Yet another Grounding Question-Separate 'Earth'

I strongly suggest you check with the local building department or electrical inspector before you let this electrician do any work.

The subpanel is not a separate electrical source since it is in the same building as the service. Therefore it must be grounded at the point of the electrical source which is your main panel. Regardless if you put a separate ground rod for the subpanel, you MUST ground that subpanel back at the main panel. You cannot ground anything upstream of the main circuit breaker on its own ground. In other words, add all the ground rods you want, but you still need to ground back to the main panel.

What I suggest, and what I did in my house (which I do not want to burn down), is to install a 2-pole breaker in the main panel. Run wires from this breaker to your subpanel (no main breaker required in the subpanel). Run a separate neutral from the main panel neutral bus to the neutral bus of the subpanel. In the subpanel, install a separate ground bus. This ground bus MUST NOT be bonded to the subpanel or the subpanel neutral. Run a separate ground wire from the subpanel ground bus all the way back to the main panel and join it to the ground at that point. Connect your dedicated circuit grounds to the subpanel ground bus and the dedicated neutrals to the subpanel neutral. This is effective and legal.

You cannot ground seperately, unless your jurisdiction permits it. The reason for the ground is to trip circuit breakers, as the ground becomes an "escape hatch" for short circuit current in the event of a fault. By using separate or multiple grounds, the possibility exists that a short circuit may be routed away from the breaker, causing a dangerous situation.

>>"But, and here's the really critical question- my electrician has proposed a pair of separate ground rods about 10' from the main ground for the rest of the house electrical system, and in his view, the audio system subpanel would be grounded just to these new ground rods, not connected, by ground or anything else, to the rest of the house."<<
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Find another Electrician! You may want to ask what else he is doing that does not meet NEC and your local codes.

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Gs5556's post is right from the text book, NEC. Follow his post and you will meet NEC code.
The earth shall not be considered as an effective ground-fault current path back to the source.

Many thanks to all of you, and to Nsgarch, for the timely responses. Work will be done by the book, according to Code and to Hoyle. The balanced power idea is also intriguing. I will let you know how it goes and will scream if I have questions in the midst of it. Thanks again, everybody.

Whart, glad to hear you will not be using a separate equipment grounding conductor and ground rods for the sub panel that does not connect back to the main electrical service panel grounding electrode system.
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>>"My electrician has installed a separate subpanel for the audio system which is 'upstream' even of the main breaker panel in the house."<<
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Just curious how did the electrician do this? Did he tap into the Hot conductor/s ahead of the main breaker, of the main service electrical panel? What size is the main 2 pole breaker, 100 amp, 200 amp? Did he install a new breaker and enclosure at this tapped location to protect the feeder that runs to the new sub panel? How did he connect to the neutral conductor ahead of the main service panel? How far is the sub panel from the main electrical panel? What size of wire did he install to the new sub panel? How many conductors, wires?

If the ground wire is only connected to a ground rod or an underground metal or copper water pipe, the circuit breaker usually will not trip if there is a short to ground. There has to be a connection to the neutral from the ground to trip the breaker. Power from the hot wire goes to ground and then to the neutral to trip a breaker in a ground fault. A sub panel does not have the neutral and the ground connected (bonded) together, the main panel does. If there was a ground fault or a short circuit on one of the circuits in the sub panel and there was two seperate grounding systems for each panel this is what will happen. The power will go to the sub panel ground rod and try to go through the earth and make a connection to the main panel ground rod which is connected to the neutral so the breaker will trip. You can not use the earth as a grounding conductor. The main neutral wire from the street makes the breaker trip and not the ground. Thats the reason that all grounds have to be connected together so the fault can go to the neutral and trip the breaker.