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Old    Curt Bowman (curt489)      Join Date: Feb 2008       04-14-2010, 6:44 PM Reply   
I have some 6x9 aerial tower speakers and they read 4 ohms on the back and the in the manual. When i ohm them out through the my tower speaker wires they ohm out a 3.3 ohms. I wired them up to my four channel sony amp( specs below) and they didn't work. So i put them on the bridged terminal they worked for about 10 mins of playing hard on them and i blew a fuse.

On the other side of the amp i have 2 6.5" polk dbs 4 ohms each on a channel by themselves and they were doing fine.

My questions is why would these speakers be reading 3.3 ohms? And should this sony amp be able to push these four speakers?

Sony marine amp
Class AB
Channel Operation 4
RMS Power @ 4 Ohms 4 x 60 Watts
RMS Power @ 2 Ohms 4 x 70 Watts
Total RMS Power 280 Watts
Peak Power Output 440 Watts
Minimum Impedance Unbridged 2Ohms
High-Pass Crossover Frequency 80 - 20,000Hz
Low-Pass Crossover Frequency 80 - 20,000Hz
Signal-to-Noise Ratio 97dB
Frequency Response 20 - 20,000Hz
Input/Output
Fuse Rating 2 x 25Amp
Old    Clotus (clotus)      Join Date: Mar 2009       04-16-2010, 10:32 AM Reply   
I am not totally sure, but I think we could all use a little more information. How are you running the speakers, one speaker per channel? it is a 4-channel amp so you have two polk speakers on two channels and two 6x9 on two channels correct? A stab in the dark, maybe the polk speakers are more efficient so you hear them and the 6x9s are getting enough juice. Have you tried removing the polks and turning the gain up (assuming its one gain for all 4 channels).
Old    Earmark Marine (david_e_m)      Join Date: Jul 2008       04-16-2010, 12:19 PM Reply   
Curt,

You are measuring DC resistance with a meter which is very different than the AC impedance used in the specs.

Its normal for the DCR to run lower than the nominal or averaged impedance which varies with frequency.

3.3 ohms DCR does seem a tad low. Some speakers cheat a little to draw more power and sound comparatively louder in the display board. When you go to bridge your amplifier or run two speakers in parallel, an inordinately low impedance can cause amplifier thermal and stability issues. Additionally, a Sony amplifier is decent but it certainly won't compare to similarly rated amplifiers from the more respected domestic brands. So run it conservatively. From your description however, it sounds like you've got another issue as to why the speakers wouldn't originally play in stereo.

Do not run a combination of bridged and parallel if you plan on keeping that amplifier for a while.

David
Earmark Marine

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