Spek is a simple Mac program that immediately gives you access to the spectrogram representations of your audio files. The application comes with a user-friendly interface, works with a wide variety of audio formats, and allows you to export the resulted spectrogram as an image file to your local folders.
All you need to do is to click over the button from the upper-left side of the interface, select the sound file you need to analyze, and the program will take care of the rest.
In my testing, I imported multiple sound files (OGG, MP3, and M4A). The program immediately generated the spectrogram representations I needed, without slowing down the performance of my system in the process. However, the application occasionally ran slow, especially when importing audio files. Another thing that's worth mentioning is that you can export spectrograms to only one file format: PNG.
Still, the application comes without a price tag and provides you with accurate results. I'd say it's definitely worth a try if you're looking for a simple and quick way to generate the spectrogram representations of your sound files.