Loudspeaker Tuning
Dr.-Ing. Peter Strassacker
E-mail: peter@lautsprechershop.de

The is considerable scope for tuning loudspeaker; in the following we'll discuss the different methods.

Cabinet material

Many speakers off the shelf are made from light material, they sometimes feels like a cardboard boxes. A good cabinet, however, has to be heavy, since they become less prone to resonance with increasing weight. Unlike musical instruments the loudspeaker cabinet should absolutely quiet and should not vibrate.

It is, therefore, advisable to exchange light cabinet material for a more heavy one. Chipboard and MDF (medium density fibre particle board) are quite heavy. There is no need to change the cabinet material when it's already heavy enough. You'll find out quickly whether the cabinet material is too light when entering cabinet volume and wood gauge into our Volume Calculator.

Perfectionist use sandwich boards where the cavities are filled with sand. The trickling sand ensures that the vibration is absorbed.

Conversion from closed cabinet to bass reflex cabinet

A bass reflex cabinet, compared to an otherwise identical closed cabinet, requires a bass driver with a considerably stronger magnet. Therefore, it usually doesn't make sense to turn a closed cabinet into a bass reflex, the bass would be boomy.

But it does make sense to do it the other way around, especially when a subwoofer is going to be added. The loudspeaker doesn't need to go that low anymore, since this has become the job of the subwoofer. When the bass reflex port has been closed, there will be less but clean bass.

A word of advice with regard to bass reflex tuning: the longer the bass reflex tube the lower the tube's resonance and the less boomy the sound. If the speaker lacks bass then a shortened bass reflex tube might help to subjectively increase the bass perception. In this case the resonance is shifted to higher frequencies, the bass becomes more distinct.

Bass relief

Those who like to listen to music at a high volume have probably noticed that their speakers cannot handle it. If the bass driver is the bottleneck then there is a solution.

If the frequency range is restricted to higher frequencies by adding a 330 uF capacitor (for 4 Ohm speakers) or 150 uF (for 8 Ohm speakers), a large part of energy and mechanical movement is kept away from the driver.

If the capacitor is added between amp and speaker the capacitor should be of high quality; At least 22 uF (47 uF for 8 Ohm speakers) should be equipped with MKP capacitors, since this capacitor represents the bottleneck for the entire speaker.

Another solution would be to add the capacitor to the bass driver section only, to make sure that higher frequencies are not affected.

Crossover tuning

Some advice beforehand: if you don't like the sound of your loudspeaker the crossover tuning usually doesn't help; an improved crossover doesn't perform miracles. There might be an exception: if the electrolytic capacitors of your old speakers have become dried out then a replacement with new ones might change the sound dramatically.

In case that the crossover's design is correct and the sound is still not satisfactory, tuning won't help.

You should only improve on something that is already good. Crossover tuning changes the sound just marginally.

Which components produce which improvement?

Resistors

How resistors affect the sound quality is a controversial subject, we are not a judge of that. However, we recommend a blind test whereby neither the demonstrator nor the listener knows which resistor is being used at the moment. To be frank, we still have to find a sound difference.

Capacitors

Electrolytic capacitors are more lossy than foil capacitors, it makes sense to exchange them. There is an exception: an impedance correction where the RLC element is in parallel to the speaker terminals doesn't require a top notch quality, expensive component.

During listening tests many of our customers noticed a considerable sound improvement when a cheap MKT capacitor was replaced by MKP capacitor, especially with regard to mid and high frequencies.

Tin foil capacitors show a smaller microphonics effect, i.e. their heavy electrodes don't have the tendency to vibration. This lack of vibration prevents the capacitor from taking on a life of its own. This would certainly affect the sound when a voltage is applied to capacitor.

Mundorf Supreme CAPS (and comparable capacitors by other manufacturers like IT and Jensen) as well as Silver Oil capacitors are completing the range of capacitors upwards.

Coils

Air core coils show the lowest distortion. Coils with a core need to reset the magnetic core. This causes losses and distortion (non-harmonic distortion, distortion factor).

A disadvantage of air core coils is that, at the same DC resistance, they are often bigger than core coils.

Copper foil coils (cfc coils) show a considerably low microphonics effect (intrinsic resonance).

PS:
Especially with regard to crossover tuning the professional loudspeaker designers believe that less has to be done than expected by the hobbyist. Many top designer are of the opinion that MKP capacitors and air core coils are sufficient even in top speakers.

Home     Amplifier Tuning