Why They Work?

The only Closefield* Monitor in The World

In recent years it has become evident that a new approach was necessary for high quality monitoring that had some kind of relevance to home playback equipment and the kind of acoustical behaviour these systems have in an ordinary listening environment.

Until now various techniques have been employed such as using very large farfield full range high power monitors in an-equalized room, backed up by cheap small monitors in close proximity, called “nearfield” monitors. This system has worked reasonably well because the quality of the consumer playback equipment was extremely variable and most cheap systems were of low quality. The arrival of digital technology has forced the manufacturers of consumer hi-fi to produce high quality playback equipment. As a result, mixes made on various recordings have started to show up shortfalls and many have become questionable.

The problem is quite simple

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Farfield monitor in an untreated room

Using a farfield monitor electronically equalized in a room does not overcome the detrimental effects of room acoustics because firstly the problem is of a time-domain nature and secondly the equalization is only effective in one listening position and for a given number bodies in the room. If any of these variables are changed, the equalization is no longer accurate, the only correct way is to treat the problem mechanically (i.e. treating the room) with the help of a reputable acoustical architecture company or to use closefield*.

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Farfield monitor in a treated room

Farfield monitoring will create a lot of reflections in a room from the floor, the ceiling and various objects along the path of the main and reflected signals which will get added into the main signal causing many losses of quality and stereo instability.

Acoustical treatment of the room will reduce many of the detrimental effects of reflected sound but cannot cure the problem totally due to the long signal path to the listener.

As many engineers were aware of this shortfall, the use of a small pair of cheap speakers placed at close proximity became a quality backup system to the main monitors. This way, a lot of the detrimental room effects were cancelled out as direct sound reaching the listener is a long time before the reflected sound off the walls. This is how the seeds of closefield* monitoring were laid and is the basis behind the technique.

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Closefield monitor* in an untreated room

This was of course a very crude solution to a complicated problem. Using a monitor in closefield* is a definite solution to room acoustics problems but the next problem was the one of sound quality of such monitors and their time domain and phasing problems in closefield* use.

Pair of SILVER 5L monitor, designed specifically to be used in closefield*, will eliminate the detrimental effects of reflected sound, due to the difference between the length of the direct signal as opposed to the now very much delayed reflected ones where the human ear is able to detect the difference and ignore them.

A step in Time

Any multi-driver monitor will suffer from time domain and phasing problems when used in close proximity to the listener. Multi-drivers placed on a baffle will have all their acoustical centres spread in both X and Y, as well as Z axis (in other word 3D). Using a single full range driver would seem to be the answer but it is not possible to make a full range driver with any quality and efficiency let alone accuracy which is of prime importance for accurate monitoring, so we can rule them out.

Using a two driver system (mid/bass and tweeter) is the next step and if designed correctly will give very good results (and there are few good ones on the market). But here there is a massive problem of time domain and phasing. Two drivers on a baffle will have different point source information and if they are not aligned correctly, will never add a totally coherent sound in closefield*.

Step in time alignment® creates correct acoustical centre, eliminating errors in playback response.

So a different approach is needed where the acoustical centres of both drivers are aligned physically as close as possible (X,Y,Z planes) and as long as the driver acoustical centres are within 10cm, the monitor will be time and phase coherent in closefield* (within 1-2m). This of course rules out any mid/bass driver larger than 130mm(5″) in diameter!

It is of course possible to place the drivers out of physical acoustical centres and then correct them electronically but in a passive system this is a huge compromise which causes serious phasing problems and in the SILVER 5L, we did not compromise. Our approach also insured the use of simple crossovers with the minimum number of components which translate into cleaner and more dynamic sound due to a simpler signal path.

Another problem with small monitors is the baffle effect. Sound produced from a speaker needs a baffle that is large enough to reflect the sound waves being produced by the driver and the baffle required to produce any kind of bass performance (say down to 70-80Hz) would require a baffle size of approximately 1m.

No baffle losses, usable frequency response down to 50Hz

No baffle losses, usable frequency response down to 50Hz

A typical baffle size of a small monitor (120mm width) will have a -6db step in its response starting from around 500Hz, so 70Hz will be 6dB lower in level (two times less!). So a large baffle is needed but this would of course defeat the whole idea of a small monitor because firstly it would be too large and secondly the size of the baffle would itself be producing reflections and vibration induced sound waves which will interfere with the main signal.

So again we did not compromise with the Silver 5L, by modifying the drivers and aligning them as dictated by our RWRS programme, the baffle losses can be replaced and the small baffle will start to act as a large baffle (no loss of bass) without losing any efficiency level. This way an accurate usable frequency response down to 50Hz (in room) can be achieved.

For set-ups requiring extended bass response down to 30Hz (in room) would require even larger size monitors but using the same aligning and augmenting techniques, we have produced the Silver BH Bass Augmentor as an add-on option to the 5L’s.

The theory is again quite simple. Due to the limited size of the drivers in a small box, the bass response has a second order slope towards the lower frequencies (from around 80Hz downwards). By designing and aligning another driver to boost these frequencies in reciprocal, an extended bass response can be achieved. By placing the bass driver in a separate box the problems of vibration is also avoided and due to the wavelength at the bass frequencies involved, the augmentor can be placed away from the 5L monitors without any loss of signal information. This makes them extremely practical for closefield* monitoring.

We did not invent the concept of closefield* monitoring, the techniques and formulae for these applications have been available to engineers for many years but what we have done is applied all this knowledge scientifically and imaginatively to our monitors, based on our experience and expertise. The Silver 5L is the testament of our research and efforts.

Closefield* not Near Field

* The small field where the listener and the speaker are placed should not be called Near Field because the term is already defined in acoustic engineering for something else.

Near Sound Field: that part of a sound field, usually within about two wavelengths of a noise source, where there is no simple relationship between sound level and distance, where the sound pressure does not obey the Inverse Square Law and the Particle Velocity is not in phase with the Sound Pressure.
http://www.acoustic-glossary.co.uk/sound-fields.htm

Obviously as the sound in a listening room does decay at 6 dB for a doubling of the distance from the speaker, the listener and the speaker are not in a near-field. Hence, all those small speakers on the market that are advertised as Near Field are using the wrong term.

This is why Silver invented the term Closefield back in mid-90s when they introduced the worlds fist Closefield Monitor Silver5L.