Yamaha NS-1000 Monitor
         Copyright 2011 Troels Gravesen       

CROSSOVER      DRIVERS      MEASUREMENTS     NEW X-OVER     THE KIT

     
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Yamaha NS-1000 has long been on my wish list for a closer inspection and I've had quite a few requests for a possible up-grade kit. Thanks to Niels in Aalborg, this came true and I had a pair of pristine condition speakers for my scrutiny. Niels brought the speakers and we sat it up in my listening room driven by my Jungson JA88D power section; the same Niels does at home.

Before reading on, please pay notice to the fact that the attenuators will no longer be operational with the new crossover. This doesn't mean you cannot adjust mid and tweeter level. A range of fixed resistors are provided with the kit that allows adjustments of mid and tweeter level. Attenuators are generally regarded as no-no in serious hifi, they may be worn over time or indeed not provide an constant load for the crossover. If frequent adjustment of mid and tweeter level is requested, a terminal bridge can be placed on the rear terminal panel for easy access.

It soon became clear that not a whole lot is needed to bring these speakers up to date. They present a level of transparency rarely heard, and by a comfortable margin supersedes many modern speakers. It's hard to believe they're not still in production as they do so many things so right. I even love the "no-no" attenuators allowing proper adjusting of mid and tweeter level to match your room, your equipment and not least your taste. This could sometimes save people serious dollars in cables and other tweaks. The middome provides a phenomenal dispersion that requires a recessed on-axis response in the midrange to present an overall balanced sound.
Actually the middome would be suitable for a modern slimline with e.g. two 8" bass drivers. The tweeter would need to be reworked to perform better in the 10-20 kHz range. Anyway...

NS-1000 can be placed fairly close to the front wall without losing too much sense of depth and perspective - and they don't mind a bit of room-gain to compensate for the early low-end roll-off. NS1000 doesn't go particularly deep. At 50 Hz we're down some 3 dB. Due to the properties of the bass drivers and cabinet tuning we have some elevated response in the ~80-120 Hz region adding volume and warmth to the overall sound and I haven' done anything to change the performance here. An LCR impedance flattening circuit could easily change this (550 uF + 18 mH + 6R8 for those who want to experiment). Trying out two Variovents could be another area of experimentation, but deep bass we're never going to get. I wouldn't consider a vented cabinet for this bass driver although 80 litres and a vent tuning of e.g. 28 Hz does look better (-6 dB @ 30 Hz).

If we imagine sitting at the conference table at YAMAHA  back then and setting the targets for a new 50 litre 3-way, there may have been arguments for using a 10" bass driver. We might even maintain system sensitivity with a 10" bass driver and we could easily get another 5-10 Hz bass extension. Two arguments may have prevailed: 1) JBL's got a 12" system out already with this size bass driver and 2) a 12" driver loads the room like no 10" does; we can't just replace cone area with increased X-max. It doesn't work that way. And a 10" version would be a logical next step for a more domesticated version at lower price. Could be fun reading the minutes from these meetings... 

The new crossover is designed to maintain the basic virtues of the old crossover, i.e. points of crossover have not been changed, neither the option of balancing mid and treble level to actual room acoustics, your system and personal taste, albeit not as much as the L-pads, but I guess no one is using these to the extremes. The improvements in sound comes from:
1/ Re-designing the bass driver's low-pass section
2/ Smoothing drivers' roll-off slopes.
3/ Substituting all electrolytics with state of the art super caps.
4/ Using better coils; thick-wire cored for bass and wax foil-coil for mid (using air cored coils for the bass does not improve performance).
Due to the high point of crossover to the middome we can get away with relatively small capacitor values (low cost).

The new crossover delivers a more balanced bass reproduction and better bass-mid integration. The mid/lower treble is seriously improved by the super caps and the increased sense of depth and perspective is hard to ignore. Treble (from the tweeter) is hard to comment on as the middome does so much of it. However, the apparent lack of response in the upper octave based on measurements are not confirmed by listening. There are lots of airiness from what the beryllium tweeter can manage.
Maybe because I just had a vinyl box-set of Sibelius symphonies from my friend Michael, I've been listening to a lot of classical music lately and should someone think "metallic" sound from the domes, try this speaker. If it's harsh, it's because the recording is rubbish, your amp or your cartridge/CD player not up to what the speakers can reveal. These speakers are smooth all the way, yet deliver a sense of presence and clarity few speakers can manage.
One remarkable thing: My CD player never sounded better than on these speakers. Hmm.....Strange!

