Ohms - Impedance question

Audio experts, help me out here. My receiver (Yamaha 2095) has a setting for either 4 or 8 ohms. All of my speakers except the center allows for 4 ohms, but are 8 nominal. I have everything set to 8. The problem is my center only does 4 and 6. Is there anything wrong with running 8 ohms from my receiver to it?

Han,

I'm not familiar with the Yamaha 2095, but in general a 4ohm load is less of a resistance to an amplifier, so the amp will be able to produce more wattage. OTOH, a 4ohm load is somewhat demanding and if the amp can't handle the lower resistance it will run hot and clip(distort) at high output levels. 8ohms is the usual resistance of most speakers(and an easier load for an amp to handle) and receiver manufacturers design their amps that are built into their receivers with this in mind.

It sounds like your 2095 has been designed to handle either load(but this can be tricky since a speaker may be RATED at 4ohms, but may actually dip into the 2ohm or lower range for some frequencies, which is usually far to tuff a load for a receiver's amp to handle continuously). I'd try both settings and see which sounds best. You'll probably have to calibrate SPLs for each setting since you'll get different output levels with the different impedances.

BTW, what type of speakers are you using?

Hope this helps,
James M.

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HT equipment: Pioneer Elite Pro-100 RPTV (ISF calibrated)
Lexicon DC-1 pre/pro, Sunfire Cinema Grand amp, Adcom GFA-555II amp, Legacy Victoria L/R speakers, Legacy CinemaII center channel speaker, M&K SS150THX side surround speakers paired with Atlantic Tech. 162PBM subs(2), Def. Tech BPX rear surround speakers, Velodyne F1800II sub., Sony HiFi VCR, Denon DCD-1500 CD player and DVD-3000 DVD player, NAD 1600 pre/tuner (used for powering up the system and radio reception only), Power Pack V line conditioner/enhancer, Adcom Ace 515 line conditioner/enhancer, LAT and Monster speaker cables, assortment of AudioQuest, Monster and XLO interconnects, various forms of component vibration isolation and room treatment

-Energy ES 12XL sub
-Energy AC 300 center
-Energy C2 mains
-Energy eXL 15 rear surrounds
-Energy eXLR front surrounds

Yeah, for some reason, the AC300 center speaker is the only one that's 4 ohms minimum and 6 ohms nominal. The rest are 4 min, 8 nom.

Well, Han, the Energys probably wouldn't be a problem for your Yamaha receiver in either mode: 4 or 8 ohm. But since they're rated at 8 ohms nominal I'd guess that you wouldn't hear a big difference between the two(except the 6 ohm center channel speaker might go a little louder in the 4 ohm setting).
One thing though, if you listen at pretty high volumes you'd probably be better off sticking with the 8 ohm setting. The 4 ohm setting may put the amps into "overdrive" causing them to shut down when over heated.

Still if it were me, I'd try both to see if it does make a difference. Even if the amp section does get hot and shuts down, no permanent harm should result and once they cool down everything should work normally.

Years ago I was using an Adcom amp, the GFA545, which put out 100 watts/channel into an 8 ohm load. I was driving a pair of Mission towers that were pretty inefficent (86db SPL 1 watt at 1 meter) and 4 ohm to boot. The 545 clipped at high volumes and then shut down for about 5 minutes. When it came back on it was fine. I still ended up getting the 200 watt GFA555II amp so I could have a little leeway during the times I wanted to crank it. Still glad I did, it's worked without a hitch for almost 10 years now.

Good luck, Han. Hope this has helped.

James M.

[This message has been edited by James M (edited 09-07-1999).]

Thanks James. I've tried it both ways now on the receiver and things seemed fine. Since I already have all the volume balance and delay settings to my liking at the 8 ohm setting, I'll stick to that. I guess since nothing wrong has happened in about a year now, I'm fine.