Ellam Discovery 15
Copyright 2014 © Troels Gravesen

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I had some black MDF leftovers. Enough for a pair of Ellam-9800 front panels. And I had a pair of 5" Discovery midbass drivers and the Discovery tweeters. It called for a moderately priced 5+1 monitor! All four drivers alone are 245 EUR.
I've come to really like the Discovery series of drivers. The 6" and the 8" are both easy when it comes to crossovers - and the sound is great too. All of these Discovery drivers seem to perform equally well within their intended operating range, even the 10" alu bass driver, which has been tested in a possible new construction.
Whenever a speaker driver manufacturer decides on a new range of drivers we usually see a 4, 5, 6, 8 and 10" range of drivers with more or less the same cone material, same basket design, etc. Not all may perform equally well. I have my favourite Revelator and Illuminator drivers from ScanSpeak and I have my favourite SEAS drivers from their respective range of drivers, Prestige or Excel.

 

     
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ScanSpeak DRIVERS
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Midbass: 15W/8434G00     Tweeter: R2604/833000
Download data files from links above.


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CROSSOVER
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My expectation to the crossover work was that it would be easy. Not so. Adding a standard coil and a cap to the midbass made a perfect LR4 roll-off. No more components needed. No midrange bump or anything.

Making the tweeter crossover fit the bass LR4 topology proved a challenge and ended up like seen above. On paper this all works very well with proper phase integration and fairly flat amplitude.
What I was looking for was an LR2 topology and for the bass this was easy by adding a resistor in series with the shorting capacitor as seen below. The tweeter section takes an LCR circuit to smooth/shape roll-off towards lower frequences, otherwise quite standard. The placement and size of attenuation resistors is a valuable tool in shaping the target response profile.

Above the simulated LR2 filter, quite nice too and usually sounds better than LR4 - to my ears. Others will dissagree and taste cannot be argued. The strange thing about LR2 vs LR4 crossovers is that we tend to tune LR4 flatter than the LR2. To my exerience. Most often I prefer a slight tilt from LR2 filters, something in the range of 2 dB from 100 to 10,000 Hz. This kind of evens the balance of basic notes and overtones from the two topologies (not shown on simulation).
Only thing to do was setting up both crossovers and listen! Eventually I decided on the LR2 filter for the lack of the dry presence of the LR4 filter.

The bass section features an LCR circuit smoothing the rool-off around 5 kHz.  A little too much energy here paid its visit in treble performance. As can be seen in the measurements section we have no need to equalise the midrange as is very often the case with small drivers on a small front panel.
The tweeter section is fairly standard second order with some smooting of response in the 1-2 kHz range. R1021 determines tweeter attenuation. My default value is 4.7 Ohm. Full schematics comes with the kit incl. instruction on crossover layout and wiring.

 

 

CABINET
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Box simulation suggest something in the range of 6-10 litre volume making -3dB at 60 and 50 Hz respectively. Not too bad, but don't expect earthquake performance from a 8.6 grams cone of 80 cm^2. With 10 litres volume and a port of 50 x 110 cm (diameter x length) we get a port tuning of 55 Hz. Make the port 40 x 110 mm and we get a port tuning of 45 Hz and bass response shelving down. Might do better for shelf placement. Actually I stayed with the 145 mm port length preferring the lower tuning.


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Any change to front panel and drivers' placement and you need at new crossover - and I can't help.

Please read here: http://www.troelsgravesen.dk/crossovers.htm

 


The lower front panel. Make bass driver hole same diameter as the midbass, 150 mm and chamfer lightly.


Outer midbass panel. Chamfer 45 deg down to 5 mm from driver rebate.


Both panels before gluring and cutting to final size. I make them +2 mm length and width before final trimming.


Testing drivers on front panels.


Gluing front panels. I make the front panels +2 mm before cutting to final width.

Further cabinet constructions images: Ellam-9800 mkII

 

MEASUREMENTS
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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 drivers, because cones made from polyprop, alu, kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of colouring the sound.


SPL of drivers in cabinet. To the left the 15W and to the right the R2604 ring radiator.


The two most important graphs. Left: SPL from final system. System sensitivity around 85 dB/2.8V.
~85 dB sensitivity is not a whole lot and I suggest some 40-50 watts minimum to drive the speaker.
Right: Impedance of final system. Port tuning here ~55 Hz.
This is an 8 Ohms speaker displaying some 7.0 Ohm minimum at 55 Hz and 6.3 Ohm at 250 Hz.


Left: Response from inverted tweeter polarity (red) and same polarity (green). Point of crossover is around 2.8 kHz.
 Right: Tweeter level options. R1021 values with the kit.


Left: CSD.
Right: Step response displaying inverted tweeter polarity and tweeter positive response coinsides with rise of midbass response.

SPEAKER-KIT
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Crossover components' values to come with the kit.
You can buy the kit with or without the drivers - or some of the drivers if you already have some.
Please ask Jantzen Audio for options.

Download Complete Kit Sale Presentations here (pdf file):

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com

 

CROSSOVER-LAYOUT
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SOUND
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What surprised me first was the bass response. This small 5" doesn't go particularly low, but what it does, it does very well indeed. Very articulate (high Qm) and it doesn't die out at low levels as experienced many times before with overly damped drivers.
The midbass' coated glass fiber cone is fairly rigid and has en excellent midrange transparency and the minor equalisation around 5 kHz provides a perfect LR2 roll-off profile. The midbass will play well up into the treble area and it's better be good not to add any harshness to the treble range. And it doesn't.
As always, the ScanSpeak ring radiator delivers a smooth treble with lots of detail and low distortion. It has to be said I used Superior-Z caps for all of the crossover in my test set-up and there's no doubt in my mind that these drivers deserve he best of the best. Not cheap but it pays off. Fall-back option is to use Standard-Z caps for bass section and a single Superior-Z for the tweeter series capacitor, C1031. Decision is yours.
I listened to jazz, classical and rock during development and didn't find it favouring any particular genre. Vocals came through very well from both jazz, rock and classical. These Discovery cones will not cover up any poor recordings, rather tell you what you've got, for better or for worse.
The final voicing of the speaker was done by connecting to my main system: vdh Colibri/Moerch tonearm/Lenco deck/vdh Grail phono stage/WOT linestage/GlowMaster power amp - and to honest I was amazed from what even modest priced drivers fitted with the best of crossover components and some great front-end can do. Even in a 25 sqm room, these small speakers will fill the room from large scale orchestral works. Yes, the deepest bottom end is missing, but the clean un-distorted midrange more tha makes up for this. These drivers will continue to excell the better things you put in front of them. Give them a pair of solid stands and enjoy!