So we are talking about huge old tube-based meters, or in the case of the Fluke a fairly pricy precision meter. It would be kind of cool but cumbersome to haul around an HP 400. Is there something more like a compact $50 meter that will catch high audio frequencies, without needing to be quite so precise as the Fluke?
It is one thing to read a sine wave on a digital meter. Quite another to read a music type signal. The meter will not "average to anything close to reality.
That is why I recommend an analog movement meter. It is MUCH easier to "average by eye" with an analog meter.
The HP 400 is not a tube meter. Yes it is a good bit larger than an handheld multipmeter- but it reads a lot lower voltages-that can also be helpful-not in loudspeakers-but in signal levels.