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Old 1st March 2010, 05:49 PM   #1
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Default Tapped horn theory

In tapped horn theory, is there some requirement that the rear of the driver sits at or near the horn mouth, a la jbell's tapped horn?

(jbell's set of four tapped horns)

Also, I'm following lilmike's tutorial on tapped horns at Simple Tapped Horn Tutorial using Hornresp - AVS Forum and in reference to jbell's design, I believe the L23 segment is the entire distance between the middle of the cone on the front side, and the middle of the magnet on the back side, irrespective of the number of folds and such in between - is that correct?

Along those lines, can anyone tell me the practical effect of having the back of the driver recombine very close to the front, i.e. a shorter L23 and a much longer L34?

And, are there any ill effects I should know about with regard to having multiple folds and such?

THX!
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Old 1st March 2010, 06:43 PM   #2
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In tapped horn theory there's the requirement that the rear of the driver sits behind the horn mouth. It doesn't have to be close, i.e. L34 can be made very long if desired.
The physical mounting of the driver is relatively meaningless, the driver can be reversed mounted if desired, which results ussually in small changes to S2, S3, etc. It's effects are often ignored in simulations. Measurements showed an 1 dB difference between standard or reversed mount in several designs (a little less on that frequency a bit more there kinda thing).

Your believe about L23 is correct. Mind you that HR offers the option of dividing "L23" into 2 segments, meaning L23 starts at one side and L34 ends at the other side of the driver.

I did some sims in the past regarding your idea of keeping L23 small, IIRC it was difficult to get anything else but a peaky response, most tapped horns build these days seem to have the driver close to the mouth. With L34 up to 55 cm I aquired some good results (L23 was more then 55 cm in those cases).

Bends have multiple effects, amongst are the increased horn path length with regards to the axial measured length and the "termination" of higher frequencies, i.e ; Lots of bends mean your not likely going to get 120 Hz plus out of the tapped horn whilst still sounding "good".

Best regards Johan
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Last edited by Rademakers; 1st March 2010 at 06:51 PM.
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Old 1st March 2010, 07:01 PM   #3
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Thanks for the reply. My questions stem from an idea to build subs where the driver is mounted in the top of a vertical cabinet, which is perhaps 48 inches tall and 24 inches wide. It would be a single 15 or single 18 inch driver. I would put a plexiglass or lexan window at the front of the driver chamber, and maybe even a neon light or small rope lights in the driver chamber for illumination of the cone. I would design it in such a way that the L23 is very short because the front and back of the driver would combine very close, like with one fold between the front and back, then multiple folds and a long path length on L34 between the back of the driver and the horn mouth.

If there are big swings in the response curve, that may be rectified by the use of another tuned circuit along with the driver (but that's a rather advanced topic that I'm not knowledgeable on - yet). I will start modeling and post back to this thread if I come up with anything nice.
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Old 1st March 2010, 11:42 PM   #4
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Originally Posted by letsbangout View Post
... I would design it in such a way that the L23 is very short because the front and back of the driver would combine very close, like with one fold between the front and back, then multiple folds and a long path length on L34 between the back of the driver and the horn mouth.
Take a look at the clones of Tom Danley's TH-SPUD tapped horn. The L34 length (driver to mouth) is quite long - the full width of the cabinet. However, the L23 length is still much longer than L34. I supect you'll have to lay out your folds in such a way that you get your desired driver placement but still have a long L23.
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Old 1st March 2010, 11:44 PM   #5
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Quote:
I would design it in such a way that the L23 is very short because the front and back of the driver would combine very close
That's kinda like saying the same thing in the same sentence twice

I really think it's a hard way of doing it. You're creating a big spike just before the low cut off and little efficiency above that, unless you're making it like a 65 Hz plus cabinet, with a large throat chamber and large mouth, which you probably aren't.

There are lots of folding scheme's to choose from, that would make it appear that L23 is short while that's not necessarly so. I've attached a quick sketch (it's up to scale but that's it) as how the image struck me, might be way off though.

Best regards Johan
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Old 2nd March 2010, 07:29 PM   #6
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Quote:
Originally Posted by Rademakers View Post
That's kinda like saying the same thing in the same sentence twice
Yes, sometimes I am redundant like that

Quote:
I've attached a quick sketch (it's up to scale but that's it) as how the image struck me, might be way off though.
Thanks for the sketch, the driver placement is correct but I would have the cone facing forward (toward the glass). When I finish modeling, I will draw something and post it. I'm still having a hard time understanding how I can model the folds though - how can I know to what degree the folds will affect the upper corner response if Hornresp does not take them into consideration? Are there any "rules of thumb" I can use?
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Old 2nd March 2010, 08:37 PM   #7
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Quote:
Originally Posted by Rademakers View Post
The physical mounting of the driver is relatively meaningless, the driver can be reversed mounted if desired, which results ussually in small changes to S2, S3, etc. It's effects are often ignored in simulations. Measurements showed an 1 dB difference between standard or reversed mount in several designs (a little less on that frequency a bit more there kinda thing).

Best regards Johan
I don't think people are factoring in the volume of the driver when they model tapped horns. I'm thinking of doing a TH for my truck. I had the original size of the mouth at 1,651.61cm^2 (16" x 16"). If I build it, I am going to use a 1,961.29cm^2 (19" x 16") mouth to account for the 0.5ft^3 volume of the driver and expect the 16in^2 frequency response.
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Old 2nd March 2010, 09:36 PM   #8
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The best rule of thumb is to ignore the effects of the folds on the upper corner response. The folds will only affect frequencies well above the upper corner. If you think about it, the folds form a series of shorter pipes, each of which will resonate at a much higher frequency than the overall pipe length. Just make sure you don't alter the calculated pipe length when you make the folds. Draw it out to scale on a piece of graph paper and measure down the mid-line of each section and through the bends to double check.
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Old 3rd March 2010, 01:31 PM   #9
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That makes perfect sense, thanks. Now one other thing I'm having a hard time understanding, as I go to model this horn, is the relationship of the segments. In lilmike's tutorial he gives the following illustration:

http://lh6.ggpht.com/_WXjTASetbPo/Sz...ped%20horn.jpg

(if that does not work, it's the same illustration at the top of post #2 in his thread: Simple Tapped Horn Tutorial using Hornresp - AVS Forum)

What I am not understanding is the relationship between S3 and the driver - he seems to locate S3 in the middle of the driver. But is there any reason S3 could not be modeled back a bit (i.e. just to the right of the driver)? I'm just trying to understand how the segments will relate to my folds when I actually go to build this thing.

Also, I saw no mention of Vtc and Atc in lilmike's tutorial - are these parameters relevant to the model in the case of a tapped horn?
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Old 3rd March 2010, 05:05 PM   #10
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Quote:
But is there any reason S3 could not be modeled back a bit (i.e. just to the right of the driver)?
S3 is per definition right in front of the driver (in a 3 segment tapped horn). Ussually when designing a tapped horn the Vtc is kept to a minimum and like the influence of the driver position ignored in simulation.

Only when building hybrides between tapped horns en rear loaded band pass horns the Vtc-effect becomes significant.

Best regards Johan
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