Originally Posted by
geolemon
I worry about two problems...
I mean sure, check the amp. If you are only using 2 of 4 channels and it's shutting off, something is wrong.
Is it going into protect? There's usually an LED for that, even on cheap amps that would dare advertise a stupid BS number like "5000 watts!" on a 4 channel amp. Or is it actually shutting off (no power LED or protect LED lit)?
Disconnect the speaker leads, measure the ohms with a handheld meter. Even the cheapest meters will be within .1 ohm of the actual DCR. That amp should be able to handle a 2 ohm nominal load, which could measure as low as 1.7, maybe 1.6 DCR without going into protect, I would think.
Resistance DOES change with temperature, and voice coils heat up when more power is applied. It's one reason to design efficiently rather than back yourself into a corner where you need 1000 (real, RMS, non-flea-market) watts to drive a single sub...
You really shouldn't have an issue with full-range speakers - that DCR ohms measurement is key.
And of course of your ground is poor or connections aren't secure, power wire insufficient (etc) that can cause protect mode also.
But my "two problems" ISN'T that.
First - I would shoot myself in short order if I only had rear speakers to listen to!
Assuming that is temporary - Stereo means two channels and "rear" ruins imaging more often than it helps it. You won't find exotic home stereo systems with rear speakers - even home theater systems run front-only stereo mode on a stereo (or 2.1) source.
You want the sound from your speakers to arrive at your ears the same as they left the speaker. You don't want another set of speakers playing from a different distance causing phase-based "comb filtering" cancellations across the whole frequency spectrum. Google "comb filtering audio" and look at an image of how many peaks and cancellation dips that can make for.
Second thing is -
You said you are shopping for a sub. I assume this is a sedan of some sort? I only say that because you mentioned 6x9s, which are (or used to be) common for rear deck speakers. Also - if those were rear door speakers, you would have more quickly realized you were only getting sound on one side.
That said-
If you are shopping for a sub for the trunk, those rear speakers are blocking the easiest path for the sub's sound pressure to enter the cabin.
Three issues with that:
1) That energy will find other ways into the cabin - buzzing and rattling everything it beats against.
2) You'll likely lose a couple dB since it's having to pass through seat foam and deck panels, etc.
3) That pressure WILL still play ping-pong with those rear 6x9s, each beat from the sub pushing on the 6x9's cones. If you only had the sub playing, you'd see your 6x9s moving like they were passive radiators.
I'd suggest
a) ditch the 6x9s, even if you figure out the amp issue. Grille is fine, but leave the openings vacant so sub bass enters the cabin freely.
b) use the 4 channels of the amp to power a midrange and tweeter up front - assuming the amp is OK.
You'll have both better sound AND bass, and you'll have tuning options with your front speakers Xover points that could even allow them to be louder (on top of cleaner) than four speakers fighting each other.
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