I have drawn up my 20Hz subwoofer horn in Google SketchUp 3D. This horn is more for home theater than for music. My smaller 40Hz loaded with B&C Speakers 8PE21’s is more musical and articulate. The 20Hz tapped horn is loaded with two Tang Band W8-740C woofers. These are high excursion heavy cone woofers. They have quite high Bl factor which makes them good candidates for horn loading for low frequencies. The woofers are arranged in a push-pull configuration with one woofer reverse mounted and wired in opposite polarity. This arrangement linearizes the excursion components of the woofers and cancels nearly all even order distortion.

The first picture is the side profile with the sides still off so you can see how it is folded. If you look over to the left top of the woofer chamber, you can just see where the throat opening is into the horn path.

The next picture is a closer look at the woofer chamber and horn throat. The entire horn is of the constant width design. There are no wired or difficult angles and tappers to cut.

The third picture is a look from under the horn. You can actually see the throat opening into the horn path from the woofer’s view point.

The last picture is looking into the mouth of the horn with the side panels on. In the finished horn, I have removable panels to access the woofers from each side. In this picture, the right side woofer would drop into the chamber with its magnet inside the chamber. For the left side, the woofer would mount with its cone facing the chamber and its magnet sticking out toward the horn mouth.

How does it sound? The best way to describe it is clean and subtle. If the gain on the power amp is adjusted properly, then it is down right acoustically invisible. It does not let its presence known until it is called on. It adds a very nice tactile sense to movies and enhances the experience greatly. I would have to say it is a success.

Physical size is 16” wide X 17” deep X 65.5” tall. The horn path length is just a hair over 19 feet.

Here is the HornResp predicted response and input parameters.

As I guessed, room gain in my place begins at 38Hz, so the actual response is completely flat out to 16Hz. Sensitivity is about 97dB with 1 watt input. It doesn’t take much power to get this thing going.

I would encourage anyone to try a tapped horn. With tools like HornResp, it is pretty easy to design a tapped horn.

Rgs, John

Above I was discussing the new integration process I used to mate the tapped horns with the rest of the system. Below is a graphic to help explain the listening arc. I just moved the tapped horns along an equal-distant arc until the phasing of the tapped horn agreed with the mid-bass horns. The equal-distant arc is time aligned at the voice coils of the woofers in both the tapped horn and horns.

Rgs, John

I have received some questions and criticism about tapped horns. In order to spread a better understand of tapped horns, I’ll restate the questions and try to answer them.

1.) The mouth of the tapped horn is too small to be useful.

Answer: A small mouth size is exactly one of the reasons to use a tapped horn. You no longer have to have a horn the size of a refrigerator to enjoy clean and powerful horn bass. The tapped horn gets around this with its special phasing properties. Usually when you have a mouth that is too small, the result is a very rippled response. See below graphic.

These are the same horn and driver. The only difference is the mouth was made too small on the first one. Their length is ¼ wavelength at 40Hz. The ripple peaks in the first horn occur at harmonics of the ¼ wavelength resonance. In the tapped horn the rear side of the woofer is very close to the mouth. This distance is too short to be acoustically visible to the horn. However, as frequency raises, the rear side of the woofer progressively begins to come more in-phase with the horn. The effect this has is the radiating surface of the woofer (Sd) also progressively gets larger until is becomes 2 X Sd. Because of the increase in driving Sd, the woofer is able to completely fill in the ripple valley in the response. This is a wonderful thing!

2.) The length of the tapped horn is too short to do what you say.

Answer: The tapped horn does not define its length like a conventional horn. In a conventional front loaded horn the length is defined as the distance from the throat to the mouth. This is not the case with the tapped horn. Since you “tap” into the horn down from a closed throat, this distance gets added twice. This is because the sound travels from the “tap” point toward the closed throat, and then gets reflected back down the horn toward the mouth. In addition, the distance from the back side of the woofer to the mouth also gets added to the over all length. So, a tapped horn is acoustically longer than it would first appear. With a tapped horn, all these sections just need to add up to approximately ¼ wavelength of the low frequency of interest.

