GB - One of your 'sources was "Rec.Audio.Misc"
-Why- Didn't you Post this Project Report 'there' ? ~ RHF
.
After-All This Is A Shortwave Radio Newsgroup
- - - Oops I Am Doing A Telamon : { Hi Telamon }
Replying to an Off-Topic Post -and- Telling the Poster
that 'it' is an Off-Topic Post -and- There-by prepetuating
the Off-Topic Post Thread - oops, Oops. OOPS ! )
.
Speaking of Shortwave Radio Listening (SWL) : I am
currently Listening to Rádio Nacional da Amazônia
on 11780 kHz @ 4:27 UTC with Beautiful Brazilian
Music in the spoken Portuguese Language. ~ RHF
.
S-Meter : S5~S8 with Good Audio
.
.
Rádio Brás - Radio Brazil
http://www.radiobras.gov.br/
http://stream.agenciabrasil.gov.br/estatico/
* Pelo Direito o Informação
.
Rádio Nacional do Brasil (RNB)
http://www.radiobras.gov.br/nacional/nacionalbrasil.htm
.
Rádio Nacional da Amazônia
http://stream.agenciabrasil.gov.br/e...l_amazonia.htm
.
Programação - Rádio Nacional da Amazônia
http://stream.agenciabrasil.gov.br/e...rogramacao.htm
http://stream.agenciabrasil.gov.br/e...na_sinopse.htm
.
BRAZIL = http://en.wikipedia.org/wiki/Brazil

? RHF - WHAT SHORTWAVE (SWL) ANTENNA ARE YOU USING ?

Well for Rádio Nacional da Amazônia the Four Element
Flat 5-Wire TV Rotor Cable 25 Foot Long Horizontal Wire
Antenna is doing the better job of pulling in the signal.
While the End-Fed-Windom Antenna {Two End-to-End
"Linner" Horizontal Wires} barily picks-up any signal at all.
.
And just for this Rádio Nacional da Amazônia Shortwave
Radio Reception Report i am using my Sounds-so-Sweet
Speaker and for a 'mono-speaker' it does Sounds-so-Sweet !
.
? WHAT Sounds-so-Sweet ?
The "Sound Sweet" Communications Speakers Maximize
Intelligibility from your Transceiver, Receiver or portable Radio.
SOUNDS SWEET = http://www.soundssweet.com/
.
.
.. .

= = = On Aug 5, 2:31 am, wrote:
Subwoofer/Amp project...

(Playmaster 300W subwoofer amp)

While walking down the hall around lunch time I walked in on a
discussion about surround sound home theater systems. After humbly
admitting I watched movies through my two channel stereo I was prodded
by my peers to get with the '90s, I started checking out the
technology.

The following week I saw a used Carver surround sound processor for
sale on the net. Perfect for upgrading my late 80's vintage two
channel stereo. However, a suround sound system requires three front
speakers (left, center, right), two rear (left and right), and a
subwoofer. The five channels provide the spacial realism, while the
subwoofer provides the physical realism... that is when Apollo 13
takes off one should be able to feel the vibrations in the chest, and
when the horses cross the battle field in braveheart, it's the
subwoofer that allows one to feel the horses through the vibrating
floor.

While I had other equipment to get by on the five channels, I was
short on a subwoofer, so I did some research. The short story is that
I built my own powered subwoofer (actually 2) and learned alot in the
process.

Here are the details...

Some info on subwoofers
Speaker Building Information Sources
Subwoofer Project
Subwoofer Construction
Amplifier Construction

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Some info on subwoofers...
Difference between a woofer and a subwoofer... subwoofers are usually
only used to recreate a sub portion of what a woofer will. While a
typical woofer may have a frequency response between 20Hz and 2k Hz, a
subwoofer usually has a crossover that limits it's frequency response
range from 20Hz to maybe 80-150Hz. Component wise (the cone/coil
thing) woofers and subwoofers are the same. There are passive
subwoofers and powered subwoofers. Passive subwoofers are powered by
your stereo's amplifier. Powered subwoofers is the same as a passive
subwoofer except it has it's own amplifier for driving the passive
subwoofer. Your stereo needs to have a sub woofer out (line out) for a
powered subwoofer. Since most power produced by your stereo's amp is
consumed by driving the low frequencies of your speakers, it's a big
win to have a separate amplifier for driving the low end. This way mid
range won't suffer from the power consumed by the low end.
There are several designs for a subwoofers. Some of the less exotic
ones are are ported, sealed, and band pass enclosures. Sealed
enclosure's advantage is that they can exist in a much smaller
enclosure, however this is at the cost of efficiency and reduced low
frequency performance. Ported enclosures are the most common. These
have a tube called a port which serves several purposes. It's
important that this port be tuned to the driver (woofer) and volume of
the box or else the sound may result in unclear, muddy bass. The
affect of a properly tuned port with the woofer is similar to blowing
a wine jug like an instrument. A band pass enclsure looks like a box
with a hole or slit. Bose subwoofers are band pass woofers. The idea
is that only certain desired frequencies (bands) end up passing
through the hole or slit while the others are absorbed internally.

