"The Sublimator" an infinity 1260w, 18hz tuned offset driver folded horn build thread

[Gary147852]

So I'm just getting my build thread ready as I'm almost ready to make saw dust.

 

[Gary147852]

 

[BoredSysAdmin]

why not THD LP :
http://www.billfitzmaurice.com/THT.html

 

[Gary147852]

No reason. Nothing against bfm. Just wanted something a little different(smaller footprint). Plus I hear corner loaded sub horns are the bee's knee's with all that extra room gain.
This is the space I have to work with.

 

[Gary147852]

On the left is a tiny marty. 20x20x30 slotported. Tuned to 20hz. On the right is the sublimator. 15x16x81.5 offset driver front loaded folded horn tuned to 18hz.

 

[JohnnieB]

This looks very interesting. I will be following this thread for sure.

 

[TLS Guy]

To me that does not look like a horn at all, but a TL.

 

[JohnnieB]

To me that does not look like a horn at all, but a TL.

I did a google search, a lot of math which admittedly I have limited skill with. In layman's terms, what is the difference between the two and how do those differences affect the final product?

 

[TheWarrior]

Gary, in researching this further, it appears you have unknowingly combined transmission line theory with folded horns. Because you did not know who to differentiate the two, I think you have effectively created a giant box that will do nothing but provide a 180 deg phase inversion at the port opening.

A folded horn sub is intended to increase efficiency (which your sub already is quite efficient) so that 'more sound' is heard for a given amount of input. A transmission line is where you create a long duct that acts as a waveguide that decreases distortion, and can increase in room response of the selected frequency over what the driver would normally be capable of producing.

The horn you have designed is barely larger than the driver itself, yet is expected to increase in-room response. Note the sizes of these basic designs for reference using 15" drivers.

Don't build this dude. The design needs to be completely revised! Keep reading and researching, it can be done!

 

[TLS Guy]

I did a google search, a lot of math which admittedly I have limited skill with. In layman's terms, what is the difference between the two and how do those differences affect the final product?

A traditional horn has a driver, an expansion chamber, a throat and flare, which can be exponential, Tractrix, or parabolic. It belongs to the family of horns, Like the French Horn, Tuba etc.

Here is a horn speaker.

The low frequency cut off is set by the diameter of the mouth. However when placed in a corner, this does add to the flare and extend bass response. However for a good sub a traditional horn would have to be huge.

There is also the tapped horn popularized by Danley, that is tapped because the driver crosses two compartments of the line. This allows for deeper bass in a smaller horn.

A transmission line also comes in various guises. The traditional lines are specialized Gaddeckt organ pipes. Therefore is a stopped pipe open at one end and not both, like an open pipe.

A stopped pipe has a fundamental frequency and odd harmonics. To lessen harmonic output, the driver is placed a third to quarter the length of the pipe at the closed end.

At the closed end of the pipe the pressure changes are high, and control cone movement well. At the lower end there is a null of pressure, but air flow is maximal.

The pipe is tapered to broaden the resonance, usually with the widest part at the closed and and the narrowest part at the open end. This is the opposite of horn expansion.

The pipe is designed to make Fp match the driver Fs, like you do with a tuned box, allthough this relates to length and not volume. The volume of air in the pipe is largely determined by driver VAS.

A line without damping has an impedance curve like a ported box. However the pipe is then damped with stuffing just, and only just to the point of suppression of one peak of impedance. The line is then critically damped and reproduction will be non resonant, with useful bass augmentation and good control of driver cone displacement. At the point of critical damping the line will roll off second order, 12 db per octave, rather then the fourth order 24 db per octave roll off, of an undamped line.

Here is my center channel TL under construction.

And then it is damped.

Unfortunately some authors have wrongly referred to pipe bases speakers as horns, which is not correct. This causes enormous confusion.

 

[MJK]

I did a google search, a lot of math which admittedly I have limited skill with. In layman's terms, what is the difference between the two and how do those differences affect the final product?

The difference between TL and horn behavior is all in the size of the open end/mouth and the frequencies being reproduced.

If the open end is large enough for the frequencies being reproduced then the sound waves coming down the expanding path will efficiently be transmitted into the room over a wide frequency band. The acoustic impedance of the mouth will be resistive and dissipate sound energy from the enclosure into the room.The electrical impedance of the speaker will be a single hump. This is horn speaker behavior.

If the open end is too small then the sound waves coming down the expanding path will reflect back into the cabinet and form standing wave resonances. The acoustic impedance of the mouth will be mass loading leading to reflections of sound energy back into the expanding path. This is TL speaker behavior generating a series of peaks at discrete frequencies corresponding to the standing wave resonances. The electrical impedance plot will exhibit multiple sharp peaks as will the SPL plots seen in the HornResp output in the earlier posts.

The acoustic impedance of the mouth is frequency and size dependent. An expanding path enclosure can start out behaving as a TL at low frequencies and then as frequency increases gradually transition to horn like behavior at midrange frequencies. For low frequencies the effective mouth area (including any boundary loading) needs to be HUGE for the speaker to behave like a horn. The original design is small enough to be a TL over its entire operating range as evident by the series of sharp peaks in the SPL plots.

That is the difference between a TL and a horn. Most tapped horns or back loaded horns seen on the Internet are in reality TLs at low to mid frequencies.

 

[Gary147852]

The pipe is tapered to broaden the resonance, usually with the widest part at the closed and and the narrowest part at the open end. This is the opposite of horn expansion.

this is the exact opposite of what is happening here.