Discovery 18 v3
SHORT PRESENTATION

Copyright 2014 © Troels Gravesen

BACK TO INTRO PAGE     

Go to: CROSSOVER    DRIVERS     CABINET    THE SOUND    COMPLETE KIT incl. DRIVERS     CROSSOVER LAYOUT    CROSSOVER WIRING    MEASUREMENTS

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.
Most likely the Dalis would be driven by the legendary NAD 3020 amplifier and we were in for a lot of good sound for the money. And the 3020 had tone-controls to manage the bass, something most people badly miss these days, not least from the dreadful designer homes with bath room acoustics. Look at recent Dynaudio brochure on the Xeo speakers. These are presented in an acoustic environment that couldn't be worse.
The good sound of the Dali was/is due to the Vifa P17 driver delivering excellent midrange and smooth roll-off, making crossover design easy. The P17 in all its variants must have been made in the tenths of thousands, and they could be found in numerous speakers in various forms, depending on manufacturers' preference for magnet size and voice coil impedance. Usually they were made with an aluminum voice former and and a not too ventilated magnet/chassis by modern standards, delivering a not too impressive mechanical Q, but all in all easy on crossovers due to inherent damping and smooth roll-off. Same goes for the Vifa P13WH-00-08, also used in countless constructions and very popular among DIY'ers, e.g. Lynn Olson's Ariels.


Click images to view large

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, D2604/830000 and R2604/832000 tweeters were acquired from ScanSpeak. All drivers will be 208 EUR from ScanSpeak webshop (D2604 option) or delivered with the crossover kit from Jantzen Audio.
Any other tweeter will require a different crossover and I cannot help you with this, so please do not ask.

 

DRIVERS
BACK TO TOP


Click images to view large

 


Click images to view large

CABINET
BACK TO TOP

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


What most first-time diy'ers want: Rectangular box, flat front panel.
Cabinets here made from 21 mm Baltic birch. Braces 15 mm Baltic birch.
Make 4 x 80 mm holes in braces and a smaller one in the middle.


Left: Ready for gluing. Right: Test front panel, here the flat, non-stepped baffle.
Right: DO NOT forget to chamfer bass driver holes, 45 deg. down to some 5 mm from edge of rebate.


Blocks added at corners to fasten test front panels. Do not add these unless you want to experiment with front panels.


Left: DO NOT forget to chamfer driver holes for bass driver! Right: Stepped front panel ready for mounting.


Damping of cabinets:
Damping of panel resonances with bitumen pads is optional.
1: 8 mm felt material on all internal panels, except front panel, rear panel behind midbass driver (crossover will be here) -
and rear panel at bottom where terminals will be.
2: One layer of 30 mm acoustilux at top and bottom. 3 layers of 30 mm acoustilux on rear panel behind 18W driver (covering crossover).
If you use bitumen pads, glue with elastic vinyl glue. The same can be used to fix 8 mm felt damping.
DO NOT obstruct air passage between 18W driver and port!
(Do not add the blocks seen above at top and bottom of cabinet. These were used to fasten test front panels.)

 

CROSSOVERS
BACK TO TOP

 


Full schematics come with crossover kit from Jantzen Audio


 

THE SOUND
BACK TO TOP

First of all, please read these comments on describing sound. OK, agree?
These Discovery drivers takes some time breaking in, which is not unusual for high-Qm drivers. The intrinsic flat response in all of the important midrange is paying off. These fiber glass cones deliver excellent midrange transparency and a responsive bass performance as far down as it goes. I favour the ring-radiator over the dome, but others may choose differently preferring the slightly more vivid performance of the dome. Good thing here is that they are interchangeable by only adjusting attenuation resistor.
Setting up V1 crossover was easy and overall tonal balance was good, but the transition from upper mid to treble appeared rather fizzy and blurred. Something just wasn't right despite the ability to play all kinds of music without any distress to the ear.
The V2 crossover solved this problem and kind of made the sound well known from many other speakers I've made, but not up to the level of stepped baffle/LR2 speakers I've made ever since the launch of the first Jenzen speaker - or the ScanSpeak Illuminator with its all-pass filter to the tweeter. The quality of the W18 driver strongly suggested there were more goodies in store.
V3 crossover: Making the stepped baffle and implementing a true LR2 filter made a world of a difference. Suddenly music started flowing and sense of depth and perspective improved vastly. I never heard the difference between a flat baffle/2nd-3rd order crossover and a stepped baffle/true LR2 filter so clearly. It's night and day. It also made me think I have to do the Ellam XT once more with an easy stepped baffle because people continue building the Ellam XT speaker rather than the much better Ellam FLEX with its more complex front panel layout. There are more to be gained from these Ellam XT. And I would love to do the 9800 tweeter again in such set-up... well, well, back to the Discovery here.
V4 crossover (stepped baffle): This has the well known 4th order characteristics. Even power response and a balanced presentation with a noticeable presence character. Good for monitoring! I know some people like this a lot but to my ears it sounds kind of flat and without the sense of depth and 3-dimensionality of the LR2 filter. Matter of taste in the end.

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
BACK TO TOP

 

For price quotation incl. shipping, please contact Jantzen Audio at: contact@jantzen-audio.com
Remember to state where you live for calculating shipping cost!

DOWNLOAD KIT SALES PRESENTATION HERE: to come

All technical questions at: troels.gravesen@hotmail.com

Buy ScanSpeak drivers directly from ScanSpeak Online Store

 

 

CROSSOVER LAYOUT for version #3.
BACK TO TOP

 

 

CROSSOVER WIRING, version #3
BACK TO TOP

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.

 

MEASUREMENTS
BACK TO TOP

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.