Good small speakers are always in demand. "Please do not always offer just black or white", is often found in our e-mail inbox. Here you go: A tiny box in magenta is making a big impact.

The shape of the Micro AMT is reminiscent of the Kolibri from 1993, a two-way miniature loudspeaker with appealing sound. The installation was already quite diverse: free standing on the sideboard, as a shelf loudspeaker, or as a wall loudspeaker, simply by hanging it on the wall. The Kolibri from 1993:

The Kolibri was already here and to admire as a play partner in surround systems. You could have used it well with a PC, but, on the one hand, hardly anyone had done it before and on the other hand, the chassis would then need a magnetic shielding.

Today, everything is different, the need for small, good PC speakers is high and magnetic shielding is no longer required with flat panel displays. Moreover, it was previously technically far from possible to manufacture such an AMT in this tiny size.

The baffle size of the Micro AMT is limited to the usual format of a paperback book and only slightly exceeds the dimensions of conventional PC speakers. Yet: 2.5 litre bass reflex housing volumes indicate that the application is not only on the desk.

Where do you use such a compact box? The fields of application are diverse: Mini and micro systems, PC loudspeakers, gaming, two loudspeakers for the holiday home - the creative loudspeaker community can certainly think of a lot of ways to replace the accessory boxes of home systems with the Micro AMT and thus improve the sound. The addition of a subwoofer is possible and makes sense if you want the bass to reach below 60 Hz, because there the Micro AMT runs out of steam. The "lung volume" of the woofer is at the end of its capacity. Nevertheless, the Micro AMT comes across more powerful than expected. I tried it at home in the party room. My neighbour said affectionately: "The little devil really revs it up, I know other brands...", but better leave that. At the latest with subwoofers can the small size play a bit louder.

The cost of the Kolibri was then quite inexpensive at less than DM 100. With the current currency conversion, we remain today again at a hundred. If you have not built any loudspeakers before, you will find a lot of advice and useful tips on loudspeaker construction in our community.

Large woofers are basically excluded and the old Gradient TPC 80 RW-4 from the Kolibri can only still be admired in the ancestral gallery. And yet we have found the ideal chassis: With our long-time partner from the land of unlimited possibilities, we took back the Dayton ND 91-4. A full-range speaker, which we use here as a low-mid-range driver and help it along in the high-frequency range.

The ND91 4 shines through its only 4 mm long voice coil in the 14 mm deep air gap. This underhung construction allows a linear stroke of 5 mm and this in a homogeneous magnetic field. FS 68 Hz, QT 0.4 and VAS 2.2L result in a clean alignment in the reflex housing of 2.5 litre net volume and a BR alignment to 65 Hz. Up to 5 kHz, the ND91 behaves exemplary, it is an ideal partner for the AMT Mini-8, which should definitely not be used below 5 kHz. ND 91-4 is quite suitable for the Micro AMT.

Frequency response:

Original measurements with Omnimic.
Note: 1/24th octave smoothing - nearfield response included in graph below 450 Hz.
Black = 0 Grad
Red = 15 Grad
Green = 30 Grad
Blue = 45 Grad

The AMT Mini-8 module kit is supplied with additional front panels. Thus, its options for the use of DIY coaxial systems are variable up to and including its application as super tweeters. This also includes a package of screws. When you consider that the Gradient HK 10, Uf-8 from the Kolibri was first able to show its full potential starting at 500 HZ, the AMT Mini-8 requires a much higher crossover frequency: It definitely should not be below 5 kHz.

The AMT Mini-8 is supplied with two front panels.

Frequency response:

Original measurements with Omnimic.
Note: 1/24th octave smoothing - nearfield response included in graph below 450 Hz.
Black = 0 Grad
Red = 15 Grad
Green = 30 Grad
Blue = 45 Grad

The crossover is extremely simple and deliberately low-priced components of small size are used. They find a place on a circuit board of just 6 x 6.5 cm. A low-pass of the 2nd order allows even the small resonance peak which is shaped as an inverse calotte aluminium membrane of the ND91 to disappear. To reliably connect the tiny AMT, a 1µF capacitor is sufficient. This, in combination with the resistor, also causes the level adjustment. Thus the box plays linearly from 65 Hz to 20 kHz.

With regard to the phase, the following has been shown during the measurements: If the AMT is at or below the ear level, it must be connected inversely phased to the ND91. This is probably the case with most applications. If you place the box above the head, it should be rotated by 180 degrees or the AMT should be connected in phase. Otherwise, a significant break occurs in the range of the crossover frequency.

This behaviour is typical in a non-coaxial arrangement of two or more drivers, but is here exacerbated by the following conditions: The crossover frequency is very high at 5 kHz and the horizontal, relatively deep slots in front of the folded membrane of the AMT act as a kind of acoustic lens. They favour the horizontal dispersion behaviour, which is shown in the lateral measurements, but diminishes the vertical.

Measurements:

With such a small reflex housing of 2.5 litres, it is not absolutely necessary to use a 19 mm MDF: 12 mm is completely sufficient (in the DIY store kind of difficult to get; more likely in speciality shops).

