LS1be Studio Monitors Manual

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page 9
sound in all directions and sound travelling backwards and sideways reects against the
walls and adds up to the direct sound. Although the ear is less sensitive to the resulting
phase errors at these low frequencies, the impact on the low frequency energy itself
can be dramatic since at certain frequencies the reected sound can cancel the direct
sound. A real solution is to apply low frequency absorption behind the loudspeaker so
the reection is attenuated. Those who cannot afford such measures are invited to spend
some time shifting the speakers back and forth untill the optimal compromise is found.
In this respect the LS1 is not different from any other loudspeaker. A special feature of
the LS1 however is that the LS1s subwoofer can be taken off the foot plate of the main
system so both can be positioned independently. If your room acoustics are particularly
difcult, feel free to experiment with placing the sub closer to the wall than the main
speaker. You can use the parameters in the subwoofer preference pane (Gain and Delay)
to compensate resulting alignment errors. Please read the chapter ‚Software Control
Settings‘ for more information.
An annoying asset of most rooms is that they resonate at low frequencies (below 200
Hz). Tones bouncing back and forth between walls interfere, and at certain frequencies
they form node and anti node patterns which means that certain tones sound silent in
one place in the room but are very loud at other spots. These resonances are called room
modes and since they are dependent on the dimensions and the weight of the walls, they
vary from room to room. Some rooms therefore sound ‚better‘ than others. Whether a
certain room mode is triggered or not is dependent on the position of the source and of
the listener. So again, it makes sense to spend some time positioning the LS1‘s carefully
to nd the optimal compromise. Consult a specialized acoustician if you have a real strong
room mode problem in your room.
Some companies apply DSP for ’room correction‘. We rather not use DSP in the LS1 for
this since the effects are inuenced by the position of the listener. If we again look at
the three acoustic factors: 1. First reections are strongly dependent on the listeners‘
position, so there is no way to correct these with DSP. This is certainly true above 200
Hz where the wavelength is short. 2. The low frequency coupling effect can partly be
compensated by DSP (please use the LS1 EQ for that). However in the region around
100 Hz where often energy is lowered due to the reection being out of phase, DSP will
not help since a louder tone will still be canceled by its reection. 3. Finally, room modes
are also strongly dependent on the position of the listener. Theoretically it should be
advantageous to attenuate peaks in the room response that reside in the whole listening
area, but all DSP solutions for this we tried so far challenged the LS1's performance too
much.
Positioning
Positioning
Room Acoustics
Keep in mind that one always hears the loudspeaker plus its acoustic environment.
Although the LS1 has superior acoustical characteristics, positioning it correctly in your
room remains of great importance. Let‘s rst have a brief look at room acoustics and then
see how positioning the LS1 inuences them.
Roughly speaking there are three factors in acoustics that inuence the audible
performance of a loudspeaker: rst reections, low frequency coupling of nearby walls
and room modes (or room resonances). Lateral rst reections inuence the stereo
image. Since high frequencies are dominant in acoustic imaging, adding fabric acoustic
absorption like curtains at the reection spots on the left and right walls helps a lot.
Since the LS1 has a wide bafe, aiming the loudspeaker away from the reective spot
helps too. Another major type of reection is via the oor and ceiling. These reections
interfere less with the stereo image, but do color the sound. Absorbing the oor bounce
with a carpet helps. A special case is reections against an obstacle in front of the
listener, like a computer screen, bouncing the sound toward the front wall and from there
back to the listener. In those cases, absorbing the reection at either the obstacle or the
wall cures the problem. Due to the wide bafe of the LS1, which focusses the sound,
reections on the wall behind the listener tend to have slightly more impact than with
other loudspeakers. Please consider to add absorption or sound scattering objects like
bookcases against this wall.
First reections also introduce phase distortion in the early sound if the walls are too
close. Psycho acoustics tells us this effect is important down to 250 Hz. One wavelength
of a 250Hz tone lasts 4ms so this is the time span that certainly needs to be ’clean‘.
Sound travels app. 1.4 m in that time. Rules of thumb are therefore that you need to
have at least 80cm distance from the side walls (1.5 m is better) and 60cm from the
back wall (1.2m is better). The wide bafe of the LS1 makes the distance to the wall
behind them less critical, but if you have the chance, please allow for some distance.
An alternative is to choose the other extreme and place each LS1 with the back directly
against a wall. In that case all reections from the back wall integrate completely in phase
with the direct sound, the speaker gets an ’innite bafe‘. Unfortunately the speakers can
not be aimed inwards in this setting to optimize the stereo image, unless the walls have
the right angle of course.
This brings us to low frequency coupling of nearby walls. Below 250 Hz the LS1 radiates
Positioning