[Ultralight]

Generally, with traditional tweeters and woofers, they are curved in different directions.  A tweeter is generally domed outward away from the speaker, while a woofer is traditionally concave inwards towards the speakers.  Why?

And what happens if the woofer is domed like the tweeter?

Curious ,
UL

[Folsom]

Human sacrifice, dogs and cats living together... mass hysteria!

[JohnR]

There are domed woofers:



https://www.madisoundspeakerstore.com/approx-6-7-woofers-morel/morel-powerslim-6-ultra-shallow-woofer-4-ohm/



https://www.madisoundspeakerstore.com/approx-5-woofers/peerless-gbs-135f25al02-04-5-slim-woofer/

Not very big though. My guess is that woofer cones tend to be optimized for rigidity and tweeter domes for dispersion.

[mresseguie]

Somehow, I suspect mass hysteria will not be the result, but anything is possible, I guess. I certainly hope the first possibility is just a dark dream in Folsom's otherwise healthy imagination. 

This is conjecture on my part, but I think it has to do with the different characteristics of sound waves. High frequency waves spread in a different pattern than mid and low frequency waves.

I eagerly await an answer from an engineer who understands the physics.

Those 3is keeping you happy, UL? I'm still searching for my 'best', but I'm sure enjoying the ride.

Michael

[guest60106]

For the most part I think it has to do with the designers goals. There are prime examples of inverted dome tweeters as well. Focal has been a proponent of this design for as long as I can remember.

[RDavidson]

My guess (note I'm not the most technical person here) : If a woofer diaphragm is domed outward then the motor (magnet etc) is much further away from the center of the cone, which would be electrically inefficient and make the diaphragm movement harder to control. With tweeters, it isn't a problem because they don't need nearly as large of motors and the distance from the diaphragm (to the motor) is always small anyway (because the diaphragm is small).

[richidoo]

Good question!     I think woofers tend toward being innies mostly just to avoid physical damage from handling if the cone were protruding beyond the box edges, and to allow protective grilles, easier shipping, etc. Early days of paper cones had to be pretty deep cones to have enough strength to avoid flexing, etc.

I think most tweeter domes are outies just to reduce cost. With an outie, the motor's iron center pole can be shorter and simpler shape, reducing cost and weight. With expensive concave tweeters like Accuton and Focal the extra cost of some extra iron in the motor is insignificant compared to the cost of the diaphragm. But what's the acoustic advantage of convex diaphragm itself?

Accuton explains why they use concave domes:
"We used a concave dome like in our ceramic tweeters because the moving part as a whole is more rigid and better damped as convex domes, they also show a better dispersion and – due to the lower sag height – show lesser phase problems."

I'm not sure I buy all of that, since damping, structural strength are the same whichever way it faces. Sag should be the same either way because it is a push pull system, so equal sag if it were flipped. But "better dispersion" might be significant.

Siegfried Linkwitz says, "Above 10 kHz the concave tweeter dome brings up the off-axis response somewhat." talking about the Aura 2" concave full range driver used as tweeter in his Pluto speaker. Maybe that's the advantage of convex tweeter domes, better top end dispersion.

[FullRangeMan]

Generally, with traditional tweeters and woofers, they are curved in different directions.  A tweeter is generally domed outward away from the speaker, while a woofer is traditionally concave inwards towards the speakers.  Why?

And what happens if the woofer is domed like the tweeter?

Curious ,
UL

In the past when were plenty of paper cone tweeters, they were concave, later become estabilished that dome tweeter have ''better sound''.

[Ultralight]

THANKS to everyone who replied.  Keep them coming - I guess no concensus. 

My intuitive sense is that outward domed woofer will help dispersion but have less intensity and sense of resolution because it has less purchase/grip on the air while one domed inward will have better trip.  Purely intuition and I know how misleading my intuition can be when it comes to engineering. But it's the same idea when one stretches one's hand out of a car's window and dome the hand in two directions.  Or swimming in water.

Mresseguie, yes, those Super 3i are very satisfying with subs.  In fact, I now have six RS5 drivers here in my room - one regular Super 3i and a pair of Bipoles.  It's the first time I've felt that "I don't need to search anymore."  I do like the Bipoles more so the Super 3i may well go on the block.  I can now run monopole, bipole, dipole and 2.0 with two drivers stacked on top of each other.  AND also 4 ohm or 16 ohms in the dual driver configurations.  Its a dizzying array of options - love the flexibility.  In terms of placement, the bipoles are two chamber sealed and the ports face forward so I can run it monopole right up against the wall if I had serious space constraints.  Now, to be fair, I am also having a 2nd set of speakers I'm testing that will travel more easily when flying/trav.  But the Omegas are the best I've had yet.  I really think they are a bargain but I feel that one needs good fast subs to match. MANY owners have noted that the RS5 drivers really blossom in a system with subs.

UL

Somehow, I suspect mass hysteria will not be the result, but anything is possible, I guess. I certainly hope the first possibility is just a dark dream in Folsom's otherwise healthy imagination. 

This is conjecture on my part, but I think it has to do with the different characteristics of sound waves. High frequency waves spread in a different pattern than mid and low frequency waves.

I eagerly await an answer from an engineer who understands the physics.

Those 3is keeping you happy, UL? I'm still searching for my 'best', but I'm sure enjoying the ride.

