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Headphone output voltage
markanini
post Apr 8 2013, 05:33
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I want to measure the output voltage of different headphone outputs for two purposes.
1. Do comparative rightmark tests at the same output levels
2. Keep track of SPLs.

NwAvGuy suggestes 1mw loaded with 32Ohm resistors(180 mV) for measurements. But wouldn't it be more meaningful to use the actual headphones for the resistance load and a target voltage that matches standard 83dB monitoring SPLs? In such case I would be using manufacturer supplied SPL specs as a reference(Etymotic ER4P are 102 dB SPL at 100mV). Also if there's a suitable unexpensive volt/multimeter that you know of please let me know.

This post has been edited by markanini: Apr 8 2013, 05:37
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saratoga
post Apr 8 2013, 06:12
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The spec sensitivity values probably aren't that accurate, so I'm not sure I would depend on them.

Nwavguy uses a resistor so that its a purely resistive load of know impedance. Headphones have some unknown reactance. You could measure it but I guess a resistor is just easier for him.
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skamp
post Apr 8 2013, 09:14
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I've had reliable results with my 25Ω Denon AH-D2000 headphones (as in, they match other results available on the web).

As for output levels: when doing RMAA measurements, in order to get significant results, you need to set the maximum output level that you can get without clipping and without introducing excessive distortion. My Denons are convenient for that, because not only do they have a (mostly) flat impedance curve, they can also take a significant amount of power without introducing any distortion. You also need to increase input gain, when the output level is too low (because the source is a DAP, or because its output impedance is excessively high), otherwise RMAA won't be able to scan the recording. You can also normalize the recording before feeding it to RMAA, you'll still get relevant results.

If you don't make sure to set the maximum output level (within the aforementionned parameters), you will get suboptimal results that will not reflect the device's true capabilities (low dynamic range figures).

HTH


--------------------
See my profile for measurements, tools and recommendations.
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Arnold B. Kruege...
post Apr 8 2013, 15:11
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QUOTE (markanini @ Apr 8 2013, 00:33) *
Also if there's a suitable unexpensive volt/multimeter that you know of please let me know.


The big problem with cheap DVMs is their frequency response. Since most are designed for measuring power line circuits it actually makes sense that they are designed to reject high frequencies. Most are reasonably accurate up to 400 Hz or 1 KHz, and if you keep your precision measurements below that frequency, they can be useful tools.

You can also use them for matching levels since in that app, all you want is the same numbers within 1 or 2 percent. As long as you can have 3 or more digits on the display, you can get the sort of matching you need for subjective testing.

It may sound awkward, but if you use your DVM for accurate voltage measurements at lower frequencies and then use a good sound card for broadband measurements and merge the two with measurement(s) using both at frequencies(s) that both can handle accurately, it can work.

Alternatively, you spend the big bucks for a DVM with good frequency response. You may find something to your liking in the Protek or Fluke catalogs. For extra fun, try to find a DVM with dB range(s).

I have a Protec 506 (legacy, has a dB range, responds within a half dB or so to 20 KHz and a Fluke that has no dB range, but is pretty flat up to about 50 KHz. I also picked up a legacy Hewlett Packard audio voltmeter for the bench on eBay for not that much, but it seems to stay in the store room.

This post has been edited by Arnold B. Krueger: Apr 8 2013, 15:12
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markanini
post Apr 9 2013, 20:36
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This one should do it? http://www.uni-trend.com/ut61e.html Or this one http://www.aidetek.com/New_products_info/D.../Vichy/VC87.pdf

This post has been edited by markanini: Apr 9 2013, 20:53
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Arnold B. Kruege...
post Apr 9 2013, 21:00
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QUOTE (markanini @ Apr 9 2013, 15:36) *



Intresting threads about it here:

http://www.eevblog.com/forum/testgear/uni-...2f3363d316a4baf

http://forum.43oh.com/topic/2380-uni-t-ut61e-for-50/

http://www.eevblog.com/forum/testgear/uni-...own-photos/450/

http://lygte-info.dk/review/Review%20UNI-T%20UT61E%20UK.html

Price seems right - pretty aggressive for a TruRMS meter.
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markanini
post Apr 10 2013, 01:01
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Yeah I've been reading about the UT61E all evening. Found it by typing 'multimeter "frequency response"' into ebay with 'search description' checked. I feel kinda lucky that the cheapest one that was up to spec is well regarded for its price.

This post has been edited by markanini: Apr 10 2013, 01:17
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