The NS-1000 was developed in the mid Seventies and part of the story can be found here at the vintage knob, and I won't engage in historical details, rather comment on what I hear and measure.

The basic set-up is this:

For bass we have hard pressed paper cone with coated fabric surround. Good, because this will last for decades. Fs is around 20 Hz and Qt = 0.27 and we have a 50 litre closed box providing an F3 of 49 Hz. The cabinet is entirely filled with glass fibre to increase virtual volume. Closed box lovers will like what it does and I agree. Bass quality is good and appears fairly deep given the modest sized enclosure. Comparing the bass to my DTQWT there's some lack of punch and drama in upper bass/lower mid, but overall good for the size.

For mid we have an exclusive 3.5" beryllium dome. Now, this dome is not solid beryllium as in later exclusive versions of the NS1000, merely vacuum deposited beryllium on an aluminium dome (as far as I can source information). Beryllium has recently been reintroduced by Focal and ScanSpeak for dome tweeters, but I think this Yamaha is the one-and-only when it comes to mid-domes. It displays an excellent frequency response and the cumulative spectral decay leaves little to be desired. In this construction it covers the 500-4500 Hz region, hence handles the troublesome upper mid/lower treble region with no 2-3 kHz point of crossover. Much like my ScanSpeak SP44 construction, only this 3" dome goes almost an octave lower compared to the Accuton C50.
Thanks to Sven for pointing out some measurements presented in Martin Colloms' High Performance Loudspeakers. Here we see an unusual low distortion profile for the NS1000 compared to a contemporary 3-way; read page 432-433, sixth edition.

For tweeter we have a 30 mm Beryllium dome and despite limited frequency extension - it drops rapidly above ~15 kHz - it blends very well with the middome and does what a tweeter dome should do. The low-end roll-off is somewhat ragged, but with the high point of crossover this is only a minor issue. It is claimed it goes way beyond 20 kHz but it certainly doesn't, and given the consistency between the two domes at hand, I don't think there's anything wrong with them.

The crossover is a fairly simple 2nd order (electrically) on all slopes mostly providing close to 4th order roll-offs. As we shall see later this doesn't work fully optimal for bass and tweeter and there are room for improvements.

NS-1000M is a special speaker by today's standard. The use of a 12" bass driver in a small closed box, the use of the beryllium domes, the unusual dispersion all through the midrange and up to its upper limit and it's ability to reveal detail and transparency like few speakers can do. It is somewhat demanding on associated equipment and it doesn't play rubbish recordings without telling you so. For those who take the time sourcing the right equipment and experiment with placement and mid/tweeter attenuation, it may be a lasting love affair. I'm not sure there's a plug'n play speaker, but this is not one of them.  


YAMAHA NS1000 Crossover
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Here the original crossover with measured coil DCRs.
Both mid and tweeter are attenuated with constant impedance L-pads.


The Drivers
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NS1000 drivers truly reveal what happens when large companies set out to do something better than competitors. The resources available for development is something that small manufacturers can only dream of. Rugged aluminium frames and machined magnet parts, tools that need to be developed to produce the various parts going into the assembly and not to forget exotic membrane materials that are far beyond small scale manufacturing.


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Bass drivers cones made from hard pressed paper pulp and fabric suspension. Despite age, these drivers display only modest sagging, something that makes most vintage drivers less than optimal (voice coil not properly centered in magnet gap). An unusual high mechanical Q of 6.5 is the result. Actually this bass driver sounds pretty awful on the MLS signal suggesting a steadily rising response and a ragged frequency response. And so it is.This is nothing unusual for a hard-cone driver but with the 2nd order, 500 Hz point of crossover, this doesn't impact midrange presentation too much, but there is room for improvements.


TS data measured by "added volume" method.

The 12" bass driver in a heavily damped 50 litre enclosure should make F3 = ~50 Hz. Go to NS1000 box simulation here


Left: Voice coils wound on paper doesn't allow excessive power handling and Yamaha wisely added a sticker to the rear of the speaker stating:
"Do not exceed the speaker's maximum input capacity". Should be on all speakers.
Right: The one-and-only, 3" beryllium dome. Click right image to view large.


