TIPS & TRICKS

In 1982 the very first issue of the Dutch Audio&Technique magazine was published. In it was a test of cassette deck players. We were astonished about the really big differences between them. Not measurable but very good audible! We then looked at the circuit diagrams. In advance we had them sorted out from the best sounding to the least performer. Looking at those diagrams the only difference was in the muting. The worst sounding machine had twelve (12) mute transistors pro channel (the best one only two).

The problem was obvious, but was the reason for this? In our opinion there's only one reason: the internal capacitance varies with the amplitude of the signal. That phenomena causes a constant varying phase shift in the audible region when music is playing. The subjective result being a haze in the stereo image. A lot of audio equipment, especially CD-players, applies this muting technology. The main reason being that "clicks" might be audible when the program, the source or the track is switched. If you don't mind some click now and then better remove these ugly things. Simply use a cutter!

In some loudspeaker designs the tweeter is connected to the filter/amplifier by a capacitor, without paralleling this tweeter by a coil or a resistance. That means that this tweeter is not controlled (or damped) by the amplifier BELOW the cross-over filter frequency. It might swing wildly! This causes an agressive behaviour of the tweeter thereby introducing fatigueness of the listener in the long run. This "problem" can very simply be solved by applying a simple parallel resistor of some 47 or 50 Ohms - 1 Watt (R2) in parallel of the tweeter. Also a resistor in series of around 1 Ohm - 5 Watt (R1) may help some. Just try it.

The solution is simple: put a resistor between the transformer and the rectifier. In a transistor power amp the value of that resistor may be 0,1 Ohm - 5 Watt. With tube power amps it could be around 1 Ohm and in preamps (transistor and tubes) some 10 Ohms. The result is a more relaxed amplification. It seems as if the sound comes easier out of your loudspeakers and the stereo image is mostly improved. A few dimes will do the job.

A lot of people prefer a small loudspeaker over a large freestanding one. In order to get a good performance (stereo imaging and depth!) it's necessary to place those loudspeakers at a distance of at least 30 cm (12") from any wall or massive object.

A large variation of stands is available from US $ 50 to over US $ 1000 each. Almost all loudspeaker cabinets vibrate and those vibrations are transferred to the stand. The stand now is an active sound source! In the past we tested and listened to a lot of different stands. It came out that some aspects are really important:

- rectangular tubes (massive or hollow!) are less good then circular ones.
- 1 round tube performs better then two or three.
- metal top- and bottomplates behave less good then MDF ones.

Having those issues as a starting point, (and with the experiences we obtained developing the Vib-One) it's obvious that constructing a stand by yourself could give a better performance then the commercial types from the shop.

When constructing this yourself it's possible to choose the best heigth. Taking the heigth of the ear at your favorite listening position; a good option is to have the center between woofer and tweeter at the same heigth. Determine that heigth and then the heigth between teh bottomside of the loudspeaker and the floor. Now subtract 5 cm (2") and that will be the length of the standing tube. This tube is best made by a local welding shop. Order a tube between 5 and 10 cm (2"- 4"), with a small light weigth loudspeaker 5 cm is enough, with heavier types you better take a larger one. Now make two steel strips fitting inside that tube. In the center of the strip a hole is made and an M5 or M6 nut is welded underneath. The strips are placed at two ends of the tube and welded some 3 mm (0,1") under the border (the welding seam should NOT reach over the border ends!).

Now measure the bottom side of your loudspeaker and saw two boards MDF of 8 and 12 mm (0.3" and 0.5") to match the same measurements. Between those boards a layer of 1,5 mm (0.6") Bitumen or Sirex is glued using kit. After the kit is dried out make a 6 mm (0.25") hole in the center and countersink it so a screwhead sinks completely into the board. This should be done at the thinnest board side.

The bottomboard is identical but at least 20% thicker then the topboard.

Paint or spray the components in the wanted color.

Now mount the tube on the bottomboard with the thickest board against the tube. Place it standing on the floor and fill the tube with dry sand to just below the nut on the strip. Thereafter mount the topboard.

The bottomside of the loudspeaker cabinet should fit as close to the board as possible. It may be a good thing to glue an extra layer of 1,5 mm bitumen on top of the topboard (also to prevend the cabinet from sliding off too easily).

At the bottom of the footboard mount three rubber stops. If the room has a concrete floor it's a good thing to mount ONE spike at the front center of the footboard (those are available in sport shops, devised for football shoes) and take two rubber stops at the back side giving the same heigth.

If you did construct a stand like this tell us about your experiences!