Midrange open-back vs. sealed-back - diyAudio
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Old 26th June 2013, 07:54 AM   #1
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Default Midrange open-back vs. sealed-back

Background: I'm considering a 4-way project, it will be an existing 3-way
cabinet with an added (sub)woofer in a separate box, one (sub)woofer
per channel.
The three original drivers will all be playing in passbands that are
nowhere near their resonant frequencies. This would be without
changing the original crossovers. All I'm really doing is stealing the
lowest frequencies away from the original woofer, thus turning it
into a low midrange.

Questions: If I understand this right, there will be no "tuning" box volume
requirements for each of the three original drivers. So, could I remove the
back of the original cabinet altogether ? Open-back midranges supposedly
sound "cleaner", but what is the price for this, is it lower power handling
before their max cone travel is reached ? Should the low midrange be
somewhat walled off from the upper midrange, even though they both
would be open-backed ?

General questions: If you increase the enclosed volume behind any
midrange driver that is not playing near its resonant freq, can you
predict what will happen to sound quality ? The larger you make the
enclosed volume, the closer you get to open-backed, so what is the
tendency of the resulting sound, does it keep getting softer yet
crisper/cleaner ?

Thanks much for any help and clarification !
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Old 26th June 2013, 08:22 AM   #2
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All I know for sure, is that you have to take reflections from the wall behind the speaker into account.
When I tried an open midrange chamber, I had to many reflection, because my speakers where to close to the wall of my room. This gave unwanted colorations in the midrange sound.
If you have alot of room and maybe more than a couple of meters to the rear wall behind the speakers in your listening room, then the reflection will be dealyed enough, so that the ear can seperate the direct and reflected sound, and chances for succes are bigger.
Dampening the rear wall is also an option, but this can be tricky to tune correctly in the lower midrange.
I learned it the hard way, that the listening room is a huge player when you try to judge performance of a particularly speaker driver in a specific cabinet design.
I play with a closed cabinet right now, with all my drivers, and is very happy with the sound.
I've heard good open designs, but they all had more space behind the speaker, than they had in front of it.

Last edited by Tordenguden; 26th June 2013 at 08:24 AM.
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Old 26th June 2013, 03:02 PM   #3
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Would be possible to do open baffle but with the added twist of dampening the backside and go cardioid. This would allow closer wall placement than OB. Heeding normal placement rules of course.


-----
Please correct me here if off.
Thx,
Mike
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Old 27th June 2013, 02:51 PM   #4
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Thanks guys. I'm leaning towards staying with sealed cabinet.
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Old 28th June 2013, 09:10 AM   #5
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But remember to make the cabinet as deep as possible. This will help to delay the reflections from the rear cabinet wall. These reflections "travel" back through the membrane of the speaker driver and hereby distorting the sound. Thats why a little to big is better than a little to small, especially when it comes to midrange cabinets. When well damped, the overall shape of the cabinet should be less important.
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Old 28th June 2013, 12:18 PM   #6
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by noslepums View Post
If you increase the enclosed volume behind any
midrange driver that is not playing near its resonant freq, can you
predict what will happen to sound quality ? The larger you make the
enclosed volume, the closer you get to open-backed, so what is the
tendency of the resulting sound, does it keep getting softer yet
crisper/cleaner ?
No, there is a limit. Too large of an enclosure might cause new problems.

Also the nearby open backed drivers isn't a perfect solution.
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Old 28th June 2013, 08:15 PM   #7
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Quote:
Originally Posted by Greebster View Post
Would be possible to do open baffle but with the added twist of dampening the backside and go cardioid. This would allow closer wall placement than OB. Heeding normal placement rules of course.


-----
Please correct me here if off.
Thx,
Mike
That approach works fairly well. The old '70s classic, the Dahlquist DQ-10 did that and managed to get surprisingly good midrange out of the Philips AD5060.

Click the image to open in full size.

Not a speaker for those who hear with their eyes, though.
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Old 5th July 2013, 09:41 PM   #8
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It was speakers like that which inspired me to design my own. With that infernal "I can do better" mentality... well at least it would look better
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Old 7th July 2013, 01:13 AM   #9
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For some of us the DQ-10 was an ear opener. We hadn't grown up with Quad ESLs in the house like some of you. Or Altec VOTT for that matter.
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Old 7th July 2013, 04:45 AM   #10
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Didn't have these things either. We did have stuff my father would build, until I entered the picture nothing was all that hifi but did sound well rounded in what it could do low level. When he designed our new home one thing he did was to have me install a 100 twisted pair, punch down blocks and all for future use (computers he's wouldn't shut up about . Intercom, whole house sound using IB speakers I designed for an 8th grade science project. That was '77

What we did have from an early age was the latest hightech. Open drum video recorder in '67, Calculator '70 for example. Most of my friends parents were engineers working at WrightPat R&D. Another, Roger Reihl, elementary school friend, father designed the worlds first solar digital watch (reihl time corporation). That was 1970 I think... anywho it wasn't that he did this first, but how he did this first. Their attic was converted into a cleanroon lab where pops made his own IC's from scratch! Now they all had they high end stuff I was exposed too.
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