Another DIY Ribbon thread

[LineSource]

Hi Denis,

My ears can sometimes hear the difference between 6u and 15u foils.

If you want to experiment with power tapering on your multi-ribbon line array it may be easier and sound more coherent to just put a non-inductive resistor in series with some of the ribbons. You can make a low ohm resistor by contact cementing household AL foil to plexiglass and cutting a serpentine pattern with an Xacto. Brass washers and screws make good contacts.

You may want to surf the web for articles on comb filtering in a line array vs. a continuous line source. There are also a few articles on Bezel function power tapering you might find interesting.

[dhenryp]

J.L.,linesource - I hadn't thought to try a shunt resistor. I'll certainly keep this in mind if I go with power tapering.

linesource - What kind of differences do you hear between the two thicknesses?

I've done a fair amount of reading on power tapering and understand the principle. I have seen many array with mid/woofs tapered but very few that do the same with the tweeters. I wondered if it was because high frequencies are much more directional than mid/woofers. This directionality may mean that you receive highs from a relatively smaller section of the array so comb filtering caused by interference caused by sound from the ends of the arrays is reduced. It's just a thought...

I will look for more info on Bessel (I assume you did not mean Bezel) function tapering. Thanks for the tip.

Regards,


Denis

[Paul W]

Hi Denis,
More homework for you...just in case you get bored

Depending on crossover frequency (1k?) and listening distance, you may be getting into near field/far field transition with a 47" line. If so, you'll probably want to decide how to deal with it. (Depending on room noise, you may be able to see it by comparing ribbon frequency response at your listening position vs 1 meter.)

With a final ribbon length of 45" and a lower crossover I had decisions to make, but I won't know if my current strategy will work until final baffles are done and I can do more serious testing...and listening. I cut MDF last weekend and have finally started building something permanent...I hope
Paul

[dhenryp]

Hi Paul,

Thanks for the homework suggestion. I'm always happy when somebody finds something more I should do.

My primary listening position will be about 11 feet from the speakers (which will be on either side of my front projector screen). I decided on the size of my ribbon (~1.3 meters) based on the near field transition chart in Jim Griffin's excellent white paper. At my expected 1.5k crossover, the near field should be good out to about 4 meters. In any case I will certainly be doing some listening position measurements when I get ready to start on the crossover.

I've made a little more progress today. I got all the cross pieces installed and squared up. Now al l I have to do to finish is build a set of ribbon connectors and cut, pleat and install the ribbons.

I've included a couple more pictures. The top shows the frame still clamped up with cross pieces installed along with my "adjuster". As I mentioned in a previous post, Once the cross pieces are placed on the poles they the magnet field makes it literally impossible for me to budge with my bare hands. This is where my rubber mallet comes in; A few whacks will usually get the cross pieces lined up with the threaded holes on the poke pieces.

The second picture is just a detail of the front of the assembly, before I install the fiberglass connector blocks. These blocks will just sit on the cross pieces attached with super glue.

[dhenryp]

One last picture of the enitire frame with magnets attached. Not much else to say except I weighed it and it comes in at 18 lbs.

[GeorgeBoles]

Hello again dhenryp,

As regards those "clamps", I meant the ones you showed in your picutres holding the work to your work bench. Are they all plastic and stainless steel, or are you just careful to move them firmly away from the magnetized frame once the neod. magnetics are in place?

Regards,
George.

[dhenryp]

Originally posted by GeorgeBoles
Hello again dhenryp,

As regards those "clamps", I meant the ones you showed in your picutres holding the work to your work bench. Are they all plastic and stainless steel, or are you just careful to move them firmly away from the magnetized frame once the neod. magnetics are in place?

Regards,
George.

Hi George,

They are regular woodworking clamps with steel shafts but most of the jaws are made of plastic. They will stick to a single pole but its really not a problem. They would attach firmly if you put the steel shaft across both pole pieces but its easy to avoid this.

Regards,

Denis

[dhenryp]

I've completed the second full size ribbon. I'm attaching a set of pictures that show the parts that make up the ribbon connectors.

The top picture shows all the connector pieces. The pieces are made of Fiberglass. I use two thicknesses: 3/8" thick and 1/8" thick. The 3/8" pieces sit on the cross pieces and have holes tapped to accept 4-40 screws. This time I used stainless steel screws and lock washers as well as a non magnetic screw driver. This makes assembly MUCH easier.

You can see the role of copper tape that I use to provide electrical connection between the seven individual ribbon segments. The tape is a quarter in wide and I put two strips side by side to correspond to the half inch ribbon width. The tape is used in making stained glass objects like lamp shades. They wrap the copper tape around the edges of each glass piece than solder them all together.

The bottom four pictures show details of the end connectors. These two connectors have an additional piece of fiberglass as well as a this copper strip that I use as the male part of a push on electrical connector.

[dhenryp]

Here is one last picture. This one is the completed ribbon. All I have left to do now is wind another transformer and attach two lengths of "T" shaped aluminum that will serve as the mounting brackets. I should be able to easily complete it tomorrow.

[dhenryp]

I finished the mounting brackets and the second transformer. I mounted the new speaker on the old test stand and listened to it. It sounds good – about the same as the first speaker. I've made no measurements yet of the new speaker and mounting method.

I've included some pictures showing the steps in building the transformer. It's the same design as the first:

Primary = 18 awg, 17 turns, 3 wire series multifilar winding (equivalent to 51 single wire turns)

Secondary = 24awg, 9 turns, 12 wire parallel mulitifilar.

The top left picture shows the primary with the three wires per turn.

The top right picture shows how the three wires are connected to get them series connected. Note that it's a good idea to mark each end of the three wires to make it easier to figure out what to connect.

The third picture shows the secondary wound on top of the primary. No need to keep track of individual secondary wires since they are all wired in parallel.

The last picture shows the completed transformer wrapped in electrical tape to keep the windings tight to the core.


This probably my last post for a while, until I get my line arrays built and can listen to everything put together.