Woofer technology - isn't it surprising...

[getz out]

Originally posted by rdepelteau:

That's my point. Is that wrong mr. Getz?

Utterly.

[rdepelteau]

Why?

[rdepelteau]

What if the speaker was built like a beehive/space frame.... with a pusher on every node. You can have a beehive with 12" cells, 4'x 8', or bigger, with 40 push-rod magnets and coils driving the thing. Each cell would act like an independent speaker. I bet the mids would not be so bad either.

[Gruuve]

One idea here that might definitely be worth latching onto regardless of any other conjecture: carbon fiber speaker cones!

 

UPDATE: Actually, come to think of it, I believe that may have already been done...probably the limiting factor is expense.

 

Dave

[Rocky McDougall]

Carbon fiber may be too stiff. It has no flex to it in most applications. I am not sure if flex is needed to prevent deterioration. Aluminum cones do not seem to be the answer. In fact when it comes down to pure, good tone, paper is hard to beat. Me Thinks,

Rocky

[Rocky McDougall]

This may be way off the subject but, being an automotive engineer, I just thought of a similar application. For many years automotive engines used a valve system where a lobe on a camshaft opened the valve and relied on a spring to close the valve. This is not too far removed from a speaker/cone/voice coil/magnet system. The new engine technology has electromagnets to open the valve and electromagnets to close the valve. We have gone from 10,000 rpm engines to 20,000 rpm engines (F-1 Race cars) producing more horsepower. This is the same basic technology we have been talking about here on this thread.

rdepelteau is thinking along the same lines and there may be a real future in it.

Rocky

[alexclaber]

Originally posted by rdepelteau:

Isn't a 10" woofer better than a 5" woofer?

 

And isn't a 16" woofer better than a 10" one, if power is required? Well then logic demands that a bigger speaker produces a louder and cleaner sound. I can be wrong of course, but I don't think so.

You are wrong. That's what's frustrating me, I'm arguing speaker design with someone that doesn't understand speaker design.

 

Originally posted by rdepelteau:

True, I don't have a degree in speaker design, as you do perhaps.

I have a degree in Mechanical Engineering. All my knowledge of speakers is self-taught.

 

Originally posted by rdepelteau:

However, your argumentation is flawed, because you argue about the particulars, and not about the concept..

No, I have been arguing about the concept and illustrating reasons why it is a bad idea. As I have repeatedly stated you are chasing the wrong goal, you need to worry about moving air not moving speaker diaphragms.

 

Originally posted by rdepelteau:

If the weight is increased by 20% I can compensate for this by increasing the power by 150%, which is plenty of power to move the cone which, in theory, may weight as little as 6 ounces.

Again, you're missing the point. Re-read my previous post.

 

Originally posted by rdepelteau:

I think you limit yourself with the conventional design, and you may be stuck in this mode, like the guys at Chrysler who'se best designs was the "K" car.

I contend that is you who is tied to conventional design, of a heavy diaphragm propelled by electromagnetics. This is an utterly inefficient approach.

 

Originally posted by rdepelteau:

Who knows if the response of a 16" speaker designed with three pusher magnets and a plastic cone is not better than that of a similar speaker with a paper cone? Given that a pusher magnet can be made long and thin, and the coil may be thick and heavy, producing a driving force on the cone much greater than a conventional set up, so the response istelf would be faster, and thus this type of speaker may be more responsive than a conventional one.

Wrong. Voice coils are very light. Even neo magnets of similar strength would be far heavier.

 

Originally posted by rdepelteau:

And I can have twenty smaller pusher magnets for any given speaker, to distribute the force all over.

Why not just have twenty smaller speakers?

 

Originally posted by rdepelteau:

Plus the material of the cone itself may be of paper, or some other lightweight space age material like fiber carbon, which has not been tested simply because paper is how cones are made and there never was a need for a better material.

Again, you demonstrate your lack of knowledge. Plenty of speakers out there that use composites and alloys for the diaphragm.

 

Originally posted by rdepelteau:

You are much too negative in your analysis, Alex. You have to think outside the box..

You need to think outside the box - in fact you don't even know the box is. You constantly talk about moving the speaker - why not remove the speaker and move the air directly?

 

Originally posted by rdepelteau:

What if the speaker was built like a beehive/space frame.... with a pusher on every node. You can have a beehive with 12" cells, 4'x 8', or bigger, with 40 push-rod magnets and coils driving the thing. Each cell would act like an independent speaker. I bet the mids would not be so bad either.

Can you explain why one large speaker is better than multiple small speakers? Certainly the mids from such a large speaker would be non-existent.

 

Alex

[lug]

http://www.philjonesbass.com/IMAGES/PRODUCTS/SPEAKERS/8T&24B/8T&24B.jpg

 

23Hz - 15KHz

3200 watts.

