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Loudspeakers: the Idiots' Guide to Tweaking

Part 2

[Italian version]

So you've tried all the tweaks in Part 1 and you still don't like your speakers... Well here I lose a few of you, because Class B and C tweaks involve opening the boxes. I will lose some of you because for many good reasons you simply don't want to do it.
The others I'll lose because a few speakers use mastic gaskets or similar which have particular properties and which are destroyed when the main driver is removed. Though these can be replaced I'd hesitate if after undoing the main driver bolts you find the driver firmly stuck.
However for most of us this isn't a problem and easy access to the innards of the speaker is facilitated by just undoing a few bolts, and very gently removing the main driver.
NOTE – have a flat surface just level with the bottom of the driver hole so that as you draw the main driver out you can place it gently face down and decide what you are up against and to plan the next phase!

Class B tweaks, inside the box but no soldering...

As you remove the main driver the leads attached will normally be long enough for you to lay the driver flat as described above. If the driver is attached by push on tags you can pull these off (noting where they came from) and lay the main driver to one side. Now get a torch or better still set up a work light and have a look in.

Assuming a typical box loudspeaker (oops! if you've an electrostatic you must be pretty confused by now) what you will find is a box lined with some absorbent material on all walls.
This can take many forms but more often than not is profiled acoustic foam (PAF), that foam stuff that looks a bit like egg carton. Also you may well find a load of miscellaneous stuffing filling the interior. All of this stuff is designed to break-up or absorb standing waves and reflected waves, and to a certain extent to slow the speed of sound to make the box appear bigger. The problem is that though this can give a better frequency response it can also kill the dynamics of a speaker.
Normally all this stuff is pretty easy to take out so pull it all out and put the main driver back in. Now you may well find your speaker sounding much more dynamic and forward, it may also be hopelessly coloured.
So now comes the fiddling time where you add/remover this damping material until you reach the best compromise. Don't be intimidated by the worry that "if the designer made it that way there must be a good reason" – the designer didn't have your room, your system, or perhaps most importantly your ears...

Now your speaker is optimally damped for your room you can look at how well the box itself is built. Chances are it's made of the thinnest cheapest material, usually chipboard or if you are lucky MDF. If the speaker is bigger than say a small bookshelf it also probably needs bracing of the side panels, but this costs money and is often left out.
It's a simple thing to cut a length of wood, broom handle is ideal, and with a bit of fiddling glue it across the speaker from one side to the other to connect the centres of the panels. This is one of the few tweaks that are almost guaranteed to bring an improvement though it may be subtle.
You can always add more bracing, this being especially useful for large cheap floorstanders whose cabinets do tend to sing along with the music...

The box itself is tuned to match the bass driver and give a particular bass response whether in a sealed box or ported box. By altering the volume of the box you can bring large changes to the sound. The simplest way of doing this is to take a freezer bag, measure out say 1 litre of sand and seal it in the bag. (then put another bag round it for safekeeping!).
Then just put the bags into the boxes and see the difference – it will be big! There is a side benefit to this in that in putting all that sand in you are increasing the weight of the speaker substantially and damping it to a certain extent. Just make sure the sand can't leak out and that the bags have the air pushed out so they won't rustle.

Lastly when you come to replace the driver you may find puny screws holding it in place. If you can use something bigger, or far better buy some proper speaker mounting bolts which will allow you to crank the bolts up tight – another sure fire improvement.

Class C tweaks – "the soldering iron's revenge..."

Before you run for cover I'm only going to talk about very basic stuff here, one step up from wiring a plug so don't be put off... For this you need a simple soldering iron, and some decent electronics solder.

First a word of warning - The only damage you are likely to do to the speaker apart from singing the wood if you're careless, is to burn through the diaphragm of the main driver. You can do this in three ways, all easy to avoid.
First you can simply poke the end of the iron through the cone – very nasty.
Secondly you can let a drop of hot solder fall from the work and onto the cone. Lastly when working on the leads to the driver you can hold the iron on for too long so that the heat gets transmitted along the lead in wires to the cone – rare this and you have to be a klutz.

Inside the box you'll find a board with some complicated electronic widgets on it. This is designed in all but the cheapest speakers to be removable for repair. Have a look and work out how to take it out otherwise you'll be undertaking keyhole surgery...

The first thing to change is the internal wiring. This is usually junk bell wire or similar. If you like your speaker cable then use that. If your drive units were wired up using push connectors then you get an additional advantage of replacing this these with proper soldered joint.

By now you will have made a lot of changes, but your speakers may still be too laid back or bright for your taste. So all that's left is the crossover. If it's a hugely complicated thing then leave well alone, but in most the two important elements for us are pretty easy to identify.
The first is the main bass inductor. This is a coil of wire, there may be several but this will be the bigger one. If your speakers are a bit laid back just unwind a few turns from the coil, 2 will do for a start. Don't cut or solder anything as then you can just wind them back on if you don't like the result.
The effect is to raise the frequency at which the bass driver is rolled off and so increase the summed response of the two drivers at and just above crossover. It will cause a harder brighter sound, voices coming forward along with drum strikes and the like.
The result may be too ‘clattery' for you but it's easily reversed, or if you like the effect increased. Conversely if your speakers are already too harsh you can reduce this midrange output by adding a couple of turns of a suitable thin insulated wire.

The second easily tweakable element is the resistor in series with the tweeter, which protects the delicate tweeter from the full output of the amplifier. Most speakers have one and it's simple to increase or decrease this slightly, 1/2 an ohm is quite a lot.
The result is a raising or lowering of the tinkly bits! Surface noise from LP's can also alter. While you're there use a decent hi-power resistor, say 5 amp or more, a useful tweak even if you don't change the value.

All these changes will alter the presentation of your speakers, some are improvements, but most will simply try to tailor the response to your own circumstances. What they won't do is turn a sow's ear into a silk purse. For that you either need to buy new or second hand speakers, or perhaps best of all make your own from a kit – something for another article...

Happy tweaking :-)

Go back to Part 1

© Copyright 1999 Geoff Husband - http://www.tnt-audio.com

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