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Ooh looky - a TH that does from ~42Hz-500Hz +/-3dB
Ooh looky - a TH that does from ~42Hz-500Hz +/-3dB
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Old 24th September 2016, 04:53 PM   #11
Brian Steele is offline Brian Steele  Grenada
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[QUOTE=tb46;4838800]Hi Brian,

Were you thinking of Don Snyder's LAB12 TH fold?

Lab12 - Tapped Horn -

That could be it, though I seem to remember that cutoff stub before S1 being a bit longer. That looks like an MTH fold with the mouth moved to one side instead of facing into the horn.

The stub doesn't actually have to be too long. According to Everest's "Acoustics" book, 4 inches of fiberglass wool 3lb/cu.ft. is enough to absorb down to 125 Hz. So the idea here is to basically make it long enough so that, when you stuff it, all the peaks in the frequencies you don't want (typically above 100 Hz) are damped.
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Old 24th September 2016, 08:14 PM   #12
tb46 is offline tb46  United States
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Hi Brian,

Here is a quick sketch @ adding a L12 stub to a THAM style enclosure, this could be combined w/ cone compensation if desired:

Regards,
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File Type: pdf THAM_Mod_L12_stub.pdf (4.8 KB, 125 views)
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Old 13th October 2016, 01:32 AM   #13
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by tb46 View Post
Hi Brian,

Here is a quick sketch @ adding a L12 stub to a THAM style enclosure, this could be combined w/ cone compensation if desired:

Regards,
Hmm, that's a pretty interesting way of addressing the requirement, and it should help to reinforce the external panel at S1 and S2 as well - one of the "weaknesses" of this type of fold (large flat panel at a high-pressure location).

I suspect that I can achieve the same result by replacing part of the extended S1-S2 path with a simple volume instead. As it's going to be pretty stuffed, its dimensions should have little impact on FR as the stuffing is going to damp the response at those frequencies anyway. This allows for some flexibility for using this approach in other types of folds like the "SS15" fold (and hmm... maybe that might explain the "stub" used in TD's designs).

HornResp can't model a TH with a volume tacked on at S1, but I'm sure it can come very close if we break S1-S2 into S1-S1'-S2, then incorporate into the horn's layout a volume at S1' that's equivalent to the S1-S1' section in the HornResp model. The length of that section should be short enough so any aberration between the model and the horn's actual response will be at frequencies outside of the bass range.
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Old 13th October 2016, 01:46 AM   #14
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by weltersys View Post
Brian,

210 L is not all that big for a "horn" cabinet, but "big" is a relative term, all depends where you plan to stick it
Any design I come up with has to fit in my car's trunk, and I think one that requires 210 L of net volume is probably going to be a bit too big for that, LOL.

I'm going to measure the available trunk space and work backwards from that. It's likely I might have to go with a somewhat compromised design, but then all designs involve some sort of compromise, don't they....
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Old 13th October 2016, 05:00 PM   #15
weltersys is offline weltersys  United States
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Originally Posted by Brian Steele View Post
Any design I come up with has to fit in my car's trunk, and I think one that requires 210 L of net volume is probably going to be a bit too big for that, LOL.

I'm going to measure the available trunk space and work backwards from that. It's likely I might have to go with a somewhat compromised design, but then all designs involve some sort of compromise, don't they....
Yes, the pair of subs I will be using for my home theater also are designed to fit in the trunk of my Mustang, so could only be 21.5 inches (67 cm) wide, 18 inches (46 cm) deep and 11.25 inches (28 cm) tall, a bit less than 210 L.

At least they will be lightweight ;^).

The subs would have been done by now had I not spent 20 hours cleaning up after Matthew, hurricanes are a compromise of living in this part of the country. At least it seems to have started cooling off a bit after the hurricane blew through, turned off the air conditioners for the first time in the four months here a few days ago, though have them on again today.

Time to vacuum the leaves out of the house, at least they are easier to clean than the coal dust I dealt with for the 20 years before moving to Florida...

Art

Last edited by weltersys; 13th October 2016 at 05:03 PM.
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Old 12th February 2017, 10:37 AM   #16
LORDSANSUI is offline LORDSANSUI  Brazil
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This thread is really old but would be very interesting to see the results if they are available.
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Old 12th February 2017, 09:20 PM   #17
Xoc1 is offline Xoc1  United Kingdom
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What would be a practical material to use for stuffing the stub?
Also what would be the best way to ensure what it stays in place?
I imagine that the material in the stub would be moving around quite energetically.
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Old 12th February 2017, 09:25 PM   #18
Brian Steele is offline Brian Steele  Grenada
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What would be a practical material to use for stuffing the stub?
Also what would be the best way to ensure what it stays in place?
I imagine that the material in the stub would be moving around quite energetically.
Polyester fiberfill should do the job.

The area is a high-pressure, not high-velocity area so it shouldn't move around that much. However, a wire mesh or a piece of speaker grille cloth stapled across the stub can be used to keep it in place. Even old t-shirt material should work well for this.
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Old 16th February 2017, 10:02 AM   #19
Xoc1 is offline Xoc1  United Kingdom
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I have been looking to find some data on airflow resistivity of lining materials which is the parameter needed by Hornresp and is measured in mks rayls/m.
It seems to be quite hard to come by this data. Has anyone got any links to how to find out this parameter for different acoustical adsorbent materials?
With a denser material it seems possible to dampen the higher frequency ripples with a 50% filling between s1 and s2 avoiding the area where the drive unit is. I have simmed with an airflow resistivity of 4000 to 20000 and that shows significant reduction in the peaks at the higher end of the passband. I note that the default record in Hornresp uses a lining with a resistivity of 40000.
Reducing these peaks could reduce the need for such a high order low pass filter in the system design.
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Old 16th February 2017, 10:05 AM   #20
USRFobiwan is offline USRFobiwan
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Ooh looky - a TH that does from ~42Hz-500Hz +/-3dB
I was also expirmenting with this in sims. I wonder if lining the first section with something like dynamat or bitumen would have impact or not. Guess i need to get my TH18 prototype out again and do some RL testing with differrent materials. Although in the Xoc1 TH18 sim I got more results with filling S4, it flatten out the peaks > 110.

Also note that the xmax is raised a lot.

Last edited by USRFobiwan; 16th February 2017 at 10:32 AM.
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