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rich31td 12th November 2012 05:56 PM

Open Baffle natural roll off?
I am currently building a pair of dipole speakers similar in design to the Orion.

I am using a Seas L22RNX/P and 10" XLS woofer in a baffle with a width of 300mm and height 1000mm and a MiniDSP for the EQ and x-overs.

I have simulated my baffle design in EDGE, it is my understanding that dipole speakers exhibit a natural roll-off of 12dB/octave.

After I have notched the dipole peak I am left with the dipole roll off and -6dB at 100hz.

Rather than correct for the dipole roll off, could I just let the midrange roll off naturally and apply low pass LR2 to the woofer at 100hz?
Or am I missing something vital?

sreten 12th November 2012 06:03 PM


Yes you can. You could low pass lower down to extend the bass,
though your not going to get much SPL with 12" wide baffles.

BTW baffle loss is 6dB/octave not 12dB. Your extra roll-
off (not loss) is caused by using very low Qts drivers.
Your Edge sim only shows the baffle loss, 6dB/octave.

Final bass roll-off low down is 18dB/octave, 6dB due
to baffle loss and 12dB due to the drivers roll-off.

rgds, sreten.

5th element 12th November 2012 06:03 PM

Cross posts with Sreten.

In the Orion LW uses a Linkwitz transform to compensate for the low Q woofer, then uses a 6dB/oct shelf to correct for the OB roll off.

rich31td 12th November 2012 06:06 PM

Opps, got my self in a muddle then.

The Peerless XLS 830452 woofer has a Q of 0.17, how would this affect it?

rich31td 12th November 2012 06:14 PM

What would you set as the target Q in a Linkwitz Transform? 0.5?

5th element 12th November 2012 06:40 PM


Originally Posted by rich31td (Post 3238882)
What would you set as the target Q in a Linkwitz Transform? 0.5?

It depends on what Q your're happy with, but people usually choose between 0.5-0.7.

Note here that the XLS drivers have a Q of something like 0.18 and a resonance close to 20Hz. These are the numbers you will use when setting the parameters for the LT and you will then pick the desired target fs and Q for it to equalise towards.

If you are wanting the main panels to give you extension down to say 40Hz, then picking a target Q of 0.7 + a target fs of 35Hz would be a good idea. If you combine this with a high pass with a Q of 0.7 and a corner frequency of 35Hz, then you will end up with an overall roll of centred on 35Hz with a Q of 0.5.

Do bare in mind that the XLS' fs and Qts will rise by a small amount when mounted on/in the baffle/frame.

sreten 12th November 2012 06:44 PM


Crossed posts.

Rereading your post I've misunderstood your post and no you can't.

You need to model driver responses as well as the baffle loss.

Look at :

A Qts of 0.17 sub in a 12" wide open baffle is a disaster area in all respects.
Baffle loss at 50Hz will turn a 10" driver into no better than a boxed 3" SPL.
Huge amounts of boost and power are required to produce piffling SPL.

rgds, sreten.

Davey 12th November 2012 06:46 PM


You can target whatever Q you desire with available EQ tools, like the Linkwitz Transform. 0.5 would probably be an excellent target.

FYI, the Orion system does not use a Linkwitz Transform anywhere in the design. Q correction of the woofers is handled by a simple 6db/octave shelving filter.



5th element 12th November 2012 06:55 PM

You can't handle Q correction with a simple shelving filter, I am sure I've seen a schematic or block diagram for the Orion that shows an LT on the woofers.

rich31td 12th November 2012 07:15 PM

I forgot to mention, the 10" woofer will be mounted in an H-frame similar dimensions as the Orion.

I think I need to get outside and measure the responce of the baffle/driver and work out the shelf filter for the midrange and H-frame.

So there is no problem in using LT on the woofer then to achive a target of 35hz, Q=0.5 and a 6db/octave correction?

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