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TH vs CH1 (SS15mod vs Half-SKHORNmod) Comparison exercise
TH vs CH1 (SS15mod vs Half-SKHORNmod) Comparison exercise
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Old 11th September 2018, 11:51 PM   #1
LORDSANSUI is online now LORDSANSUI  Brazil
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Default TH vs CH1 (SS15mod vs Half-SKHORNmod) Comparison exercise

Hi all,

Just sharing a comparison case I made between Tapped Horn and Compound Horn after became curious reading the design published by Josh Ricci indicated below:

Ricci's Skhorn Subwoofer

TH under comparisson (SS15mod):

TH 15" flat response to 35Hz (-3dB) - By LORDSANSUI

I got the hornresp input published by Josh and made some changes in order to consider only one driver per cabinet and also considering 15" over 21". The result was promising but it wasn't easy to keep all variable under control, mainly the port particle velocity.

To keep the design simplicity and to keep port particle velocity under 30 m/s I decided to change the design from Offset Horn with rear vented chamber [OD] to Offset Horn with rear chamber coupled to other Horn or to a flared port if you prefer, and this design can be modeled using the new feature in the Hornresp: CH1

Attachment #1 - Josh hornresp input modeled as OD compared to the same design modeled as CH1, the results are exactly the same as expected.
Attachment #2 - The cab layout was changed from port with constant cross section area to a parabolic flared port.
Attachment #3 - An sketch was made using solidworks in order to have parametric geometries

To proper compare TH vs CH1 the constrains below were frozen:
  • Single driver per cab
  • Driver model: Snake HPX2150 15"
  • Compression ratio: ~1,76:1
  • External cab dimensions: 783mm x 586mm x 647mm [HxWxD]
Attachment #4 - TH vs CH1 cab layout comparisson (otimization can be done)
Attachment #5 - Hornresp input comparisson
Attachment #6 - Hornresp result comparisson

Considering above constrains the CH1 present the pros and cons below:

Pros:
Higher efficiency
Flatter frequency response
Big dip at higher frequency
Lower phase response decay
Significantly simpler to build
Better driver and baffle couple to avoid leakage
Cons:
Higher diaphragm displacement
Higher group delay at tunned frequency
More power compression (driver assembled internally)
Needs removable panel to access the driver
Attached Images
File Type: png OD vs CH1.png (43.1 KB, 227 views)
File Type: png Flared vent.png (12.9 KB, 225 views)
File Type: png Sketch.png (98.2 KB, 228 views)
File Type: png TH and CH1 - Comparison - Layout.png (56.0 KB, 231 views)
File Type: png TH and CH1 - Comparison - Hornresp input.png (26.5 KB, 227 views)
File Type: png TH and CH1 - Comparison - Hornresp results.png (69.5 KB, 91 views)
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Old 12th September 2018, 01:26 AM   #2
Brian Steele is offline Brian Steele  Grenada
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Interesting comparison.

The higher GD would nix the "compound horn" design for me. It's significantly higher than that of the TH, if you look at the delta change in GD across the passband. It's also higher than the ~18ms @ 40 Hz that I try to stay under. And if I'm measuring vent compression with vents as large as 2/3rds Sd, we're definitely going to see vent compression with that design at low frequencies.

Concerning complexity, the requirement for a removable plan IMO makes the CH design more complex. The internal panels in the TH also act as cross-bracing for the side panels, which improves upper bass performance.

For an interesting comparison, take a known TH design and just convert it to an OD alignment instead (by just changing the option from TH to OD).
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Old 12th September 2018, 11:09 AM   #3
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by Brian Steele View Post
Concerning complexity, the requirement for a removable plan IMO makes the CH design more complex.
That should be "removable panel"...
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Old 14th September 2018, 01:29 AM   #4
LORDSANSUI is online now LORDSANSUI  Brazil
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Note: The compound is the black line, the gray one is the tapped Horn.

The group delay at tuned frequency comes from the vent at rear chamber, in this case it can be optimized as all bass reflex. Check the horn 1 and horn 2 output separately to confirm. I just need to figure out how to do it
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Old 14th September 2018, 08:32 AM   #5
David McBean is offline David McBean  Australia
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Quote:
Originally Posted by LORDSANSUI View Post
I just need to figure out how to do it
Step 1 - Select Window > Acoustical Power
Step 2 - Select Tools > Output > Horn 1 (or Horn 2)
Step 3 - Select Window > Group Delay
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Old 14th September 2018, 12:19 PM   #6
LORDSANSUI is online now LORDSANSUI  Brazil
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Hi David,

Thanks but I know how to check de simulation, what I don't know is how to change the GD by changing design parameters
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Old 16th September 2018, 06:40 AM   #7
David McBean is offline David McBean  Australia
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Hi Marcelo,

Sorry, it seems that I misunderstood your post :-).

I assume that you have already tried changing slider values in the Loudspeaker Wizard, to see the effect on group delay?

Kind regards,

David
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Old 18th September 2018, 10:28 PM   #8
LORDSANSUI is online now LORDSANSUI  Brazil
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Hi David,

Yes I tried, Loudspeaker Wizard is an amazing feature that short cut many things, but when I fix the GD other characteristic was compromised, like reducing rear chamber volume the GD reduces and the lower end was impact as well, I tried to compensate it changing the vent but wans't possible. To have the same GD as TH something will be lost. I don't know if the difference is so bad, Brian indicated ~18ms @ 40 Hz but just adding HP filter the values will double.
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