3.) The tapped horn suffers from cavity resonances. That’s what all those peaks are above 150Hz.

Answer: The tapped horn suffers no more from resonances than a conventional folded front loaded horn. In any folded horn you have to deal with 90 and 180 degree bends, and the resonances associated with their ½ wavelength cancellations. This is just normal life with a folded horn. It is possible to build a straight unfolded front horn and avoid all this. However, you better have a very large room and a very forgiving wife. It is completely impractical for 95% of people to have a straight front loaded bass horn.

Actually, you can use the ½ wavelength cancellations to your advantage with the tapped horn. You can model it in HornResp and see where the first high frequency peak occurs. Now just design the horn to have a fold that makes the distance between the fold and the mouth or throat ½ wavelength. This will cancel the peak and then some. Lemonade from lemons! It is also important to remember that the peaks HornResp shows for the tapped horn are exaggerated. I have measured and found the peaks to be at least half the size as calculated from HornResp. In addition, these peaks occur outside of the frequency band of interest. You should not be using a bass horn much above 80Hz anyway. It becomes too directional above 80Hz in my opinion.

Rgs, John

From: Tom Danley
Sent: Tuesday, May 05, 2009 5:56 PM
To: Romy
Subject: From Tom Danley

Hi Romy

http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=10359#10359

I hope you don’t mind the intrusion, it was suggested I could answer your questions.

“Still, I did not hear the Danley’s tapped horns and I have no idea what he is trying to do.”

Well I can explain and hopefully it will make sense.

When you make a bass horn “too small’ and by that I mean a mouth that is significantly less than a wl in circumference in full space and by making it a quarter wavelength long instead of ½ wl., you have a number of tradeoffs.

By making the horn shorter, only a quarter wave long at the low cutoff, you prevent the system from having high electroscoustic efficiency  conversely you’ll find that the short bass horn does reach efficiency until it’s about an octave above low cutoff, again where it is a half wl or greater.  The classical horn, needs to have the driver at the motional maxima, which begins at a half wavelength.

Also, one finds the response of such a horn typically droops off instead of being “flat” down to the low corner.  When the mouth is made smaller in area, then one finds the horn’s modes become increasingly revealed by the reduced radiation resistance (which fully damps them in a larger horn).

When you make the horn mouth a convenient size (too small), then you have a response curve with a large peak defining the low corner, with a deep valley then another peak with a series of smaller and closer together peaks after that.

It is the magnitude of these peaks and dips which define how small you can make a horn.

Acoustically, what you see is where there are peaks, there is the maximum acoustic loading on the driver, the point where the motion and impedance is minimum.

Where the deep valley is, there is little load on the cone, motion and impedance are maximum.

The quarter wavelength bass horn can’t be efficient down low because the driver’s parameters that are ideal for operation where it is ½ wl long or longer, are totally different than those needed for the quarter wave mode which is a motion minimum instead of motion maximum (1/2 wl)

The Tapped horn idea began when I was thinking about the quarter wave length reflection that places a notch in the response of the side mounted drivers (as used in the synergy horns), that notch defines where the usable upper response corner is.

I wondered, “what happens if I substitute a source of the opposite phase for that reflection”  Having that source already available in the drivers rear radiation, I made a computer model.

It took a long time before I had anything I felt like building, but occasionally I would see predictions of a nice sensitivity.

The Tapped horn idea is that you use a driver which can efficiently drive the quarter wavelength mode which defines the low corner. This driver is too massive for efficient horn loading normally.

At the low corner, the front driver is approaching 90 degrees out of phase from the radiation at the throat.  The acoustic load is nearly entirely on the throat side of the driver at the low cutoff.  As the frequency climbs into the range where one has the deep valley, now the shorter wavelength means the front and rear radiation are separated by 180 degrees of path length and now are additive in the horn.

“When everything is right” (the horn dimensions and driver parameters), then where the valley was, is now flat, filled in by the added radiation load on the cone.

