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Old 15th February 2014, 03:25 AM   #31
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You know your stuff!

Quote:
Originally Posted by Joseph Crowe View Post
Yes isobaric will also work with the onken enclosure thus reducing the required internal volume to half. The other benefit is that the effective Fs of the drivers is cut in half so for example if your pro audio drivers have an Fs of 40hz, you would now have an Fs of 20hz! There is no free lunch though. With a traditional dual onken each drivers efficiency is combined so 92db x2 = 95 Db. But with an isobaric configuration your looking at 92 Db /2 = 89 Db. Which is why you don't see it used in pro applications. However for home theater it's perfect. Save space, get deep bass, and class d power is cheap. Isobaric does have another advantage too which is lower distortion, especially if the drivers can oppose each other, thus cancelling out the physical non linearities in the cone's travel. Also any non linearities caused by poor motor design will be overcome, so bad drivers tend to sound their best aka cheap inexpensive drivers on clearance from parts-express.
Ahh, the language of happiness to me!

Just so it's unnecessarily clear, you say opposing and I say push-pull, meaning the same thing.

I went out on an unproven limb on a whim and actually made quadruple opposing drivers. Two of the drivers are push-pull magnet-magnet, the other pair is push-pull cone-cone.

I have yet to determine if it actually helped to further decrease distortion. The result of the dual opposing pairs--whether or not there are benefits beyond a single opposing pair--was not immediately evident.
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In one thousand years, will they still be called the Thiele Small parameters?
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Old 15th February 2014, 11:15 AM   #32
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When I say apposing I mean either back to back or front to front. Some designs are back to front ,like standing in a lineup for example. The other thing is that isobaric doesn't require identical drivers. You can even use the next size down if that simplifies cabinet construction.

The mass of air trapped between the two drivers contributes to lower the Fs. I would think magnet to magnet would allow a larger air mass thus an even lower Fs, but we are talking only a few Hz as compare to cone to cone.

My father has a sony push pull subwoofer (sa-wx700) that is very clean sounding and goes very low. Another great design although not isobaric.
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Old 15th February 2014, 04:08 PM   #33
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Quote:
Originally Posted by Joseph Crowe View Post
When I say apposing I mean either back to back or front to front.
Exactly, that is precisely what I mean by push-pull. When drivers are apposing, one is pushing in the instant the other is pulling. Forgive my slip of interchanging apposing with opposing, it was late last night.

Quote:
Originally Posted by Joseph Crowe View Post
Some designs are back to front ,like standing in a lineup for example.
Right, so those designs wouldn't be push-pull. The only reason for confusion I can see is you can design a push-pull speaker without isobaric alignment, for example with two radiating drivers in a single enclosure, one being turned "backwards" in relation to the other. This is also considered push-pull. I have adopted most of my terms from this website Audio Innovation - by Dan Marx www.danmarx.org And Vance Dickason calls it push-pull isobaric too I believe in his book.

Quote:
Originally Posted by Joseph Crowe View Post
The other thing is that isobaric doesn't require identical drivers. You can even use the next size down if that simplifies cabinet construction.
Until now I have only heard the opposite of this. I've always read you must use identical drivers, otherwise you may get the worse of both. Also, if you link a 21" driver with a 15" driver, the 21" would have it's effective xmax cut in half. I can't imagine very many if any instances where mis-matching drivers is a good thing, but I would love to be enlightened if you know otherwise.

Quote:
Originally Posted by Joseph Crowe View Post
The mass of air trapped between the two drivers contributes to lower the Fs. I would think magnet to magnet would allow a larger air mass thus an even lower Fs, but we are talking only a few Hz as compare to cone to cone.
This is true, and honestly may be the source of my disappointment. I have been evaluating the cost and effort of switching the cone-cone pair around for dual magnet-magnet pairs. Then I saw the cubo sub design and noted it would be extremely easy--virtually free--to do cone-cone isobaric alignment. As to boot, the drivers can be flipped either way in the cubo designs.

I think another dissatisfaction may come from the xo I am using. It's currently a Radio Labs stick on, I think much could be gained from using a driverack or similar speaker management.

Quote:
Originally Posted by Joseph Crowe View Post
My father has a sony push pull subwoofer (sa-wx700) that is very clean sounding and goes very low. Another great design although not isobaric.
Cool!
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Last edited by Thetwinmeister; 15th February 2014 at 04:11 PM.
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Old 15th February 2014, 07:38 PM   #34
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Darn, the B&C DE120 is out of stock until 3/20/2014.

