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Old 7th November 2004, 05:15 AM   #1
r0cket- is offline r0cket-  United States
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Default Upgrade or replace NHT Model Ones?

My main system is currently comprised of a Rotel RCD-950 feeding a Rod Elliott P88 preamp to a Classe CA-101 power amp and NHT Model One bookshelf speakers. I'm pretty happy with the system for the most part, though I'm starting to get that itch to do something new with the speakers.

My budget is fairly limited, which brings me to my question--

Given a budget of, say, $200 or less for drivers and crossover, am I likely to build something that will perform better, overall, than the NHTs? My listening is done mainly to ecclectic rock and folk and the like and is usually nearfield. I have the option of integrating a 10" Paradigm sub, and I don't have a preference as to whether I end up with stand-mounted "bookshelf" units or floorstanders, though I'd prefer a design with a fairly simple cabinet. I'm just trying to figure out if the final product on that budget would put my current speakers to shame, or whether I should look at some upgrades for the current units (rebuilt crossover, any other tweaks anyone can think of, etc).
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Old 7th November 2004, 07:01 AM   #2
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Default DIY upgrade first.

Hi r0cket-,

Most speakers can be upgraded to sound MUCH better than they sound in stock form.

1. You can stiffen the cabinet with braces if needed . The braces must not take up too much volume.

2. The inductors must be measured and changed to air core coils.

3. All capacitors should be changed to a good quality film type with a voltage rating of at least 200 volts.

You will find that higher voltage caps can handle HF better. Doesn't seem to matter at af by measurement, but sounds better.

4. Change all resistors to non inductive types.

5. Decent internal wires . I don't use exotic types . Lengths are too small .

6. All joints are soldered. No oxidizeable plugs.

7. Crossover to a sub at a low frequency - 70 to 90 Hz ? Determined by the speakers LF performance.

8. If the speaker is ducted , seal it and try to run it with an active high pass 12db/octave crossover . You can electrically determine its frequency response at lf and design a suitable crossover.

As a simple start , you can split the crossover and make it biwireable. You will need to change the speaker input terminals to a biwireable type which you can easily get in the market.
Component change and biwiring will make a huge difference.

Next will be biamping .
And last will be active crossover with no passive crossover components - a huge jump in performance.

After all that you might want to look for a better speaker . Might find your system better than a lot of expensive ones !

Get your working clothes on and get cracking .
Cheers,
Ashok.
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Old 7th November 2004, 07:32 AM   #3
r0cket- is offline r0cket-  United States
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Default Re: DIY upgrade first.

Yeah, I was thinking that if nothing else, even if I do end up building new ones, it can't hurt to improve the sound of these.

They're sealed, stout boxes, so that eliminates a couple of those options. I've thought about bi-amping, but it just doesn't seem like it'd be worth it, since they're just simple 2-way bookshelves and I think the money I'd spend on an active crossover and another power amp would be put to better use just building/buying some better speakers.

The bi-wiring sounds like a decent idea, though, as do the crossover upgrades. I'm considering some sort of active crossover to separate the LF signal before it gets to my power amp. The sub has its own crossover, of course, but just between its input and power amp, so my NHTs are driven full-range even with the sub hooked up.
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Old 7th November 2004, 07:45 AM   #4
r0cket- is offline r0cket-  United States
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Well, upon further review, there's not much of a crossover to upgrade--the woofer is driven full-range and the tweeter just has a 10W 4 ohm power resistor and 4.7 mf cap in series, both of which should be easy enough to replace.
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Old 7th November 2004, 08:00 AM   #5
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Hi r0cket,
You can still biwire the speaker since the amp will be direct coupled you can easily make an active crossover to experiment.

A chip power amp ( a Gain Clone ?) can drive the tweeter ( later ).

So to conclude.
Bi wire the unit.
Use good quality caps and non inductive resistors.
Bi wire the unit to the amp and see how it sounds.

Removing LF from the woofer will improve the midrange and sometimes the treble. So LF roll off does help . You better try that out . In some systems the difference is huge. Here the crossover can be active. To start with a simple capacitor at the input to the power amp will give you a 6db roll off to see if there is any improvement.

You will not only get cleaner sound but they will play apparently louder with ease. The sub should be good.
Cheers.
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Old 8th November 2004, 01:05 AM   #6
r0cket- is offline r0cket-  United States
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Regarding the crossover, I'm considering using a Solen polypro cap and Dayton power resistor from PE. Would it also be beneficial to bypass the Solen with an Audiocap or Dayton film and foil cap, and if so, what value should I use?
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Old 8th November 2004, 07:53 AM   #7
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Default Crossover

So few crossover parts! I doubt you will see much change at all with the upgrades.

I would build a pair of good subs to use directly under each one.

Something like a 10" or 12" Peerless. It will make a Big difference in both the bass and the mids.

Sound like a new system.

Tim
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Old 8th November 2004, 10:05 PM   #8
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How much is another Paradigm?
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Old 8th November 2004, 10:34 PM   #9
SY is offline SY  United States
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The NHT is built with a somewhat different philosophy than normal. The designer felt that most of the work of the crossover was better handled mechanically, through careful driver design. If you go in and start replacing parts and modifying the crossover, chances are you'll end up with something much more colored- the speaker is already pretty neutral, just lacks extension and the last word in detail. Subwoof it properly (a biamp approach) and you'll have to spend a PILE more money to get better results.
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Old 9th November 2004, 07:35 AM   #10
r0cket- is offline r0cket-  United States
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Tim- Another Paradigm sub would be fairly spendy (they're going for $200-$300 on eBay right now). Bass isn't that big of a deal for me, I just find the NHTs a little lacking in that regard, though still impressive for their size. I have an old sub cabinet here I may end up doing something else with, though.

SY- Before I got these, I had been considering some Axiom speakers designed around a similar principle. It seems fairly sound, anyway (er, sounds good to me, at least). I'm considering some sort of high-pass on the woofer, though, to ease the transition into the sub. Supposedly these things are good down to around 63Hz, and the lowest I can cross my sub over is 100, so I'll have to see how awkward that sounds when I have it all hooked up. I think probably the most important thing I need to do at the moment is get some decent stands for thems, though. I have a feeling the sound will tighten up a lot if I can get them properly mounted.
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