There's a thing called a crossover to consider. A crossover is like a
frequency filter except rather than filtering out frequencies, it
redirects frequencies to other channels. A typical powered subwoofer
will have a built in crossover that directs low end frequencies
(usually 80-150Hz) to your subwoofer while sending higher
frequencies on to another channel (the rest of your speaker system).
The high end frequencies rapidly diminish in the channel sent to the
subwoofer and the low end frequencies rapidly dimish in the channel
going to the higher frequency response speakers. So the tweeters get
the high frequencies they are designed to produce and the woofer get
the low frequencies they are designed to produce. Almost all multi
speaker system will have some sort of crossover. separating
frequencies between tweeter, midrange and woofer. In crossovers, there
are both passive and active crossovers. Passive crossovers are typical
in most speakers. Since they take their power from the incoming
signal, they do have an impact on power/responsiveness. Active
crossovers get there power externally. However we're starting to go
beyond the scope of the subwoofers project.

The prices for powered subwoofer can get pretty expensive. I was
looking at models between $200 and $1500. $1500 for a 12 or 15 inch
woofer plus amplifier just seemed ridiculous considering the cost of
parts to make them... So, I decided to look into making my own. The
route I chose to take was not cost effective if time for learning,
designing, and implementing is factored in. However what I've learned
while doing this makes it all worth while.

---------------------------------------------------------------------------*-----

Speaker Building Information Sources
I started with two books I picked up at Radio Shack called Speaker
Building and Advanced Speaker building. Both are heavily oriented
torwards building speakers with Radio Shack speaker components, and
can almost double as a Radio Shack speaker catalog. Lot's of shameless
Radio Shack marketing through out. They have a nice intro into
building speakers, with a lot of the theory left out. The first book
contains graphs to crossreference parameters required to make a
speaker so that one doesn't need to use a calculator. The advance
speaker book throws in some formulas but is a little lacking in
discussion on how the equations were derived. In case you don't know
how to plug a formula into your calculator, no worries... the Advanced
Radio Shack book will tell you which buttons to press.
Vance Dickason's "The Loudspeaker Design Cookbook" (ISBN
1-882580-10-9) was recommended by several sources. It reads like a
collection of white papers on speaker building theory and is heavy on
the technical side. Towards the end it contains several commercial
advertisements for part sources. Good book.

There is quite a bit of wave theory, frequency dampening factors that
needs to be taken in to consideration. Everything from cone tensile
strength to acoustic frequency dampening of dacron fiber fluff or
maybe beach sand, resonant frequency of particle board versus a harder
wood, etc., etc. factor into the volume of the box and the optimal
length of the port so that it resonates properly. So many factors, it
takes some time to become comfortable with weeding out the meaningful
parameters from those that are negligible in the quest for making the
ultimate speaker. Box dimension I later learned really dosn't matter
much for a subwoofer. The main concern in box dimension is standing
waves where waves are cancelled out to the tune of +/- 5dB in the
worst case. Sufficient dampening material inside to absorb standing
waves can cancel this out. In the case of subwoofers, it's not an
issue since the box dimensions are so much shorter than the
wavelengths (20-100Hz).

Here are some information sights I've found on the web....

rec.audio.misc FAQ list
Speaker Project PageLouis Lung
DIY Audio pages Craig Stark
The Subwoofer Page
The Speaker Building Page
A "Do-It-Yourself Speaker Project
3 Way Vented Speakers
Dolby Labs
THX home page
AC-3 White Paper
HiFi on WWW (extensive audio web list)

---------------------------------------------------------------------------*-----

Subwoofer Project
Being a neophyte in the audiophile world, my first thought was to get
the biggest driver I could find to produce the lows and push volumes
of air that one could feel. I ran across some 18" woofers, however I
liked the specs on some 15" woofers I later found better. After doing
the calculations I found that for my ported cabinet, I would need an
enclosure that was 14 to 24 cubic feet! I decided that there is no way
I would want to dedicate this much space in my living room to a box
this big. These calculation were based off of an optimal volume
formula I got out of the Radio Shack books. I later discovered that
this optimal volume didn't agree with the manufacturer, several
software design packages, and the loudspeaker cookbook.
An alternative was to go with a sealed enclosure, however this reduces
the responsiveness and pushes the F3 upwards. End result is a
subwoofer with a reduced ability to produce low end. Since it seems
the whole point of having a subwoofer is to produce the low
frequencies, a sealed enclosure which raises the low end didn't make
much sense to me.