Michael

[Wayner]

High frequencies tend to "beam" in a single direction, therefore, the tweeter has a dome to it, although there are tweeters with inverted domes such as those found on Focals. This shape helps to diffuse the "beaming" characteristic, resulting in a more uniform high frequency coverage.

Low frequency drivers tend to radiate sound in all directions, or at least more omni-directional then their counterpart. Because the lower frequencies require lots of air movement, woofer strength is important, so a low frequency driver is shaped the way it is to cup the air to move and be firmly supported at the outside, to handle the larger, driving magnet assemblies.

'ner

[mresseguie]

"MANY owners have noted that the RS5 drivers really blossom in a system with subs."

That was my take after reading dozens of posts in the 'appropriate' circle. Unfortunately, a certain 'cheerleader' made it difficult to figure that out.

Let me know if you decide to send that pair of 3is along. I'm still interested in trying them out.

Michael

[SJ David]

Generally, with traditional tweeters and woofers, they are curved in different directions.  A tweeter is generally domed outward away from the speaker, while a woofer is traditionally concave inwards towards the speakers.  Why?

And what happens if the woofer is domed like the tweeter?

Curious ,
UL

More to do with practicalities of design. Flat diaphragms could perform best for in many applications. Theoretically they behave more like pistons. Hard to make a flat diaphragm that is both as light as need be and still be able to use it with a typical coil-in-magnetic-field drive motor. A tweeter (or a mid/tweeter) does not have to move as much air so it can be lighter (less mass) and can be driven at or near the dome edge. Whether it is a concave or convex shape or flat can depend on the application.

Woofers have to move much more air and need the cone shaping to help with rigidity, keeping the moving part from breaking up, as well as make for a reasonable means to connect to the drive motor. You could use a woofer "inside-out" and it would still work well for the lower frequencies.

[Duke]

It's largely a matter of physical and acoustic considerations. 

The physical considerations include, how big is the voice coil and where's it going to go, and what sort of suspension system is needed and where's it going to go.   And, what size and shape diaphragms would result in acceptable diaphragm stiffness, SPL, and bandwidth. 

Acoustic considerations include, how much air do we need to move at what frequencies, and with what radiation pattern.

So if we want to produce low frequencies, we need a cone that's big relative to the voice coil size, and it needs to be stabilized in two planes so that it doesn't develop severe rocking modes.   The voice coil will be near the apex of the cone, and the suspension system will have one section (the surround) around the outer rim, and a second section (the spider) around the apex/voice coil area.   This is more practical to accomplish with a concave cone or dome than with a convex one.

A tweeter on the other hand needs to have a very lightweight moving mass and small diaphragm relative to the voice coil diameter, so typically the diaphragm is inside the perimeter of the voice coil.  The diaphragm can be either convex or concave in shape, either one is good from a stiffness standpoint, but since the motor is right behind the diaphragm it's usually more practical to use a convex dome.   For a tweeter we can get away with a single-plane suspension system because the excursions are very small, but some high-end dome midranges use a two-plane suspension system. 

Note that the shape of a dome tweeter is primarily for rigidity, not dispersion.  Its small size is what gives it wide dispersion.  If it were a pulsating dome that would enhance dispersion, but because it moves back-and-forth the dome shape doesn't really matter.  In breakup mode, where the center of the dome moves out-of-phase with the perimeter, a dome tweeter starts to approximate a ring radiator, which actually has worse dispersion than a rigid dome, so in that sense the stiffness of a rigid dome does help to maintain dispersion that would be degraded by breakup.   A woofer or midrange cone, on the other hand, because it's driven at the apex, typically has wider dispersion in breakup mode.

I've made some generalizations and simplifications here of course.

[Carl V]

interesting reading...not much mention of Ring Radiators, dimple domes,
it's the various midrange drivers of the audio world
which might tell us more...Accuton VS Scanspeak or ATC, not to mention Planars

[*Scotty*]

Woofers have to move much more air and need the cone shaping to help with rigidity, keeping the moving part from breaking up, as well as make for a reasonable means to connect to the drive motor.

This statement is incorrect.
 The acceleration forces the loudspeaker diaphragm experiences increase as the operational frequency rises. If the design is intended to have pistonic behavior within its pass-band, then it must be rigid enough to resist deformation due to the forces of acceleration acting on it. If it must start and stop 20,000 time a sec, the G-forces become very large indeed.
Scotty

[stereocilia]

I've also wondered why some woofer surrounds and dust caps are concave.

 The human speakers website gives a good description of why a concave tweeter makes sense to their designer: "The concave dome allows a smaller diameter voice coil which is then better coupled to any given point on the dome. This concave shape also produces an almost perfect waveform (its main strength), reproducing the original signal with an accuracy that a convex dome never can. This accurate sound is also dispersed widely (its second main strength), down only a few dB at the highest frequencies even at 180 degrees off axis.".  This is from  http://www.humanspeakers.com/diy/drivers.htm

[G Georgopoulos]

Generally, with traditional tweeters and woofers, they are curved in different directions.  A tweeter is generally domed outward away from the speaker, while a woofer is traditionally concave inwards towards the speakers.  Why?

And what happens if the woofer is domed like the tweeter?

Curious ,
UL

woofers in the early days were low efficiency today they have strong/large magnets and there is no problem with different shapes,tweeters too use strong/large magnets and are domed...i guess the other thing that comes to mind is "marketing something new" lot's of people buy into that!

cheers