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Discovery 18
v3
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Go to: CROSSOVER DRIVERS CABINET THE SOUND COMPLETE KIT incl. DRIVERS CROSSOVER LAYOUT WIRING MEASUREMENTS Crossover schematics (Kit Instruction)for version 3 can be bought from me: troels.gravesen@hotmail.com This speaker really started with a client
bringing in a pair of
Dali 310
speakers for upgrade. The Dalis had the venerable
Vifa
P17WJ-00-08 (maybe -00-06) polyprop midbass driver and a fabric dome tweeter
protected by a grill. The crossover was tuned for near-wall placement,
thus a somewhat forward upper midrange to compensate for the inevitable
room-gain. The Dali people knew that despite being presented on nice stands, people would
set up the speakers against the wall - or even on a bookshelf near a
corner. For speaker designers the impossible task is to predict where
people will actually place their speakers, and tune the frequency response
accordingly. No need to tune for ideal set-up if people put them on
the shelf anyway. What if we could revitalise the "6+1"/P17 concept from modern ScanSpeak Discovery drivers? Can the 18W/8434G00 make up to the Vifa P17WG driver? On paper it delivers a fairly promising frequency response and an impressive mechanical Q of 7.58 due to its glass-fiber voice coil former, vented chassis and low-loss suspensions. The magnet system has an aluminium ring - somewhere - a low-cost semi-Symmetric Drive feature. Fs is in the range of 55 Hz and we won't get kick-butt bass from such driver, but neither did the P17WJ. If we want something in the 30-45 Hz range add a subwoofer. And today we might substitute the NAD 3020 amplifier with the NAD D3020, the digital revival of the 3020 legend, and use almost any kind of source material. Thus, pairs of 18W/8434G00 and R2604/832000 tweeters were acquired from ScanSpeak. Any other tweeter will require a different crossover and I cannot help you with this, so please do not ask.
Useful links (Please read before writing!):
FAQ (Please read before writing!):
I've had the question on vented vs. closed box designs many times. Modern drivers generally feature low Qt (high mechanical and electrical damping) and if we put them in closed boxes we just don't get any bass. Simple as that, regardless of the closed box' superiority in transient response. Thus, vented it must be. If you have a router - and you need a router to make loudspeaker cabinets - then you may also have a 45 deg. router bit to chamfer driver holes. Whether you chamfer the sides of the front panel or not will have little impact on performance - but it looks nice. From the images below you can see how to make the outer bass front panel. I rounded the outer bass panel towards the tweeter a little for the stepped baffle. If you do not have a rounding bit, leave it sharp. This is as easy as it gets for making non-stepped baffles.
Use 19-22 mm MDF or 21 mm Baltic birch. For bracing I used 15 mm Baltic birch. You do not have to adjust volume regardless of panel thickness, just stick to outer dimensions. All internal panels are covered with 4 mm bitumen pad, which reduce volume, but the felt/acoustilux will increase virtual volume and +/- 1-2 Hz variance in Fb (port tuning) does not matter. Port is Ø50 x 120 mm length for Fb = 40 Hz. You can boost bass a little by reducing port length to 8 cm (Fb = 45Hz).
Cabinet construction pics
First of all, please
read these
comments on describing sound. OK,
agree? General for all versions is the dynamic bass. These high-Qm Discovery midbass drivers has the ability to not only let your hear the bass, but also feel it. OK, not like a 15" on an open baffle, but for the size, quite remarkable. And this driven by my GlowMaster KT88 PP tube amplifier. A good 40-60 watt PP valve amp is all these speakers need.
COMPLETE KIT
incl DRIVERS
Crossover schematics (Kit Instruction)for version 3 can be bought from me: troels.gravesen@hotmail.com
CROSSOVER LAYOUT
for version #3.
CROSSOVER WIRING,
version #3 |
Value of components comes with the kit.
Fully mounted crossover.
Left: Crossover mounted on rear panel in cabinet.
Right: Two layers of 30 mm acoustilux covering crossover.
Upper left: Response
from drivers driven from V3 crossover and summed response (red). Upper
right: The red and green graphs show the impact of the upper mid LCR
circuit (R2031/L2031/C2031). This may seen very little but it does
reduce and tendency to a too forward upper mid and just increasing L2011
leaves a dip in the middle midrange, thus the LCR circuit is to stay.
The W18 response bump at 8-10 kHz is insignificant and removing it by
another notch filter didn't prove worthwhile. Upper right: Inverting tweeter polarity leave a huge suck-out in the 1-5 kHz range suggesting good phase integration of the two drivers over a wide range. |
Upper left: The clean frequency response of V3 crossover,
merged at 250 Hz with woofer near-field response.
System sensitivity = 87-88
dB/2.8V.
Upper right: Impedance of final system.