GB2399473A

GB2399473A - Loudspeaker with low distortion precise imaging and deep bass

Info

Publication number: GB2399473A
Application number: GB0405145A
Authority: GB
Inventors: Feuvre Nicholas Paul Le
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-03-13
Filing date: 2004-03-08
Publication date: 2004-09-15
Anticipated expiration: 2024-03-08
Also published as: GB0305770D0; GB0405145D0; GB2399473B

Abstract

A high fidelity acoustic loudspeaker, using sound absorbent enclosure materials 4, a single high performance elliptical driver 1, airtight seams and highly efficient bend reflectors 2,3. The loudspeaker may; be a transmission-line ('TL') type enclosure, absorb all the rear wave sound 7, have no unabsorbed rear path 8, have an exit open to air 9 which may point downward. The reflectors 3 may be backed by concrete. The material 1; may be airtight, covered, thick, slotted, fitted into slotted top and bottom 17. The top and bottom may be; of a stronger material, wider, raised. The driver may be; coaxial, mounted outside, full-range 23, powerful, elliptical 25 26. The loudspeaker may be; waist height, not very wide, not very deep. The sound absorbent enclosure material 4 may be gypsum-based particle board. The reflectors 3 may be glazed tiles.

Description

TITLE

Loudspeaker with low distortion, precise imaging and deep bass.

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DESCRIPTION

Loudspeaker with low distortion, precise imaging and deep bass.

BACKGROUND OF THE INVENTION

1. FieW of the Invention In most conventional speaker systems an enclosure is needed to contain or control the driver's back wave so it will not destructively interfere with the front wave. The three main types of enclosure are À 'Open Baffle' - an open-backed driver plate, allowing uncontrolled rear sound e.g. guitar combo À 'Infinite Bame' - a sealed box, which heavily resonate from the partially attenuated rear wave.

À 'Reflex' 'Labyrinth' or 'Ported' - deliberately allowing rear sound to exit and interfere with the front sound via an indirect path.

e 'Transmission Line' - basically a long pipe filled with wadding. This is the invention's type 2. Definition A Transmission Line enclosure (TL); À Confines the rear wave within a paralle1-sided pipe that has roughly equal area to that of the duver -as c -;= }5:'l- a. least;2 'e= - c:,,nc need bass, -togae Acres Is open ended thus preventing the rear wave Feflechng back onto the driver À Is stuffed to gradually but completely attenuate the rear sound wave, so it cannot interfere with the front-driver sound, and yet offer little resistance to the drivericone motion.

3. Faded Transmission Lines Transmission lines are often folded to conserve space, which usually creates several persistent problems.

For example, the loss of acoustic energy at all frequencies, and also the distortion of the rear wave front.

Such disadvantages are caused by abrupt discontinuities encountered by the advancing wave at each bend, i.e., direction change in the line, or reduction in cross-sectional area.

Further, sound from rear waves imperfectly reflected around the brat and subsequent bends, return to the driver and are audibly transmiffed forwardly through the cone. Also, the pressure on the cone created by early reflections causes the drivers electrical impedance to vary at different frequencies, thus presenting a more diffiluit load to the driving electronic amplifier, altering frequency response.

4. Prior work Transmission lines can cause unwanted resonances' which affect sound reproduction A. R. Bailey is believed to be the first to describe a stuffed and folded transmission fine in 1965, addressing the problem of unwanted resonances by stuffing the line with acoustically absorbent fibres. Previous to this, the best work on the idea of controlling the rear wave were un-stuffed and flared designs e.g. Strombergarlson (U.S. Radio consoles).

Tannoy, used their dualoncentric 'reds' drive unit in refleiabinets, giving adequate bass, but were very bulky being over 18 inches wide, again the cabinet was not completely stuffed.

IMP (Freid) introduced the TLS80 design from Bailey's results, but decided to abandon imaging for power by using separate woofer (KEF b139) and tweeters (Celestion); this time the line was lined with foam, but intended bass sound to emit from the bottom ports. Although marketed as a Hybrid transmission-line', it was obviously an elongated reflex or labyrinth.

