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Old 22nd February 2009, 12:07 AM   #1
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Default Sealed box to OB?

Given a suitable MTM crossover design...what would be the outcome of eliminating the box yet keeping the same XO.....minus the addition of a highpass filter of course and the addition of a powered bass unit. I would imagine the baffle dimensions would have to be adjusted if this is at all possible in the first place. The Midwoofers in question have a QTS of .56 if that matters.
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Old 22nd February 2009, 05:39 AM   #2
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Default Re: Sealed box to OB?

Quote:
Originally posted by mayhem13
Given a suitable MTM crossover design...what would be the outcome of eliminating the box yet keeping the same XO.....
You would rapidly lose bass response below the dipole cut off frequency for you baffle dimension.

Quote:
Originally posted by mayhem13
I would imagine the baffle dimensions would have to be adjusted if this is at all possible in the first place.
Most likely, the MTM crossover was designed for the particular baffle dimension...

Quote:
Originally posted by mayhem13
The Midwoofers in question have a QTS of .56 if that matters.
The QTS will affect the loss in bass response.

Quote:
Originally posted by mayhem13
minus the addition of a highpass filter of course and the addition of a powered bass unit.
A lot of 'ifs', but if the crossover frequency is high enough, it all might just work.
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Old 22nd February 2009, 09:17 AM   #3
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- Very noticable loss of bass, depending on baffle and driver parameters

- Shouty mid due to 1st dipole peak.

Those are the negatives. I'm sure we can go on and on about the positives...

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Old 22nd February 2009, 07:12 PM   #4
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If the speaker cabinets are sufficiently deep and you are removing the back panel only but not the side panels, you probably don't need to change the crossover at all for the frequency above about 200Hz and it will still work very well provided that the "box" is fully stuffed. There would hardly be any changes to the frequency response from about 200Hz up, depending on the baffle width and cabinet depth. You would need to design a new XO between the MTM and the woofer box.

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Old 22nd February 2009, 09:28 PM   #5
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Good question, and I'll watch with interest as you build.
I happen to have a pair of powered sub-woofer boxes that i have thought about doing just this with.

Look at Andy Gs "Blackwoods" and Paul Carmodys "Aethers" arent these the same thing but different??
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Old 23rd February 2009, 04:00 AM   #6
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Just what i was thinking about, the Aethers but with a powered bass module and a more dynamic MTM. Say for the sake of arguement that the MTM configuration was for 200hz and up, and the subs used plate amps. The thought was to deliver signal to the sub amps with speaker level inputs and cross the sub using it's onboard filter at 200hz. Then using the sub amp speaker level outs to the MTM section. Could a passive network be designed in between for a 200hz Hipass or is active the only way to go. I'm very fond of the drivers in the sealed box( 2 CA18rly/27TDFC-WGuide loaded) which are reported to have a very flat response on an open baffle. I just feel i'm lacking some spaciousness that the OB might provide. Besides the fact i've got two Dayton RSS315HOs that are dying for a use!
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Old 23rd February 2009, 04:34 AM   #7
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I would say that , depending on the quality of the amplifier active was better, but you could use the high pass in the plate amp in conjunction with a capacitor of suitable size, what about a pair of O-Audio plate amps with the RCA input and RCA output and using a dedicated amp on the mids??
Do you have a separate pre-amp?? or an integrated with a pre-out main - in function??

Is 200 Hz too high for those Daytons??
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Old 23rd February 2009, 04:51 AM   #8
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Quote:
[i]. I'm very fond of the drivers in the sealed box( 2 CA18rly/27TDFC-WGuide loaded) which are reported to have a very flat response on an open baffle. I just feel i'm lacking some spaciousness that the OB might provide. Besides the fact i've got two Dayton RSS315HOs that are dying for a use! [/B]
I have not seen dipole speakers which are flat without eq. The dipole 1st peak is a theoretical +6db and varies with baffle dimension and driver parameters.

Measure 1m on and off-axis (30, 45, 60 deg.). Unequalised OB will shout in midrange.
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Old 23rd February 2009, 11:47 AM   #9
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Quote:
Originally posted by Moondog55
Is 200 Hz too high for those Daytons??
The Subs look good till about 800hz with cone breakup setting in, and the low pass filter on the amps is 36db/oct at 200hz. The speaker level in/outs have no high pass...simply a parallel connection so some type of high pass at 200hz would be needed between the amp and MTM section. I could purchase another amp and simple two way active xo, but i'd prefer passive if possible.
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Old 23rd February 2009, 11:51 AM   #10
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Quote:
Originally posted by gainphile


I have not seen dipole speakers which are flat without eq. The dipole 1st peak is a theoretical +6db and varies with baffle dimension and driver parameters.

Measure 1m on and off-axis (30, 45, 60 deg.). Unequalised OB will shout in midrange.
Can the peak be tamed with altering the baffle dimensions or adding 'wings', or is a passive notch the only way? Can the dipole peak freq be calulated, or measured only?
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