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Old 28th August 2012, 07:28 AM   #141
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Over the last couple days I built my first Paraline using 6.35mm wood. (All of my other Paralines used Luan (sp?), which is 5mm)

Switching to 6.35mm really nuked the output above 16khz; it's been reduced by about 6dB at least, while using a compression driver that routinely goes to 20khz. (Celestion CDX1-1425.)

Just something to look out for if you try and build these; the height of the line really seems to set a steep limitation on high frequency output.

Click the image to open in full size.
Have been tempted to drive over to Tap Plastics and try to make one out of plexiglass, I think that might simplify lining up all the devices, plus it would look rad

Geddes uses plexiglass to line up compression drivers on his waveguides, and I copied that trick with some ribbons a few months ago. Works really nice.
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Old 28th August 2012, 01:56 PM   #142
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Originally Posted by Patrick Bateman View Post
Over the last couple days I built my first Paraline using 6.35mm wood. (All of my other Paralines used Luan (sp?), which is 5mm)

Switching to 6.35mm really nuked the output above 16khz; it's been reduced by about 6dB at least, while using a compression driver that routinely goes to 20khz. (Celestion CDX1-1425.)
Patrick,

Did going from 5 mm to 6.35 mm drop output by 6 dB @16 K, or is the 6.3 mm Paraline down 6 dB @ 16 K from a "normal" horn?
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Old 28th August 2012, 02:23 PM   #143
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weltersys,
I think what Patrick is saying that compared to his earlier design with the thinner cross-sections that the high frequency roll off was that severe. I am just watching this thread, I am not a big fan of these designs but I see what seems to be going on here. What I think is happening is that the Paraline is acting as a resonant trap that is tuned by the different dimensions of the folds. By changing the height of the sections you have increased the filtering or trapped the upper frequencies by setting a resonant trap at this particular frequency and anything above is attenuated. I would think if you decreased the cross-sectional height that just the opposite function would occur and the upper frequency output would increase but probably at a cost of the lower frequencies due to increased restriction. It looks like you are adjusting a band pass filter in this section. I will wait to see what Patrick or someone else says about this. I am only making these observation thinking about how I believe this folding mechanism is functioning.

Steven
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Old 28th August 2012, 02:27 PM   #144
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Originally Posted by Patrick Bateman View Post
These things are so easy to build, I say just dive in and make one. No need to make this too complex. If you can live with a flat wavefront, then cut five pieces of wood and make each piece twice as tall as it is wide. Draw the 'eye' by hand. Array the driver(s) around the center. Make the mouth about 2cm wide, and as tall as the long end of your wood.

Boom! You got a Paraline.

Humor me and post videos of it plz
Now you've done it. Cheapie drivers ordered. :P Will report back on my shenanigans soon.
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Old 28th August 2012, 02:55 PM   #145
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onebadmonte,
Your last statement is one that I just can't understand or abide by. Just because this construction seems so simple why would you or anyone think that this would make a cheap device sound good. A poorly designed device with poor frequency response is not going to be improved by this loading scheme, that doesn't make any sense at all. You may be band limiting some of the extreme problems of the driver but they are still there and will be in the end. I see all these people talking about using cheap poor devices and I wonder where they think the magic is that is going to fix them? A terrible sounding compression driver will still sound terrible and have the same problems it has had all along. What I believe is even with this device is that thoughtful design would improve the accuracy of the frequency response and haphazard dimensions will only make the frequency response that much more ragged. I have already thought of some major way to improve this design but they would be much more difficult to produce. This follows with the design of any and all waveguides, there is no free lunch......
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Old 28th August 2012, 03:52 PM   #146
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Originally Posted by weltersys View Post
Patrick,

Did going from 5 mm to 6.35 mm drop output by 6 dB @16 K, or is the 6.3 mm Paraline down 6 dB @ 16 K from a "normal" horn?
Jury is still out - my measurement system is anything but elite. But it seems like going from a Paraline with an internal height of 5mm to one with a height of 6.3mm really rolled off the output above 16khz. (same compression driver on both)

Another possibility is simply that my woodwork is too sloppy. (Having said that, the 5mm Paralines were even sloppier, and they had significant output above 16khz)

Danley's 'rule of thumb' is that the internal height of the Paraline should be set to no more than one third of the highest wavelength. For instance, an internal height of 0.5cm should get you to 22,666hz. Perhaps it's more like one quarter wavelength? That would indicate an upper limit of 17khz for an internal height of 0.5cm.

