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Old Yesterday, 03:53 PM   #8481
thejessman is offline thejessman  United States
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I week or so ago I posted about the difference in port velocity numbers between HornResp and WinISD. I have since received my hot wire anemometer and was able to do a quick test on an enclosure I had sitting around.

The enclosure I tested is a home theater subwoofer using a JBL GTO1014 driver in 2.0 cu ft net tuned to 23 Hz. The port is 10.5" x 1.875" for a port area of 19.6875 sq in (127.02 sq cm). I measured port velocities from 13 to 35 Hz at 20 volts and 26.2 volts.

The anemometer I have is a Testo 405i. You can see more about it here: testo 405i Hot-Wire Anemometer Smart Probe | Portable devices - Operation via smartphone | Portable devices | Product Type | Testo, Inc

Here is the inputs to HornResp I used:
Click the image to open in full size.

Here is the peak port outlet velocity:
Click the image to open in full size.

Here is the peak port velocity graph out of WinISD for the same enclosure:
Click the image to open in full size.

Here are the results from the measurements:
Click the image to open in full size.
The anemometer measure RMS velocity so to get the peak I multiplied the anemometer measurements by 1.41. I measured at both 20 volts and 26.2 volts but I only entered the values from WinISD and HornResp into the spreadsheet for 26.2 volts.

My measurements came in significantly below what both HornResp and WinISD predicted. I suspect my meter measures a little on the low side since its not optimized for bi-directional flow, it would be nice to know just how much lower its measuring, but I have no way of determining that.
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Old Yesterday, 05:13 PM   #8482
mwmkravchenko is offline mwmkravchenko  Canada
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Hornresp
Quote:
Originally Posted by thejessman View Post
I week or so ago I posted about the difference in port velocity numbers between HornResp and WinISD. I have since received my hot wire anemometer and was able to do a quick test on an enclosure I had sitting around.

The enclosure I tested is a home theater subwoofer using a JBL GTO1014 driver in 2.0 cu ft net tuned to 23 Hz. The port is 10.5" x 1.875" for a port area of 19.6875 sq in (127.02 sq cm). I measured port velocities from 13 to 35 Hz at 20 volts and 26.2 volts.

The anemometer I have is a Testo 405i. You can see more about it here: testo 405i Hot-Wire Anemometer Smart Probe | Portable devices - Operation via smartphone | Portable devices | Product Type | Testo, Inc

Here is the inputs to HornResp I used:
Click the image to open in full size.

Here is the peak port outlet velocity:
Click the image to open in full size.

Here is the peak port velocity graph out of WinISD for the same enclosure:
Click the image to open in full size.

Here are the results from the measurements:
Click the image to open in full size.
The anemometer measure RMS velocity so to get the peak I multiplied the anemometer measurements by 1.41. I measured at both 20 volts and 26.2 volts but I only entered the values from WinISD and HornResp into the spreadsheet for 26.2 volts.

My measurements came in significantly below what both HornResp and WinISD predicted. I suspect my meter measures a little on the low side since its not optimized for bi-directional flow, it would be nice to know just how much lower its measuring, but I have no way of determining that.
Looking at your post I'd be inclined to say that the graphs are in pretty close agreement.

Try changing the size of your horizontal and vertical axis to match that of the Hornresp graph and I think that you will find almost perfect agreement.
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Old Yesterday, 07:08 PM   #8483
thejessman is offline thejessman  United States
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Quote:
Originally Posted by mwmkravchenko View Post
Looking at your post I'd be inclined to say that the graphs are in pretty close agreement.

Try changing the size of your horizontal and vertical axis to match that of the Hornresp graph and I think that you will find almost perfect agreement.
I totally agree the shape of graphs out of WinISD and HornResp are very similar to each other. They also are very similar in shape to the port velocities I measured. Where I have concerns is the difference in the simulated values between WinISD, HornResp, and what I measured. For example, on 26.2 volts at 21 hz I measured 7.57 meters per second RMS. That works out to a peak velocity of 10.71 m/sec. WinISD predicts 15.17 m/sec and HornResp predicts 22.19. That's a pretty big difference. When designing enclosures I try to keep port velocities under a certain speed and its hard to know which numbers to trust.
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Old Yesterday, 09:22 PM   #8484
mwmkravchenko is offline mwmkravchenko  Canada
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Hornresp
Quote:
Originally Posted by thejessman View Post
I totally agree the shape of graphs out of WinISD and HornResp are very similar to each other. They also are very similar in shape to the port velocities I measured. Where I have concerns is the difference in the simulated values between WinISD, HornResp, and what I measured. For example, on 26.2 volts at 21 hz I measured 7.57 meters per second RMS. That works out to a peak velocity of 10.71 m/sec. WinISD predicts 15.17 m/sec and HornResp predicts 22.19. That's a pretty big difference. When designing enclosures I try to keep port velocities under a certain speed and its hard to know which numbers to trust.
I get stung by my phone again. It's a Note 8 and you think with a screen that large I would be able to follow what was what! Sorry. On the idiot box I get to see your point.

Perhaps there is an explanation. I'm pretty sure Bjorn did some pretty stringent comparisons when he was working on his Phd. And from what I can remember Hornresp was pretty darn close to what was measured.
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