TH (Tapped Horn) vs FLH (front Loaded Horn) vs Sealed vs Bass Reflex design subwoofer - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 8 Old 10-05-2013, 01:38 AM - Thread Starter
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Good readings from Romy the Cat - and what do you think about.............:

"Before I go into how I designed my tapped horns I would like to touch on some very important things that separate tapped horns from conventional horns. I will break this down point-by-point. I will point out both positive and negative aspects of the tapped horn. I will continue to add to this thread as I have more to add. I hope you guys find this interesting and it motivates you to build your own horns.

1.) The primary reason behind using a tapped horn is its size. It is now possible to make a horn extremely small in relation to the lowest frequency it will play. For all practical purposes, you only need a mouth large enough to allow you to mount your woofer. That’s it, it can be quite small.

2.) The tapped horn does not suffer from group delay as bass reflex and conventional front loaded horns. Group delay is the primary culprit that causes “slow” bass. If you have ever heard bass that sounds like it is half a beat behind, you have heard the effects of group delay. The tapped horn avoids this by virtue of its design. Because the backside of the woofer is in close proximity of the mouth, time of flight for the sound is the same as a direct radiator. Due to the air volume inside a tapped horn being much less than a conventional horn, it can quickly pressurize this air and keep proper phase with the back side of the woofer. This has allowed me to finally time align my horns the way I wished I could. Integration is much better than my old 37Hz subwoofer horns. Not to mention the tapped horns are ¼ the size.

3.) One of the most magnificent benefits of tapped horns comes again from the woofer being in close proximity of the mouth. I have come to realize that this can contribute to much more interesting sonic textures. The tapped horn allows the higher harmonic content of instruments to come through. In a conventional front loaded horn, all the folds act as a muffler and acoustically attenuate these harmonics. What I have found is these harmonics are important in reconstructing a convincing field of depth. The realism is greatly enhanced with these harmonics present. A very interesting effect. This works well in my 40Hz tapped horns because the horn’s overall sensitivity is within a dB or two of the woofer’s own raw sensitivity. I’m using B&C Speakers 8PE21 woofers with 98dB sensitivity. The horns overall sensitivity is 100dB. The combined high sensitivity with the detailed light weight cones is capable of resolving the complex textures involved. In addition, the light cones help control over shoot and stored energy smearing of the signal. You may be thinking that the tapped horn is not providing much loading being it is only doing 100dB and the woofer was already 98dB. Here’s the deal, high efficiency woofers have a falling low frequency response. The 8PE21’s sensitivity is only 70dB at 40Hz, while in the tapped horn it is doing 100dB. That’s 30dB of gain on the low end. This type of gain is hard to come by even in a conventional front loaded horn.

4.) Now for a few issues you must consider with tapped horns. The most pressing issue to me is distortion. While the tapped horns still have much less distortion than a bass reflex, infinite baffle, or acoustic suspense subwoofer, it still has more than a conventional front loaded. Let me explain why. In a conventional front loaded horn you usually have a rear chamber that has its volume tuned to resonate the woofer at the horn’s flare cutoff. This is all part of annulling the throat reactance to get the lowest frequency output from the horn. Due to the design nature of the tapped horn, there is no rear chamber. In a tapped horn you must use the back side of the woofer in a phase additive manner to fill in the dips in response. Since there is no back chamber acting as an air spring to help control cone motion, the result is more even order distortion. This is because the uneven excursion (dumax) becomes a little pronounced in a tapped horn. When the pressure wave inside the horn is phase additive, it pushes on the cone, when the pressure wave is phase subtractive, it pulls on the cone and exaggerates uneven excursion. So, how bad is the even order distortion of the tapped horn? Well, I don’t have exact numbers, but from all indications and past experience, I would say if all things were equal (but size of the horns of course) a conventional horn would have 1.5% distortion, then the tapped horn would be in the neighborhood of 8% - 10%. That does look bad, but it is almost all even order harmonics. Remember people have been living with fart machines for subwoofer for a long time. Most home theater subwoofers push 20% or more distortion at high excursion.

5.) Distortion is not all gloom and doom for the tapped horn. If we are smart we can still design a tapped horn with distortion almost as low as a conventional front loaded horn with a rear chamber. The way around this is to use push-pull woofers. The two woofers share a common chamber that feeds the horn throat. One woofer is reverse mounted and also has its polarity reversed. This sets up a push-pull pair that will cancel the uneven dumax of the woofers. It will also cancel even order harmonics just the same as it happens in push-pull amplifiers. In addition, it linearizes excursion cased Bl fade. As one woofer’s coil begins to leave the gap, the other drives deeper.

