What is swamp resistance

Level reduction with ohmic resistors

In the case of passive boxes, it is often impossible to avoid adapting the different efficiencies of the individual chassis with the help of ohmic resistors. Usually, midrange speakers have an efficiency that is between 2 dB and 6 dB higher than that of bass speakers in the low frequency range. If this level difference is not compensated, the speaker will sound weak.

When adjusting the level with ohmic resistors, no tonal disadvantages are to be expected if the following requirements are met:

  • You must never lower speakers with resistors that operate at their natural resonance - i.e. all speakers that are used as woofers. An upstream resistor worsens the Q-factor of the bass loudspeaker and thus the impulse behavior in the range of the resonance frequency.

  • You have to make sure that with upstream resistors the total impedance with which the crossover is loaded does not change. If you were to solder a 4.7 ohm resistor in front of an 8 ohm speaker, the crossover would have a load of 12.7 ohms and would no longer separate correctly.

  • Therefore you always have to work with two resistors, namely a series resistor and a parallel resistor. They are dimensioned in such a way that the nominal impedance (e.g. 8 ohms) at the crossover network is retained.

The following table gives values ​​for the most common applications (8 ohms):

- 2 dB2.2 ohms22 ohms
- 4 dB3.3 ohms10 ohms
- 6 dB4.7 ohms8.2 ohms

Fixed resistors or level controls?

In the VISATON building proposals, some fixed resistors and some level regulators are specified. Level controls also have two resistors, both of which can be changed using two sliders that are coupled to one another. You have the opportunity to continuously and quickly find out the optimal set-up.

As is well known, this optimal coordination depends heavily on the listening room, listening distance and, last but not least, personal taste. With level controls you are always able to react flexibly to these variable parameters.

If you do not want to use a regulator under any circumstances, you can use the following method to determine the optimal values ​​for voltage divider resistors: You do not install the switch during the first test run of the box, but rather lead the extended cable of the switch through an opening in the box (e.g. Bass reflex tube, hole for connector). Then you solder different possibilities of the resistance combinations of the table for level reduction between midrange or tweeter and you can find out the correct reduction. Finally, you can assemble the switch completely and insert it into the housing.