push-pull design

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fwater said:



Jeff Bagby's Box Modeller 3.20 shows differently. In some (maybe many) cases, the f3 will appear similar in numbers, but the Qts is different for either wiring, even if you're using the same volume. The curve also appears different, the rolloff often having a hump or sometimes a more "rounded" bottom. The volume requirement for similar output isn't exactly 50%, more like 60-70. I can't recall exactly why this is, maybe someone a little more well-read will jump in.
You might want to get that clarified before assuming it is correct. If you mis-size the box you will get incorrect results that may need a rebuild to correct.

I don't have time to re-do all the math now, but I found this with a quick google search from a company that makes T/S testing kit.
See under "Multiple Driver Tests"

I see no reason for there to be a difference.
 
Brett said:

That sounds like isobaric.

I guess that depends on one's definition of isobaric, when it first appeared on the market the Mani-2 was not typically referred to as an isobaric design by reviewers because Totem had the midbass drivers mounted magnet-to-magnet in bipolar fashion instead of the more common cone-to-magnet isobaric configuration but it's not a bipolar because there is no rear baffle, the second midbass driver is sealed inside the cabinet.

So here we have both drivers bass-loading the same chamber. However this speaker is now commonly called isobaric, perhaps because there seems to be no clear definition of what constitutes an isobaric configuration.
 
hm. i've been looking at the micromain posted up there again.. the enclosure definitely doesn't seem big enough for the 2 huge woofers.. however they said they just mounted the motors together, i thought that would cancel all the bass? that design is a whopping 3grand.. man. i think big =P
 
nukaidee said:
is a drinking straw strong enough to allow for resonance?

Lol I wasn't being serious, I cannot conceive of a 0.5 inch diameter port that would emit any usable bass unless you have several of them. Even though it is very possible that a vent calculation formula could yield such dimensions, these results are not always practical in reality. Such a tiny tube would have huge resistance and bottleneck air movement to such a point that the system would behave like a sealed speaker.

ProAc did use drinking straws in at least one of their models, the Response 2, but there were hundreds of them stuffed into a much larger port.
 
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Willitwork said:
However this speaker is now commonly called isobaric, perhaps because there seems to be no clear definition of what constitutes an isobaric configuration.

Sure there is. iso-barik = constant pressure. A 2 driver arrangement where the front driver sees constant pressure (above the roll-off of the back driver), Tiefenbrun got a patent, so it is pretty well defined.

dave
 
no point making the port half the size i want my box to be right? and the bigger the port.. the longer the tube and .. yeah. doesn't work.

continuing on with isobarick.. i know about the constant pressure, so if i am mounting them in phase, motor to cone ... does the front or the back one need the 1/2 volume while the other one needs the smallest air possible?
 
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How small is your box really
Sounds like its VERY small
Not sure what strange things may happen when the volume between the drivers begins to be equal size of the box volume...not sure I would rely on calculations if thats the case and on that to work properly :confused:
 
nukaidee said:
no point making the port half the size i want my box to be right? and the bigger the port.. the longer the tube and .. yeah. doesn't work.

A tube port of any size is not always practical especially in smaller enclosures but that doesn't mean porting can't be done using, for example, a slotted port built into the cabinet's internal structure.

These ports are usually the same width as the front or rear baffle, tuning is done by varying the height of the slot and the thickness of the baffle and size of internal braces provide depth. Many high-end bookshelf kits use such ports and more than a few large speakers as well. It's too costly for mass-produced cabinets but not much more work for DIY'ers, and it makes for a studier box.
 
nukaidee said:
umm.. then how does the sound come out? its just like placing the drivers facing each other, wont that muffle everything? from what I am reading here, there are many ways to mount it. http://www.audiogearreviews.com/tech/theory/enclosure_design/isobaric.asp

and I'm guessing that isobaric only works for subwoofers and not particularly good for the high ends.. maybe I will mount my subs like this and use a stand alone tweeter.. usually tweeters don't need a big volume right? maybe I can just place one on top like something sticking out?

I built my first succesful iso (clamshell design)
I am using 2 MTX 5500 12" subs in a 3.5 cubic sealed box
Win isd comes back with "down 9.75 db 20-100 hz"
I mounted the drivers on top of the cabinet and put it in in cornor .
It goes real good !
 
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