• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

NHT Xd system and other digital active speaker systems

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#1



I got these new on closeout for $3k circa 2008 (original price was $6k). I hauled them out of the side room yesterday and hooked everything up.

This is still a great sounding speaker system!

It also measures extremely well (including impulse response), apart from a dip at the subwoofer crossover frequency when using a single subwoofer.

Spinerama measurements: https://www.soundstagenetwork.com/measurements/speakers/nht_xd/
Stereophile measurements: https://www.stereophile.com/content/nht-xd-active-loudspeaker-system-measurements

The Xd system has been reviewed a lot, but in brief, it’s a pair of very small, two-way, crossover-less satellite speakers on dedicated stands, one or two “dumb” powered subwoofer(s), and an amp/DSP crossover module (with a DEQX badge) that handles the crossover between tweeter, midrange, and subwoofer.

There are a few reasons these have been sitting idle in the side room for 10 years:

* The amp emits an annoying mechanical high-pitched whine (airborne, not thru the speaker outputs). I sent the amp in for repair, and it came back the same. Amps should not make noises of their own! I assume the noise is from the switching power supply.

* NHT abandoned this ambitious system (there is, for example, an XLR mic input on the back, never used for anything AFAIK). They then went into “restructuring”. It was clear the Xd system had no future. (NHT is back, but I don’t think they ever regained their former glory.)

* Butterfingers here managed to break the subwoofer volume level pot clean off. Luckily the level is stuck at “fulsome” rather than a too low setting. It looks like it’s a simple job of desoldering/resoldering a new pot on one of the PCBs in the subwoofer amp, but I’ve never done this in anything that actually had to work before.

So now I’m thinking of ways I can update the electronics. I believe I can measure the impulse response of each amp/DSP channel and then repurpose these in something like a MiniDSP OpenDSP 8 channel unit. Amplification might be Hypex modules or something from Emotiva. Then add one or two powered subwoofers.

Or I could put the money into a modern digital active system like the KEF LS-50W. I do worry about their QC issues, but they do seem to be in it for the long haul.

What other options are there for, say, under $3k?
 
Last edited:

SIY

Major Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
2,218
Likes
3,586
Location
Phoenix, AZ
#2
Blast from the past! I used to live down the street from NHT and got a chance to do some serious and extended listening. They were superb speakers. I think it would be worthwhile to refurbish them in the way you proposed.
 

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
18,981
Likes
19,284
Location
Seattle Area
#3
I have a set of NHT One's with their sub on my workstation. Sounds great. It was a shame to see them go sideways despite their strong brand recognition in pro world.
 

D700

Active Member
Patreon Donor
Joined
Dec 21, 2018
Messages
104
Likes
74
#4
I regret selling my NHT 1.5 based home theater system, loved those speakers.
 

Dan R

New Member
Joined
Jul 6, 2018
Messages
2
Likes
1
#5
I love my XD system. I too bought it on closeout, with the second subwoofer. It had some issues three years ago--power going on and off, flashing lights--and I sent it up to NHT to be worked on. They were terrific, fixing the problem and also changing out a bunch of resistors to bring it up to better than new spec. I think that some of the engineers that worked on the XD system are still up there.
 

SIY

Major Contributor
Technical Expert
Joined
Apr 6, 2018
Messages
2,218
Likes
3,586
Location
Phoenix, AZ
#6
I think that some of the engineers that worked on the XD system are still up there.
I think the Finnish guys who did the electronics are gone, likewise Jack Hidley. Gordon Chang might still be around, and he's very sharp.
 
Joined
Nov 2, 2018
Messages
85
Likes
45
#7
I also have a sidelined XD system. My amp/eq unit became unwilling to start-up reliably so I sent it to the factory for repair. It was better, but occasionally would get stuck in the turn-on sequence. My main issue with it was fan noise that was audible at the listening position late at night with very low level listening. When everything was working properly at moderate listening level, they were a very fine system. I am using the woofers eqed and actively crossed to a pair of CBT24s.
 

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#8
I think the Finnish guys who did the electronics are gone, likewise Jack Hidley. Gordon Chang might still be around, and he's very sharp.
PowerPhysics is the badge on the Xda chassis. They seem to be alive and still selling amp modules.

http://powerphysics.com/

Despite the noise coming from the Xda itself, I think the amp modules must take some credit for the good sound.
 
