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In the Forum: Audio Discussions
In the Thread: Mastodont DIY Rack: Wall Mount?
Post Subject: Floor ResonancesPosted by Paul S on: 12/2/2013
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N-set, you may remember that from the beginning I encouraged you to try a wall mount, for all the reasons you have just cited, and this approach seems even more obvious if the walls are concrete/masonry vs. floor joists and sheet subflooring, not to mention open joist bays. A stethoscope will tell you broadly about noise in the frame, but it will take spectral analysis to narrow it down. A cheap pick-up should work, but you will probably have to figure out and write a curve for it, if it will do <20 Hz in the first place. The idea with spikes is not to couple directly to a wood floor system but to couple directly to an effective interface between the rack and the wooden floor system; that's why I suggested you try felt. Various band pass "breaks" like bladders, etc. should help with 20 Hz, but (of course) they may result in other mostly ULF motion(s). Naturally you are only ultimately concerned with output from the device or devices that sit on the rack. I can tell you that long-span floor joists often have very persistent vibration, both primary and modal, so good luck coupling to a wooden floor system. It is generally better near the walls as far as primary resonance, but all bets are off for cavity and modal resonances.
Best regards,
Paul SRerurn to Romy the Cat's Site