5. I took your eight drivers to be per side, but if total, then the sim I did would be a bit more sine-wave in appearance down low and 6 dB lower in output, though making it longer would smooth it back out, not that you would hear any difference. 
6. Yes, as I previously noted you ideally need to model the room/horn combo, but some reasonable assumptions can be made and I arrived at a ~1/3 shorter and 2/3 smaller system that combined with room gain should get you there. For sure close enough to EQ flat in-room and allow you to shape the mouths like you want since they will be just rolled over terminations that will only further smooth their HF response.
That said, with the advent of high SQ, Xmax, power handling sub drivers and relatively cheap high power amps I began suggesting IBs for serious infrasonic installs since if you can build in a huge horn system you can build in an IB and it's a whole lot less effort.
GM
6. Yes, as I previously noted you ideally need to model the room/horn combo, but some reasonable assumptions can be made and I arrived at a ~1/3 shorter and 2/3 smaller system that combined with room gain should get you there. For sure close enough to EQ flat in-room and allow you to shape the mouths like you want since they will be just rolled over terminations that will only further smooth their HF response.
That said, with the advent of high SQ, Xmax, power handling sub drivers and relatively cheap high power amps I began suggesting IBs for serious infrasonic installs since if you can build in a huge horn system you can build in an IB and it's a whole lot less effort.
GM
AndrewT said:
Seems to me the length of the horn was set for an 1/8 wave at 18Hz. I wasn't sure if it would work out since the two adjacent corners of the room basically function as the mouth of the horn. This made it difficult to predict where the actual mouth would end up, but there was a definite resonance at 18Hz, so I think it worked out that way. Or, maybe that was sheer luck and coincidence!
http://www.geocities.com/xobt
3hz flow modulators
Biggest basshorns in the world
ive noticed that the rear chamber your using is huge - How does a scoop model?
What existing subwoofers have you heard?
What about having a 50hz 0.5pi horn to hit the majority of energy - and ported tuned to ~14hz below this?
I notice that SPL attained is near 135dB in your simulations, have you measured a typical sub operating near 110dB? I find that SPL quite nice.
But then if you want to feel like your heart is having palpitations,go ahead with ~140dB.
My point is,try out a good 15" on a low tuned ported enclosure first,rather than jumping into a 10,000Litre subwoofer
3hz flow modulators
Biggest basshorns in the world
ive noticed that the rear chamber your using is huge - How does a scoop model?
What existing subwoofers have you heard?
What about having a 50hz 0.5pi horn to hit the majority of energy - and ported tuned to ~14hz below this?
I notice that SPL attained is near 135dB in your simulations, have you measured a typical sub operating near 110dB? I find that SPL quite nice.
But then if you want to feel like your heart is having palpitations,go ahead with ~140dB.
My point is,try out a good 15" on a low tuned ported enclosure first,rather than jumping into a 10,000Litre subwoofer
I've seen all the big stuff (on the internet). What have I heard? Not much... Aside from PA gear at larger venues, I've heard nothing commercial at all. But to be mildly self indulgent and fully answer your question...
A BRIEF HISTORY OF ME AND BASS
1. Maybe 15 years ago or so I made a few manufacturer suggested ported boxes for low/mid price car audio woofers for car audio use. I was IMMEDIATELY hooked on diy and despite mediocre results I thought I was pretty clever, since at the time I thought the results were FANTASTIC.
2. 6th order bandpass for dual 15 inch pyramid woofers for home audio use. Plans supplied by a friend. Back when I thought power handling was the most important spec, I thought this box was the best thing EVER.
3. Decware Wicked One - As a result of my complete inability to follow plans to the letter, my WO turned out looking exactly like photos of Danley's small tapped horns, with the driver in the horn mouth, not bandpass as the decware plans show. The drivers I used were wildly unsuitable for this application, much more suitable as OB woofers. As a result it was loud as all hell but would not go low. BUT when I put in the car's backseat and fired it into the trunk - the bandpass effect tuned it just right and it BLEW MY MIND.
