Wow! Another one (I'm working on a 3rd!)

[elena]

Hi Mr. D-MAN,

check this out.

It looks like a reflexed-horn, but I call non-resonating horn in Italian.

It has a twin bass reflex feature below cutoff, midway the cutoff and the woofer free resonance, and a non resonating horn response, with a couple of reflex slits along the horn profile, mirroring the horn resonance to the back volume of the woofer lodging chamber.

It takes advantage from the corner folding and a single split-plane bifurcation.

It was born in the late 90'ies, patent was far beyond my reach, would have been expensive and no fast pay-back was expected, I tried to get a feedback on how it looks from the AES, but the peer review process went wrong, due to the lack of proofs -I made no measurements- and more I made no reference to the work of Mr. Leach Jr. on horn design.

I hereto attach a short pdf doc and a few pictures, I look forward for anyone willing to undertake the task of building and measuring a second prototype.

Review the theory before embarking on it!!!

ELENA

The ultimate horn_1.pdf

[elena]

Sorry, pictures were missing.

Open the zip file to display.

ELENA

photo.zip

[D-MAN]

Very cool, ELENA. Beware of posting plans on the internet, though, or you will lose all rights and ownership of them. However, please tell us more about them.

What is the Fc of the horn, and what frequency is the port(s) tuned at, etc.?

DM

[elena]

Hi,

Sorry, I made a mistake, the pdf file is void.

Check this, pls.

I've got a sad history about patenting. Last year I applied twice for two patents in my company, of course he's got the rights, I don't blame my company, he's got my intellectual rights when I joined, but for the 2.nd patent my colleague signed the application, he didn't call me, and the idea was mine solely, OK never mind, I'm working for the glory.

You find all tech. in the pdf file, the cross section of the cabinet has been amended, the dim of the first reflex slit was wrong, sorry again.

Feel free to do whatever you want with the design.

Anyway to clear up the matters, cutoff is at 55 Hz, the woofer free resonance is a about half, 29 Hz, cross over for the low frequency is an inductor to achieve an even band pass midway the horn cutoff and the woofer resonance, it should be a 4.rd order Butterworth filter: that is a twin reflex, at least I call this way. The twin reflex should be a well proven loading technique.

The two reflex slits are tuned at a little bit below 150 and "perfectly" 300 Hz.

I didn't accomplish a tuning of the tunes! it could be done by checking the resonances by plugging the slits and afterwards removing the blinds. For, to exactly match the resonance, you may alter the aperture by choking or by cutting more and more till reaching the required size.

It could be completed easily by means of oscilloscope, I do believe.

Resonance and dissonance depneds upon compression ratio and flare, you may find theory in the pdf doc, this time I hope to have attached a suitable file!

Now it's time to go, tell me what you think of the entire theory, better would be to go straight forward to a practical approach, building a hypex horn for increasing the air loading with a premature mouth area cut.

For the high freq, low pass front chamber may avoid the break-up of the woofer, at the same time would be good to go up to 500-600 Hz and build a two ways system.

Stay tuned, see you and really thanks for reading, sharing your time with me, I was feeling alone, in Italy I've got a very few occurence.

ELENA

The ultimate horn_1.pdf

[elena]

Here is the cross-section, the first slit is 20 mm wide instead of 40. Damping factor was established by more or less calculating first and then putting the required amount of acoustic material inside each aperture.

Transient ringing of twin reflex and reflexed horn ought to be checked by oscilloscope, so as to adjust whatever necessary to be done, maybe mitigating the unexpected interference betwwen the reflex ports too.

When I built the cabinet, I proceeded with no complete plan, I worked out a feedforward construction, changing the layout on the way step by step.

upon completion, I realized a few detaild were missing, so I did track what I built backwards, but when I did the reverse engrg. study I did some mistakes too!

Now everything should be settled.

Awaiting your opinion

ELENA

[DrWho]

Interesting idea...
I only skimmed through the PDF, but what is the difference between this and a tapped horn?

