Crossovers
Copyright 2018 @ Troels Gravesen

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If you change front panel dimensions, actual drivers, placement of drivers and cabinet tilt in the constructions shown on these pages, you need a new crossover, and I can't help. The crossover will no longer work as intended, so please do not ask because I would need your speakers in my workshop to adjust the crossover. DIY Service is provided if you live within driving distance (Aarhus, Denmark).

In short: The frequency response of a driver depends on the baffle on which it is placed due to reflections and diffraction, and the crossover must correct for the impact of the baffle, thus any change = new crossover. Watch the animated issue here.


Rounding the edges of a cabinet doesn't eliminate diffraction.
A very large rounding, large radius, will even out the diffraction phenomenon.
If driver is placed with the same distance to to top and sides, the problem can be severe.
Placing the e.g. tweeter with different distance to all nearby edges will often help, but every driver needs to given optimal conditions. Thus, acoustics before design.

Loudspeakers are a frequent target for designers who know little of acoustics and the result is often disastrous, with cabinets providing the worst possible working conditions for loudspeaker drivers and the need for elaborate crossovers to correct for all the problems derived from improper front panels and drivers' placement. Design and acoustics must go hand in hand to make the best of it. 

A crossover is not just a crossover intended for either 4 Ohm or 8 Ohm drivers and a given target level. Sorry, it doesn't work that simple. To be that simple, the drivers would need a flat frequency response, flat impedance and flat phase profile. Sorry, doesn't exist.

Most common mail goes like this: "I have these and these drivers; can you please make me with a crossover?" I cannot help you here, because to make a crossover I need to measure what your drivers do on your cabinet front panel in terms of frequency response, phase and impedance. The frequency response will depend on the dimensions of your front panel and the placement of the drivers. It must all be measured from your speaker to get it right.

The question is whether we can make a crossover at all without measurements - and the answer is NO.
It cannot be done, and crossovers cannot be calculated.

We cannot use manufacturers' data sheets to simulate crossovers either, although I know some dealers do so. The frequency response data are most often taken from an "infinite" baffle that does not in any way resemble your cabinet. These data do not contain proper phase data, etc. We also need to measure the actual acoustic distance to drivers from an assumed listening point to get proper phase integration. This simply cannot me calculated, only careful measurements can tell.

Yes, you can set up a speaker with a crossover based on theoretical values that will ensure you won't burn your tweeter or midrange and you may sit back and think this is a great speaker - and maybe it is - but maybe you wouldn't like it if you saw its measuring performance. I have a friend who refuses to let me measure his speakers because he knows he won't like them if he sees how they perform. You may object that this person is perfectly happy with his speakers and so what? And this is perfectly true!

- nothing can compete with "good enough" -

I see a lot of people spending minor fortunes on expensive drivers and "high-end" components and never get the full potential of the drivers due to improper crossovers. The crossover is the heart of the speaker and can be made in numerous ways. Only minor changes to the crossover can turn a great speaker into mediocrity and visa versa. I receive mails from people having made a construction from some presumed "all-round" series crossovers that floats around on the web. They're awful! They won't work, so don't waste your money - and please read example #1 below.

Example #1

1st example here is from a visitor I had, bringing in a beautiful Accuton 2-way from C220 and C23 drivers. The tweeter was hung from a hook on top of the cabinet (three O-rings), so no baffle support for treble. Usually a free "flying" tweeter measures pretty bad and this one was no exception:

Left: Tweeter response with (blue) and without (red) baffle support. Right: SPL from drivers with no crossover attached.


Response from speaker with new crossover - tweeter still without baffle.

Below you can see the response from a series crossover my visitor had found on the web and which was recommended as a generally applicable crossover. Shame on whoever launched something like this! It's a disaster! Two C220 and two C23 Accuton drivers are serious money and throwing in some phantasy web-nonsense like this is a total waste of money. Tweeter level is some 5dB too low and the gigantic peak at 3.5 kHz is hard to ignore. Right where the ear is most sensitive. I can tell this speaker had a weird and ear-shredding sound!

 

Example #2:

Making the 2.5 clone from calculated crossover components: Let's take a look at the 2.5 clone: ScanSpeak 18W/8535-00 and D2010/8513. The clone is basically an 18/18 dB filter at 3 kHz. Try to calculate component values for a 18/18 dB filter at 3 kHz for two 8 ohm drivers and compare to the actual crossover: Try this site: http://ccs.exl.info/calc_cr.html.

The calculation sheet cannot take into account the impact of bypassing the 1.75 mH coil with the 47 ohm resistor. Not to mention baffle-step compensation. The calculation sheet is not taking into account the needed tweeter attenuation - nor tweeter polarity for that matter. So, the real "2.5" filter does not look very much like what we have calculated. If we made a 2.5 clone crossover based on theoretical component values we would get a speaker that would yell off our heads from having an upper mid some 5-10 dB higher than intended and probably some serious problems in the crossover region as can been seen (out-phasing).

OK, so we have heard that tweeters need attenuation and we add a 5R6 to the tweeter:

Well, we got the tweeter level down, but an even more serious dip at 4 kHz.

- And we have heard that we may need to invert polarity of the tweeter:


Better!, but still upper mid and treble level is some 5 dB too loud.


Above when the 2.5 clone is right - for better or for worse.....not my favourite speaker.

My best advice is to choose some well documented commercial kits or well documented diy-constructions from the internet if you want to enter the fascinating world of DIY loudspeaker construction. Take great care if you change cabinet construction.

 

Happy workshop hours!

 

DIY SERVICE

Unless you're living in driving distance of Aarhus, Denmark, DIY service is probably not a good idea. As can be read above, I need both your finished speakers in my workshop to make the crossover.
To make a loudspeaker successfully normally takes quite a few experiments on choice of drivers, baffle size, shape and drivers' placement before we have something worth starting the crossover work. Placing a pair of driver on a baffle based on design rather than acoustics is most likely bound to fail. Design and acoustics must go hand in hand.
I cannot assist you in design via email, nor can I tell which drivers go well together. Specs do not tell what goes and what doesn't. It has to be tried and it may take many tests with different drivers before we get it right.
If you are certain of a combination of drivers and design, I can make you a crossover if you ship both speakers to my address. But absolutely no guarantee this will be your dream speaker regardless of how much money you put into drivers and cabinets. The design and choice of drivers may force me to use complex crossover to equalise and compensate for not taking acoustics into consideration before anything else. If we're talking a single pair of low-cost speakers it doesn't pay off. Transport and fee will simply cost too much and you better pick something from the web already tested and documented.

If you're in the position of being able to manufacture cabinets and should have the ambition to start a loudspeaker company, please look elsewhere. Sorry, this has been tried so many times before and it has caused me a great deal of work and no return of investment.