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GAMMA 30 experiement

Adda

Adda

Super Member
I just finished making new crossovers for my GAMMA 50 speakers.
I replaced the old three way crossover with a two way one, made for a GAMMA 30, a two way speaker that uses the same bass (GAMMA BK3013A) and tweeter (GAMMA VLD-12) as the GAMMA 50 speaker.

This is my first encounter with a new speaker in my system, ever, I have always had the GAMMA 50's.
They did replace the midwoofers with KEF B110 in stead of the original BK138A.
This did not work out though, they just don't seem to fit in and decided I'd rather try going two way before getting in to building a passive crossover from scratch.

Anyway, I just finished the experiment, my arms feel leaded, as I have done everything by hand, lots of tight screws and just a basic screwdriver.

The result was not so good at first, the bass woofer and the tweeter sounded disconnected somehow, and there where a bad peak at around 2500-3500Hz, though not very wide, but bad.
This made them sound squeaky and piercing.
I then remembered I had forgotten to wire the tweeter out of phase, so I did that, and now the peak is much more subtle.
Judging from the frequency response of BK3013A/LA1231 drivers, the peak may persist (although nothing intolerable or even annoying at this point) because the bass woofer is located near the bottom of the box, so I hear it at an angle, this, according to the frequency response, could cause the peak I'm hearing.
Lowering my head so I stare directly in to the woofers helps, so this must be it.
So the next thing on the list is to convert the box.

Here is a sketch I made of my plans, incl. crossover and specs for bass reflex calculation.
The box is ~52 liters, reflex tubes have a diameter of 7mm (inside measurement) and a length of 18cm.

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Now that it's not late in the evening anymore, I can play louder and that spike really is very annoying.

I'll have to experiment with the crossover.

The crossover is crosses at 3000Hz 12/18dB.

The spike is right around 3200Hz.

So my guess is that it's the bass woofer network I have to look at, if anyone has any suggestions, I'd very much like to hear them

If you need more info in order to suggest anything, please let me know.
 
Turns out one of my VLD-12's caused the nasty peak at 3100-3200Hz, donno why, the same ribbon in another VLD-12 of the same type, has no such peak.
 
I have come to a crossover configuration that seems to work well.

It's pretty much the same as the diagram above, only in stead of a 0.3mH coil I use a 0.33mH one, 0.7mm wire, tried a 3mH coil 1.4mm but it was no good, made a peak around 3200Hz.

The coil for the bass is the same as on the diagram 0.5mH with 1.4mm wire.

All air coils.

The caps are as on the diagram.

Still need to do the high volume test, but it's late.
 
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Oh my goodness, when my head is at woofer height, they sound wonderful!

These should make awesome speakers when the box has been modified, although not the loudest around, but very efficient.
 
I found the problem with the peaky tweeter, under the ribbon there is a piece of fabric, made of loosely woven strands.
Under that, there is sheep wool, a few hairs had made it's way through the fabric, touching the underside of the ribbon.

After removing the hairs and making a new ribbon, the problem has disappeared.
 
Instead of using 10x more inductance (which would cause a major change to the filter), try adding a little resistance in series with the 0.3mH.
 
dumptruck said:
Instead of using 10x more inductance (which would cause a major change to the filter), try adding a little resistance in series with the 0.3mH.
Click to expand...

Well, it seems I made a typo, it's a 0.33mH not 3.3 (I'll just correct that).

But what you suggest, what kind of effect would it have? attenuate the tweeter or?
 
Oh, that makes more sense. I was thinking that maybe the original inductor for this speaker you're copying was higher resistance than yours, which would mean your filter was too high Q, creating a peak before it rolls off.
 
dumptruck said:
Oh, that makes more sense. I was thinking that maybe the original inductor for this speaker you're copying was higher resistance than yours, which would mean your filter was too high Q, creating a peak before it rolls off.
Click to expand...

Ah yes, I was thinking the same thing, so I went for the thinner coil I have, with good results, the speakers really sound great right now.
My guess, based on the original GD-8500mk4 for the GAMMA 50, I think Audioscan would have used a iron core coil for the low pass filter, and a air core for high pass, both using rather thin wires.

They do become peaky at loud volumes, but I think it's because the bass woofer is too close to the floor and I get all sorts of reflections.

At low to medium volume, they sound flat to my ears, when giving them a tone swipe.

The next step is to modify the box and see what they'll sound like then, and then modify the crossover further if needed.

Here are a few pics of today's work, I put together an almost pristine VLD-12 with the nicest ribbon I have ever made.

The yellow at the bottom of the tweeters is wax, it keeps everything in place inside.

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My best VLD-12

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I modified the terminals.

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Closeup

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Adda said:
Here are a few pics of today's work, I put together an almost pristine VLD-12 with the nicest ribbon I have ever made.
Click to expand...

Would you mind sharing how you make your ribbons? I made DIY ribbons years ago, but never made solid foil ribbons with beautiful pleating like yours.

Thanks,
John
 
nerdorama said:
Would you mind sharing how you make your ribbons? I made DIY ribbons years ago, but never made solid foil ribbons with beautiful pleating like yours.

