Subwoofer placement and calibration
If several subwoofers are used, they must be controlled in the same way. If a sound control network (equalizer, FIR or IIR filter, sound processor) is used, this should be switched off during the first measurement.
This suggestion is not universal and mathematically provable. After all, many loudspeakers also have permanently installed filters, of which the buyer will never know unless he opens and measures through them. But: At the beginning of each series of measurements, the system under investigation must be in a clearly defined, reproducible state. This is not improved by a previously configured setup. In addition, it sometimes only becomes apparent after the correct positioning of subwoofers, loudspeakers, listening positions and damping material how much better the direct sound is compared to the electronically filtered sound.
Polarity, Phase and Delay (if present) should also be switched off or set to neutral for the first measurement.
Die Messungen sollten unter definierten Bedingungen starten. Im Idealfall zeigt sich, dass die gemessenen und per Hörtest ermittelten Werte mit den vorgeschlagenen Einstellungen in der Bedienungsanleitung des Verstärkers übereinstimmen. Andernfalls sollte dem Höreindruck die höchste Priorität gegeben werden. Messwerte können durch Reflexionen an den Wänden, die unser Hörsinn automatisch ausblendet, u.U. verfälscht bzw. irreführend werden.
Subwoofer on "LFE + Main" vs. "LFE": "Main" should only be switched on after it has become clear that the front speakers also when listening to music (ie not only for sound effects in movies) need support in the bass range.
For the background of the LFE channel see here. The AV receiver receives the following input signals for a Dolby 5.1 soundtrack: 5 channels (front right, center and left, surround right and left). The ".1" is used for the low frequencies (Low-Frequency Effects, LFE) < 120 Hz. This is defined by the Dolby Laboratories, represented in Germany by Dolby Germany GmbH.
This does not necessarily mean that the 5 channels do not get any low frequencies. With a "normal" stereo source, all low frequencies are naturally distributed to both front are distributed to the two front channels.
In the AV receiver, you can now set how these signals are distributed to the speakers and subwoofer. There are different arguments and experiences, whether e.g. stereo reproduction is improved by subwoofer (" + Main"). PRO: Subwoofers are designed, set up and (hopefully) calibrated for this task. Through this specialization, the results per invested money and effort are better. The front speakers sound better and last longer because the bass-conditioned large diaphragm strokes are eliminated. The reproduction of the bass range is subject to other physical laws anyway (see link above) and should therefore be done by a separate system. CONTRA: In the end, you always hear that 2 different components should play together: The travel times of the sound cannot be the same to every listening position over the entire frequency spectrum, because several sound sources play from different places per channel. This is one of many audible effects. A good loudspeaker, of course, covers the entire required frequency range and its components are much more finely tuned against each other. And a good listening room allows for sufficiently low-resonance speaker placement.
The positioning of the subwoofers plays a decisive role for the sound. Nevertheless, it must not be audible where the bass comes from. For this, the crossover frequency or "XO" must be 80 Hz or lower. Basically, the lowest frequency that the speakers can handle should be selected.
- The real crossover frequency can be higher than the electronically selected one, because the loudspeakers, their cabinets and the surrounding room are also physical "crossovers".
- With a crossover frequency of e.g. 80 Hz with 12 dB/octave 160 Hz is attenuated by 12 dB. This frequency range therefore remains clearly audible: 10 dB difference is perceived as "half the volume".
- Wind noise in the reflex channels (port noise) or other distortions of the subwoofers can also be audible and thus reveal their placement.
- Our sense of hearing is very fine in localizing low frequencies (where the growl comes from), probably this was of vital interest evolutionarily.
- Visible localization leads to psychoacoustic localization. At concerts, the drums are sometimes illuminated more brightly when the bass is too faintly audible.
How many subwoofers and where to start the positioning?
The relationship between the sound image and the positioning of the subwoofers is very complex. Experience has shown that you should therefore not start with a "particularly clever" set-up but with the following common scheme:
- Zwei Subwoofer sind deutlich besser als Einer, Vier Subwoofer meist besser als zwei [Welti Devantier]. Mehr (z.B. double bass arrays) sind für Spezialfälle.
- First subwoofers: First(!) in the corner, close to the Mains.
- Second subwoofers: Not in the corner, but near the center of a side or the back wall.
- More subwoofers: away from 1 and 2, not on the floor.
Placing a single subwoofer in the corner of a room should be avoided. If in doubt, it should be placed close to the main speakers. Often asymmetrical setups with 2 subwoofers prove to be favorable -. It is certainly worth a try.
[Welti Devantier] Todd Welti, Allan Devantier: Low-Frequency Optimization Using Multi Subwoofers. Harman International Industries Inc. Northbridge CA 91329 USA, Manuscript received 2006
[earl Geddes] mehlau.net/audio/multisub_geddes