What level is this spell?

[Omnicrat]

What it says on the tin, what level does the playground think this spell should be?

Stabilizing Resonance

Level: Sor/Wiz ?
Components: V, S
Casting Time: Standard Action
Range: Medium/Long (50 ft. per caster levels)
Target: area
Duration: 5 minutes per caster level
Saving Throw: None
Spell Resistance: No

Upon casting this spell, a resonant tone is heard in the area, that quicly fades to a barely audible background hum. For the duration of the spell any attacks made against all inanimate construction (walls, roof, floor, and so on) within range (this includes the effects of a horn of blasting, a disintegrate spell, or an attack from a ram or similar siege weapon) are completely negated.

[Dionon]

I'd honestly put this at 7th level (As it negates a function of Disintegrate). Most of the reasoning behind this besides what's already mentioned, is that it's duration is very long for a negation spell and honestly it's a very powerful anti-siege spell

[Omnicrat]

Yeah, I was putting this at 6 or 7, but wanted unbiased corroboration.

That's the not building component of a lyre of building turned into a spell. I'm making a custom item that is basically the same, but without that ability, so I needed to know approximate spell level so that I could reverse engineer it's part of the cost of the item.