I am involved in a project where we are play some pulsatile stimuli to listeners who may have a hearing loss. To do so we need to produce high peak levels in order to obtain sufficient loudness. The test will be run in different clinics
worldwide, which means both that we can’t choose an expensive solution, and that, at least preferably, we should be using USB devices – although I realise that the voltage provided by the USB will impose some limitations.
I would be grateful for suggestions on how to maximise the audio output, and list below the general options & limitations as I see it
Choose a sensitive transducer
At present we are using Sennheiser HD650s which produce about 106 dB SPL/V for a 1-kHz sinusoid. In a recent post Mike Stone mentioned the HDA200 which produces 117 dB SPL/V, but that is very expensive; does anyone know of cheaper headphones
that are also very sensitive? Another option is to use insert earphones such as the Etymotic ER 5. However the highest input impedance these come in is 50 ohms, which is similar to the output impedance of the USB sound cards I have tried (see below)
Choose a USB sound card with “better” specifications
The USB sound cards that I have seen have output impedances of around 50 ohms or higher, making them unsuitable for driving low impedance phones, so a low-output-impedance USB sound card with decent maximum output would be one solution
The two cards that I have been calibrating differ by more than 8 dB in the maximum output they can produce into a 300-ohm load without clipping – the winner being the Roland Quad capture at a peak value of approx.. 2.6V. If anyone knows
of a USB sound card that would exceed this, or even match it at a cheaper price (The Roland is about UK£150, so say US$225) I would be glad to hear of it
Use a separate headphone amplifier
Does anyone have experience of relatively inexpensive(say < US$150) headphone amps? As mentioned above something USB driven would be ideal, but maybe at a pinch we could use something driven by a 12V power supply using a mains adaptor.
One option (just gleaned from the internet) is the ART headamp 4, but I have no experience with this and so if anyone has calibrated any such device and has suggestions again I’d be grateful
I’d be happy to collate responses and post them to the list
Dr. Bob Carlyon
MRC Cognition & Brain Sciences Unit
15 Chaucer Rd.
Cambridge CB2 7EF
Tel: +44 (0)1223 355294
Fax: +44 (0)1223 359062
See also the