N00B asking for loudspeaker help (Altec 620 cab)

[SpyStyle]

Hello from Maine,

I built an 15" Altec 620 cabinet and want to make it into a mono 'full range' speaker, I have a few questions and would very much appreciate some help :)



All the cabinet has in it right now is an Eminece woofer from 1980, here are the specs from Eminence tech support :

Eminence 15" woofer "661056 67-8020"

It was manufactured for the Wurlitzer Company in 1980. It has a stamped steel frame, 54 oz magnet, zurette dust cap, 2" voice coil and is 8 ohms. It was manufactured before there were T/S params. This spec is particularly unique because it uses a paper cone with a paper edge and a 4 layer coil (Very unusual combination). The wattage is 150Watts rms continuous.





I have ordered a 4" midrange and a 3" tweeter (Fisher, they are en route)

My questions are :

1. Where in the cabinet should I mount the mid+tweet?

2. Where can I buy an inexpensive 8 ohm amplifier that'll send 150 watt rms to the woofer, 50 watt rms to the mid and 50 watt rms to the tweet (can I build a cheap one?)

3. Where can I buy inexpensive crossovers for these 3 drivers? (can I build cheap ones?)

4. Approximately where should I crossover each driver ?

5. There are a few "pin holes" in the woofers paper surround, what can I use to repair these holes?

Thank you in advance for your help,
Craig

p.s. wanna build an arcade machine? see my tut here :
http://spystyle.arcadecontrols.com

[SpyStyle]

Hello again, I e-mailed this thread to Robert A. Booty, here is his advice (posted FYI, maybe it'll help other N00Bs)

on 8/6/04 12:42 PM, Craig Conway wrote:

> Could you please look at my dilemma here?
>
http://www.diyaudio.com/forums/showt...242#post451242

***************************
> 1. Where in the cabinet should I mount the mid+tweet?

Hi Craig,

The mid & tweeter should be mounted above the woofer in a vertical
alignment. Since your image of your cabinet shows the woofer toward the
top,
I'd recommend turning it upside down so that the tweeter ends up around ear level height.


Having the tweeter unequal distances from nearby diffraction edges (eg:
speaker cabinet edges) is good. (Assymetry in general is good in
audio.)
You'll of course need to build internal enclosures for the mid and
tweet to
isolate them from the woofer's internal back wave, unless they are
closed
back frames. I'm not familiar with the "Fisher" cone units you mention.

> 2. Where can I buy an inexpensive 8 ohm amplifier that'll send 150
watt rms to
the woofer, 50 watt rms to the mid and 50 watt rms to the tweet (can I
build
a cheap one?)

An amplifier is not what controls the proportion of power that goes to
the
drivers. That's the crossover's job and it depends on the crossover
points
and the frequency content of the program material you play (the type of
music).

Modern solid state amplifiers are fairly inexpensive these days. Mono
amps
are not very common, but you should be able to buy a 50 to 100
watt/channel
stereo amlifier (or probably more commonly a complete receiver) at
something
like "Best Buy" stores for around $100. You might try cruising this
site:

http://www.jr.com/

You don't need to have a 150 watt/chan amplifier just because your
woofer is
supposed to be rated at "150 watts". Remember 150 watts is only 3dB
louder
than 75 watts. :-) I would expect that woofer to be fairly sensitive
(probably 90+ dB/watt @ 1 meter ???).

Around $300 is probably a fair price for a new 150w/chan home stereo
power
amplifier.

My amplifier page

http://home.new.rr.com/trumpetb/audio/schem010.html

could provide some ideas to build a 150 w/ch amp, but not necessarily
any
cheaper than you might buy a complete unit. Familiarity with
schematics,
sizing and purchasing the components, some basic shop skills and
soldering
skills are prerequisites for a project like that. It's a lot of work.
The
payback is not much cost saving, but the self satisfaction and learning
new
tricks that come with it.

> 3. Where can I buy inexpensive crossovers for these 3 drivers? (can I
build
cheap ones?)

Thses are good sources for components (coils, capacitors, resistors) or
complete crossovers...

http://www.madisound.com/

http://www.mcmelectronics.com/

http://www.partsexpress.com/

You can build crossovers, but some research and study is probably
involved
to take off from my crossover pages, eg:

http://home.new.rr.com/trumpetb/audio/xoversch.html

A book like David Weems: "Designing, Building, & Testing Your Own
Speaker
System" is a great resource to learn nearly all these things you should
know
for success in audio speaker projects like this. Check out

http://www.amazon.com/exec/obidos/tg...112782-2499060
?v=glance

or maybe Google for
weems speaker book

> 4. Approximately where should I crossover each driver ?

If the page
http://home.new.rr.com/trumpetb/audio/crpts.html

doesn't make any sense, then I'd just suggest that a 15 in. three way
system
like you're proposing probably would use cross points of 500 to 800 Hz
for
woof to mid, and 3000 to 5000 Hz for mid to tweet. "Second order" or
12dB/octave slope is good. You'd normally connect the mid with reverse
polarity to compensate for the phase reversal of this circuit.

500 Hz is good for the woofer but your mid would need to have a
resonance of
250 Hz or less, and I suspect that a 4 inch mid would be higher than
that.
(The cross should be at least an octave above the mid resonance.)

> 5. There are a few "pin holes" in the woofers paper surround, what
can I use
to repair these holes?

Hmmm, you might try diluting some "Elmer's" glue (with water) and
brushing
it around the areas of the "pin holes". Practice on some paper scrap
pieces
first.

Good luck, Craig.

Bob
--
Robert A. Booty
Oshkosh, Wisconsin, USA
Oshkosh Brass Quintet - http://home.new.rr.com/trumpetb/
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