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IMPEDANCE
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one 8 ohm enclosure, you know you can add one more 8 ohm speaker safely (8 divided by 2 = 4). Although much less com-
mon, you could also add one, or even two, 16 ohm cabinets: two 16 ohm cabinets in parallel have the same total impedance
as one 8 ohm speaker.
To get the most efficiency out of your system with the fewest cabinets, your best choice would be to connect two 8 ohm
enclosures. Since you would be driving two cabinets of equal impedance, each will receive half the power your amp can deliv-
er. If your amplifier delivers 200 watts RMS at 4 ohms, then each cabinet will receive 100 watts RMS maximum under clip-
ping. (Clipping is the point where the power amplifier runs out of headroom and begins to distort.) If you had four 16 ohm
enclosures, each one would receive a maximum of 50 watts RMS under clipping.
Continuous clipping is very harmful to speakers, especially in a bass system: the lower the note, the longer the duration of DC
content in the clipped signal. To understand what happens under this condition, remember the example of what speakers do
when a 9 volt battery is applied to them. Now imagine what 20 or even 50 volts would do at the rate of 40 times per second!
The results can be overheating, disfiguring of the voice coil, overall fatigue, and—eventually—complete failure.
TROUBLESHOOTING GUIDE
"I'm hearing unwanted distortion through my cabinet."
This could be for a variety of reasons, but is probably being caused by one of the following three sources: 1) the amplifier, 2)
the cabinet's woofer(s), and 3) the cabinet's tweeter.
The best way to figure it out is to try and isolate "the big three." If you have access to another (working) bass cabinet, hook
your amp up to it. If things are still distorting, it's probably your amp. Consult your amplifier owner's manual for troubleshoot-
ing that piece of gear.
To determine whether the distortion's coming from the tweeter or the woofers, first put your ear up to the cabinet, play some
notes, and see if you can hear where it's emanating from. If you can't quite narrow it down, try turning the Tweeter Attenuator
control all the way down (counter-clockwise). When this control is all the way down, the tweeter is effectively "off." Play some
notes—if you hear distortion, you know it's not the tweeter (see next paragraph...). If you don't hear any distortion with the
tweeter off, try turning up the Tweeter Attenuator. It may be that you just need to find the optimum tweeter level for your bass,
amp, or style of playing. If the tweeter distorts no matter what level the Tweeter Attenuator control is set to, it's probably best
to call SWR's Service Department. The number's (818) 253-4797.
If the tweeter's off AND the amp's okay, and you're still hearing distortion, there may be a problem with your woofer(s) and/or
the cabinet's internal workings. Inspect your woofers' cones for folded edges. There's a very slight chance you have a defec-
tive woofer. Or, you may have blown one or all of them by driving them too hard. Speakers that have been overdriven are easy
to detect, and generally do not fall under a manufacturer's warranty. You should call SWR's Service Department to determine
your next move. The number's (818) 253-4797.
"I hear intermittent distortion and/or crackling coming from the cabinet."
This could be due to a bad speaker cable, or a bad speaker cable connection. First, make sure the cable is securely connect-
ed to both the cabinet and the amp (or other cabinet). If you're using more than one cabinet, check all cable connections in
the chain. If you then suspect that the problem may be a bad cable, you can use a 9 volt battery as a cable-tester. To do so,
plug one end of the questionable cable into your speaker cabinet, and then touch the phone plug on the other end to the two
terminals (+ and –) of the battery, contacting the tip and sleeve. When you connect the battery to the phone plug, a good
cable will will pass the voltage to the speakers, which will be indicated by both an audible noise and the physical reaction of
your speakers—the cones will move out. Disconnect the battery, and the cones will move back in. (Reverse the battery, and
Professional and Custom Pro Specialist Series • 23
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