Questions about ghost sound

[Dunditschia]

The ghost sound description says "Ghost sound can enhance the effectiveness of a silent image spell."
But silent image itself says it has a duration of "concentration", and you can't cast a spell while concentrating on one. So is there some mechanic to combine the two, or am I just supposed to have an illusionary sound appear a round before the illusionary image?

Also, if used to complement a silent image like that, would that give someone who interacts two separate will saves, or just one for the whole illusion?

If anyone knows some cool uses for silent image and ghost sound in general, I'd be happy to hear them too.

Edit: I should have specified, this is 3.5

[Nibbens]

The ghost sound description says "Ghost sound can enhance the effectiveness of a silent image spell."
But silent image itself says it has a duration of "concentration", and you can't cast a spell while concentrating on one. So is there some mechanic to combine the two, or am I just supposed to have an illusionary sound appear a round before the illusionary image?

Also, if used to complement a silent image like that, would that give someone who interacts two separate will saves, or just one for the whole illusion?

If anyone knows some cool uses for silent image and ghost sound in general, I'd be happy to hear them too.

In Pathfinder at least, there are several image spells. Silent Image (http://paizo.com/pathfinderRPG/prd/spells/silentImage.html#_silent-image), Minor Image (http://paizo.com/pathfinderRPG/prd/spells/minorImage.html#_minor-image) Major Image (http://paizo.com/pathfinderRPG/prd/spells/majorImage.html#_major-image) Persistent Image (http://paizo.com/pathfinderRPG/prd/spells/persistentImage.html#_persistent-image) Permanent Image (http://paizo.com/pathfinderRPG/prd/spells/permanentImage.html#_permanent-image)

Each one beyond "silent image" has a longer duration than just "concentartion" says something to the effect of "Functions like silent Image with the exception of X." So I think what's happening here is that Ghost sound could make any "image" type spell (whenever you're not concentrating on it) seem more convincing. (As a DM i'd say a +1 or +2 added to the DC to disbelieve the illusion - depending on how creative the ghost sound is used, but that would vary from DM to DM, i think.)

Ghost sound + ability to speak goblin + goblins holed up in a room. If the PC's entered they would be at a disadvantage. So I used ghost sound to speak in goblin "CHARRRRRGE!" All the goblins came running out the room into our waiting barbarians axe. It was nice. lol.

[Jeff the Green]

Two things. There are a couple of ways to make silent image last longer than concentration, though as far as I know none were in place when that flavor text was written. Second, you can cast ghost sound first. It's situational, but a 1st level spell and a cantrip is a lot less to expend than a 2nd level one.

[Duke of Urrel]

Jeff the Green made an excellent point: Cast the Ghost Sound spell first.

I believe combining the Ghost Sound spell with the Silent Image spell enables you to duplicate the Minor Image spell for as long as both spells remain in effect. Indeed, when I'm the DM, I even allow you to raise the save DC for this combination of spells to 12 plus your relevant ability modifier – the same as the Minor Image spell would be.

I believe the Ghost Sound spell becomes especially useful once you have gained the power to turn yourself invisible. While you stand still, you can use the Ghost Sound spell to make the sound of footsteps leading away from you.

[jedipotter]

The text is a hold over from 2E, back when Silent Image had a duration. Remember that Wizards could not be bothered to Edit anything, because that would have taken someone like a whole day. The Ye Old duration was ''special''.

You could cast one spell quickened or have your famailair take over the spell...

[ericgrau]

I believe the Ghost Sound spell becomes especially useful once you have gained the power to turn yourself invisible. While you stand still, you can use the Ghost Sound spell to make the sound of footsteps leading away from you.
That's clever. I gotta use that one some time.