Conference napalm::commusic_v1

For what it's worth, The new Radio Shack Catalog has either a 12 or 15 inch
woofer that has 2 voice coils such that you can configure it up exactly as
you suggest (the coils remain independant). I have no idea how this 
would work, but it mighwork out just fine (why else would someone make 
a speaker that is constructed this way). You'd still have to build the
box to put it in, but that isn't that hard either.

							Jens

    The biggest reason not to use passive crossovers after a stereo power
    amp is that high quality, high power crossover components are
    expensive or unavailable. Low power crossovers (between the preamp and
    amp) can be high quality and low cost.
    
    Try looking for a 1000 ohm 0.1% resistor rated for 200 watts.

RE .1

	Thanks for the reference, I just looked it up and found it!  (now to
decide what size to build it - any suggestions?)

RE .2

	Well, the passive x-over is gonna be there whether I use the subwoofer
or not.  The question is not so much whether to use a passive x-over (for now, 
anyway) but whether hardwiring the low frequency outputs from two of them is
safe and reasonable.

	Dan

    
    At first guess I'd say no. What you are attempting to do is bridge the
    low frequency output of both amps. Both channels would be driving the
    same source with just a low pass filter between the amp outputs and the
    driver. That wreaks havoc with the outputs. When you switch a bridge-
    able amp into bridge mode, you electronically reconfigure the outputs,
    and feed them with the same signal. This is not what you are
    attempting.
    
    RS, Cerwin-Vega, MTX, Pyle, among others make dual voice coil
    subwoofers. The other option is to use two drivers in a single cabinet
    and feed them stereo.
    
    CdH
    

	Thanks all for the help.  I'm getting some ideas refined as I go and 
your advice is indispensable.

	I tried an experiment last night.  I took out an old speaker cab that 
had blown its tweeter and an old reciever that had one intermitten channel.  I 
then connected a cable from my main reciever's pre-amp out into my graphic EQ 
(Rat Shack special).  The output from the EQ went to the good channel of the old
reciever and the output from that went to the woofer of the old speaker.

	I boosted the lowest three bands of the EQ, and completely cut the upper
four bands.  I did the same with the knobs on the extra reciever, cutting the 
treble and boosting the bass.  

	When I turned the unit on I had the normal sound I get from the regular
system.  I slowly started to add bass by bringing up the volume from the old
reciever.  It started to sound real nice.  When I pulled the volume of the extra
bass cab back, it sounded horrible - much worse than I remember it being before 
I added the bass.

	I guess what I did was create a makeshift satelite system, right?  It
wasn't perfect, as I had no way to remove the lower frequencies from the small
speakers (if I had cut the bass on the main reciever, I would have also cut the 
bass going to the other receiver).

	Dan

    
    By messing with the tone controls, you are effectively adding an
    electronically processed subwoofer to the system, even though it is not
    a crossover, as the highs are full range.
    
    This is not what the base note is suggesting. 
    
    Have fun
    
    CdH
    

    
    Dan,
    
    	Are you running your system stereo for a reason? And is it
    	really dual mono?
    
    	If it is really dual mono, you have the opportunity to acc-
    	omplish what you propose for a lot less bucks. If it's true
    	stereo, you are looking at spending about twice as much.
    
    	Stereo - Whether you go active crossover or passive, you will
    	need 2 subs. Mainly because I am not aware of any subs made for
    	sound reinforcement with dual coils. Sure there are some 12"-15"
    	spkrs with dual coils for the stereophile, but I wouldn't rec-
    	omend any of those for PA, and forget about building a cabinet
    	that's correct. There's a lot more to speaker building, especial-
    	ly subs, than most people think. Also, if you go with an active
    	crossover, you need another stereo power amp.
    
    	Mono - You can use only one sub. You can use one side of your
    	amp for the subs and go active. If you still have that old Heil
    	crossover, you might have it modified to crossover at around
    	100Hz or so. It might be a longshot though.
    
    	Neal-on-a-roll
    
    	

RE < Note 2122.7 by LEDS::ORSI "Cuz I felt like it, OK?" >

	Well, Neil, I guess I hafta come out of the closet sooner or later.  I'm
really asking for the purpose of improving my home stereo, not a pro system.  I
know the better place to ask, theoretically, would be the AUDIO notes file, but
I get the impression that most people who write in that conference don't 
understand when a person doesn't have x amount of dollars to spend on a stereo
system.  I'm asking here because it seems the level of ingenuity and "here's_how
_I_got_a_better_sound_out_of_a_cheaper_system" is a lot higher.  I know I could 
solve the problem of getting a better sound by spending more money, but I'm 
trying to get by with less money, and learn something in the process.

	So, ...

	I see it as being solved one of three ways (seeing as how many have 
recommended against what I originally proposed)...