6.) Having built both push-pull and single woofer tapped horns; I can say the push-pull pair is the way to go. The sound difference can be heard if you listen to recordings with very dry and tight bass. The even order distortion of the single woofer horn rounds and smoothes the attack of the bass notes. It is not the end of the world, but well worth the extra effort to design with a push-pull pair."
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post #2 of 8 Old 10-05-2013, 04:58 AM
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there are so many errors in that post that I can only conclude that he has no idea what he is talking about.
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post #3 of 8 Old 10-05-2013, 07:33 AM
 
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Quote:
Originally Posted by LTD02 View Post

there are so many errors in that post that I can only conclude that he has no idea what he is talking about.
He actually does possess a fair amount of technical knowledge, but he has all the people skills of Tomas de Torquemada. Having been banned from every forum he's ever joined he had to start his own, and he's totally isolated from the main stream, so some of his theories are way out in left field.
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post #4 of 8 Old 12-31-2014, 05:02 AM
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Quote:
Originally Posted by LTD02 View Post
there are so many errors in that post that I can only conclude that he has no idea what he is talking about.
An older thread but I found the comments from Romy interesting.
Do you mind sharing what you find wrong with what he's sharing?

I question what he says about distortion after seeing the article below. Using stacked and several bass reflex subs seems to have a lower distortion then at least the Danley DTS-10.
http://www.data-bass.com/data?page=content&id=82
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post #5 of 8 Old 12-31-2014, 06:49 AM
 
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Originally Posted by omholt View Post
I question what he says about distortion after seeing the article below. Using stacked and several bass reflex subs seems to have a lower distortion then at least the Danley DTS-10.
This is their conclusion: The tapped horn maintains better overall distortion levels from 12-33Hz and 65-100Hz even when being driven 8dB harder.
There is a narrow bandwidth where the tapped has higher THD, but it's of little consequence overall. Also note that the DTS was measured at a much higher SPL than the others. If measured at the same level, some 6dB lower, driver excursion in the DTS would have been halved and THD would have been much lower.

Last edited by Bill Fitzmaurice; 12-31-2014 at 06:57 AM.
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post #6 of 8 Old 12-31-2014, 07:37 AM
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A good point. Still I was a bit surprised when I saw this the first time. I doubt distortion as low 12-30 Hz matter at all.
It would be interesting to see a distortion measurements of stacked monopoles. Especially big bass reflex'.

When it comes to group delay I personally don't see this as audible at all below 80 Hz unless it's very high. With a front loaded horn though, it might be in this threshold of audibility if the room has a quality response in both amplitude and time domain. I guess no one knows this for sure.

The use of push pull woofers in a tapped horn design is intriguing.
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post #7 of 8 Old 12-31-2014, 07:53 AM
 
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Tapped horns make a lot less distortion when not being pushed near their limits. Actually just about all subwoofers do. That's the supporting logic in overkill. In the reasonable operation you'll never get near the limits or bad sound.
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post #8 of 8 Old 02-22-2016, 12:08 PM
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Quote:
Originally Posted by Mfusick View Post
Tapped horns make a lot less distortion when not being pushed near their limits. Actually just about all subwoofers do. That's the supporting logic in overkill. In the reasonable operation you'll never get near the limits or bad sound.
Eh ! I thought this was one of the best insights into a Tapped horn I've ever read.
Why? Because it sets up the classic argument about bass. And where would we be without that.
"Mfusick" just brought it full circle. Lets go round one more time.
I'll start it. Is push/pull the answer or should we just use two drivers and cut the liner excursion in half ! (ie. " tapped horns make a lot less distortion when not being pushed near their limits")
When you add the improved control and headroom of the amplifier (half the power), which is a big deal with bass demands. Much has improved.
I also like his comment on enclosures (ports and boxes). I spent the late 80's and early 90's chasing the mythical beast, The "fourth order band pass"
It ended with me pouring a lot of concrete. Some one declared it synthesized bass. I declared that the coupling of a driver to free space with ports and boxes was not the way. But that high order passband sure was a big carrot.
Then I saw the physical layout of of a tapped horn. It's the closest thing I've ever seen to high order efficiency with very little enclosure interaction.
Thank you Tom Danley.
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