In the mean time, I don't think I will be able to pursue an onken enclosure due to height increase requirements. Assuming the box compliance remained the same, (which it won't) I would still have to add several inches to the height of my already huge box. It is barely just not too big as it is. Attached is a photo with the grill removed to demonstrate the tight spacing of the 18" driver. Maybe I could downgrade to 15" and keep the same box size, but I really don't want to lose SD. I already get plenty of depth from this isobaric configuration, so porting isn't precisely advantageous to me.
Attached Images
File Type: jpg sub no grill small.jpg (130.6 KB, 49 views)
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Old 16th February 2014, 12:42 AM   #35
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Found this: "Push-pull drive is particularly attractive when used in a horn subwoofer. The front chamber and mass-rolloff tend to reduce third and higher harmonics. Push-pull drive reduces the second harmonic. This in addition to the already low distortion due to reduced excursion from horn loading. Horn subwoofers with push-pull drive offer excellent low-distortion performance even at very high power levels."

Here: AudioRoundTable.com: Pi Speakers => Push-pull verses shorting rings

The cubo design looks even more attractive, although I think the designer does not claim it is an actual "horn" but simply calls it a "hybrid." What he means by that is not something I am aware of.
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Old 16th February 2014, 01:46 AM   #36
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The cubo concerns me because the back of the driver is exposed which would cancel out any sound waves that are longer than the length of the horn.
The b&c website has plans for a similar design type horn but they've wisely enclosed the back of the driver. This design gives good extension down to 40hz.
I've learned a lot from studying various manufactures suggested designs. They know what they are doing.
http://bcspeakers.s3.amazonaws.com/2...15/57/205/file

Fostex includes plans with their drivers and they are in Japanese, but man they seem to have an attention to detail and at first you wonder what the heck they are doing but then it all comes together. Unfortunately they are not available online.

I ordered my DE120's and the ME20 horn together because b&c added special mounting holes to that particular horn special for the de120 since it's so small. It's a tiny little thing, but it sounds marvellous.
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Old 16th February 2014, 02:53 AM   #37
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Quote:
Originally Posted by Joseph Crowe View Post
The cubo concerns me because the back of the driver is exposed which would cancel out any sound waves that are longer than the length of the horn.
Your concern is duly noted.

Looks like research needs to be done. In the near future I will put my spare time towards understanding the cubo designs.

Today I spent a lot of time evaluating the PPSL design concept. Interestingly enough, it would be possible to apply my 4 18" drivers towards a dual isobaric pair PPSL onken hybrid alignment. Just combine all the things!

Apposing isobaric + PPSL is redundant. There seems to be a lot of advantages to PPSL but I still favor isobaric at the time of this posting.

Quote:
Originally Posted by Joseph Crowe View Post
The b&c website has plans for a similar design type horn but they've wisely enclosed the back of the driver. This design gives good extension down to 40hz.
I've learned a lot from studying various manufactures suggested designs. They know what they are doing.
[url]http://bcspeakers.s3.amazonaws.com/2013/02/12/16/15/57/205/file[/url
Actual horns tend to be too big. The "hybrid" cubo seems an appealing compromise.

Quote:
Originally Posted by Joseph Crowe View Post
Fostex includes plans with their drivers and they are in Japanese, but man they seem to have an attention to detail and at first you wonder what the heck they are doing but then it all comes together. Unfortunately they are not available online.
Interesting, I will keep my eye out. Random fact: I speak a decent amount of Japanese, but reading is another ball game: Kanji

Quote:
Originally Posted by Joseph Crowe View Post
I ordered my DE120's and the ME20 horn together because b&c added special mounting holes to that particular horn special for the de120 since it's so small. It's a tiny little thing, but it sounds marvellous.
I'm looking forward to hearing it! Come the restock date a pair should be headed my way.
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In one thousand years, will they still be called the Thiele Small parameters?

Last edited by Thetwinmeister; 16th February 2014 at 03:01 AM.
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Old 17th February 2014, 03:24 PM   #38
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There are response graphs for the Cubo in the forum pages on freespeakerplans, I don't think it can be considered to be a horn as it's just too small but it delivers the goods regardless. I was curious about it so I built a 15 extended version last fall with a driver I had in a reflex box and sure enough it's about 3-9db more sensitive between 35hz and 100hz.
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Old 17th February 2014, 03:43 PM   #39
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Quote:
Originally Posted by conanski View Post
There are response graphs for the Cubo in the forum pages on freespeakerplans, I don't think it can be considered to be a horn as it's just too small but it delivers the goods regardless. I was curious about it so I built a 15 extended version last fall with a driver I had in a reflex box and sure enough it's about 3-9db more sensitive between 35hz and 100hz.
Thanks for the feedback! Did you notice any audio quality differences with the cubo vs the reflex box?
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Old 17th February 2014, 08:41 PM   #40
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Response is somewhat peaky with the Cubo so it will require more EQ to flatten. There are 2 driver loading options too, frame out or cone out and each one produces a slightly different response. I have not had a chance to measure it cone out but my ear tells me that config produces a smoother response.. in my listening room at least. I noticed both the cubo and reflex box have a similar peaky response when I measured them originally so obviously the room is affecting things.
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