Last edited:

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#9
I love my XD system. I too bought it on closeout, with the second subwoofer. It had some issues three years ago--power going on and off, flashing lights--and I sent it up to NHT to be worked on. They were terrific, fixing the problem and also changing out a bunch of resistors to bring it up to better than new spec. I think that some of the engineers that worked on the XD system are still up there.
I wish I'd bought that second subwoofer, they are impossible to find now. I've wondered about replacing them with a pair of subwoofers from some other manufacturer and using the LFE inputs.
 
Joined
Nov 2, 2018
Messages
16
Likes
20
#10
Cool - interesting to see that there is still a presence for these. I picked up 2 of the satellites during the NHT liquidation process - presumably after they sold as many as they could at the discounted $3k price point. I think it was $250 for each monitor, which of course didn't have any xover. I got the black/brown version which IMHO is absolutely beautiful. I had Rick Craig at Selah make a passive xover as a stop-gap since my intent was to recreate the active DSP setup of the original. Had them running sporadically, but never really got a turnkey working DSP system, though. I even miraculously managed to pick up a 3rd unit including the Zaph passiver xover off the Tech Talk board, and used them as LCR for a while. (although this 3rd one was maple/maroon)
I still have the satellites, although I'm not sure what to do with them since I really don't have a spot for another speaker system. I've tried listing them for sale a couple times, but no interest at any reasonable price point and they have so much potential that I don't want to let them go for what basically amounts to the raw driver cost.

I wish I'd bought that second subwoofer, they are impossible to find now. I've wondered about replacing them with a pair of subwoofers from some other manufacturer and using the LFE inputs.
I ran mine with Dayton RSS210HF woofer modules, and thought the combo worked quite well since the 210HF can reach up high enough - it's more of a woofer than a sub. The problem with the Xds is that they roll off pretty high - about 120Hz which is much higher than the typically recommended LFE cutoff, and so you 'should' want stereo woofer modules rather than a simple mono LFE channel. Not to say that it won't work with a mono sub, just that there may be a bit of localization
 

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#11
Cool - interesting to see that there is still a presence for these. I picked up 2 of the satellites during the NHT liquidation process - presumably after they sold as many as they could at the discounted $3k price point. I think it was $250 for each monitor, which of course didn't have any xover. I got the black/brown version which IMHO is absolutely beautiful. I had Rick Craig at Selah make a passive xover as a stop-gap since my intent was to recreate the active DSP setup of the original. Had them running sporadically, but never really got a turnkey working DSP system, though. I even miraculously managed to pick up a 3rd unit including the Zaph passiver xover off the Tech Talk board, and used them as LCR for a while. (although this 3rd one was maple/maroon)
I still have the satellites, although I'm not sure what to do with them since I really don't have a spot for another speaker system. I've tried listing them for sale a couple times, but no interest at any reasonable price point and they have so much potential that I don't want to let them go for what basically amounts to the raw driver cost.
I've been looking for someone online with experience of using, say, a miniDSP as a digital crossover for the satellites and subwoofer. I'm looking specifically at the OpenDSP DAC-8, which can do both IIR and FIR filters, but don't want to pull the trigger unless I have some idea that this would be a success.

I ran mine with Dayton RSS210HF woofer modules, and thought the combo worked quite well since the 210HF can reach up high enough - it's more of a woofer than a sub. The problem with the Xds is that they roll off pretty high - about 120Hz which is much higher than the typically recommended LFE cutoff, and so you 'should' want stereo woofer modules rather than a simple mono LFE channel. Not to say that it won't work with a mono sub, just that there may be a bit of localization
Good to know the Daytons worked well, thanks.

Yes, with one Xdw, there is sometimes a sense that you are losing localization of the mid-bass.

120 Hz seems to be the upper crossover point for many standalone subwoofers, but that's for 12 or 24 dB/octave crossover slopes, so I'm betting that 135 Hz crossover point with a 48 dB/octave crossover slope that a DSP crossover can achieve would work fine.
 

