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Posted: 6/22/2014 1:10:20 PM EDT
| I have a BK 2209 with a couple of mics and source. All are calibrated and I am getting repeatable and consistent readings. Can anyone give me a bit of advice about how to get the AC out into a sound card for getting additional information rather than just peak hold? My initial attempt using the 124 dB 250Hz source recorded the sound of the piston phone but the signal was way down when I took the AC out to a sound card. Any advice would be appreciated. |
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Are you trying to sample the signal to do spectrum analysis? Off the cuff, I don't think your average sound card is going to cut it as far as sampling rate and number of bits (dynamic range) and perhaps even frequency response. You're probably going to have to invest in a full blown setup from somebody like National Instruments (which, I believe Silencerco uses) - I think they've even written VI's so that all you have to do is hook up your signal (in additional to any preconditioning you might need to do) to the DAQ board and start sampling away. If you're looking for general measurement info, here's a paper to read: Measuring Recreational Firearm Noise --- ETA, if you're signal levels are low, what's the input impedance of your DAQ? Real data acquisition cards have input impedances in the MOhm region while sound cards are typically in the hundreds to kOhm region. Are you doing any signal conditioning before you sample? |
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Yes, I have a quote for a two Gras mic national instruments package. It was about 30K plus tax. I would need a decent generator to run the units in the field as well. At this stage it is too expensive and too bulky to get me what I am looking for now. Even if I used my own mics and BK2209 into the NI package it would be around 13K plus tax but I could get away with a notebook and battery packs.
I am aware that my spectrum analysis will not be as good as what NI gear would produce, but at 48 or 94 khz sampling it would give me unfiltered data (the peak hold uses A weighting as per mil std 1474), time domain and frequency analysis. I have an analogue octave filter for the 2209 but the amount of ammo necessary for a sample at each octave sort of puts me off this method and it would lack a lot of other detail. I will check the impedance on the meter and sound card tonight. Thanks for the response. |
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I haven't tried the output with an o-scope yet. Good idea. I will have to wait til the source is back from service to get a decent correlation.
The output impedance in most modes is 600 ohms with any permissible load. In the Batt position impedance is less than 200 ohm with a minimum load impedance of 10 K ohm 200 pF. If the batt position is used, the normal meter will not work and all reading will be from the AC out. |
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