why is a tapped horn more efficient than ported? - diyAudio
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Old 28th August 2011, 05:13 AM   #1
60ndown is offline 60ndown  United States
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Default why is a tapped horn more efficient than ported?

i recently put 2 subwoofers in a tapped horn, i then tried the same drivers in separate ported boxes. using the exact same amp and equipment the tapped horn was much louder.both ported boxes and tapped horns use both sides of the cone (i think) so why was the t.h. so much louder? 6db ive heard but why?
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Old 28th August 2011, 02:45 PM   #2
tb46 is offline tb46  United States
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Hi 60ndown,

Maybe Tom Danley's white paper would be helpful: http://www.danleysoundlabs.com/pdf/danley_tapped.pdf

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Old 28th August 2011, 05:09 PM   #3
60ndown is offline 60ndown  United States
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your right

although these 2 statements seem to conflict?

To illustrate just how much low frequency extension and overall output can be gained from a small horn loaded box using this technique, modeled simulations of a Tapped Horn and a vented box, loaded with drivers optimized for the performance of each one, are compared in Figure 1. Each enclosure has the same outer cabinet dimensions; 40 in. x 22.5 in x 28 in.
While the SPL is comparable for the two units, one of the real advantages of the Tapped Horn is seen in Figure . The diaphragm excursion of the driver is greatly reduced due to the acoustical loading of the horn. With an input of 63 V (500 W) the vented box exceeds 5 mm (0.2 inches) at 90 Hz. The Tapped Horn is well below this until just above 55 Hz. The vented box reaches 9 mm at 55 & 35 Hz while the Tapped Horn’s excursion peaks at just over 6 mm at 46Hz. This decrease in excursion will translate directly into lower distortion and higher output capability from the Tapped Horn.

Last edited by 60ndown; 28th August 2011 at 05:14 PM.
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Old 28th August 2011, 05:31 PM   #4
iand is offline iand  United Kingdom
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Quote:
Originally Posted by 60ndown View Post
your right

although these 2 statements seem to conflict?

To illustrate just how much low frequency extension and overall output can be gained from a small horn loaded box using this technique, modeled simulations of a Tapped Horn and a vented box, loaded with drivers optimized for the performance of each one, are compared in Figure 1. Each enclosure has the same outer cabinet dimensions; 40 in. x 22.5 in x 28 in.
While the SPL is comparable for the two units, one of the real advantages of the Tapped Horn is seen in Figure . The diaphragm excursion of the driver is greatly reduced due to the acoustical loading of the horn. With an input of 63 V (500 W) the vented box exceeds 5 mm (0.2 inches) at 90 Hz. The Tapped Horn is well below this until just above 55 Hz. The vented box reaches 9 mm at 55 & 35 Hz while the Tapped Horn’s excursion peaks at just over 6 mm at 46Hz. This decrease in excursion will translate directly into lower distortion and higher output capability from the Tapped Horn.
Can't see your figure (did you attach it?). When I did the same comparison years ago when Tom first announced the tapped horn, my conclusion was that you could get the same efficiency and maximum output with a tapped horn or a reflex the same size -- but the tapped horn typically needs 1 heavy-cone high-power driver (lots around nowadays), the reflex needs 2 lighter-cone lower-power drivers the same size (not so easy to find -- the B&C 18PS76 was the best choice, but it's now obsolete). Even total weight and cost ended up similar (2 cheap drivers in a simple box vs. 1 expensive driver in a complex box).

So if you can get truly optimum drivers there's no difference, but many drivers nowadays are better suited to tapped horns (or horns) than reflex, they haven't really got enough Xmax to deal with their high power ratings without a horn to reduce cone travel.

Last edited by iand; 28th August 2011 at 05:46 PM.
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Old 28th August 2011, 05:40 PM   #5
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Quote:
Originally Posted by 60ndown View Post
your right

although these 2 statements seem to conflict?

To illustrate just how much low frequency extension and overall output can be gained from a small horn loaded box using this technique, modeled simulations of a Tapped Horn and a vented box, loaded with drivers optimized for the performance of each one, are compared in Figure 1. Each enclosure has the same outer cabinet dimensions; 40 in. x 22.5 in x 28 in.
While the SPL is comparable for the two units, one of the real advantages of the Tapped Horn is seen in Figure . The diaphragm excursion of the driver is greatly reduced due to the acoustical loading of the horn. With an input of 63 V (500 W) the vented box exceeds 5 mm (0.2 inches) at 90 Hz. The Tapped Horn is well below this until just above 55 Hz. The vented box reaches 9 mm at 55 & 35 Hz while the Tapped Hornís excursion peaks at just over 6 mm at 46Hz. This decrease in excursion will translate directly into lower distortion and higher output capability from the Tapped Horn.
He's talking about sensitivity vs maximum SPL
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Old 28th August 2011, 05:55 PM   #6
60ndown is offline 60ndown  United States
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Quote:
Originally Posted by 454Casull View Post
He's talking about sensitivity vs maximum SPL
ah yes, i got it now.....
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Old 29th August 2011, 05:27 AM   #7
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Then there's that "iron law" thingie...
The most effective cheat is to sacrifice
some usable bandwidth for efficiency.

