I can only speculate. It certainly would have to do with complexity of construction. And maybe, just maybe, the lowering of the motor strength and compliance of their later drivers. When you've got something with a reasonably low Vas and a high Qts (like too many of the later Dynaudio drivers), there's no real advantage to isobaric loading, just expense.
If you ever happen to run across some old Dynaudio DA-500s, grab them. These are probably the best isobaric speakers I've ever heard.
kensetsu said:
This one is quite interesting... it is a very low efficiency design thou.
Having built & lived with isobarik speakers i always felt there was more benefit than just the halving of the Vas... the back driver, IB, isolates the radiating driver from the box. A push-push isobarik is quite a complex beast, i have a sketch somewhere from 20-some years ago showing what would be required. The push=push in this configuration would yield a monopole with active vibration cancelation -- which may well be the big gain in this design since the aperiodic loading of the rear driver would in itself act as pressure relief. A properly done aperiodic box has good technical merit, having the flattest and smoothest 1st derivative of the impedance curve.
The use of mids with no XOs is, in spirit, in-line with my mostly full-range approach to speaker design...
This i have heard and IMHO is another one of Bob Carver's smoke & mirrors products...
dave
planet10 said:
Just curious as to why you think that a .5 driver is best at the back of the box. In this frequency range, you're probably in an omnidirectional pattern anyway. The wavelengths are long enough that the driver is and the relative distance between the front and back of the cabinet to walls is not so drastically different in wavelengths. And inside the box, the wavelengths are too long to be concerned with delayed reflections.
planet10 said:
It's aperiodic loading if it vents from the inside of the box to the outside. But in the Dynaudio speakers, it went between the two speakers in the isobaric; it was attached to a board which fit over the face of the inner driver. The overall isobaric was a sealed design.
FWIW, the Dynaudio design used a smaller driver on the inside (30W5412 on the outside, 21W5412 on the inside).
pooge said:
In an x.5-way speaker the low frequency driver is rolled off 1st order at the baffle step. This filter causes the driver to roll thru 90 degrees of phase shift. The driver that goes up to meet the tweeter does not -- so the two drivers are out of phase.
If the LF driver is placed on the back of the box, this phase roll is hidden in the shadow of the box. Further, since it is on the back of the box, you can take advantage of that to load the drivers push-push and use the active vibration cancelation to improve downward dynamic range and reduce the transmission of driver vibration to the box.
As well by placing the drivers on the back you guarantee perfect BSC (as long as the XO is at or above the BS frequency and the box has a width-symetric shape)
dave
SY said:
Gotcha... it wouldn't be called a variovent in that application -- it is simply damping material used to kill off some of the HF stuff to extend the usable upper range -- the Linn isobariks had similar (wool inbetween to cloth sheets). When i was building isobarics i'd trim up a piece of acoustic damping foam and fit it over the magnet of the front driver and kept the inner chamber as small as possible.
dave
It may n ot be a variovent, but it was indeed a Variovent (in the sense that it was the specific plastic'n'fiberglass dealie that Dynaudio sold). IIRC, "Variovent" is a Dynaudio trademark.
In any case, yes, its use was for lowpass filtering, but I would not be surprised if it also didn't have an effect on the driver damping, much like the old trick of putting tight-weave cloth on the back of a driver basket. I've still got a pair of these asymmetrical isobarics in my garage. If the weather moderates a bit so I can actually work in there (over 100F yesterday!), I'll run a quick impedance curve and see if my hypothesis is correct.
In any case, yes, its use was for lowpass filtering, but I would not be surprised if it also didn't have an effect on the driver damping, much like the old trick of putting tight-weave cloth on the back of a driver basket. I've still got a pair of these asymmetrical isobarics in my garage. If the weather moderates a bit so I can actually work in there (over 100F yesterday!), I'll run a quick impedance curve and see if my hypothesis is correct.
Well I'm assuming your talking about Carver's True Subwoofers. They use circuitry to overcome physical limitations. They use a variant of the shelving circuit. Linkwitz Transform is close. May not be kosher to some, but it is effective.
Course they also made the Amazing loudspeakers, those were "different", but many poeple swear by them.
