Metal speaker cabinets - damping or just embrace the ring?

I built a small pair with folded aluminium skins about four years ago and I'm firmly in the damping camp. The panels absolutely rang. I measured a big peak around 400 Hz just by holding a cheap measurement mic inside the cabinet and tapping the side wall. The bass reflex tuning itself was fine but that panel mode coloured everything I played. I stuck automotive bitumen sheets on the inside, two layers on the side panels, one on the back, and the peak dropped to almost nothing. Voices went from slightly honky to clean in a single afternoon of work. The stiff box arguement is real as far as it goes, but stiffness only helps if the panel resonances sit above where your driver and crossover matter, and with thin folded sheet they ussually do not. You can brace, but every hole you cut in folded metal weakens the fold and adds cost at the shop. My suggestion is to build it as planned but budget for damping from day one. Buy the pads before you finish the cabinet so you are not tempted to ship it bare. Also mock up one panel with a temporary baffle and play pink noise through it before committing, you will hear instantly whether the metal is talking over the driver. It is not a headache of a build, it just needs that extra step that an MDF box never asks for.

I lean the other way from the damping crowd, but with a catch. I built a small pair from folded sheet a couple of summers back and instead of gluing pads everywhere I ran an internal frame from aluminium angle, bolted through the folds with rubber washers between the skins. Tapping test afterwards was dead and thumpy, no ring at all, and the cabinets came out much lighter than anything I could have made from MDF.

The catch is that the folds themselves are the weak point. My first version had a seam along the back edge that buzzed like crazy at certain frequencies untill I packed it with silicone and re-torqued the rivets. The flat panels were never the problem, the joints were.

Honest take though, if you are on the fence alredy, the sandwich idea might be the sweet spot. Metal skins over a plywood core gives you the look you want and the stiffness for free, and it is way more forgiving for a first build than bare folded sheet.

For me the game changer was a cheap mechanic's stethoscope, a few quid from the auto parts shop. I built a single skin aluminium cabinet years back and could not work out where the ringing was coming from until I pressed the probe against diffrent spots while playing bass-heavy tracks. Turned out the worst offender was not the sides at all, it was the top panel right above the driver. Padded the sides out of caution and the top got the thick treatment, problem gone. So before you commit to a layout, poke around and let the cabinet tell you wich panels are actually the loud ones. Sometimes it is not where you expect.

I did the sandwich thing on my second pair after a bare sheet first attempt that drove me mad. Two thin skins with a timber core between them, glued up flat on the bench before the panels went to the folder. Knocked on them dead as a doorknob from day one and I never touched a damping pad. If your friend can fold the outer skins anyway, ask whether he can also laminate a ply core to one of them before bending, saves you the whole argument. Only thing to watch is the glue needs a full cure before folding or the skins can lift at the corners.