SBA 941
Copyright 2018 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT     SOUND

The range of 3-way classics found on my website are among the most popular kits of all. Featuring 8" bass drivers, 4" midrange drivers and tweeter they deliver an awful lot of good sound for the money. From fairly simple crossovers and simple rectangular cabinets, they are within reach of most DIY'ers, both financially and practically.
As said many times before, having a small 4" driver bridging the gap between bass and treble is a good idea. The reason we do not see this more often is price. For a manufacturer it does add significantly to production costs, not so much for DIY'ers. Having recently visited a hifi show in China, I noticed a lot of smaller low-price speakers featuring 3-4" midrange drivers. Apparently not a big deal over there, so they do the right thing. To me the transition from a 6-7" mid-bass driver to a 1" dome is a bigger compromise compared to the extra complexity of having a dedicated driver for upper-mid/lower-treble.
Here we aim at some more power handling and low-end extension from the use of the magnificent SBAcoustics Satori 9½" WO24P-8 bas driver, the no less magnificent midrange driver MR13P-8 and not least my favorite fabric dome tweeter, the TW29RN-B. Should you want to upgrade to the Be dome, the TW29BN-B can be used without changes to the crossover.
Cabinet is slightly larger than the other 3WCs, but most of the extra volume needed comes from extending cabinet depth some 5 cm.

Basics:
3-way speaker from 9½" bass driver, 4½" midrange driver and 1" dome tweeter, either fabric or beryllium.
Dimensions: 31 x 38.5 x 60 cm, WxDxH.
System sensitivity: 87 dB/2.8V/1 meter.
Impedance: 8 Ohms, minimum 4.0 Ohm @ 150 Hz.
Point of crossover: 580 Hz and 2700 Hz, LR2 and 1st order filter topology.
Power requirement: 20+ watts/channel.
Power handling: 100 watts. Please also read: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

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

 

DRIVERS
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Click images above to view large

 

Download data sheets:
Satori WO24P-8     Satori MR13P-8     TW29RN-B-8     TW29BN-B-8

Please note we here use 8 Ohm tweeters. This saves uF in the crossover.


CROSSOVER
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The crossover features a simple 2nd order topology, LR2, for the bass low-pass section and midrange high-pass section.  The midrange low-pass and tweeter high-pass sections feature 1st order filters. Some attenuation of the midrange and tweeter is needed to match the bass driver response. I deliberately picked the 8 Ohm version of the bass driver to better suit tube amplification. Higher sensitivity could have been had from the 4 Ohm bass driver, but it in end it only draws more current from your amplifier. Box simulation predicts -3dB @ 33 Hz. This bass driver goes low.


CABINET
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Click image to view large.
Do not forget to mirror cabinets and front panels!

Cabinets were made from 20 mm Baltic birch and 15 mm for the midrange cabinet. Cabs were further damped by adding bitumen pads as can be seen from pictures  below. I had the rear panel made detachable, as this will ease crossover placement and tweaking during development, but can obviously be glued in place should you prefer this.

Cabinet damping:
All internal panels were added 8 mm felt material except rear panel where crossovers are placed.
The midrange cabinet is damped with felt and filled with 25 grams wool.
Cut 2 pcs of 15 x 50 cm acoustilux and place round midrange cabinet towards front, see image X below.
Cut 4 pcs 15 x 50 cm acoustilux and add double layer on top/rear and bottom/front, see image Y below.
Cut 4 pcs 25 x 50 cm acoustilux, slice halfway in the middle and place on top of crossover on rear panel. Image Z below. 

As always: Do not change the front panel design or drivers' placement or you'll need a new crossover - and I can't help.
Please read here: http://www.troelsgravesen.dk/crossovers.htm


Workshop images

I suggest taking a look at all the other 3-way classic to get more ideas of construction. This speaker follows the same routines.

http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm#3-WAY_CLASSICS


Mark up the panels for the midrange cabinet and distribute the holes evenly.


My rear panel is attached by screws, thus the fillets. This is something you may choose not to do, but make sure you can pass the crossover boards through the holes in the vertical brace to be placed on rear panel.


Bitumen pads in place.


All interior panels covered by felt damping. No felt on front panel and no felt on rear panel where crossover boards are placed.


Routing of the front panels.


Chamfer inner front panel midrange driver hole as seen. Mark the midrange cabinet to get the boundaries.
No need to chamfer bass driver hole due to large diameter.


Left: Here with the Be dome. Right: Add 25 grams wool to midrange cabinet.


Left: Image X, damping around midrange cabinet. Right: Image Y. Damping front bottom and top rear.


Left: Image Z. Make sure port has proper ventilation. Right: Crossovers mounted on rear panel.

 

 

MEASUREMENTS
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SPL from drivers normalised for 2.8V/1 meter. Red = tweeter, green = midrange, orange = bass.


SPL of speaker merged with near-field bass response. The dip around 1.5 kHz is to my best inaudible.
Generally narrow notches are inaudible. Peaks are another matter, but no such thing here.
If we make and average of horizontal dispersion, the overall power response is fairly flat. See below.


Horizontal dispersion @ 0, 10, 20, 30 and 40 deg. off-axis.


Final system impedance. Minimum 5 Ohms @ 125 Hz.


SPEAKER-KIT
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Remember to state tweeter option!

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

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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Above the crossover for bass and tweeter.

 

 


Above the crossover layout for midrange.

Click images to view large

 

Wiring

 


SOUND
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Moving the speakers around it becomes immediately clear it's a bit bigger than most of my other 3-way classics. Heavy! So is the bass response from the 9½" bass driver. It goes deep.
What took the most time was the point of crossover between bass and mid. 400 Hz, 500 Hz, 600 Hz, etc. Starting at 400 Hz made the middle midrange a bit weak on vocals, lacking the fullness and warmth I wanted. Thus, gradually the point of crossover was moved upwards and ended at 580 Hz making the best blend of lower-mid and middle-mid. Lower-mid does take some membrane area to give the fullness of vocals and instruments. The distance to the floor becomes a factor here too in making the best bass-mid integration. I found 50 cm stands ideal, but try it out. It can have a significant impact on sound how high your midrange are above floor level.
What thrilled me the most was the seamless integration of upper-mid and treble from its 1. order crossover and the smooth - and utterly dynamic - presentation of e.g. cymbals and other instruments with high-frequency content. This speaker surely rivals the AT-3WC and also the PRELUDE speakers - and at a much lower price. Not since the PRELUDE had I done a 1st order crossover, but I remember what it did. And this all thanks to the MR13 midrange drivers, which is not necessarily flat, but smooth all the way to 14 kHz without any excessive dips or peaks. It takes equalisation, but only from an RC circuit across the series coil.
I sometimes have mails asking for a construction giving "dynamic deep bass, smooth and transparent midrange and silky treble". Well, we all want that. Only way to find out if we can have it is building loudspeakers. Enjoy!