Crossovers
Copyright 2021 @ Troels Gravesen

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.

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. Below you can see the frequency response of the same driver on two different baffles.

Sorry, but time doesn't allow assisting in any hypothetical combination of drivers of your own choice, nor renovation of vintage speakers not listed on my website.


Above the response from ScanSpeak -7140 tweeter on an optimised baffle (red) and from his modified baffle (green).  Actually he only made the cabinet 2.5 cm higher than advised - and he has to live with a nasty dip at 2200 Hz.

 

To get an idea of edge diffraction, watch the animated presentation here.

1. Rounding the edges of a cabinet doesn't eliminate diffraction.
2. A very large rounding, large radius, will even out the diffraction phenomenon.
3. 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 be given optimal conditions.
4. So, acoustics before design! Form follows function, not the other way around.

Loudspeakers are a frequent target for designers - and furniture makes - 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.  

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!