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Old 19th March 2011, 09:00 AM   #721
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Join Date: Nov 2007
Quote:
Originally Posted by kenpeter View Post
Karlson K15... Definately tapped and "keystoned?", but horn???
Karlson himself often claimed it was mathematically equivalent.
And Klipsh would flip his BS tie every time that was said...
...and Klipsh was correct, IMO .


Quote:
Using multiple stagger tuned resonant chambers rather than a
much longer and voluminous expanding path, its never been
modeled correctly that I know of.
I'll bet that it can be modelled with Akabak. The topology looks similar to an idea I came up with for modifying a TH to remove the first notch in the output. Search for "Subwoofer Dogfood Duct" to see what I'm talking about. However, modelling it is one thing - coming up with an optimized alignment is another.

I'll bet that the shape of the exit has little to do with the overall FR in the effective passband (i.e. before massive cancellations and peaks show up in the output), and it can be replaced with an equivalent circular cutout.
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Old 19th March 2011, 10:20 AM   #722
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Djim View Post
graphic representation of 2 Butterworth 48dB per Octave - lowcut filters. One is set to 40Hz (for standard SS15) and the other at 33Hz (Extended SS15)
it looks like you have cascaded a pair of 4pole Butterworth filters to end up with a 6dB cut at the 40Hz and 33Hz.
These are no longer Butterworth, which by definition must be -3dB @ the turn over frequency.
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Old 19th March 2011, 02:35 PM   #723
tb46 is offline tb46  United States
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Default Post #720

Hi Djim,

In the .pdf in Post #718 I tried to make the difference clear. On the left is an overlay drawing of the handdrawing you presented in Post #691. On the right is a drawing of what I assume a SS15-type TH would look like using your provided Hornresp input dimensions (obviously give or take a little). The layout on top is for the drawing on the right (I call it actual).

The one on the left cannot be build, you could build a layout like that, but you would have to use different Hornresp input values - or you could try to match the layout to the Hornresp values, which means you get a different layout (about the one on the right if you use the SS15-style). You just cannot have it both ways.

I have rechecked the drawing and values, and they still look correct. You are asking: "...what am I doing wrong here?...". I would suggest updating your tools. You would find even a rudimentary 2D drafting package to be a lot more accurate than your current method. It just forces you into putting real numbers with the items you draw, and if it has dimensioning capability you can extract just about any angle, line length, area you want to. You can turn layers on and off, that way you only see what you just want to look at.

If you are looking for a low cost version "Solid Edge 2D" is available free from Siemens PLM Software. There is nothing rudimentary about that package its quite nice. I know the learning curve may appear somewhat daunting, but luckily we forget about that after just a little while.

In addition to that you need to use a spreadsheet to verify your calculations, e.g.: duct cross-section v. width w. duct height.

So, I don't think you are doing anything wrong, I think your tools led you astray (been there, done that many a times, and I promise I'll do it again :-)).

Regards,
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Old 19th March 2011, 04:44 PM   #724
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Quote:
Originally Posted by AndrewT View Post
it looks like you have cascaded a pair of 4pole Butterworth filters to end up with a 6dB cut at the 40Hz and 33Hz.
These are no longer Butterworth, which by definition must be -3dB @ the turn over frequency.
Need a little help, guys. I'm trying understand the finer points of how a HiPass filter affects
the diaphragm displacement below the minimum displacement at 48Hz. I did a little work with HornResp
and it seems to indicate that I can use a 32Hz LR HiPass on the SS15 and do minimum damage to the
40Hz signal.

The d curve was plotted using the b-c intersection and the deflection at 16 Hz with 2 Watts (-24dB).
I know that this could get dangerous if the SS15 deviates from the HornResp simmed values.
Attached Images
File Type: gif ss15xo.gif (74.5 KB, 381 views)
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Old 19th March 2011, 05:37 PM   #725
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by AndrewT View Post
it looks like you have cascaded a pair of 4pole Butterworth filters to end up with a 6dB cut at the 40Hz and 33Hz.
These are no longer Butterworth, which by definition must be -3dB @ the turn over frequency.
Yep Andrew they are two 24's in serie, but you also know it doesn't matter. If you set Butterworth or any other kind of 48dB/Oct filters to -3dB at 40Hz for one cab and -3dB at 33Hz you still have 6dB difference at 33Hz. If you count that with the natural roll-off from the SS15 (47Hz) and the Extended (40Hz) you still get that 6dB difference at 40Hz...

