It is depends what kind horn it is. For LF horn the resonance should not be “an octave lower then lowest frequency you can realistically get from the horn”.  In fact the common way is to much the assembly resonance to the horn cut off by squashing the back chamber. Theoretically it cancels out the throat reactance in the horns with the small throats but in practice only God knows how those upperbass horn would sound when you are done. For the HF horn it is kind of correct: people hide the primary resonance behind the horn rate but I do not know the rules how far. In realty no one manage the compression drivers resonance intelligently but people use whatever compression garbage was already accidentally made for us. I was playing with managing the Fs of compression drivers, got very inconclusive and uninterruptible results and … abandon to think about it. In compression drive the secondary resonances and the resonances due to the crappy driver design are more effective then the Fs.

The caT

NBC wrote:

Can you please clarify what you mean by "active biasing" -- in relation to the caps?

"I think the ultimate length of the upperbass horn is 3”- 4” throat. With longer horn it would be very complicated to time-align it as the horn will mask out the MF driver." 
Is this also why you use tractrix curve for expansion? 
To shorten the horn, and keep the centerlines of all horns closer together, instead of exponential? 
Is this a guess (length), or have you actually tried both curves, in this frequency range? 


Where did you come up with these numbers for an "ultimate driver" from? 

Throat (driver diameter), flux, cone material, resonate frequency? 
Why no phase plug? 
Are these all guesses, experiments, or physics? 

I don't mind building several horns, and drivers to experiment, but I'm trying to ask as many questions as possible first, to shorten the learning curve.  I've been digging for patents/white papers,and through physics and acoustics texts, but haven't turned up enough to actually base anything off of without a LOT of experimentation, or outright copying.  
Thanks,
Robert

serenechaos wrote:

"I think the ultimate length of the upperbass horn is 3”- 4” throat. With longer horn it would be very complicated to time-align it as the horn will mask out the MF driver."  Is this also why you use tractrix curve for expansion?  To shorten the horn, and keep the centerlines of all horns closer together, instead of exponential?  Is this a guess (length), or have you actually tried both curves, in this frequency range?

The type of curve used for upperbass horn is slightly different subject the slower rate the more bass extension you get but also your horn become longer. With faster opening you have less low end but in some way better quality of the lower end you get. There is no rule there but I feel that approximately 120-150 Hz is the region where the profile makes sense (deepens how you upperbass MacroImbeded in your room) to switch from fact opening (Tratrix, LeCleach) to slow opening (exponential, parabolic). The problem with 80-120Hz parabolic for instance is the size and vignetteing of MF channels in nearfield.

serenechaos wrote:

Where did you come up with these numbers for an "ultimate driver" from?

I presume you meant the "ultimate throat  size" not the "ultimate driver". The answer would be:  Practice of listening, thinking and experimenting with different solution. Do not make a mistake confusing the upperbass horns with midbass horns – they are different animals. For an upperbass horn (70-120Hz mouth) 3”- 4” throat is, all thing considered, is perfect in my view. For an upperbass horn (45-70Hz mouth) I feel a throat of 5”- 8” will be more appropriate.  Sure the people who use a single horn-loaded Lowther, driving with it full range will be laughing. Welcome to my world.

serenechaos wrote:

I don't mind building several horns, and drivers to experiment, but I'm trying to ask as many questions as possible first, to shorten the learning curve.  I've been digging for patents/white papers, and through physics and acoustics texts, but haven't turned up enough to actually base anything off of without a LOT of experimentation, or outright copying.

Robert, unfortunately the “patents/white papers, and through physics and acoustics texts”, equally to pontification of classically trained acoustic systems boulders have absolutely nothing to do with sound you will be getting from horn sand 99% of BS written about hors is juts worthless garbage. I know it sound like my personal attitude but it will take for you a looooong time to appreciate what I am trying to say. If you do not believe me then I would let you know that what I said is actually the private quote from a person why from my point of view know more about horn sound more than any other living person. I do not try to convince you or encourage you to embrace a specific point of view. All that I ask you is that what you found a source that from your point of view construct up a presumptive theory how to get Sound form horns then let me know.

By “midbass horn” I’m talking about a horn with about a flare frequency of about 60 Hz,
to use with Fane 8” drivers, to start with.   

 (Was planning to use this horn from wherever it sounded best, trying for around 80 Hz to ~350 Hz). 
I was planning on using a slow opening (exponential) for this horn. 

