SBA 16 MTM
Satori TW29BN Be dome optional
Copyright 2017 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT

It's a bold choice of the SBA people to call a loudspeaker driver Satori. According to Merriam-Webster: "Sudden enlightenment and a state of consciousness attained by intuitive illumination representing the spiritual goal of Zen Buddhism". Let's stick to Sudden Enlightenment or just Enlightenment. This is probably what they had in mind. Now, there are certainly a lot of things behind the driver that will add or detract from that enlightenment, but let's say the Satori MW16 driver is not the bottleneck in reaching that goal. Add the best in front of it, and it delivers. This doesn't mean it doesn't leave a sonic fingerprint, but so does any other cone material available for dynamic drivers.
Like the name Satori, Egyptian Papyrus adds to the myth we try to build around drivers to catch attention from our customers. Organic fibers vary in chemical composition and subsequent physical properties depending on how it is isolated and incorporated into the basic paper pulp mix. So does the resin used, the pulp pressing as well as shape and size. It's all OK, as long as the product delivers something good. The Satori cones are rather rigid, promising a transparent midrange and what's unusual is the lack of conspicuous cone break-up. It's a delicate balance as we can see from the MW19 driver, where high order filters are needed to suppress cone-break-up due to increased diameter.

During set-up of the SBA-10 construction I initially tested the midrange and tweeter as stand-alone 2-way and was mighty impressed with what I heard, not least the bass performance from this relatively small 6" driver, 119 cm^2. How about two drivers doing 238 cm^2, more than an average 8" driver? The MW19P is similar in size to the venerable Vifa C17 and it also features the ability to be run full range without distressing the ear noticeable. This is also where comparison stops. MW16 is not as efficient as Vifa C17 but it features almost everything drivers of the 80'ies doesn't when it comes to overall construction. Download spec below to read what under Features. Even the frequency response of the MW16 is flatter and more extended than the C17. With two drivers in parallel we can tune the system to a healthy 91-92 dB sensitivity. Not bad at all. 38 litre net volume for two drivers provide an F3 of 44 Hz, not bad either. The nice basic behaviour of the drivers allows a simple 2nd order filter at 1.7 kHz, ensuring excellent dispersion in upper-mid/lower-treble.

Now, getting 238 cm^2 midrange membrane area does its thing! From the SBA-10 I knew the MW16 has a significant dynamic head-room. Like the AudioTechnology 18H52, the MW16 can play loud before sounding bad. This probably mostly due to proper symmetric drive. This is the copper sleeve on the center pole piece manufacturers are talking about. Symmetric drive means the inductance caused by the voice coil moving in the magnetic gap is the same whether the coil is moving inwards or outwards. It goes without saying the sound generated by a cone that doesn't move symmetrically in the magnetic gap will be somewhat distorted. Hence, well engineered drivers can play bass and still maintain resolution in upper-mid and lower-treble. They have a dynamic headroom and can be played louder compared to conventional drivers. That said, I was really surprised to hear how loud this MTM could play before sounding compressed. Having a low point of crossover obviously helps too, not having the midbass beaming in upper-mid/lower-treble. Beaming is to my mind a serious issue as discussed on several occasions. Not least when we're dealing with fairly rigid cones like the one used on this MW16. For soft cones we may get away with higher points of crossover as the effective radiating area is reduced towards higher frequencies.
So, all in all a firm and potent bass for the size, ultra transparent midrange and treble as good as it gets these days from this doped soft-dome. I'll stick my neck out and say any other tweeter is a matter of taste, not quality. Last, but not least, we don't need to crank up the volume control a whole lot to make these speakers sing. Overall system sensitivity is immediately felt.

Latest addition to this construction is the TW29BN Beryllium dome tweeter. No changes to the crossover, but do experiment with R1 being by default 2R2. Try out 2.7 Ohm for the Be-dome tweeter. It's a matter of taste and what you add in front of the speakers.
In short: More clarity in all of the treble range.