Ported box probably had more bandwidth
than tapped horn, wasted when limited to
the same bandwidth by your crossover.

Last edited by kenpeter; 29th August 2011 at 05:31 AM.
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Old 29th August 2011, 04:30 PM   #8
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When I think about THs, I always see in my mind those 19th century engravings sent to the patent office about the most amazing new inventions that double the force of your plow horse, pluck corn grains off cobs, allow people who are diabetic to sew buttons on their pants, or otherwise solve the problems of humankind in profoundly simple ways.

Ben
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Old 29th August 2011, 05:48 PM   #9
Djim is offline Djim  Netherlands
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In a basreflex one side of the cone is loading 'full' space, the other half is loading a closed box with a bas reflex pipe. Since basreflex (straight) pipes have narrow Q (small band) it only operates in a very small area of the frequency range. Also these pipes are normally tuned the lowest octave possible of the system where efficiency is the lowest already. In other words the basreflex doesn’t add extra gain to the rest of the efficiency and it only 'amplifies' the part where the efficiency already is dropped.

In a TH both sides of the cone load (drive) a tapped horn/pipe. The advantage is that tapped ends are wide band efficient. Although a TH has more in common with 6th order bandpass it the tapped end(s) that makes the difference. While Bandpass system has normally straight pipes the TH uses tapped pipes. Again, straight pipes have narrow Q’s (small bandwidth), tapped 'pipes' have wide Q (wide bandwidth).

The extra efficiency from TH’s comes from the dual type of loading. Both sides of the cone load (drive) a 1/4WL tapped horn/pipe. Therefore the excursion becomes 2 times more effective. So actually if you want to compare a basreflex to a TH you have to use two drivers in a basreflex to get the same amount of loading into 'full' space. The maximum gain from a TH is 3dB gain over a basreflex system. If you double the drivers (2 drivers per box) it becomes 6dB. Another doubling (4 drivers per system) can raise the max output to max. 9dB.

The most genius part of the TH is that both cones sides see a tapped end but in reality these two tapped ends are physically the same tapped horn. This makes the TH in my opinion so interesting for PA use. If you would design a traditional horn from the same dimensions as the TH, you will see lower efficiency below 1/2WL because:
  • The smaller than optimal horn mouth size
  • One side of the cone is radiating into a compression box.
In traditional horns for PA you also will see a big dip between 1/3WL and 1/4WL. This is also because the horn mouths are 'squeezed' down to give the horn a practical handling dimensions. One of the important advantages of a TH is that it provides additional acoustic loading between 1/3WL and 1/2WL. Depending on expansion ratio and chosen volume the acoustic loading can even be lowered from 1/3WL to 1/4WL, but of course at costs of total efficiency. For example, Jbells SS15 and Xoc1’s TH18 have the highest efficiency (3dB gain) and are therefore effective to 1/3WL. For example Josh Ricci’s Gjallerhorn is 'extended' to 1/4WL and is therefore lower in efficiency.

Last edited by Djim; 29th August 2011 at 05:55 PM.
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Old 29th August 2011, 06:13 PM   #10
18Hurts is offline 18Hurts  United States
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Quote:
Originally Posted by Djim View Post

In a TH both sides of the cone load (drive) a tapped horn/pipe. The advantage is that tapped ends are wide band efficient. Although a TH has more in common with 6th order bandpass it the tapped end(s) that makes the difference. While Bandpass system has normally straight pipes the TH uses tapped pipes. Again, straight pipes have narrow Qís (small bandwidth), tapped 'pipes' have wide Q (wide bandwidth).

The extra efficiency from THís comes from the dual type of loading. Both sides of the cone load (drive) a 1/4WL tapped horn/pipe. Therefore the excursion becomes 2 times more effective. So actually if you want to compare a basreflex to a TH you have to use two drivers in a basreflex to get the same amount of loading into 'full' space. The maximum gain from a TH is 3dB gain over a basreflex system. If you double the drivers (2 drivers per box) it becomes 6dB. Another doubling (4 drivers per system) can raise the max output to max. 9dB.
Interesting, I understand for roughing out what a TH will do--at a minimum is +6 dB over the efficiency rating of the driver. I'm wondering about the compression ratio's effect on efficiency, 3:1 or 5:1 or... JBells monster 8:1 with the MCM 8" subwoofers.

If two subwoofers in a ported box can produce the same output and size as a single subwoofer in a tapped horn--why build it?

From what I gather, the higher the compression--the more efficiency so a 3:1 compression TH would easily be more than 3dB efficient over a ported box. As always, I will cut up some wood to try it out--trying 3:1 on a 10" sub tuned just below Fs to get the efficiency up. Time to get my Horn Response programming down to really get my understanding before I add yet another ugly box to my arsenal.

Back to Horn Response...
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