Bookshelf-3WC
Copyright 2018 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT

This 3-Way-Classic is designed for bookshelf placement or on stands up against a wall. You can also build the speaker into the wall having the front panel flush with the wall. I know it's out of fashion to have books on display in your living room these days, which is a mystery to me, but I'm an old fart.
Placing a speaker up against the wall takes special voicing of the speaker in order to balance the significant room-gain we experience. Please google room-gain to learn more.
Against the wall is what's called a 2pi situation, half-space. Check here. Against a wall, against a wall + side-wall (quarter space) - or literally in the corner (eighth space) will gradually increase response at lower frequencies. We have a bass boost - and it comes for free! To compensate for this we have to increase midrange and treble and manage bass accordingly to make an overall balanced sound.
All my former constructions are tuned to be out on the floor, thus midrange and treble is attenuated according to the bass response in this position. There are always compromises to be made here, because people may have to place their speakers in less than ideal acoustic environments - and we badly miss the tone-controls of our 70'ies amplifiers.
The Bookshelf-3WC is also designed to provide a significant sound-pressure, thus we start with a powerful 8" bass driver. The 22W bass driver comes with a 235 cm^2 membrane area, quite high for an 8" driver. For midrange I picked the 12W/8524G00 used in my mini-12W some time ago. This midrange is extraordinarily linear and easy on crossovers - and it sounds great too! For tweeter the D2608/913000 used in two of my recent constructions (Ekta mkII and NOMEX 164 mkII). You hardly find better for the money and you may check out this test to see how well it performs.
I also wanted this speaker to be easy on cabinet construction, hence a flat front panel and a 4th order crossover between mid and tweeter, allowing proper phase integration - and not least reduced crossover lobing in upper-mid/lower treble, as this speaker is likely to be used for "music in a room" - and not "head-in-vice" pin-point-imaging kind of situation. Most of us listen to music while doing something else. The cabinet may be added a front grille to increase WAF should this be needed. As can be seen from the measurements below, impact on frequency response is modest.

Basics:
Three-way floor-stander from 8+4+1 inch drivers.
Sensitivity: 90 dB/2.8V/1 meter.
Impedance: 8 Ohms, minimum 3.3 Ohms @ 125 Hz.
Points of crossover: 350 and 3000 Hz.
Cabinet dimensions: 45 x 30 x 28 cm (WxDxH)
Power requirement: 20+ wpc. Actually depends on how loud you play.
Power handling: 120 watts, please also read this: http://www.troelsgravesen.dk/power-handling.htm. Any burned driver is a misused driver!

Useful links:
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm

 

DRIVERS
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Click images to view large

Download specs:  22W/8534G00     12W/8524G00     D2608/913000


CROSSOVER
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The crossover features LR2 filter for bass-mid and LR4 for mid-tweeter sections. As these speakers are designed to be placed horizontally, crossover lobing is a concern and here the LR4, due to reduced overlap does better. LR4 for bass-mid was tried but didn't pay off, hence the simpler LR2 at this stage. LR4 for mid-tweeter also allows us to use a flat front panel and do proper phase tracking between mid and tweeter, the most critical range.
Initially I tried a point of crossover around 700 Hz between bass and mid, but this made a fuzzy midrange when moving horizontally. Knowing the 12W driver from previous construction, I knew this could go much lower and the point of crossover was moved down to around 300 Hz and things started working out. Only disadvantage is the need to double C3 compared to the earlier version, which adds to the kit costs, if really good caps are chosen.
The midrange/treble here is tuned some 2 dB higher compared to the Discovery 3WC featuring the same bass. This due to room-gain adding weight to the lower octaves. To guess what level of room-gain you will have in your room on your shelf is impossible for me to tell, but unless you also place the speaker in a corner, the chosen voicing should fit most situations. There are options for tuning the bass in case of excessive room-gain by placing resistors in front of the bass crossover section. Some will point fingers to this, but I don't care, it works. More on this in measurement section.

 

"I think they're beautiful" my wife said, entering the dining room. YES! High-WAF accomplished.
The 12W taken down to 350 Hz and the 4th order crossover between mid and tweeter works really, really well. So well, I might consider a stand-mount version from the same drivers. Vocals, violins, saxophones, everything come trough smooth and easy. The bass is powerful despite the reduced cabinet volume. From my set-up above I have 1 meter to side walls and the aperiodic tuning works very well.

