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Old 8th December 2014, 06:18 PM   #1
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Default Question about OB bass

Question;

Lets say i wanted to build a OB (dipole) speaker with a low end cutoff of about 80hz and maybe go up to about 300 (as high as 500hz) and sensitivity of about 88db. Lets not discuss mid/tweeter for now. Would this have to be extrordinarily large? I am hoping that by limiting it to 80 hz that might make the size more manageable. What Driver size/baffle size are we talking? (Roughly) Thanks.
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Old 8th December 2014, 09:33 PM   #2
Scott L is offline Scott L  United States
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By the very nature of an "open baffle" it does NOT like to reproduce bass.
The front wave and back wave cancel each other out. The cut off is related to the baffle size. Equalization is used to bring the bass level back up to where it would have been anyway if there was a proper enclosure.

There's plenty of that topic to read about, even here at the DIY.

Proponents and enthusiasts of the "open baffle" claim to enjoy the absence of any "box" sound.

I admire their enthusiasm, but I don't share it.
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Old 8th December 2014, 11:51 PM   #3
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Quote:
Originally Posted by Scott L View Post
By the very nature of an "open baffle" it does NOT like to reproduce bass.
The front wave and back wave cancel each other out. The cut off is related to the baffle size. Equalization is used to bring the bass level back up to where it would have been anyway if there was a proper enclosure.

There's plenty of that topic to read about, even here at the DIY.

Proponents and enthusiasts of the "open baffle" claim to enjoy the absence of any "box" sound.

I admire their enthusiasm, but I don't share it.

Scott, my Lambdas are a hybrid (Mid is dipole) I would love to do some bass equalization/correction, but the woofer in my sealed cabinet goes up to 275 hz and I am thinking of building something new that I can use with a sub from 30-80hz and do bass correction on the sub.
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Old 9th December 2014, 12:25 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

The short answer is the question implies you don't really
understand the problem in any sensible respect AFAICT.

Baffle size does not determine the LF cutoff, unless you
want it to, and for 80Hz it is utterly humungous, and
won't fit it any sensible room.

80Hz rather than 40Hz as a target will reduce the possible
practical baffle size given a set of performance targets,
but baffle size is intimately related to the mid x/o point,
and the trade-offs that implies for bass SPL levels.

Search on "MJK" and "open baffles".
Then "LinkwitzLabs" and "MusicAndDesign".

rgds, sreten.
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Last edited by sreten; 9th December 2014 at 12:29 AM.
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Old 9th December 2014, 12:47 AM   #5
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Old 9th December 2014, 01:13 AM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by jimbones View Post
Hi,

Not the intention. Asked a question in conversation you can
reply with lots of questions about the question that simply
wouldn't work on a forum without appearing insulting.

The brusque reply is intended to quickly point you in the right
direction, you should never apologise for asking a question.

The general gist of your question is correct, but in no way
will a thread sort the wheat from the chaff theoretically.

rgds, sreten.
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Old 9th December 2014, 02:08 AM   #7
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Got it.
I wanted to vet out an idea of a sub 80 hz and below crossed over to a mid woofer. I'll continue research on the site. Maybe I can use a previous design for the low end (that uses equalization)however I am concerned about finding good sounding electronics.
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Old 9th December 2014, 08:00 AM   #8
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Hello Jim,

88dB for a dipole bass after equalization, it will be a little large.
Take a look to these projects :
http://www.quarter-wave.com/OBs/OB_Design.pdf
OBL11

If you want a compact baffle you need to go to active

The best sensitivity in a compact baffle have is 83dB with 2x12" (Peerless 830669) F3=40Hz. With 2xAlpha 15, in a compact baffle (16/18"), you should be near 90dB with a good bass extension
(My latest design)

Hope this helps.
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Old 9th December 2014, 02:28 PM   #9
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The Alpha's look interesting. I would think the baffle would be larger than 16/18 (if i interpret you correctly) Since it is a 15 inch woofer.
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Old 10th December 2014, 05:30 AM   #10
Pano is offline Pano  United States
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Look up the Manzanita project on this forum. That will give you a real world idea of what to expect.

Too get proper bass on OB you have to throw away midrange from the woofer. That works to lower sensitivity. Once you understand that, you will begin to understand OB bass.
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