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post #31 of 113 Old 01-19-2019, 03:36 PM - Thread Starter
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Originally Posted by kennyandersen View Post
I will go back a bit and again suggest the dual bandpass subwoofers.

If you go ported you lose the efficiency, and you would need to meet with a high pass filter to protect the driver.

My guess is you could make enough SPL with (4) 18" band pass subs. You might could add 2 more, but you will have to be careful how everything is wired up so that you have the right impedance match with your amp i.e. if your amp will drive a 2 ohm load you want the speakers to present that. That might mean it is difficult to do 6, defending on the driver impedance.
I am all for the most efficiency and do not mind a complicated fabrication. If 18" band pass subs would get enough SPL I am for that.

I am unsure exactly what a dual bandpass box looks like. Does it have 2 drivers like the images attached? Or is it 1 dual bandpass box per driver?

Does the "tuning" come from the box design / shape or the EQ?


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post #32 of 113 Old 01-19-2019, 05:14 PM
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Originally Posted by subbuilds View Post
I am by no means wedded to the UM-18's but the Skars that you linked to have a frequency response of 37hz vs the 19hz of the UM-18's. Wouldn't i have farther to go to get down to 15hz?

I do like the price. I would be able to get 6 of the Skars if they would work for the low hz requirement.

How does the 4 layer coil add more displacement?
The fs is 37 hz, frequency response is 20 to 400hz. Which does not mean you cannot go low with them. You get out of them
what you put in them, Its not all about specs its about enclosure, woofer size etc. Then your amp must be able to amplify it,
and of course the content has to there. The dayton were 19.5fs and 19 to 500hz. Then of course you have crossover, and
parametric eq to make the content what you want.

The size of the coil 4 layer is double the metal in the coil vs a 2 layer. The dayton will have 1 layer per coil. The skar
2 layers per coil. That is double the size, which adds to power and heat handling ability. Some re audio have 8 layer coil.
The top reason the dayton will fry is because of the wimpy two layer coil.

The skar is just one example. Subwoofers with bigger voice coils tend to take their rated power better. Take longer to heat up, etc.
Heat is dispersed through more metal. The skar also has the same or better peak to peak excursion.

It is just one example. I just suggest to shop for a strong sub that will last you the test of time, and the test of your punishment you
want to give it.
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A Good amplifier requires a adequate power supply, It does not matter what the amplifier is capable of if the power supply will not provide the power required. Most amplifiers have under rated power supplies. It is up to you to make sure you get the ones that are least under rated if at all.

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post #33 of 113 Old 01-19-2019, 06:32 PM
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Originally Posted by subbuilds View Post
I am all for the most efficiency and do not mind a complicated fabrication. If 18" band pass subs would get enough SPL I am for that.

I am unsure exactly what a dual bandpass box looks like. Does it have 2 drivers like the images attached? Or is it 1 dual bandpass box per driver?

Does the "tuning" come from the box design / shape or the EQ?


Attachment 2513230

Attachment 2513232
A bandpass is actually to boxes hooked together. The driver is between them and there is a port coming out of one of the boxes. All you actually hear is the port. You could tune the port to say 24 hz which would give you output down to 15 and up to 30.
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post #34 of 113 Old 01-19-2019, 06:34 PM
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here is what a bandpass sub box looks like:
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post #35 of 113 Old 01-19-2019, 06:52 PM
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there is no other way to get significant SPL in the limited range you need on less power. It is one of the cases IMHO where there is a very specific solution to the problem you are posing.
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post #36 of 113 Old 01-19-2019, 07:22 PM
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Dual Opposed Dayton UM-18's for infrasonic art installation

@subbuilds
As @BassThatHz can attest and has already mentioned, more cones the better to not only pressurize a large area but to also share the acoustical load.

Have you looked into using pro audio woofers? They are designed to be very efficient and when used in numbers can be very effective in ultra low frequencies. Search for “the official VBSS subwoofer design” thread.

The VBSS is a ported design that uses the Dayton Audio PA460 18” woofer and can be tuned at a dedicated 15Hz tune. The Dayton Audio Ultimax 18 is 88dB efficient the PA460 is 98dB. You can purchase 3x PA460’s for the price of 1 Ultimax 18. You can run 16 of the PA460’s off of one Behringer NX6000D. 8x on one channel and 8x on the other while using the onboard DSP and having a stack of dual opposed VBSS on each side of the room would definitely fill that size room. Plus using one amplifier would maximize your electrical efficiency as well, it is a proven designed system, and with 16 of them would be the same price as 4 Ultimax 18s.