[Y]

Btw, what HF horn is that and what driver are you using?

[D-MAN]

A low-pass tuned filter on the side of the horn channel preceding the reflex port? Interesting! I haven't seen both used in the same horn before (I assume I'm understanding it right).

DM

[elena]

I present the philosophy behind the design and lay it down clear for a better understanding. I feel it may be illunderstood, for hold the line, I shall be preparing a pdf doc from a more practical perspective with all numerical information: from now onwards forget what I wrote in the other file, hold still, rewind and start from the beginning. Loudspeaker are coming from an Italian company, RCF, surf the net and find it, the woofer is the old model L15P200AK, still under manufacturing, with different Thiele parameters. There should be a very similar woofer from BEYMA, Spanish company. The high freq driver is a 4" carbon diaphragm, 2" throat compression unit with a constant directivity horn. I will give you all information next.

Aim is to get rid of reactiveness of the system; mean is to rearrange it so as to wipe off resonances. reactiveness cannot be canceled out, can only be modified to the purpose. This is the significance of adding reactive elements (as many as you like, depends on the number of horn resonances). A tapped horn, Danley design, is different, it employes a connection between the two sides of the woofer, but the target is that of the reflex concept, to align the acoustic phase of forward and backward sound wave. This is what I understood. Reflex ports along the horn behaves as Helmoltz resonators, this is the intention: they should stop resonance build-up.

This is what I tried to materialize over the cutoff frequency. For, to restrain cabinet dimension, the cutoff has been put quite high, a twin reflex design gives advantage, along with the reactance annulling technique can be implemented too.

The system works like a twin reflex below the horn cutoff, say 55 Hz. A twin reflex is capable of high efficiency, at least approaching a 100 dB/1W/1m. It balances the loss of output below the cutoff frequency, this was my intention.

At very low frequency, below cutoff horn loading is zero, horn behaves like a capacitor, the low pass filter adds an inductor to the system, on the other side there is the capacitor-inductor series of the reflex port and that of the woofer, hence the system is a twin reflex, it radiates as a band pass with high freq being the cutoff of the horn and the low freq being the free resonance of the woofer, in this case it's a 29-55 Hz band pass system. In comparison, I think that reactance annulling falls short.

Do reference to the electric equivalent circuit of the system, beware of locating the horn "lumped", here it is not a distributed circuit, the aim is to semplify and better determine the main frequencies, twin reflex and high freq cutoffs. To calculate the horn reflex port, then move to the distribuited circuit of the horn solely.

Combination of moving coil inductor, filter inductor, front cavity inductor and the like shouldn't be forgotten to avoid surprise! All reactive elements must be put on an equal footing, horn capacity well above the cutoff freq ..., resonance interference can be avoided by pulling them apart, for instance if a reactive element is more then root-ten fold, that is 3 times another one they may be terated separately.

ELENA

[D-MAN]

That is a unique implementation. I have seen capacitive spaces used in rear-loaded horns to reduce the high frequencies, but not to specifically control reactance peaks in a front-loaded multiple-flare horn. I haven't had time to sit down and really go through the pdf file so that I understand everything being discussed, but I will. I promise!

DM

[elena]

Will be fruitful to talk to you and whoever has anything to object: we shall get in mental shape!

And I promise to come up at the earliest with a more concise and practical presentation of the system. Meanwhile we may share my small, but direct experience with the twin reflex operation: a double reflex technique, a far as I know, has been adopted for instance by ALTEC and JBL. You cannot found the review of the double reflex design in my previous pdf, so that to complete the first rough description of the system I give an overview of that.

Think of splitting into two frequency bandwidth the operation of the system; we start with the very low frequency, below the cutoff.

So we deal with the twin reflex operation first: I think this is a common design in PA and outdoor reinforcement system.

