I'm thinking that the 9V test for resonance suggested by (IIRC) BFM might be misleading for the 212MBE I just bought.
After reading 100+ pages of posts, hearing some concerns and peering inside the cab, I became concerned about lack of damping/lining. BFM suggested a knock test and a 9V test. I'm a TB noob, so my apologies for not having the patience to respond in an optimum format with pix, etc. The three cabs I tried passed the knock test - no obvious hollowness/resonance. The 9v test consists of touching a 9V battery to the tip and sleeve of a speaker cable connected to the cab and observing ringing as contact is made and broken. The 212MBE showed a damped sinusoidal ringing, indicating resonance/underdamping. I estimate Q=5 at about 75 Hz (D2), undesirably resonant IMHO. The other two cabs were much lower Q/less resonant, at about 100-110 Hz (G2 to A2). I've used those cabs 4-5 years and have no big complaints. However, when driven by an SVT3-PRO, all three cabs, including the 212BME, were low Q, I'm guessing Q=2. That there's less resonance when driven by an amp seems consistent with the idea, borne out by circuit theory and experience, that the low source resistance of a real amp controls resonance. No doubt the SVT3 Zsource is much, much lower, and the current capability much, much higher, than a 9V battery! I haven't read everything on TB or this thread, I realize that there are more sophisticated measurements than I've made, I understand that low Q is good, cab resonances are bad, there are AES papers on lining, etc., but I suspect that perhaps too much is being made of the lack of lining in this particular cab.
I have gigged the 212MBE once so far. It sounded fine live and in the recording. It's definitely brighter than my other two Ampeg cabs, see below, but I've no objections. I suspect that a lot of frequency response detail is masked on stage. The 34 lb. of one cab is a significant advantage compared to the 110 lb. of my other two cabs!
How did I test with a 9V? By ear, first, then with a Shure beta58A mic about 4" in front of each driver into a mixer and a Mac running Amadeus Pro, which enabled waveforms, normalized amplitudes and spectra. Yes, the vocal mic has presencethe same for all three cabsthe measurement wasn't anechoic, I don't think I clipped, etc., etc. I've been playing since '65 and have a BS Physics and an MSEE, which all together with $2 will get you a latte. I just mean I'm only a noob to this forum and tried to do a reasonable quick and dirty measurement.
The cabs: 1) SVT15E, 2) SVT210HE, 3) 212MBE (4ohms).
There are 6-10 TB stalwarts whose contributions have helped immeasurably in updating my rig. BFM is one I've paid a lot of attention toI don't mean to contradict his wealth of experience and knowledge nor anyone else's. Everyone has helped out tremendously with the ratings/specs issues, which remind me of the bad old 70s days of hi-fi pre-FTC regs. That combined with the recession-induced decimation of retail stock makes it difficult to judge new cabs by ear, so TB has been incredibly helpful.
I just think that the 9V test perhaps overstates the cab resonance concerns for the 212MBE.
Cheers,
LOLeaux
