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Old 12th June 2007, 04:46 PM   #1031
Hartono is offline Hartono  Indonesia
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Quote:
Originally posted by soongsc


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.

Hi Soongsc,

probably there's a lower limit in the supension (spider, surround) compliance, to soft/flexible compliance and the driver might sags, and to reach lower frequency one has to depend on the mass of the cone.

I've heard multiple ceramic (stiff) cone driver showing huge amount of bass and large PA driver as well, what I notice is, with lower power amp (100 watt), we couldn't get the "punch" but the bass sounds very good and have good resolution.

one the other hand, normal speaker, even small ones when driven by large power amp (300 watt++) shows more punch, probably the "punch" came from : the amp lower bandwith limit(governed by input coupling caps) , or an intermodulation distortion inside the amp itself. when asked to deliver huge amount of power, the ground bounce in the circuit and the charging pulse of the capacitor might cause this "punch".

Edit: Everything else equal heavier cones have lower efficiency compared to light cones, and probably also has less real amp-speaker interface damping and need more power to drive. this might contribute to the sound as well.


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Old 12th June 2007, 07:08 PM   #1032
ScottG is offline ScottG  United States
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Quote:
Originally posted by mige0



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


Greetings
Michael
In effect its all about controlling the driver at resonance.

In an aperiodic design you are basically targeting the driver's in-box resonance. This gives greater control at and near that region. The "price" to be paid is higher compliance distortion below resonance, but hopefully the servo system and driver (in tandem) are better than other offerings at these lower freq.s.

In a vented system with a *very* low tunning freq., (at *least* an octave below the in-box resonance and preferably an octave and a half), the vent effectively loads the driver and dampens it (..and not at just the driver's in-box resonance - and in this respect its rather like a poor servo). The lower vent freq. virtually ensures that the vent "operates" for a much greater passband than a normal venting "alignment". The price to be paid here is some additional compliance distortion (though less than an aperiodic and sealed), and greater vc heating. Additionally the actual vent resonance is cr@p, but presumably its down so low (both in freq. and output) that there is little detriment for most recorded material. The "upside" to this is some additional freq. extension (above the vent tunning freq.) & believe it or not, better time decay for both the driver and the vent (..except near resonance).

Unfortunately BOTH systems (when utilized properly), require larger enclosure volumes than either traditional vented or sealed designs.
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Old 12th June 2007, 09:52 PM   #1033
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I have been puzzled by a couple of the recent postings about LF drivers.

Cone weight surely relates to strength and rigidity for generating SPL whilst maintaining low system resonance when acting against any cabinet managed air-spring, not a deliberate intention for creating cone inertia ?
Inertia is stored energy, and this needs to be minimised in order to improve reproduction accuracy.

"Punch". Is this not an entirely false and undesirable characteristic caused by the heavier cone LF drivers being capable of generating considerable initial air-spring pressure in small sealed systems when powerfully driven by NFB controlled voltage drive at a sub-resonant frequency (initial drum kick or bass string pick), the stored energy of which then modifies/transforms the waveform due to loudspeaker system resonance after the initial empowering peak has passed ?
"Punch" does not arise with aperiodic or baffle LS systems, so these are of no use to ICE boomers.
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Old 12th June 2007, 10:14 PM   #1034
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"Punch" - hmm, that's an interesting one.

Small diaphragm speakers try, but don't quite succeed. I really think surface area has a lot to do with it - and oddly enough, line-radiators just sound wrong to me, weird somehow. There's a certain phasey quality that I'm very sensitive to - all those years working with quadraphonics and twiddling with high-order crossovers that were misaligned.

But big horns and arrays of LF drivers do sound big, in a realistic way. It's not so much "punch", which I suspect for hifi reviewers is a certain artificial quality of overdesigned minimonitors, but a big, solid, tactile quality. Back when I lived in Silverdale, I had a hifi friend named Gary Dahl, who played a full set of concert-quality tympani drums in the local symphony. Man, you stand 2 feet when those when he ran through his practice drumming, and you feel it, even though it didn't sound that loud. Everything else in the room was jingling and rattling along, but it still didn't sound all that loud, nothing like a PA or hifi system.

