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NHT 3.3 & 2.9 in a 5.1 system


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#1 of 7 Peter Karras

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Posted January 04 2005 - 02:00 AM

For all you users of 2.9's and 3.3's you need to be aware of something...
The design of the crossover for these speakers has the midrange and tweeter connected in REVERSE POLARITY... this is true of the AC2 and the L5, M5, M6, T5 and T6 systems as well.
This means that ANY speaker BESIDES those listed above will be OUT OF PHASE from the croosover region of the woofers(approx. 350hz) on up!
NHT recommended connecting the AC1/2.5's/1.5's/etc. in REVERSE POLARITY when used in a system with the 2.9/3.3's... the problem there is then the BASS freqencies from 350hz on down would be OUT OF PHASE.
Tho bottom line is that if you are using anything but the AC2/M6 with your 2.9/3.3's you will experience poor/indistinct imaging OR lean bass response due to PHASE CANCELLATION depending on which polarity you have the speakers connected.
Obviously the AC2 is the IDEAL choice, but the new EVOLUTION speakers utilize a similar design with slightly different crossover points.

#2 of 7 Jon W.

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Posted January 04 2005 - 06:20 AM

Interesting, never heard of this. I have NHT VT-2.4's mains and VS-2.4's for center/rears. My mains have the rear ambient drivers and are switchable so maybe they aren't like that.Posted Image

#3 of 7 Dmitry

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Posted January 04 2005 - 11:38 AM

Peter, this is indeed very interesting. I have a 2.9 + AC2 upfront and 1.5 + AC1 in the back, so I'm very likely to be affected. Can you site the source? I don't recall reading that in the speaker "manuals".
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#4 of 7 Mark R O

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Posted January 05 2005 - 07:37 PM

You can find info about this at nhthifi.comLook in the Technical section where you will find the customer forums. In the meantime Dmitry, flip the leads on your AC-2 and give a listen. By the way, this does not apply to the VT series to my knowledge.
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#5 of 7 Dmitry

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Posted January 06 2005 - 02:58 AM

Thanks, I'll check it out.
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#6 of 7 Peter Karras

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Posted January 06 2005 - 08:10 AM

I own the 3.3's & Ac-2 as well as a complete Evolution T6 system and have verified this...
In addition, the original schematics of the 3.3 & AC-2 I have show the woofer and bass drivers in positive polarity and the mid & tweeters positive terminals connected to ground(negative polarity)... the reverse polarity of the upper drivers was also stated in the Stereophile review conducted about 10 years ago.
You won't notice it drastically with the rear speakers, but anybody using anything but an AC-2 or M6 for the center is doing their ears a severe injustice.
I am trying real hard to find a nice pair of 2.9's to replace my M6 rear speakers and really get the house rockin!

BTW - NHT recommends connecting the 1.5's in reverse polarity if used as rears with the 3.3 & 2.9... if you do this, I would recommend setting the crossover in you processor as HIGH as possible for the 1.5's to avoid the issues involved with out of phase bass frequencies.
Hopefully you have an advanced processor that allows for different crossovers per channel as the AC-2 sounds great crossed over very LOW

#7 of 7 Dmitry

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Posted January 06 2005 - 08:41 AM

Thanks, Peter. Yes, I was playing with flipping over the polarity, but it was hard to notice in the rear, I don't like multi-channel music (prefer stereo) and it wasn't obvious which movie scene would be a good test. I have Integra DTR-10.5 running this system, so I'll set the crossover for the rear three as high as possible and flip them over.
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