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#12
I also have a sidelined XD system. My amp/eq unit became unwilling to start-up reliably so I sent it to the factory for repair. It was better, but occasionally would get stuck in the turn-on sequence. My main issue with it was fan noise that was audible at the listening position late at night with very low level listening. When everything was working properly at moderate listening level, they were a very fine system. I am using the woofers eqed and actively crossed to a pair of CBT24s.
So maybe it's a fan that I'm hearing? Perhaps it can be replaced with a quieter fan....
 
Joined
Nov 2, 2018
Messages
16
Likes
20
#14
I've been looking for someone online with experience of using, say, a miniDSP as a digital crossover for the satellites and subwoofer. I'm looking specifically at the OpenDSP DAC-8, which can do both IIR and FIR filters, but don't want to pull the trigger unless I have some idea that this would be a success.
There are a few ways of doing a DSP speaker, but obviously there isn't a consensus 'great one', or else we'd see everyone using it. Something like JRIver makes a good platform, but struggles handling external sources. The Hypex DSP amps are attractive, but if you want to feed them digitally you need a digital preamp/switcher which doesn't appear to exist at the moment (except maybe for Meridian - I'd love to have a slightly updated 518) and they're IIR only. The MiniDSP units are popular as they're cheap, but are only uncomplicated if you're ok with analog input - as soon as you want digital inputs you're back to the switching problem; plus, they all SRC to 48/96 which isn't the worst thing in the world but (see below) I'm not convinced it's ideal. The MiniDSP SHD or SHD studio is probably pretty close to ideal if you can live with a 2-way system and accept being limited to IIR filters + Dirac, but putting all that effort into something and being limited to 2-way is a bit disappointing.


I don't have any experience with the MiniDSP OpenDSP units, but I do have a NanoDigi that I'm evaluating for a DSP speaker project. My current gut feel based on some A/B testing is that the SRC on the input of the NanoDigi is NOT audibly transparent, but I need to do more due diligence before actually concluding that. The NanoDigi is IIR only, unlike the OpenDSP. I do wonder whether the OpenDSP unit really has enough FIR capacity to be viable though - only 9600 taps shared across all channels. Assuming they're not providing any clever multi-rate capability, it's tough to see how you could do woofer xovers with that few taps. It might be viable for a setup with IIR filters between woofer and mid and FIR between mid and tweet, though. (for reference, when I was running BruteFIR in the past I'd use 16k to 64k taps per channel)

My current project is a pair of Kef Q150's that I want to add a pair of woofers to for my desktop use, but I've been putzing around with DSP crossovers for almost 20 years with varying degrees of success. More 'lessons learned' than true successes, sadly, but this time - THIS TIME - it'll be different :)

The short form blurb is that my current thought/plan (assuming I don't go with the NanoDigi) is to use a Linux pc running BruteFIR as the DSP engine. I'll probably run jackd for connection management, and will have to write some relatively simple software to handle remote control for input switching and potentially volume control. (I'm a software guy, and have done some jackd clients etc in the past so in theory this is only a matter of finding the time)

For output, I'm currently think of using the MiniDSP UDIO-8 running into a setup of the Khadas Tone Board plus JDS Atom for each output. I'm only looking at a 2-way system, which means this will run $300 for the UDIO-8 plus $200/way for ~700 total. Not too bad. If you're looking at a 3-way or 4-way system it might make more sense to look at the Okto Research Dac8 Pro (which isn't shipping yet, unfortunately). It's only ~1200 and appears to outperform everything out there AND provides global remote-controlled volume control. (the inclusion of the Atom in my setup is simply to provide a way to gain-match each channel fairly closely so that digital attenuation can be kept moderate to avoid too much compromise of performance. In my past DSP setups, the woofers have generally been a problem, requiring a fair degree of attenuation of the mid/high)

The key factor in both of the above setups is that the *output* runs at native sampling rate, but there is SRC on the digital inputs. This suits my specific application where all of my ripped content is 44.1 and that is what I'm prioritizing, so I can play my 44.1 content via MPD or Squeezelite etc directly into jackd with no conversion, but still handle external digital sources transparently due to the SRC on the inputs - all that is needed is to change the port routing in jackd. Without SRC, you are faced with having multiple filters sets - one for each sample rate - and having to re-initialize the filter engine any time you change rate.