The fully prefabricated housing kit of 12 mm MDF can be as simple to set up as Legos. Instead of the use of Lamello biscuit joiners, the side walls are mortised in fluted form.

In the case of such a thin front panel, the question is whether loudspeaker openings cut out with the jigsaw will not suffice if you want to fall back on the boards from the DIY store. A router is helpful, if you have one available.

As you can see, even the little details can make you happy, even if you do not see them from the front.

Package or adhesive tape replace the screw clamps, if you don't have these available.

You should allow 30 minutes time for the gluing of the boxes. A tube of glue and a tape called Tesssss... or from another manufacturer. Packing tape is fine as well. Those who do not constantly builds speakers will not necessarily need clamps, but you once have tasted blood, the right tool travels into the tool cabinet all by itself.

Dry construction as shown above helps in later gluing, because once the glue sticks to the piece, it becomes difficult to exchange the parts again. In addition, the glue sticks so nicely on your fingers.

Then you can finally start:

Wet everything well with glue, better too much than too little. It should not whistle through the cracks, but through the bass reflex channel as the only opening next to our American friends, the Dayton Duet.

Excess glue residues are always wiped off right away: A small bucket of water and an old cloth are sufficient to remove the sticky glue, and saves a lot of work in retrospect, as glue residues can be quite persistent to remove and need elaborate grinding.

Inside, excess glue increases the stability.

Now, it gets exciting: The second side wall can be fitted. Carefully cover all edges of the loudspeaker with adhesive tape while pulling the roll of adhesive tape over the loudspeaker housing. Be sure to use plenty of adhesive tape, better too much than too little.

Clean work is required so that the box is not out of square.

Important: Place as much pressure as possible on the tape.

Main thing stable: Well packaged is half glued.

At current temperatures of 30 degrees, you can begin working on it after two hours. In the winter, it is better to wait until the next day.

Remove glue residues, if present, using a damp cloth, because then, as mentioned above, less grinding work is necessary and the sanding block moves easier over the wood. Please do not forget to sand the edges with the sanding block so that the primer and/or paint then finds a good adhesion.

The whole box can be sanded before priming with sandpaper, depending on which kind of wood you used. You can ask questions in the forum, the boys (and girls) enjoy a lively forum discussion.

Any remaining glue residues are removed with a chisel or knife before grinding.

Do not forget: Sand the edges with the sanding block to help the paint adhere.

We used white primer. They are available in different tones.

In the next construction reports, I will try several paint-primer combinations. So, now it's time for shopping in the DIY store. For primer Express and 2-to-1 coloured paint, a small lambskin roller and a brush as well as a bit of paint masking film to cover the table before you get started.

The protective layer of several brushes should be removed before painting.

Neat and clean: Now you can start with the magenta permanent make-up.

First apply the Express undercoat with roller and/or brush. It dries very quickly and can be applied several times a day.

Since today the brushes and the rollers are mostly made in the Far East, one should wash them thoroughly under warm water, as they are provided with a protective layer. Depending on which paint colour is used, you can choose the right colour from white to light grey to coloured primers.

If you want, the primer or paint can be dosed with the brush ...

... and then cleanly distributed with the roller.

The priming or paint application on the front is somewhat tricky.

A small brush helps paint the loudspeaker openings neatly.

Before applying the magenta paint, sand again and dust well.

This time the choice was magenta. Apply with a roller and brush and allow to dry overnight. A tip on our part: Applying the paint with a spray can is difficult on such a small surface - so just use the brush and/or roller.

Please do not leave this paint open if you have vampires in your house.

The first layer of paint is really neatly applied, it is time for the final finish.

It is so slow: On the following evening, the second paint layer is applied.

Here, too, the roller is much neater.

A small brush helps for the paint application in the bass reflex channel.

Help, someone is drilling holes in the almost finished box ...

... to mount the loudspeaker connection terminals.

Pre-drill the pole terminals, screw them in and solder them to the switch. The assembly of the switch is anything but difficult due to the number of components and the pre-milled circuit board.

Connect the cables to the chassis and the switch while observing the polarity.

Put a little Sonofil in the case and tighten the screws of the chassis.

Do not slip when screwing the chassis - DONE: Onto the sound test!

Such small dwarfs are often underestimated in sound quality and condemned to a shadowy existence between the great colleagues, who are in the spotlight of the DIY construction community. One searches and quickly remembers when the DIY urge (here in the positive sense) won't leave you alone: "Build something again!", comes the voice from within. But where do we put the big boxes? This is where the small ones come into their own. Even more pleasing if they bring a solid bass foundation.

As one of the smallest of its type, the AMT Mini-8 supports the Dayton ND91-4 which came into the world as a full-range speaker. It mastered its new role as a low-mid-bass speaker with bravura in all aspects of the music and, is in top form at the top of the musical scale, and with every musical genre, but I left out the heavy metal concert I have to admit. Those who believe in the small boxes, can catch up and report it in the Forum. I am all ears.

Otherwise, the dwarfs fill whole concert halls with sound - or the living room becomes a concert hall. The dwarves do not produce profoundly deep basses, of course, but they a lot much better. What physics allows. The Micro AMT cuts a good figure in our work room and there they do not shy away from good room volume.

Voila: It's Micro Time!