Crossover calculation

Hello,
I'm about to build a couple of speakers with Eton drivers. The configuration is
2 ETON 5-212/C8/25HEX and a ER 4 tweeter. I downloaded a document from Eton that gives a schematic for the crossover but it's a different driver 7-375 for the low.

This one is a schematic for the the speaker configuration i'm aiming for. Could you please point me in the direction of how to calculate the values

It's a 2-way crossover, with a resonance compensation network on the driver.

You pick an alignment (like Linkwitz-Riley, Butterworth, etc), then using the impedance of the woofer and tweeter, along with the crossover frequency, you can use a calculator.

https://www.v-cap.com/speaker-crossover-calculator.php#secondOrderCalculator

To calculate the compensation circuit, you'll need the Thiele/Small parameters of your drivers, notably Re (voice coil resistance, usually 4-6 ohms) and Le (coil inductance, typically somewhere around 1mH), and the resonant frequency of the driver.  There are calculators for that as well, see here:

https://www.calsci.com/audio/X-Overs3b.html.

Thanks Matador

Beware that x-overs built according to calculations are seldom correct.
Final tuning is a quite complex job and takes several iterations.
It can't be done properly without a decent test set-up.
You need at least a reference mic and a decent software.
I can recommand REW. They have a cost-effective USB reference mic. The software is free.

Thanks Abbey, actually i have REW and a test mic already. I'm just trying to get started and in the ball park. I'm looking at the 2 schematics and trying to understand first if i can adapt the one with the known values to the other one. I found another one that is also close but different drivers

The Eton 24 is for a 4ohm system, the 7.3 is 8 ohms. Both are asymetric, in the sense that the low-pass section  is 1st-order and the Hi-pass is 2nd-order. It is very often used for compensating the boomer roll-off.
The problem with most calculators is that they propose theoretical filters based on perfectly resistive ransducers, which is far from reality.
Softwares like Akabak or Vituix are much closer to reality, but require accurate loudspeaker data, in the form of .frd (response) and .zma (impedance) files. these can be often obtained from the manufacturer.

Thanks Abbey, i started reading and trying to figure it out but i'm too far behind on this one. So i'm thinking of doing the 7.3 with the only change being the use of a more recent boomer. The recommended one in the kit is 7-375-32HEX and i'm thinking of using the
7-212-C8-32-HEX-Symphony-II
Hopefully the crossover can stay the same

Don't know what to say, you can't just pick some drivers, put these into an enclosure, design a crossover for them and expect them to give you a super response. You need to first know the polar responses of the drivers, the weak spots in response to avoid etc. to match them acoustically. All drivers cannot be matched properly, for an example that 7-212 with the Hexacone cone is not  very good midrange performer (there's large peak at about 3.2kHz for an example), but with ER-4 which is know to be difficult to use you should use quite a high crossover point (>3kHz) which is no good as you don't want 7-212 to be crossed over that high. With 7-212 you should use a tweeter which can be crossed over low between 1.5 - 2kHz (has low resonant frequency and large enough dome). A waveguide can help there and also help matching the polar patterns (directivity) of the drivers. So use a tweeter like Eton 29 HD 2 or cheaper SB Acoustics SB26ADC which is 1/4 of the price, or with your proposed drivers add a proper midrange there, though it will complicate matters even more.

Yes thank you for your reply, i clearly didn't know what i was getting into when i started this. I just got 2 ER4 and i have some Adam s3a so i too quickly assumed that building the DIY 7.3 speakers on the Eton site would yield some speakers in a familiar territory . But the more i learn the more i realize that i might not really get there

Now if you don't sell those ER4s you could get yourself a pair of Radian LT2 waveguides (https://radianaudio.com/products/lt2-wave-guide there's an AudioXpress test of it here: https://audioxpress.com/article/test-bench-the-lt2-ribbon-transducer-and-waveguide-from-radian-audio-engineering) which should fit (the fixing bolt holes on LT2 are 92mm and on ER4 90mm apart so they are like a match, you should be able to use long bolts to fix the tweeter onto the WG) and build a test baffle, get a microphone, download VixxxxCad (that's f-word in Finnish, meaning something like a f**ked Up Cad, odd humor from the author) and start measuring from different angles (0-15-30-45-60). I don't really know those AMTs that well, they usually have quite a funky response. Anyway, you may need to use some 4" or so midrange between it and the woofer though Eton designs seem be able to go without (but they haven't published the polar patterns). Adam S3H/V has some 4" (?) dome (hybrid) midrange with smaller waveguide (compared to LT2) for the tweeter. Anyway, with the waveguide you could go as low as 2kHz, and the directivity would still match quite a large driver (maybe even a 6.5" one). There are many options for the midwoofers, and when using the WG designing the crossover may be quite an easy task, for an example a single capacitor can be enough if the 1st order crossover frequency is set close to 10 kHz using about 3.3-4.7uF cap (just a guess) - the waveguide has rising response towards the acoustic 2k crossover point. For the woofer(s) a 2nd order LP with the baffle step correction is needed, just two components (about 1.5 - 2.7mH coil with a cap like 15 uF, though the values cannot be known before measurements, they can be simulated in software).

thanks for the suggestions i will go through if and learn a lot. From looking at the waveguide dimensions 92mm and ER 4 90mm do you put the bolts slanted? or just drill new holes in the waveguide ?

ubxf said:

thanks for the suggestions i will go through if and learn a lot. From looking at the waveguide dimensions 92mm and ER 4 90mm do you put the bolts slanted? or just drill new holes in the waveguide ?

Click to expand...

I thought the slanted option could work but after all there is another problem preventing the use of the common bolts as the ER4 has to be enclosed from the back per the datasheet. I guess it is not possible to remove the front  plate of the tweeter either so you have to mount the ER4 first to a larger piece of MDF with another MDF for closing the back (see the datasheet) and then mount that from the inside against the back of the waveguide by screwing the MDF piece with the waveguide to the front panel.

That makes sense, i'll give it a try. Thanks for the tip