Using two different woofers in one enclosure

[rhapsodee]

I was reading about the Galactica, incredible design and implementation!

Humble Homemade Hifi

My burning question is, how does one design a bass enclosure (sealed or BR) for two separate woofers of different T/S specifications? Is it a pure trial and error process, or are there some guidelines to start from, and then adjust subsequently based on actual measurements?

I recall reading something about this previously but cannot find it. What are the benefits of using two different woofers for the same frequency range through the same crossover?

Thanks.

[Jay]

Originally Posted by rhapsodee

I was reading about the Galactica, incredible design and implementation!

Humble Homemade Hifi

My burning question is, how does one design a bass enclosure (sealed or BR) for two separate woofers of different T/S specifications? Is it a pure trial and error process, or are there some guidelines to start from, and then adjust subsequently based on actual measurements?

I recall reading something about this previously but cannot find it. What are the benefits of using two different woofers for the same frequency range through the same crossover?

Thanks.

The enclosure will be different for both woofers because T/S are different. Method of calculation is as usual (with single woofer).

Different woofers to produce same frequency range might have issues, but in very low frequency the issue is not critical, especially if the phase tracking is good.

The benefit is we can get the good character from each of the woofers. Subwoofers usually have good low end but something wrong in the upper bass. Usually we need at least 4 ways if we want each critical range is handled by suitable drivers. Using different woofers for the same frequency range will give the same effect.

[rhapsodee]

So we calculate the enclosure separately for each woofer, and then just combine the volume? That's all, an arithmetic sum of the volume from both woofers calculated separately using each woofers T/S parameter?

[Jay]

I mean different enclosures. Two enclosures, one for each woofer.

[Moset]

If you're referring to the speakers in the link above, they use two separate chambers, one for each woofer. In that speaker, one is ported and the other one sealed, even. There's definitely no way of using a single chamber that is both ported and sealed.

Nice build, though.

[speaker dave]

Originally Posted by rhapsodee

My burning question is, how does one design a bass enclosure (sealed or BR) for two separate woofers of different T/S specifications? Is it a pure trial and error process, or are there some guidelines to start from, and then adjust subsequently based on actual measurements?

I recall reading something about this previously but cannot find it. What are the benefits of using two different woofers for the same frequency range through the same crossover?

Thanks.

Yes, those are fully seperate enclosures. Generally you never put 2 different woofers in the same enclosure because there is no easy way to predict what the combination does. One unit can drive the other and give a strange combined output.

Even with seperate enclosures there is the chance that the units aren't in phase at low frequencies and outputs cancel rather than add. This might have happened with one cabinet sealed and the other vented. In this case his response curves seem to show that he is okay in that regard.

David S.

[PeteMcK]

I can't find the link to Thorsten's page where he gives a method to do this, but you calculate the combined parameters as follows:
Re is the series or parallel sum depending on how you want to connect them;
Sd & Vas is the sum of the two parameters
Fs, Qe, Qm is the geometric mean of the two parameters (multiply the two parameters together then find the square root)

I have tried this & it works very well (the drivers in question were reasonably close in parameters though)

[rhapsodee]

I see, it was not obvious from the pictures and descriptions that the 12" and 15" were in different chambers. They were electrically in parallel, which got me scratching my head.

Thanks PeteMck for the formulas. I'll try them out.