This middome holds a gigantic magnet providing some 93 dB sensitivity. Impressive.


NS1000 tweeters. Large magnet for the size and a healthy 93 dB sensitivity. 10-20 kHz range is nothing to write home about.
Click left image to view large.


An unusual crossover in terms of choice of component. 6 x 3.5 uF bipolar electrolytic cabs is part of the mid's high-pass filter.
2.7 uF electrolytic cap for the tweeter; there may be room for improvement in both places.


Excellent cabinet work!

 
The JBL L100 should have been made this way! Decent thickness of panels, bracing and the remains from routing bass driver hole is glued and screwed to
the rear panel. Excellent thinking! Sides are heavily damped with 10-12 mm felt material and the entire volume filled with glass fiber damping pads.
  


Measurements
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Left: Lower graph is SPL @ 1 meter, 2.8 volts. Both mid and tweeter with -3 dB attenuation. Setting mid and tweeter at min. attenuation all of a sudden
increases response to some 92-93 dB (orange). These tweeters/mids could be used in a rather high-efficiency system.
Right: System impedance with mid/tweeter attenuation -3 dB. Minimum ~4.5 ohms.

Left: Response of all drivers taken at 0.25 meter, normalised for 1 meter/2.8 volts. The bass response left me a little confused as it appears we have a basic sensitivity of some 92 dB, but even at 0.25 meter the response is only valid down to around 250 Hz due to room reflections. Making nearfield measurement isn't easy with the grille preventing placing the microphone 1 mm from the cone. Measuring with the microphone as close to the grille as possible (image to the right) reveals the black graph. Adding the used low-pass filter makes the green graph. At 0.25 m distance (red graph) it appears the point of crossover is around 500 Hz and a system sensitivity around 88 dB. This is more like it. The NS1000 is not for SET fans unless you never play very loud. They could easily drive my Audio Mirror 45 wpc SET amps to clipping. These speakers need a healthy 80-100 watts or more.


Left: Impedance of all drivers. Green = tweeter, red = mid and orange = bass. Right: A closer look at the response from mid and tweeter. 

Left: Impact on frequency response from mid attenuator. Green = "normal" as the dial says. Beige is -2 dB and red is the preferred position, -3 dB.
Right: Response with mid at -3 dB and readings taken at 0.5 meter distance with microphone at tweeter height (red), between mid and tweeter (grey) and at mid height (green). Optimal listening height is really at mid height as later crossover modeling suggests. Phase integration between mid and tweeter is not completely perfect, but at 4.5 kHz anything can happen depending on microphone placement, so, a grain of salt, please.
Ideally the tweeter should have been recessed by some 8-10 mm to make a better phase integration and an optimal listening height at tweeter level. If you listen at tweeter height I suggest tilting the cabs some 5 deg. 


NS1000 on my test stands in the middle of my workshop. Here with a 170 ms signal length and 1/2 octave smoothing.
An overall balanced response with (still) mid and tweeter at -3 dB attenuation.


The New Crossover
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Initially I thought there was little to do on the NS1000 crossover, but there's a honeymoon for all good things. After extended listening a few things come to mind. As mentioned earlier some trouble in middle midrange (320-640 Hz), minor harshness in upper treble range and last but not least, what happens if all electrolytic caps are replaced by modern super caps?

First of all, let's examine the crossover. Here we have the original again:


For all drivers we have a 2nd order filter on the electrical side, but for most slopes LR4 on the 
acoustic side except for the bass, suggesting some misalignment between bass and mid-dome.


Actual response from bass driver against an LR4 slope @ ~500 Hz. 
Something tells me we need a 3rd order filter to produce the target LR4 slope.


Slopes of midrange drivers from actual crossover against a target LR4 topology.
The high-pass section is a bit brute against the driver pushing up response at 700 Hz. Adjusting L2021
and adding are resistor in series may prove beneficial.


Tweeter response against a target LR4 topology. The hump at 3 kHz would be nice seen gone.

 


Above a slightly modified and fine-tuned simulated crossover. 


Here we have the response profiles against LR4 topologies. Actually the middome adds a considerable amount of upper treble energy.


NS1000 new crossover.

