Discovery-18W-mkII

DIY Loudspeakers: HOME INDEX UPDATES RESPONSE WHAT'S NEW

ScanSpeak Discovery-18W-mkII
Copyright 2023 © Troels Gravesen

Go to on this page:

DRIVERS CROSSOVER CABINET WORKSHOP PICS MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

The Discovery series of drivers are popular due to their high performance/cost ratio. I never had to do edge-coating to any of the Discovery drivers due to their exceptional linear response in all of their operating range. Rather unusual, I would say. When manufacturers launch a new range of 4-8 inch drivers with similar design in baskets, cone materials, etc., we usually find some good, some not so good. The different size of cones and property of suspensions may work very differently whether it's a 4" driver or a 6" or an 8" driver and not all manufacturers go the full length of adjusting suspensions to a particular cone and get it all right. Not so with the Discovery series. They all lack the all too common rubber resonance around 800-1200 Hz. Their modest break-up in the treble range make them easy on crossovers and whatever trouble we may experience is mostly due to poor front panel design. As always we should try out different baffle geometries before settling on a specific design.
I can understand why some people refrain from seriously expensive drivers - and not only for economical reasons - but for the very simple reason, that if we never play very loud, a cheap drivers can sound just as good as an expensive one. What expensive drivers should give us is dynamic headroom. The ability to play loud and still keep distortion low. And to be fair, quite a few expensive drivers do that.
For midbass here I picked the 18W/4434G00 rather than the 18W/4424G00 due to it's larger voice coil and increased power handling. The 4 Ohm version due to it's enhanced sensitivity and we can manage a system sensitivity of 89 dB, even with a decent bass extension.
Nothing to add on my tweeter choice, the venerable D2608/913000. I have used this tweeter extensively, even together with high-cost midbass drivers.

Basics:
2-driver speaker.
Dimensions: 22 x 25/30 x 45 cm, WxDxH.
System sensitivity: 89 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 20+ watts/channel.

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

DRIVERS
BACK TO INDEX

Download specs here: D2608/913000 18W/4434G00

CROSSOVER
BACK TO INDEX

CABINET
BACK TO INDEX

Cabinets were made from 20 mm Baltic birch. Front panels from 25 mm HDF. Use min. 20 mm.
If you use 18-19 mm MDF, I suggest buying the optional bitumen pads.
Faceting the front panels is optional, but can be done by hand.

Workshop pics
BACK TO INDEX

Just a few pics. Not much to show from a simple box.

Left: Remember to chamfer the 18W driver hole. Right: Testing driver rebates and port.

Panel faceting: Front panels were cut ~12 mm/45 deg. in full length.
Top faceting is optional. I sat the table saw to 27 deg vertical and 8 deg. horizontal. Cut to a depth of 20-22 mm (from a 25 mm panel).
Remember faceting can be done by hand.

Left: Adding felt to all sides except rear panel where the crossover will be placed.
Right: Gluing front panels in place.

Make two pieces of 18 x 50 cm acoustilux and place on in upper section and fold the other and place on top of crossover.

MEASUREMENTS
BACK TO INDEX

A few comments on MEASUREMENTS before you start interpreting 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, although dispersion characteristics play a vital role here. A two-way 7+1 and a three-way 7+4+1 may display similar horizontal dispersion, yet sound very different. 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 we 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, yet sound very different.

SPL of drivers on actual baffle with no crossover.
It does not get more easy than this.