Compared to a vented box, these typically have about half the group delay for a given low corner and they often have a roll off slope between a vented and sealed box.

In a conventional horn, one normally sizes the rear volume to put the Fb somewhat above the system low corner. The drivers suspension spring is in parallel with the box compliance or spring.  By choosing the horns hyperbolic or shape, one can adjust the acoustic mass the horn presents to the driver as you approach the low corner. The proper relationship between the two results in “reactance annulling” which lowers the low corner to its lowest value.

In the Tapped horn, the acoustic mass in the horn also exists but with no rear volume, the drivers suspension spring does the entire job. As a result the ideal Fs for a Tapped horn is usually the better part of an octave above the low corner.

Anyway, like a normal horn, once you have “all” the parameters right, they can work very well and provide flat smooth response, like a much much larger horn..

I don’t know if there are home bass horn systems that are measured in half space 1W/1M or have real response curves at all, but here are a couple tapped horns which  one could compare to.

http://www.danleysoundlabs.com/pdf/TH%20215%20Spec%20Sheet.PDF

http://www.danleysoundlabs.com/pdf/TH%2050%20Spec%20Sheet.PDF

Granted these are made for movie theaters and large-scale sound and are big and ugly but the up side is they are absolutely loafing when used in the home.

On the other hand, there are some hifi “horn people” who are finding our stuff nice in the home. 

You might find the SH-50 interesting; it can reproduce a square wave from about 260Hz to about 2900Hz, a span covering all three sets of drivers.  There are no lobes at crossover or anywhere else and appears to be one source in time and space with nearly constant directivity down to it’s mouth dimension governed pattern loss.

In large spaces the rooms problems are much more formidable, hence all the focus on directivty and no interference between sources etc. the time coherency seemed like an obvious target which as taken over 10 years to zero in on.

Something you may have noticed too, as you make a speaker better and better in time, it becomes harder and harder to estimate how far away it is, if you stand in front of it with your eyes closed.   What I am hearing consistently is that a system, which does not deliver audible clues, that “shout” where it is in depth when listened to singly, provides a more faithful center image and stereo image.

Anyway, don’t want to ramble, hope this helps explain the Tapped horn.

You may post this if you wish.

Best,

Tom Danley

Try a couple of these outdoor uncompressed two channel recordings on your horn system, go to the bottom of the page here;

Play softly at first, NO compression, large dynamic range, deep bass on the fireworks recording.

Well, be afraid to get what you wish people say and it is exactly what happens in this thread: last week I expressed curiosity about the tapped horns and today I have more information about them than I wished.  I appreciate John, Robert, Tom and others for sharing this thoughts and experience about the tapped horns. I print all of it out (I do not like read from screen) and carefully read it a few times. I would like to express my view on the subjects.

I know horn installations, I know what to do with them, I know drivers and I know how different design decisions impact results. In many instances I do not have experience with a particular design decision but my personal familiarity with similar design decision gives me an opportunity to a very high degree to predict the result that people get from unknown to me installations.  Being able in some cases to correlate my predictions with the actual afterwards listening I was always please how accurate my forecasts were. It is very far from ego statements but just recitation of the facts. What is important to understand is that in all cases of my experimentations, evaluation  or prediction there is my own personal experience and deep familiarity how my own listening awareness reacts to the given design decisions or the associative  design decisions.

In case of the tapped horns I feel very different as I have absolutely no, even associative experience how this type of the solution my sound subjectively. Therefore, reading the observation to others I have no tangible feeling behind them using words. I have no doubts that tapped horn would hit the SPL numbers and the LF equalization curve that were named but it hardly give me any idea about Sound or how it might sound. If someone knows any “interesting” installations with tapped horns in New England then let me know and I would not mind to familiarize myself. At this point I do not have any expectations or understanding about the tapped horns sound. Sure I understand how it works but it kind of reminds me something that I usually call the Iolanta Syndrome.  Iolanta was a Danish girl from Hertz’s “King Rene’s Daughter” (or Tchaikovsky’s opera with the same name)  who has been blind from birth and did not know about her blindness as no one in her father kingdom was allowed to talk with  Iolanta about light, colors and sight)…