That's what I'm aiming for with this system (along with a classical-music tonal balance and a you-are-there spatial quality). Those of you who know drummers know how rare it is for hifi systems to get that part right - it sounds loud, all right, but the tactile quality isn't there. That's why I suspect magazine hifi reviewers don't really know what live, acoustic music sounds like - the sheer dynamism and bright, shimmering tone colors almost never happen with audiophile equipment.

P.S. Thanks, ScottG, for the reminder about the Jensen Neo 15-150. Not much Xmax (+/- 2mm), but the Q and Fs are just about right. A Midbass/Bass array of three of these things, in the delta pattern shown on Post #940 would certainly have the kind of tactility I've been talking about.

As you can see, I keep trying to drag things away from audiophilia, more towards horn dynamics, but not an all-horn multiway system. There's a fairly empty region in the audio ecosystem halfway between audiophile line arrays and prosound horns, and that's where I want to go.
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Old 12th June 2007, 11:23 PM   #1035
ScottG is offline ScottG  United States
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"Punch" is a descriptor relating to the physical sensation occurring around the body's abdominal cavity resonance (i.e. the upper bass low midrange area 65-90 Hz). Its a concussive feeling in your gut - hence the "punch" appellation (..as in "punched in the gut").

High force, moderate to high mass drivers, in a moderately small sealed cabinet - seem to provide this sensation the best. However, its still a matter of force vs. mass vs. radiation ("forward directed" toward the listener offering the greatest sensation). This means that even small sd drivers can provide this sensation. Similarly, aperiodic and OB designs can also provide this sensation. It is however, a matter of "degree".

(example.. ask Paul W about the subjective difference in sound between his single BMS 18 inch driver vs. 2 10" Al/Mag Excel drivers.)

One notable attribute to this sensation is that exciting a room mode at this freq. (in anything but a very small room) does NOT enhance the sensation (rather it lends a "boomy" character to the sound if substantially elevated). Boundary gain does enhance this though.

All of the above is different than the subjective descriptor: Slam (..which is a lower freq. sensation and IS related to room modes and gain).
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Old 12th June 2007, 11:32 PM   #1036
Salas is offline Salas  Greece
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Think about the 130Hz region. There lies average size chest resonance and there is where 'punch in the chest' is being experienced.
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Old 12th June 2007, 11:38 PM   #1037
ScottG is offline ScottG  United States
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Quote:
Originally posted by salas
Think about the 130Hz region. There lies average size chest resonance and there is where 'punch in the chest' is being experienced.
Yeah, thats a "hit and miss" thing.. one source says one thing, another says something else. I think the difference between the two is where the "listener" experiences it the most.. I.E. while the cavity resonance may well be 130 Hz for an average adult, this may not be the freq. for the greatest physical sensation.
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Old 14th June 2007, 12:48 AM   #1038
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Default Lambda Woofers...Acoustic Elegance

I used 50 Lambda woofers some years back because they just sound right. John Janowitz, the owner of Acoustic Elegance in GreenBay is said to be re-starting production of the Lambda line this summer. Following the philosophy of this thread with Lambdas, I would probably construct a 15"h * 0.5"w DIY dipole ribbon for 1K-20K, use the TD15M for the midrange down to 100Hz, and put a pair of the Qts=1 TD15D dipole woofers in a separate vibration isolated base baffle. I have found it necessary to go dipole from 20K Hz down to the room mode bass wavelength frequency (~ 30 Hz) to get the correct image. I have also found it necessary to put a diffuser on the wall behind the dipoles.


Here are the original TD15M specs:

T/S parameters:

Fs 30.5 Hz
Qms 4.47
Qes 0.29
Qts 0.27
Vas 405 Liters
Cms 0.4 mm/N
Mms 70 grams
Sd 855 cm2
Rms 3.0 Kg/S
Bl 27.6 T/m
Re 6.6 ohms
Z 8 ohms
Le 0.2 mH (low inductance due to underhung plus Faraday)
1WSpl 98.1 dB
Xmax (linear) 3mm
Xmax (mech) 10mm
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File Type: jpg ribbon_lambda_dipole.jpg (64.0 KB, 1014 views)
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Old 14th June 2007, 06:37 AM   #1039
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Not exactly a line source, but a pair of 18Sound 8NMB420's in a vertical (MMT, not MTM) array look appealing as the wideband partner for either compression-driver or ribbon tweeters. (If ribbons are chosen, the best location would be directly to the left or right of the vertical driver array, with the ribbons on the "outer" edge of the L/R loudspeaker pair.)

