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For Sale: NHT Loudspeaker drivers and amps-Discussion Thread

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#83
The NHT X1 and X2 are excellent crossovers. They have a lot of features that you regular run of the mill active crossovers don't have. If you go to the NHT website and download the X2 owners manual, it has a block diagram inside it. Schematics are available for both units.

The X2 is designed to be a general use sub/sat active crossover. It has a wide range of crossover choices and a 2nd order HP filter at 15Hz on the subwoofer output. The X1 is designed to be used with specific NHT subwoofer models. As such it has a narrower range of crossover adjustments and a high Q 2nd order HP on the subwoofer output (about +12dB at 26Hz). You need to change about 12 resistors and caps to modify an X1 into an X2. Instructions are available.

Here is a link to a new X1 I just found on Ebay. Full list on the crossovers is $350. Probably kind of expensive for the DIY market, but at $190, I think it is a great deal.

http://cgi.ebay.com/NHT-X-1-Crossov...ryZ14977QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
 
#86
Mr Trotsky,

Coming up with a power handling specification for a tweeter is very difficult. It is too much a function of the frequency distribution sent to the driver and the duty cycle of the applied power. It is easy to overdrive the tweeter at 1kHz and damage it mechanically with only 2-3W. The exact crossover frequency and slope therefore has a huge effect on the power rating. Most companies that give specifications for tweeter power handling are not talking about how much power the tweeter can take without damage. They are talking about how much "power" you can send into the input side of the crossover. Once the crossover filters out the low frequencies, there isn't nearly as much power getting to the tweeter.

A well designed tweeter can handle 50W of power for a second or so without damage. If you drive it with 50W for 30 seconds, it will be destroyed. Take a look at a tweeter voice coil sometime. It is usually a 1" diameter coil wound with very small gauge copper wire (0.005" diameter or so). The winding height is usually only about 2-3mm. Even when this is put on an aluminum former, the total mass of copper wire and aluminum former is well below 1gram! Put 50W of thermal energy into this and do the math. The temperature rise is going to be huge. Easily 100+ Degrees F.

The best solution is to use ferrofluid. This allows the heat from the voice coil to flow into the motor structure with much less resistance, so it flows faster and the voice coil heats up much less. When used with typical ceramic magnets, the power handling of a tweeter, at high frequencies (above 4kHz), can be an honest 25W RMS. As soon as you use a neo magnet in the motor, you have about 1/10th the physical mass of magnet and steel in the motor. With a neo motor, the tweeter heats up much faster than with a ceramic motor. The solution we used was to install a heatsink on the tweeter to increase the thermal mass available for the input power. We typically made these out of aluminum bar stock that was 15-20mm in diameter and about 200mm long. One end was tapped with a M4x0.7 hole. A small set screw was put in the end of the bar then this was screwed into the M4x0.7 hole in the back ofthe tweeter. The opposite end of the bar was also tapped for a 1/4"-20 hole. We made a through hole in the back of the cabinet. Then a 1/4"-20 machine screw was run into the hole and into the end of the bar. This bar performed a couple jobs. It was a heatsink for the tweeter and a brace for the cabinet. With the aluminum bar installed, the tweeters have as much power handling as any 1" voice coil tweeter made. Without the bar installed, the tweeters have a lot less power handling than a normal ceramic motored tweeter, but have the same power handling as ANY other 1" voice coil neo tweeter.

The tweeters on the sale page have 1" voice coils, ferrofluid, neo motors, fabric surround and tinsel lead out wires. When used with the heatsink, we have used virtually identical tweeters in speakers such as the VT3, which is a four way tower speaker that can play very loudly.

I hope this answers your question.
 
#89
The only way to make a proper heatsink for the driver is with a solid metal bar. Aluminum is good, since it is cheap and has good thermal conductivity. You can purchase it online from www.mcmaster.com. The cut the bar ends square, drill the small counterbore in one end and tap both ends, you really need a lathe. With a lathe, it is very easy to do.

The woofer in the photo is that from an SB1. It has nothing to do with any of the drivers on the sale page. The frame is ABS plastic.
 
#92
Amp controller

Jack, would either a SUBONE or SUBTWO controller, including their respective umbilicus cords, work with the VT-3 amp? I can see from your pic of the amp that it has a unique 'S-Video in' type receiver labeled 'FROM VT-3 CONTROLLER'. From a pic of the SUBONE controller I can just make out the same type of connection labeled 'FROM SUB'.
Thanks
 
#93
Both the VT-3 controller/amp and the Sub1/Sub2 controller/amps used a cable with mini-DIN connectors on the ends. The photos of the VT-3 amplifiers show the amplifiers as they are now. I'm actually removing the preamp card and relacing it with an RCA jack before shipping them. It would be easier for me to not do that at all and just leave the mini-DIN jack there.

I'll have to do some poking around to see if the Sub1 or Sub2 controllers will work with the VT-3 amp. At some level, I'm sure they will. You may have to cut some traces on one end or the other to make this work. You definitely will have to modify the limiting circuits in the controller and the eq to suit your particular subwoofer.
 
#94
Thanks for the info Jack.
I will be using two 12" 's with the folowing specs in a 4cu/ft sealed box.
Qts : .375
Qes : 0.49
Qms : 1.506
Fs : 25 Hz
Re : 1.8
Vas : 157 L
MMS : 90g
BL : 7.2 Tm
SPL : 89.1 dB
SD : 510 M^2
Xmax : 9.1 MM
Power max : 250w
Music power : 200w
 
#95
Jack, I will be buying one of the VT-3 amps and whether I require one with the preamp card and mini-DIN jack left in place or replaced with an RCA depends on how my negociations for a SUBTWO controller go.
Eagerly awaiting your feedback on whether or not the SUBONE/TWO controllers will work with the VT-3's amp.
Thank you!
 
#96
It looks like you can use the Sub2 controller with the VT-3 amplifier. I haven't tested the actual combination, I've just looked at the relevant schematics. You will need to modify the eq and limiting circuits in the controller for your particular subwoofer. I would just remove the limiting circuits completely. If you don't get the DIN cable with the Sub2 controller, you will need to buy one from NHT. A generic one won't work.

You do plan on wiring your drivers in series I hope? Do you know what the top plate thickness, voice coil winding height and how many layers of wire are in the voice coils? I assume they are four, but they might be two.
 
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