Building a pair of DML speakers

I have always been fascinated by loud speaker technology.  I have owned several pairs of speakers over the years, but all of them have been conventional cone speakers.  I fell in love with the flat panel speakers the moment I saw them, be it Martin Logans or Magnepans.  I never owned one though.

I recently stumbled upon a new type of speaker technology.  It is called Distributed Mode Loudspeaker (DML).  It was fascinating to see how simple it was yet how incredible the sound reproduction was, based on the reviews online.  I watched a few youTube videos on how to build one and read a few online forums for more info and got ready to build one.  Here is an account of how I built two pairs of the DML speakers and how they turned out.

The DML speaker is built out of a flat panel made of a light but stiff material and an exciter.  The exciter is like a speaker without the cone.  This exciter vibrates the panel to produce the sound output.  The DML speaker is unlike any cone speakers or flat panel electrostatic (Martin Logan) or magnetic ribbon (Magnepan) speakers.  The DML speaker randomly generates vibrating nodes that translate into sound output in different frequencies and amplitudes.  Due to its nature, it generates equal sound both from the front as well as the back of the panel.

The first speaker is a 2'x2' flat panel speaker made out of:
- 2'x2' (1" thick) Foamular XPS insulation board (Home Depot)
- Dayton Audio DAEX25FHE-4 24W exciter (PartsExpress)
- Gorilla wood glue
- Speaker wire
- Solder

That is it!

I rounded the corners of the board with a 3" radius.  Rounded the edges as well and removed all sharp edges.  Sanded the entire panel with 110 grit sandpaper using a orbital sander.  Applied a 1:1 mixture of wood glue and water to the entire surface.  Once dry, I applied the second coat.  This produced a sandpaper kind of finish which is what makes it an amazing sound generator.  Attached the exciter 2/5th from the top and side.  Soldered the speaker wire to it and I was done.  Check out the youTube video for more details on the steps and the reasoning behind them. 

Rounded corners.

Ready for prime time!

I hooked it up to the amp and was amazed by the sound it produced.  I was not expecting this big of a sound stage from such a small (and inexpensive) exciter.  Because of the wide panel, there is no sweet spot like with conventional speakers.  High frequency is a bit pronounced due to the size of the panel.  Imagine a tweeter the size of the panel!  It acts like that.  But, the sound stage is incredible.  I have the speaker placed about 8 ft from the back wall and 1 ft from the side wall.  Maybe the distance from the back wall as well as its omni-directional nature, the sound stage appears to be behind the speaker.  This works great for me when watching movies since the screen is far behind the speaker.

Once I completed the first test speaker, I was ready to build the larger one.  I wanted to see what effect the larger panel would have.  Boy, was I rewarded.  The larger panel had a more flatter response.  Better mids, lower highs.  I am still breaking it in.  Hopefully, it will get better as it ages.

I used the same process for building this speaker as well.  Below are the parts used for the larger speaker:
- 4'x8' (1" thick) Foamular XPS insulation board (Home Depot)
- Dayton Audio DAEX32EP-4 Thruster 32mm Exciter 40W (PartsExpress)
- Gorilla wood glue
- Speaker wire
- Matte spray paint
- Solder

This exciter is the bigger brother of the previous one and there is a marked difference in quality and sound reproduction.  It is also heavier and bulkier.  The only problem with this foam board is that it is scored to make it easy to break it into pieces.  I was afraid that the score lines would create unnecessary vibrations and hence I poured glue into the cracks and sealed them.  I was a bit over zealous and ended up with awkward looking glue lines in the speakers even after sanding them.  Lesson learned.  I would take a fine tube and just squeeze the glue into the cracks and wipe off any extra.  This will keep the surface clean looking.  From this large board, I was able to cut out 2 20"x44" pieces and I am still left with half of the board.  Is 20"x44" the golden ratio?  Absolutely not.  It is not even close to the bronze ratio (if there is such a ratio).  I had to choose between great sounding speakers and good looking speakers.  I chose to compromise and go for good looking ones in order to make sure I could keep them "inside" the house and not in the garage collecting dust. 

I followed the same procedure as earlier to prep the boards, paint them with glue to generate the sandpaper-like surface.  Once the glue dried, I painted it gray with the matte spray paint.  I attached the exciters using the same formula (2/5th) and soldered the speaker wires.

Cutting the corners with a knife.

Filling the scored cracks with glue.

Painting it with 1:1 glue-water mixture.

Panel is ready for testing.  The ugly lines are the scored lines where I applied glue.

Big brother with the younger brother, before the final paint job.

A-B testing.

I also took this opportunity to design and build a pair of stands for the speakers.  I went to Home Depot and bought some poplar boards of different sizes.  The design is a simple inverted T supported on the back by a beam.  I cut the wood to the desired size put the stand together with one screw.  I then coated it with polyurethane to protect it.  I bought dual-ended gold speaker binding posts from PartsExpress and affixed them.  I use one end to connect to the amp and the other end to go to the speaker.  This allows me to disconnect the panel from the stand for transportation or storage.  It also lets me switch panels on the same stand.  I attached soft foam for the bottom and back support so that the speaker is not touching any hard surface.  I used a soft multipurpose cleaning sponge to create these supports.

The final product.

Back supported by a soft sponge.

Dual-ended speaker posts.

I did not expect the panel to reproduce the entire range of frequencies from 20 Hz to 20 kHz.  The smaller panel has pronounced high frequencies whereas the larger panel is well balanced.  The smaller panel lacks mid freq response.  It completely lacks low freq (below 150 Hz) response.

As seen in the youTube video, I think making panels with 2-3 different materials and using a crossover will give the best full range speaker.  I am happy with the results so far and am going to enjoy these speakers for the time being.

Here is the final setup.  The speakers were moved into the room to fit in the picture:

Here is a demo of how the speaker sounds.

The larger panel is better at reproducing mids whereas it also lacks low freq response.  I had to pair it with a sub-woofer to take care of 20 - 150 Hz.  Overall, I am very satisfied with the build.  It was a fun experiment and a great DIY speaker to show off.

Customer service is dead!

That is what I thought, especially in the air travel industry. 

Until my visit to China recently. 

During my domestic travel within China, three things reminded me that customer service in the airline industry was still alive.  At least, outside of the United States. 

First, everybody was offered a free hot meal on any flight over 2 hours!  I still remember the days when Continental would offer hot meals to everybody on domestic flights.  Gone are those days in the US. 

Second, personalized service for every passenger.  On one leg, my neighbor was fast asleep during the entire flight.  When the flight attendants came with food and drinks, they noticed he was asleep and left a note (see note on the right in the pic below) letting him know that they missed him.  And, just before landing, they noticed that he was still asleep and came back with a second note (one on the left) providing information about the arrival city.  They did this to every passenger who was fast asleep!  Now, that is what I call good customer service. 

Third, I noticed thoughtful service even at the airport.  We are all used to the luggage carts lined up in their parking spot.  In some airports, you have to pay to pull out a cart.  In the Shanghai (Pudong) airport, I was surprised to see the luggage carts neatly lined up along the conveyor belt.  Passengers would just come to the belt, grab their bags and load it onto one of the nearby carts and roll away! 

Companies need to look for simple ideas like these to improve their customer service.  Simple gestures like this is what makes up delightful customer service.  You don't have to spend a lot of effort or resources to make your customers happy.