Last edited by Djim; 19th March 2011 at 05:39 PM.
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Old 19th March 2011, 05:42 PM   #726
AndrewT is offline AndrewT  Scotland
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The shape of the roll off for a Butterworth is defined.
A pair of cascaded Butterworth is a different shape of roll off. This can be compared by looking at the Q of the two arrangements.
Butterworth has Q=1/sqrt(2).
cascaded Butterworths have Q=1/2
An 8pole Butterworth can be assembled with a Q=1/sqrt(2). This will have a different rolloff from a Q=1/2 filter.
The cascaded Butterworths are what Linkwitz Reilly use for their cross over.
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Old 19th March 2011, 05:46 PM   #727
AndrewT is offline AndrewT  Scotland
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Don,
I have seen other graphical solutions similar to yours. so I tend to agree that what you conclude is that the 4pole filter protects the driver from over excursion.

I can see from your graphical solution that the Filter (line C turn over frequency) could be moved up in frequency slightly and still protect the driver from over excursion.
A secondary effect is that the heating effect of the filtered LF is also removed from the driver VC.

As an aside,
if the filter slope matched the rise in excursion with lower frequency then the driver excursion would tend towards a horizontal line. Your steeper slope which gives reduced excursion at constant power input gives cooler running for no loss of bass.
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Last edited by AndrewT; 19th March 2011 at 05:50 PM.
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Old 19th March 2011, 05:52 PM   #728
epa is offline epa  Netherlands
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Quote:
Originally Posted by Don Snyder View Post
Need a little help, guys. I'm trying understand the finer points of how a HiPass filter affects
the diaphragm displacement below the minimum displacement at 48Hz. I did a little work with HornResp
and it seems to indicate that I can use a 32Hz LR HiPass on the SS15 and do minimum damage to the
40Hz signal.

The d curve was plotted using the b-c intersection and the deflection at 16 Hz with 2 Watts (-24dB).
I know that this could get dangerous if the SS15 deviates from the HornResp simmed values.
hi don
this is how i guestimate my hpf.
i simulate a br box with the same driver tuned @the same fs as the th horn minimum excursion in winisd alpha.
ad power to go to x-max/x-damage
then ad a filter then you can see what the excursion does
Click the image to open in full size.

Last edited by epa; 19th March 2011 at 05:56 PM.
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Old 19th March 2011, 05:54 PM   #729
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by tb46 View Post
Hi Djim,

In the .pdf in Post #718 I tried to make the difference clear. On the left is an overlay drawing of the handdrawing you presented in Post #691. On the right is a drawing of what I assume a SS15-type TH would look like using your provided Hornresp input dimensions (obviously give or take a little). The layout on top is for the drawing on the right (I call it actual).

The one on the left cannot be build, you could build a layout like that, but you would have to use different Hornresp input values - or you could try to match the layout to the Hornresp values, which means you get a different layout (about the one on the right if you use the SS15-style). You just cannot have it both ways.

I have rechecked the drawing and values, and they still look correct. You are asking: "...what am I doing wrong here?...". I would suggest updating your tools. You would find even a rudimentary 2D drafting package to be a lot more accurate than your current method. It just forces you into putting real numbers with the items you draw, and if it has dimensioning capability you can extract just about any angle, line length, area you want to. You can turn layers on and off, that way you only see what you just want to look at.

If you are looking for a low cost version "Solid Edge 2D" is available free from Siemens PLM Software. There is nothing rudimentary about that package its quite nice. I know the learning curve may appear somewhat daunting, but luckily we forget about that after just a little while.

In addition to that you need to use a spreadsheet to verify your calculations, e.g.: duct cross-section v. width w. duct height.

So, I don't think you are doing anything wrong, I think your tools led you astray (been there, done that many a times, and I promise I'll do it again :-)).

Regards,
I used Photoshop to put both designs on top (not my drawing but yours.) and somehow I ended up with something like 6 or 7 inches longer path. But if you checked it I'm sure I have made a mistake somewhere down the line.
I'm looking for a drawing program but everybody seems to use another and I only need it for this kind of work. Google Sketch is not really my thing somehow. What I need is a fast learning curve (Adobe style would be great), output compatibility with CAD, I want to be able to draw simple lines just like in paint, and what i prefer is that I can work straight on the picture also instead of filling endless numbers all the time. Any tips?
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Old 19th March 2011, 06:18 PM   #730
Djim is offline Djim  Netherlands
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Guys I think you are all forgetting something important, the cone can show instabilities under the the 1/3 wavelength and theoretical models are not showing that. And that's beside the fact that music signals are complex and dynamic modulations and also can have big effect on excursion. When you powering to the max these things are important...

Last edited by Djim; 19th March 2011 at 06:26 PM.
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