[Rocky McDougall]

Why don't we invent a speaker that moves massive amounts of air without a speaker cone or a coil.

That would be cheap, lightweight, portable and would have much better tone and volume. Now, how can we do that?

Rocky

[alexclaber]

Originally posted by Rocky3840:

Why don't we invent a speaker that moves.. ...air without a speaker cone or a coil.

http://www.metaxas.com/images/masproduct5/emperor.jpeg

 

http://www.buyingloudspeakers.com/speaker-electrostatic.JPG

 

Alex

[Rocky McDougall]

I am very familiar with electrostatics. I had a pair in my home stereo for many years. Wonderful speaker system but could not produce realistic bass notes. All designs needed the aid of a subwoofer which would disqualify them for our purpose as Bass Guitar speakers. But this proves that there may be substitute for the common cone & coil of our present disigns. We just need someone to find it.

Rocky

[Rocky McDougall]

Another thought on this subject. The electrostatic system is very close to the technology that Dave Sisk discussed in the original post of this thread. Using coils to move the cone in both directions and not using a big heavy magnet.

Rocky

[getz out]

Sound Transmitter .

[TimR]

What exactly are we trying to do?

I think all these designs are solutions to something that is not actually a problem. The speaker and magnet weight are not the actual problem, until you start to carry the thing around.

 

We can build a speaker as large as we want, but the larger the speaker the more mass it will have and the more difficult it will be to vibrate quickly without using lots of energy. This mass is not due purely to the mass of the cone but mainly to the mass of the air we are pushing against. We are trying to accelerate a block of air about 1m in length (the approximate wavelength of low frequency sound) and with the cross sectional area of the speaker. AND We're are trying to accelerate this mass from 0 m/s to 330m/s, instantaneously.

 

The higher the frequency the shorter the Wavelength and the smaller the volume of air. Couple this with the fact that lower frequency sounds appear quieter. Means we have to have a bigger speaker to make the same volume for the low frequencies than we do for the higher ones.

 

Current materials technology limits us from reducing the weight of the magnets.

 

I think the next logical step is to reduce the resistance and the current and therefore the heat in the coil, this would allow for greater efficiency. As the coil heats up its resistance increases as well. Unfortunately the electromagnetic force is dependent on the current, so we can get around this by using more dense turns of less resistive material. This is what we are trying to do with superconductors. Whether there are composite materials yet to be created that will conduct electricty while remaining cool remains to be seen.

 

Before you try to come up with a solution, you must know what the REAL problem is.

[alexclaber]

Originally posted by TimR:

I think the next logical step is to reduce the resistance and the current and therefore the heat in the coil, this would allow for greater efficiency.

Except that 4 ohm speakers are no more efficient than 8 or 16 ohm speakers. The dissipated energy (i.e. heat) is due to the inductance of the coil creating further AC resistance (i.e. impedance) as the speaker moves. The ideal way to reduce the heat build up in the speaker is by releasing more of the energy as sound.

 

Originally posted by TimR:

Before you try to come up with a solution, you must know what the REAL problem is.

Exactly. And the problem is Hoffman's "iron law". And I don't see a way to get around that!

 

Alex

[TimR]

The ideal inductor will be lossless, it is the fact that it has resistance that creates the heat losses. It doesn't matter whether the current is generated by the amplifier or generated by the moving coil itself.

So reduction of resistance and current is the silver bullet.

Iron law is just a method of getting the most out of the sound wave being produced. So you're right, a two pronged approach is called for.

 

1. build a cabinet that emphasises the frequencies you are interested. The cabinet cannot be efficient at all frequncies, that goes against the Iron Law.

2. Reduce the resistance of the coils. But this in turn will then affect the Amplifier design....

[alexclaber]

Originally posted by TimR:

The ideal inductor will be lossless, it is the fact that it has resistance that creates the heat losses.

But it can't have inductance without generating impedance (i.e. AC resistance)!

 

Alex

[Gruuve]

Man, isn't it fun having a bunch of engineers (both degreed and non-degreed) debating a technical problem and how to resolve it? These types of dicussions are where a lot of innovation originates.

 

So, here's a thought...there's a wire material that expands as current is passed through it...I can't remember what it's called...Actinol wire or something like that? IIRC it would expand very quickly when current was applied and contract very quickly when current was removed. (Is it capable of doing this at up to a couple hundred cycles per second? I dunno...don't remember.) This is just a completely off the wall thought, but what if you concocted some fixture of this material, and attach that fixture between the speaker cone and the driver frame so that IT directly moves the cone rather than an electomagnetic voice-coil/permanent magnet combination?