4. Jensen Imperial - I figured a little horn was good so a big horn would be better, and go as low as I wanted it to. I used the Jensen plans, but left the entire chamber area open, as the decware imperial does. It didn't go very low but the sheer output, especially when firing into a corner with me IN the corner ROCKED MY WORLD. I've since tried different things with it, such as front loading, as in the pic, but still never tried it with optimal drivers. (Mostly made from 2 inch thick wood - this thing is HEAVY)
5. Jensen Transflex / Tapped Horn - I had studied horns long enough to know the Imperial would never be tuned low enough so I thought the transflex would be a good sub for it. The Danley DTS-20 had just been introduced so I thought I might move the driver further down the line and have a tapped horn (along with a couple of other changes, since I am incapable of following plans). GM held my hand through this process but (very understandably) would not provide Danley's tapped horn secrets. Otherwise he was extremely helpful, and he did warn me it wasn't going to work before I even started and every step of the way. Obviously he was right and it didn't take long before I moved the driver to the front of the box to make it a tl instead of a tapped horn. Tremendous learning experience thanks to GM and MJK's website.
The first incarnation was a tapped horn. I didn't know how to model that (many months before the collaborative tapped horn thread even started) so there are no graphs to show but response was super bad in reality. (Actually I didn't personally do ANY of these graphs, IIRC they are all courtesy of GM) The second incarnation of this box changed it to a tl, response graph below (unstuffed).
The third incarnation incorporated a lower tuning, shown below (with stuffing). It hits low for sure, but not extremely high spl potential. I knew from the start I'd need at least 2 to get anywhere near live levels in a larger room, but only ended up making one. Awesome for late night movies in a smallish sized room. I'm planning on more tweaks on this box, including a much higher tuning with much higher gain, some day.
6. A brief affair with OB bass. These are open backed boxes (U baffle)
7. Alternate technologies. My (internet) buddy and I decided we could make rotary woofers. The premise was to make one for 2 - 4 percent of retail cost ($13000 USD). This has been ongoing for months and has almost become an an embarassment due to lack of progress and no guarantee it will work well. Originally I thought I was going to make it with spare parts in my garage, but it didn't take long to cure that misconception. The hardest part is making a variable pitch fan and the cheapest way to do it is with rc helicopter parts, so the whole design is based on an rc heli main rotorhead. Our designs use single phase ac motors to reduce the cost and eliminate the need for 3 phase power. Speed control (in my design) is not necessary. I use a 1725 rpm motor and will counter noise with a smaller blade span and careful blade design.
At this point, I'm estimating that I can make something about 25 - 35 percent as effective as the commercial model for about $400 - $500 (with all brand new parts). As you can tell, this blows the original budget all to hell, but so what, it's the best I can do. At this point, I've removed the dustcap and screen from the driver, had a motor shaft - fan shaft adapter professionally built and attached the r/c rotorhead. There are several steps to go and problems to overcome. The driver and the motor have to be bolted together (with precision alignment), the vc has to be attached to the swashplate, blades must be designed and made, and the cone and surround have to be cut out. Not sure if I will ever get that far. Also many problems to address. The motor overheats very quickly with no load, so I need a new one. If I have to buy one I will get a 1025 rpm blower motor but then I will need a new adapter. This design may prove to be NOT maintenance free, which will be a devastating blow to the entire concept. And furthermore, I don't really have anywhere to mount this at this time.
(Not going to cut the driver frame apart. The bladespan will be ~13.5 inches and the blades will ride inside the rim - just imagine blades instead of a cone diaphragm)
Along the line I've explored a couple of other ways to do this (5 - 20 hz). First I played a bit with valves like the 3 hz Danley design you linked to. Mine was a bit smaller, using a shopvac in IB, and waving my hand over the hole to simulate half a sine wave. As you can imagine (if you are more imaginative than I was) I can't wave my hand very fast so the tests really mean nothing, although testing did show that moving air at high velocity through a small hole is extremely noisy. This idea has HUGE potential but it would require 2 fans of some type, one to push, one to pull, and it would require LARGE valves connected to LARGE csa lines (to reduce velocity) and the valves would have to be "Y" type, to direct the airflow. The air lines don't like to be closed by a valve, they much prefer if you direct the air in one direction or the other (into the listening room or back out where it came from). This is by far the easiest way to make very low IB bass, but the valves that would be required are large and crazy expensive.