I opted for a 12" woofer with a 3 cubic foot enclosure. I decided to
go with Ultimate's AU1290 "Attitude" woofers. They have a frequency
response range of 18-1k Hz. They have a dual six ohm, 90oz magnet, 2"
kapton coil capable of handling 500 watts sustained, 1000 watts max.
Headroom is .44". SPL is 88.9dB, but I don't care about this since
it'll be driven by it's own separate amp with it's own gain control.

Test Data from Factory:
SPL 88.9dB 1W/1m
Fs 23.5Hz
Vas 5.3
Qts .38

I decided to go with 3 cubic feet ported enclosure since that would
give me the lowest frequency within factory recommendations.... With a
3 cubic foot enclosure, this driver has an F3 of about 26Hz (pretty
good!). I decided to go with a 4" diameter port tube since that would
give me the least amount of port noise. The port for this is about 14"
long. I ended up picking up some PVC tube at the hardware store. This
worked quite well.

---------------------------------------------------------------------------*-----

Subwoofer Construction
I decided to make a prototype out of particle board since wide oak
boards are expensive and I was afraid of ruining them, especially
since I have very little wood working experience. Particle board cost
about 1/8 the price.
Being new to wood working I only had a circular saw which I had
learned through experience is not for precision wood working. I was
able to pick a used craftsman table saw in perfect shape for about a
third of the price of a new one. And this is what I built the
prototype with. For the speaker and port hole I used a saber saw.

The prototype came out pretty good. Some things I learned from the
prototype is that cross bracing is important so as to cut down on the
side board vibrations. Also, all seams should have a good fit and must
be well sealed. I used some silicone wood calk I picked up at the
hardware store. If the seams aren't sealed, the gaps tend to make a
raspy whistling noise when the driver is pushing large volumes of
air.

I picked up a used 60's vintage radial arm saw which I found for about
1/5 the price of an equivalent new one, however it needed some work. I
spent a Saturday cleaning, oiling, calibrating, and building a new rip
fence for it. I discoverd that a radial arm saw is really the way to
go for precision cuts. Rather than moving a big block of heavy wood
towards the blade, the heavy material stays in place while the blade
runs along a track and makes a perfect precision cut. The end result
is that the oak boards had a much smaller seam between the boards in
the cabinet. I think this will help reduce board vibration as well as
make it easier to seal.

I put about 2 pounds of a Dacron fiber called "Acousta-stuff".
Supposedly it's better than Dacron fiber that one can get at a craft/
fabric shop because the fibers are triangular rather than round.....
Don't know about that, but the Loud speaker cookbook had some test
results that said it was better, so I paid $8 per pound for this
fluff. Fiber glass is suppose to be better, but for other reasons I
decided I didn't want to use that. Dampening material is important for
the speaker so as reduce standing waves in the enclosure which can
mess with sound to the tune of a variable +/- 5dB! I just stapled this
to the side of the walls excluding top and near the port tube.

I picked up a gold plated 8 post screw/banana speaker terminal which
is intended for a dual voice coil subwoofer with individual crossover
for each channel for hook up to additional speakers. Currently I use
the active crossover from the subwoofer out in the Carver surround
sound processor, so I've delayed on the passive crossover for now.

I have some small Polk speakers (4b?) I'm using as the satelite front
channel speakers now. They have a 6.25" woofer. I don't have any
performance spcse on these speakers.... so I'm guestimating by looking
at other 6.25" of comparable quality that they will begin their roll
off around 100Hz. I'm considering putting together a 2nd order low
pass filter at 100Hz for the subwoofer. I had underestimated the cost
for a crossover for this subwoofer. Doing some rough calculations for
this low 100Hz filter looks like I'll need a 12mH inductor coil and
~200uF capacitor. Because of the high power nature of this subwoofer,
I'm looking at $15-$30 for the inductor, and ~$50 for the
capacitor.... Since this is a dual coil driver, everything will be
mulitplied by two.