 

And another thought...there certainly are many electomagnetic acutators used in industrial settings...some of them are quite powerful and work for decades without failing. Thinking in terms of moving the speaker cone directly, perhaps some sort of self-contained electromagnetic actuator that is (like the wire fixture mentioned above) physical connected between the driver frame and the cone so that it physically moves the cone. Thoughts? Rocky, I'll bet you've seen these types of acuators in the automotive industry. This isn't really any different than current driver designs in concept...however, it could be quite different in practice, depending on what this did to the Theile-Small parameters of the resulting driver.

 

Either of these would certainly introduce some interesting numbers into the Theile/Small equations for cabinet design, wouldn't they? I'd expect the T/S equations would probably still work...as long as it functions similar to a spring...which presumably it always would since you presumably still have a cone surround and spider (of some sorts).

 

These may be totally whacked ideas, but just trying to "think outside the enclosure". (Pun intended. )

 

Dave

[Big Red 67]

Originally posted by C. Alexander Claber:

Originally posted by TimR:

The ideal inductor will be lossless, it is the fact that it has resistance that creates the heat losses.

But it can't have inductance without generating impedance (i.e. AC resistance)!

 

Alex

If it was lossless then you couldn't drive it, it would burn out, it would look like a short to the amp.

[Gruuve]

Originally posted by Big Red 67:

Originally posted by C. Alexander Claber:

Originally posted by TimR:

The ideal inductor will be lossless, it is the fact that it has resistance that creates the heat losses.

But it can't have inductance without generating impedance (i.e. AC resistance)!

 

Alex

If it was lossless then you couldn't drive it, it would burn out, it would look like a short to the amp.

Ah...but who says you have to drive it with an amp? Hmmm...instead of just brainstorming on the driver/enclosure part of the equation, maybe the right perspective is to focus on what could replace the drivers, enclosure, AND power amp? As Alex has said, we're actually trying to move air, and it's mostly irrelevant whether we actually do that with a speaker cab and power amp, or some other means.

 

Starting from scratch, how could you run a preamp-level signal into a "black box" that causes the air to move in a way that mimics the signal? What means are there to move air given a low frequency sine wave?

 

Dave

[TimR]

Originally posted by Big Red 67:

Originally posted by C. Alexander Claber:

Originally posted by TimR:

The ideal inductor will be lossless, it is the fact that it has resistance that creates the heat losses.

But it can't have inductance without generating impedance (i.e. AC resistance)!

 

Alex

If it was lossless then you couldn't drive it, it would burn out, it would look like a short to the amp.

OK so we agree the 'ideal' cannot be created. Its an ideal. Physics won't allow it. Reducing the resistance can be done but the lower the resistance seen by the output stage of the amp means that the amp will run away. So it's a no win situation, hence I wrote that this would affect the amplifier design. So why are we limited with the convention of 2 Ohms minimum, are the frontiers being pushed enough there. If we could get an amplifier to run into tenths of an ohm that would reduce the problem further.

[rdepelteau]

Alex: "Wrong. Voice coils are very light. Even neo magnets of similar strength would be far heavier."

 

Alex: "Neo magnets are so small and light that they would weigh less than an equally powerful electromagnet."

 

Alex: "Have you seen the huge magnetic field strength you get from neo magnets? To equal that with an electromagnet is not going to happen, unless you supercool it."

 

_____________

 

I'm sorry Alex, but you seem to contradict yourself here...

 

 

Rocky: "I am very familiar with electrostatics. I had a pair in my home stereo for many years. Wonderful speaker system but could not produce realistic bass notes. All designs needed the aid of a subwoofer which would disqualify them for our purpose as Bass Guitar speakers. But this proves that there may be substitute for the common cone & coil of our present disigns. We just need someone to find it."

 

So we're back to the cone/coil. Moving air for bass. Perhaps improving the electrostatic model by finding why it doesn't produce bass. My guess is the flat mover between the plates doesn't have enough gump to do the job. So perhaps by curving the surface and finding another means of moving it, other than electrostatic plates. Which brings back the coil/magnet pusher.

[TimR]

Now if we could magnetise the actual air, or maybe dose it with enough ions. Hmm

 

High voltage Rock and Roll?

[Gruuve]

Why do I have this mental image of some new-fangled 20' diameter electrostatic woofer and all the band members in front of it with their hair standing up like they're about to be struck by lightning?

[rdepelteau]

How about a microwave? Just like a microwave oven, only tuned to air molecules, say nitrogen? The microwave to act against the nitrogen molecules in the air and push against them. And use a magnetron and a parabolic reflector to push the air?

 

I bet that would cause the hair on the head to stand up?

 

[Rocky McDougall]

Originally posted by rdepelteau:

_____________

So we're back to the cone/coil. Moving air for bass. Perhaps improving the electrostatic model by finding why it doesn't produce bass. My guess is the flat mover between the plates doesn't have enough gump to do the job. So perhaps by curving the surface and finding another means of moving it, other than electrostatic plates. Which brings back the coil/magnet pusher.

