Re: Headphones for virtual acoustics

["Bernhard U. Seeber" <seeber@xxxxxxxxxxxxxxxxxxxx>]

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?
>
> br,
> Bernhard Laback