TH-18 Flat to 35hz! (Xoc1's design) - Page 48 - diyAudio
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Old 27th January 2012, 05:11 PM   #471
epa is offline epa  Netherlands
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Quote:
Originally Posted by tb46 View Post
Hi epa,

I'm running Xp, and will as long as possible. Sorry, but no further help.

Regards,
tnx oliver
i got it running on a vm.
a got an extra section in ,and a hpf.
now i want to put in a eq,but cant figger out how .

sorry 4 the oftopic
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Old 28th January 2012, 12:13 AM   #472
Zero D is offline Zero D  United Kingdom
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In Post # 31 here - Crazy box design - Input please! - i posted a screeie of a design i did, which included an extended mouth.

Djim posted an extender in Post # 461 here - TH-18 Flat to 35hz! (Xoc1's design) - His graph clearly shows improvements below 55Hz, & also up to 150Hz

So based on that, i'm wondering how my design would fail to offer some LF improvement/s ?

Quote:
Originally Posted by djk In Post # 32 Crazy box design - Input please!

The 'horn' part of the port adds nothing below 100hz, it's just a port.
TIA
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Old 28th January 2012, 12:49 AM   #473
Djim is offline Djim  Netherlands
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Hi Zero D,

Your example is based on a basreflex system and my example is based on a 1/4 wavelength resonator (horn/tapped horn/ pipe). In other words my example is increasing the length of the hornpath.
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Old 28th January 2012, 01:18 AM   #474
Djim is offline Djim  Netherlands
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Yellow parts represent the extenders:

Click the image to open in full size.

Last edited by Djim; 28th January 2012 at 01:21 AM.
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Old 28th January 2012, 02:48 PM   #475
tb46 is offline tb46  United States
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Hi Djim,

There is a big step in Post #461 that is not reflected in #474.

Regards,
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Old 28th January 2012, 04:02 PM   #476
Djim is offline Djim  Netherlands
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[QUOTE=tb46;2881596]Hi Oliver,

The model was only intended to show the difference in principles. In reality the 'big step' isn't a big problem below 120Hz. Its length is much smaller than 1/6 of the hornpath length.
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Old 31st January 2012, 05:56 PM   #477
Zero D is offline Zero D  United Kingdom
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@ Djim

Quote:
In other words my example is increasing the length of the hornpath
Gotcha Thanks
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Old 31st January 2012, 08:51 PM   #478
Xoc1 is offline Xoc1  United Kingdom
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Default Compression Ratio?

Iím Thinking about the horn throat design for the TH18
My first observation is about the compression ratio (as reported in Hornresp when you hover over the S2 area.)
Most people on DIYaudio try to keep this ratio fairly low. 2:1 or thereabouts.
At this point in a TH you are only looking at half the driver, the other half is past that point in the horn. Does this reduce the supposed compression ratio at the S2 area by at least 50%.?????
Your thoughts please!
Regards Martin. (Xoc1)
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Old 31st January 2012, 09:46 PM   #479
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I do think tapped horns can support higher compression ratio's than front loaded and back loaded horns can.

When sound is seen from the perspective of moving particles (part of the dual theory) as well as behaving as a mass (spring/mass). Air molecules in a front loaded horn, are pushed by one side of the cone. The entire air mass is thus "resting" on one side of the cone and in the example of an outward cone movement are pushed through the throat and simultaniously counteracting/pushing on the cone.

In a tapped horn (and other similar designs the mass/molecules are pushed by one side of the cone whilst the other side pulls them through the throat (vacuum). That could help to easy the stress on one side of the cone, as it's helped from near the mouth.

Best regards Johan
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Old 1st February 2012, 08:28 AM   #480
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by Rademakers View Post
In a tapped horn (and other similar designs the mass/molecules are pushed by one side of the cone whilst the other side pulls them through the throat (vacuum). That could help to easy the stress on one side of the cone, as it's helped from near the mouth.

Best regards Johan
Hi Johan, that makes sense but only at low frequencies. Is that not what happens when the driver becomes unloaded below the resonant frequency and a hi-pass filter is needed to avoid excessive excursion.

I think that the maximum compression in the TH horn is reached at the point in the horn next to the edge of the driver, not the centre.
As such the Hornresp compression ratio reported is still useful information but does not specifically relate to the actual S2 point in the horn.
Flow analysis sim screenshot attached to illustrate this.
I am trying to concider what is really happening in the TH horn throat.
Regards Martin
Attached Images
File Type: jpg Flow 1 Braced TH18.jpg (148.0 KB, 918 views)
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