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.
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.
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.
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.
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.
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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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.
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.
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.
Just how unwieldy are we talking about..OK, Speed of sound at 13,503.94 inches per second, divided by 80 Hz gets us a FULL wave of 14.06 Feet long.
If I'm not mistaken we need half that value, 7.03 Feet....in all directions mind you... One could fit that in a common eight-foot ceiling, perhaps a panel resembling that of a giant tombstone, the top half of sorts, the driver center just a foot off the ground, a giant radiused panel....all the way to the ceiling.
_____________________________________________________Rick........
If I'm not mistaken we need half that value, 7.03 Feet....in all directions mind you... One could fit that in a common eight-foot ceiling, perhaps a panel resembling that of a giant tombstone, the top half of sorts, the driver center just a foot off the ground, a giant radiused panel....all the way to the ceiling.
_____________________________________________________Rick........
ouch!!
Uh just a bit too big. But obviously it's not just baffle size because there are OB bass with smaller baffles that go down to at least 80 or a bit lower no?
Uh just a bit too big. But obviously it's not just baffle size because there are OB bass with smaller baffles that go down to at least 80 or a bit lower no?
Don't worry about the theoretical or practical issues just too soon.
Do you have any spare drivers on hand? Pick a biggest one and build a cheapest baffle around it as you can (by cardboard, scrapped wood, carpet... anything you can pick up for free). Start experimenting and have fun. Like these:
http://www.diyaudio.com/forums/full-range/256437-quick-cheap-dirty-speaker-challenge.html
And then build something more durable and better looking once you find the right recipe.
Do you have any spare drivers on hand? Pick a biggest one and build a cheapest baffle around it as you can (by cardboard, scrapped wood, carpet... anything you can pick up for free). Start experimenting and have fun. Like these:
http://www.diyaudio.com/forums/full-range/256437-quick-cheap-dirty-speaker-challenge.html
And then build something more durable and better looking once you find the right recipe.
Was rolling eyes at the replies you have gotten so far...
Can you build an OB with a low end cutoff of 80Hz... sure, no problem.
On the other hand, you can't really assign a "sensitivity". This is because, without correction, the OB has a much different response than a closed box speaker.
As some have pointed out and you probably know, as the baffle gets larger the "corner frequency" of the high-pass characteristic of the OB moves lower in frequency (making some gross generalizations here). You can think of the response from and OB as a combination of a first order HP (at say 200Hz) plus a second order HP response of the driver in free-air, e.g. Qts @ Fs. This is an oversimplification but close enough for this example. Typically one boosts up the first-order HP part of the response of the OB (in the lower frequencies) to create an extended flat passband. What ever driver that is used will only have so much excursion capability, and eventually that becomes the limiting factor to how low AND how loud the OB system will play.
To give you a concrete example, I recently developed a 3-way speaker with a 12" open baffle woofer. The driver has 9mm Xmax. The OB measures 17x30 inches. I use this down to about 80Hz where it reaches Xmax at the SPL that I am aiming for (just over 100dB@1m IIRC). I had to boost the power to the woofer by about 12dB to get the passband to have a corner frequency of 80Hz or so, so that is 4x the power. Some consideration of the thermal power limit of the driver is therefore a good idea. Here is a pic of the system:
Now if I had wanted I could extend the passband of the woofer lower. The tradeoff would be that the SPL that I could generate before Xmax was reached would be less, much less in fact. This is why there are not too many OB subwoofers. About 60-80Hz is what I feel is a practical lower limit for modestly sized OB systems. Below that you can make a small transmission line like a U-frame, W-frame, etc. or even a standard 1/4 wave system.
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Really? Why? I gave him a very practical, no nonsense answer. Sure, 80Hz isn't hard to achieve with a reasonable size baffle. One can go almost an octave lower without getting crazy big. You just have to know the trade-offs.
No need for eye rolling, Charlie.
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