I've also toyed with the idea of using driver motors to push incredibly large and light diaphragms (compared to the cone they come with). That's a study for another day, but some of today's driver motors (like the mach5 ixl18) can push a LOT of weight around before the q gets too high.
Then in another forum someone started talking about making a planar wave horn woofer system to cover 42 - 240 hz and off the top of my head I drew the pic in post 1. The idea was rejected quite quickly but I never stopped thinking about it, and applying it to subwoofer frequencies.
That's where I am and I have no idea where I'm going from here. I don't think I'll be done until I've tried everything at least a couple of times. No such thing as too loud or too low.
This is my first crack at hornresp, as well as my first try designing a horn so...
I don't really know what I'm doing, but despite being slow and stupid I'm learning.
Have you tried using a not too big and well sealed listening room, to maximise the room gain and use a couple of normal drivers in closed boxes or IB? This should be linear to DC.
When you think in therms of very low bass, the box in front of the driver (your room) maybe is more important than the mechanism that generates the bass. Minimising the losses instead of maximising the output may be a way to go, because the engineering you need to accomplish this is alot less complex than the one to generate high output bass. This stuff with air flow and valves was designed to be used outdoors. Why not use the biggest advantage the home listener has in comparison to open air audio, namely the room, which acts like a pressure chamber with a +12db gain per octave in the low frequencies?
When you think in therms of very low bass, the box in front of the driver (your room) maybe is more important than the mechanism that generates the bass. Minimising the losses instead of maximising the output may be a way to go, because the engineering you need to accomplish this is alot less complex than the one to generate high output bass. This stuff with air flow and valves was designed to be used outdoors. Why not use the biggest advantage the home listener has in comparison to open air audio, namely the room, which acts like a pressure chamber with a +12db gain per octave in the low frequencies?
Not specifically, but when I said the tl I made didn't have much SPL potential, I meant maybe 110 db peaks at 12 hz (IIRC) so not too bad. This was in a smallish room (11 x 14 x 7.5 feet) so it performed fairly well and fairly low.
I want to do both as much as possible. In the first post I mentioned that the walls would have to be strong (concrete or metal) by default. I think this would imply an airtight seal as well, but didn't specifically mention that.
OTOH, minimizing losses is why I mentioned that if I end up trying OB I will probably vent straight up from under the listening couch, placing the listener ~ 1m from the drivers to minimize loss from traveling distances, so I agree that minimizing losses is important.
Danley's valve was designed for outside out of necessity, but there is a rotary woofer specifically for use in IB (thigpen rotary woofer - trw17) and rotosub.com has them for various purposes. No reason at all that any of these would not work in home IB systems.
That's the absolute theoretical max, isn't it? I'd never count on room gain like that, I'd be happy with 6 db/oct in reality, and even then, only down to about 10 hz or so, below which I wouldn't count on any room gain at all due to massive losses from the room being less than infinitely rigid.
You got 87dB/1w/1m at 15hz with your tline?Thats impressive enough at that frequency. It takes alot of physical volume to get sensitivity down low.
Im not up to date with the tapped horns,but they seem slightly more sensitive,and larger.
It seems your asking for extreme SPL at low frequencies. Your only other option is to go for MULTIPLES of subs.
Having the sub very close to the listener is another option I like.
Id look around for beefy 12"s and 15"s for ported enclosures.
Im not up to date with the tapped horns,but they seem slightly more sensitive,and larger.
It seems your asking for extreme SPL at low frequencies. Your only other option is to go for MULTIPLES of subs.
Having the sub very close to the listener is another option I like.
Id look around for beefy 12"s and 15"s for ported enclosures.
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