SMT – The Great Diffusion
Note: this is not standard artcile that will be appear under "technology".
When people start treating their listening rooms the first thing they have in mind is to absorb the unwanted reflections and resonances. However, absorbers tend to make the sound weaker and less efficient than it could be. If you’re clever enough you can absorb without killing the sound - with diffusers. That’s the approach of the Swedish SMT.
Mr. Matts Odemalm studied mathematics at the Uppsala University and completed his Master of Engineering degree at KTH Stockholm. In 1994 he founded SMT (Svanå Miljöteknik AB) with two unique products. The first was the ODSS (Omnidirectional Sound Source), built under license by B&K Denmark and with over 1200 units sold. The second was the Golden Horn, a broad-banded diffuser with nearly 2000 diffuser units per square meter.
Over the years Matts and SMT have invented numerous room treatment products ranging from tunable bass traps to diffusion modules with integrated broadband bass absorption. The company now offers also their room tuning services. Under Matts’ instruction, over 50,000 square meters of diffusion products have been installed in various studios, control rooms, performance spaces and listening rooms worldwide.
In 2000, SMT began building unique Level 3 Reference Rooms, in which the room’s deteriorating effect on the sound has been limited to its absolute minimum. The key for understanding the idea behind the Level 3 room - and SMT’s philosophy in general - is to recognize the importance that the company attaches to the sound diffusion.
A diffuser is a reflecting surface which doesn’t produce a sharp reflection but spreads the returning sound energy in time so that the sound in the room grows without colorations and other side effects. Proper use of diffusers creates deep soundstage and strengthens the spatial experience of the recording venue. And the room sounds bigger than what it actually is. To avoid colorations caused by the diffusers themselves, it is momentous that the surface structure of a diffuser does not have regular patterns, and that the time differences between different reflectors of the diffuser are calculated according to sound mathematical principles. And this is exactly where SMT claims it excels.
In other words, for Matts and SMT diffusion is the number one method of treating the room acoustically. Which does not mean that absorbtion would not needed. Especially in industrially produced, small square rooms it is often impossible to get away with all the unwanted resonances, and the presence of absorptive surfaces is a necessity for a good listening experience. The question is how to absorb without killing the sound? Absorbent surfaces damp distracting and unwanted reflections effectively but at the same time the total sound energy in a room is reduced which is why the direct sound gets less "support" and is perceived as weaker. Too damped rooms are perceived as oppressive and uncomfortable. The number of absorbers used must therefore be in strict balance with other surfaces.
Golden Horn (H 550mm, W 550mm, D 128mm) has a special form and flexibility. Crossover frequency is 2000 Hz Diffusion up to 2000 Hz is achieved with 40, 80 and 120 mm diffuser pads, 216 pieces per m2. Diffusion over 2000 Hz is realized with 9 squares separated by 1mm thick walls placed at the top of each diffuser pad. The total range of diffusion is 800-16000 Hz.
SMT’s solution is to build well balanced diffuser panels in which bass absorption from upper bass to lower midrange is adequately taken into account. The narrow deep compartments (which are absorbing in the field where they are supposed to be diffusing) of common diffusers were abandoned and replaced with 200-300 mm wide Creation Panels with a mathematically balanced depth. The exact depth of each panel is important because the lower limit for the diffusion is determined by it. With the aid of 16 mm thick partitions SMT’s panels can be placed with different depths and the sound can be diffused down to the preferred frequency.
Due to variations of the closed volumes behind each Creation Panel it is possible to, by means of slits on the sides, create Helmholtz resonators in order to absorb the lower frequencies over a broad frequency band and with a high absorption coefficient. This is how the MA-modules (Modulated Arrays, MA200/300/600) were born. The MA-modules diffuse large areas without loosing the efficiency of the sound and at the same time master the standing waves of the room.
Does it work in practice?
Level 3 rooms are not common but there are a few here and there around the world. I’ve visited one located in the basement of Audio Concept. All the things explained above are, naturally, taken into account in the Audio Concept Level 3 Room too. When I was explained what was done in the room, I was amazed how meticulously each frequency band was addressed. I soon learned that to deal with frequencies below 100 Hz is a completely different story than handling frequencies between 100 and 200 Hz, and so and so forth all the way up to 20 kHz. The products that have been used in this room include SMT’s bass traps V-4, V-6 and V-12 enabling +- 4dB passive adjustment under 80 Hz. First reflections are diffused with Golden Horns, and later reflections with the mix of TP300 and AD 40 panels. According to Matts the room measures extremely well.
A similar room using the same strict SMT principles was constructed in Marek Sound, Helsinki, Finland. It too was measured, and measured well as shown here for the frequencies below 2 kHz.
