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Friday, July 20, 2012

Making the Good Better: NHT 1.2 Speaker Upgrade

A friend who reviews speakers once described the NHT line of speakers from the 1990s as "nothing special".  Of course, he was used to listening to $6,000 speakers, so his perspective was slightly skewed.

In fact, the smaller line of NHT bookshelf-size speakers (1.2, 1.5 etc.) were a stunning innovation and an incredible bargain for their time.

 State-of-Art Cabinets

In an era where speaker cabinets were typically made of formaldehyde chip-board covered with plastic 'wood finish' mactac, the NHTs were shocking in their high-quality materials:  heavy density MDF, and a 7-layer black finish coated with car-paint clear-coat.  This resulted in a near bullet-proof piano finish rivalling a Steinway or Yamaha baby grand.

Secondly, the heavy cabinet weight and inertia gave a razor-focus to the sound-stage.

Furthermore, the design itself was innovative, with a built-in 22-degree inward tilt to the front baffles, making the ideal angle for cabinet placement a snap, and allowing the cabs to blend tidily with a rectangular room, and point toward the listening area.

This design gave the added genius-bonus of eliminating standing waves from  front to back of the cabinet completely! (The front and back are the pair of walls with the strongest potential, being directly driven in line with the woofer).

High Quality Drivers

Also, given the price-point ($399 - $800), at the low (more popular) end of the high end hi-fi market, these speakers offered a surprising sound quality and clarity, mainly because of the very high quality metal-dome tweeters, stunning in comparison to speaker systems of previous eras.

The weakest point in the design was the very simple (1st order) crossover, simply an air-coil and an electrolytic capacitor (4.7 uF for the 1.2 model). 

Its unfortunate however, that the NHT woofers of the 1990s suffer from that so common malady, deteriorating foam surrounds, a result of the foam type and manufacture available in those ancient 'Dim Times'.    Some 12-20 years later, the surrounds on most NHT woofers are either falling apart or ready to go.

One could simply have the woofers re-surrounded, but at about $50 a pop in most repair places, replacing them with new woofers might be a better bargain.  (Labor is as always, the most expensive component of anything.)

Yet it would be ludicrous to simply cast these lovely well-made cabinets away. 

What better time than now, then, to replace the drivers and crossover, and give them a whole new life for another 10 - 20 years as the ultimate near-field monitor!

Better than the Original Drivers

I turned to a local celebrity, Frank Fabian (designer of the Max Fidelity line of speaker drivers and systems).  He immediately understood the problem, and suggested a more state of the art and much higher performance woofer and tweeter combination, which would allow the minimum alteration of my original 1.2 model cabinets:

MF165/77L8 Max Fidelity woofer (Fabian Acoustics)

T26AFF5neoB Max Fidelity tweeter (Fabian Acoustics) with Neodymium magnets!

I had already had a wonderful experience using Mr. Fabian's Max Pentivent 10" subwoofer (PV-1050/4) in a pair of Tannoy-style cabinets.  These amazing drivers are rated at a conservative 240 watts RMS, or 480 watts peak power, but at normal control-room listening levels (100 watts) appear virtually distortion-free!  The design of those drivers incorporates five different venting methods for the most efficient cooling possible.

Installation of Drivers

All that is required for the woofer is to shave off a small amount of the inside rim of the speaker-hole to allow for the heavy cast frame of the new driver.  The tweeter-hole similarly needs a bit of rasping to allow for the Neodymium magnet. A new gasket, and pilot holes for the screws, and voila. 

Here is the new look:

Finally, Mr. Fabian offered a modification of the original crossover, which allowed re-use of the existing coil, and replacement of the original (electrolytic) capacitor with a proper polypropylene capacitor network with proper amplitude adjusts.  We made the appropriate mods and plugged in these reborn near-fields for a test-listen.

The result is neither an original NHT speaker, nor a true Max Fidelity design, but a great home-modification for the novice.

It wouldn't be right to leave the cabs appearance as if they were actually still NHTs, so we carefully removed the original stickers on the back, and the grill logos, and placed the Driver decal on the back.   

Test Results:

Fabulous!  We have now replaced our regular near-fields with these Rubies!
Sparkling clear and open soundstage.  An order of magnitude better than the original NHT cabs. 

Contact Mr. Fabian at  The Speaker Shop (Toronto), if you are interested in doing this mod to an old pair of your NHT bookshelf speakers!

- Naz

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