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Loudspeakers: the Idiots' Guide to Tweaking

Part 1

[Italian version]

Time and time again I hear, or read on forums and the like, of people asking what upgrade route they should take. "The sound's too dull/bright/no-dynamics/boomy..." etc. The replies often involve spending thousands of pounds, and yet there may be a simple and cheap solution tweak the speakers.
In this guide I'm not going to talk about expensive tuning, rebuilding boxes or the theory of third order crossovers, just give a few cheap (or more often free) tweaks that will change the presentation of your speakers. Whether these are improvements only you can decide.

What many people don't realise is how staggeringly approximate the frequency response of a hi-fi is. Any CD player can give you a ruler flat response, a few are rolled off by a tiny amount in the highest frequencies. Amplifiers must show frequency responses almost as flat. Loudspeakers on the other hand routinely show variations of 3-6 dB's in the limited bandwidth of 100 to 10,000 Hz.
To add to this wild response is of course the room. I've just been testing a pair of Cabasse Farella's, and Cabasse spend a lot of time getting a flat frequency response. I saw the test pair in their huge anechoic chamber giving a response +-2 dbls for 100 20,000 hz, a tremendous result. In my room they showed a plot that struggled to stay +-12 dbls over the same range.

The effect of this room/speaker interaction is that designers are faced with the impossible task of designing a speaker to appeal to the average person in the average room with an average (in the price range) system.
Some designers such as Cabasse (French loudspeakers Company) just try to make the response as flat as possible in the lab and hope the room doesn't screw this up. Others voice their speakers to take account of a "typical" room or to emphasise a particular trait, say bass extension, in the hope that this will lift their speakers above the rest in a shop demonstration.
All this makes one wonder how most speakers manage to sound bearable in your own room, and that the chances of a speaker being ideal for your room are practically zero.

So accepting that any speaker system, no matter how expensive, is a mass of compromises it gives us penniless enthusiasts an ideal opportunity to try and better the manufacturer's product by simple tweaking. The best bit is that unless you're staggeringly clumsy you're unlikely to damage the speaker and can always reverse any changes also, unlike fiddling with amps and the like, the chances of frying yourself or your family are limited.

I'm going to place these tweaks into three classes. Class A tweaks are those that require no alteration to the speaker itself, Class B tweaks need you to open up the cabinet and class C tweaks are those that require the use of a soldering iron.

Class A tweaks: First I'll state the obvious, you need to move speakers about in your room to find the best place for them. The WASP method is excellent and well described in this publication, but you feel a prat and it takes ages.
Single men/women can get away with this sort of thing, but not me. Generally it's best to start with the manufacturers recommendations regards placing, but remember that like the speakers themselves, these are very much a compromised average guide.
As a rule of thumb bringing speakers away from walls, especially end walls, will lower the bass level and improve imaging and visa versa. Some speakers e.g. Naim and Mission are generally voiced to be close to rear walls, but even here this may not work in your room.
Once you think you've found the best position you need to think about what goes under the speakers. Trying half a dozen decent stands isn't in the reach of most of us so what goes beneath them is more relevant. Try putting the stands on a paving slab, great if you live in a flat as this will reduce the sound going downstairs, or screwing cross head screws into the floor and locating the stands spikes into them. Try *Blue Tac* to couple the speaker to the stand, then try spikes. All of these will make a difference, but whether they are an improvement is another matter.

OK, so the speakers are all set up and you still don't like them. Try swapping the speaker leads over on both speakers to reverse the phase. This will have an effect, whether a good one is again a matter of experimentation though the fact that many records and amps reverse phase shows that there is no *correct* way of connecting the speakers.

One dodge that a few manufacturers use to get a good flat response at crossover is to run the tweeter out of phase with the woofer, using the cancellation to lower output at crossover frequencies. If your speakers are bi-wired it's very easy to do this yourself just by swapping the red and black leads to the tweeters over.
Again the effect is unpredictable, especially if the manufacturer may have swapped them already inside the speaker, but it will sound different in both imaging and frequency response and perhaps better.

Lastly, most modern speakers are ported boxes, i.e. they have a hole in them which reinforces bass. You can do a lot with this! An old tweek is to fill the port with a bundle of drinking straws, this reduces turbulence in the port, but also by using shorter or longer straws you can actually effect the frequency at which the port operates.
Similarly port output can be reduced by putting something in the port, such as wool, a foam plug or an old sock. This will reduce port output but also effect the way the bass driver is loaded, moving it closer to a sealed box design. You might hate the result, but you won't know unless you try... Still hate the sound? You'll have to wait for part 2

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

Go to Part 2 !

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