Open Baffle Desktop Speakers

[borispm]

Hi guys,

I just came up with an idea of utilizing a Tangband W6-789E woofer and a Tangband W3-1318SA full range driver for making a pair of small open baffle speakers, but there's a problem I can't really find a way to solve, and that is the crossover problem.

The baffles will be 8" wide, so I expect the woofers, without filter, to start its 6dB/Oct roll off at 570Hz (-3dB point). To compensate this roll off, I can use an inductor (maybe around 12mH) to low pass the driver at 6dB/Oct after around 100Hz. With the inductor in place, I will get a 6dB/Oct roll off above 570Hz.

Assuming the full range driver is capable of running open baffle without major problems and roll off at 570Hz (-3dB point) too, does that mean I do not need to high pass the full range driver? Will I get a 3dB peak at 570Hz? It seems that the -3dB point of the filtered woofer roll off is above 570Hz, according to my very simple graph plotting... Should I roll off the full range with a cap?

I know a 3dB peak is unlikely to be that disturbing as the tolerance of most speakers out there can do a lot worse, but I want to be engineeringly correct... Do you think I need an LRC notch filter to iron that out?

Please point out any mistake. Thanks.

[borispm]

Opps, I'm sorry... It shouldn't be a 570Hz but somewhere higher, I suspect it's around 850Hz as it seems to be half an octave higher.

Any input, guys?

Thanks.

[chazdrumzalot]

I'll bet gainphile can help you; he's all over the desktop, nearfield open baffle as I recall. See for example:

S11 OB - Revisiting Desktop OB design using Seas 8" and Tang Band Full-Range

[60ndown]

if i were at a desk any amount of time a month id want great sound there.

[borispm]

Hi Chazdrumzalot,
Thanks for giving me the link. I was actually inspired by Gainphile's design but I don't want to mess up with bi-amp, equalizer and electronic XO, so I am going for a passive version. I am not so familiar with asymmetrical slope XO so I am not sure whether I should add a high pass to the full range driver or not...
Thanks anyway.

[picowallspeaker]

I suggest you to try a push-pull of two TB W6-789 with a regular box ( even the OB baffle is too tiny ) and the little FR on top . P-p will help in making the low-pass coil littler (mutual movement conditioning ,same mass ! ) and the little FR will follow its natural rising response with an easy HP .

[borispm]

Hi Picowallspeaker,
Will I end up with asymmetrical slopes between the high pass and the low pass?
And I can't really understand why I can make the low pass "littler". Will I trade bass extension for a "littler" low pass?

Thanks.

[picowallspeaker]

Because in a push-pull ,the woofers are tied together but the air mass in between can couple to the membrane movement only at low frequencies .
Plus , it requires a 'slimmer' inductor for a 4 Ohm load !

[borispm]

Picowallspeaker,
I am sorry I still don't quite get it... My fault for being dumb in physics, would you mind telling me more about the benefits of push-pull dipole and why it is better? Some guys at the OB Gallery in the Multiway side said it is a bit stupid to get push-pull dipole (due to the cost?)... I don't really know.

Thanks.

[picowallspeaker]

No ,no ,I was talking about two woofers in a regular box ,vented on the back , with the woofers positioned nose-to-nail (in axis ) or with magnets sharing the same plane ,but with one cone firing frontally and one firing in the vented volume .
For an OB you'd need bigger woofers and larger baffle .