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Old 14th March 2011, 06:31 PM   #641
jbell is offline jbell  United States
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djim:

so I make the front panel 1/2" longer and the vertical panel attached to point one, 1/2" shorter to raise the rear of the driver, and things are better?

It would make point 21 bigger, but also point 10-14...

Click the image to open in full size.

Last edited by jbell; 14th March 2011 at 06:33 PM.
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Old 14th March 2011, 06:52 PM   #642
tb46 is offline tb46  United States
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Hi AndrewT,

This is based on my best effort to draw what jbell built to fit with one sheet of plywood (48"x96").

I'll attach the latest greatest Hornresp Input/SPL.

Regards,
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Old 14th March 2011, 06:55 PM   #643
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by AndrewT View Post
1.)Are these pinch points designed into the flow path?
2.) Are we/you measuring the layout accurately?
3.) There is no reason to insert a restriction around a bend, if the design does not need a restriction.
1.) Yes
2.) You always should take exact numbers with a certain tolerance when it comes to reality. But I have no reason to doubt Oliver his art.
3.) ?
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Old 14th March 2011, 07:01 PM   #644
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by jbell View Post
djim:

so I make the front panel 1/2" longer and the vertical panel attached to point one, 1/2" shorter to raise the rear of the driver, and things are better?

It would make point 21 bigger, but also point 10-14...
Jbell, can you make quick drawing of your changes over the cab as it is? You don’t need to worry to much about expanding corner 10 and 14 cause you can always use corner correction if needed.
Btw, do you have measurements above 120Hz?

Thanks oliver...

Last edited by Djim; 14th March 2011 at 07:03 PM.
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Old 14th March 2011, 07:16 PM   #645
Djim is offline Djim  Netherlands
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Let’s check how accurate Oliver is:

Total path length = 2,4118 meter

1/3 wavelenght = 47Hz (below this point you should see a drop in SPL)
2/3 wavelenght = 94Hz (above this point the design/driver reaches is max efficiency)

Measuring results from JBell & Runrod1948:

40hz 98.5.............40hz 101db
45hz 100.5...........45hz 104db

1/3 wavelenght = 47Hz
50hz 102..............50hz 108db
55hz 103.5...........55hz 109db
60hz 105..............60hz 111db
65hz 105..............65hz 111db
70hz 105..............70hz 112db
75hz 104.5...........75hz 112db
80hz 104.2...........80hz 110db
85hz 104..............85hz 112db
90hz 104..............90hz 113db
2/3 wavelenght = 94Hz
95hz 104..............95hz 112db
100hz 104.5..........100hz 113db
105hz 105............105hz 112db
110hz 105............110hz 112db
115hz 105.5..........115hz 113db
120hz 106.5..........120hz 113db

Or should I say how accurate the builders are?

To me it proves the SS15 is one of the best balanced cabs around and it will be very difficult to get a few dB's extra without losing its low-end. But I still think you can optimise its design, but how far that will result in real dB's???

Last edited by Djim; 14th March 2011 at 07:28 PM.
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Old 14th March 2011, 07:40 PM   #646
jbell is offline jbell  United States
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DJIM:
I'm not sure if I kept measurements above 120, I know I did up through 200hz and it was basically flat, but that's from (faulty) memory -- so take that with a grain of salt... It also snowed last night / this morning, so I'm not doing any outdoor tests just yet....

Here's what I was thinking of. Keep in mind that the 8" board with the angle on it, is the last board cut against the baffle -- and the baffle has zero give in it's dimension, so it is never quite 8", usually it's about 7.75 or so at it's longest.

When I assemble these I always use the 'swinging gate' method. I find point 32-36, and then make the baffle/vertical board fit so that it lines up with that point and the front panel. Everything else is a piece of cake once that is done.
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Old 14th March 2011, 08:16 PM   #647
Djim is offline Djim  Netherlands
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JBell, when I compare it with Oliver’s’ latest HornResp your point 21 is getting even more narrow. But when I look to Oliver’s prediction you see a peak around this freq. So they can equalize each other and maybe that’s why you measured a flat response around this area (in my earlier statement I thought there was a dip in HornResp like in most TH's but that isn’t the case, sorry for that).

My worry is about the dip in prediction of HornResp, so that's why I asked for >120Hz responses.

The inch (12,7mm) rise of the driver-panel brings the narrowing between points 40 and 41 back to 1/8 of the horn path. This means the narrowing now falls with “acceptable tolerances”

By rotating the driver panel just by half that inch and the slightly rotation of the panel above should raise the S2. That would explain why your ‘dip’ around the 90Hz is just 1dB. Did Runrod1948 use your ‘changes’ also?

It looks like you already did changes for the better. But I think we should seriously look at Oliver's suggestion earlier on this threat.

Last edited by Djim; 14th March 2011 at 08:21 PM.
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Old 14th March 2011, 08:31 PM   #648
jbell is offline jbell  United States
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Forgot I had this:
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Old 14th March 2011, 08:54 PM   #649
Djim is offline Djim  Netherlands
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Click the image to open in full size.

Remember this? In the last picture you can see how your SS15 looses it's effectiveness when driving harder. This is the result of BL dropping and complex air mass and speed changes. That's why I asked you a while ago to measure your SS15 at full load. And this is the real key for improvement.

Or does anyone design PA cabs for 1V/1m use or believe HornResp predictions at Xmax and *higher*...

(*higher* = [Xmax +Xlim] : 2 )
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Old 14th March 2011, 09:03 PM   #650
tb46 is offline tb46  United States
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Hi jbell,

You have done such a fine job with the original SS15 layout that I don't think it will improve acoustically, but if you want to redesign the exact locations for the internal baffles then maybe the changes that I proposed for 4pyros in Post #627 would be applicable. It would require working all the way through the hornpath, just tilting the driver baffle, and the opposing board won't quite do it. You have to find the correct angle to arrive at the correct internal path width to fill the complete width of the box across the top (hope that makes sense), then you continue that same angle down the horn section at the backboard to the point where it meets with a board coming of the right lower corner of the driver baffle (right angle to the driver baffle). I've done this a number of times now, and it is time consuming, and just to make it more fun it changes everytime you tilt, and or raise or lower, the driver baffle, or the driver position (sometimes only slightly, but it changes). And just because you improved the flow through the horn does not mean, that the composite output is also improved; maybe quite to the contrary.

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