How about a DIY sub?
Thanks to some really wonderful help I have decided to build my own subs, it may be an option you might want to consider if you have any craftsman type skills at all. I have found that there is 3 to 4 times the value in a DIY Sub vs. a mass manufactured sub and there is a lot of info available in the DIY portions of many AV forums. Imagine, dual 15" subs, capable of 20Hz with 1KW Class G amps for a little over $1000 and the satisfaction of knowing that you built the beasts yourself! Just a great little bit of info a tech sent to me to follow, great advice and technical info about subs. Good luck!
The design of audio subwoofers has, for many years, been predicated on a
theory known as "Hoffman's Iron Law" which provides:
Loudspeaker effiency = volume of enclosure / ( cube of cutoff_frequency)
where cutoff_frequency(F3) is the desired low frequency cutoff or limit for
the subwoofer.
F3 = the frequency where the output drops 3dB (half amplitude)
Unfortunately, because of the physics involved that dictate "Hoffman's Iron
Law," if one wishes to reduce the low frequency cutoff of a subwoofer from,
for example, 50 Hz to 18 Hz while retaining the same efficiency, the volume of
the enclosure must be significantly increased. Or, if one wishes to decrease
box volume from, for example, 1 ft3 to 0.4 ft3 and, at the same time, decrease
the low frequency cutoff from, for example, 50 Hz to 18 Hz, efficiency drops
by a factor of approximately 53.
Consequently, a woofer designer finds that where a 50 watt or 100 watt
amplifier might have operated a 1 ft3 woofer at a 50 Hz low frequency cutoff,
a 0.4 ft3 box at 18 Hz low frequency cutoff will require an amplifier that is
approximately 53 times larger than the first design. In other words, an
amplifier somewhere between 2500 watts and 5300 watts. They would also require
an subwoofer driver able to handle this amount of power without burning up and
without running out of linear excursion. (don't want the voicecoil bottoming
out or being launched into the room) This explains why you will not find any
small subwoofers that can play very deep with any respectable
sound-pressure-level. Basic physics get in the way. This is the reason your
comparing a 600 watt sub with a 1000 watt sub has no meaning at all unless you
compare everything else on how they will perform in your size room.
Today, there are many DVDs with sound-tracks with low-frequency effects down
to 10Hz and lower. Many commercial subwoofers have low frequency cutoffs
somewhere 50 and 100 Hertz and amplifiers around 100 to 200 watts, these subs
don't even come close to reproducing the low bass on these sound-tracks, but
might be fine for music where low-frequency bass seldom goes below 50Hz. Other
subs sold for use in a home theater may have a response down to 20 Hz. These
are usually a bit larger, with larger amplifiers, trading larger size and
efficiency for lower frequency response.
There are many commercial subwoofers that employ amplifiers that are capable
of over 1000 watts. My brother has a small "James" subwoofer that has a 1000
watt amplifier. Again, they traded efficiency for a small enclosure size. It
does very well and reproduces down to 20Hz. The "Sunfire" brand is another
example of a high quality small, inefficient subwoofer.. They use a powerful
2500 watt amplifier in a small enclosure to produce very good quality low
frequency bass. They also traded efficiency for small enclosure size. Does it
play any louder than the "James" subwoofer... probably not.
Most brands of subwoofers have much larger enclosures and much smaller
amplifiers (Most subwoofer "plate-amplifiers" produce from 75 to 250 watts)
So...
Hoffman’s Iron Law says that the efficiency of a woofer is proportional to
cabinet volume multiplied by the cube of the F3. In other words, even though
you want a small box, high efficiency and deep bass, you only get to pick 2...
the third is decided by physics. (Despite what the marketing departments want
you to believe)
If you want a small box, you can have deep bass or high efficiency, not both.
Likewise, if you want deep bass, you get a small box or high efficiency, not
both. Last, if you want high efficiency, you get deep bass or a small box, but
not both.
There is no way to cheat this law until you find a way around the laws of
physics, so it’s something that you need to be aware of when evaluating your
needs, and also when evaluating manufacturer’s sometimes outlandish claims. It
is also what you need to consider when comparing a 600 watt subwoofer with a
1000 watt subwoofer. In reality, the 600 watt sub could go lower and louder
than the 1000 watt sub... it depends on the enclosure size.
How many "watts" do you need for your size room??? I'll say you probably need
somewhere between 50 and 50,000 watts. To reproduce loud low frequency sounds
you need to move (pressurize) lots of air, again physics dictates this. The
larger the room, the larger amount of air your drivers must move to pressurize
it to play at a given db sound level.
For your size room you need either large drivers, or multiple smaller drivers,
and probably drivers with a large XMAX (excursion max) that will displace a
lot of air as their cones move within their excursion limits.
Once you decide how loud you want the sub (in your size room), and how low in
frequency you want it to play, and then pick an enclosure size, you can
determine the size of the amplifier you need based on the efficiency of the
driver. Amplifier power is the LAST thing you should be looking at when
considering commercial subwoofers. In fact, it does not matter at all if the
sub can play the low frequencies you desire at the volume that keeps up with
the other speakers in your theater. Will the "James" subwoofer my brother has
work in your room? Probably not, but in his very small theater it works well.
His room is probably 15x8x8... your room is way bigger and much harder to
pressurize.
Now, do some more research, with your room size and SPL requirements first.
Don't even consider amplifier wattage. If the sub can play as low and as loud
as you require, the wattage required doesn't matter and will vary greatly
based on the subwoofer design.. Building your own subwoofer is fairly easy,
and lots of folks will assist if you take advantage of their experience. All
said, there is no replacement for displacement, so for HT use, go as big as
you can.
Marantz SR8001... Marantz DV7600... BA Lynnfeild VR965's. NHT Classic 3's and NHT Classic 3C
