NOMEX-mkII

DIY Loudspeakers: HOME INDEX UPDATES RESPONSE WHAT'S NEW

Nomex 164 mkII
Copyright 2022 © Troels Gravesen

Go to on this page:
DRIVERS CROSSOVER CABINET MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

I've always liked these Peerless drivers with their paper pulp/Nomex cones, delivering a level of transparency that by far supersedes the cost of the driver, and easily rivals similar products costing 4 times as much. I recently bought two more units of this P830875 driver and compared to two other units I bought some years ago - and they're exactly the same, proving consistent availability of driver parts from spiders to cones - and consistent production. It may be built by robots to keep cost down, but who cares as long as build quality is impeccable?
The only rationale for keeping the ScanSpeak D2608/913000 tweeter in the low-cost Discovery category is price. Quality wise it easily competes with Revelator and Illuminator tweeters.
What I wanted from the mkII version was taking the point of crossover down to a little below 2 kHz, where former version was above 3 kHz and left some dispersion in upper mid/lower treble to be desired. In addition to this, a time-aligned 2nd order LR2 crossover rather than former 4th order.
A lot of people have built the first NOMEX-164 version as we have outstanding quality for a very low price and the objective here is to deliver better and keep the price level. I have chosen the luxury to use the best possible capacitor the tweeter - because it can handle the very best. The only "problem" this tweeter has is its low price. Many people simply won't believe it rivals the very best domes on the market. Hear some cymbals from a 45 rpm vinyl - and from some very good amplifiers - and hear for yourself.
Making the cabinets is easy, the crossover is simple. Amazing how good sound we can get from a modest investment.

This speaker runs very well from my 32 wpc EAR-861 tube amp, transparent midrange, smooth treble. If we want the bottom octave, 20-40 Hz, add a subwoofer like the ScanSpeak 26W. The two 6" drivers have enough power in the important 80-160 Hz range to make a bigger system by adding subwoofer(s). I tried with a single subwoofer crossed at around 50-60 Hz, and it went well. But don't think the NOMEX drivers are bass-shy. What they can do, they do very well. The combined membrane area of the bass drivers equals a 9" bass driver.

Moving the speakers to my living room and setting up the speakers next to my reference ATS4-HE one might expect some serious shift in quality and some mental adjustment. Not al all! All I can say is that I fully understand why some people would question the rationale in investing some 10 times the money for the ATS4-HE drivers compared to NOMEX 164-mkII. Yes, we pay dearly for small increments in quality. No, the NOMEX does not have the low-end weight of the ATS, but nevertheless a solid bass presentation and magnificent midrange and treble. Feed them the best source material you have and they will deliver.

Basics:
2½-way speaker in a 40 litre vented cabinet.
System sensitivity: 90 dB/2.8V, 1 meter.
Impedance: 4 Ohms, minimum 3.2 Ohms @ 200 Hz.
Crossover: Low-order LR2 filter, 1.8 kHz.
Power requirement: 10+ wpc.

Useful links (Please follow all links before e-mailing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm
http://www.troelsgravesen.dk/choices.htm
http://www.troelsgravesen.dk/power-handling.htm

Click images to view large

DRIVERS
BACK TO INDEX

Click images to view large

Download specs here: HDS-P830875 D2608/913000

CROSSOVER
BACK TO INDEX

Nomex 164 mkII crossover topology.
The mkII follows a quite simple 2nd order topology.

CABINET
BACK TO INDEX

As always: Any change to front panel design and drivers' placement and you need a new crossover and I can't help.
Please read: http://www.troelsgravesen.dk/crossovers.htm. And please, all of it before writing.

I used 22 mm standard MDF for the basic cabinet and 2 x 19 mm for the front panel. 15 mm for bracing.

Port length = 120 mm. http://www.troelsgravesen.dk/tips.htm#PORT_DIMENSIONS

Obviously you can make the cabinet 210 mm width and compensate the volume by increasing depth. You can also make the cabinets like a straight forward rectangular box and tilt the cabinets 5 deg. by adding out-riggers with various spike length like seen here. Nice looking solution!

Check out this file regarding construction tips: http://www.troelsgravesen.dk/tips.htm

Workshop images

Do remember to chamfer the driver holes for the midbass drivers!

Shaping up!

Cabinet damping

Add felt to all internal panels, except front panel. Add double layers at top and bottom.

Add 4 layers of acoustilux at bottom and top.
Ad 1 layer of acoustilux (19x 50 and 24 x 50 cm) behind bass drivers.

MEASUREMENTS
BACK TO INDEX

Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.

A few comments on MEASUREMENTS before you start interpreting all the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of us diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range.
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct.

Individual response of drivers driven from crossover (orange, yellow) and summed response (red) +/- lower bass (green).
Point of crossover around 2 kHz.

Final system impedance (red) and electrical phase (green).
Overall a very easy load making my 32 wpc EAR-861 tube amp very happy driving the speakers from 8 Ohms tabs.