Hey all, I'm the owner of the defective speaker.
I'd like to present my side of this for balance.
Some facts regarding the amplifier used to test the speakers:
The GrandHigh A280 power rating according to the user manual is as follows;
120W ( 1Khz 2% T.H.D. 4Ω )
I believe that's an EIA (Electronic Industries Association) rating of a single channel driven in short bursts (usually microseconds) at a mid-band frequency (in this case a 1Khz sine wave) to clipping at 2% THD on a 4Ω load.
That's pretty much the best an amp can perform under ideal conditions over a very short time. However, that rating is often and unfortunately used as a headline figure which manufacturers push to inflate an amp's power capability.
You'll never get that in the real world as an amp has to drive speakers (2 channels) across a bandwidth, usually 20Hz-20KHz, at much lower distortion (0.01%).
The latter is the FTC rating that gives you the average power (RMS) output for both channels running over a wide frequency range at lower distortion levels. A much more conservative and true rating with figures usually 10-30% lower than the EIA rating.
So the GrandHigh A280 rated at 120W under ideal conditions, would now realistically only put out about 100W per channel at full bandwidth into a 4Ω load.
The A280 has a fairly robust power supply (a 1200W transformer) so it can be inferred that the power output would double as impedance halves, or vise versa. So the amp rated at 100W RMS into 4Ω would put an average of 25W into a 16Ω speaker - that again is with each channel driven to clipping.
Now the Goodmans Triaxiom 212C speakers are 16Ω and rated at 15W RMS, or 30W maximum. The speakers have an unpublished sensitivity rating but are generally thought to be around 100dB/1W/m.
As it happened:
I received the speakers via a friend of the seller's (delivered for a fee) transported in a van and lying on their backs.
I placed them in the listening position and connected them to the amp via my existing speaker cables straight to the attenuator units (the cabinets have push fit and easily removable ARUs mounted below the triaxial drivers which gives access to the inside of the cabinets and to the hole in the back of the cabinets via which the speaker cable was fed through to the attenuators).
I switched the amp on with the volume down - as per good practice I always turn the volume down before powering any amp off. It has a soft start of about 10 seconds before coming on.
I cued up a vocal track which I thought would be a benign test, pressed play and slowly turned the volume up. I was less than 3 foot away from the speakers.
I'm confident I didn't exceed more than 65dB at that distance as my general listening position is 12 feet away and I listen at 80 dB most of the time - my party days are long gone.
At that level I'm pretty certain that the amp was only putting out a couple of watts.
Almost instantly I noticed the imbalance in output - the 'left' speaker sounded weak so I put my ear right up to it and listened - I couldn't hear any bass at all - just the treble and mid units were working. I immediately checked the right speaker and that seemed just fine.
I removed the ARU from the left speaker and reached through the port and to the back of the driver to feel if the cone was vibrating - nothing.
All this took hardly any time - it was that obvious that the woofer was *dead.
I heard no thump, no scraping or rattling while the speakers were playing.
I turned the volume down and switched the amp off.
Disappointed, I called the seller to tell him.
*I have since removed the faulty driver from the cabinet and using a voltmeter measured across the driver's terminals. It measured 8.4Ω - it should be around 15-16Ω - which was confirmed by the working driver - it measured 14.9Ω. I then inspected the driver for any loose wiring - there was none.
I pushed down onto the cone to check the freedom of movement of the voice coil and was met with some resistance and a scraping sound. This all confirmed that the voice coil was blown.
The eBay ad stated that the speakers were "in good working condition". However, the speakers were run in conjunction with a set of Goodmans Triaxiom 301s (Impedance is unknown as they came in either 8Ω or 16Ω). Is it possible the seller didn't pick up on the faulty driver as the sound was masked by the other pair?
Is it possible the driver was damaged during transport - a mechanical failure due to shock? After all it was a 60 mile journey in the back of a van.
How likely is it to blow a woofer at low listening levels playing a program with limited peaks and particularly small low-level frequency information over a period of 5 or so minutes?
How much more likely is it that the speakers were overdriven by the seller's Quad 303 amp which is rated at 28W RMS - remember the 212C drivers are rated at 15W RMS?
This set-up was run "for many many years" at unknown output/listening levels. The seller has told me though that this is the second pair of Goodmans drivers he has installed in the cabinets as he "had damaged my first set on to(sic) many watts"
Sorry for the long-winded post but I feel it was necessary to get all the information out. Apologies also if this comes across as an eBay spat. I hope there's enough take-away to inform other members about the perils of buying untested speakers.
Looking forward to hearing your feedback. Thanks
TL;DR - Never buy second-hand speakers without a displayed impedance reading.