TDL (until recently manufacturers in the UK), and now PMC made what were marketed as 'transmission line' loudspeakers, but again, they have a port, front or rear that emits bass sound, thus contradicting the claim.

5. Advantages Even in specialist expensive loudspeaker designs e.g. Logan, TAG McLaren, B&W Nautillus, there is no transmission line design which boasts an eight foot line length with efficient bend reflectors, which are both necessary to achieve the best from a single drive unit in a confined space.

The argument 'against' using a single drive (without reinforcing woofer) unit is because in inefficient enclosures, the love bass is destroyed. The argument for' using a single drive unit is, it is obviously the best and only way to get precise imaging, realism, and high efficiency. s Retail-focussed manufacturers today, save money by building in resonance to the enclosure, drivers and crossover circuitry to boost the bass at roughly 100 300 hz, giving the familiar bass the consumer market is used to, but at the expense of undistorted or deep bass (100hz).

There is adequate deep bass, even in narrow elliptical drive units' provided the enclosure resonance does not attenuate, reflect or impede the rear wave at those lower frequencies, but the only design which i can do this is an foot transmission line. Folding the 8 feet up into an acceptable-popular floorstandng size requires bends which Will usually reflect back instead of round at these points - thus shortening the Eden = i as length- and attenuating the bassdeep Lass Because of the general acceptance of multiple driver iouds,oeakers for full range use, the improvements on imaging have hitherto not been realsed. By using soundabsorbent panels instead of MDFlplylchipboard etc. the enclosure resonance is further eliminated, especially with deep bass. Again there is no manufacturer offering such an advanced enclosure material - probably because there are no other loudspeaker designs that wish the rear wave to be completely absorbed and have no subsequent resonances. A<

SUMMARY OF THE INVENTION

The invention provides a high performance' easily manufactured design for transmission line loudspeakers. Although there have been designs before similar in proportions with a double folded line (to use less space), the previous designs suffered from the following: À Excessive construction procedures, due to wood-based enclosure materials needing extra thickness, bracing or lining to reduce resonances.

À Coloration of sound and diminished bass, due to vibrations from woodbased enclosure materials.

À Incapable of high levels of sound reproduction due to inferior speaker selection and internal fitment.

À Compromised stereo imaging and phase reproduction due to multiple drive units and associated crossover circuitry.

1 The use of sound-absorbent wallboard (4, Fig 1) significantly increases bass performance and - reduces enclosure vibrations. This material is only recently (post 1990) commercially available and research has discovered how significant sound improvement results compared with other materials such as chipboardiplywood/MDF.

The use of modem elliptical-coaxial speaker allows high levels of sound and yet narrow enclosure, such speakers (>40 Watts HISS) were rare and expensive prior to 1995, and my i research showed how effective they are in transmission lines for the first time 3: only navr,g a single speakers rig j, 6' 'S avodr' virtually all parallax and crosscve, d!storhons it gives a particularly convincing reproduction - superior positional (imaging') and musical charactenstcs ('realism').

4 Mounting the speaker externally (1, Fig 1) allows a larger driver (particuiady for improved bass and power), easier driver maintenance and smaller enclosure depth, retaining the modest enclosure proportions. i The speaker cross section area (main diagram) area (1, Fig 1) is sightly greater than the line area (5, Fig 1), this in a departure in conventional design, and improves performance. This is a unique feature developed by experimentation 8 testing rather than accepted Transmission Line theory which stipulates the areas need to be the same, but fails to take into account the effective cone area is less due to cone losses, which are impossible to calculate absolutely 6 Ceramic (2, Fig 1) and concrete backed (3, Fig 1) reflectors reduces enclosure vibrations and increases reflecting efficiency. This allows the bends to significantly reduce early reflected sound back along the line, which other folded designs suffer so badly from.

7 The enclosure is efficiently designed to assemble with glued joints along routed slots, thus reducing air leaks, and reducing machining time. Conventional double folded designs were flawed by the excessive use of joints and potential structural and airtight weaknesses - by using continuous glued slots makes the line rigid stable and airtight.

