Article: How to Fit Speaker Spike Inserts to Speaker Cabinets
A basic introduction to Speaker Spike Inserts and how to install them
Loudspeaker spikes are usually used to isolate loudspeaker stands and floor-mounted / standing speakers from floor vibrations.
They are more effective on wood-based floor coverings as concrete or tile coverings are less vibrant.
The component parts consist of a speaker spike, a threaded locknut and a spike insert.
These parts can all be purchased as a Kit of parts or as separate items.
To buy tee nuts and spike inserts review Tee Nuts & Inserts.
Spikes are generally of steel construction, (for moderate cost), chemically blacked, of M6, M8 or M10 in diameter, see typical speaker spikes M6 Speaker Spikes and available in various lengths with knurled or plain body sections. Dual-ended, ball and point versions are also available in alternative materials, brass, chromed, blacked, etc. but are less popular and more expensive due to the small quantities involved.
In order to fit loudspeaker spikes to cabinet bases, a Wood Insert and optionally a matching thread size Locknut are required. The inserts are available in two styles, those, that knock-in and those, that screw-in. This is in addition to shouldered or unshouldered, i.e. flanged designs which are also available in various lengths. However, the inserts used for loudspeakers cabinets are generally within (10 - 15)mm in length. Many speaker cabinets being from (18 - 19)mm MDF provide sufficient wall thickness to install the insert without breaking through into the cabinet interior.
Each type of insert has it's own advantages and problems. Screw-in types have a sharp cutting thread and generally a small lipped shoulder which aids in depth setting. Their advantage is high pull-out resistance. The disadvantage when used with a locknut, is that they can unscrew, having minimal torsional / twisting resistance. Hence they unscrew along with the locknut and spike. Normally fitted once and forgotten, this isn't usually a problem. However, a dose of wood glue on the threads before insertion should sort it altogether. Note, the difference in thickness between a Half-Nut and a standard Full-Nut.
Push-in types have a number of tangs / pointed teeth which, a) hold the insert in place and b) prevent twisting. The advantage is high twisting resistance but only moderate pull-out resistance. As they generally sit "underneath" the cabinet, pull-out is not a problem.
Each insert requires a pre-drilled hole. The size / diameter of the hole is important for best fit. Holes should be blind-drilled, i.e. do NOT drill through into the cabinet interior as this may create an air leak along the insert / spike thread. If you have a thin walled cabinet base, glue packing pieces about 40mm square and 10mm thick or so on the cabinet base, inside or outside, to provide a thicker cabinet depth in which to fit the insert. As previously mentioned, the hole size is important and the harder the wood, the larger the pilot hole should be. Solid Ash or Elm etc. requires a larger pilot hole than needs to be used for MDF or plywood. The following tables suggest drill sizes for various insert sizes and materials.
Tee Nuts are similar in that they have 3 or 4 pointed tangs which, due to the tang profile, close inwards as the nut is driven home, preventing them from coming loose. They have high torsional resistance but low pull-out resistance. There are no International Standards on dimensions for these types of fitting and sizes can vary accordingly, depending upon manufacturer / supplier.
The insertion of Spike-Inserts of the screw-in variety is intuitively obvious but not quite so obvious is that a portion of the internal thread space is used as an insert for Hex Key or Ball Ended Hex drivers. This limits the minimum length spike which can be used if more than a small height adjustment is required, as you run out of spike thread.
Using knock-ins, one needs to be careful. MDF is compressed wood dust and glue. It is compressed in layers and does not like shock, i.e. hammering. It splits and falls apart. If you have access you can use a G-clamp and compress the insert into the material, it's a bit fiddly, but it works. A better technique however, (this only works on through-hole insertions) and not restricted on overall reach like a G-clamp, is to use a set screw (all-threaded bolt), and a large washer or two, (mudguard washers).
Locate the insert in position, Place the washers on the bolt and thread the bolt and washers through from the reverse / cabinet inside. The bolt will thread onto the insert and slowly draw the insert into place as you tighten the bolt. For a successful outcome it is necessary to keep the insert and drawbolt square to the wood surface. Once fitted, withdraw the bolt and repeat as required. As mentioned, this only works for through-hole drilling's so you need to plug the hole interior with a blank wood piece. Alternatively or use some silicon mastic to seal it, thereby making it airtight.