"A Cohesive Soundstage with Plenty of Punch"
To complement Solo and other systems, Arcam has designed the Muso loudspeaker. The Muso partners beautifully with Solo and offers the benefits of discreet looks and stunning performance.
England's What Hi-fi? magazine praises Muso for having "a cohesive soundstage with plenty of punch."
The Muso enclosure is made from a clever combination of aluminum and steel components bonded together with the latest adhesive technology for the lowest possible resonance. The result is an extremely 'dead' cabinet, and Arcam's use of SDA 'sound dead aluminum' further dampens cabinet resonance.
A Small But Full-Range System
The Muso two-way speaker offers a bass performance far beyond that of a typical satellite speaker, meaning it can be used as a simple stereo pair when placed close to a wall. With the addition of the Logo sub woofer, a full range system can be configured for stereo music or movie systems. However, it is in the full 5.1 combination where the Muso / Logo really shines, offering a dynamic performance that would put many a "big box" speaker to shame.
The drivers consist of a 1" aluminum dome, magnetically-shielded tweeter. Arcam chose aluminum for this tweeter due to its ultra light weight and maximum stiffness. The 3.5" polymer/aluminum cone, magnetically-shielded woofer has a vented pole piece woofer magnet for very low distortion. The smooth flowing flared 'L-shape- port offers extended bass response. The acoustically transparent tweeter woofer grill is magnetically mounted. Muso's front-ported design allows positioning close to walls or in cabinet fixtures.
The eight-component crossover has an air-cored high-frequency inductor on a fiberglass PCB. Muso uses gold-plated 4mm binding posts and includes a compliant rubber isolation mat.
Muso measures 9.1" high, 4.7" wide, and 6.1" deep, and weighs 6.6 lbs.
Muso Project Background
Muso is designed to fill two roles; to be a high quality home cinema speaker for 5.1 (or more) channel systems working with its dedicated subwoofer Logo and to be a full range mini monitor for smaller systems where a very high playback level is not required.
To this end, Muso is based upon a medium power mid/woofer and companion tweeter. The result is a discrete speaker that can reproduce bass information down to 70Hz and still have good dynamics and accurate midrange replay.
When used with a sub woofer in a surround sound system, such as the solo Movie, the Muso speaker is rated at 100wpc. This is because a large proportion of the audio power developed by Sub/Sat systems is delivered by the sub-woofer. By using a satellite speaker with a better bass response, it is much easier for Muso achieve a good integration between it and the Logo sub woofer. This is because Muso still enjoys a flat response in the region where the crossover operates rather than starting to roll off.
When used as a full range speaker, the MUSO is rated for working with systems of up to 30W using the IEC power rating system. Muso can cope with systems up to 50W, so long as it is not played at high volumes for extended periods of time.
Muso Cabinet Design
Muso was developed using many of the same anti-resonance technologies as used in Arcam's electronic equipment. For example, Muso's cabinet utilizes dissimilar materials in its construction to reduce the propagation of vibration around the cabinet. The side walls are an aluminum extrusion and the front baffle is made of machined steel. The top, bottom and binding terminal plate are die cast aluminum.
To further reduce the propagation of sound waves around the cabinet, its component parts are held together with an absorbent compliant adhesive. This means that at each transition between different panels resonances are damped by the absorption in the material holding the panels together.
To reduce any build up of panel resonance, the cabinet walls use constrained layer damping. This is based on separate layers of materials of different thicknesses bonded together with vibration absorbent adhesive. It works in the same way as the Sound Dead Steel Arcam uses in its chassis designs. As the vibration moves through the region with the different thickness layers of material, the vibration is damped down by the conflicting resonant frequencies of the two panels.
The internal walls of the cabinet are covered in acoustic foam. This has two beneficial effects; firstly it reduces the build up of standing waves inside the cabinet as high frequency sound is absorbed by the foam. This reduces the energy inside the cabinet so that less sound is radiated from the cabinet walls. Secondly, the foam slows the speed of sound, as sound moves much slower through the foam than it does through air. The sound waves therefore take longer to hit the cabinet side walls thus increasing the apparent volume of the cabinet and extending the low frequency response.
The combination of these effects is a cabinet with very low radiation of sound and good bass response. The low radiation of sound from the cabinet significantly improves the accuracy of the sound the listener hears as it is not contaminated with sound radiated from the cabinet.
