What Are Folded Tweeters? - Rapallo New Zealand :: Home Theatre & Hifi | Design & Installation
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Written by Deano Lambert, Posted by Simon Bell

July 22, 2020

Folded Motion Tweeters are a variation of speakers that is used to produce very high frequency sounds, as in the tweeters (but you knew that anyway right?)

They differ quite a bit in design and function from a standard dome tweeter you’d find on most of the mainstream brands of speakers. The Folded Motion Tweeter are constructed of 4 main parts:

  1. the front plate
  2. the diaphragm
  3. the magnet,and
  4. the back plate

Though they sound simple, constructing them is much more complicated process. They are a somewhat delicate part and take careful planning to sound their best when you sit down to listen to them.

Rapallo | MartinLogan | Folded Motion Tweeter

A SUM OF THE PARTS

So let’s take an in depth look at those “parts” we mentoned above.

The plates on the front and back have a fairly simple role to play, they hold the assembly together like a sandwich. Between those, there is a diaphragm made typically of polyethylene. It has a pair of electrical circuit traces along it, one positive and one negative. The change in charge along the electrical circuit traces causes the folds of the tweeter diaphragm to move like an accordion, in and out. Each fold, as it squeezes together forces air to move outward from the fold, which is why the generic term for the motion tweeter is Air Motion Transformer.

Directly behind the diaphragm of the tweeter are magnets. The type, layout and number of them depends on the manufacturer. MartinLogan uses multiple neodymium iron boron magnet strips. The strength of the magnet will effect how much force is exerted upon the air in the folds, and thus the sound it creates.

Simple right?

Rapallo | MartinLogan | Folded Motion Tweeter

WHAT ABOUT THE BASS?

Folded motion tweeters do not produce bass well at all, and it theory it is not their role in the make-up of a speaker. In almost all applications you will have a hybrid speaker that handles the bass, so there are also standard bass drivers installed in the cabinet for either mid bass or low bass, or, sometimes both.

They produce incredible neutral highs due to the effective surface area of the driver. A 1 inch wide strip has about the same area as an 8 inch circular shaped driver. It is able to move much faster though, which allows it to produce such detailed sounds.

Rapallo | MartinLogan | Folded Motion Tweeter

ARE THEY A RIBBON TWEETER?

Some people may confuse the Folded Motion Tweeter with a ribbon tweeter. Though similar, they are not the same.

A ribbon tweeter uses an aluminum ribbon that is suspended in the electromagnetic field. The positive and negative current that is passed across the aluminum diaphragm cause it to move in an out. Some ribbon tweeters are flat, some pleated and some have the same shape as an Air Motion Transformer. The design and function is very similar so confusing them is easy.

Rapallo | MartinLogan | Folded Motion Tweeter

*FREE OFFER – buy a pair of MartinLogan Motion Series speakers in July or August and receive a free set of pre-made speaker cable. 

View the Motion / QED Cable Offers >>

Rapallo | MartinLogan | Folded Motion Tweeter

THE FOLDED MOTION TWEETER

The Air Motion Transformer, or the Folded Motion Tweeter (FMT) as it is called by MartinLogan is a great sounding component for almost any listening environment.

The FMT produces detailed and directional sound that creates a stunning sound stage. They are extremely fast and neutral, which are two great qualities of any speaker. When combined with a standard mid-range bass driver the whole package covers a wide range of frequencies.

The only small negative is that in smaller speaker set ups in bigger rooms, you may want to add a sub-woofer to fill in the lower frequencies. This is much less an issue with something like the Motion 60 that has larger bass drivers. One concern many listeners do have is the brightness, as they can be very bright and fatiguing at times. This is mainly due to the speakers not being correctly paired with the right amplifiers. I (Deano) actually prefer speakers with the correct treble balance, so they work perfectly in my room.

If you would like to see more you can check out Martin Logan’s Page explaining their design here>>

Rapallo | MartinLogan | Folded Motion Tweeter

SO THE ALL IMPORTANT QUESTION, THE SOUND

As you maybe aware, I (Deano) am not very forgiving when to comes to some speakers. If they are badly built or sound bad due to bad treble control or have sloppy mid bass, then the physics behind the reproduction of sound and how it is reproduced for home listening is just flawed. It doesn’t matter how much you spend, there is not a perfect speaker that can do it all. That is why we try and demo as much or our product as possible, so you know what you are getting before you spend the money.

Every once and while a speaker comes along that is not perfect, but just simply sounds great. And by great I mean I could happily live with this speaker in my HiFi setup (oh and I’m a picky so and so too!!)

The MartinLogan Folded Motion Tweeter is incredible, has great timbre, air, the speed is superb and the attack of the instruments is breathtaking.

And the best part is these are on demo, and we welcome you to hear how special these speakers are!

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