Subject: Re: Driving headphones at high peak levels From: Bob Masta <audio@xxxxxxxx> Date: Thu, 11 Dec 2014 12:02:17 -0500 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Bob: I tested the cheapie no-name 5.1 channel USB card at 50 ohms, and found that it can only deliver 1.14 Vrms (down from 1.5 with no load). This is not so much an output impedance issue, it has more to do with limited drive capability. (The output clips, so you have to reduce the output level to 1.14 Vrms to avoid the clipping.) Also tested low-frequency response versus load per Steve Beet's suggestion, and find that with no load the cutoff is under 0.1 Hz... too low to measure. With a 1000 ohm load it's 1.6 Hz, and with a 100 ohm load it's 16 Hz. Best regards, Bob Masta ========================== On 10 Dec 2014 at 8:48, Bob Masta wrote: > On 10 Dec 2014 at 9:57, Bob Carlyon wrote: > > > Hi Bob, > > > > Thanks very much for your suggestion. It sounds great, > > although I am slightly nervous about using an unbranded > > product for clinical research; having said that I may as > > well order one and try it out, as they are very cheap > > even in the UK. As a matter of interest, though, what was > > your "second best" for driving low impedance headphones > > at high levels. Mike Stone recommended some Sennheisers > > that produce 112 dB/V at 1 kHz and that are 50 ohm, so > > if I can drive these without loss at 1.5 V maximum then > > I would be in business! > > > > Thanks again > > > > "Second best" (out of only 5 USB devices so far) would be > the Creative X-Fi (US$85), which can deliver 1.14 Vrms into > a 100 ohm load. It's output impedance is 35 ohms, however, > so no hope of driving 1.5 Vrms into 50 ohms. Just for > completeness I'll try to test it today with a 50 ohm load, > as well as the cheapie no-name device. > > The separate headphone amp is starting to sound like a > safer bet. Unfortunately, I haven't tested any. Note that > standard 5 V, 100 mA USB power is theoretically capable of > driving 1.5 Vrms into 43 ohms without clipping, but to > actually drive 50 ohms at this level may require more > juice. > > Best regards, > > 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! 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!