Originally Posted by Alan P
Don't waste your time. The SPL apps just don't have good enough resolution in the lower octaves to be worthwhile.
Alan, that was not my experience when testing out my phone as an SPL meter app. I do agree with regards to RTA style phone apps that do an FFT to show the overall spectrum response for white noise being played back on the system. Those apps have terrible resolution and are useless for looking at sub response.
However, using a test tone generator (REW) or test tones from youtube, and a phone SPL meter, I was able to create excel plots for different listening positions such as the one below (this was for my Sub-1200):
In all cases, the measured responses matched with what my ears heard at the different listening positions. Subsequently, I was able to use REW with my internal mic on my laptop (after disabling all post processing and noise cancellation/filtering for the mic in the driver settings) and got RTA mode as well as frequency sweeps working and giving me surprisingly consistent readings that matched with my ears and phone readings while making measurements a lot easier. I do understand that the absolute SPL level is certainly off, and that there may be some general roll-off across the 20-100Hz region of interest, but even the uncalibrated mics don't have any sharp resonances in their response in this region, and with some common sense checks (making sure my ears heard what the mic was measuring, and that the overall sub-woofer response I measured matched well with published response) I was able to use these mics to dial in my sub quite nicely. It was certainly extremely beneficial in comparison to simply doing a sub crawl and trying to gauge things with my ears.
Here is the REW measurement of my PB12-NSD using laptop mic.
As you can see, the measured response matches very well with the expected profile of the response curve for the sub. Some of the room resonances are also very obvious. I would like to mention, that this approach is risky as your mic may behave strangely, and hence the recommendation of commonsense checks. I tried using an external logitech webcam mic and that didn't work as I believe it had undefeatable signal processing at the low end for noise cancellation. But that failed the commonsense checks, and so I didn't use it to make measurements.
I'd still recommend a calibrated mic, but in the mean time, there isn't any harm in trying this approach. I know from personal experience that I gained a LOT from doing all of the above and was able to achieve a much more pleasing response at my MLP, which would have been impossible to do without taking measurements. In my 5000+ cu ft living room, my sub would also have been extremely underwhelming in any of the other locations except for the corner loaded option (as shown in my first set of plots). Hence why I feel it is so important to stress to people that if they are investing a lot of money on their subs, they owe it to themselves to take measurements and try different locations for their subs. From my measurements, it is quite clear to me that even if I spent $1000 on a sub, I would be very underwhelmed with it in any of the other 3 locations in my living room.