All of this 'should' result in something close to a digital preamp w/ crossover functionality - similar to the MiniDSP SHD, but much more powerful (aside from lacking Dirac) but unfortunately less user-friendly - generating the FIR filters is always going to be finicky, and getting ergonomics / usability is always difficult. My ultimate goal is something stable/useable enough that I could conceivably consider it for a living room system (I have a vision of a DIY project emulating the look of the Sonus Faber Stradivari which I could only take on as a DSP project)

Good to know the Daytons worked well, thanks.

Yes, with one Xdw, there is sometimes a sense that you are losing localization of the mid-bass.

120 Hz seems to be the upper crossover point for many standalone subwoofers, but that's for 12 or 24 dB/octave crossover slopes, so I'm betting that 135 Hz crossover point with a 48 dB/octave crossover slope that a DSP crossover can achieve would work fine.
I'm a big fan of the Dayton subs. The RSS210HF worked quite well IMHO when paired with the NHTs, and I'm hoping to try using them with my current Kef Q150s. For a bigger room, the RSS265HO-4 does amazingly well in only 1-2 cu. ft ported. For a music-only system, I think these are very good choices as long as you can absorb the box size - they'll be bigger than the Xdw I would imagine. I also have 2x RSS390HF in our theater space, and they're great as well but massive overkill for an audio-only system.


BTW - I'm not sure whether you've seen this. Audioholics already measured the transfer functions of the digital filters in the Xds system, as well as the acoustic output of each driver individually. Not the best image, but I'm guessing you could use it to get pretty close using RePhase to generate the filters (I'm almost certain the Xds filters were linear phase)
https://www.audioholics.com/soundba...xd-loudspeaker-system-review/XdAOut.jpg/image

Main page with measurements is here https://www.audioholics.com/soundba...review/nhs-xds-measurements-and-analysis.html
 

Daverz

Active Member
Joined
Mar 17, 2019
Messages
188
Likes
97
#15
There are a few ways of doing a DSP speaker, but obviously there isn't a consensus 'great one', or else we'd see everyone using it. Something like JRIver makes a good platform, but struggles handling external sources. The Hypex DSP amps are attractive, but if you want to feed them digitally you need a digital preamp/switcher which doesn't appear to exist at the moment (except maybe for Meridian - I'd love to have a slightly updated 518) and they're IIR only. The MiniDSP units are popular as they're cheap, but are only uncomplicated if you're ok with analog input - as soon as you want digital inputs you're back to the switching problem; plus, they all SRC to 48/96 which isn't the worst thing in the world but (see below) I'm not convinced it's ideal. The MiniDSP SHD or SHD studio is probably pretty close to ideal if you can live with a 2-way system and accept being limited to IIR filters + Dirac, but putting all that effort into something and being limited to 2-way is a bit disappointing.


I don't have any experience with the MiniDSP OpenDSP units, but I do have a NanoDigi that I'm evaluating for a DSP speaker project. My current gut feel based on some A/B testing is that the SRC on the input of the NanoDigi is NOT audibly transparent, but I need to do more due diligence before actually concluding that. The NanoDigi is IIR only, unlike the OpenDSP. I do wonder whether the OpenDSP unit really has enough FIR capacity to be viable though - only 9600 taps shared across all channels. Assuming they're not providing any clever multi-rate capability, it's tough to see how you could do woofer xovers with that few taps. It might be viable for a setup with IIR filters between woofer and mid and FIR between mid and tweet, though. (for reference, when I was running BruteFIR in the past I'd use 16k to 64k taps per channel)

My current project is a pair of Kef Q150's that I want to add a pair of woofers to for my desktop use, but I've been putzing around with DSP crossovers for almost 20 years with varying degrees of success. More 'lessons learned' than true successes, sadly, but this time - THIS TIME - it'll be different :)

The short form blurb is that my current thought/plan (assuming I don't go with the NanoDigi) is to use a Linux pc running BruteFIR as the DSP engine. I'll probably run jackd for connection management, and will have to write some relatively simple software to handle remote control for input switching and potentially volume control. (I'm a software guy, and have done some jackd clients etc in the past so in theory this is only a matter of finding the time)

