Australian Sound Design Project
Olsen System Tubular Loudspeaker Enclosure (TLE)The Pipe
Olsen System TLE (Tubular Loudspeaker Enclosures)|
(IPA design registrations No 122810 and 143321)
Why TUBES not BOXES?
The simple answer is that boxes usually have flat sides. So what?
What a loudspeaker system is trying to do is to reproduce sound as accurately as possible without any unintended ‘extras’. Just pure ‘original’ sound, nothing else.
Speaker enclosures make speakers work better. Try running a speaker without a ‘box’ and see how tinny it sounds. Unfortunately, most speaker enclosures make some secondary, unintended sound, as the action of the speakers makes various parts of the enclosure vibrate. This extra sound is known as ‘secondary colour’. Some of this secondary sound can be an annoying rattle, a booming resonance or worse, a set of very low frequency noises that are perhaps below the normal range of the human ear.
If you cannot hear them, what is the problem? Unfortunately humans are not the only things that react to low frequency sound. Materials such as window glass, wallboard and flooring materials can be made to vibrate and provide additional unwanted noise.
Most people have experienced the THUMP, THUMP, THUMP, outside a party house, or down the street from a teenagers car with its $5000+ sound system that vibrates the whole car, not just the eardrums of the occupant(s). Some forms of secondary sounds are less troublesome than others. The most annoying loud noises are those that travel as flat ‘sheets’ of sound past the observer. These flat, or ‘plane’ pressure pulses, if repeated often and over a longer time frame, can make people tense, even angry for no apparent reason. You will probably have noticed that you feel ill at ease when exposed to gusty wind for a prolonged period. Your balance system uses lots of mental energy as it continually adjusts your muscles to compensate for the variable wind forces.
The balance system gets much of its information from your ears, the inner ear especially. Your eardrums detect small differences from one side of your body to the other as one eardrum gets pushed in, on the wind side, while the other eardrum moves the other way responding to the lower pressure on the downwind side. This event causes a message to be sent to the balance control centre raising it to ‘alert’ stage at least. Low frequency plane pressure pulses generated by the flat sides of conventional speaker boxes probably produce much the same effect as they travel around a room, especially if the sound is loud.
Most models of Olsen System TIE enclosures have round sides (a pipe), so that any extra sounds generated are curved, making them much less of a problem. Curved surfaces are also more rigid so less stray sound is generated, further reducing any potential problem.
This is just one reason why the sound from the Olsen System TIE is so comfortable, even when quite loud. You really feel the difference. The air around you feels pressure free, hence the term ‘Transparent Sound’. (Where a round ‘pipe’ shape is not desired, alternative multisided tubes, such as octagons are used, with very thick walls to reduce vibration.)
Even where a cuboid or square tube (box) is used, the speaker board is still the top. This surface is usually smaller than any other, is attached firmly to the heavy speakers and therefore is least likely to add colour.
The Olsen System TLE uses small loudspeakers with very large magnets so that they can accelerate very quickly, and a lot of them to create a large effective cone area, like a big speaker. These small speakers are placed very carefully so that they behave like a single speaker, with no crossovers, and only one signal shape to reproduce. If you can leave out a problem it is a problem no more! (The old KISS principle.) This is another of the many reasons why the sound from an Olsen System TLE sounds so very clean and real. The fine detail of the natural timbre of an instrument or voice is retained.
Vertical Speakers and the Conical Passive Radiator
Normal loudspeakers, with their horizontal drive units tend to create sound shadows as the sound is projected in one direction from one side of the ‘box’. Vertical speakers, as used in the Olsen System TLE, create sound that radiates in all directions from the speaker enclosure so that no one direction gets more than another. This Radial Sound feature creates more natural sound, especially with spoken voice. The curved cone, or passive radiator, above the speakers is the means by which the ‘radial’ sound is achieved. It is also the reason for the unique appearance of an Olsen System TEE. It is an important part of the system, and makes an interesting ‘conversation piece’ as well. Yet another reason for the pleasantly ‘clean’ sound from the Olsen System TLE.
Several reasons: firstly, the natural resonances of the tube, or pipe, are a function of length, tall enclosures work better, secondly the sound is emitted at about head height, so that less sound is lost into clothing. Many Hi-fl shops sell speaker stands to raise normal ‘box’ speakers to about this level and slope the box back to get better sound spread. TLE’s could be made a little shorter, but ‘fatter’, to compensate, then would need to be raised anyway. Why go against the KISS principle? For whatever reason, the quality of the sound is important ‘naturally’.
John Olsen, Olsen System, PO Box 612 Mt Eliza Vic Australia 3930 Ph.+61 3 9787 3762.
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Published by The University of Melbourne
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Updated: 18 January 2007