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Fostex RS-N2 (RS-2) Reference Speaker System (Hyperbolic Paraboloidal Diaphragm)

mononoaware

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https://www.fostex.jp/products/rs-n2/
Only recently discovered these Fostex speakers.

Price is ¥2,178,000(税込)/1台 which I assume means for 1 unit. So take two zeroes off thats roughly a whopping $21,780 per unit.

Design is 3-way Bass Reflex with 12-inch (30cm) woofer, 5-inch (13cm) mid-range, 0.78-inch (20mm) tweeter.

It seems to include an Accuphase "PRO-30" Power Amplifier (well at least they list the full specifications including dimensions of the PRO-30 in the RS-N2 Spec sheet).

https://www.fostex.jp/wp/wp-content/uploads/RS-N2_spec.pdf

Low frequency extension strangely rolls-off early for a 12-inch woofer with Bass Reflex design according to the Frequency Response (maybe a compromise of the "Hyperbolic Paraboloidal Rotation" diaphragm since the GX250MG also suffers from the same average bass extension), but I thought maybe some here would be interested to know the RS-N2 exists.

- the RS-2 is the same model but with black speaker cones instead of yellow.

- I assume due to its pricing this is a professional/commercial use product. In Japan many professionals in film/TV/music industries probably see this speaker everyday and consider it a “tool” and are not aware of the model name.
 
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mononoaware

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The Hyperbolic Paraboloidal diaphragm is explained in detail here.
I found the information in the NF-1WP Technical White-paper.
https://www.fostexinternational.com/docs/tech_support/downloads/nf_wp.pdf

BASICS OF THE HP SYSTEM

'HP' is an abbreviation of hyperbolic paraboloid which is normally called an 'HP shell' or hyper shell, and is a 3rd-order curved surface structure. This structural theory has long been well known in the field of the structural mechanics.The Orchestra House in Sydney, Australia, a good example to which the HP structure is applied, is famed world-wide for its beautiful form.The HP structure is characterized primarily by the fact that movement of a line connecting 2 line segments which exist on different surfaces results in composition of a hyperboloid and paraboloid.

Our purpose and reason for the world's first application of this HP structure to the NF-1 near-field monitor as an ideal diaphragm configuration can be explained by 3 acoustic advantages which were not available from conventional diaphragms.Without solution to these 3 items, it would be impossible to predict what the next generation near-field monitors should be.

APPLICATION TO DIAPHRAGMS OF THE HP SYSTEM

1) HP diaphragms composed of lines
Being a curved surface, and unlike conventional diaphragms structured with curved lines, the HP structure basically consists of straight line structures. As a result, involved in-plane stress is only a shearing force without the presence of bending stress, culminating in strength at high level. Strength of such level can raise the resonance frequency of diaphragms to reproduce fast-rising sounds that make listeners perceive faster responsiveness over conventional diaphragms.Besides, the straight lines, being of varied lengths, prevent any specific standing waves from being created on diaphragms, with subsequent freedom from peaks, and thus, resulting in smooth response.


2) HP Diaphragms having torsional curved surface
Nothing is free of natural self-resonance frequency. It has been known that self-resonance frequency creates sound inherent to the material, perceptible as sound unique to it. Speaker diaphragms are no exception and have material-specific sound which characterizes the speaker. In the case of home use speakers, such timbre may appeal to listeners as being comfortable and pleasant. However, when using speakers A and B for the purposes of monitoring the same program source in different timbre will mean that some particular frequencies are restricted by speakers with their natural resonance frequency. It can be, therefore, reasonably assumed that ideal diaphragms for monitor speakers should have natural resonance suppressed to the fullest possible extent. The HP structure is characterized by its torsionally curved surface structure. Figures 2 and 3 show FEM modal analysis results of the 1st to 4th free resonances observed on a 150torsional HP structure and on plane structure, where no evidence of major resonance is apparent on the HP stvucture.
(Figure 2, 3, images included in PDF link)

One of the properties of the HP structure is the unlikelihood of development of inherent timbre because of widely dispersed resonance.This finding has made it possible to use, without encountering any particular major resonance, materials such as metal and carbon fibers having high propagation velocity and low tan δ(internal loss) which used to be regarded as properties to be overcome. The Figures 2 and 3 indicate that resonance is shifted up on HP diaphragms by one decimal point and is narrower, when compared to a plane surface. This represents that HP diaphragms provide higher strength and finely dispersed resonance. This property of dispersed resonance can be used as a good proof that HP diaphragms are ideal where no particular resonance disturbs reproduced sound.

