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Old 11th June 2007, 08:37 AM   #1021
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For open baffle, I don't think that lightness of cone, and minimal voice coil inductance should be overlooked.

Did Fostex make a larger driver along these lines, which is then unsuitable for 'normal' cabinetted usage ?

Cheers ......... Graham.
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Old 11th June 2007, 04:31 PM   #1022
ScottG is offline ScottG  United States
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Quote:
Originally posted by Graham Maynard
For open baffle, I don't think that lightness of cone, and minimal voice coil inductance should be overlooked.

Did Fostex make a larger driver along these lines, which is then unsuitable for 'normal' cabinetted usage ?

Cheers ......... Graham.

This depends on the freq..

If the driver is limited to the bass region (<70 Hz), then its OK.

Beyond obtaining a suitable driver Fs - you actually want more mass as freq.s decrease (..otherwise the sound becomes "lightweight").

Here is a more suitable 21" driver:

http://www.shredmuzic.com/product_p/813-008.htm

Note that such a driver will place SERIOUS demands on the driver's support structure (..which should NOT be "hard" connected to other portions of the speaker).
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Old 11th June 2007, 06:35 PM   #1023
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Quote:
Originally posted by ScottG

Beyond obtaining a suitable driver Fs - you actually want more mass as freq.s decrease (..otherwise the sound becomes "lightweight").

Here is a more suitable 21" driver:

http://www.shredmuzic.com/product_p/813-008.htm

Note that such a driver will place SERIOUS demands on the driver's support structure (..which should NOT be "hard" connected to other portions of the speaker).
Certainly cheap enough, at $169. Nothing wrong with a Qts=1.0 at 31 Hz and a (claimed) linear Xmax of 0.75" either.

The required passband is the same as the triplet of 12" drivers - 80 Hz to 220 Hz, where it is intended to overlap with the 12" WR driver. No FR curve, so it's difficult to tell if it's going to need an aggressive lowpass filter or not.

The 338 gram cone gives food for thought. That's a lot of mass to swing back and forth in the 80 to 220 Hz range. The magnet will obviously have to have its own support strut, going to a rigid baseplate, and a pair of sand-filled buckets on either side of the baseplate would be a very good idea. Maybe even put some lead shot in the bottom of the buckets while you're at it.

The difference in cone masses is the most obvious difference between the 3 x 12 and the single 21". Typical masses for the 3 x 12 is around 120 grams, while typical values for 21" drivers seems to be in the 300~340 gram range. That's not a small difference - and all of that is transmitted as reaction forces to the rest of the OB structure. The rear strut, which bears the magnet weights, is going to have to be well-engineered - strong, resonance-free, and low emissive area.
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Old 11th June 2007, 08:31 PM   #1024
Pano is offline Pano  United States
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Quote:
Originally posted by ScottG
...you actually want more mass as freq.s decrease (..otherwise the sound becomes "lightweight").
I've often read and been told that, but why?
Does the large mass of the cone move the air "better?"
Is the extra inertia needed to give the bass more subjective "weight?"

The moving mass of the 21" Madison would be the equivalent of about 270L of air. Or 9.5 cubic feet.

Is that mass needed to launch a good, solid wave? Would a lighter cone not do as well? Is the higher energy in the heaver cone thus imparted to the air?
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Old 11th June 2007, 09:55 PM   #1025
mige0 is offline mige0  Austria
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Hi

Quote:
Each of us pursuing individual goals just zooms in a portion of the picture. But some still have the veteran character control not to forget that the goal must be the total picture (music) and not specific technical perfection. Its a twist. We don't seek music many times when making stuff. We seek technical achievement. We get to like the sound of 'technique'. Real danger is that we may get to feel that it is the real thing, and become addicted. We are perverts many times. Its part of the game, but at a point we can get over it. And we have a powerful tool for waking up. Boredom! Non natural may succeed feeling even great, but at a point we get sick. Its like eating in fast food chains only, for too long.


salas,
I agree 100% - especially the point with boredom as a cure for us technophile addicted made me laugh out loud really great frame!