Muso Midbass Driver
The mid/bass drive unit in Muso uses a polymer and aluminum composite cone. This delivers a breakup characteristic much better controlled than a pure aluminum cone. Pure aluminum tends to “ring” in the breakup region thus adding harmful sonic distortion. The improved breakup characteristic simplifies the design of the crossover giving a speaker with a well controlled response and a more dynamic sound.
The large inverted dust cap on the Muso is made of doped paper as this is the lightest material available for this application. Using different materials across the driving surface of the speaker also reduces the build up of resonances in the cone.
The drive unit’s chassis is constructed from die-cast magnesium alloy. This is used over a cheaper steel chassis as it is an inherently better damped material. In addition it allows for much thinner parts to be used. Having thinner parts allows sound to pass from the back of the speaker cone to the inside of the cabinet more easily and reduces reflected sound back towards the cone which, in turn, would add distortion.
To reduce the build up of air pressure behind the dust cap the magnetic pole piece is vented so that air can pass through it into the cabinet behind. This reduces compression distortion in the drive unit particularly at higher volumes.
To reduce any build up of pressure behind the spider (the part of the driver which holds the voice coil in place), the magnesium chassis has holes to allow air to pass out the sides of the chassis. This reduces also distortion and improves sound quality as the spider can move freely.
The Muso midbass drive unit is shielded so that the speaker can be placed close to a TV or monitor screen.
Muso Tweeter
The Muso tweeter is a pure aluminum dome tweeter. As a tweeter dome is much smaller than a bass/mid cone the breakup region of the tweeter cone is outside the region of human hearing. This means that the tweeter behaves as a piston throughout the audible range giving the most accurate presentation of the sound. Even outside the human hearing range, the ringing caused by breakup can still cause some audible problems, so the Muso crossover is designed to electronically reduce the ringing that would otherwise be present.
The Muso tweeter is acoustically damped on the rear surface of the magnet using specialist dampening rubber. The high frequency sound waves from the tweeter pass in both directions out of the front of the speaker and to a certain extent backwards through the tweeter itself. When the sound traveling backwards through the tweeter reaches the back surface of the tweeter some of it is radiated into the cabinet and some of it bounces off the back surface and starts traveling forward again. This delayed sound causes confusion in the sounds presentation. The damping on the back of the tweeter significantly reduces this distortion improving the clarity of the sound, particularly fine detail.
The tweeter uses a neodymium magnet that is magnetically shielded so it can be placed close to a TV or monitor screen. The voice coil of the tweeter is Ferro fluid-cooled to reduce any problems with a build up of heat. This heat would otherwise cause the resistance of the voice coil to vary. The Ferro fluid is held in place by the magnetic field of the magnet. It is designed to have good thermal conductivity so that heat is carried away from the voice coil.
Muso Bass Alignment
The Muso speaker uses a front facing port so that it can be used close to walls without the wall interfering with the port response. The port itself extends the bass response of the speaker. The port frequency is set to 63Hz. To achieve this without causing “chuffing” a long port of a large cross sectional area is needed. As the Muso box is not deep enough to accommodate a long port, the port is bent inside the cabinet to achieve the required length. The port has a small flare at each end to reduce any noise caused by air entering and leaving the port. The port uses extra thick side walls so it can support itself with minimal vibration even when the speaker is playing loud. The port combined with the acoustic foam enables the MUSO to have a bass response much deeper than would be expected for such a small unobtrusive speaker.
Muso Crossover
The crossover in Muso was designed using a combination of computer simulation and many hours of listening tests. This enabled Arcam to develop a crossover that not only achieves a superb frequency response but also has a balanced sound, integrating the drive units together perfectly. The crossover uses eight parts rather than the usual five to provide additional control over the tweeter in the supersonic range where it can start to ring, and also to control the midbass drive unit in the breakup region.
The crossover is built on a fiberglass PCB to provide a good firm base for the parts. Each part within the crossover is carefully matched to a very specific requirement. The tweeter uses air cored inductors for their improved linearity and polypropylene capacitors for their stable high frequency response and sound quality. The parts within the crossover are damped, where required, to reduce any micro-phonic interaction between the sound field inside the cabinet and the parts of the crossover. | 
