Thiel ss2 Verweisanleitung

If the subwoofer is to reproduce the bass range of the

main channels, in addition to the subwoofer channel, there
are major potential problems with the crossover between the
subwoofer and the main speakers.

There are two possible ways a subwoofer can be used to

reproduce main channel bass: augment or crossover.
Augment operation allows the main speakers to operate
normally, without a crossover, and the subwoofer is used
“fill-in” the deep bass below the range of the main speaker.
Crossover mode transfers some of the bass range from the
main speakers to the subwoofer. Each of these types of use
can be used with two types of main loudspeakers, sealed or
reflex.  Following are examples illustrating typical results for
each case.

The simplest case is to use crossover with sealed main

speakers. In the special case where the crossover frequency
is set to the speaker’s limit (-3 dB) frequency, the crossover’s
HP will combine with the speaker’s bass response to achieve
a total 4

th

 order, Q=.5 hi pass response that will, in theory,

perfectly cross over with the 4th order, Q=.5 sub low pass
response. However, in practice, even this simple case is upset
by the complication that the sub’s response does not extend
to DC. For an 80 Hz crossover, if the sub has a 4

th

 order

rolloff at 35 Hz, the interactive phase effects will cause the
whole bass range to be 2 dB weak (Fig. 1).

Increasing the signal level to the sub solves this

problem, but the system response still suffers from excessive
output in the 100 - 200 Hz region.

In the more general case where the crossover frequency

is higher than the main speaker’s frequency, the results are
not as good. For example, if the main speaker’s response
extends to 50 Hz and the crossover is at 80 Hz, the bass

response is 4 dB weak (Fig. 2). Even when the phase and
level are adjusted to be optimum (180

°

, -1 dB) the response

is not nearly ideal (Fig. 3).

In cases where the main speakers are ported, things are

no better. For example, if the main speakers are tuned to 50
Hz and you want to implement an 80 Hz crossover with the
sub extending to 25 Hz, the results achieved without phase
adjustment are not what is desired. Even when the phase
control is set optimally (80

°

 @ 50 Hz) the results are not

good, giving a hump in the bass while still giving weak
upper bass (Fig. 4).

Fig. 1  Subwoofer extending to 35 Hz and crossing-over at 80 Hz with a sealed, 80 Hz main
speaker. Standard settings.

Fig. 2  Subwoofer extending to 35 Hz and crossing-over at 80 Hz with a sealed, 50 Hz main
speaker. Standard settings.

Fig. 3  Subwoofer extending to 35 Hz and crossing-over at 80 Hz with a sealed, 50 Hz main
speaker. Optimum phase and level adjustment.

Fig. 4  Subwoofer extending to 25 Hz and crossing-over at 80 Hz with a reflex, 50 Hz main
speaker. Optimum phase and level adjustment.

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