3) HP diaphragms, easy to analyze and excellent in reproducibility of simulation
HP diaphragms' complexity in configuration can be overcome by development of a design method which involves CAD/CAM techniques, whereby optimal configuration design of curved surfaces and mold machining will become possible.Configuration of HP shells is optional, i.e., the number of divisions and degree of torsion of curved surfaces (height of ridges and depth of troughs) can be determined by the aimed response characteristics/sound quality. In addition, articulate configuration, though the curved surfaces are complex, provides ease in analysis and reproducibility of simulation.
Figure 4 presents comparison data of frequency responses taken from 16 cm woofers with an HP or conventional straight diaphragms. The HP diaphragm speaker is free of evidence of either dips
at around 600 Hz or peaks at the high end of around 4500 Hz due to anti-resonance of the edge. Figures 5 and 6 compare the FEM modal analysis results.
Figure 5 represents a conventional straight cone. Cone break-up is present at 596 Hz in the axis-symmetry mode (in the direction of circumference), causing the 3rd harmonic distortion which is said to be detrimental to sound quality, to develop.Figure 6 shows an HP diaphragm. Axis-symmetry mode resonances can be seen at neither of the vicinity of 596 Hz nor at any other frequencies.At this stage, we can say that it is has been successfully verified that the use of HP diaphragms can surmount the shortcomings of conventional cones, eliminate speaker-specific sound colorization, and finally, attain ideal speakers capable of offering precise sound reproduction.
(Figure 4, 5, 6, images available in PDF link)

FEATURES OF THE WOOFER UNIT. . . (continued in PDF link)

There is a lot more information which some of you who are knowledgeable may be interested in reading, but is all a bit over my head. The link to the White-paper is at the very top of this post.
 
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Looks promising and sexy. That price though...

Was very impressed by 4" GX100 back in the day. Despite being very small, they sounded very room filling and lively.

gx100.jpg
 

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mononoaware

mononoaware

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Looks promising and sexy. That price though...

Was very impressed by 4" GX100 back in the day. Despite being very small, they sounded very room filling and lively.

View attachment 126417


Here is the English page for GX100BJ.
https://www.fostexinternational.com/docs/products/GX100BJ.shtml#content-3-tab-tab

Fostex has 2x HR series drivers from their “Speaker components” range so I was aware of the driver in these smaller sizes.

The GX100BJ uses an aluminium HR diaphragm which is news to me even though the speaker release date is 2017.
(Up until recently I thought all HR drivers used “banana-pulp”)

You can tell the category (series) of Fostex products by their model name, so just like the GX250MG I mentioned in the first post the GX100 would be considered from their “HiFi” series.

The NF-1 is their near-field Studio monitor model.
So maybe it is a fairer comparison to the Genelec (but NF-1 is passive, and 8030c is active).
NF-1 measurements are available on Page 15 of the NF-1WP white-paper I linked.

I think Bass-extension will always be the inherent weakness when comparing any HR diaphragm speaker to it’s similar sized equivalent.
 
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Ilkless

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Someone distributed the GX speakers locally for a bit. Gorgeous lacquer and funky driver design. But ultimately tizzy as hell. A shame. Like the new Paradigms with the funky phase shields.
 

BrokenEnglishGuy

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Someone distributed the GX speakers locally for a bit. Gorgeous lacquer and funky driver design. But ultimately tizzy as hell. A shame. Like the new Paradigms with the funky phase shields.
Can you elaborate please that thing about paradigms?
The news paradigm looks good :(.
 

BrokenEnglishGuy

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Most paradigms I've seen measurements of are pretty mediocre, which is strange because they are totally capable of making excellent speakers.
The new Founder look amazing :/ hope someone measure them
 

redshift

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I know there exist designs with internal flow restrictions/acoustical “resistors” to combat ringing and nulls in the cabinets and midbass drivers. Carefully crafting of a rock/glass wool “wall” between the chamber and port seem to dissipate most of the nastiness.

It is fairly common to add resistors in series with digital pins in electronics (FPGA’s) to avoid ringing/EMI from traces.

I guess the same applies here without going into the gritty STEM-level detail about complex impedance and lapalace transforms with poles and zeros of a system.

Stig Carlsson used resistors extensively in basically all of his late designs. (OA12/14 pictured)

1626949186843.jpeg


1626949374325.jpeg
 
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