GB2440598A

GB2440598A - An edge supported sound barrier vacuum panel

Info

Publication number: GB2440598A
Application number: GB0615218A
Authority: GB
Inventors: Michael John Rickards
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-08-01
Filing date: 2006-08-01
Publication date: 2008-02-06
Also published as: GB0615218D0

Abstract

A sound barrier vacuum panel comprises upper and lower sheets separated by a peripheral wall 9 supported by internally mounted posts 13 adjacent to it the whole enclosing a hermetically sealed space evacuated to less than 100 Pa. The support posts may be arranged in the middle of the sides, such that there are four posts in total, additional posts may be provided in the corners so that there are 8 posts in total. Two or three posts may be provided along each side with an additional post in each corner, giving 12 or 16 posts in total.

Description

An edge supported vacuum panel The attenuation of sound is usually

achieved by interposing sound absorbing material between the source and the listener, the energy of the absorbed sound being dissipated as heat. In contrast vacuum panels, acting as sound barriers, function by reflecting the incoming sound back to the source allowing only a small fraction to pass through the panel via the perimeter wall and the residual air inside the panel. The factors affecting that small fraction of sound passing through the perimeter wall and the means for reducing it are described herein.

The following figures are used to describe the application of the inventive ideas applied to the improvement of the stability and sound attenuating ability of vacuum panels: Figure 1 shows a cross section of an ideal vacuum panel, Figure 2 shows a projected view of the same panel as figure 1, Figure 3 illustrates a cross section of a vacuum panel showing the inward flexing of the upper and lower panel sheets, Figure 4 shows a projected view of the panel described in figure 3, Figure 5 illustrates a warped vacuum panel, Figure 6 shows edge support consisting of four cylindrical posts placed within the perimeter wall and mid-way along each side, Figure 7 shows edge support consisting of eight cylindrical posts placed one third of the way along each side, Figure 8 shows edge support consisting eight cylindrical posts, four placed mid-way along each side with an additional post placed in each corner, Figure 9 shows edge support consisting of eight cylindrical posts placed one third of the way along each side and one cylindrical post placed in each corner, Figure 10 shows edge support consisting of twelve cylindrical posts equally spaced along each side and an additional post in each corner, Figure 11 shows edge support consisting of eight square section pillars distributed as shown in figure 8, Figure 12 shows edge support consisting of eight tubular pillars placed as shown in figure 8, Figure 13 shows a detail of a square section pillar, Figure 14 shows a detail of a tubular pillar.

That sound cannot travel through a vacuum is well known and a panel as shown in tiguresi and 2 comprising upper I and lower 2 sheets separated by a perimeter wall 3 and hermetically sealed to enclose a vacuum (a term used in this document to mean air at a pressure less than lOOPa) would ideally be a very effective sound barrier since almost all the transmitted sound must pass through the perimeter wall. By making the perimeter waIl 3 thin (i.e. of thickness less than one tenth its height) the extent of contact it makes with the upper I and lower 2 sheets will be reduced thereby reducing the transmitted sound.

In a practical example, illustrated in figures 3 and 4, of a vacuum panel the action of atmospheric pressure on the upper 4 and lower 5 sheets causes them to flex inwardly and consequently the perimeter wall 6 must be high enough to prevent the sheets making contact at the centre.

It is apparent that the perimeter wall has on the one hand to be thin so as to reduce the contact area it makes with the upper and lower sheets and on the other hand be strong enough to support atmospheric compression and yet high enough to keep the upper and lower sheets from touching..

Attenuation measurements obtained with a square panel for various ratios of the upper sheet area to the contact area of the perimeter wall strongly support the relation: Attenuaiion(dB) = lOLog(Ratio)2 This equation quantifies the importance of making the perimeter wall thin to reduce the contact area it makes with the upper and lower sheets. The equation is also used to calculate the theoretical attenuation in the examples described below.

An unexpected behavior of vacuum panels during the evacuation process is their tendency to warp or fold along a diagonal, as illustrated in figure.5. This tendency to warp is all the greater as the perimeter wall is made thinner.

During an investigation into ways of supporting the perimeter wall with internally mounted cylindrical posts, pillars and tubes it was discovered that by placing such a support in each of the corners of the vacuum panel the tendency to warp both during and after evacuation was eliminated. This is a significant and important advance in the design and manufacture of vacuum panels.

It was also discovered that the contact area an unsupported wall makes with the upper and lower sheets was reduced to a much smaller value when it was replaced by a thinner perimeter wall supported by posts. This arrangement gives the substantially increased sound attenuation values quoted in examples 2 to 10 below, the attenuation measurements being made at 10Hz intervals and averaged over the range 100 to 800Hz.

Example I

A square vacuum panel, as illustrated in figures 3 and 4, with upper 4 and lower 5 sheets of 0.7mm thick mild steel and 400mm sides separated by a 50mm high and 0.4mm thick mild steel perimeter wall 6 gave a theoretical attenuation of about 48dB and a measured attenuation of 43 to 45dB. The contact area that the unsupported perimeter wall 6 makes with the upper sheet 4 is 640mm2. Panels made to these dimensions show a marked tendency to warp during the evacuation process.