Thanks,
John
Click to expand...

Sure, I need to make another ribbon, I'll take some shots of the process.
It's tricky though, as it's easy to loose the upper hand when handing such delicate material.
 
And here it is, the guide to refit your GAMMA VLD-12 with cheap ribbons that require basic tools to make.

Needed tools and materials list:

Knife
Aluminum foil capacitor
Strip of cardboard of the same width as the ribbons
Ruler or straight piece of cardboard
Two pieces of floppy/IDE33 cable
Arctic Silver 5 conductive silver cooler paste

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First break open the capacitor and unroll the foil (more info here: http://www.audiokarma.org/forums/showpost.php?p=7098161&postcount=86 )

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Cut out a piece of foil that's longer then you need

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The foil is in four layers, basically two poly films with aluminum on them, with the aluminum facing inwards.
Peel them, so that you have two strips of poly film with aluminum on them.

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Take a strip of film and put it under the ruler, use your cardboard piece to measure width.

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Cut out your strip

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Now the difficult part, peel the aluminum ribbon off the poly film

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Now use the floppy/IDE cable to stamp the ribbon in to shape.
This is easier then it looks, if you make a minor mistake, they can just do it over again until the entire ribbon looks good.

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Now take out your disassembled VLD tweeter and put some small blobs of Arctic Silver paste where the ends of the ribbon attaches to the PCB.

bee98b8e_AUT_5918.jpeg


Now put on the ribbon and stick it down, one end at the time, never work both at the same time, it will end badly.
Be very careful at this point, you have gotten far, but one mistake could force you to start over.
You can still fix minor problems by stamping the ribbon again with the cables.
Be very careful not to get any paste on the back side of the suspended part of the ribbon.

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Use your strip of cardboard to push the ribbon down so it sticks in place

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Adjust the ribbons with a finger until it's nice and straight.
Don't make it too taut or too loose, GENTLY blow at the ribbon to check tautness.

Still need work

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This looks good

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Cut out some pieces wire mesh or whatever it's called, I found this in an old monitor, make them as long as the width of the ribbon.

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Gently put them at both ends of the ribbon, once the top piece is put on and everything screwed together, this will clamp down the ribbon very effectively.

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Practice makes perfect, and the result I got here isn't.
But it doesn't matter all that much as long as the ribbon can move freely, no section of the ribbon must be stiff due to deformation of whatever.

Hope this helps, I might have went overboard on the pics though.
 
To test the ribbons, I hook them up to my Aragon 18k, wonderful tool to have.
I then open SineGen on my computer, witch is hooked up to the Aragon, and give them a tone sweep.

If I install two ribbons, I hook up both tweeters, and compare their sensitivity and listen for peaks.
Peaks are a sign of something rubbing against the ribbon, or that the ribbon can't move freely for some reason.

Thick ribbons can sound a bit harsh, thin ones will be very transparent, but much harder to make.
Thinner ribbons are less efficient, have lower power handing and poorer low end performance, but are more transparent.

That said, the ribbons I have made here, are better then the original mylar ones, these have much higher power handling, better low end performance, and the same efficiency.
They may be a bit brighter then the original ones though.

Lastly I do something I really enjoy, I play music on the ribbons full range, my home made ones have surprisingly good 'bass' or at least something that resembles bass but is so good it's astounding.
They sound thin though, but with some recordings they are amazing, it's like you get a field of sound in mid air, you can't really tell there are any speakers involved.

A good set of ribbons have been made.
 
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I'll have to roll off the ribbon more steeply I think, the 2000-3000Hz area is just too forward, making the speakers painful when I start playing loud, it can't just be room reflections.

Snare drums are too hot, S, shh, ch, sounds are like lasers.

Edit: or maybe it would be easier to roll off the bass quicker, maybe a bigger cap in the low pass filter.

Edit2: or maybe a smaller cap(s) in the high pass?

Edit3: one way communication is boring...
 
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By the way, I have tested the drivers individually, with crossover.
The forward 2000-3000Hz range is not caused by a single driver, but by the crossover.

As far as I know, increasing the value of the cap on the lowpass filter, would make the roll off steeper, am I right?

As for the tweeter, reducing the value of the first cap, would move the crossover point up higher, reducing the value of the second cap would make the roll off steeper?

Edit: research has taught me it's not that simple.
 
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I guess I should stop poring energy in to this, I'll just keep my findings to my self from now on.

I'm talking to my self, and that seems to be the case for most threads I start, so no one cares I guess.

Edit: naa I'm just tired, way too tired
 
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I have returned to using the 1.4mm coil for the high pass filter, from what I read, reducing resistance in the network, should move the crossover point up higher.

I'm thinking that my home made ribbons may have slightly higher impedance then the original ones, and I also think I have been experiencing the caps settling in.
I use Mundorf M-Caps, I have read that these caps need time to settle in.

Oh and I have made the nicest set of ribbons I have ever made, they sound very linear, the ones I started out with where bit more peaky.
 
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