Topic: SPL meter - Can I use my gear instead?

[midside]

I know I should have an SPL meter for subwoofer setup.  But, it seems like I should be able to use my gear for this.  I have a SD 7-series recorder and schoeps mics.  Can anyone give me some tips on how to use this as an SPL meter for sub setup.  I would prefer not to have to buy more stuff.
Thanks!

[willndmb]

i guess you could do that with mics
but you would first need to establish what you are measuring

what i mean is how do you know what is "0"db?
if your mics are close to the sub it will read louder then if they are 10 ft back

if you measure it compared to the other speakers then it would be easy

(man this is a hard topic to explain what i am thinking)

[midside]

Well,
I would setup the mic from my listening position.
Then,  I would try to match levels across all frequency ranges.
But, most advice is given for using an SPL meter.
If I use my recorder, how much gain should I be using and how loud should the receiver be?
That is the part that I am unsure about....

[BC]

I would put the volume at about your normal listening level, for recorder levels you just need to make sure that you don't clip over the whole frequency range, maybe -10 to -15dB at 1KHz? I suggest this based on guessing that bass peaks due to speaker/room effects can be around 10dB or so. Most of the real big bumps/valleys will be in the bass, sub-~200hz. 

Do you have freq. response curves for your mics? You could use these to normalize your measured results.

[midside]

Good solid advice, thank you.

The best caps I have for the job will be either my MK5 (in omni position):
http://schoeps.de/E-2004/specs-mk-ccm5.html
or my MK6 (in omni position):
http://schoeps.de/E-2004/specs-mk6.html

According to Schoeps, these will be good and flat from 20hz to at least 2000hz, plenty good for the job.
Actually, I would think this would do a lot better than a cheap Radio Shack meter
(please correct me if I'm wrong here)

[anodyne33]

Paging Rokpunk...

If I'm correct, the dB scale is logarithmic and what you're seeing on the meters of your 7xx is not.

[BC]

FWIW The front panel of the 722 meters is labeled dBFS.


 http://www.sounddevices.com/download/photos/722-master.jpg

[Church-Audio]

I know I should have an SPL meter for subwoofer setup.  But, it seems like I should be able to use my gear for this.  I have a SD 7-series recorder and schoeps mics.  Can anyone give me some tips on how to use this as an SPL meter for sub setup.  I would prefer not to have to buy more stuff.
Thanks!

Its all relative.. if you use a mic with a vu meter and your matching it with the level of your stereo you simply put the test tone through and set the sub so its at the same level as everything else. I prefer to use my ears for this though.

[Gutbucket]

Keep in mind that SPL measurements have both an averaged time response window and a frequency weighting curve applied to them to try and better match the human perception of loudness.

But if you're just aiming to graph the relative response in the room to find peaks and dips in the bass region vs. determining absolute SPL measurements then I think you can do it using your gear and without a lot of calculations or calibrations.  You will need to take into consideration the response of the mics of course.

I did this a few years ago with the RadSack SPL meter and a downloaded CD of windowed noise or tones (can't recall which it was now) at 1 hz intervals.  The tones go from 20hz up to 200hz as I recall.  It was a free download from an online source I can't recall.  If I can find the source I'll post it here.  You just set up the gear with the mic at the measurement position and record each value as the progression of tones progresses one by one, then transfer those values to graph paper and the result is a graph of the frequency response in the room with 1 hz resolution.   It takes a while to do, but is far more accurate than a RTA which can't resolve finely enough for meaningful measurements in the low bass region anyway.  In your case the vertical axis of the resulting graph will be compressed or exaggerated from the SPL value since it does not reflect an SPL reading, but I assume the shape of the graph is what you are really interested in anyway.

You'll be amazed at the sharpness  of some of the resonances and dip you find.  That 1hz resolution is really telling down low.