Any alternative to Radio Shack sound level meter?


MIne is kaput. I want to use to optimize sub setup.
oldears
Absolutely. Use a $20 calibrated mini-mic:

https://amzn.to/2XxZ4bl

Requires a normal headphone/mic plug on your phone. I use AudioTools on Android. You go to the manufacturer’s website, and copy the calibration file to your phone.

Best,

E
There are several iPhone apps that work very well and are free or a few dollars.

RTA Audio Pro, , RTA    ( also spectrum analyzer)

Decibel X, dB meter Pro    (can be calibrated)
+erik_squires

I'm willing to bet a new calibrated USB mic is more accurate as well then a radio shack old style one. specially used. 
 
or just the app one may be enough for your purposes. 

that said you can get professional quality ones form various places that supply the film-studio-recording industry. you may get one from an industrial safety equipment sales place as well.