	1)  Get meself a couple of passive x-overs and build either a single
subwoofer (with a dual-voice-coil driver or using two separate drivers in the
same cab), and use the same amp to drive the whole array,

	2)  Find an electronic x-over (cheap) and use a cab like mentioned in 
(1), but powered by my spare reciever, or

	3)  Find some who way to build or buy (kits?) a passive (or active, 
for that matter!) x-over that will sum the low frequencies (say, under 250 hz)
to mono, while maintaining stereo separation for the upper frequencies.  This
would be my first choice.  I just don't know if its feasible.

>    	amp for the subs and go active. If you still have that old Heil
>    	crossover, you might have it modified to crossover at around
>    	100Hz or so. It might be a longshot though.
    
	How would I go about changing the cutoff frequency of the Heil - or 
better yet, is there some way to make it variable?

	Dan
    	

    BOSE and others offer a single subwoofer (dunno if 1 or 2 drivers) box
    along with two mid/hi smaller speakers for stereo.  It'd be interesting
    to know how it was wired

	
	I got this from one of my speaker building books. It
	seems to be a simple way to add a sub so that its
	output adds to the Lo freq output of the main spkrs,
	which remain full range *AND* you keep stereo separa-
	tion. I think I may try this scheme myself.
	
    	Neal
    
    
	These crossovers are 12 dB/oct at ~140 Hz for an 8
	ohm cab. The components are available mail order 
	from McGee Radio.
	
		12mH Iron Core Coil	$11.20 ea.
		100mfd Non-polarized
		       Capacitor	$ 2.19 ea.
	

+-------+       +---------+ (-)   	    (-)	+-------+
|	|	|	  |---------------+---->| Reg	|
|       | ----> | Amp Chan|-----+---------|---->| Cab   |
|       |	+---------+ (+)	|  	  | (+)	|8 ohm	|
| Stereo| 			+---||----+	|	|
|	|           		|  100mfd |	+-------+
| Source|             12mH Coil O   cap   |
|	|			O 	  |
|	|			O	  |	+-------+
|	|			|	  |  (+)|  Sub  |
|	| 			+---------|---->|Woofer	|
|	|			|	  |	|	|
|	|	      12mH Coil O	  +---->| 8 ohm	|
|	|			O	  |  (-)|	|
|	|			O  100mfd |	+-------+
|	|			|   cap	  |
|	|			+---||----+
| 	| 	+---------+ (+)	|	  | (+)	+-------+
|	|	|	  |-----+---------|---->| Reg   |
|       | ----> | Amp Chan|---------------+---->| Cab	|
|       |	+---------+ (-)		    (-)	|8 ohm	|
+-------+                               	|	|
						+-------+

RE < Note 2122.10 by LEDS::ORSI "Cuz I felt like it, OK?" >

	Great!  That looks EXACTLY like what I wanted.  I'll look in my McGee
catalog as well.

	Dan

    Try MCM electronics for the dual coil subwoofer 1-800-543-4300.
    They are one of the few places I know that even has passive radiators.
    They will even have the crossover you need.
    
    Jim
    

RE < Note 2122.12 by CCYLON::ANDERSON "If winning isn't important... Why keep score?" >

>    Try MCM electronics for the dual coil subwoofer 1-800-543-4300.

	I tried this number just now and got "Bonjour!  Thank you for calling 
Meridian Motels..."

	Dan

    
    
    According to the AT&T 800 directory it should be 1-800-543-4330.
    Off by one number...
    
    Ralph
    
    

    Type-O sorry 1-800-543-4330. at least it's an 800 #.
    
    Jim
    

    
    
    Parts Express has a dual crossover for subs, as well as spkrs,
    passive radiators, cabinets (home and auto), hardware, etc.
    They are inexpensive and prompt.
    
    	1-800-338-0531
    
    Neal
    
    

>CLYPPR::BANZAI::NOVA::LEDS::ORSI

    ????????????  What th' heck kinda path is THAT?!?!?

signed, amazed

    >"Catch me if you can..."
    
    Catch you? With that path we'd be lucky to *find* you!!!
    
    Edd

    
    
    	Hey, I don't know what happened, but I think I fixed it.
    
    	Neal-who-doesn't-know-sh*t-about-system-stuff
    
    

    Hey - no climb on here.  I'd just like to know how you did that. 

-b

    
    Brad,
    
    I think the problem came when I did;
    
    MOD ENTRY COMMUSIC/FILE=node::node::node::node::COMMUSIC
    
    I think I fixed it by doing;
    
    MOD ENTRY COMMUSIC/FILE=NOVA::COMMUSIC
    
    I also think I'm not going to screw around with it anymore.
    
    Oh and please disregard my sarcasm, thats just my lame sense
    of humor.
    