Just my 2 cents... good luck with your endeavors.


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post #37 of 113 Old 01-19-2019, 09:49 PM
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I think the VBSS is a great idea as well. With four our more and 15 hz tune you should get adequate output at 10 hz plus you can run 8 off an inuke/nx3000 and it would keep costs down.
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post #38 of 113 Old 01-19-2019, 09:57 PM
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Originally Posted by subbuilds View Post
I could add up to 6 UM-18's but am not sure if there is enough available power to drive them.
This project is a bit of a one-off... what works best for a HT and what works best for this project are two entirely different things.

Normally I would recommend a single 24 and a SpeakerPower amp for HT, or a nu1kdsp and PA-460 for chest-kick.
But even that won't be near-enough for this project...

Haven't box-modeled it BUT if you can afford 6 UM-18's, then you MIGHT actually be better off with 18 of these 18's instead (with bulk discount and sales codes): https://www.parts-express.com/dayton...4-ohm--295-475

They are 96db/w/m and have more excursion than PA-460's have, for not much more money.
The UM is only 88db/w/m and 3x the price, it does have more excursion and power handling though.

Trust the box modeling software, they usually aren't far off. Whatever it says is best, buy that...

Cone area vs excursion ratio is very important for ULF on the cheap. Likely more FAR important than available-watts or power-handling in this case... as I mentioned earlier.

You may actually want to rent a few Powersoft K20's for a day, those have PFC which is super important when limited by the breaker. PFC makes the amplifier draw a smooth waveform rather than drawing spikes of amperes when the 120V drops to 0V 120 times a second, and by renting you aren't committing to it for later personal ownership. You can usually rent pro amps at your local pro-sound shops (if you have any good shops that have the good amplifiers. i.e. Powersoft).

Otherwise just get the SpeakerPower amps, those are known-good for single digit Hz into 1-ohm loads. Especially their rack mountable amps.

What works well for this project vs personal ownership in HT is two entirely different things...
This is one of the freak cases where 18 of the Dayton Classic 18's might just outperform both the UM and PA Dayton's for the same $.

Make the box as big as you can lift or transport, and as many of those big boxes as you can afford to transport, and put as many 18's as will fit in a 14hz tuning in each one.
Rent the largest moving truck for a day and a pallet jack (or fork lift if available).

Bigger boxes are more efficient vs smaller boxes,
but really it is ALSO the ratio of cones per cuft... and your ability to lift/transport/place the things.

You don't want the port velocity to be too high or you will get nothing but port chuffing. That is the one downside of ported boxes vs sealed.

Ported is the goldilocks zone of box types, more efficient than sealed nearing the tuning frequency, and easier to make than horned...

Ported is about 8-12db louder than sealed, near say 14hz...
Horned is about 6db louder than ported. Which WOULD come in handy in this case.
Horned boxes tend to be about 25-50% bigger than ported boxes.

No free lunch.

No matter how many cones you end up buying or which ones, I'd still have computer fans blowing directly on the coils to cool them in this project. They are cheap and they work.

Sinewaves put a LOT of stress on both the coils and the amplifier.
Maximum stress, in fact...

The only thing worse is clipped-sinewaves or squarewaves
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Last edited by BassThatHz; 01-19-2019 at 10:13 PM.
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post #39 of 113 Old 01-19-2019, 10:19 PM
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Originally Posted by BassThatHz View Post
That said, if you get too close to the sub you will be in the nearfield zone where ULF is weakest....
Why is this the case?
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post #40 of 113 Old 01-19-2019, 10:45 PM
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Originally Posted by CrusherW9 View Post
Why is this the case?
Nearfield will only be the wave generated directly off of the cone, sans reflections.
In the farfield in a normal room, it will have reflections that add additional SPL to the direct wave, and at infrasonic frequencies that is likely to still be in-phase, as the wave doesn't even fit in the room anymore.
Especially true if the room is made of sealed concrete or bricks on all 6 sides.
Especially true for continuous sinewaves where it is all the same ultra-low frequency note.

For small spaces like cars, the time between the reflected sound and the direct sound and the distance will be small/short and thus less attenuated and thus even better summation and phase coherence, at relatively higher frequencies even...
And so they hit 184db on a TermLab, and we HT-people can't ever hit that score to matter how many resources we throw at the problem.

