Re: Driving headphones at high peak levels (Bob Masta )


Subject: Re: Driving headphones at high peak levels
From:    Bob Masta  <audio@xxxxxxxx>
Date:    Mon, 8 Dec 2014 08:58:13 -0500
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

> 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 I have tested several USB sound cards. The hands-down winner for low output impedance (2 ohms) can deliver nearly 1.5 Vrms into 100 ohms. I especially like it because it has no hardware controls on the unit that can get accidentally changed in a lab setting. It has pretty good specs in most other respects as well. See the Comparison Table under "Sound Card Perfomance Tests" at <http://www.daqarta.com/dw_gguu.htm> The unit is based on the CM6206 chipset and is sold by various suppliers. I got mine from HDE through Amazon. Search for "5.1 channel USB sound" and look for a picture that matches the one for "5.1 Channel CM6206 USB" on the link above. I just did that and found HDE's price has jumped up to US$16.95... it was under $15 when I bought mine! The only drawback I've encountered is that the mini-USB connection on the back of the unit can loosen up... very annoying in the middle of a test. I've temporarily resolved this by some selective crimping, but a better solution would be to remove the chassis and cable connectors and hard-wire the USB cable to the unit. Best regards, Bob Masta ================== On 7 Dec 2014 at 13:29, Bob Carlyon wrote: > Dear list, 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 > > > Cheers > > Bob > > > Dr. Bob Carlyon > Deputy Director > MRC Cognition & Brain Sciences Unit > 15 Chaucer Rd. > Cambridge CB2 7EF > England > Tel: +44 (0)1223 355294 > Fax: +44 (0)1223 359062 > www.mrc-cbu.cam.ac.uk<http://www.mrc-cbu.cam.ac.uk/> > See also the > Cambridge Hearing Group<www-hearing-research.eng.cam.ac.uk/Main/WebHome> > > Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!


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