Vibration isolation fittings for Loudspeakers

      There are a number of ways Loudspeaker Drivers can be attached to their panels. In using semi-rigid enclosures, driver vibrations are mostly transmitted / absorbed by the enclosure and with the correct internal panel damping little extraneous cabinet vibration will reradiate to form cabinet colourations.

(1) Prepared hole for Rawlnut
Prepared hole for Rawlnut

      Dipole arrangements based upon flat panels do not have the luxury of a supporting cabinet structure and so are inherently more noisy unless steps are taken to reduce panel vibrations / colourations.

      There are a number of high tech ways of isolating panel vibrations but most of these are beyond simple DIY techniques, eg. composite, differing material sandwich panels.

(2) Rawlnut insertion
Rawlnut Insertion

      In general driver mounting, the three most used techniques rely on screws, bolts or inserts. Screws are easy and cheap but if the cabinet material (wood, MDF, etc.) shrinks then they can become loose. Bolts require access from the front and rear. However, in conjunction with spring washers, they can take up any material shrinkage.

      Inserts require a precision in drilling and insertion which is difficult to find in a DIY environment, etc. None of the above can provide an elastic / suspended driver technique. Enter the Rawlnut. A flanged rubber tube with an embedded nut at the reverse end. Used for attaching / fitting goods to soft panels, which will not hold screws easily.

(3) Flush fitting the Rawlnut
Flush fitting the Rawlnut

      With a little ingenuity these devices can be used to provide a moderately successful floating driver fitment. Available in three sizes / diameters, M3, M4, M5, (there are others but of no interest here) and of different lengths.

      The Rawlnuts are fitted / replace the standard screws, bolts, etc. The body diameter is (8 or 10)mm, depending upon size.

(4) Flush fitting the Rawlnut
Flush fitting the Rawlnut

      The downside, if you are rebating the drivers into the panel, the rebate width must be at least 11mm for an 8mm insert, M3 or M4, and 14mm for the larger 10mm insert, M5.

      A small recess for the Rawlnut flange of around 1.3mm needs to be made so everything sits flush when the driver is mated to its cutout. See the picture guide (Fig.1 to Fig.3). Without using special tools this can be approximated by hand-twisting the appropriate sized drill.

(5) Rawlnut with bolt
Flush fitting the Rawlnut

      If you are using Neoprene or PVC tape to seal your drivers around their rims, then it will be necessary to glue / stick the inserts in place. Evostik works fine. This requirement arises because as the bolt starts to tighten it will pull the insert forward against the easily compressible tape and this needs to be prevented. Further tightening will compress the rubber rawlnut, providing a secure fit which will not pull through (Fig.7).

      It's also possible, with some ingenuity, to construct a compression jig which will compress both the loudspeaker chassis and foam seal hard down onto the front panel. You need to avoid obscuring the mounting holes as you are going to bolt the chassis onto the Rawlnuts. Once tightened down, you remove the press. All this is easy said but more challenging to do.

(6) Rear view uncompressed
Flush fitting the Rawlnut

      It's worth noting that if you don't use foam underlay between driver and panel, you will be wasting your time as chassis vibrations will pass directly from the chassis to the panel, bypassing the suspension.

(7) Rear view compressed
Rear view compressed

      If you want to try this with regular enclosures, you need to make the chassis / panel interface airtight. Glue the Rawlnuts in place with Evostik or similar and use a 'breakable' thread sealant on the bolt threads. Non-breakable sealant is not recommended as later removing the bolts could turn into a real problem.

      NOTE: It's well worth trying out the process first on scrap material before you drill and possibly spoil your front panel.

(8) Wood inserts & bolts
Fittings Selection;
(9) Assorted Rawlnuts.
Rawlnut Selection
(10) Rawlnut with fitting
M3 Rawlnut with Bolt