GB2060314A

GB2060314A - Loudspeaker enclosures

Info

Publication number: GB2060314A
Application number: GB8031718A
Authority: GB
Original assignee: Hutchings L H
Current assignee: Hutchings L H
Priority date: 1979-10-03
Filing date: 1980-10-01
Publication date: 1981-04-29
Also published as: GB2060314B

Abstract

The interior of a vented loudspeaker enclosure, to the rear of the loudspeaker cone, incorporates a lattice of sound reflectors (X) made of acoustic hard material such as hard wood so disposed that the rear waves of acoustic energy generated by the cone are reflected in such a manner that they add to the forward radiated waves. <IMAGE>

Description

SPECIrICATION Improvements in acoustic enclosures The present invention relates to acoustic enclosures and is more particularly concerned with the construction of such enclosures when used in conjunction with loud-speaker units.

For high quality sound reproduction it is well known that the sound radiated from the rear of the acoustic radiator (for example a loud-speaker) must be controlled. Unless the sound pressure waves are controlled the waves generated from the front and rear of the acoustic radiator will interfere with each other producing undesirable variations in amplitude with respect to frequency on the resulting output.

It is an aim of the present invention to provide a loud-speaker enclosure which controls the rear acoustic radiations in such manner that interference between the rear and forward acoustic radiations is substantially reduced.

According to the invention there is provided an acoustic enclosure incorporating a loud-speaker unit having an acoustic radiator which produces both front and rear waves of acoustic energy, in which the interior of the enclosure to the rear of the acoustic radiator is arranged such that the rear waves of acoustic energy generated by the acoustic radiator are reflected in such manner that they add to the forward radiated wave.

In one embodiment of the invention the interior of the enclosure includes a lattice of acoustic wave reflectors positioned such that the interior of the enclosure produces form the rear waves reflected acoustic waves which add to the forward radiated waves.

Preferably the reflectors comprise rectangular strips of acoustic reflective material arranged to lie transverse the interior of the enclosure and to form a continuous reflection arrangement extending from the periphery of the loud-speaker cone. Typically the strips are arranged at an angle to the transverse axis of the enclosure and are located such that their ends are aligned thereby forming a continuous reflective surface. Typically the strips are arranged to be parallel to each other and are disposed above and below the horizontal plane extending through the vertical centre line of the enclosure.

The invention will be more readily understood from the following description which should be read in conjunction with the accompanying drawings. Of the drawings Fig. 1 shows a typical loud-speaker cabinet, Fig. 2 shows the loud-speaker cabinet with the front removed to show the lattice of acoustic wave reflectors according to one embodiment of the invention Fig. 3 shows the back of the cabinet Fig. 4 shows one row of reflectors Figs. 5a and b show the side elevation of the cabinet with the side removed while Fig. 6 shows the electrical equivalent of the invention.

With reference to Fig. lit can be seen that the loud-speaker enclosure has an upper and lower vent A and E, a high range or tweeter loud-speaker B a mid range loud-speaker D and a bass unit C.

Typically the tweeter may be a KEF T27 while the mid range unit is a Pioneer (100 m.m.) and the bass is a Dalesford D70/250. The tweeter and mid range units are sealed leaving the enclosure to handle the bass unit only.

Reference to Fig. 2 shows that the inside of the enclosure accommodates a lattice of acoustic wave reflectors. Each reflector such as X consists of a strip of rectangular section hard wood or similar acoustic reflective material. The bass loudspeaker cone is provided with two sets of reflectors positioned at or near the periphery of the loud-speaker cone and extending horizontally across the depth of the enclosure as shown in Fig.

5. Fig. 4 shows how the strips X are located at an angle to the transverse axis of the horn parallel to each other with their opposite ends aligned to form a "continuous" strip effect. The reflections produced form the rear edge of each strip are greater than those produced from the front edge of the strips and they are of opposite sign. The total continuous reflections produced by strips are substantially in phase with the forward radiated acoustic wave generated by the acoustic wave generator or loud-speaker cone LSC in Fig. 5 which therefore adds to the acoustic energy generated by the loud-speaker cone. The alignment of the alternate ends of the strips as shown in Fig. 4 ensures that the reflections produced are continuous. The number of strips shown is exemplory only, more or less strips may be used in practice.In addition to the reflective effect, the addition of the strip X has the effect of lowering the Q of the air in the acoustic enclosure at resonance as well as improving the loading on the speaker unit. Further rows of strips may be used in the regions occupied by the tweeter and mid range speakers to enhance the reflective effects such additional strips may have be omitted from the drawings for ease of presentation.

Fig. 5 shows the addition of a strip or strips Y n the vertical plane again located at or near the periphery of the loud-speaker cone. Similar reflections are produced from the edge of the strip or strips.

The principle of operation is continuous reflection and is the acoustical equivalent of an electrical transmission line having series resistance.

The electrical equivalent is shown in Fig. 6 and contains sections of ideal line of constant impedance ZL connected by series resistors RS1, RS2 etc. Because of the mismatch caused by the resistance a 'reflection' occurs at each section and this adds (+vely) to the signal a 'a'. (The generator is assumed to have a source empedance equal to ZL). The signal appearing across each section of line is attenuated to the same extent as the magnitude of the reflection. Hence, ideally the signal at the end of the line would be zero and all the signal would have been added at 'a'. (Delays occur, hence phase shifts with frequency).

The values of series resistance are not constant, by design, in order to make the magnitude of the reflection constant with time and the resistor values are related to the number of elements.

The resistive effects are achieved in the enclosure by the strips X and it will be appreciated that the use of further arrays of strips in the areas of the enclosure occupied by the mid range and tweeter units will add to the overall reflective properties of the arrangement.

Claims

1. An acoustic enclosure incorporating a loudspeaker unit having an acoustic radiator which produces both front and rear waves of acoustic energy, in which the interior of the enclosure to the rear of the acoustic radiator incorporates acoustic reflective means adapted so that the rear waves of acoustic energy generated by the acoustic radiators are reflected in such manner that they add to the forward radiated waves generated by the acoustic radiator.

2. An acoustic enclosure according to claim 1 in which the acoustic reflective means comprise rectangular strips of acoustic reflective material arranged to lie transverse the interior of the acoustic enclosure extending from the periphery of the loud-speaker cone.

3. An acoustic enclosure according to claim 2 in which the strips are arranged at an angle to the transverse axis of the enclosure and are located such that their ends are aligned to form a continuous reflective surface.

4. An acoustic enclosure according to claim 3 in which the strips are arranged parallel to each other and are disposed above and below the horizontal plane extending through the centre of the enclosure.

5. An acoustic enclosure according to claim 4 in which the interior of the enclosure includes vertical strips located at or near the periphery of the loud-speaker cone.

6. An acoustic enclosure substantially as described and shown in the accompanying drawings.

New claims or amendments to claims filed on 8th January 1981.

Superseded claims 1.

New or amended claims

1. An acoustic enclosure incorporating a loudspeaker unit having an acoustic radiator which produces both front and rear waves of acoustic energy, in which the interior of the enclosure to the rear of the acoustic radiator incorporates acoustic reflective means adapted so that the rear waves of acoustic energy generated by the acoustic radiator are reflected in such manner that they add at the acoustic radiator to the forward radiated waves generated by the acoustic radiator.