I installed a similar DynoMax 17676 one in one out on my 84, and there is no resonance at any rpm. It has worked well, but I have heard that they eventually burn out, especially if used for racing. For under a hundred bucks I paid for it, I will just replace or try something different.
Here is a clip of the sound.
84 Porsche 911 Carrera Dynomax sound clip.WMV - YouTube