Course they also made the Amazing loudspeakers, those were "different", but many poeple swear by them.
isobaric subwoofers
There are a lot of good and bad reasons to use any technology for a conmmercial product. The Eggleston hype reads like most high end copy, targeted at the insecure and making a lot out of not much. (I have done more of this myself than most manufacturers so I know of where I speak). He has done his copy well. (And too many reviewers listen with their eyes to be trusted with your money.)
For an engineering driven project without a big R&D budget (read DIY) going with known successful solutions can save a lot of heartache and wasted time and money. Go one step at a time.
For the record I have also used the spaced "isobaric" design in a commercial product that works very well: www.element.us.com ,but I have also been very involved in a line of conventional subwoofers, mostly ported, that also work well for Monster Cable (soon to be released).
My reaction to doing both at once is to look at the the desires of the target end user. Very high accuracy and low coloration will take you in one direction, huge dynamics and window shattering levels will take you in another. Its all compromises and the real art of engineering is balancing compromises.
-Demian
There are a lot of good and bad reasons to use any technology for a conmmercial product. The Eggleston hype reads like most high end copy, targeted at the insecure and making a lot out of not much. (I have done more of this myself than most manufacturers so I know of where I speak). He has done his copy well. (And too many reviewers listen with their eyes to be trusted with your money.)
For an engineering driven project without a big R&D budget (read DIY) going with known successful solutions can save a lot of heartache and wasted time and money. Go one step at a time.
For the record I have also used the spaced "isobaric" design in a commercial product that works very well: www.element.us.com ,but I have also been very involved in a line of conventional subwoofers, mostly ported, that also work well for Monster Cable (soon to be released).
My reaction to doing both at once is to look at the the desires of the target end user. Very high accuracy and low coloration will take you in one direction, huge dynamics and window shattering levels will take you in another. Its all compromises and the real art of engineering is balancing compromises.
-Demian
Demian,
The Entec's "Big Mamu" looks very cool what kind of woofers implementation does it use. Also, why are the smaller drivers mounted almost on the floor does that cause a problem.
I just can find an advantage to the Isobaric nor can I see that need from an engineering stand point. If want bass that super low BAGE-END woofer proved you can do that with out multiple drivers all you need is the electronic crossover with a lot of gain to defeat the roll off, of course that very simplistic.
Dave,
I have never heard the Linn Isobaric where I though they sound good. However, it was always in a show room.
-----------------------------------------------------------
Sometime the simplest way is the best way.
The Entec's "Big Mamu" looks very cool what kind of woofers implementation does it use. Also, why are the smaller drivers mounted almost on the floor does that cause a problem.
I just can find an advantage to the Isobaric nor can I see that need from an engineering stand point. If want bass that super low BAGE-END woofer proved you can do that with out multiple drivers all you need is the electronic crossover with a lot of gain to defeat the roll off, of course that very simplistic.
Dave,
I have never heard the Linn Isobaric where I though they sound good. However, it was always in a show room.
-----------------------------------------------------------
Sometime the simplest way is the best way.
Woofers
The Entec woofers were all direct radiator sealed boc with a position servo and electronic eq. The Element woofers are modified isobaric with extra volume between the drivers. They also have seperate amps for each driver. They have no eq and are flat to 23 Hz (a good reason to play with an isobaric, but the box mods are a bear).
The Bag End woofer is very similar to the Entec without the servo. The cabinets tune the drivers near the top of the range and lots of EQ and amp power flattens them. Not a bad solution and the newer car drivers can withstand the abuse.
-Demian
The Entec woofers were all direct radiator sealed boc with a position servo and electronic eq. The Element woofers are modified isobaric with extra volume between the drivers. They also have seperate amps for each driver. They have no eq and are flat to 23 Hz (a good reason to play with an isobaric, but the box mods are a bear).
The Bag End woofer is very similar to the Entec without the servo. The cabinets tune the drivers near the top of the range and lots of EQ and amp power flattens them. Not a bad solution and the newer car drivers can withstand the abuse.
-Demian
planet10 said:
I remember this too. I even tried to duplicate this an build isobariks for my car where box volume IS an issue. what i noticed is that while isobariks work well in the bass they tend to muddy up the midrange atleast the speakers i constructed did that. so they were really only useful below say 100/120Hz.
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