For output, I'm currently think of using the MiniDSP UDIO-8 running into a setup of the Khadas Tone Board plus JDS Atom for each output. I'm only looking at a 2-way system, which means this will run $300 for the UDIO-8 plus $200/way for ~700 total. Not too bad. If you're looking at a 3-way or 4-way system it might make more sense to look at the Okto Research Dac8 Pro (which isn't shipping yet, unfortunately). It's only ~1200 and appears to outperform everything out there AND provides global remote-controlled volume control. (the inclusion of the Atom in my setup is simply to provide a way to gain-match each channel fairly closely so that digital attenuation can be kept moderate to avoid too much compromise of performance. In my past DSP setups, the woofers have generally been a problem, requiring a fair degree of attenuation of the mid/high)

The key factor in both of the above setups is that the *output* runs at native sampling rate, but there is SRC on the digital inputs. This suits my specific application where all of my ripped content is 44.1 and that is what I'm prioritizing, so I can play my 44.1 content via MPD or Squeezelite etc directly into jackd with no conversion, but still handle external digital sources transparently due to the SRC on the inputs - all that is needed is to change the port routing in jackd. Without SRC, you are faced with having multiple filters sets - one for each sample rate - and having to re-initialize the filter engine any time you change rate.

All of this 'should' result in something close to a digital preamp w/ crossover functionality - similar to the MiniDSP SHD, but much more powerful (aside from lacking Dirac) but unfortunately less user-friendly - generating the FIR filters is always going to be finicky, and getting ergonomics / usability is always difficult. My ultimate goal is something stable/useable enough that I could conceivably consider it for a living room system (I have a vision of a DIY project emulating the look of the Sonus Faber Stradivari which I could only take on as a DSP project)



I'm a big fan of the Dayton subs. The RSS210HF worked quite well IMHO when paired with the NHTs, and I'm hoping to try using them with my current Kef Q150s. For a bigger room, the RSS265HO-4 does amazingly well in only 1-2 cu. ft ported. For a music-only system, I think these are very good choices as long as you can absorb the box size - they'll be bigger than the Xdw I would imagine. I also have 2x RSS390HF in our theater space, and they're great as well but massive overkill for an audio-only system.


BTW - I'm not sure whether you've seen this. Audioholics already measured the transfer functions of the digital filters in the Xds system, as well as the acoustic output of each driver individually. Not the best image, but I'm guessing you could use it to get pretty close using RePhase to generate the filters (I'm almost certain the Xds filters were linear phase)
https://www.audioholics.com/soundba...xd-loudspeaker-system-review/XdAOut.jpg/image

Main page with measurements is here https://www.audioholics.com/soundba...review/nhs-xds-measurements-and-analysis.html
Wow, thanks dwkdnvr, that' s a lot of good info to absorb.

My current source is a RPi 3B+ running piCorePlayer, so I have thought of going the Brutefir + multi-channel DAC route. However, I think the Okto would put this little project way over budget, especially as I don't have any other uses for a multi-channel DAC. As the projected costs add up, getting a new pair of powered speakers instead becomes more attractive.

Is clock synchronization not an issue when using multiple Khadas tone boards?

Did you build your own enclosures for the Dayton drivers?

Thanks for the Audioholics links. The Xda impulse response is just the sort of thing that I wanted to measure.
 

TimW

Active Member
Joined
Aug 15, 2018
Messages
171
Likes
288
#16
My current gut feel based on some A/B testing is that the SRC on the input of the NanoDigi is NOT audibly transparent, but I need to do more due diligence before actually concluding that.
SRC? I was thinking about getting the NanoDigi for integrating a sub and experimenting with active crossovers. If you come to a conclusion on the performance of this device I'm interested in what you have to say.

I've also been looking at the OpenDRC-DA8 but it bugs me that there is only coaxial input and unbalanced outputs of unknown quality. There is a cool kit for adding a screen to OpenDRC boxes though. I also like the OpenDRC-DI which can be used with AcourateDRC. But I would have to send spdif out of that to a NanoDigi to do any kind of crossovers. Does it sound crazy to have source>spdif>OpenDRC-DI>spdif>NanoDigi>spdif>multiple DAC's?
 
Top Bottom