Quote:
There is one XTA DP 226 for $1400 on e-bay right now.
Seen on a bigger scale, the revolutionary thing about the DCX is its price. This was the very first DSP device that told us that sophisticated XO audio processing can be really cheap.
Copy the concept - throw in caps that do their job - a power supply that works use less hot melt glue but ribbon wire connectors that don't fail - and set the auto router to "audiophile mode" and Behringer could launch a smashing next generation DSP-XO unit for around 50.- 100.- more expensive than the old one. This is what I would like to see also from other companies like DBX, XTA...






fiacono,
an other candidate for your list ? :

http://www.precisiondevices.co.uk/as...s/super/17.pdf
"http://www.precisiondevices.co.uk/asps/uploads/super/17.pdf"

maybe it would give an additional insight to also look at the division of moving mass against force factor ( B*L / Mms ) . This gives a clue about the limitation of acceleration.





Quote:
just to set the record straight -
MBL,
sorry that I got you wrong, thanks for correction and also for the links!

I would have been happy to have the Griesinger paper at hand, when I installed a low cost LARS "equivalent" system in a cinema several years ago.
Cinema acoustic is dictated by the needs of artificial control of room perception in other words: relative highly damped room with relative short RT60 and lots of surround speakers to achieve any acoustic ambience at the movie art directors will.

This works great for movies and in fact is one of the biggest benefits of the THX "standardisation" but does NOT work well for lecture or live music for silent movies.

Reverberation of the main mic's in such cases is OK but not really sufficient. You still HEAR the dead room giving a feeling of isolation.

What worked great is to mount a boundary mic into each side wall and play their reverb signal through the surround speakers. It is not that complicated to balanced towards a concert hall sound by ear, while preserving really good intelligibility.
Apparent source width ASW increases dramatically that way.

All what was needed were two low noise mic's (AKG C 562 CM ), an additional - fairly good - reverb ( TC M-ONE ) and a mixer to change room acoustic with the push of a button.


Greetings
Michael
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Old 11th June 2007, 10:30 PM   #1026
mige0 is offline mige0  Austria
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Hi

ScottG,
this 21" is one of the few that hits the price versus displacement volume relation of the Peerless SLS 12 (assumed that Xpp linear is > 7 mm) !

Do you think it is available also in Europe?

Greetings
Michael
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Old 12th June 2007, 12:19 AM   #1027
ScottG is offline ScottG  United States
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Quote:
Originally posted by panomaniac


I've often read and been told that, but why?
Does the large mass of the cone move the air "better?"
Is the extra inertia needed to give the bass more subjective "weight?"

Is that mass needed to launch a good, solid wave? Would a lighter cone not do as well? Is the higher energy in the heaver cone thus imparted to the air?
I'm not sure why this is.. chalk it up to one more of those "voodoo" things that makes loudspeaker construction as much an art as a science.

I believe Freddyi (who infrequently posts here, and more on the Hi Eff. board of the Audio Asylum) has either this woofer or one similar to it. In fact on the Hi Eff. forum he had (at one time) posted a measurement of the driver in an open baffle configuration.

IMO its strictly a "helper" woofer to reinforce (as an open baffle dipole) the bass freq.s. It WILL require a LOT from the pairing amplifier (current-wise), so in effect - do NOT consider it unless you are going "active".

I doubt the driver will ever be distributed (as a component) in Europe. When I purchased my Knight 10's from them they didn't even offer shipping outside the US, perhaps thats changed now?

Personally, I'd stick to the Rythmik Audio subs (..in an aperiodic enclosure OR a vented config. similar to what I recommended earlier on.. but NOT a sealed design). Its already "active", it goes lower at higher spl's, and there is no real compelling reason for a dipole at lower freq.s.