      
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Basics:
2-way d'Appolito speaker in a 38 litre vented cabinet.
System sensitivity: 91 dB/2.8V, 1 meter.
Impedance: 4 Ohms, minimum 3.6 Ohms @ 150 Hz.
Point of crossover: ~1.7 kHz.
Power requirement: 10+ wpc.
Power handling: 100 watts, but please also read this: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

As always: Any change to front panel design and drivers' placement and you need a new crossover and I can't help.
Please read: http://www.troelsgravesen.dk/crossovers.htm

 


Be domes.


DRIVERS
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Download specs here:  MW16P-8   TW29RN-B   TW29BN


Beryllium dome tweeter


CROSSOVER
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Setting up drivers on a fairly narrow baffle poses some problems due to baffle step loss, that is, at lower frequencies sound becomes omnidirectional where at higher frequencies sound becomes more and more directional. Sound will decrease 3 dB at a frequency calculated from 11500/baffle width in cm, thus 11500/21.5 = 534 Hz. How this emerge in real life depends on the drivers intrinsic performance on an infinite baffle, which we usually find in manufacturers specs. Download MW16P-8 data sheet here. Quite a flat response from this driver on an infinite baffle. Now, this "problem" usually doesn't present any major problem except for very narrow baffles where the loss may start so high we from have a depression in the middle midrange in order to decrease response around 1 kHz, where many 5-7" inch drivers have their maximum output. From a proper value of L2 we tilt the drivers response to make the best possible response in all of the midrange, 160-1280 Hz. From the simple crossover seen above we have a +/- 1 dB from 100-1500 Hz, not bad at all and the actual measurements even looks better. Simulation doesn't tell everything.
From the crossover seen below we're more nitpicking and target a ruler flat response in all of the midrange by using a smaller coil for L2 and insert an LCR circuit to tame the response around 700-1500 Hz. So, which sounds the best?
Both crossover were set up during testing and although the difference was audible, the simple solution, due to a slightly elevated response around 1 kHz, had a very nice presence to the sound delivering a little more detail and engagement without ever being aggressive or too much right-in-your-face. The two tweeter crossovers were exactly the same during tests and to be honest, this comparison turned out more tricky than anticipated and lasted for several weeks because both had qualities and we need to get past any bias due to knowledge of what is going on. The latter is very difficult. The flat response is kind of what it should be, but it had a slightly flat presentation, where the simple crossover had slightly more depth to the soundstage. From opera to hard rock the simple crossover was preferred, which was a bit annoying as the flat should be more correct. The long and the short of it is that simple wins. Tuning a speaker system is all about compromises - and taste not to forget.
So, two resistors, two caps and two coils does it! Very simple indeed - and a lot cheaper also, because there were quite a few uF in low-pass section of the "flat" version.



Above the actual response from the two crossovers. Green is"flat".

Basically the simple crossover is wobbling around the "flat" at only +/- 1 dB.
We wouldn't think this could make any significant difference, but it does. Red just sounds better, which shows that
at the end of the day, speaker tuning is all a matter of taste and choices. 


CABINET
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Using two drivers doubles Vas and reduce Re to half, all other parametres stay the same. Around 20 litres seems appropriate for a single MW18 driver, hence some 38 litres here as damping materials will increase virtual volume a little.

As always: Any change to front panel design and drivers' placement and you need and new crossover and I can't help. Please read: http://www.troelsgravesen.dk/crossovers.htm

Check out this file regarding construction tips: http://www.troelsgravesen.dk/tips.htm

Target here is to make the simplest possible cabinet, thus a straight forward rectangular box of 215 x 270 x 920 mm, placed on a 100 mm stand where we conveniently can place the crossover for easy access and keep it away from any vibration coming from the bass drivers. If you want to add spikes, pads or whatever is fully to your preference.
The cabinet is constructed from 20 mm Baltic birch and you can use 19 mm MDF if BB is not available. Do not use light-weight plywood ("Eastern"). High density solid wood is fine if this is what you like.
The only critical dimension for the two braces is the 80 mm middle hole of the lower brace. Center should be 78 mm from the side to the rear to fit the angled port.

Obviously you can make the cabinet i one piece and place the bottom to make 880 mm internal height. The bottom cavity is very convenient for housing the crossover. Both for keeping crossover away from resonances and for easy tweaking of crossover.