Here are the woofer Thiele parameters:

Vas=280 l, qts=qes0.28 [qm=10], fs=29 Hz

From the reactance annulling theory we have: Vb=2xfsxqesxVas/fc, then must be multiplied by a factor Cas/Cab+1/(QtsxQb) to get into account the reflex loss (qb may be set down to 10 or even less for large enclosure, C is the compliance). Then the rear volume is 114 l (84 + 36% l).

From now onward we distinguish between the electrical and acoustical equivalent circuit. Do reference to the electric circuit, we do have more confidence with. I recall we are dealing with the louspeaker solely, [the very simple] crossover electrical network shall be put forward later.

Below the cutoff horn behaves like a capacitor, while the front cavity inductor approaches a short. Hence the front loading is a capacitance element plus a little radiation resistor, which delivers sound power to the outside: this is the foundation of the reactance annulling theory and technique. On the other side the reflex port is the series of an inductor and a capacitor, as the woofer is.

Now tune the port resonance onto the woofer resonance, you get a 4.rd order notch, double tuned over the woofer resonance.

The center frequency is then 29 Hz, the two twin reflex frequencies are coinciding, fb1=fb2=fb. We set fb=fs=29, and fc=2xfs, fc=55 [even if 2xfs is 58, this is an acceptable approximation]: this is a must.

This may ensure trivial interference.

Impedance and reactiveness of horn can be calculated by modified Bessel [Henkel] function, see for instance Beranek textbook or even better MacLachlan textbook on Bessel function or Loudspeaker: is there anybody out there possessing this very rare book, I have been looking for it all along!

Beware that the cutoff is due to resistor vs frequency curve, which more or less smoothly jumps up well above the cutoff and inductor/capacitor vs frequency curve as well. By large the reactive part of the horn has a double inherent nature, both inductive and capacitive, their influence depends on the geometry of the profile by itself, that is compression ratio and flare. After that remind that the influence of the radiation space is to add reactive and active elements at the far end of the horn network, this alters to some extent the behaviour of the system. Think of the different loading condition in full and quarter space!

Now go back to the twin reflex.

The reactance annulling help to sustain load below the cutoff, where the cutoff is around double the twin reflex frequency. Below cutoff reactivness of horn is by large capacitive, matching the equivalent capacitor to the inductor of the rear volume you get a new resonance.

The relevant frequency of the system are now at 29 Hz, woofer resonance, and 55 Hz, cutoff resonace. The twin reflex works centered at the woofer resonance, but due to the cutoff reactance annulling the band pass moves midway the two frequencies.

I recall that mean value for resonance is square root value, in our case sq(29x55)Hz=40 Hz! That's good, if I am right. I don't care that the reactive characteristic of the horn, that is the capacitance, dies away by 24 dB/oct [the active part raise by 12db/Oct], even the reactance annulling technique balance with a simple 6dB/oct inductive element.

Anyway this would be an inherent limitation of the system, more you push downward the cutoff, more you need a very low resonance woofer to get advantage.

A shortfall of my reasoning is that the analysis has been over-semplified, assuming trivial interference among resonant circuits and reactive element, they are spaced apart over a narrow frequency range!. This could be better assessed by measurement! The experimental approach is ever the most straight forward!!!

See you next time, looking forward to getting more and more people into the loop and having someone willing to construct and test a prototype

ELENA

[elena]

Hi,

I forget to tell what I call twin or double reflex is something like the Acoustimass load, patented by BOSE Corporation in the late 80'ies (also the implementation of the Acoustic Cannon Wave System, a double cylindrical horn, may be framed into the context of a vented band pass system).

One more thing, thinking of the balance of the impedance of the horn below the cutoff, even if the slope of the reactive element for a loudspeaker mounted onto an infinite baffle or at the end of a long straight tube is a +6 dB/Oct , in case of a finite size horn it may reach higher value, on the other side the slope of any electric filter element is 6 dB/Oct irrespective of the horn geometry.

Last thing, the Q of the twin reflex is Qt=qesx(Vas/Vb), in this case we get a smooth 0.4, it may ensure a sufficient efficiency (around double the loudspeaker efficiency) and a very good transient response.

