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Tapped Horn for B&C 15NW100
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Old 10th January 2017, 06:43 PM   #41
turbodawg is offline turbodawg
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Quote:
Originally Posted by martinsson View Post
Due to the way the THAM folding scales making it deeper alone will not work without messing up the expansion, but that might be self explanatory, the only way I know to keep the height intact and increase the depth with maintained expansion throughout the path is to reduce the S1 & S2 and /or the S3 & S4 areas.

If you want to make a lower tuned THAM folded TH here are a few things I kept in mind when designing the original :

Decreasing the S1 & S2 will increase the stress on the driver at higher power levels which might introduce distortion.

Decreasing the S3 & S4 will leave you with less surface coupling to the air outside the box which might negatively impact the overall efficiency.

Increasing the path length alone to tune it lower will most likely reduce the efficiency, if you want to keep the efficiency and tune it lower you need to scale the cross section surfaces along with the path lengths meaning scaled up box dimensions overall.

I do not mean to discourage you from trying this, I only wanted to make sure you know what I see as the potential downsides that might arise in this so you can balance it in a better way from the start if you want to pursuit a lower tuning.
Thanks! I agree the height (and areas) would get larger too or it would lose some efficiency. For example, I calculate your tham15 at 6.6 ft^3 overall, while I could go for a design that's in the 8+ cubes range with a simmed f3 of 35hz in a single. I'll have to take a much closer look at it at some point.

Last edited by turbodawg; 10th January 2017 at 06:48 PM.
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Old 11th January 2017, 12:51 AM   #42
tb46 is offline tb46  United States
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Default Just pondering... :-)

Hi Y'all,

Post #36: "...there are 3 horizontal path sections..."

The THAM15 has four horizontal sections, when you add what I call the Forsman extension to it you get five horizontal sections. How much you gain in which horn section depends on if you move the driver forward towards S5 in the mouth or leave it back against the vertical duct. The reason I like it back is that I found a small improvement in the first dip below (in frequency) the two big tapped horn peaks.

If you have freedom for the external size you can just scale an existing fold, then the areas and the length increase at the same ratio; if you don't want an increase in e.g.: S2 you have to change the flare rate, i.e.: rotate the internal duct inside the external box. If you have to fit a fold into a given box size you most often will have to change the flare rate (angle) to make things fit. It can become a rather time consuming trial and error exercise. Martina's dimensions were almost a natural fit for the THAM15 w/ extension, so it didn't take too many tries to arrive at something that looks pretty good on paper. Bye the way, this can be build w/ only one additional board over the THAM15 if you use a mouth without the additional 45° flares. I think the flares-and some corner reflectors-may help, but I don't know this for sure, and they are not a basic design requirement.

The more I look at the "cone correction" it does look like the way to go as it can be viewed as placing the center of the driver right @ the end of the horn w/ the S1-S2 section becoming a tuning stub of sorts (?). It also makes it very easy to get a sturdy construction in the throat section; you can completely bridge the duct at the center of the driver, and still bring in the duct sides until you just have two S2 size slot openings left and right of the blocked horn path; one opening towards S3, and the other towards S1. You have to watch for excursion clearance...

Regards,
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Old 11th January 2017, 08:59 AM   #43
USRFobiwan is offline USRFobiwan
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Interesting arguments from all of you. TB46 I lost you in your last sentence about the tuning stub, I try to visualize it in my head but I draw a blank there.

Seems like making a deeper version is out of the question.

Below is one of my tham15 prototypes:
Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

I extended the sides to make room for some handle cutouts. It also makes it stronger in the cone area.
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Old 11th January 2017, 03:08 PM   #44
tb46 is offline tb46  United States
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Default Cone correction

Hi USRFobiwan,

Post #43: "...about the tuning stub..."

I'll attach a picture, hopefully that'll make it clearer? In Hornresp you would just use the usual TH simulation w/ L12 being part of the horn path, in AkAbak you can start the horn flare @ S2, and independently model L12 as a duct attached to S2. More often than not it does not make a difference, but may explain some of the differences between measurements and simulation. I don't have any way to build and measure this.

Nice work on that THAM15!

