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How to integrate a sub-woofer into a hi-fi system.
I would like to start this “brief” dissertation on systems with sub-woofers by quoting word for word what audio pro states on the first page of a brochure: “everyone needs a sub-woofer”.
I
think that this statement should appear in a possible “hi-fi Bible",
however, in my view, with a tiny but essential adjustment: “everyone
needs an audio pro sub-woofer”
Generally speaking, I highly recommend the use of a top quality sub-woofer with
any type of speakers. Audiophiles often forget, or just do not know,
that, by definition, a hi-fi system must reproduce frequencies across
the audible range, from 20Hz to 20kHz ± 3dB. So, if you want to use
the term “hi-fi” for your sound system, you must have a dedicated
sub-bass speaker, as NO traditional full-range speaker can achieve
decent infra-bass.
A
quality active sub-woofer (perfectly set up and tuned into the system)
is essential if you would like your hi-fi to reproduce a bass drum or an
organ as perfectly and as accurately as it does a violin or a piano.
Bass instruments do not deserve to be considered “ugly ducklings” – they
are the foundation, and hence, an essential part of a musical
composition or, indeed, of any sonic event !
Many
“conservative” audiophiles believe that the addition of a sub-woofer
will muddy the sound of a “high-end” system, and I have to say they are
very often right! But I should explain that this mostly happens for two
main reasons: the first is very poor integration of the sub-woofer into
the system, so that “booming” bass from the pair of main speakers is
made worse by the sub-woofer’s additional output. The second reason is
that the large majority of the sub-woofers around (or rather, almost
all) do not have acceptable sound-accuracy, because they don’t avail
themselves of advanced electronic technologies.
A
traditional sub-woofer, simply made up of a normal amplifier and a
woofer (usually tragically large), is something to deliberately avoid,
unless you do not care about obtaining pure and real sound. The
inevitable result, due to the high distortion and lack of control (no
matter the crazy price, the “noble” brand or the astonishing opinion of
pathetic reviewers), is a sub-woofer affected by so called “slam” or
“punch”, that is a nasty thing for audiophiles who understand and want a
real serious sound, but very enjoyable for young guys and car-audio
lovers, who think that real bass is just a “boom, boom” matter and these
things actually deserve to be called “boom boxes”.
To
compound the problem, when you buy a sub-woofer it is more than likely
that you will not be instructed in the correct way to integrate it into
your system, so most people instinctively connect the sub-woofer in
parallel with the main speakers and unwittingly commit a tragic “hi-fi
crime”. Finally to sum up, all these negative factors combine to result
in a disgusting bass range!
With audio pro sub-woofers, thanks to their patented, exclusive ACE-bass
technology (see the explanation in the audio pro part of this web site), it is quite another story
and, with the help of this instruction, you can achieve a perfect set-up
of your system, resulting in a fantastic bass & infra-bass range.
You may be interested to know that in 1978 audio pro produced the very first active (and ACE-bass
patented) sub-woofer in the world – the legendary B2-50 – which, after
32 years of service, is still delighting the ears of thousands of
audiophiles around the world, and I’m absolutely thrilled and proud to
be one of them! In spite of its longevity, the B2-50 still sets
standards that other sub-woofer manufacturers nowadays try in vain to
match!
Now I
would like to give you some important advice on how to set up the
system for best results. A right set-up is essential, as the quality of
the sound of your entire system depends on it: do not worry, it is not a
difficult process and it is good fun too!
To begin, position the speakers and the sub-woofer following these directions:
1) Possibly,
situate the speakers and the sub facing the long side of the room, with
the speakers (not the sub) at least 1 metre from the corners. Do not
place the speakers and/or the sub inside an item of furniture, such as a
cabinet, or in a semi-enclosed space.
2) Always try to put the
sub-woofer close to a corner, or at least against a wall, in order to
increase its efficiency and consequently reduce its distortion.
Definitely avoid putting it far away from a wall or, even worse, raising
it from floor level.
When
you introduce a sub-woofer into a hi-fi system, the absolute rule is:
always “cut” the deep frequencies in your main speakers, no matter what
type they are! This way, you create a roll-off in the frequency
response of the main speakers, in order to achieve a perfect crossover
point with the sub-woofer. Furthermore, given that the majority of
normal speakers (not audio pro) have a "hilly" frequency response in
the bass range (the cause of "booming" bass), if you apply a roll-off on
this range, you manage to put down this tragic "hill" and to reduce the
distortion of the bass too! For example, floorstanding speakers, which
usually “boom”, (once again, no matter the crazy price, the “noble”
brand or the astonishing opinion of pathetic reviewers), if you do not
roll-off their bass response, the result is always appalling. In the
case of small main speakers with a sub-woofer, what happens is
technically different, but you still have to cut their bass response,
mostly in order to reduce the distortion of the woofers, which is
generally high in this type of speaker.
