How
to Buy Home Theater and Surround Sound
Speakers
In this article I am
going to cover some of the basics, including
some rules of thumb about how to judge
speaker quality.
There are 3 main configurations
for home theater systems termed loosely
5.1, 6.1, and 7.1 channel surround systems.
These include variations with names such
as Dolby Digital, Pro Logic, Dolby Digital
EX, DTS, and many others. Receivers capable
of 7.1 channel surround will also work
fine with 5.1 and 6.1 channel surround,
and a 6.1 channel receiver will do 5.1
channel just fine.
The number of channels
determine the number of speakers. The
.1 in the figure is the subwoofer. Thus,
a 5.1 system includes 5 speakers and a
sub woofer, and a 7.1 surround system
has 7 speakers plus the subwoofer. More
speakers improve the immersion in the
surround experience, however, most persons
have a limited budget. On a limited budget
you will be able to afford better quality
speakers by buying fewer and using a 5.1
channel system. You will have to decide
if you want better quality speakers or
the more complete surround system. You
also need to think about the fact that
you will have to do more work to place
more speakers. Make sure that your home
theater receiver can do 7.1 channels before
buying 7 speakers and a subwoofer.
The speaker setup consists
of 2 or 3 special types of speakers in
addition to the standard type. You need
a subwoofer for the .1 channel, which
is a speaker specifically to produce the
bass content efficiently. You also must
have a center speaker which anchors dialog
(and sounds that need to be centered)
to the video source. You can use a standard
type speaker for this, but a dedicated
center channel speaker is preferable.
It has specific characteristics built
in to allow all listeners to hear an even,
clear sound no matter where they are sitting.
Most configurations have a high frequency
driver (tweeter) with a midrange/woofer
on either side of it. The usual setups
use standard style home speakers for the
rest of the system, but some manufacturers
make dedicated surround speakers. They
are made to provide a diffuse sound source,
and work very well for the purpose. They
may be called dipole or bipole, a technical
term referring to the construction type
and operation of these speakers. It is
not recommended to use these in the front
left and right speaker locations. For
more on proper speaker locations you can
read an article on my speaker website.
Now that you have an
idea of what you need, we can get into
some specifics.
Specifications:
Power Rating: The speakers
should be rated at least as high as the
output of the receiver. They can be rated
much higher and will work fine. Power
is rated in Watts. You need to make sure
you are comparing apples to apples. Unfortunately,
there are quite a few manufacturers that
will inflate power ratings by various
cheats. The proper rating is RMS or continuous
watts. One method of exaggerating wattage
is by specifying in peak power, which
is the power the speaker can handle only
for a fraction of a second before burning
out. Advertising peak power is fine if
the manufacturer also specifies the RMS
wattage for proper comparison.
Frequency Response: All
the speakers for a surround system should
respond down to at least 80 Hz in the
bass to work correctly. If they are rated
to lower frequencies it is better. Human
hearing limits are from 20 Hz in the bass
to 20Khz (20 Khz = 20,000 cycles per second).
Most adults cannot hear higher than 16
Khz. Obviously you want the subwoofer
to go as low as possible. You may see
a rating such as +/- 3db or some such.
In this case the smaller the number the
better. +/- 1.5 db (rare) is much better
than 3 db. This figure indicates the flatness
of frequency response, and thus how accurate
the frequency balance is. The more accurate,
the better sounding the speaker. Again,
compare carefully as the figure may be
specified at different frequency limits
than the overall response limits.
Sensitivity: The higher
the better. A typical rating is 88 Db
@ 1 watt, 1 meter. This is an interesting
specification as it indicates a relative
measurement of how loud the speaker will
play with a specific amplifier wattage.
