Input on 2nd try at active 3-way sbacoustics build (ceramic series drivers)?


A couple of years ago I tried building an active 3-way with hypex FA123 with the drivers:

8″ SB23CACS45-8 / Ceramic (

5″ SB15CAC30-8 / Ceramic (

SB26CDC-C000-4 / Ceramic (

I failed on the finish line, glued the box together wonky and then a lot of life stuff happened and I lost interest. The box was a constrained layer damping cabinet with a special swedish glue made for that purpose.

I am debating either selling all the stuff (don't know if I could get it sold) and just buying some cheap speakers (looking at the kali in-8) or trying again, but this time a simpler construction.

I tried calculating the volume for a sealed cabinet for the 8 woofer and used winISD and got around 44l for a wtc 0.707, and also tried the calculator on loudspeakerdatabase and got 39liter? I am confused.

My question is what software to use to calculate this if they all show different? What volume would you guys go for and why? For both the mid and the woofer respectively? I read up a bit on it and want a flat FR (my goal is studio monitors for my hobby music studio) and that seems to be qtc .707.

Sorry for the wall of text but would really appreciate some input! Seems like i have forgotten everything i knew about speakers in just 2 years...

Attatching a pic of my previous failed build for size-reference of what I'm after


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diyAudio Moderator
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Maybe you can.

Maybe they are giving different values since some modern simulators include box losses (damping). Using old school straight methods from the factory spec sheet I was able to determine 41 litres for 0.707 at 44Hz.
A Qtc of 0.707 is often idealised, but it becomes almost irrelevant when placed in a room. All that a low Q bass response gives you is reduced effects of room gain. Kindof the same thing we do when we cross over away from a driver's breakup modes to avoid breakup effects. Consider that you will probably need a subwoofer to complete your setup; and then you will unavoidably have to deal with the bass region. It is unlikely that you will get smooth bass without the help of some EQ and acoustic devices. This implies that you are doing acoustic measurements to enable you to evaluate problem areas. "Make Qtc 0.707" is only a rule of thumb from decades ago, but we can do much better these days.
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Thanks for replies! I think I am getting it now. Will use the hypex yes and plan to tweak the response using dsp so i guess it is really quite flexible, will probably go for around 41 litres as previously suggested and this also seems to be around the mean of 44+39 so it feels good.

How about the sealed enclosure for the 5" mid? Should I go about it the same way? around the ballpark of qtc of 0.707 for starters? And then tweak it further down the road.

Also yes i plan on a sub in the future! So I want to design the speakers with that in mind, part of why i went for sealed enclosure (the other reason being less room for failure) however one thing at a time hehe, right now using a bluetooth speaker for my non-headphone use so i guess a proper three way is a good starting place regardless