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

Subject: Re: Driving headphones at high peak levels
From:    Bob Masta  <audio@xxxxxxxx>
Date:    Tue, 9 Dec 2014 09:41:18 -0500

On 9 Dec 2014 at 12:56, Steve Beet wrote: > > Bob, that's a very interesting and thorough analysis, > but the weak point of the sound card you recommend seems > to be the low-frequency response. The output low-frequency cutoff is 3 Hz. Line In is 41 Hz, which is why the loopback plots look bad. >As the 2 ohm output > you refer to is labelled "line out" in your document, > doesn't that suggest that it is designed for driving > high imedance loads? The device has no separate headphone output. There is no problem with using a low-impedance output to drive high- impedance loads... that's the ideal situation. It's harder (more expensive) to build a high performance output stage with low output impedance, so it's common to have high-Z Line outputs and low-Z (and maybe reduced performance) Headphone outputs. But since this is a 6- channel output device they probably wanted to eliminate the need for a separate Headphone jack on the compact case. > If so, there is probably a > decoupling capacitor on the output so that low > frequencies are attenuated and driving a low load > impedance (e.g. headphones) will decrease the time > constant and make this defect worse. There is definitely a decoupling capacitor on the output, as on pretty much all sound cards. (They need to produce ground-referenced AC signals, and they have a single +5 VDC power source, so they use AC coupling on the inputs and outputs, and reference the internal signals at typically about 2 VDC.) But you have mentioned a valid point, which I will check out shortly. If I find big differences for loaded low-end responses, I'll add another line to the test report. Thanks for pointing this out! Note, however, the OP wants to give pulsatile stimuli, not steady sub-sonics. <g> Best regards, Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

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