Crossovers

[Mustang Marvin]

I will admit I'm a little ignorant when it comes to crossovers. It is my understanding the only purpose of the crossover is to direct the required frequencies to the various drivers.

Maybe this is an overly simplified explanation since I have seen some crossovers that are very complex IMO. There are even active vs. passive ones. My 846B's have a very simple crossover. Since most os the Altec systems I am familiar with are two way systems I don't understand why the crossovers are so complex.

Am I missing something here?

[Panomaniac]

Yes, a lot.

You are correct that the basic function of the crossover is to direct the required frequencies to the various drivers. But that's just the basics.

EQ is often needed to get a flat response. For example horns often need a lift in the top end, woofers may need a boost in the low end. Traps may be needed if the is a resonance peak somewhere.

Then there is the matter of impedance compensation. Drivers don't have a flat impedance at 4, 8 or 16 ohms. So there are ways to flatten the impedance curve to make the crossover behave more as it theoretically should. Phase needs to be taken into account as well, tho that usually does result in a higher parts count.

Levels also need to be matched between drivers. This can be done at a fixed level (usually a resistor or 2) or at a variable level - the L-Pad level control you see on the back of Altec crossovers. Even some midrange tone control can be done with L-Pads.

Passive or active, they do much of the same thing. Crossovers can be simple, but often they are not, and for good reason.

[Mustang Marvin]

So, diagnosing the needs of drivers isn't an easy task.
How would you go about determining the crossover for a DIY system?

Let's say you have a two way system. A bass driver and a horn with compression driver.
You also know the range of the drivers. I know I have a simple 2nd. order Butterworth design in my 846B's. The crossover is at 800 Hz. It is very simple. I have a 800 hz. Eminance crossover in my A7's. It appears fairly simple, but more complex than the N800 version in the 846's. How do you know what fits best in a particular system?

Do you need test equipment or is there a simpler method?

I would like to build some DYI systems and I would like to understand the methods used to fit the correct crossovers. I know I am showing my ignorance but, I need to understand before I spend money on something.
Thanks...

[Panomaniac]

Crossovers, at least good crossovers, are very hard. It can take years to learn how to get them right.

But if you want to get started, then off you go!

Having measurements is very important and will speed you on your way. There are some guys who can do it all by ear, but they have many, many years of experience.

The easy way out is to use an active crossover. Any of the pro units with 24dB/octave slopes. They will never be the best, but your chances of getting something listenable is highest.

If you want to undertake passive crossover design, then you'll need a mic, mic stand, mic preamp, sound card and software. (some soundcards have built in preamp and phantom power). You will also need a way to measure the impedance curves, such as the WT3 from P.E.

Having a lot of caps, resistors and inductors on hand makes it go much faster, as you will definitely need to tweak. That can get expensive, mostly the inductors.
Most or all of the software you need is free.

[Altec Best]

[QUOTE=Mustang Marvin;1813773] How do you know what fits best in a particular system?

Do you need test equipment or is there a simpler method?

QUOTE]


Hi Marv, I'm kinda in the same boat as you but this is where your EAR comes in to play I'm pretty sure, you can tweak a crossover till the cows come home.But it is really how it sounds the best to your ear.Once you get inside of the parameters of your drivers then you can make small adjustments either way to get a differant sound I think.Don't QOUTE ME on that though.:2thumbsup:

[Panomaniac]

It can - and at some points should - be done by ear. But unless you have a lot of experience, doing ti all by ear can be very frustrating. You can easily be lead astray. Ask how I know.

But the trouble can come if you just want to make crossovers for a single pair of speakers. The measurement equipment will set you back minimum $250-300.

• M-Audio Mobile pre soundcard. $100
• Behringer or Dayton mic $70
• mic stand $20
• WT3 or other impedance tracer $100-$150

That seems like a lot to invest for just one project. However, if you want to do more than one project and/or build more speakers, it's worth it.

[Altec Best]

Hi Marv, I was talking about the fine tuning with the ear.Once all the other adjustments and parameters have been met.Cut-off freq, etc,etc.. Then it is a matter of preferrance I think I'll defer to Pano's opinion though, as he is much more qualified.What sounds good to you may not sound good to me and so on that is why I said your fine tuning should be done by ear.That is what L-Pads try to do to adjust the XO to your listening room Acoustics although only for the High-Mid frequencies to get the speakers to sound the best to you in your space.

[Panomaniac]

Oh yeah, I agree for sure. Your ear is the final judge. But getting the crossover really close can be tricky by ear alone. One you are there, tho, it needs to be fine tuned by ear.

BTW Marvin. If you want to go ahead with this, I'd be glad to help.

[bfish]

Just a quick question from the objectivist camp, how does one go about tuning a crossover by ear? Not trying to be a smartass, I'd really like to know.

[GM]

If you can tune an instrument by ear, i.e. have perfect pitch, then you can hear when the response is flat enough through the XO's BW and whether it's causing any 'ringing' higher up. Folks that can't typically opt for highly resonant responses same as they like their TV colors to 'pop' out and I guess one reason why you-know-who is the world's most successful consumer speaker manufacturer.

GM