For anechoic chambers or outdoors, the reflections are minimal to none so the farfield acts similar to nearfield, as per nearly every data-bass measurement at 2m vs 10m or whatnot.

That's my understanding of it at least... I could be wrong.
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post #41 of 113 Old 01-20-2019, 07:41 AM
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Originally Posted by BassThatHz View Post
This project is a bit of a one-off... what works best for a HT and what works best for this project are two entirely different things.



Normally I would recommend a single 24 and a SpeakerPower amp for HT, or a nu1kdsp and PA-460 for chest-kick.

But even that won't be near-enough for this project...



Haven't box-modeled it BUT if you can afford 6 UM-18's, then you MIGHT actually be better off with 18 of these 18's instead (with bulk discount and sales codes): https://www.parts-express.com/dayton...4-ohm--295-475



They are 96db/w/m and have more excursion than PA-460's have, for not much more money.

The UM is only 88db/w/m and 3x the price, it does have more excursion and power handling though.



Trust the box modeling software, they usually aren't far off. Whatever it says is best, buy that...



Cone area vs excursion ratio is very important for ULF on the cheap. Likely more FAR important than available-watts or power-handling in this case... as I mentioned earlier.



You may actually want to rent a few Powersoft K20's for a day, those have PFC which is super important when limited by the breaker. PFC makes the amplifier draw a smooth waveform rather than drawing spikes of amperes when the 120V drops to 0V 120 times a second, and by renting you aren't committing to it for later personal ownership. You can usually rent pro amps at your local pro-sound shops (if you have any good shops that have the good amplifiers. i.e. Powersoft).



Otherwise just get the SpeakerPower amps, those are known-good for single digit Hz into 1-ohm loads. Especially their rack mountable amps.



What works well for this project vs personal ownership in HT is two entirely different things...

This is one of the freak cases where 18 of the Dayton Classic 18's might just outperform both the UM and PA Dayton's for the same $.



Make the box as big as you can lift or transport, and as many of those big boxes as you can afford to transport, and put as many 18's as will fit in a 14hz tuning in each one.

Rent the largest moving truck for a day and a pallet jack (or fork lift if available).



Bigger boxes are more efficient vs smaller boxes,

but really it is ALSO the ratio of cones per cuft... and your ability to lift/transport/place the things.



You don't want the port velocity to be too high or you will get nothing but port chuffing. That is the one downside of ported boxes vs sealed.



Ported is the goldilocks zone of box types, more efficient than sealed nearing the tuning frequency, and easier to make than horned...



Ported is about 8-12db louder than sealed, near say 14hz...

Horned is about 6db louder than ported. Which WOULD come in handy in this case.

Horned boxes tend to be about 25-50% bigger than ported boxes.



No free lunch.



No matter how many cones you end up buying or which ones, I'd still have computer fans blowing directly on the coils to cool them in this project. They are cheap and they work.



Sinewaves put a LOT of stress on both the coils and the amplifier.

Maximum stress, in fact...



The only thing worse is clipped-sinewaves or squarewaves
Since he is only looking to make sound from 15 hz to 30 hz this could easily be handled by the port alone, but not if tuned to 15 hz, unless I'm not looking at this wrong. In particular the come excursion would be less near tuning, and in a standard ported box I get you would want to bias the tuning toward the lower end of the range you are interested in, but with a bandpass, the closed box prevents large excursions of the driver, and it's more efficient than a standard ported box.

Now, one consideration would be you might end up with a very large box required for a bandpass sub (especially with an 18" driver) -- guess we'd need to see the driver first... And I suppose you could make the boxes in two pieces that bolted together, or latched together, which would make transport easier.

Up side
More efficient
Less driver excursion

Downside
Potential big box
Serviceability

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post #42 of 113 Old 01-20-2019, 11:22 AM
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So I modeled a number of different drivers when limited to $1800 and 2400w and 15cuft per cone to a max of 100cuft total,
and a tuning of 13hz.

Turns out the UM-18 faired well against most of them, regardless of the various other driver capabilities.

I tried B&C, 460's, Classic, XXX, UM, IB3.

The IB3 and XXX did best in IB or super large boxes.
In smaller boxes of 15cuft per cone, UM-18 won in most of the other categories or did no worse than any of the others.
So you should be safe to just buy as many UM-18's as you can afford, 6 or whatever...