I never provide cutting plans as this will depend on materials available locally. Baltic birch varies in thickness and any fixed cutting plans are likely to fail. It also depends on how you are going to assemble the cabinet, having sides and top/bottom cut 45 deg., or just simple assembly adding veneer at the very end. All methods go.
Never route for drivers before you have them at hand and can measure exact diameter. These things have tolerances as can be seen from specs, e.g. MW16 states 165 mm +/- 0.5 mm diameter. It's a real pain having to increase a driver hole diameter.

Please check my "tips" page for additional info: http://www.troelsgravesen.dk/tips.htm

You can place the port to the front or to the rear to your liking. As we have a decent bass response from these drivers I decided to use a 70 mm angled port as seen on drawing. No port chuffing here!


Workshop images 


For front panels I cut 25 mm sticks of 20 mm Baltic birch and glued 10 pcs + some mahogany fillets to make 215 mm total width.
Now, routing such laminate takes some precaution not getting severe edge ripping. Start lowering the router some 0.2 mm and sand the surface. Repeat by lowering another 0.2-0.3 mm and repeat sanding. Now you can start digging deeper for each turn, but watch out and rotate the router slowly!
Never route for drivers before you have them at hand and can measure actual diameter!


Chamfer bass driver holes as seen on image, approx. 15 mm, 45 deg., for a 25 mm front. 10 mm for a 20 mm front is OK.


Trying out the drivers.

The laminated front panels had quite a surprise in store. The panels were made some 3 weeks ahead of final assembly and at that time I found the driver rebates 165 mm width vertical but only 164 mm horizontally! Drivers couldn't go in! Hmm.. Cutting BB in strips and turning them around 90 deg. all of a sudden exposes an enormous evaporating area and the panel width shrinks. So, I placed the panels 48 hours in our attic (winter time and high humidity) and the panels were back in shape. Pfeww... So, if you make your panels like this, either wait trimming side fillets and driver routing until width doesn't change any more - and this may take weeks!
 


Top brace to the left and bottom brace to the right.


Cabinet assembly. Tape and a few clamps.

 

Damping: Add 8 mm felt to all internal panels except front panel. Ad one layer of 30 mm acoustilux on top and two layers behind bass drivers on rear panel. Add 4 layers of acoustilux at bottom to prevent any internal standing waves between top and bottom. That's all.

With the kit follows 1.3 sqm 8 mm felt and 0.8 sqm 30 mm acoustilux

 


Cabinet damping. I used cheap acrylic pro filler for gluing.

Felt:

4 pcs 22 x 34 cm: bottom section, side panels
4 pcs 22 x 28 cm: middle section, side panels
2 pcs 22 x 58 cm: top section, top and side panels
2 pcs 20 x 15 cm: top rear panel
2 pcs 28 x 15 cm: middle section, rear panel
2 pcs 36 x 15 cm: bottom section, rear panel
2 pcs 22 x 15 cm: bottom panel
Total 1.12 m^2. (1.3 sqm provided)


Acoustilux:

Follow drawing. (0.8 m^2 provided)
I cut 8 pcs 50 x 15 cm and folded the strips.



MEASUREMENTS
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Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.

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 down to 20 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.


Above the response @ 1 meter, 2.8 volts, merged with near-field response at 200 Hz. System sensitivity ~91 dB/2.8 V, 1 meter.


Above individual and summed response of drivers. Point of crossover ~1,700 Hz.


Final system impedance. This is a 4 Ohm speaker with a minimum of 3.6 Ohm @ 125 Hz.

 

TW29BN Beryllium dome tweeter


Response of Be dome (green) compared to TW29RN (red)
Overall a slightly flatter response from the Be dome.


Be dome, response of left and right speaker. Quite a matched pair.


SPEAKER-KIT
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 For level 2, Silver-Z is used for tweeter and STANDARD-Z for the bass section.
Both coils are air-cored wire coils with the same series resistance as the WAX coils in level 1.

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 and include your zip code for transport cost.
Feel sure prices are competitive!

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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Hard to make it more simple than this!


I used the WAX coil terminations directly, hence moved R9 to the other end.
The large WAX coil is secured by two stainless steel screws. View images here.
Drill two 3 mm holes in the wood plug at 17 mm distance and secure by screws, brass or stainless steel.

Wiring

 


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