Anyhow, from what I read so far I think my doubtfulness and my natural presumption of negativity (fewer disappointments) would be divided into two directions. What I do not like in the tapped horn idea is not the “tappedness" itself (something that I do not know yet if it is good or bad) but rather the horn “foldedness”.  John said: “The tapped horn suffers no more from resonances than a conventional folded front loaded horn.”  That is good but I hate the folded front loaded horns as I feel that the condom of resonance chamber in the wave pass impact sound too unforgivingly. So, would it be possible to separate the idea of “tapped horn” with the idea of “folder horns”. How about to have straight “tapped horn”? We are taking about the long horn but look at the mouth of the John’s tapped horn. In the long horns the destructive part is a huge moth but if we have no big mouth then we have virtually a long narrow pipe…

OK, let me to share with you the visualization that I have.  Would you fill that THIS idea of the use of the straight tapped horn makes sense for you? The idea is to have a long and narrow pipe, perhaps suspended above the main speakers and running across the whole presentation filed. The pipe is divided internally into two separate independent sections: one runs right and another run left channel. I did not think yet how it might be implement but if the tapped horn do sound OK then I think what I propose might a VERY cool solution to have a straight tapped horn with very low frequency (the bigger room the longer pipe), with practically no valuable footprint?

Romy,

     I like your idea. However, I would caution you on having the outlet of the one side firing backwards. One of the things that is not talked about with tapped horns is they are more directional than a normal subwoofer. They do not excite the entire room with omnidirectional sound. If you had one firing forward and one backward it would probably screw up the sound. A slight variation that would be better is to have both tapped horns exit on their side so you can aim them both in one direction.

     Your double tapped horn idea will work if both woofers are the same and they are wired in parallel. It is interesting because instead of each woofer using its own front and back side, it uses the other woofer's front or back side to complete the phasing that makes the tapped horn work. Very good thinking.

JLH wrote:

One of the things that is not talked about with tapped horns is they are more directional than a normal subwoofer. They do not excite the entire room with omnidirectional sound.

 John, 

this is serious drawback I my book, even though you told before that the tapped horns become non-direction below 80Hz. Despite I do not argue that you might have the targeted SPL level I do not know how useful would be this SPL if it does not couples with room.

 Any LF acoustic system has two SPL levels: the SPL of pressure and the SPL of tone. (People do not talk about it as this is an absolutely alien concept for audio people. The unfortunate who sell far-machines to audio morons did not pre-sell and did not implant this issue into the feeble minds of the audio hoodlums and thankfully I write about it cryptically and marketing industry idiots do “get” it). With many LF solutions that I do not appreciated the pressure rises faster than tone. The pressure also reduces with different speed in relation to tone. It is not the attack and decay or room reverberation decay - it is a different subject. It has more to do with heating the correct SPL number and with having us as the listeners the practical benefits from specific pitch in musical information that exposes itself at given SPL. I wrote about it before, impaling that there are some listening techniques that allow differentiate the SPL pressure and SPL of tone.

So, in what you say about tapped horns it sound to me as the tapped horns do have the problem with pressure vs. tone.  It was very much expected by me, let me to explain why. There is a pattern in the pressure vs. tone subject that I observe. Being familiar with many many many LF solutions and implementation I was able to observe that the targeted lowest frequency has to be in accordance with lower frequency radiation surface. There are zillion solutions how can get more bass from smaller exerting surface, most of them would do right pressure SPL. However, the more misbalance between the size of the “exerting surface” and pressure SPL the more we have pressure SPL rise faster than tone SPL, I can bring as evidence very many famous models . BTW, this pattern is reversible: with higher targeted lowest frequency the pattern works compliantly and this explains why in some cases the pressure SPL marks let say 100Hz but the tone SPL impressers a listener as it was 40Hz.