Again, jury is still out on this. It may be poor workmanship. I've also noticed that there seems to be a correlation between Paraline size and high frequency output.
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Old 28th August 2012, 04:03 PM   #147
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Patrick,
I think that you just discovered what I said earlier. The height is acting as a frequency trap and the 1/4 rule applies in every instance of waveguide design that I have ever done. If you decrease the distance or thickness of the cross-sections below the 0.5 cm and leaving all else the same let's see if the high frequency doesn't get over the 17khz figure you sighted. What I am wondering is what is happening on the other extreme at the lower frequency leaving the final mouth size and cutoff the same. I would bet that you are increasing the Q of the horn and the response curve will have an increase in the middle of the band. I also wonder if your compression driver even has any real output in the upper frequencies, this is a standard issue with almost every compression driver. Most 1" drivers start to turn down by about 12Khz and fall from there.
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Old 28th August 2012, 04:41 PM   #148
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Originally Posted by Kindhornman View Post
Patrick,
I think that you just discovered what I said earlier. The height is acting as a frequency trap and the 1/4 rule applies in every instance of waveguide design that I have ever done. If you decrease the distance or thickness of the cross-sections below the 0.5 cm and leaving all else the same let's see if the high frequency doesn't get over the 17khz figure you sighted. What I am wondering is what is happening on the other extreme at the lower frequency leaving the final mouth size and cutoff the same. I would bet that you are increasing the Q of the horn and the response curve will have an increase in the middle of the band. I also wonder if your compression driver even has any real output in the upper frequencies, this is a standard issue with almost every compression driver. Most 1" drivers start to turn down by about 12Khz and fall from there.
Haha I am a tool.

It looks like one of the reasons that I'm losing output in the top octave is because the midrange is playing much higher than I'd expected.

Click the image to open in full size.

Here's an example of this. Let's say you have a midrange diaphragm that's 10cm away from our compression driver diaphragm. If both diaphragms are radiating 2000hz, then they can be about 4.25cm apart before the pathlength difference begins creating problems. (The formula is [speed of sound / pathlength / 4]

But by 8khz, our margin of error is 1.0625cm! And by 16khz, it's a fraction of a centimeter!


So - long story short - I'm a tool

It's likely not the height of the line that's hosing me up here, it's likely the very extended response of the 2" midranges that I'm using in my Paraline. They're creating a mess of comb filtering above the point where they're more than 1/4 wavelength apart, or about 1900hz or so.

The reason that the other Paraline didn't suffer from this problem was because I was using the Pyle 5" midrange, which does not play as high at all. It has a treated cone, AND it's larger, AND it has more inductance.




One thing about the Paraline which is a bit mystifying is that the sound does not radiate until it reaches the mouth but that doesn't mean that the pathlength doesn't matter. This was one of the things that sorta made my head explode when I first realized it, the idea that you could have a midrange and a tweeter that aren't even radiating sound, but you still have to be conscious of driver geometry. (IE, even if the duct is too small for the wave to form, there's still an inherent time delay due to pathlength differences.)

In fact, I'd argue that you have to be MUCH MORE conscious of driver geometry in a Paraline than in a conventional horn, or on a flat baffle. For instance, let's say you have one of the Lambda Unity horns. It has a coverage angle of sixty degrees. At the point where the midranges tap into the horn, the energy radiated by the compression driver is already covering about one hundred square centimeters. I have a feeling that this would minimize comb filtering to a degree. The worst case-scenario for comb filtering would be a situation where you have two drivers that are more than 1/4 wavelength apart, *and* they're radiating the same energy, *and* that energy is constrained into a duct where the radiation is very intense. Like in a Paraline


Last edited by Patrick Bateman; 28th August 2012 at 04:58 PM.
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Old 28th August 2012, 05:18 PM   #149
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Patrick,
Please turn off the midrange drivers and then tell me what the frequency response of only the compression driver is alone on the different thickness sections does. This is the effect that I want to see, not the interaction of the two devices after combining. I want to know what the actual folded section is doing with the variation in thickness.
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Old 28th August 2012, 06:32 PM   #150
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Originally Posted by Kindhornman View Post
Patrick,
Please turn off the midrange drivers and then tell me what the frequency response of only the compression driver is alone on the different thickness sections does. This is the effect that I want to see, not the interaction of the two devices after combining. I want to know what the actual folded section is doing with the variation in thickness.
To actually do a valid comparison would also requiring covering up the mid range exit ports, as they will allow some amount of HF energy in, which will take a longer time to come out (unless it is absorbed, in which case it is lost output) than the rest of the HF driver's output, also contributing to HF loss or peaked response.

That said, for a quick comparison, shorting the mid drivers out while testing the HF will get part way there in determining what is causing the HF loss.

The high frequencies above 14,500 Hz or so in my Paralines using 1/4" gap (about 6mm) roll off at a steeper rate than using a standard conical expansion horn with the same driver.

Art
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