Regards,
Attached Files
File Type: pdf THAM15_Forsman_Mod_2_cone_correction.pdf (15.6 KB, 26 views)
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Old 11th January 2017, 03:32 PM   #45
Josh Ricci is offline Josh Ricci  United States
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Quote:
Originally Posted by martinsson View Post
This is a work in progress, this far the folding I found that makes the best use of the cabinet dimensions, specially the depth which is critical since it determines the QWR function tuning, can be seen below, this also allows for the minimum amount of outer single wall surfaces (two) in need of coupled bracing :

Click the image to open in full size.

This is a work in progress, so don't take the above picture to seriously.
Quote:
Originally Posted by epa View Post
i modelled this a few years back
Click the image to open in full size.
Quote:
Originally Posted by Circlomanen View Post
Attachment 591322

Attachment 591323

Here is my TPQWR build from about a year ago.
I use two Beyma 12P80Nd.

Cheers,
Johannes
Here is a fold I messed with and modeled briefly but never built. From what I recall the length was shorter than required for the low frequency extension wanted and the cab size available at the time so I moved on.


Symmetric TH fold .jpg
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Old 12th January 2017, 07:02 AM   #46
martinsson is offline martinsson  Sweden
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When looking at the differences in characteristics between an expanding tapped fold (TH) and a constant area tapped fold (TP) it seems that the expanding fold is more efficient while the constant area has a slightly wider pass band.

Johannes design proposal uses a constant fold in the pre-tapping segment (L23) to set the pass band upper and lower limits, he then adds second (post-tapping) constant area segment which acts as a quarter wave resonator tuned to a mid pass band frequency, this boosts the entire pass band efficiency without compromising the pass band width.

The only expanding segment in his design proposal is the un avoidable L34 transition between the two constant area segments L23 (pass band function) and L45 (the QWR function), the result is a very easy to build and very efficient design consisting purely of perpendicular interfaces.
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Old 12th January 2017, 03:29 PM   #47
tb46 is offline tb46  United States
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TPQWR v. TH

Hi martinsson,

Thanks for clarifying, Post @46: "...differences in characteristics between an expanding tapped fold (TH) and a constant area tapped fold (TP)..."

I didn't get it, that the lack of taper was an essential part of the design. But, it still leaves me with a lot of questions. Have you tried to see if there is a difference in simulation between Hornresp and AkAbak? It looks like it may take AkAbak to properly model the L34 transition area. Or could we just assign a very short length to L34 (as in simulating a MLTL) and use TH1 in Hornresp (L23 would go from one side of the driver to the other side, and the end of the L23 pipe @S3/S4 would cradle the driver similarly as you show in your blog for the DSTHAM)? This is all very interesting work.

Regards,
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Old 12th January 2017, 03:35 PM   #48
USRFobiwan is offline USRFobiwan
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I assume the driver panel is going on the back of the cabinet. Otherwise driver maintenance is going to be hell, or maybe you have the same mutant power as the flexible member of the fantastic 4.
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Old 12th January 2017, 04:36 PM   #49
Circlomanen is offline Circlomanen  Sweden
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The TPQWR is a series-tuned 6th order bandpass box that uses quarter-wave resonance instead of Helmholtz resonance. You avoid having to use ports, and large cross sectional area quarter-wave resonators sound much better and have a very high efficiency at high power levels. There is no port-compression or distortion due to turbulence. It has a very large radiating surface and a very narrow beam-angle. Just a few steps to the side of the mouth and the spl drops a considerable amount.

I don´t have any problem mounding the driver through the mouth of the quarter-wave resonator even though I need to stretch my arm a bit to reach the springloaded cable connections on the drivers.

Cheers,
Johannes
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Old 12th January 2017, 04:55 PM   #50
Circlomanen is offline Circlomanen  Sweden
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TP115.jpg

QW115.jpg

115COMBINE.jpg

115-compare.jpg

115TPQWR.jpg

Here is a series of Hornresp simulations showing the transition from a simple tapped pipe via a simple frontloaded quarter-wave resonator, a combination of the two and the fused respons of the two.

Quite an increase in efficiency.

Cheers,
Johannes
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