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Two NAD 2200 bridged amps w/6 ohm speakers - OK?

My brother-in-law has lent me two NAD 2200 power amps and my current two-channel setup includes two Thiel CS2 speakers - 6 ohms and efficiency of 87 (I forget the units). My high end dealer here in town told me (when I thought I had 4 ohm speakers) to not use these amps in bridge mode with 4 ohm speakers, that the NAD amps would not like seeing the 2 ohm load. (And then, I've read in one forum the offhand remark that these amps are stable down to 1 ohm.)

Well, I have 6 ohm speakers, should I go ahead and try the amps in bridged mode? If I keep the volume at low to medium, will I mitigate my risk, or will the amplifiers be unhappy with 6 ohm speakers regardless of the volume? If I get too ambitious, do these amplifiers have protection circuitry, or will they just fry? How will I know if the amps are starting to complain - heat? Any chance of damaging my speakers before an amp shuts down?

Also, these speakers seem to spend most of their "time" between 7 and 9 ohms (see chart in this article:
http://www.stereophile.com/content/thiel-cs2-loudspeaker-measurements ). Is the fact that at most frequencies the speakers are above 6 ohms of any benefit?

I've searched many forums for several hours, for three or four days, but can find no info other than if one uses 8 ohm speakers with these amps in Bridge mode, one will certainly be OK. So, if anyone has experience with using these amps with 6 ohm speakers, or know what to try, not to try, how to be careful - or just want to recommend: don't do it! - I'll be glad to hear your suggestions. (Except, bi-amping is not an option with these speakers- that would have been too easy.)

THANKS very much.
delsfan
5 responses Add your response
2002ss335
84 posts
 
I never tried using the 2200 bridged when I had a pair but from the manual.

Note: in the bridged mode the loudspeaker’s impedance is effectively halved as “seen” by the amplifier. An 8-ohm load looks like 4-ohms, a 4-ohm load looks like 2-ohm, and a pair of 4-ohm speakers operated in parallel will look like a 1-ohm load. Driving paralleled low-impedance speakers to high levels may cause the amplifier to overheat and shut down, or cause internal fuses to blow in order to protect the amplifier. For best results the bridging mode should be used with a single 4-ohm or 8-ohm speaker in each channel.

If you try it start with a low volume and feel how hot they get. Most of the NAD manuals can be found here:

NAD

Regards,
Todd
hifihvn
943 posts
 
For best result the bridging mode should be used with a single 4-ohm or 8-ohm speaker in each channel.

I wouldn't use anything less than the 8 to 16 ohms,like it states on the back of the amp.Link to NAD.[http://nadelectronics.com/content/100420124039-NAD2200.pdf]
systembuilder's avatar
systembuilder
111 posts
 
I personally wouldnt recommend trying them out running 3ohms as my first thought is that you could possibly strain capacitors and run the life of them down signifigantly, but it sounds to me like a soustained high power 3ohm load that has to dip lower is like building a diesel truck up to 1000+ FT. LB. of torque and not installing a new transmission or torque converter IE. it blows the tranny quick, it will handle it for a bit but it wont do it for more than 20% of its standard life.

I dont know that this is true with amplifiers but it seems more logical to upgrade to a stereo amp as it allows you more flexibility in impedence dips and with speaker choices.

Also Believe it or not Speaker modification is possibly an option. I have had my celestions upgraded years ago with all new capacitors, internal wire, and binding posts for a very reasonable price. If you are in the SF BAY look up Soundscape AV in santa rosa and ask for there tech.
almarg's avatar
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almarg
9,670 posts
 
As shown on the last page of this datasheet the 2200 is rated to deliver considerable short-term power into a 4 ohm load (which would be seen as 2 ohms) when in bridged mode. It is not rated to deliver continuous power into a 4 ohm load when in bridged mode.

So I suspect that at the low to moderate volume levels you referred to there would be no problem (the lower volume levels will mitigate the risk, to answer your question). But on the other hand, if you will not be listening at high volume why bridge? Just use one amp in stereo mode, particularly given that the amp has extremely high dynamic headroom (interpolating from the specs, probably about 500 watts of short-term power capability into the speaker's 6 ohm nominal impedance).

Regarding your question about the fact that the speaker's impedance is higher than 6 ohms in much of the spectrum, what is most important is its impedance in the bass and mid-bass regions, since for most music those frequencies require the most power. The speaker does reach its minimum impedance within that part of the spectrum.

Regards,
-- Al
delsfan OP
19 posts
 
Fabulous, thanks for your responses. I'll try it in stereo mode and think maybe about getting either better monoblocks or a Superior (expensive) stereo amp.

Al makes a great point: if you aren't going to play it too loud, why bridge at all.

Thanks again.
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