If you roll-off the lowest
frequencies in the main speakers, their dynamic range and “speed” will
increase and their distortion, as I have already said, will decline.
This happens because the woofers of the speakers will no longer struggle
(in vain) to reproduce the low frequencies that the sub-woofer is much
better qualified to manage. An additional “magical effect” (due to the
reduced distortion in their bass spectrum) is that the “image” and the
clarity of the mid and high range will improve. Finally, due to the perfect "marriage” between the main speakers and the sub-woofer, low
frequencies stop “booming & yowling”, and the infra-low ones are
deep, fast and undistorted, as if they are “carved out of the air”.
To
help you understand what I mean, I’d like to quote the words Scott
Bartley used about the “bass department” of an audio pro system with
sub-woofer (perfectly set up), in a review in FFWD magazine: ”bass
response is wonderfully tight, incredibly fast and, above all, really
deep … to create a distortion-free sub bass effect that feels as though
it’s rising up out of the very floor. Call it low-end imaging, if you
will”.
Now,
where you have a stereo amplifier (without a Sub-Out RCA socket and no
possibility of cutting the main speakers electronically), the only way
to solve the problem is to connect the sub-woofer between the amplifier
and the speakers, using the speaker terminals on the back of the
sub-woofer. So, connect the amplifier outputs to the sub-woofer’s
inputs, and then connect the sub-woofer’s outputs to the speakers. This
way, an audio pro sub-woofer cuts the bass of the main speakers at
around 150Hz (6 dB/octave), resulting in the above-mentioned benefits.
Even if this solution is not adjustable and for some speakers not perfect (the roll-off depends on the impedance of the speaker), it remains the best possible in these cases and ... far
better than nothing! In the case your sub doesn't have this facility, you can solve the problem connecting in series to the positive cable of each speaker a non-polarised capacitor (possibly audio-grade quality) and the sub in parallel to the speaker cables. The value of these capacitors could be 150uF (100V) if your speakers are rated 8 Ohm and 300uF (100V) for 4 Ohm speakers (in NZ you can find these capacitors by any branch of Jaycar Electronics). If your speakers are very "booming" reduce the value respectively to 100uF and 220uF. Any doubts? just call Franco!
If,
instead, you have a home-theatre amplifier, the solution is easier:
whatever type of speakers are being used as main speakers, even if they
are huge, go to the “speaker set-up” menu and select for all the
speakers (front, centre and rear) the “SMALL SPEAKERS” option, and
connect the sub-woofer to the “Sub-Out” RCA socket of the amplifier,
using the screened cable provided.
Many home-theatre amplifiers also
have the option of selecting the roll-off frequency of the main
speakers: if so, be sure to select a roll-off point between 80 and
120Hz (it depends on the quality of the bass department of the main
speakers). It is advisable to increase the roll-off point (even higher
than 120Hz) in the case of very “booming” floorstanders: by increasing
the crossover frequency you usually manage to clean up their
bass-mid/bass range.
To
adjust the sub-woofer’s low-pass filter, the “Low Pass” frequency knob
should normally be set at 50Hz. This knob may be turned toward “twelve
o’clock” (almost never further), if you have chosen a quite high
frequency for the roll-off point of your main speakers (see the previous
paragraph).
All right, I know what you are thinking right now, but
do not worry: even if you cut the speakers at 100 Hz and the sub’s “Low
Pass” knob is set at 50 Hz, you will not create any “hole” in the
frequency response at the crossover point. It’s too long to explain why
right now, but just trust me.
However, it is much better to have a
small “hole” in the crossover point than a “hill”! Take also into consideration that when
you increase the low-pass frequency, you will, consequently, slightly
increase the distortion and reduce the dynamic range of your sub (this
is valid for every sub-woofer in the world).
The
next step is to adjust the level of the sub-woofer. Unfortunately, it’s
not likely that you have a spectrum analyser, so here is an empirical
method to adjust the infra-bass pressure.
With
any kind of amplifier, at first you must set the tone controls flat (in
my opinion, there is no need for them to exist any more, so never use
them) and be sure that no filter is active.
