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Old 23rd October 2008, 07:35 PM   #1
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Default Will active crossovers make cheap drivers sound well?

I was "BoxSimming" and put some relatively cheap drivers in a random box. At first the response looked horrible but after five minutes of active filtering I found a reasonably flat response from 100 to 20 000 Hz. +-3 db. Will active filtering make cheap speakers sound great? And if so, why don't people do that?

Soldering together an active filter only takes about one afternoon, 20 dollars and multi-input amplifiers are all on ebay

Have I found some sort of Holy Grail or have I just disgraced the entire DIYaudio forum?
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Old 23rd October 2008, 08:20 PM   #2
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Neither - unfortunately frequency response will never tell the whole story, you must consider also distortion, including harmonic, non-linear and phase distortion. Cheap drivers tend to have plenty of the first two, and active filters can have problems with the third.
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Old 23rd October 2008, 08:35 PM   #3
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Flat vresponse is only a small part of the equation... active XO definitly helps -- probably more so for the amps than the speaker drivers themselves.

dave
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Old 23rd October 2008, 08:44 PM   #4
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An active crossover is not necessarily better than a passive one, and cheap speakers remain cheap speakers.
It is easier to achieve good results with active crossovers than with passive ones, because
  • - their reactions are more easily predictable. Their components do not interact with the complex speaker impedance.
    - their components are much cheaper than for passive filters, which makes tweaking and correcting cheaper. That is why they are especially common with subwoofers, because big coils and big capacitors are just too expensive.
    - you can do some things that are very difficult otherwise, e. g. equalizing, narrow notch filtering, boosting, continuous phase adjusting, etc.

Why doesn't everybody go active? One reason is that it takes more amplifiers, which are expensive and require more space. Another reason is that it takes much more calculation and less Trial-&-Error, which is what hobbies are about as opposed to professional working.
The most important reason of all is that big coils and caps are sexier than small caps and rectangular, black beetles (op amps).
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Old 23rd October 2008, 10:18 PM   #5
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Quote:
Why doesn't everybody go active? One reason is that it takes more amplifiers, which are expensive and require more space.
It takes less heat sink, a smaller power transformer, and smaller capacitors to achieve a given SPL level with the active solution . The ouput devices can be the same just wired to more than one line level stage. It's that whole power dissipated is V^2/R thing - in a 2-way with equal sensitivity drivers 30V peak goes as far as 56V peak which subsequently gets divided into 30 and 26V peak signals. IOW, the amplifiers themselves can be smaller and less expensive for a given target SPL.

You can put the whole mess inside or beneath the speakers if you want like the Linkwitz Pluto. SL's boards are 7 or 8" on a side including XO and three power amps.

A photo of my Pluto boards with transformers is attached. They're cute little things.
Attached Images
File Type: jpg 01_both_boards.jpg (57.8 KB, 654 views)
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Old 23rd October 2008, 10:32 PM   #6
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Quote:
Originally posted by TheSeekerr
Neither - unfortunately frequency response will never tell the whole story, you must consider also distortion, including harmonic, non-linear and phase distortion. Cheap drivers tend to have plenty of the first two, and active filters can have problems with the third.
Active analog filters can have identical phase response to passive ones, and if you want you can electronically delay drivers to aim the main output lobe from the cross-over without physically moving the drivers.

IIR digital filters are the same.
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Old 23rd October 2008, 10:46 PM   #7
infinia is offline infinia  United States
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How do you define boxsimming?
Box modeling programs are only good around the LF cutoff region.
Untill you start measuring things with microphones then your perfect world will be "rocked" again.
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Old 23rd October 2008, 10:55 PM   #8
cotdt is offline cotdt  United States
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The OP is correct, EQ can make cheap drivers sounds well. Yes it will have higher distortion, but this does not make it necessarily sound bad. Frequency response is still the most important factor to how a speaker sounds. Try it out for yourselves and you'd be surprised. Theorycrafting only gets us so far.

However, some cheap drivers have a lot of mechanical noise at high output. So you can't have everything. And it's not that expensive drivers are immune to this, the scanspeak revelator woofers have quite a bit of mechanical noise itself, at higher output.
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Old 24th October 2008, 08:26 AM   #9
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Quote:
Originally posted by infinia
How do you define boxsimming?
Box modeling programs are only good around the LF cutoff region.
Untill you start measuring things with microphones then your perfect world will be "rocked" again.
This is the software BoxSim and I realised that using random cheap Visaton drivers in a random case doesn't make it a bad speaker after using some very basic low and high cutoff filters.

That would make a 8-year-old able to build speakers. There must be some disadvantage except from using very cheap drivers with lots of distortion?!

The ultimate DIY solution would be using modules of these little circuits with a pot:

Click the image to open in full size.

Click the image to open in full size.

And just use it for trial-and-error. "Too much bass. Turn the lowpass frequency lower or put another module behind the first to make the slope steeper." The same for the High frequency drivers. Too loud, change the gain on the final opamp.

Again, this is just thinking out loud. Please tell me what I am doing wrong/right!
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Old 24th October 2008, 09:17 AM   #10
Calvin is offline Calvin  Germany
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Hi,

the answer to Your Q is: "It depends!"
Putting some cheap driver (remark: cheap doesn´t necessarily imply bad) in a random cabinet won´t result in a good result in the vast majority of cases. No equing and filtering will make a good speaker out of such a construction in any way. Wonders and miracles are other peoples business
So lets assume that You did your homework and used drives of reasonable quakity in a reasonably fitting cabinet.
Even than active filtering isn´t necessarily superior.
Every good passive filter design includes some equalizing. Modern simulators are quite exact, so that basically everybody who is able to switch on the PC can get a fairly good result.
When You are not familiar with active filter design, nor You don´t realize which end of the soldering iron is the hot end...You could only use standard off-the-shelf active filter modules/crossovers. But those just filter..they miss out on the equing functions. The result will be much worse than a good passive filter. Too many have gone this way and this is probabely one of the major reasons that active filtering still has a bad reputation.
If done properly active filtering offers some serious advantages which can lead (imo) to a better sound device.

jauu
Calvin

ps. The pic doesn´t show a typical Lowpass, but rather a basslift (LP with gain) and no, this little circuit doesn´t qualify for the label ´ultimate´
That this here isn´t true:
Quote:
That would make a 8-year-old able to build speakers
is simply proofed by the fact that there are so many mediocre speakers around and just so very very very few very good ones.
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