What has surprised me the most is the soundstage depth and spaciousness. There's a thing with a loudspeaker tuned for playing with the room, rather than - sometimes at least - against the room. It energises the room in a more natural way. I came to think of an article of Roy Allison of Acoustic Research and his research into boundary effects on loudspeakers. Here's his patent. And here's the article thanks to Bruce/US. You may visit this interesting site.


CABINET
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Cabinet is made from 20 mm Baltic birch. Obviously you can use 19 mm stabdard MDF. Bracings and midrange cabinet can be made from 15-20 mm materials. The bracing left to the bass driver is 20 mm wide and 100 mm deep and goes to the front panel. This to contain a sheet of acoustilux, 200 x 240 mm, folded and stuffed up against the 20 x 200 mm slot in front panel. This makes the aperiodic tuning. The midrange cabinet is 6 x 13.5 x 15 cm internal dimensions = 1.2 litre.

Useful links:
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm

 


Fitting in front and rear panels.


Preparing for the drivers.


Making braces.
One reader asked if I really made these holes with the router... Indeed I do.
This time I recorded the time making one 105 mm holes. 70 sec. I mean, even with a bunch of holes, this doesn't take long.
Smooth the edges with a rounding router bit.


Left: Routing for drivers on Baltic birch can be a real pain! After a perfect rebate, I slid back the router and it made this! New front panel.
Right: Chamfer mid-driver hole! No need for bass due to large diameter.


Left: Testing driver rebates. Right: As the speaker is meant to be up against a wall, the binding posts need recessing.


Binding post panel. Place it behind the midrange section as you need the space behind bass driver for the crossover.


Damping felt I cut with a scalpel and a ruler. Takes quite some blades! They go blunt very quickly.


MaxiBond for glueing felt sheets.


Fold a piece of 200 x 250 mm acoustilux. Fold over a piece of cardboard and slide into the slot.

Acoustilux damping:
Add a piece of 15 x 15 cm to the midrange cabinet.
A piece of 20 x 50 goes behind mid tweeter section.
Fold a piece of 25 x 50 cm over the crossover on the rear panel.


Preparing for the final measurements for simulation and making the frame for the front grille.


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, 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.


Response of drivers with no crossover. All of these drivers are very easy given the baffle size and drivers' placement.
Bass response merged with near-field response @ 175 Hz.


Final system response. Overall system sensitivity around 89 dB.



Displaying points of crossover, ~300 Hz between bass and mid and ~3 kHz between mid and tweeter.
Bass response merged with near-field response @ 175 Hz. Orange = summed response of drivers.


Final system impedance. Basically an 8 Ohm speaker with minimum of 3.3 Ohm at 125 Hz.
Thanks to the acoustic vent, this speaker is indeed an easy load and my 32 tube watts plays it to thunderous levels.

Now, placement!
You may have to place this speaker in less than ideal positions, e.g. close to the corner and render just too much room gain. Above you see what happens to the bass level from adding resistors in front of the bass crossover section. Red, green, yellow, orange and blue respectively: 0R, 0R47, 1R0, 1R5, 2R2. I suggest 20 watt resistors. Due to the fairly low point of crossover between bass and mid, this is a viable solution in case you don't have tone-controls, which most people these days have not.


Response w/wo front grille. Green = with front grille. Very little impact in tonal balance and no peaks/dips.


SPEAKER-KIT
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In the STANDARD-Z version all caps, except the Premium ELKO, are STANDARD-Z, everything else is the same.
Specify front grille fabric colour if you want this!
And order grille pegs and grille peg catchers. See Jantzen Audio website.

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

http://www.jantzen-audio.com/bookshelf-3wc/

Download Complete Kit Sale Presentations (pdf file):

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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Bookshelf - wiring


Connect PLUS in to R1 with wire.
Pay notice to inverted polarity of midrange and tweeter.

 


I don't think you've ever seen a bookshelf speaker with such high-quality crossover.
Overkill? Not at all. Why should bookshelf speakers not be allowed performing their best?
Obviously you can replace all caps with standard PP caps, STANDARD-Z, and it works fine, but you loose detail and resolution.

In the actual crossover, I expanded the width a little allowing R1 and C1 to reach the input of L4.

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