That said: box models don't consider heat or cooling, so 16 PA-460's or 16 Classic-18's would likely have the longest run-time simply because there are 16 coils to spread out the heat vs 6 coils, or in the extreme case of a SI-24 or B&C 21 or XXX-18 only 1-3 coils because it is so expensive to have more than just a few of them!

They'd also have high efficiency from the 3db per doubling law, and the fact that they are already sensitive drivers from the start!

Now you just have to figure out what box you'd like to build, given your resources and skill level.

Would 16 24's beat it at ULF? especially with infinite watts on hand?
But of course!
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post #43 of 113 Old 01-20-2019, 05:45 PM
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Originally Posted by aron7awol View Post
6 ported boxes as big as you can reasonably make them.

This. In a space that size with one 20a circuit big ported tuned very low. You can have the ports outside the boxes too so with it behind fabric you could use large diameter pipe and run the ports silly long. You could use 6” sewer pipe and some bends to bring the outlet back nearer to the driver. For home use it would be hideous but maybe easy solution.

The 6000dsp will actually make 1200 wpc, you can’t trust the published specs, but that should work. If you really don’t care about fan noise get a clone and just run it where it doesn’t trip the breaker. The xbs 14000 would probably be fine just mind how the drivers are wired to get around 3-4 ohms per channel I guess. The clones have better response down low so that might work better. The speaker power would be great too and quiet but more money.

Another driver option would be two hs24 ported, probably more expensive than the six 18s though by maybe 6-800$.



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Considering they will be hidden from view, it might also be worth mounting the drivers backward so that you could easily cool them externally. Then if you convert them to HT use when you are done with this application, you can simply reverse them.

You're getting plenty of good information from everyone here. I also modeled a bunch of different options before I recommended the 6 UM18s, it just seemed like a great balance as far as number of boxes and output.

While I agree a bandpass is technically the most efficient solution for this application, I just thought that the 6 UM18s would easily deliver what you want out of them, while being simpler and more flexible for future use. Do you have any desire to use them for HT after?
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The band pass suggestion is good and the probably somewhat increased distortion could actually add to the experience. I think whatever gets max output within budget is what you should do. Bandpass will be less forgiving but with multiple drivers and limited power would be fine.


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post #46 of 113 Old 01-20-2019, 10:31 PM
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Quote:
Originally Posted by aron7awol View Post
Considering they will be hidden from view, it might also be worth mounting the drivers backward so that you could easily cool them externally. Then if you convert them to HT use when you are done with this application, you can simply reverse them.

You're getting plenty of good information from everyone here. I also modeled a bunch of different options before I recommended the 6 UM18s, it just seemed like a great balance as far as number of boxes and output.

While I agree a bandpass is technically the most efficient solution for this application, I just thought that the 6 UM18s would easily deliver what you want out of them, while being simpler and more flexible for future use. Do you have any desire to use them for HT after?
MDF is cheap. Could always build another box... It's not like the drivers themselves would go bad... but, if HT speakers would work -- you are right -- you'd get a two-for! The cheapest solution those is still the bandpass in this case because he's looking to create such a narrow response curve.
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post #47 of 113 Old 01-21-2019, 07:47 AM - Thread Starter
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Thank you to everyone for your help and advice.

Quote:
Originally Posted by kennyandersen View Post
there is no other way to get significant SPL in the limited range you need on less power. It is one of the cases IMHO where there is a very specific solution to the problem you are posing.
The images of bandpass boxes do not seem much bigger than the driver. Do you recommend a certain size / design calculator?

Quote:
Originally Posted by Purenv View Post
having a stack of dual opposed VBSS on each side of the room would definitely fill that size room. Plus using one amplifier would maximize your electrical efficiency as well, it is a proven designed system, and with 16 of them would be the same price as 4 Ultimax 18s.
To make these dual opposed do I just glue the backs of the boxes together and then I can stack them up? I would like to keep all of the boxes on one side of the room.

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Originally Posted by Zarkoff500 View Post
I think the VBSS is a great idea as well. With four our more and 15 hz tune you should get adequate output at 10 hz plus you can run 8 off an inuke/nx3000 and it would keep costs down.
Do you think 8 VBSS would be enough? I would like to make 4 dual opposed VBSS if it would work. @Purenv said to use 16 which would start to take up quite a bit of space and fabrication time.

