831857 impedance question
Hi Bjørn, I like your dipole speakers using the 831857.
I wish I had seen your project earlier as I had two 831857s lying around from an unsuccessfull isobarik project. I then decided to buy another two and go back to basics by putting four 831857s in four sealed 125 L cabinets and mount them in the ceiling of my home theatre. The cabinets are made of 25 mm thick MDF with bracing and a modest amount of foam and fluff. Apart from the heavy work of lifting the boxes into the ceiling, the building was straightforward - I had the sheets precision cut by the supplier so gluing and screwing was all I had to do.
The speakers sit in a line firing downwards into the back area of the home theatre.
Anyway my question relates to the electrical side of things. I am using a NAD C272 poweramplifer in bridge mode. On the second night of use a faint hum sound appeared twice while no sound was playing. I got up and checked the amplifier and everything seemed OK, but later the amp wouldn't make any sound. I am having it looked at but I am worried about what caused the problem and wonder if you or anyone have any comments on the problem, please?
The four 831857s are connected in series-parallel configuration - which I think means the combined impedance should be the same as a single speaker - that is, nominally about 8 ohms. If the amplifier problem was caused by the impedance being too low, the next configuration I am thinking of will be two woofers in series running to each channel in the power amp (and not using bridge mode to prevent the instability that might involve). This will present a higher impedance, although loose a bit of power by not operating the amplifier in bridge mode.
The other option would be to buy two more woofers and have six subwoofers to increase the impedance but my wife and daughter's really will think I've gone mad!
Thanks ... Peter Eriksen, Melbourne - Australia
Hi Bjørn, I like your dipole speakers using the 831857.
I wish I had seen your project earlier as I had two 831857s lying around from an unsuccessfull isobarik project. I then decided to buy another two and go back to basics by putting four 831857s in four sealed 125 L cabinets and mount them in the ceiling of my home theatre. The cabinets are made of 25 mm thick MDF with bracing and a modest amount of foam and fluff. Apart from the heavy work of lifting the boxes into the ceiling, the building was straightforward - I had the sheets precision cut by the supplier so gluing and screwing was all I had to do.
The speakers sit in a line firing downwards into the back area of the home theatre.
Anyway my question relates to the electrical side of things. I am using a NAD C272 poweramplifer in bridge mode. On the second night of use a faint hum sound appeared twice while no sound was playing. I got up and checked the amplifier and everything seemed OK, but later the amp wouldn't make any sound. I am having it looked at but I am worried about what caused the problem and wonder if you or anyone have any comments on the problem, please?
The four 831857s are connected in series-parallel configuration - which I think means the combined impedance should be the same as a single speaker - that is, nominally about 8 ohms. If the amplifier problem was caused by the impedance being too low, the next configuration I am thinking of will be two woofers in series running to each channel in the power amp (and not using bridge mode to prevent the instability that might involve). This will present a higher impedance, although loose a bit of power by not operating the amplifier in bridge mode.
The other option would be to buy two more woofers and have six subwoofers to increase the impedance but my wife and daughter's really will think I've gone mad!
Thanks ... Peter Eriksen, Melbourne - Australia