So, with tapped horns we are in very disadvantaged situation to begin with as we have very harrow radiation hole and very low targeted lowest frequency for the size of this hole. This is in a way a recipe for “pressure SPL vs. tone SPL” disaster.  What I would propose you is trying to use the tapped horns intentionally non-directional with intentional 3-5msec delay. You might for instance try to reversed you LF listening arc and turn your highly  directional tapped horns in opposite direction from you listing spot, letting the tapped horns to work “off the wall”.  If your upperbass channel is good enough then it might be interesting. In particularly it might be interesting to play in THAT configuration with low pass on the tapped horns as it will not be only moderate the frequency but also the virtual delay. There are some further tricks that you might do in this work “off the wall” configuration: you might put in the end of your room, right at the bouncing wall a subtraction channel but this is another subject….

Again, all of it juts my thinking on the subject that is NOT based upon the tapped horns experience. Sure, sitting in the same room, listening the same inhalation and comparing notes would be more productive…

Romy the Cat wrote:

Any LF acoustic system has two SPL levels: the SPL of pressure and the SPL of tone.

Ahhh! Very good Romy. I don't recall you talking about Pressure and Tone SPL before. The tapped horn can be designed any 3 ways. It can be balanced, tone heavy, or pressure heavy. The Tang Band push-pull tapped horn is pressure heavy and is best used below 60Hz. The 8PE21 tapped horn is tone heavy and light in pressure. The most balanced tapped horn I built was one using a B&C Speaker 12PS100 woofer. Since I have built several different kinds of tapped horns, I've now kind of have a feel for what they will behave like. It is worth saying that your room will also determine how balanced the tapped horn should be. Larger rooms need to be a little more pressure heavy so by the time the room is properly pressurized, the tone is present. If the tone comes forward too soon, then the tapped horn becomes fatiguing to listen to. On the other hand, there is nothing more boring than a tapped horn that has no tone SPL.

Even so, the bass that the tapped horn makes is still more directional than a fart-machine subwoofer. You can steer the bass where you want it. I see this as an advantage over other kinds of bass.

Rgs, John

JLH wrote:

I don't recall you talking about Pressure and Tone SPL before.

http://www.RomyTheCat.com/TreeItem.aspx?PostID=3675  

Romy the Cat wrote:

I know this effect but if it happen with bass horns then I do not call it “"pulsating room effect" but I rather call it “+1dB effect”. Some bass horns being placed in their rooms increase the density of pressure faster then the density of sound. It is bizarre concept of mine and no one understands it. Let try to explain it. Density and Pressure of tone has purpose and this purpose is described by artistic value of musical peace. With the expressive intentions of a given composition and the given interpretation there are always inner-reasons what density and what capacity of a note should be. In this case density, capacity and potency of a tone are almost the synonymous. However, not the Pressure. Pressure is an absentminded parameter that has relation to objective deviation of one volume over another but it has no relation to musical intentions. So, when you told that your have that “"pulsating room effect" across full MF range then I had no problem with it – it looks you are getting good sound out there. However, what you said that your have the same effect from basshorn I recognize it as a problem (your friend Trombonist with his "picking up the room" is very much irrelevant because he plays MF-HF instrument). The load a room with a dense, phase-perfect MF is wonderfully and we in a way experience it in “live” sound. (I said “in away” because in “live” sound we have also “space” and unlimited dynamics…., but it another subject) However, in “live” sound we never experience dense bass. Of course I’m talking about Sound of classical music, opera or any acoustic music not about the electrons surrogate).

http://www.RomyTheCat.com/TreeItem.aspx?PostID=3852  

Romy the Cat wrote:

Vowelness describes harmonic infliction to a note and has a lot to do with a parabola with which a tone rolls to its pitch. Why “vowelness”? Because vowelness is about injection of different vowels into other vowels.  The vowels themselves are “pure tones” and they are characterized by open configuration of vocal tract, so that there is no build-up of air pressure above the glottis. A person with healthy breathing has a perfect inner-references and a clear cognitive recognition of vowels. Any coloration of vowels is a coloration! I had many people were pissed on me because I did not like their bass-horns or subwoofers juts after a few seconds of listening. They accused be for not spending enough time and rush with my negative judgment. What those people do not get is that I know (in most cases) what I’m listening while I listen. I care less how “fast” those subwoofers were and the very first thing I need in LF section is to be able to render vowels without colorations (Ironically the “vowelness” has practically no relation to room response and it is almost exclusively the topology of LF topology). What I mean that “e” should not have “o” in it any “u” should not have “opened a” in it. Russians even more lucky as then have an amassing vowel “ы”, which it superbly useful to assess the LF sections…. Anyhow, I think you got the picture… and what you GOT IS NOT WHAT I AM PROPOSING to deal with the “Oops Techniques”. Sure what I describe in this paragraph is a large part of “Absolute Tone” but it is NOT what I am after in CONTEXT OF THIS THREAD. What I am after is the Absolute Tone’s bubbleability. The bubbleness of sound is an ability of Absolute Tone demonstrates a high rate of bubbleability. Let I give you an association. Pretend you put a pot with a gallon on water on over and the water begin to boil. As you see the small bubbles of air begin to build up under the bottom of the pot and they run up to surface. Then, while the water is boiling, you increase the temperature of heaters and you see now that the bubbles begun more intensely and more aggressively rash to the surface. The very same is with Sound. The Tone is a Tone but beside the Tone there are those bubbles that are popping up at surface of Sound and burst like microscopic explosives. These bubbly explosives do not affect Tone but they affect the Radioactivity of Sound ™ of the force with which Sound injects itself into listener’s skin and mind.  This bubbleness is what I am targeting with the notions of “Oops techniques” or as Rony Weissman brilliantly descried: “cellos were extremely hairy”. (BTW, the bubbleness is where the S2 is uncontestable emperor) So, the direction I a looking is slightly opposite then juts use the wood of musical instilments. I formulated VERY EXACTLY and I know VERY PRECISELY what kind “noise” I need to overlay over Sound in odder to get that feeling of bubbleness. I just have no idea what would be able to produced that “noise” in context of horns. So, what I would be interested would be most likely very far for what musical instilments do and is more aligned with the affords of the folks who record noises for cinema films ….

http://www.RomyTheCat.com/TreeItem.aspx?PostID=412  

Romy the Cat wrote:

I would consider it, however my experiments with notching lead me to feel that high level parallel notching is as bad as series. A series network removers meaningful tone out of acoustic pressure. The parallel network does not do it but it eats transient response. In both cases the “bad things happens”.  Also, what whatever reasons the parallel network provides different effect with the different but identical drivers. I think I have to explore more opportunities of a parallel notching at line level…

As I understand the tapped horns have very small output whole, right? Here is a cool configuration for the folks who have suspended floors and would like to have a relatively large tapped horn do not take a  lot of space  in room – install the tapped through the floor.

I think this is a very cool idea. Pretend we have a listening room with 8 feet basement. So, we make 10 feet tapped horn that we install on the basement floor.  In the listening room will extend only 2 feet appendix with the horn exit. The benefits are very clear: the exit whole will be loaded to the floor and the body of the tapped horn will serve as a solidifying column to reinforce the floor above. I think it is a very good idea.

Thanks, Josh. I looked for it and found a good link that accumulates a lot of recourses about Danley DTS-10.

http://www.avsforum.com/avs-vb/showthread.php?t=1189404

I did not know about DTS-10 but this morning I did sent to Tom an email asking his view about the whole notion of Trapper horn vs. infinite baffle direct radiator array.

I will look into DTS-10 with more attention but no one knows what kind of “sound” it produces. I am sure it will hit the targeted pressure level but there is so much more to it. Also, if I use Trapper horns then I would like them to be narrow thin column but very tall. Let say sq. 1 foot of footprint and 8 feet tall.  I will read more information about Danley DTS-10 kit and will see if among the people who will be taking about sound of DTS-10 I find anything interesting.