"Bob-Stanton" wrote in message
om
Going to an electronic crossover is a good idea if one can't afford a
high-end ($2000-$10,000) power amplifier.
Not really.
An electronic crossover can
greatly reduce the distortion of medium priced power amplifiers.
As if high price makes an amplifier necessarily more distortion free, or low
price means it has to have audible distortion. Just isn't true!
With
an electronic crossover, medium priced amplifiers can come very close
to (or sometimes equal to) the sound quality of high-end amplifiers.
The decision to use electronic crossover should be based on points that are
irrelevant to amplifier price.
For example, the near-universal choice to use electronic crossovers with
subwoofers has a lot to do with the costs and inconveniences related to
making a passive crossover at say 50 Hz for a 8 ohm speaker that is designed
to work with a low source impedance.
You can build your own electronic crossover for about $7.00. Below is
a schematic of a 2 kHz electronic crossover:
From preamp--------------------10K Ohm--------- To low frequency amp
| |
| 0.01uF
| |
| Gnd
|
-----------0.01 uF-----
|
10 K Ohm pot
--- To high frequency amp
|
Gnd
The above crossover is 6 dB per octave and is designed to work into an
amplifier input impedance of 50K Ohms.
Potentially problematical given that so many power amps have input
impedances of less than 50 K.
Since the crossover has only four components, (two capacitors, one
resistor, and one pot) it is easy to build. You can build it on a
Radio Shack eight phono jack board. Part# 274-370, (cost $2.19).
IMO if you are going to do something, do it *right*.
This crossover has the advantage over active crossovers, in that it
has less distortion.
It has less noise, too but in fact noise and distortion from reasonably
good, modern electronic crossovers just isn't a problem. Furthermore, we are
seeing more and more digital crossovers, and if you drive and load them with
digital equipment, they are theoretically free of nonlinear distortion.
Here's an example of a good, modern, relatively inexpensive but
comprehensive electronic crossover of the digital persuasion:
http://www.behringer.com/02_products...X2496&lang=eng
The disadvantage is it has only a 6 dB per octave
rolloff rate. Only the highest quality (read expensive) drivers can
handle 6 dB per octave crossovers. Medium priced tweeters, for
example, will distort at higher sound levels.
Again price really doesn't have that gosh awfully much to do with it. Once
you get past the crappy drivers (which sell for a wide range of prices
ranging from low to high) you can find a lot of reasonably-priced drivers
with good performance including ability to work with low-slope crossovers.
Most drivers require at least a 12 dB per octave rolloff rate. This
can be achieved by adding a passive component in series with the woofer
and the tweeter.
From low side power amplifier------------640 mH----------
|
8 Ohm woofer
|
Gnd
From high side power amplifier ----------10 uF----------
|
8 Ohm tweeter
|
Gnd
The electronic crossover (top) and the passive crossover (above) will
combine to give a 12 dB/ octave rolloff to the system.
Use the 10K pot to balance the levels of the system. (Pick a tweeter
that is 3 dB more efficient than the woofer. For example, a tweeter
with 91 dB sensitivity, and a woofer with 88 dB sensitivity.)
With the money you save by building your own electronic crossover, you
could buy high quality drivers from Madisound.
In fact one of the major costs associated with using electronic crossovers
is the double or tripled number of power amps, and using dirt-cheap
hyper-simple electronic crossovers won't help you with that!
Vifa, Audax and Morell all make good drivers, that are not too
expensive.
Agreed about Vifa and Audax.
If you don't like woodworking, you could, go to the Salvation Army
Store or a garage sale, and buy some old bookshelf speakers. Rip out
the old drivers and put in high quality ones.
This can work. You can also often find speaker enclosures as surplus parts.
You will need to do some homework to be sure you get the correct
drivers/enclosure combination. Other than that, this is a no-fail
recipe :-)
Rolling your own loudspeakers and getting good results is far from simple
unless you stick to subwoofers. Doing a two-way woofer/tweeter speaker
system *right* is actually one of the tougher technical chores around.
Here's your chance to invest in measurement and analytical tools! The good
news is that they are far less costly today than they were years ago.
If you want to have a lower crossover frequency you can increase the
size of capacitors and inductor. For example, doubling the size of the
capacitors and the inductor (to: 0.02 uF, 0.02 uF, 20 uF and 1280 mH)
will drop the crossover frequency down to 1000 Hz.
If you want two good small two-way speakers, you will probably save money
(not to mention time!) in the end by looking at speakers from manufacturers
like Paradigm, NHT, PSB. Boston Acoustics, etc.