To increase the efficiency, Vb must be less, hence the Q increase and above 0.7 ringing appears.

ELENA

[D-MAN]

Ok, I read the PDF document (more than once) and I think I have a handle on what you are trying to acheive. Let me paraphrase the issues for others for the sake of discussion...

The purpose for the thing is that it is an attempt to cancel the reactance variations typical of short horn pathways, this being exascerbated by the fact that a reflex-ported front-horn cannot be effectively reactance annulled due to the requirements of the Fr (cabinet resonant frequency) needed to "activate" the reflex ports at the desired frequency, that frequencybeing well below that of the front-horn's Fc. Did I get that straight?

The use of "tapped" frequency-specific filter cavities along the horn pathway are tuned to frequency values that would appear as peaks in the frequency response curve and are absorptive at that tuned frequency, hence removing the "peak" in the response at that frequency, and other active tuned reflex-ports are for "filling in" troughs if needed?

The problem I see is that we can't determine the values needed without a frequency curve and a reactance curve by frequency. Preferably, we need a set of curves showing the "without" (before) and then a set showing the "with" the cavities (the "after"). That is all that you are missing in the document, which you already know, of course. The missing "proofs"...

From what I can tell, it is a valid approach, somewhat unweildy though without test equipment, but in theory, it should get the job done. The question is, is it too complicated to be economical?

I think it is somewhat related to this reflex-ported patent (attached).

DM

[elena]

Hi Dana,

you have got the handle on it. Theory I put forward is quite simple, though the dynamics of [distribuited] circuit is often illunderstood by the most.

Of course, what is missing is the complete lack of proofs, theory might derive empirical forecast by preceding experimental facts. This is the way physics should go. Now we have to proceed straight forward to substantiate the forecast.

Best approach is to characterize the without and with system, to understand is it worth doing that, to weigh the advantage over a simple short horn. I fully agree, that is my hope, to find someone able to build a prototype and test it. For I will be preparing a short guide to calculate the system.

More I hope to test my own prototype at the soonest, I desperately need the equipment!

I repute the system is economical and easy to be worked out, look at the cabinet cut away view, a good deal is to take advantage from horn folding to lodge the back volume and achieve the reflex porting; of course there is an inherent limitation in the costruction, as the layout of the pathway cannot be too complicate, depending on the back volume and the tuning frequencies requirements.

I built the horn first, then by a stroke of "empiricism" I decided to go for the reflexing. It was easy to cut the slits owing to the particular simple layout, anyway implementing the system requires a layout optimization to materialize the reflex apertures to the back volume and nothing else.

I shall read the patent and give my feedback on the regard.

ELENA

[D-MAN]

Note that the patent posted above is NOT the same thing as you are attempting to achieve, I only think that some elements are related. The patent doesn't have any mechanism to reduce reactance peaks, it is concerned mainly with having various reflex-ports that are separated in frequency also feeding into the horn channel.

This would have no impact on your implementation, of course, other than simply having some of the same elements. Your implementation would be considered an improvement and is quite patentable, even as it sits, IMO (patents do not require scientific proofs, in the technical sense). They have to APPEAR to those schooled in the art that the elements involved in the combination would work as indicated and presented. They cannot "fly in the face of known scientific principles", in other words. How well the invention actually works is up to the market place to determine, not the patent office.

In the case of a loudspeaker, it has to essentially make noise in order to qualify as "work" for the patent office. It also has to be an improvement to the state of the art. I am relatively assured that there is no patent that I know of that attempts the solutions to the problems you suggest in the same manner. But then, I'm not a patent attorney, either. But perhaps you should talk to one.

Dana

[elena]

Hi,

I just read the patent document, it's quite interesting, inasmuch as it looks rather complicate, like a parallel path-way labirynth, but I guess it couldn't work as it is. I built my system, then I focused on how to get the resonating circuits work properly, as long as the porting arrangement diverts the sound wave shorting it to ground pressure (back of loudspeaker, against the enclosure wall)!

