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Re: Headphones for virtual acoustics

Hi Bernhard,

As previously suggested, equalization of headphones will (theoretically) do the job. However, if you are using short FIR-filters for the HRTFs the ability to equalize large, sharp, local spectral transitions will be limited, but those transitions might occur due to resonances. Additionally, bear in mind that equalizing the spectrum by +/-10dB equals a power factor of 100 between min and max, which can get you quickly into dynamic range or nonlinearity problems with your playback system.

To limit the amount of equalization many people use diffuse field equalized headphones which more or less resemble the average HRTF from all directions. Since this also "sounds good" most consumer headphones follow the diffuse field equalization to some degree. The widely used Sennheiser HD580 is in that category and it works well with HRTFs. Two headphones that I know of are manufactured to stringent diffuse field specs: the STAX Lambda Pro with a special driver, and the AKG 240DF. The first one is an expensive, but amazing electrostatic headphone. The AKG 240DF is relatively cheap, manufactured to diffuse field specs, and works reasonably well with HRTFs. Sennheiser/Head Acoustics also make an electrostatic system for virtual acoustics.

Some other questions which you might want to think about:
- Do your headphones also have to be approved for audiometric measurements?
- Do you want them to be in production 10 years from now with the same specs?
- Do you want to use several headphones of the same type, all with identical specs? Consumer grade headphones may not fulfill this requirement because design changes might be introduced during the production run. To get around this you can buy several of them at once from the same batch.

With respect to headphone placement variability I can't judge these headphones in comparison to others.

I hope this helps a bit, good luck!

Bernhard Seeber

-- Dr.-Ing. Bernhard U. Seeber Department of Psychology office: +1 510-643-8408 University of California, Berkeley lab: +1 510-642-5352 3210 Tolman Hall #1650 fax: +1 510-642-5293 Berkeley, CA 94720-1650, USA web: http://www.bseeber.de

Date:    Tue, 13 Dec 2005 10:19:32 +0100
From:    Bernhard Laback <Bernhard.Laback@xxxxxxxxxx>
Subject: Headphones for virtual acoustics

Dear list,

We are looking for headphones to present virtual sound sources by filtering stimuli with HRTFs. They should have 1) a flat frequency response up to about 18kHz and b) high reproducibility of sound intensity - particularly at high frequencies - when putting the headpnones off and on again.

We currently use the Sennheiser HDA200, which appear to fulfill the second requirement but not the first one.

Can anyone recommend a device fulfilling both requirements?

Bernhard Laback