    Neal
    
    
    
    
    

	Just a quick question about crossovers...

	Do crossovers carry any impedance?  That is, when configuring a two or 
three way speaker, do you have to take the crossover into account when figuring
impedance?  How about an L-pad?

	For whoever may attempt to answer this, please consider both active and
passive X-OVERing.

	Dan

    
    No problem with acive crossovers, because you're doing the processing
    at line level. As long as your ins/outs are the same type (low
    impedance, 600 ohms balanced or high impedance, 10K/20K ohms
    unbalanced) you're all set.
    
    With a passive xover it's a whole different story. You choose the 
    inductor and capacitor values of each section depending on the nominal
    impedance of each driver (and the xover order, of course).
    
    CdH
    

RE < Note 2122.23 by STROKR::DEHAHN >

>    With a passive xover it's a whole different story. You choose the 
>    inductor and capacitor values of each section depending on the nominal
>    impedance of each driver (and the xover order, of course).

	O.K., gotcha.  Now for a practical example...  I have a 2-way passive 
xover for a backup (should active xover or amp go down).  Lets assume it is
eight ohms, and both upper and lower drivers are also 8 ohms.  What impedance 
would I come up with wiring them together as follows:


                         +-------------> high freq horn (8 ohm)
                         |
                         |
 from amp ---> passive x-over (8 ohm)
                         |
                         |
                         +-------------> low freq driver (8 ohm)

	Is this a parallel wiring arrangement?  Would it be 4 ohms?  If so, how 
can I make this an 8 ohm system?

	Dan    

The load (if you properly cross over) will average out at 8 ohms because
the Woofer will be conducting the lows, and the mid/tweeter will conduct
the mids/highs. For example, the Radio Shack Cross overs (about 100 watts
capability) allow you to choose the cross over points (they have 2 way and
3 way cross overs available) & these will create a load that appears to
be an inductive load of 8 ohms impedance (provided that all of your speakers
are also 8 ohms).


        +            2 to 20 uf                 +   /
	o-------o---------||----------------------o/ Horn/Mids/Tweeter
                |                          +------o\
                |                          |    -   \
                |                          v
                |       To Neg terminal on Woofer
		|                                     /
		|    5 to 9 uHenrys            +  +--/
        -       +------((((()---------------------|    Woofer
	o-----------------------------------------|  
					       -  +--\
						      \


Impedance relates to AC signals, and cannot be measured statically using
an OHM meter.

Some people do not put the inductor in series with the WOOFER and only add
a midrange Capacitor & horn. This would have the LOWS always a part of the
load (8 ohms), and have the MIDS/HIGHS conducting at 2000 HZ or above. Since
this load is frequency dependant, it still looks like 8 ohms to most systems,
with a percentage load going down to 4 ohms. This would look like this:


        +            2 to 20 uf                 +   /
	o-------o---------||----------------------o/ Horn/Mids/Tweeter
                |                          +------o\
                |                          |    -   \
                |                          v
		|    To Neg terminal on Woofer        /
		|			       +  +--/
        -       +---------------------------------|    Woofer
	o-----------------------------------------|  
					       -  +--\
						      \

The colored dot on the speaker is the + terminal (if not marked with a +).
The center tap on a phone jack is +, ground (the case) is -.

Piezo tweeters do not require any form of crossover network, they do not
conduct low frequencies (below 4000 HZ), ie, they handle it themselves.
If you use a drum machine, Piezo tweeters (even the $4.95 Rado Shack
models) make a huge difference.

								Jens

    
    When using just a high pass filter on the mid/high horn, you'll get
    response irregularities because the woofer is also putting out the
    same frequencies. Plus the woofer wasn't designed for high frequencies,
    and even though they may be several dB down, they will have much
    higher distortion than the driver designed for those frequencies, and
    thus the system won't sound as clean.
    
    If you use piezos (ugh) then don't run them without at least a high
    pass cap in series with the hot lead. They may go down to 4KHz-5KHz but
    they sound real raspy and harsh. From 8KHz and up they are not quite as
    bad. If I remember correctly a 2 uF non polarized cap is what you'd
    need to high pass at 8Khz, 6dB/octave.
    
    Dan, I can't remember the charts and formulas, I have them at home.
    Jens is right in that the crossover impedance should be the same
    impedance as each driver. Otherwise there will be losses. The values
    you choose will also depend on what order crossover you want (1st
    order=6dB/octave, 2nd order=12dB/octave etc). 
    
    CdH
    
    
    

	O.K., it seems, then, that the main thing I need to be concerned about 
is matching the impedances of the various components.  So, if I have a 8 ohm
horn and an 8 ohm bass cab, If I match them with an 8 ohm xover, I'll have
an 8 ohm system, right?

	Dan

    
    CdH