8 The top and bottom parts, which are made of a strong material are slotted to allow the sides to fit in, which increases strength and protection of the more delicate sides 9 The bottom part (6, Fig 1) has a hole cutout for the end of the line (8, Fig 1), and is raised on feet.

The line is entirely stuffed with polyester (7, Fig 1) or other wadding, to progressively, gradually and completely absorb the rear wave along the line. The stuffing density Is increased at the anti node points, which are the reflectors.

11 Use of OFC cable and gold plated rear connector minimises losses from the increased power and fidelity of the speaker.

Claims

CI^IMS Essential Claims 1 A loudspeaker with sides and bafRes made from

sound-absorbing gypsumbased particle-board.

2 A loudspeaker as claimed in Claim 1 where there is only one drive unit, which may be coaxial.

3 A Loudspeaker as claimed inClaim1 or Claim 2 where the sound travailing away from the rear of the drive unit, is efficiently reflected around bends, using angled acoustic mirrors made from glazed tiles.

4 A loudspeaker as claimed in Claim 1 or Claim 3 where ail enclosure joints between sides and baffles are made airtight.

A loudspeaker substantially as herein described and illustrated in the accompanying drawings.

Dependant claims 6 A loudspeaker as claimed in any preceding claim including the enclosure type 'transmission line', wherein the rear wave is absorbed to such an extent, that it makes no significant audible sound and the end of the line is open to air.

7 A loudspeaker as claimed in any preceding claim where the sound is absorbed by stuffing the line with sound absorbent filling 8 A loudspeaker as claimed in any preceding claim where there is no path the sound can take between the rear of the driver to the exit, without passing through enough stuffing and bends to attenuate the sound to a virtually inaudible level 9 A loudspeaker as claimed in any preceding claim where the enclosure exit is open to air A loudspeaker as claimed in any preceding claim where the enclosure exit points downward 11 A loudspeaker as claimed in any preceding claim where the glazed tiles may be stuck to masses of concrete 12 A!oudspeakerasclarmedin any p,eceding claim nowhere the enclosurelonts between sides end bafies are madea.g;,.b',euesisa.,Jsesla.?tfadhesve 3.-'oudspeakeras clamedn any preceding camvhere the enc)osuresaes are coveredn a strong street material 14 A loudspeaker as claimed in any preceding claim where the enclosure sides and baffles are at least 5mm thin< A loudspeaker as claimed in any preceding claim where the enclosure sides may be slotted to accept the bafnes 16 A loudspeaker as claimed in any preceding claim where the enclosure top and bottom are made of a tough strong material 17 A loudspeaker as claimed In any preceding claim where the enclosure top and bottom may be slightly wider and deeper than the sides 8 A loudspeaker as claimed in any preceding claim where the enclosure top and bottom may be slotted to accept the sides 19 A loudspeaker as claimed in any preceding claim where the enclosure bottom is raised from the ground by feet or other apparatus A loudspeaker as claimed in any preceding claim where the single drive unit is mounted near the top of the front of the enclosure 21 A loudspeaker as claimed in any Seceding claim where the single drive unit may be of single, two-way coaxial, three-way, or more provided that the other transducers remain within the circumference of the largest cone.

22 A loudspeaker as claimed in any preceding claim where the single drive unit may be mounted from the outside of the enclosure 23 A loudspeaker as claimed in any preceding claim where the single drive unit has a wide frequency response 24 A loudspeaker as claimed in any preceding claim where the single drive unit has an RMS power exceeding 30 Watts A loudspeaker as claimed in any preceding claim where the single drive unit is approx. 130mm wide 26 A loudspeaker as dammed in any preceding claim where the single drive unit approx. 210mm high 27 A loudspeaker as claimed in any preceding claim where the loudspeaker depth is approx. 300mm deep 28 A loudspeaker as claimed in any preceding claim where the loudspeaker height is approx.

900mm high 29 A loudspeaker as claimed in any preceding claim where the loudspeaker width Is approx. 220mm wide