With home-theatre
amplifiers, start by presetting the system to “stereo mode” and setting
all the gains of the speakers and sub-woofer at 0dB.
Select a few
well-recorded, recent CDs with real infra-bass content (i.e. bass drum
or organ). Do not use poor recordings that are void of very deep
content and avoid using “disco music” CDs, because they are surely full
of awful, saturated mid-bass, but devoid of infra-bass (usually they do
not go deeper than 40Hz)! Be warned that, with this type of poor
recording or with old CDs, people with limited experience usually try to
achieve a decent infra-bass – that doesn’t exist in the recording - by
continuing to turn up the sub-woofer’s level knob! You should also note
that an audio pro sub-woofer, due to its low distortion and control,
does not have the nasty tendency (common amongst normal sub-woofers) to
fake a rounded bass, if this is not present in the recording.
So, to
do the right thing, you may choose a Telarc CD, as this brand makes
top-quality recordings (mostly of classical music). So buy (if you
haven’t any) and play a Telarc CD that includes a well-defined bass drum
or an organ and simply rotate the sub-woofer “level” knob until you are
satisfied with the infra-bass pressure. If, in order to be happy, you
have to turn the knob past “eleven o’ clock”, either there is still
something wrong in the set-up of your system, or you may simply have …
bad musical taste and habits!
I STRONGLY recommend that you do not
set up your sub-woofer with an excessive bass level. Be aware that
unnatural and over-emphasized bass causes listening fatigue and
headaches, not to mention its hiding and dimming of the clarity of the
upper audio band!
Anyway,
if you have set everything up correctly, but still have a “dirty and
booming” bass, almost certainly you have to blame the main speakers.
Very rarely the problem lies with the sub-woofer, if it is an audio pro. Here are a few suggestions:
1) As
mentioned above, if you have the option in the amplifier “set up”,
increase (even up to 160Hz, if needed) the crossover frequency for the
main speakers and set the “Low Pass” knob of the sub-woofer around
half-way. This normally is the exhaustive solution.
2) If
that is not an option, try moving the main speakers further away from
the corners of the room and from the wall too, and reduce the length of
the speaker cables, which should always be as short as possible (this is
a general must).
3) Finally, try to move the sub-woofer from the corner along the wall.
If
the problem persists, you have to blame the acoustics of your room.
Experiment by relocating the system to a different part of the room or
in another room: sometimes the result is miraculous!
In this
connection, note that poor quality bass range does not always depend on
the system itself. The acoustics of your listening room is essential to
build a pure sound and sometimes, even with a top (and perfectly set
up) audio pro system, the dimension, the shape and the reverberation
factor of the room can mercilessly nullify all your efforts.
Be
aware that the frequency of 20Hz has a wavelength of around 17 metres
and you cannot physically hear this frequency in a closed room with a
diagonal shorter than 8.5 metres! This practically means that deep bass
needs big rooms: it cannot expand and “go deep” properly in small
closed rooms, but will produce a feeling of saturation and a lack of
sound pressure.
The shape of the room is very important too, so try
to avoid rooms with “cubic” shape. These rooms are generators of
“standing waves”, which tend to confuse and draw out the bass, killing
its clarity.
In all these cases, there is not much that can be
done: you can only try to improve the bass potential of your room by
opening doors and, if possible, windows too (please do not laugh, I am
very serious)!
You should also note that the pressure, depth and
quality of the bass vary a lot around the room, so tune your system for
best result in your habitual listening position. You will also find that
just moving your listening point forwards, backwards, up or down, often
makes a huge difference!
To finish I would like to say two words about the mid-high range. If you use audio pro
main speakers and are not satisfied about the mid-high range (too
bright), you probably have a very reflective room, so try to reduce the
reverberation by adding rugs, curtains, furniture … or in general things
which can absorb the sound. The other possibility is that their
mid-high sounds too “dull” and in this case you have to increase the
reverberation of the room, removing the most absorbent stuff and in
extreme cases the carpet too!
Be aware that both these opposite
situations will only slightly modify, if at all, the infra-bass response
of your system: this is determined 90% by the shape and dimensions of
the listening room and the position of your listening point.
Anyway,
the room that will sound perfectly in the mid-high range is one where
human voices, during a normal conversation, sound natural and clear,
and, when you clap your hands, you don’t hear any echo and/or
reverberation.
I
have tried not to use too technical a language and I do hope these
recommendations will help you to succeed in setting your system up
perfectly, or at least in the best possible way, but if you have any
problems, questions or just curiosities please do not hesitate to
contact us.
Franco Viganoni
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