I noticed you used a tractrix. 

I didn’t think one could “get away” with using a tractrix down this low, without major penalties in sound quality.  
The tractrix is attractive in that it is much shorter…

Have you tried (heard/listened to) both? 
I was planning on fixing this horn to the ceiling anyway, which helps get it out of the way somewhat, but it is still seems a problem to place everything (time aligned) without the mouths in front getting in the way of wavefronts of the mouths behind them. 

When I ask about the “ultimate driver”, I was referring to what you started this "The ultimate upperbass?" thread with: 

Romy the Cat wrote:

I think the ultimate length of the upperbass horn is 3”- 4” throat. With longer horn it would be very complicated to time-align it as the horn will mask out the MF driver.  The ultimate driver for upperbass should be a compression driver, low to medium flux, with no face plug, most likely with aluminum cone and resonant frequency ~20-50Hz below the horn rate. I personally do not know such a driver, if someone do then let me know… The Cat

serenechaos wrote:

By “midbass horn” I’m talking about a horn with about a flare frequency of about 60 Hz, to use with Fane 8” drivers, to start with.     (Was planning to use this horn from wherever it sounded best, trying for around 80 Hz to ~350 Hz).  I was planning on using a slow opening (exponential) for this horn.  I noticed you used a tractrix.

I have my motivations to go for Tratrix but do not forget that my horn is 115Hz not 60Hz and it sits under and in front of MF channels not above or on side. For 60Hz I think I would go for slow opening and locate it on the side, unless you have you original idea how to locate 60Hz horn within the limited and prefixed height of MF channels.  Be careful with idea of using the Fane 8” drivers (I presume it is the Studio 8M) for 60Hz horn. The Fane has 68Hz it’s resonance frequency and it will be a huge starch trying to use this driver in 60Hz horn. I afraid the driver will be suffocated. The Studio 8M in open air goes down to ~450Hz and  down to 150Hz in sealed box. Loaded into 4” and compressing it with back chamber it get EQed down to 110Hz. You migh get out of it another 10-20Hz by beter horn EQ but it will be I feel a huge compromise. Search for your  60Hz horn another driver with open air resonance of around 35hz-50Hz.

serenechaos wrote:

I didn’t think one could “get away” with using a tractrix down this low, without major penalties in sound quality.

I agree but I would not insist that it is true. It is controversial as “sound quality” is not the same as bass extension.

serenechaos wrote:

When I ask about the “ultimate driver”, I was referring to what you started this "The ultimate upperbass?" thread…. .

I see. I was talking not about an “ultimate driver” but an “ultimate driver for a given horn rate. This is very different and I very much agree with what I said in there. For your 60Hz horn try to find an above 100dB sensitive 10-12” driver with Fs of ~40Hz, look at throat of 6-7” and use the driver as a compression driver. Do not ask me specific recommendations what driver to use – I honestly do not know.

Romy the Cat wrote:

skushino wrote: • total horn length (incl. back chamber) shall not exceed 1,00m • the horn shall have conical approximation of a hyperbolic flare contur with m=0.6 • the horn shall have a 5/16 mouth size of a free space horn • the horn shall have a 1:1.6 mouth ratio to minimize mouth reflections • the horn shall not be folded to reach 500Hz upper xover frequency • the horn shall use an EV EVM15L Well, if people threw the comments “the horn shall” then they should provide reasons for it. Perhaps the guy does have his reasons. I believe I know some of them and I do not agree with his reasons, not to mention that some of his reasons are absolutely laughable.  skushino wrote: These horns are an alternative to my 150Hz Tractrix. They are 77Hz, 3/16 mouth front horns with a conical shape. This is because the simulated difference to initially designed hyperbolic m=0.6 horn seem to be negligible. The horns are built from 40mm MDF. So the horn shell is pretty stiff even without a surrounding box. The driver is an EVM15L. No surprise he posted at AA: those morns swallow everything! Kill me but I do not see in this horn 77Hz, horn loaded. A 15” EVM15L has primary resonance of 40Hz, with this back chamber he might jack it up a little. Why the back chamber has such a huge volume (at least external) only God knows.  If he runs Fs of this horn under the 77Hz then he screw his horn overloading the mouth with LF. To increase the Fs via back chamber from 40Hz to 75-80Hz he would need superbly small space behind the driver. In fact so small that it would make the driver too “stiff” and convert this horn in the acoustic suspension arrangement with attached horn. The only explanation would be if he uses in his horn an oversized throat: I would say 8-9 inches (considering the length of the horn). This would explain absolutely anything including how he was able to get 77Hz form this size mouth. I do not know the dimensions of this thing but if to pretend the MF driver sits at it default highs then this upper bass horn has a mouth of approximately 35”x20”. This thing, considering the 8”” throat is loaded as horn down 150Hz no more. All the rest the EVM15L driver shots through the horn like a direct radiator. This was the reasons why he need to make this huge back chamber because he needs a lot of exertion form this driver, actual he might wide open it with the same result. I visited Erick site before and I believe his site is for years in the bookmarks of my site. I like him but it does not make his new upperbass horn to comply with my views of what good upper bass horns might be. Rgs, Romy the caT