Looking at the spec.s of drivers - my OB midbass driver of choice (preferably 2X16 ohm drivers connected in parallel), is still the Jensen Neo 15-150. Its simply MUCH more efficient than other offerings EXACTLY WHERE ITS NEEDED, while having extraordinarily low mms for its sd (..for details and delicacy with the right amplifier - i.e. like the kind Lynn has). It also has its fs in the right place for such a design when considering its use in open baffle and its Qts. It does however need an appropriate low pass filter.

When I factor in cost and other attributes this is what I'd propose:

Esthetically similar to the Ascendo System M:

http://www.ascendo.de/english/frameSW.htm

Top down:

Top Module:

OB 175 mm's wide, 750-800 mms "tall" (height dependent on tweeter size).

4 PR170MO's in a vertical line.

..immediately below that:

A High eff. tweeter of choice (the Audax "line" gives you some options here because you can either cross at a lower freq. OR at a higher freq.). Though more costly, I'd choose the Aurum Cantus G1 at a lower freq. (close to 2 kHz). There are however MANY options available - including the recently mentioned Beyma Heil driver OR even the Hi Vi RT8-II that Gary Pimm uses (..as a low cost, yet low crossover capable driver).

Bottom Module:

OB 425 mm's wide, 850 mm's "tall".

2 16 ohm Jensen Neo 15-150's in parallel vertically mounted.

The surrounding "box" for this bottom module could be a cloth or perforated (yet dampened) metal panel(s) or a metal mesh.

Crossover design to suit the drivers (..Lynn's specialty, not mine. .)

Not a "small" loudspeaker.. and there is still the lower freq. to contend with. On the other hand it should be exceptionally "clear/transparent" with a very low compression character, while still being stunningly "dynamic".

Oh well, just my current thoughts - which are always subject to change..
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Old 12th June 2007, 12:42 AM   #1028
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by panomaniac


I've often read and been told that, but why?
Does the large mass of the cone move the air "better?"
Is the extra inertia needed to give the bass more subjective "weight?"

The moving mass of the 21" Madison would be the equivalent of about 270L of air. Or 9.5 cubic feet.

Is that mass needed to launch a good, solid wave? Would a lighter cone not do as well? Is the higher energy in the heaver cone thus imparted to the air?
There air force on large cones are large enough that the cone has more air resistance such that you either need a strong motor to drive the cone completely, or you need cone interia to fight the air resistance to get more travel. I recall the resistance increases proportional to the squared velocity, this actually makes light cones act like they are soft clipped.

I think most heavy cones are also stiffer, so it cam maintain the same amount of air being pushed as in the beginning of the travel.
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Old 12th June 2007, 08:34 AM   #1029
el`Ol is offline el`Ol  Germany
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There is a guy at a german forum who removed the whizzer of a Beyma 12" fullrange driver and was very pleased with the result. He said all the sharpness was gone. The price was the need of a supertweeter, off course. For people like Lynn, who don`t like midrange compression drivers, this is probably a better solution than a coaxial with 1.5 kHz x-over, and it is closer to the Bastanis solution. And a crossover that is close to the 2kHz region where the human ear is most sensitive is problematic anyway.
By the way, I also thought that compression drivers are better kept away from the midrange, until I listened to the Martion Orgon at the Highend in Munich this year.
A question to Lynn: what compression midrangers did you hear?
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Old 12th June 2007, 08:51 AM   #1030
mige0 is offline mige0  Austria
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Hi

Quote:
and there is no real compelling reason for a dipole at lower freq.s.


I agree on the very first and obvious level of listening effects.

On a more closely examination there is a subtle interaction between the room and the loudspeaker in it.
Any box with a hole ( = the speaker ) basically also acts as Helmholtz resonator.
"The Scottish company" brought that into the mind of all audio people by their strictly policy of single speaker demonstration several years ago.

But sadly I can not compare from own experience now.


What makes the difference that you rate aperiodic over closed with the Rhytmic Audio subs?


Greetings
Michael
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