Complicated reflex-loading question

[DeonC]

Hi guys

I have a complicated reflex-loading question. I want to use three 6.5" drivers in a reflex enclosure. So far so good. However, I want to roll the top driver off with a high-pass cross-over at 100Hz. Now here is the question- do I optimize the box for only two drivers, as only two drivers will be loading the box at bass frequencies (it will be tuned to between 30Hz and 35Hz). This is seems correct to me. However, then logic jumps up and says: "But hold on, there are three dirvers in the box," and that's were my problem and confusion lies. Do I optimize the box for two drivers, and ignore the effect of the third as it will not be loading the box at low frequencies, or do I optimize it for three? Can anyone help? PLEASE! Thanks. :-)

Enjoy,
Deon

[Salas]

See the rolled off one as passive radiator if you dont want to build a separate chamber for it, which I would recommend.

[sreten]

Hi,

a decent passive high pass at 100Hz is almost impossible due
to the drivers impedance peak - so it would have to be active.

As already stated an unloaded driver would act as a ABR / PR,
which is not you want I assume, it will get driven to its end stops
severely by the other drivers and bypass any low port tuning.
I think your only choice is to separately seal load the top driver.

Depending on parameters the acoustic response will be 2nd order high
pass by default, with a low Qts driver you could get very near 100Hz.
If bi-amping Qtc can be quite high (above 0.8) and by reducing
the amplifiers input capacitor you'd get a third order roll-off.
The top driver should need less than 20% of the box volume.

Obviously the other 80% is a standard two driver bass reflex.

/sreten.

[Svante]

I agree with the others, and wonder why you want to do this? Are the other two drivers going fullrange (up to the tweeter crossover)?

[DeonC]

Hi guys

Thanks for the answers. I guess I will have to put it in it's own cabinet-space. To answer your last question Svante, I am going to put a 1st-order low-pass on the bottom driver. That way the top driver will have a cleaner mid-range. The middle driver will be for BSC.

Enjoy,
Deon

[sreten]

Originally posted by DeonC
Hi guys
To answer your last question Svante, I am going to put a 1st-order low-pass on the bottom driver.
Enjoy,
Deon

Hi, will need an absolutely massive inductor, /sreten.

[FullThrottleRic]

I am going to put a 1st-order low-pass on the bottom driver. That way the top driver will have a cleaner mid-range. The middle driver will be for BSC.

That seems unnecessarily complicated to me

So you're running the top driver from the HP upto the tweeter, the middle driver from f3 upto the tweeter and the bottom driver from f3 to the LP?

Why not give each driver their own enclosure? It will take up more or less the same space as having them all in one box, you can load each one as you want and you eliminate potential crosstalk between each driver.

You could even run the top driver sealed and use it's rolloff to help with your HP crossover

[DeonC]

Hi Ric

So you're running the top driver from the HP upto the tweeter, the middle driver from f3 upto the tweeter and the bottom driver from f3 to the LP?

Yes, sort of. The middle driver will obviously be at 6dB lower than the upper driver at the tweeter XO point, but yes.

Why not give each driver their own enclosure?

I would like to, but the driver spacing would become to much. I have decided to put the upper driver in it's own space, but I am still thinking if port-loading it. It will addd nothing to the sound, but the loading will be closer to what the other are facing, so there will be less of a discontinuity (sealed vs. ported) between the various drivers (or that's my thoughts anyway).

Enjoy,
Deon

[FullThrottleRic]

I would like to, but the driver spacing would become to much.

Sorry I didn't mean physically seperate box's for each driver, I meant dividers in the main enclosure to isolate each driver

[DeonC]

Hi Ric

Sorry I didn't mean physically seperate box's for each driver, I meant dividers in the main enclosure to isolate each driver

That's what I thought you said, but with aroung 20 liters needed for each driver, the seperation could still become a bit crazy. While I could put the top driver in it's own space (with the tweeter, and just put them lower on the front baffle), putting all in their own seperate space could involve driver-spacing that could be too much. Thanks for your help though.

Enjoy,
Deon