Dresden wrote:

I'm a new reader of your website and one subject which interests me a lot is that of upper bass horns. As you have noted time and again (with which I agree almost completely, after reading a lot of 'research' [many claiming to defy the laws of physics]), is that most designs claiming horn bass loading under 100 Hz are false.  The laws of physics cannot change. In light of this fact, I have one question concerning horn loading in the range of 40 Hz to 400 Hz:  Is it possible to attain good performance in this range in a design with both the front and back of the driver horn loaded?  (I'm in the process of designing a horn for this range, but I'm really interested in knowing if a design using the energy from both the front and back of the driver might yield good results--perhaps higher efficiency--without unacceptable phase, cancellation, or other potential problems.  One reason for wanting to limit the upper range to 400 Hz is that I may implement a partial bend near the throat to accommodate the proper length of the horn [the horn will be vertical with the driver facing downward and the sound exiting 90 degrees to the audience].  My aim is to use the system without a subwoofer.) Any light you can shed on the matter will be most appreciated.

Dresden,

great question, complex question and I feel that it well-worth a separate thread: front and back lording and radiation. I, whatever it worth, generally against any dual loading. Unfortunately I have no time now to compile all my arguments into a sensible reply. I also do not exactly know why I am against it I need person some time to do some thinking and to rationalize it.  I might do it later. The front and back lording and radiation is certainly own animal and need to be viewed from own perspective…

You need to decide what length of the horn you can afford. When I mean “afford” I ment the position of the horn in context of the rest of your system. You know the lowest cut off - 40Hz. So, the most suitable for you length and the mouth size will give you the throat diameter. If you have unlimited space in your room then be advised that starting form some point the increase of length and minimization of the throat will increase loading but also will introduces some unwanted colorations. You see, the longer horn is them more “parallel” it is. A horn that we use for audio have very slow opening at beginning and in very long horn the “beginning of the horn” section is very long, it might be a foot or two of virtually parallel walls. For the frequencies that the 40Hz horn will be caring the “virtually parallel walls” are the essentially the parallel walls.  I have no idea when it becomes a factor but too long horns tend to be congested and colored.

So, you have a horn, you have a throat diameter, then you need to find a driver. To decide on a driver is very complicated ceremony and my absolute rule is following in it: “It is absolutely imposable to predict with a serenity how a driver will sound after it will be loaded in a given horn.” You might do for compression driver, or for conventional driver, in fact any driver that you will be using with back chamber will become a compression driver.   The section of driver is a big subject… Linearity is not something that I would even care; do not think about it as you have no control over it anyhow. I laugh when people talk about linearization of bass horn frequency response.

Where are you? A well-sounding 40Hz horn is very interning accomplishment to experience. If you are near US’ New England and if you listen serious music then I would like to be invited after you finish the projects.

"Meant to be?"

With 100.5 dB efficiency in quarter space I plan to use a dedicated tube amp.  

Yes, some people use high powered amps to see how loud they can get Def Leppard, but I don't see any reason to.  And some tapped horns are also used in PAs with PA amps. 
Just like front loaded horns have different applications, etc. 

I don't have GOTOs... (only in my dreams) just Radians for now, I'll baseline with them. 
I had thought of using a Lowther or pair of Fostex for mid-bass, actually using a pair in parallel. 
I have several options, driver sizes, and throat sizes to play with. 
Somewhere between 8" and 15", with corresponding throat size. 
Probably Fane 8, B & C 10s, or 18 Sound 15? 

It's down to build, listen, change, listen... 
How else can you know how it's going to sound in the horn???
Robert