The Electrostatic panel is a good example of surface movement. It has a very large surface but only moves 1-2mm. It is just not a good air pump. However it is wonderful at mid frequencies.

Rocky

[Big Red 67]

Yes! they had a surround effect when I listened to them.

[Rocky McDougall]

We are all going down the wrong path, trying to accomplish something with the outdated technology. We need to have a speaker cone generator that is powered by light impulses. The amp only has to produce light flashes via fiber optic cables to the cone generator.

Simple,

Rocky7

[rdepelteau]

Rocky: "The Electrostatic panel is a good example of surface movement. It has a very large surface but only moves 1-2mm. It is just not a good air pump. However it is wonderful at mid frequencies.

Rocky."

 

Which leads me to believe a panel of beehive shaped cones pushed by a serie of coil/push-rod magnets can also produce a good response over all. And that would mean the speaker may have good midrange as well as a good bass. But that is all hypothetical at this point.

 

I do have a question: Why is it necessary to enclose the speaker in a cabinet? The air mass behind the speaker acts as a spring to pull back the cone? Is that it? What's the difference between an open cabinet and a closed one. Bass amplifyers have open backs, while stereo ones don't. Opem back cabinets have a lot of power, so if I designed a speaker, I would think an open back is less trouble.

[alexclaber]

Originally posted by rdepelteau:

Alex: "Wrong. Voice coils are very light. Even neo magnets of similar strength would be far heavier."

 

Alex: "Neo magnets are so small and light that they would weigh less than an equally powerful electromagnet."

 

Alex: "Have you seen the huge magnetic field strength you get from neo magnets? To equal that with an electromagnet is not going to happen, unless you supercool it."

 

_____________

 

I'm sorry Alex, but you seem to contradict yourself here...

Yes I do don't I? But actually, it's all a question of context. A speaker motor consists of two magnetic fields - one very powerful and static and created by the permanent magnet, and one of much less power but variable and created by the voice coil. To use an electromagnet to create the more powerful field would generate a lot of heat - i.e. wasted energy. If you were to build a conventional speaker but with a very small magnet you'd find that you needed to push massive power through the voice coil to get any volume from the speaker. Does that make sense?

 

Originally posted by rdepelteau:

My guess is the flat mover between the plates doesn't have enough gump to do the job.

Two reasons - lack of travel (i.e. Xmax) which even the huge surface area does not compensate for. Back wave cancelling the front wave at wavelengths greater than 4x the distance between front and back of the radiator.

 

Originally posted by rdepelteau:

Which leads me to believe a panel of beehive shaped cones pushed by a serie of coil/push-rod magnets can also produce a good response over all. And that would mean the speaker may have good midrange as well as a good bass. But that is all hypothetical at this point.

The big problems with using large drivers to create midrange is the beaming effect. If electrostatic speakers were not open-backed hardly any mid and high frequencies would get out to the listener due to the incredibly poor dispersion from a large radiator. And as open-back speakers do not work well for bass then if you want bass and midrange from a large driver then you will really struggle with off-axis response.

 

Originally posted by rdepelteau:

I do have a question: Why is it necessary to enclose the speaker in a cabinet? The air mass behind the speaker acts as a spring to pull back the cone? Is that it? What's the difference between an open cabinet and a closed one. Bass amplifyers have open backs, while stereo ones don't. Opem back cabinets have a lot of power, so if I designed a speaker, I would think an open back is less trouble.

You can put a bass speaker in an open back or large baffle cabinet. The problem is that any frequencies whose 1/4 wavelength is greater than the distance between front and rear of driver will be cancelled out, so you don't get any bass response unless the cab/baffle is huge.

 

You can make 'infinite baffle' speakers where you use a sealed cabinet that is so huge that the spring effect of the air in the cabinet is negligible. But this takes an enormous cabinet.

 

A sealed enclosure is basically a small infinite baffle design but the spring effect of the air changes the response of the speaker, reducing the bass extension/sensitivity.

 

A ported enclosure uses a helmholtz resonator to take advantage of the energy from the back wave of the woofer to create an in-phase output at and above the tuning frequency. This gives you another ~3dB of bass at and above the tuning frequency but causes the response to roll off at 24dB/oct instead of the 12dB/oct of a sealed cab below the tuning frequency.

 

And finally a horn cabinet uses a horn to load the driver so instead of moving a large amount and causing a small pressure change it moves a much smaller amount and causes a large pressure change. Then as the soundwave travels down the horn the change in pressure diminishes as the energy is spread across a larger wavefront. This means the diaphragm gets to push against an apparently denser medium and the sensitivity/efficiency skyrockets. The downside is that the speaker will only be horn loaded by frequencies whose 1/4 wavelength is less then horn length and whose 1/4 wavelength is less than the horn mouth perimeter (IIRC).

 

Alex