Quote:
Originally Posted by BassThatHz View Post
This is one of the freak cases where 18 of the Dayton Classic 18's might just outperform both the UM and PA Dayton's for the same $.

Make the box as big as you can lift or transport, and as many of those big boxes as you can afford to transport, and put as many 18's as will fit in a 14hz tuning in each one.

You don't want the port velocity to be too high or you will get nothing but port chuffing. That is the one downside of ported boxes vs sealed.
Is the Full Marty a big enough box? I can fit 6 Full Marty's along the wall. Should there be multiple cones in each box or many individual boxes? I am concerned about box movement and vibration sounds so if a dual opposed setup would be good if possible. I will definitely have fans blowing on the coils.

Quote:
Originally Posted by BassThatHz View Post
Turns out the UM-18 faired well against most of them, regardless of the various other driver capabilities.

So you should be safe to just buy as many UM-18's as you can afford, 6 or whatever...
If the UM-18s faired ok then I would rather just have 6 drivers as it would be less complicated. I will use a CNC to cut out all the box pieces so I do not mind which kind of box, I just want to get the best outcome with the power and budget limitations I have.

Quote:
Originally Posted by Vince_B View Post
This. In a space that size with one 20a circuit big ported tuned very low. You can have the ports outside the boxes too so with it behind fabric you could use large diameter pipe and run the ports silly long. You could use 6” sewer pipe and some bends to bring the outlet back nearer to the driver. For home use it would be hideous but maybe easy solution.
Big ported is different than the Full Mary?

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Originally Posted by aron7awol View Post
While I agree a bandpass is technically the most efficient solution for this application, I just thought that the 6 UM18s would easily deliver what you want out of them, while being simpler and more flexible for future use. Do you have any desire to use them for HT after?
I would not have desire to use all 6 but could make a small dual sub box later.

I think I want to keep it to 6 18" drivers to save fabrication time. I am ok with bandpass, ported, VBSS, or Full Marty.





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post #48 of 113 Old 01-21-2019, 08:09 AM
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I don't think vibrations are as much of an issue as you think. If it ends up being a problem, put them on some furniture sliders to dampen the vibration. Between the PA460 and UM18, if you did 15 cubic feet and a 15hz tune for both, this is what you'd be looking at. The 6 UM18 config would be around 130db at 15hz and the 16 PA460 config would be around 135db. I think I'd probably go for the six UM18s. It's significantly fewer cabs to build and you get much smoother response between 18-40hz (comparing using the max SPL of both systems).
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I don't think vibrations are as much of an issue as you think.
...
I think I'd probably go for the six UM18s. It's significantly fewer cabs to build and you get much smoother response between 18-40hz (comparing using the max SPL of both systems).
Thanks. The Full Marty seems to have 11 cubic feet. Do I just increase the proportions until it has 15 cubic feet?

I am still a bit lost on the box designing. I tried to model a ported box online but got strange calculations.

If I knew what size to build a bandpass box, ported box, Marty or VBSS, I could build them but am not getting how to calculate them yet.



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post #50 of 113 Old 01-21-2019, 10:23 AM
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If you took the standard full marty design and kept the width and depth the same, then made it taller to get to 15 cubic feet internal you could keep the same port config (3 ports, each 7.5" wide and 3" tall) but just extend the port to 44.5" in length. That will give you a port velocity of 14m/s which is actually less than the regular marty design. Don't forget that you'll lose some internal volume because of the extra port length so factor that in. Band pass may be a better option, but I am not knowledgeable about them so hopefully someone else will chime in.
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post #51 of 113 Old 01-21-2019, 10:38 AM
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@BassThatHz I'm going to tag you since if anyone in this thread would know its probably you. But what if he went with a large horn setup with a bunch of 18's? Or would the horn not be able to be tuned low enough?
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post #52 of 113 Old 01-21-2019, 11:06 AM
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Again, not super knowledgeable about horns but the wavelength of 15hz is 73 feet so the horn would have to be 36.5 feet in length to get perfect summing at that frequency. I believe 1/4 wave is also viable in which case you'd "only" need a horn that is 18.25' in length.
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post #53 of 113 Old 01-21-2019, 11:18 AM
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Quote:
Originally Posted by CrusherW9 View Post
Again, not super knowledgeable about horns but the wavelength of 15hz is 73 feet so the horn would have to be 36.5 feet in length to get perfect summing at that frequency. I believe 1/4 wave is also viable in which case you'd "only" need a horn that is 18.25' in length.
Oh I know litterally NOTHING about building a horn or if it would even work in this situation. Being that it is behind a curtain I would assume size would not be an issue, but then again as you mentioned even a folded horn of 36.5 feet would lead to a MASSIVE box, and not exactly be easy to build lol.
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post #54 of 113 Old 01-21-2019, 12:05 PM - Thread Starter
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If you took the standard full marty design and kept the width and depth the same, then made it taller to get to 15 cubic feet internal you could keep the same port config (3 ports, each 7.5" wide and 3" tall) but just extend the port to 44.5" in length.
I could do that. I could make them up to 7.5' ' tall. I would not want to have the depth increase.

