Which was louder, SRBs or SSMEs?

Question

The space shuttle's SRBs each produced ~2x the thrust of the three main engines. Which source produced the majority of the sound volume at liftoff?

Answer 1

Submitted as a somewhat subjective answer - you never know what sound editors did.

These are two clips from the early shuttle IMAX file The Dream is Alive. This agrees fairly well with my experience of hearing the more white-noisy main engines followed by the louder crackly, snappy rumbling of the solids.

There are significant differences between the sound in the two clips, perhaps due to microphone placement and characteristics, or ?

Answer 2

(not an answer yet, I have yet to find SPL data for the SRBs)

Thanks to the discussion and videos it does seem that the SRBs are louder. However, I had a vague notion that turbulence was important, and Reynolds number scales with jet velocity.

The paper "Arenas, Jorge P., and Ravi N. Margasahayam. "Noise and vibration of spacecraft structures." Ingeniare. Revista chilena de ingeniería 14.3 (2006): 251-264." appears to be an excellent review of the principles involved.

A quote:

"The total acoustic power radiated by a jet exhaust is proportional to the eight power of the jet efflux velocity (between the cube and the fifth power of the jet efflux velocity for rockets, see figure 3), and the square of the jet diameter."

Figure 3 shows that the jet power to sound power efficiency is, surprisingly, actually higher for the SSMEs:

For sub-sonic flows this is apparently called "Lighthill's eighth power law".

SRB: $242 s * 9.8 \text{m/s}^2=2371\text{m/s}$ SSME: $366 s * 9.8 \text{m/s}^2=3586\text{m/s}$

Given the diameters of 0.26 m vs 3.8 m, and a pessimistic cube scaling for both engines,

$14.4 * 2371^3 \approx 191 $ GW sound power $0.0676 * 3586^3 \approx 3 $ GW sound power

So indeed, despite the much faster jet velocity, in terms of total power SRBs could win by a factor of ~20 or so.

This answer doesn't make sense however because the total power at liftoff is only about 12 GW.

It would be interesting to see how this normalizes to thrust.