frequency response of headphones

[bobopi]

Hi,

in the context of physiological recordings with small animals (guinea
pig) in a small anechoic chamber, I would like to use headphones as
speakers between, say, 100 Hz and 35 kHz. I'm interested in the
flattest response possible. I've selected a bunch of headphones, but
the shape of their frequency response is never given on their
constructors websites. Has someone performed tests ? I wonder, do they
have a flat response (more or less) or has their response been adapted
to the human ear ? Do you have some advice on some of these models ?
Here are the selected models:

*Beyer*

dt 770 pro
closed
5-35000Hz
<http://www.beyerdynamic.de/en/broadcast-studio-video-production/
products/headphonesheadsets/headphones.html?
tx_sbproductdatabase_pi1[showUid]
[showUID]=44&tx_sbproductdatabase_pi1[showUid]
[backPID]=93&cHash=cd6f9075a1>

dt 880 pro
semi-open
5-35000
<http://www.beyerdynamic.de/en/broadcast-studio-video-production/
products/headphonesheadsets/headphones.html?
tx_sbproductdatabase_pi1[showUid]
[showUID]=1851&tx_sbproductdatabase_pi1[showUid]
[backPID]=93&cHash=cef9b324c4>

dt 990 pro
open
5-35000 Hz
http://www.beyerdynamic.de/en/broadcast-studio-video-production/products/headphonesheadsets/headphones.html?tx_sbproductdatabase_pi1[showUid][showUID]=45&tx_sbproductdatabase_pi1[showUid][backPID]=93&cHash=cb51219012

*Fostex*

T50RP
semi-open
15-35000Hz
<http://www.fostexinternational.com/docs/music_products/
rp_series_spec.shtml>

*AKG*

K 702
open
10-39800Hz
<http://www.akg.com/site/products/powerslave,id,1082,pid,1082,nodeid,
2,_language,EN.html>
available in august

*Sony*

MDR 7509HD
closed
5-80000Hz
<http://pro.sony.com/bbsc/ssr/product-MDR7509HD/>

*Sennheiser*

HD 595/600/650
open
10-39000 Hz
<http://www.sennheiser.com/sennheiser/icm_eng.nsf/root/09969>

*Ultrasone*

Pro 750/2500
closed/open
8-35000Hz
<http://www.ultrasone.com/index_en.php?
level=1&CatID=13.37&inhalt_id=45&shop_level=2&shop_CatID=1&shop_inhalt_id=0&do=showDetails&artikel_typ=allgemein&artikel_id=17>

I like this last one because it is magnetic shielded, which is
especially interesting when we perform intracerebral recordings which
are perturbated by magnetic fields but their S-logic system is not
that nice for my use I guess.

Thanks
Boris