# DSP1124P roll off?



## Chrisbee (Apr 20, 2006)

I'm sure I read somewhere that the DSP2496 has a fairly high roll off point.

Does anyone have any hard figures for the DSP1124P? (-3dB point and dB/octave slope?)

The manual just says 20-20Khz(-3dB) Do we a built-in rumble filter like the SMS-1?

Do we have a likely figure for the -3dB point of the electronics alone in a complete (typical) HT system just before it reaches the sub drivers?


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## brucek (Apr 11, 2006)

> Does anyone have any hard figures for the DSP1124P?


I tested my DSP1100P when I first got it and it extended down to 5Hz ~-3dB. It was fairly gradual from about 15Hz.

In fact (to verify my memory) I just used REW to test the low end of my 1124P. I used the REW signal generator along with (frequency follows cursor) function. I fed the input of the BFD with a 20Hz tone and set the level into the BFD to just start the -3dB LED to turn on (BFD filters off). The next LED down from the -3dB LED is -6dB.

So the -3dB LED just flicked off at about 15Hz and then the -6dB started flicking off at about 5.5Hz. That's 3db down.

Theoretically my soundcard can output flat that low with its calibration file, but who knows the accuracy.

brucek


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## Chrisbee (Apr 20, 2006)

Thanks brucek. It sounds as if there's nothing to worry about with the 1124P if one is seeking ultimate extension.


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## JohnM (Apr 11, 2006)

If you want to measure the 1124P's response easiest is to just connect its output straight back to the soundcard's input in place of the SPL meter.


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## brucek (Apr 11, 2006)

> If you want to measure the 1124P's response easiest is to just connect its output straight back to the soundcard's input in place of the SPL meter.


Yeah, good idea.

There you go Chrisbee. 

The graph below shows the looped back response of my soundcard after calibration (in green) and the red line shows the BFD put into the loop with the filters shut off.

Look at the vertical scale. It's not even down 0.5dB at 5Hz That's a very good response. The horizontal scale starts at 2Hz.

Note the overall insertion loss of about ~0.5db










brucek


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## Chrisbee (Apr 20, 2006)

Thanks. I believe you could obtain an inverse curve of your BFD filters using this method.

So nothing is nibbling on our last few hertz down there in the dark at the end of our audio spectrum. 

Hey! Are we getting a sneak preview of the incredible LF extension of of the new REW? 

Are we going to need something better than the RS meter to make any meaningful real-world measurements?


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## brucek (Apr 11, 2006)

> Hey! Are we getting a sneak preview of the incredible LF extension of of the new REW?


Yeah, the new version of REW will go this low to 2Hz..... but even the ecm8000 microphone only has reliable information down to 10Hz from its calibration file. I would probably rely on the 10Hz from an ecm8000 probably a bit more than a RS meter though. Trying to take responses below 10Hz just isn't too realisitic in my opinion.

brucek


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