Finally taking the plunge (Dayton PA310-8 TH) - Page 2 - diyAudio
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Old 19th July 2010, 04:20 AM   #11
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Here's the latest iteration I'm working with. It's a combination stepped and tapered TH. The cross-section drawing is the output from an Excel spreadsheet (still being tweaked) that I'm using to try to optimize the layout (using Excel's "goal-seek" function). Basically I put in a few parameters, select the "goal-seek" option, and it chucks out the cross-section in a chart. I could probably modify it to do a full-tapered cross-section, but that might end up in the path length being shortened a bit.

The question though is how should the path length around the corners be determined? At one time I thought that a simple arc would do it, but my measurements with POC #1 suggests otherwise, that actual path length lies somewhere between the arc length and the centerline (and closer to the latter).
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Old 19th July 2010, 03:08 PM   #12
tb46 is offline tb46  United States
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Default Hornresp_Schematic_Export

Hi Brian,

You can export the horn data from Hornresp.

Regards,
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Old 19th July 2010, 03:12 PM   #13
tb46 is offline tb46  United States
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Default Corners

Hi Brian,

I use the arc (center of bend) around the corner:

LIVE SOUND Specific Tapped Horn thread...

This should get you close.

Regards,
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Old 19th July 2010, 06:02 PM   #14
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Quote:
Originally Posted by tb46 View Post
Hi Brian,

I use the arc (center of bend) around the corner:

LIVE SOUND Specific Tapped Horn thread...

This should get you close.

Regards,
I did some quick checks with my POC #1 and it seems that the "arc" approach results in an effective length measurement that's lower than what is suggested by the measured lower resonant frequency. I'll repeat the measurements this afternoon in a bit more detail to confirm this.
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Old 19th July 2010, 09:20 PM   #15
tb46 is offline tb46  United States
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Default Path Length

Hi Brian,

The arc method arrives at a slightly shorter path than the actual box measurements indicate. But the difference is not significant, that's why I send you the reference. Maybe you can provide more accurate numbers/measurements. That would be great.

Regards,
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Old 20th July 2010, 01:25 AM   #16
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Quote:
Originally Posted by tb46 View Post
Hi Brian,

The arc method arrives at a slightly shorter path than the actual box measurements indicate. But the difference is not significant, that's why I send you the reference. Maybe you can provide more accurate numbers/measurements. That would be great.

Regards,
I repeated my measurements, using my POC#1. Here's a summary:

Design: tapped-pipe, c-section 290cm^2, split into four equal lengths of 51 cm, built using 0.75 in thick ply.

Design path length = 204 cm
Design Fb (from HornResp impedance data) = 41.5 Hz

Calculated path length = 199 cm (using arcs rather than center line)
Measured Fb (from WT3 impedance data) = 43 Hz

Hard to draw conclusions. I'm not sure what value HornResp is using for c, and it doesn't provide the option to adjust this. It should be about 347.8 m/s here, if this is different to what's built in to HornResp, then that's going to skew things a bit as well.

I'm going to switch my optimization calcs to use arcs, just in case .
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Old 20th July 2010, 03:22 AM   #17
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Quote:
Originally Posted by Brian Steele View Post
I'm going to switch my optimization calcs to use arcs, just in case .
I made the switch. Calculated horn length is reduced by a whopping 3%, resulting in enormous 2% increase in Fc. I'm not going to worry too much about it.
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Old 20th July 2010, 07:00 AM   #18
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Originally Posted by Brian Steele View Post
I'm not sure what value HornResp is using for c.
Hi Brian,

Hornresp assumes that the velocity of sound in air is 344 metres per second, and that the density of air is 1.205 kilograms per cubic metre. Note 1 on page 17 of the Help file refers.

Kind regards,

David
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Old 20th July 2010, 07:09 PM   #19
Xoc1 is offline Xoc1  United Kingdom
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Brian
Regards the folding of you TH
Here is a possible layout that might suit.
This is a cabinet I am working on that has a horn that is a similar shape to the one in your first post.
I have used the small S1 dimension to make more room for the flared mouth, and have tried to minimise any wasted space.
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Old 24th July 2010, 08:51 PM   #20
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Default Effect of Inductance on TH passband...

The first image is a TH alignment with no inductor in series.

The second is the same TH alignment with a 4mH inductor in series.

The last compares the two responses.

Of interest here is the flattening of the TH's passband, particularly the apparent increase in SPL between the two main peaks.

In theory, based on the other TH observations made on this forum, the peaks and dips will likely be a lot less than predicted, which suggests that a lot less than 4mH of inductance will be needed to flatten the passband.
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File Type: jpg Dayton PA310-8 TH (8).jpg (44.8 KB, 384 views)
File Type: jpg Dayton PA310-8 TH (9).jpg (47.3 KB, 113 views)
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