, is often misused with other fixtures, leading to measurement and interpretation errors due to differing acoustic transfer impedances. We compared several headphones on the original fixture and two newer models, specifying calibration and target curves for each to improve accuracy. The purpose was to define Harman target equivalents for these new fixtures that account for differences in their acoustic impedances and produce similar sound quality. Listening tests assessed how similarly headphones sounded when measured and equalized on all three fixtures using these revised targets.
The paper is a bit difficult to follow. But essentially, they measured a number of headphones on three fixtures: the original modified GRAS used by Harman for its listener preference papers. Then on GRAS 45CA with 5000 pinna (what I use). And B&K 5128. Differences were then incorporated as EQ profile and listeners were asked if they thought the translated targets for 5000 and 5128 matched the response of the original research fixture.
The reference itself was in the randomized test, setting the upper bound of similarity at around 90%. Compared to that, GRAS KB5000 single profile for the tested headphone came closest to the reference. B&K 5128 underperformed it some.
Average of 7 headphones reduced similarity to the reference for both fixtures but much more so for B&K 5128 for Noire X headphone. Results are somewhat similar for Noire XO.
In other words, for a specific headphone you can develop a rather accurate target on the new fixtures. But a generalized one based on averages as developed in the original research, does not work that well, and much worse for 5128.
Here are the differences for the 7 headphones under test with each fixture:
Visually, we can see that the reference research fixture matches new GRAS KB5000 (read and green) quite well up to about 3 kHz to 4 kHz. Above that, KB5000 shows higher treble response than the reference. Fortunately, in my testing, I don't put a ton of value on upper treble and at any rate, adjust filters by ear.
B&K 5120 is a different story. Its response varies based on headphone and has a very different shape from bass up to 10+ kHz. This makes it impossible in my opinion, to create a target for it which translates well from the research reference.
It is kind of fascinating that the DCA Corina produced almost identical response in all three fixtures below 1 kHz.
Please note that all of this is my interpretation of the paper. Actual presentation in next week (Friday or is it Saturday) at the AES conference in Newport Beach.
This is the first such formal study and much needed research to inform us of variations we need to consider in these fixtures. I may develop a new target to overlay on the existing one I use in my reviews with GRAS 45-CA/KB5000.
