OB, where to place drivers?

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Basically yes. Below resonance excursion of the driver will be
frequency independent.

A very low fs driver will have still rising excursion below the baffles
frequency limit. If there is much reserve in excursion such a driver
could be used with an active compensation. But it needs a lot
of excursion to shift the lower frequency limit downwards.

So the more realistic and cheaper way (without active compensation) is
to use a high Qts driver and keep the lower freqency limit in a sane range.

I think <=40 Hz for an OB is OK, and due to room gain this is achievable.

Have a look at Xmax of the driver, the higher linear excursion the better.
Xmax x "summed cone area" = displacement volume.

You can have a look at Linkwitz' page, there is an excel calculator relating
- frequency
- SPL,
- needed displacement Volume and
- effective path length of dipole

Making compromise at lower frequency limit is a good idea with OB.

Kind Regards
 
Thanks guys for your thoughts!

GM, as you have experienced such "suroundings", what about cavity effects du to so many cones placed arround the mid driver and tweeter?

You're welcome!

Hmm, never noticed any cavity effects per se. These will only be an issue if the XO's high enough for the drivers to be beaming somewhat.

I've offset tweeters in mirror image stereo pairs to help with phasing issues, but of course if you have a wide listening distance it's not going to be very effective.

GM
 
Concerning the woofer configuration i told my opinion before.
That circular arrangement may work well, but the
geometric extension of the bass source is unecessarily enlarged
compared to wavelength at XO. So the "point source approximation"
is hampered in making the bass source wider than has to be by nearly
a factor of 2 ... directivity of (summed) bass source and midranger
will differ more than necessary in the crossover region.

You lost me here. With the three square perimeter he laid out, its acoustic center is 15" x 15", so at worst, from the central mid to the corner driver it will be ~21.21"/2 = ~10.6" = ~320 Hz @ 1/4 WL.

Clustered at the bottom for sure better meets his max SPL requirement if setting on, and perpendicular to, the floor, but to get the mids/tweeters up anywhere near ear height means a very low XO point for best performance. Using your cluster, the acoustic center will be around 10" off the floor, so ~28" to ear height = ~121 Hz, probably too low for the mids unless a large one is used.

Even if the mids were directly above, it would have to be < ~5.6" in diameter to be closer acoustically than the perimeter layout, so how can it be 'enlarged' compared to yours?

WRT directivity, the woofers should be at ~2pi around 678 Hz in the horizontal and vertical place, so I don't understand your concern over differing directivity issues through the XO BW since it will be somewhat lower. I mean it's mimicing an 'FR' driver which has anything but a ~flat power response, so can't expect a derived one to be either.

GM
 
"...so how can it be 'enlarged' compared to yours?"

I was comparing the width of the "Perpendicular" woofer configuration
with the width of my initially proposed "Rows" configuration (see pictures).

"Interleaved Rows" would have been, considerably taller.
I think of beaming in the horizontal plane harder to deal with,
than in the vertical.

Because of "crazyhub's" high LF output requirement the "triangular"
approach evolved ... as a compromise.

Concerning just interference when the XO frequency to the midranger
is made quite high, i share your opinion, that this "Triangular" config
is not an improvement.

But we should not neglect the interference of the woofer configuration
with itself via bottom reflection ....

Color of Curves
----------------------
Green : "Perpendicular"
Pink : "Rows"
Red : "Triangular"

The pics have to be rotated by 90 degrees to show the intended
woofer configuration including its mirror caused from the bottom
of the listening room.


It is just a simulation, not the truth. But the "compromise" seems to
work very well.

Rolling off say 4 of the bottom woofers at lower frequency stays
and interesting option too with this configuration.


Kind Regards
 

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