What has happened here is modest finetuning of crossover slopes and the attenuators are gone. Bass low-pass section is replaced by a 3rd order filter, providing LR4 slope and enhancing phase tracking between bass and middome.
R2031 is optional as we may need to adjust mid level. R2031 can be inserted without spoiling slopes and phase integration.
Tweeter here is set fairly high; hence some may prefer additional attenuation. This can be done by changing R1051 in accordance with the instruction following the kit. This doesn't impact mid-tweeter integration.
The DCR resistance of bass coils are chosen so that they match the DCR of the original single coil.


Left: SPL of new and old crossover for sonic comparison.
Right: Slopes and summed response from new crossover. Black and purple are summed response w/wo tweeter notch filter.


Left: Nearfield response of bass driver with new crossover. Right: Checking phase integration between bass and mid with inverted mid polarity.

Mid attenuation


Predicted response from R2031 = 0, 1.0, 1.8 and 2.7 ohm respectively. As can be seen below, this is pretty much what happens.
The placement of the attenuation resistor at this place make a progressively tilt of middome response. If we place the resistor before C2011, this happens:


- we get a general reduction in middome's response over its operating range. I prefer the first option to leave 500-1000 Hz midband unaffected.

Tweeter attenuation


Above the result of changing R1051 from 5R6 (highest level) to 4R7 and 3R9. My default is 4R7.


Left: This one is important as it shows middome attenuation from R2031 = 0 ohm, 1.0 ohm, 1.8 ohm and 2.7 ohm. My preferred setting is 1.8 ohm.
Right: This graph displays the phenomenal dispersion of the NS1000, here at 0o, 10o, 20o, 30o, 40o and 45o respectively (red to blue).
Very few speakers can mange this. As can be seen treble starts declining above 15 kHz.

An in-room measurement from a 32k length MLS signal, average of 10 measurements and with 1/6 octave smoothing. As can be seen my room does fairly well; some +/- 5 dB up to 1 kHz and above very smooth. Left and right speaker shown. As can also be seen the NS1000 really doesn't do much below 50 Hz (please note 20 dB scaling!).

Left: Speakers on 45 cm stands (image below) and with 50 cm between rear of cabinet and front wall (about 80 cm from the front of the speakers)
Right: Speakers on 27 cm stands only 18 cm between rear of cabinet and front wall.
If you save the two images and swap between them in e.g. Windows photo viewer, you can seen this change happen for both speakers:

The red line is what happens when close to front wall. This provides and overall balanced and pleasant sound - but at the expense of depth and perspective.

 


During development of new crossover A-B testing was performed in mono. Workshop image.
The super caps do their thing and adds several meters to the perceived depth of the sound image.
Next was building the second crossover and start evaluation under living room conditions.

The Up-Grade Kit
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Click image to download pdf file.

For price quotation incl. shipping, please contact Jantzen Audio: contact@jantzen-audio.com

PLEASE: All technical questions to troels.gravesen@hotmail.com

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For installing a new crossover you may also want to make a new terminal panel.
Click image to view large the measures to fit exactly into existing rebate. I suggest 25 mm MDF or Baltic birch.

Mark, UK, found these dimensions on his NS1000. Check out your own before cutting sheets.


The Kit


Included in kit is full size image of crossover layout (incl. component values), full-size images of finished crossover and pics of final implementation.


Kit comes with full schematics, crossover layout, connecting drivers and large crossover images.


The finished crossover.

If you have found your level of attenuation, I suggest placing the crossover in the upper compartment of the cabinet. This will increase distance to drivers' magnets.
Alternatively the attenuator resistors can be placed on the terminal panel by using a terminal block and e.g buy some CADDOCK thick film resistors.  


Polarity of mid and tweeter domes

The tweeter has a clear indication of polarity on the frame, so no problem here. The middome unfortunately does not, and there's only one way to connect the middome - the right way.


Left image: Middome. Seen from the rear with terminals up, the terminal to the right is PLUS
Right image: As can be seen the tweeter has markings of plus and minus on the chassis. Note tweeter connected with inverted polarity. Although magnets are none conductive, I suggest adding a piece of tape on the magnets below the terminals. Next, I strongly suggest using the cable ties following the kit to secure the leads. Ripping terminals just must not happen.


Left: New crossover mounted up against bracing to allow space for terminals. Right: New terminal plate with binding posts. 

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