Speaker Tweaks

updated 05-nov-07

Over the last 30+ years local DIYers have developed what is now called the "standard mod" (of a commercial speaker). These mods are:

  • Puzzlecoating paper cones
  • ductsealing baskets
  • stiffing the cabinet
  • retrofitting decent speaker wire


Puzzlecoat is a brand name from when we started this, i haven't been able to find this brand in the last 5 years, but the name stuck because it is very descriptive -- it is more commonly used to coat assembled puzzles before framing them. Classified as a "decoupage sealer and adhesive".

This stuff is a PVA compound very similar to white wood glue. Same smell, same color, a little thinner, and is more flexible when it dries.

There are two kinds i have used of late -- Mod-Podge and Lewiscraft Podgy. Both are available in shiny & matte.

I expect there are many clones of this*. Try a craft store. It is fairly cheap.

30+ years of using this trick on paper cone woofers & mids. It consistently gives a better sounding speaker (caveat -- too much can roll off the top end of the driver too much).

The theory we have built up is that:

  1. the cone if made more acoustically opaque so there is less time-delayed reflection from inside the enclosure coming back thru the cone
  2. it bonds the paper fibres together so that it is harder for them to resonate/rub together
  3. the cone is stiffened. With one or both sides of a paper driver plastic coated, you end up with a very well-damped, multi-layer cone.

Warning: This mod is not reversible. Use at your own discretion/risk.

I apply it with a paintbrush -- i have a range of artist brushes in various sizes for different jobs. I ususally start with a thin coat, then use a bit more in subsequent coats. Usually more coats on the front than on the back (sometimes no coats on the back). You can use too much -- i have a pair of Eminance 15" co-axials that i now need to add a midrange to ...

I have used it on all manner of drivers. Bass drivers, mids, mid-basses, even dome mids, and paper cone tweeters. I used one thin coat to clean up the MCM 55-1855 Aluminum mid-basses. These 12s have been generously treated.

* It is also useful to stiffen & damp other things too. One coorespondant in England coated (inside & out) the heavy cardboard tubes used as mid enclosures in his TLS80s and noted a very noticable improvement.

  Here are some comments on the material and it's additives.

A vinyl resin, one of the clear, water-white, thermoplastic synthetic resins produced from its monomer by emulsion polymerization. Polyvinyl acetate, abbreviated PVA , has the advantage over the other resinous adhesives in that it is available in the form of an emulsion that is readily diluted with water, is easily applied, and is safe to use because it contains no flammable solvents. In addition, there is no need to use preservatives or fungicides because it does not deteriorate quickly and is unaffected by mold or fungi. The emulsion does slowly hydrolyze, however, and should not be stored for more than one or two years before use. Freezing also destroys the emulsion; therefore, precautions must be taken to avoid exposing it to temperatures near or below the freezing point

The synthesis and patenting of vinyl acetate monomer by Dr Fritz Klatte in 1913, in Germany, provided the foundation for many valuable and now essential plastic products. He found that the catalysed reaction of acetylene with acetic acid gave a readily polymerised low boiling liquid (vinyl acetate) to yield a potential range of dense solid materials. These are now often denoted as (PVAc) or (PVA) polymers.

Klatte and others found that PVA was compatible with other polymers and plasticisers which could give valuable adhesives and coatings for cellulose and textile products. From c.1930 many companies manufactured a range of products such as PVA for liquid solutions and emulsions and hot melt adhesives and paints.

PVA is not an ideal moulding plastic so the development of many economic and attractive alternatives rapidly ensued based on the ability of vinyl acetate to co-polymerise with many other monomers. Hence, co-polymers with vinyl chloride, acrylic monomers, styrene, ethylene and others gave a great range of moulding, coating, sheeting, adhesives, insulating materials, etc.

Hydrolysed versions of PVA gave polyvinyl alcohol as a water-soluble coating and binder. The polyacetal derivatives of these have provided superior bonding and electrical insulation with good stability.

Emulsion paint and adhesive sticks, so readily accepted, are simple examples of these truly outstanding contributions to modern life.

Mod Podge -- Les Enterprises Plaid, Norcross, GA 30091-7600 USA

Podgy -- Lewiscraft, Toronto, ON, Canada

At least one other on-line source is Craftopia, but a search on the internet turned up references all over Europe (particularily in Germany) & North America.


Used in HVAC to seal ducts. A non-drying putty-like material that is easy to shape and will stick to metal. This tweak is reversible (ie i've peeled duct-seal i applied to speakers 25 years ago and reused it.

There are various suppkiers for this kind of product, some not as well suited as the Ideal brand shown in the picture.

I use this to damp speaker baskets & to shape the rear of a driver into a smoother more aerodynamic shape to reduce reflections.

Sometimes it gets used for speaker gaskets as well.

[ <-- Back to T-Line Speakers | Design ]