Note the response curve, the smoothest I've seen for a prosound driver, and the resulting simplicity of the lowpass crossover. (I'd start with low-Q 2nd-order filters as a starting point.) As with the lower-frequency drivers, there is the option of separate lowpass crossovers for the 8NMB420, so the driver furthest away from the tweeter starts to roll off earlier, say at 1 kHz, while the upper driver rolls off at 2 kHz.

The cones are quite lightweight at 14.9 grams each, cone area (for two) is about equal to an 11" driver, and the combined power handling is rated 400W continuous pink-noise. The Theile/Small power efficiency for a pair is 98.6 dB/metre/watt, and the voltage sensitivity is a bit higher due to the 4-ohm load.

0.8dB compression happens at 40W input, or 114 dB/metre - plenty of headroom, I'd say. The Xmax is generous, so they should mesh well with the MB/B driver array.
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Old 14th June 2007, 11:00 PM   #1040
ScottG is offline ScottG  United States
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Quote:
Originally posted by Lynn Olson
Not exactly a line source, but a pair of 18Sound 8NMB420's in a vertical (MMT, not MTM) array look appealing as the wideband partner for either compression-driver or ribbon tweeters. (If ribbons are chosen, the best location would be directly to the left or right of the vertical driver array, with the ribbons on the "outer" edge of the L/R loudspeaker pair.)

Note the response curve, the smoothest I've seen for a prosound driver, and the resulting simplicity of the lowpass crossover. (I'd start with low-Q 2nd-order filters as a starting point.) As with the lower-frequency drivers, there is the option of separate lowpass crossovers for the 8NMB420, so the driver furthest away from the tweeter starts to roll off earlier, say at 1 kHz, while the upper driver rolls off at 2 kHz.

The cones are quite lightweight at 14.9 grams each, cone area (for two) is about equal to an 11" driver, and the combined power handling is rated 400W continuous pink-noise. The Theile/Small power efficiency for a pair is 98.6 dB/metre/watt, and the voltage sensitivity is a bit higher due to the 4-ohm load.

0.8dB compression happens at 40W input, or 114 dB/metre - plenty of headroom, I'd say. The Xmax is generous, so they should mesh well with the MB/B driver array.

Ah.. you've been thinking about what I suggested!

Note that Audax PR17M0, (in a vertical line of 4 drivers placed next to each other), will not behave as a line source at any reasonable* listening distance around 2 kHz.

(* at a distance of 6 feet the 4 driver PR17M0 will not display a line source character under about 5 kHz.)

A 4 driver array will also "naturally" increase the driver's output from about 450 Hz to 1.2 kHz. This compensates for the open baffle's loss (from the extremely narrow baffle).

Of course "combing" will exist, but its effect should *not* be substantial around 2 kHz.

Another factor to consider is that the PR17M0 has a vastly superior off-axis behavior at higher freq.s - which would work well with a non-directive tweeter like a ribbon or a planar (..horizontally speaking).

Now the 8NMB420 has a more directive off-axis output for use with tweeter'ed waveguides. So if you are still thinking compression tweeter then this would be a better driver.

Yes, the x-max of the Audax driver is pitiful.. but from about 500 Hz to 2 kHz in a 4 driver config. it shouldn't be a problem at even fairly high spl's. (..in fact I don't even think that a high-pass filter would be necessary for most users.)

On final note: The overall *efficiency* of the 4 driver (Audax) would be superior to the 2 driver 8NMB420. (..in fact with the 2 driver Jensens, I believe you could obtain a nearly stable 8 ohm impedance in a 2.5 way loudspeaker (parallel crossover) - with a sensitivity of over 99 db from 90 Hz to 20 kHz.)

Final note:

While I've recommended both driver's (for differing designs) in the past, of the two - I've only heard the Audax ..and I (and others) can tell you that it is *VERY* special.
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