This thread discusses making a 15cu "Fuller Marty"

@CrusherW9 made a graph for it.
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That would put you at roughly 15cf. All lines are with a UM18 at 1000w. Green line is a normal full marty, orange line is with the bigger enclosure (no port tune change), blue line is the bigger enclosure tuned slightly lower to 15hz.


This thread says that if you change the Marty port height from 3" to 2.5" its tuning changes from 17hz to 15hz. So should the ports be 3" tall or 2.5" tall?

I like the idea of making bigger Martys since the construction is pretty straight forward. I am also ok with the bandpass. It would be more complicated to build but not overly.

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Being that it is behind a curtain I would assume size would not be an issue, but then again as you mentioned even a folded horn of 36.5 feet would lead to a MASSIVE box, and not exactly be easy to build lol.
I think I am going to rule out a horn due to complexity, There is a visual fabric structure in front of the subs but there is not infinite space for long pipes.

So now down to Taller Full Martys or Bandpass boxes of unknown size.
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post #55 of 113 Old 01-21-2019, 12:19 PM
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At 2.5", port velocity goes up to 17m/s due to the smaller cross sectional area but you'd only need a 37" port for the 15hz tune.
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post #56 of 113 Old 01-21-2019, 12:24 PM - Thread Starter
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At 2.5", port velocity goes up to 17m/s due to the smaller cross sectional area but you'd only need a 37" port for the 15hz tune.

Ah, ok. I believe earlier in the thread someone said I want to keep port velocity down to avoid port chuffing so maybe it would be best to keep it at 3" tall. The main intent is to have inaudible infrasonic sound. I don't want to have stray noises from the boxes when below 20hz.

I will work out a 15cu Taller Marty design and post it.
If I can figure out the bandpass design sizes I will model that up as well.

Thank you.
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post #57 of 113 Old 01-21-2019, 03:30 PM
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Big ported is different than the Full Mary?

Marty is a specific big ported design. Not sure if you’ve said your ultimate goal in low end cutoff but ported design drops off response very rapidly below the tuning frequency so if you really want low like 10hz you might want a modified Marty or similar that tunes lower. If you’re good with output down to 15 you’re all set with the Marty.



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post #58 of 113 Old 01-21-2019, 04:30 PM
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Looks like you are looking at six um18s now but for your initial post two um18s don't work out impedance wise with the sp1-2400. You'd need 2 ohm support which means you'd have to step up to the 4kw or 6kw models.

You had mentioned that you will basically be playing sine waves continuously - this is a worst case scenario for the driver and amp. Be careful you don't let out the magic smoke.

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post #59 of 113 Old 01-21-2019, 04:48 PM
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That said, if you get too close to the sub you will be in the nearfield zone where ULF is weakest....

in many cases you will find that walls, ceilings and floors amplify the bass louder (it can also cause them to null out.)
I don't believe this is accurate. ULF is strongest in the very near field. The further you get away from the cone, the more spl you lose. Rule of thumb being to place the body within the diameter of the driver I believe.

For example, Chinook scene in Lone Survivor. With the subs right behind the loveseat, I can feel the 7Hz. If I walk away to the other end of the basement, I dont feel it. Even though the 7 Hz doesn't "fit" in my basement, its not a case where the whole the room is filled with 7 Hz. It's still a point source and dropping off with distance.

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post #60 of 113 Old 01-21-2019, 05:12 PM
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How much space is BEHIND the wall? Can you cut into the wall at all?
I ask, because IIRC, the best way to get infrasonic sound is by using an Infinite Baffle (IB) manifold. You could have three manifolds with two drivers each (you may have to look for IB-specific drivers) and you -should- be able to reach your target SPL slope.
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