---------------------------------------------------------------------------*-----

Amplifier Construction
I needed a mono amplifier to drive this subwoofer. While a cheap and
easy way to do this would be to buy a bridgeable automobile amp, I had
been looking for an excuse to build my own amplifier. Acoustic Labs
has designed several high end amplifiers. Their designs are then
marketed as "high end audio" project kits. Mark V Electronics, Inc. -
Mark V Electronics, Inc. 8019 E. Slauson Ave. Montebello, CA 90640
Phone: 323-888-8988http://www.markvelectronics.com/storeE-mail:
-out of California
markets. A mono amplifier(s) has a lot of uses in a component stereo
system, especially in a 5.1 channel AC-3 or Dolby Pro Logic (THX)
surround sound system that I can see using it for the forseeable
future. As such, my thinking was... if I'm going to put all the time
into making this, why not start with the best possible design. I
decided on the AF-3 design which is a 300 Watt constant current MOSFET
amp. MOSFET amps are known for having very similar characteristics to
pentode vacume tubes without the drawbacks of being a vacume tube. The
design has a built in speaker protection cicuit relay for protecting
the speaker from power surge during power up. The design, PCB, mega
heatsinks, and components that go on the PCB sell for $165. Not bad I
thought... that is until I picked up everthing else I needed. The
design calls for 4 filter 80-100 volt 10k uF capacitors which sell for
about $25 each with mounting hardware. I picked up an 8 amp toroidal
transformer (low hum, low EMF) for $66. Also I needed a cabinet of
which I found a nice black anodized aluminum vented case with rack
handles for $44. Other miscelaneous components such as an optional
(quiet 23dB) fan, gold plated mega 4AWG capable speaker binding post,
wire, rectifier bridge, fuse holder, switch, some extra capacitor and
high wattage resistors, etc. brought the total price up to roughly
$400 for this mono channel amp. Had I known this would be the price
ahead of time, I probably wouldn't have done it. However, I now
rationalize that I've learned alot making it and that I have the best
mono amp for my forseeable future needs.
I built two amps (Mom wanted one). Each amp took approximatly 50 hours
assembly time. The end result is a nice sounding extremely powerful
amp. 300 watts for this subwoofer is more than adequate. I have the
subwoofer line out on the surround sound processor turned down to
about as low as it will go. The subwoofer itself will handle 350 watts
sustained, 500 watts peak. Watching the movie "Braveheart" during some
of the battle scenes tends to set the whole house vibrating. One can
feel the horses running across the wooden floors in the house.

After a couple weeks, I noticed the first amp I built would run much
hotter than the other. I opened up the amp and recalibrated. There are
two potentiometers that need to be adjusted. One is adjusted by
reading the current to the amplifier board, the other is adjusted by
zeroing the ouput voltage to the speaker when no input signal is
present. I had adjusted these after assembling the amplifiers. However
after running the amps for a while, one of the two potentiometers
needed recalibrating. Now they seem to run at a reasonable temperature
with my typical use.

I had picked up a 120 volt cooling fan at Radio Shack for cooling the
amp. At the time, I didn't know how loud 38dB was which is what the
fan noise was rated at. After trying it out, I decided this was too
loud for an audio amplifier application. I found a 23dB fan + fan
guard in a Jameco Electronics catalog. It's quiet enough, however,
cutting the hole in the metal case has become a problem. I found a 3"
circular saw, however this requires a drill press that one can set at
100rpm and can apply 150 lbs of pressure. I don't own a drill press,
and haven't found one that can operate as slow as 100 rpms. I just
finished a welding class, where in addition to stick welding, MIG and
TIG, we learned to use a plasma cutter which is as easy as using an
exacto knife. I think if a circular wood template was made ahead of
time, the plasma cutter would be the easiest. I think the local
welding shops rent a 110 volt plasma cutter for about $40. ...an
expensive hole. I also needed to cut the case to install the oversized
speaker binding posts. I used a coping saw for this. It was hard
frustrating work and the results were not very nice. Fortunately, the
cut is hidden by the speaker post mount, and so doesn't matter. A
plasma cutter would have been great for this too.

Even though components in the amplifier would probably last longer
running cooler, I've decided to wait on installing a fan until I have
a better understanding of how hot it will run and can justify all the
trouble of installing one. This also gives me more time to think up
some way to wire up a thermostat controller.

---------------------------------------------------------------------------*-----

Glenn Baddeley