From: jch@teak.Cray.COM (J.C. Hamlin)
Subject: Re: Questions: "for Ele. X-over GURU's"
Organization: Cray Research, Inc.
Date: 22 Jul 92 13:39:53 CDT

In article <11910004@hpwrce.mayfield.hp.com>, daves@hpwrce.mayfield.hp.com (Dave Sudaria) writes:
> Hi, I have been thinking lately about adding electronic crossovers to my
> car stereo system.  From what I can remember, if your running seperates 
> (ie: tweets, mids, woofers) with multi amps, the optimal solutions was to
> use a electronic passive X-over.  Now-a-days, many people are buying (just as
> i did) 2-way woofer/tweeter speaker combinations with its own passive 
> non-electronic X-over's. For example: BA's 851's, 861's, Polks, Infinity,...
> 
> Questions:
> 
> (1) First, differences between passive X-over's -vs- electronic "passive"
> crossovers.

Here is the big problem with naming conventions of car audio components--
especially with equalizers and crossovers.

active - requires external power source to operate
preamp - operates on pre-amplifier (low power) level signals
passive - uses power from the music signal to operate 

Active devices are usually adjustable but more expensive because of that; and 
passive ones are usually not adjustable but less expensive and flexible.
(Notice I said usually.  There are some adjustable passive devices, and some 
 non-adjustable active ones, but they are rare).

You'll notice that the terms "active" and "preamp" are interchangeable in the 
"lingo" of common car audio.  However, this is not the case--you can have a 
passive (no battery power) preamp device.  Also, the term "passive" usually 
implies post-amplifier operation because it uses power from the signal--but 
this is not true either.

An Equalizer is usually called a "passive EQ" or an "EQ booster".  The 
"passive EQ" functions only as an equalizer and not an amplifier and is 
therefore commonly referred to as "passive".  The use of the word "passive" in
this sense is incorrect (since it requires battery power to operate) and often 
leads to confusion with the term "passive" used to describe crossovers.   A
"passive EQ" is more properly called an active preamp EQ.  And the EQ booster 
is also an active preamp EQ with a built-in amplifier.  A truly "passive" 
equalizer would be something that didn't require a battery power to operate.

Crossovers are usually called "active" and "passive".  Active ones are usually 
assumed to be preamp, and passive ones are usually assumed to be post-amp.  
There is such a device as a passive preamp crossover--made by Harrison Labs, 
and it is conceivable to have an active crossover that goes in-line after 
an amplifier.  However, both of these items are very rare.

Now, since we know that most adjustable crossovers are active, this means you 
need a preamp device.  However, for each output of a preamp device, you also 
need an amplifier (surprise, eh?).  This means with a preamp device, be it 
an EQ, crossover, DSP, etc, you need a channel of amplification for every 
channel that comes out of the device.  If you have a 3-way active crossover 
and you plan on using each of those channels, you'll need 6 channels of 
amplification.  Thus the popularity of passive crossovers, you don't need 
additional amplifiers.

So what should you do?

Using a large active crossover with many output channels leaves you 
with the need for multiple channels of amplification which can get expensive.
For this reason, it may seem that using passive crossovers with a single 
amplifier is the way to go since an amplifier does have the ability to 
reproduce the entire range of music.  This is almost the way to go;  the cost 
of the passive crossover network at lower frequences increases dramatically 
since you need large wire wound air coil inductors with low DC resistance.  
Getting 4 quality inductors with large gauge wire (two for a pair of 2nd 
order high pass filters, and two more for a pair of 2nd order low pass 
filters) can be quite expensive, and it leaves you without adjustment 
ability.  Therefore, you should consider the option of a 2-way active preamp 
crossover with a crossover point adjustment and levels controls and then 
bi-amping your system with a subwoofer amp and a satellite amp.  You can 
the use passive crossovers (like getting matched component sets) for any 
other crossover network you need (such as a midbass/mid or mid/tweeter 
network).

There are benefits to breaking up the frequency range sent to an amplifier--
it isn't producing any signal that is not needed and does a better job with 
the signal it has.  However, with the quality of most of today's amplifiers, 
there is not need to worry as they are built to reproduce the entire audio 
spectrum with little problem.  In my opinion there is little to no benefit to 
splitting the audio spectrum into more than two pieces (sub/satellite) to be 
amplified independently.  

Using the passive crossover that comes with a matched component set is almost 
always better than using a generic active crossover and bi-amping.  The passive
crossover network can have many other passive elements to compensate for the 
specific response problems of the drivers--something which an active crossover
doesn't have.

> (2) 2nd, if using 2-way woofer/tweeter speaker seperates (2 tweets, 2 woofers
>     to produde the lows & mids) , Is an electronic X-over really necessary
>     since the speaker sets come with passive X-overs.

If you want to bi-amp the system, yes.  (also see above)

> (3) 3rd, if an electronic X-over is added to say 2 sets of (2) above with 1
>     amp running each set of 2-way woofer/tweeter speaker's, what is the
>     benefit of adding the electronic X-over?, (for the avg cost $200 plus
>     labor), Will you hear a $200 sound difference?

There's no benefit -- you can't use it.  Remember, that for each preamp 
output of an electronic crossover, you need a channel of amplification 
to drive a speaker with that signal.  In your setup, you don't have the 
extra amplification.

> (4) Does a electronic X-over need to have a sub-out?

No, but almost all do since that's the main purpose of two-way crossovers 
is to bi-amp a subwoofer/satellite system.  What you're looking for 
sounds like the Sony XEC-1000 or Audio Control 4XS.  They both have a front 
and rear high/low, and a subwoofer out.

> (5) If everybody is Pro electronic X-over, how about some advice in what
>     to buy, I'll never use more that 3 amps.

Is that 3 amps with two channels each?  

If so, then I would either use one amp for left, one for right, and one for 
sub.  You would do this if you wanted to bridge the amps (to get 4 times the 
power) and use each amp to run a mono signal.  I use this with three Orion 
225 HCCA amplifiers (2x25).  I bridge the left and run front left and rear 
left in parallel for 100 watts to each the front and rear, and do the same 
for right.  I also bridge the sub amp and run four woofers in parallel for 
100 watts to each woofer.

Or, if your amps are powerful enough into 4 ohms per channel, use one for 
front, one for rear, and one for sub.

> Now to throw in a monkey wrench, 3/4 way amps say 30x4 watts or 30x2 + 1x80
> How does an electronic X-over work on this kind of amp?  

The high pass to the 30x2 for the stereo pair of seperates (satellites), and 
a the low pass as mono bass signal to the 1x80 to the single subwoofer.

> I surely hope these are not Too DUMB questions............please help!!!!!

No, lots of really good questions. :-)

J.C. Hamlin
jch@Cray.COM