That is the only experimental element I gathered, cutting the slit bass disappears, forward and rearward sound waves interfere destructively, the sound is shorted to the back volume without reaching the horn mouth, it takes the short cut to the ground pressure.

Then I plugged completely the slits and get back the original sound, finally I went on calculating the rough value of the resistance element of the resonanaitng circuits: aim is to "clog" the ports, as is done in the non-periodic reflex enclosure, this shoots the target of balancing horn reactance peaks smoothing and notch filters off-center impedance raise.

I am willing to catch an oscilloscope and a wave function generator to check what happens with and without the porting, with and without the lining of the porting; I did the excercise by hearing, the difference is quite clear, but you know I love my baby horn as I love my kids, so I am in no position to give a unbiased feedback!

Should there be anybody out there who wish to build the horn, the complete set of formulae to calculate the system can be found in the pdf document and previous thread messages, anyway I am preparing a short design list of formulae step by step, with amendments to whatever mistook.

ELENA

[elena]

Dana,

I will be abroad for work so I won't be able to complete my summary on reflex ported horn design. Meanwhile I'd like getting more feedback, have you talked about that to anyone else? Take in the loop as many as you know!

Would be great to test the system and get the definite proof whether it works as expected. My desire has been all along to build one more cabinet with an on-line tuning of the porting, before the summer comes I should be able to do that, maybe I have found an oscilloscope to control how to intervene and offset the notch filter frequency to the horn resonance. Drawback is not to match the exact resonances, as the formulae cannot take into account layout geometry of the system, hence altering the response of the system more than curing. Foa a home audio system, the design could give advantage to shorten the patway and reduce the mouth area without any adverse effect on listening.

PA and outdoor sound reinforcement apparatus do not need such a trick, which is a mean of cheating physics of sound, suppressing overall oscillation inside the circuit rather than damping out single portion oscillation.

Do you think it would be worth constructing a prototype by yourself?

ELENA

[D-MAN]

I posted a link to your pdf file and plans in other forums. Many there will be interested in your work, I'm sure.

Here's one: http://audioroundtable.com/HighEfficiencySpeakers/messages/3366.html

I hope you'll post on it too, some people have already inquired about what we are calling the "ELENA horn".

Dana

[elena]

Hi

I'm back after a fast travel abroad, I posted to audioroundtable, here is the link http://audioroundtable.com/HighEfficiencySpeakers/messages/3397.html

In the message, I attempt to give a self-explaining clue to get physical insight into horn reflexing technique. Also I am thinking of a reflexed horn, loading a reflex enclosure, the woofer and the vent duct lean to.

PA systems I presume use both reflexinf the back volume and loading the reflexed back volume, novelty would be to duct the horn pathway too. The topic to be discussed will be how to determine most appropriate back volume and tune.

At a glance I cannot say which system gives advantage over the other, I've to check the acoustic equivalent circuit. Aim is to take advantage from the back volume more than the reactance annulling does, what has to be ascertained is whether swaping the back volume porting into radiation space for porting into horn throat is worth doing.

Anyway porting the horn pathway might not have shortfall, the only pitfall may be not to determine the resonances on the theory formulae as they actually are. But this has been already agreed and holds still in our minds.

ELENA

[ajsons]

CHECK OUT THIS THREAD TO FIND OUT WHERE THIS MAN STEALS HIS DESIGNS FROM!

http://forums.klipsch.com/forums/6/ShowForum.aspx

[elena]

Hi, ajsons

I'd be astonished, should I be stealing something from anyone I apologize, think whatever you like.

You like to get into this loop, you are welcome, otherwise I don't mind you blaiming me, but go back to the very first messages, check out my pdf file on reflex horn theory and tell me where you find something alike, wherever you do.

Could be I have got the idea of somebody else, maybe we all have got the idea of a pioneering time, but ain't gonna steal horn design!

Hope to get feedback and to build a relationship

ELENA