Every 3 db increase is the same as doubling
your amplifier power (keep in mind all
these statements are true, but are not
laboratory precise in order to avoid making
this too complicated for the layman to
follow or bother with). In other words,
speakers rated at 88db on a 100 Watt rms
amplifier will play at the same maximum
volume as speakers rated at 91db sensitivity
on a 50 watt amp. By the way, the most
common cause of burned out speakers is
an underpowered amplifier being turned
up too high. Yes, that is correct, I said
underpowered. There is not room to get
into the explanation in this article.
Impedance: This is a
very important, confusing and complex
subject, so rather than get into it I
will give general rules of thumb. For
more info you can see articles on the
speaker website. If the speakers are rated
8 ohms or higher, you are in good shape
whatever the rating of your home theater
receiver is. If the speakers are rated
at 6 ohms or lower (4 ohms is not uncommon)
your receiver must be rated into that
low of an impedance. If it is not, you
may damage your receiver by connecting
them. It will also probably overheat and
shut off easily, and will not provide
the proper frequency response and impact
your speakers are capable of.
Magnetic Shielding: This
is a must for speakers within 6 feet or
so of a video screen or computer monitor
(unless you are using a projector) and
doesn't matter for the rest of the speakers.
Drivers: Don't worry
about this too much, it is only generally
descriptive. Larger woofers usually go
deeper in the bass, which you can see
in the frequency response. Generally,
larger drivers might produce more impact
depending on how well the speakers are
built. More drivers may also produce better
results. This can get complicated and
confusing. For example, two six inch woofers
may produce better and deeper bass than
a 10 inch woofer provided the speaker
is properly built. They provide a large
surface area like a single large woofer,
but can respond faster to changes in the
music because of being lighter weight.
This provides better transient response,
and can subjectively result in more “punch”
to the music and a less muddy sound. There
is a large amount of learning needed to
draw proper conclusions from driver configuration.
One specific configuration I want to mention
is called passive radiators. These can
work great in a properly built system,
but since they cost little to make some
manufacturers throw them in to make their
speaker look like it has more drivers
and fool the customer in that fashion.
These are usually cheaply built speakers
and don't work well. Passive radiators
are drivers that look like speakers but
have no magnet or voice coil and are not
electrically driven. Properly configured,
as in BIC America speakers, they are very
effective. Their purpose is not to look
like expensive drivers, but rather to
provide a way of properly tuning an enclosure
for increased bass response. The most
common method of doing this is with a
bass reflex port. The passive radiators
replace a tuned port, providing much the
same effect but with improved transient
response, thus better sound quality –
provided the system is properly built.
Weight: This can be a
good rule of thumb indicator of a well
built speaker. Good speakers will be heavier
because of many factors. Two important
ones are bigger driver magnet size, and
heavier, non resonant cabinets that don't
improperly color the sound.
Magnet Size: Generally
speaking, the bigger the better. Small
magnets are usually a sign of a cheaply
built speaker, since magnets are expensive.
A larger magnet means more control over
the cone movement and thus clearer, more
defined sound.
Cabinet Solidity: This
is hard to test when buying on line, but
speakers that advertise solid, non resonant
cabinets will have better sound. Cheaper
cabinets will resonate which causes some
sounds to be louder and some quieter.
This can cause many different unpleasant
results in the sound. This is usually
not hearable as an actual vibration, but
rather as an unwanted and unpleasant character
to the sound. It may not be obvious without
measurement that cabinet resonance is
causing the unpleasant character. If you
can get to the cabinets, knock on them
with your knuckles, in particular the
back of the cabinet because this is where
manufacturers may hide cheap construction.
Ideally, knocking on the cabinet would
be the same as knocking on a slab of concrete.
The more of a woody sound you get, the
more that speaker will color the sound
with the cabinet resonance.
About the Author:
Ron from SmartBuySpeakers.com
has 27 years technical experience including
8 years as owner of an A/V retail &
installation business. Certifed by Cedia
(Custom Electronics Design & Installation
Association). Technical experience includes
Audio/Video, computers, typewriters, copiers,
video gaming machines, video slot machines,
satellite systems including 2 way vsat
systems and cable TV systems.
