speaker-to-receiver connection question

[DaRealzG]

I have had this question in my mind for a while. I found this site today, and registered immediately. So, I finally let this one out of my chest.

I have a pair of 4-ohm impedance speakers that I wanna connect to my receiver(Aiwa AV-D57) for stereo playback. The receiver's user's manual mentions no information on a recommended speaker impedance range. The receiver came with a set of five speakers rated at 8 ohm. I know connecting a 4-ohm speaker will put more stress on the receiver, but I don't know if my receiver will handle it. I asked a guy at Aiwa technical support, and he said "the receiver will be OK, but we don't recommend that you connect them." What confuses me more is that the receiver's "set-up instruction" manual has a diagram of back panel of the receiver, which says "8ohm/4ohm" under the front speaker terminals. However, it only says "8ohm" on the actual back panel of the receiver. So, surely, the manual says it's OK to connect a 4-ohm speaker, but the receiver only says 8ohm speaker; that's an inconsistency in between product documentation and the actual product.

Generally, is it OK to do this? The receiver is like any home theater system ones with AM/FM tuner, Dolby Pro Logic, Dolby Digital, and a bunch of connectors for other audio devices.

I can't wait till I try my speakers on this receiver, but I don't wanna risk the chance to mess up the receiver.

I would appreciate any comments.


John

[woodman]

John:
The question that you're asking really cannot be answered with any certainty ... it may work out OK - then again, it might not. If loudspeakers actually had a fixed impedance, things would be a lot easier to figure and predict, but they don't. Any speaker will exhibit a range of impedances based primarily upon frequencies being handled - both above and below their "rating" figure, which is correctly referred to as the nominal impedance.

When a speaker's impedance drops too low, some amplifiers tend to upchuck their lunch - usually tripping a protective circuit (if the amp has one). If there is no protective circuit, there could be damage to the amp. Just how low an impedance any given amplifier will tolerate before it seriously objects is a total unknown. Likewise, just how low any speaker's impedance will drop is also a mystery. This makes the prediction of how any amp will react to any given loudspeaker that's rated outside of the amp's "specs", nothing more than a guessing game.

If you don't try to drive the speakers to window-rattling levels, you'd probably be OK - but don't bet your life on it!

So just what are these 4 ohm speakers that you "can't wait to try out with this receiver", anyway? Of even greater importance - what is their "sensitivity"? If they present a difficult load to drive, you might be in deep doo-doo!

[skeptic]

Hi Woody. I saw you here so I decided to drop in and say hello.

I hope those speakers are AR3As. But if they're not, they can still be a problem.

Woody is as usual right about the risk to your receiver's power amplifier output stage. Here's what I'd do. First of all you have 2 ways to go if you want to try to use it. One idea is to instally an in line fuse. You'll need a couple of fuse holders if you don't already have some. I'd try a slow blow AGC-3 of about 2 amps which would allow 32 watts into 8 ohms, 16 watts into 4 ohms. If you intend to play these loud, you might go to 3 amps but before you do, check to see if the amplifier is running unusually hot or if the sound is distorted at about the point you are about to blow the 2 amp fuses. If either are the case, you are heading for trouble. The other possibility is to install a resistor in series. I'd try a 2 ohm 20 watt resistor for each speaker. This will increase the impedence the receiver sees but waste power and cut down on the amplifier's damping factor increasing any inherent bass resonance. If these are really good speakers, they deserve a better amplifier which can handle them.

[DaRealzG]

Thank you, Woodman and Skeptic. Both of your inputs are very helpful. I'll probably wait till I get a new amp/receiver to try the speakers. If I try your method though, Skeptic, I'll post a reply to say how it went. The speakers are hand/self-built 2-way acoustic suspension design. I built an enclosure for some speakers I bought off some catalog company. I forgot specs for these speakers except that a soft dome tweeter handles up to 75 watts RMS and a 6" woofer handles up to 60 watts RMS.

John