Example 2

A square vacuum panel, as illustrated in figure 6, with upper and lower sheets of 0.7mm thick mild steel and 400mm sides having a 50mm high mild steel perimeter wall 0.225mm thick supported with 50mm high steel posts 2mm in diameter 8 placed internally midway along the edge of each side 9 gave a theoretical attenuation of about 53dB and a measured attenuation of 47 to 50dB. The contact area for this panel is 373mm2. This panel showed a marked tendency to warp during evacuation.

Example 3

A square vacuum panel, as illustrated in fIgure 7, made to the same dimensions as in example 1 but with eight posts 10 each placed at one third of the length of each side 9 also gave a theoretical attenuation of 53dB and a measured attenuation of 45 to 50dB. In this case the contact area is 385mm2. This panel also showed a tendency to warp during evacuation.

Example 4

A vacuum panel, as illustrated in figure 8, was made as described in example 2 but with an additional post placed in each corner. The theoretical attenuation in this case is 53dB and the measured attenuation was 49 to 51dB. The contact area was 385mm2. This panel showed no tendency to warp during evacuation.

Example 5

A square vacuum panel, as illustrated in figure 6, with upper and lower sheets of 0.7mm thick mild steel and 400mm sides having a 50mm high mild steel perimeter wall 0.127mm thick supported with four 50mm high steel posts 2mm in diameter, 8, placed internally midway along the edge of each side, 9, gave a theoretical attenuation of about 57dB and a measured attenuation of 53 to 55dB. The contact area for this panel is 2 16mm2. This panel, however, showed a strong tendency to warp during evacuation.

Example 6

A vacuum panel, as illustrated in figure 8, was made as described in example 5 but with an additional post 11 placed in each corner. Though the contact area was 228mm2 the theoretical attenuation and the measured attenuation were the same as stated in example 5 but this panel showed no tendency to warp during evacuation.

Example 7

A vacuum panel, as illustrated in figure 9, made to the same dimensions as in example 5 but with twelve 3mm diameter mild steel cylindrical posts 12 one placed in each corner and one third along the edge of each side 9. The contact area for this panel came to 288mm2. The theoretical attenuation was 55dB and the measured attenuation came to 51 to 53dB. This panel showed no tendency to warp during evacuation.

Example 8

A vacuum panel, as illustrated in figure 10, made to the same dimensions given in example 5 but with sixteen 3mm diameter mild steel posts 13 one placed in each corner and eve7 10cm along the edge of each side 9. The contact area for this panel came to 316 mm. The theoretical attenuation was 54dB and the measured attenuation came to 50 to 52dB. This panel showed no tendency to warp during evacuation.

Example 9

A vacuum panel, as illustrated in figures 11 and 13, made to the same dimensions as in example 5 but with eight pillars 14 having a square cross section 2mm wide made of mild steel and placed in each corner and midway along each side 9. The contact area of 235mm2 gave a theoretical attenuation of 57dB and the measured attenuation came to 52 to 54dB with the panel showing no tendency to warp during evacuation.

Example 10

A vacuum panel, as illustrated in figures 12 and 14, made to the same dimensions as in example 9 but with the pillars replaced by mild steel tubes having an external diameter of 4mm and an internal diameter of 2mm. The contact area of 279nim2 gave a theoretical attenuation was 55dB and the measured attenuation came to 50 to 52dB. This panel showed no tendency to warp during evacuation.

Claims

Claims I. A square sound barrier panel comprising upper and lower

sheets separated by a peripheral wall hermetically enclosing a space evacuated to less than Pa with supporting posts mounted internally and adjacent to the peripheral wall and having sufficient height to prevent the upper and lower sheets from touching and with the total contact area that the peripheral wall and the posts make with the upper and lower sheets being at least thirty times less than the total internal area of the said sheets.

2. A panel as described in Claim 1 in which the supporting posts are placed midway along each side to make a total of four posts.

3. A panel as described in Claim 2 whjcbthesupportiflgpOStsarePl one third of the way along each side to make a total of eight posts.

4. A panel as described in Claim 2 in which four additional supporting posts are placed one in each corner of the panel to make a total of eight posts.

5. A panel as described in Claim 3 with four additional posts one placed in each corner to make a total of twelve posts.

6. ApaneIasdesctibedinClaim1withaP0stPm1er along one quarter of each side and one in the middle of each side to make a total of sixteen posts. 7.

cross-section.

8. A panel as described in Claim 7 in which the posts have a tubular cross-section. S. * S

*.. 9. ApanelasdescribedinaIlyoftheClamnhS It0S andhavingarectaflgUlar shape.

10. A panel as described in any of the Claims! to 8 in which the upper and lower sheets have a triangular shape. S..

S

Apanel as described in any of the Claims 1t0 8in chthe I1PpeT and : * lower sheets have the shape of a regular hexagon.

12. A panel as described in any of the Claims ito 8 in which the upper and lower sheets have the shape of a trapezium.