And how do they sound?
From the moment one steps in a Level 3 room it’s obvious that it’s not a normal room. One can hear it from speech voice which is free of distracting colorations and easy to follow. The number one sin of such treated rooms is that they sound strangled, with the feeling that the speakers have to work hard to produce enough sound for music to come alive. Is SMT Level 3 room a room, which is treated straightforwadly by best engineering principles, sounding fine and smooth but lifeless and tasteless like an used bubble gum?
In Stockholm the system consisted of McIntosh electronics and JM Lab’s Utopia-series speakers placed roughly 1,3 m from the back wall. I was releaved to notice that the room did not kill the sound that had enough positive energy and liveliness to allow music breeth freely and effortlessly. Dynamic classical music retained well its dynamism, and the impact of the fierest transients was impressive. At the same time, and as one might expect, the sound was hugely transparent in a sense that all the nuances and micro level events in (eg. guitar) music were easily perceivable. The soundstage was perfect too: very stable, very three dimensional and unaffected by the speakers.
The Marek Level 3 room in Helsinki is slightly softer and rounder sounding, otherwise retaining the same positive sonic properties. And it should not be forgotten that the Level 3 rooms are tunable systems.
If the aim is to hear 100% of what’s recorded on the disc - the space, the dynamics, the details etc. - without the room interfering with its own sound, the Level 3 Room of SMT must represent a final goal, or something very close to it. I really fail to see how audiophiles with a disposition to perfection could seriously not consider building a Level 3 type of room for themselves. This is why all speakers that are reviewed for INNER-AUDIO will be auditioned in the Marek Level 3 room in order to provide the speakers with conditions as ideal as possible, and in order to lay down a common ground for all such reviews. The reviews will not directly tell how a given speaker will sound in an ordinary room. On other hand knowledge of how a speaker sounds when it does not get help from a room or when the sound is not spoiled by the room, provides indirect indication of a speaker’s sonic virtues or vices.
In a way the Level 3 Room sounds too good; it sounds too perfect. As said, for professional purposes (eg. reference recording performances) such perfection is largely welcomed. But for more mortal purposes, the ear might enjoy, at least for a change, a sound that is not so far from a compromised normal listening room.
For those music lovers who are content with less treatment and who prefer not to invest big money in room treatment right away SMT offers less ambitious treatment solutions (eg. Level 2 and Level 1 Rooms). When purchased separately SMT diffuser panels (eg. 2 x 1 m2 diffuser panels for the first reflections) can be an enormously cost-effective way to improve the sound of the system.
In Finnish.
Svenska Miljö Teknik – tuotteet ja akustiikkakonsepti
SMT toimii enemmän "konsepti"- kuin tuotepohjalta. Käytännössä tämä tarkoittaa, että yksittäisiä tuotteita ei ole varsinaisesti hinnoiteltu, koska ne valmistetaan aina asiakkaan tarpeiden mukaan. Tietyt tuotteet, kuten V-sarjan resonaattorit, ovat aina toiminnaltaan vakioita, mutta asiakkaan toiveiden mukaisesti niidenkin viimeistely ja ulkonäkö on pitkälti muunneltavissa. SMT:n tuotteista suosituimpia ovat juuri V-sarjan resonaattorit, joiden hinnat alkavat noin 300 eurosta per kappale.
SMT-akustiikkakonsepti käsittää kolme "astetta" (level):
Level 1 = "entry level"
Level 2 = "mid level"
Level 3 = "high end"
Nämä eroavat toisistaan käytettyjen elementtien ja akustisten ratkaisujen määrän osalta. Nämä johtavat haluttuun lopputulokseen, jonka mukaan huone sitten täyttää Level 1 -, Level 2 - tai Level 3 -kriteerit. Level 1 -tason toteutuksen kustannukset ovat keskimäärin noin 5000 – 7000 euroa ja ylemmät tasot sitten enemmän. Konseptiin kuuluu, että asiakkaan tila, johon akustiikka asennetaan, käydään mittaamassa ja kartoittamassa. Kyse ei siis ole vain tietyn tuotepaketin toimittamisesta, vaan tarpeiden kartoittamisesta, oikeiden tuotteiden valikoimisesta ja kalibroinnista kunkin tilan ja käyttötarpeen mukaan.
Mikäli asiakkaat haluavat ostaa SMT:n tuotteita ns. moduleina, onnistuu sekin. Diffuusoreiden hinnat vaihtelevat mallista riippuen n. 200-450€/m2. Lisätietoja SMT:n tuotteista ja niiden oikeaoppisesta hyödyntämisestä: