Dual Opposed Dayton UM-18's for infrasonic art installation - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 113 Old 01-21-2019, 06:35 PM
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Quote:
Originally Posted by CrusherW9 View Post
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).
You are using the Max SPL chart, that artificially inflates the mid-bass. Amplifiers do not behave like the max-spl chart does, amplifiers put out fixed voltage in terms of sinewaves and sweeps. They will both be equally smooth, as the normal SPL chart shows...

Here is 6 UM-18's each in a 30cuft box tuned to 14hz. (Optimal size for that tuning)
Here is 16 PA-460's each in a 40cuft box tuned to 14hz. (Optimal size for that tuning)
2400w given to each

126db vs 132db
Load on the UM's 40% (400w x 6)
Load on the PA's 30% (150w x 16)

Reduce the PA's to the same SPL as the UM-18 array:

Now it only needs 600w to hit that SPL. That's well under 20A rms, that's Dayton plate-amp territory.
Load is 7.5% (37.5w x 16) LOL!

Even if you only used 8 PA-460's, that would 32.5% load at 162.5w x 8 or 1300w, that's well under 20A rms and still less than 40% stress (and the PA's are WAY WAY cheaper... cheap enough to have a few spares on hand for just-in-case.)

16 PA's can do 126db all day long (and the breaker won't trip), the 6 UM's will smoke within minutes (and/or the breaker might trip constantly until it dies too, and the amplifier will also NOT be happy with sinewaves at 100% load).

I'd stick with 16 PA-460's @ 600w to keep the excursion and heat and power reasonable. My 2 cents.

As far as making them dual opposed, you definitely want to do that to reduce vibs, just screw the boxes together with small pieces of scrap wood.

Horned although better, is too big and too complicated.
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post #62 of 113 Old 01-21-2019, 06:56 PM - Thread Starter
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Quote:
Originally Posted by Vince_B View Post
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.
Thank you for the clarification. I am ok with the 15hz standard Marty but would like to tune it lower if possible without making the port velocity to high that I get weird wind noises. Is the best way to build one first and see?

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Originally Posted by Pradeep2 View Post
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.
Yes, I do not want to burn out the drivers since this will be a 3 month installation. The plan is to have sound play for a bit above 20hz in the 30 - 40 range, then it will drop down to the lower hz I can get. It will hold for a bit and then go completely silent. After a minute or so of rest it will begin another cycle.

I won't play the sine wave continuously but it will be always going through the cycle.

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Originally Posted by sigpig View Post
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.
If this project works well then the next sound project will definitely make the whole room the sub. I have to have one sound win first. Thanks for the idea.
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post #63 of 113 Old 01-21-2019, 07:03 PM
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Originally Posted by subbuilds View Post
3 month installation
3 months at 8 hours a day continuously I would imagine?

Hopefully the cops don't show up.
We've been getting reports of people within a 1/4mile feeling ill and vomiting, time to shut it down. Puts hand on gun... (hehe! )
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post #64 of 113 Old 01-21-2019, 07:06 PM - Thread Starter
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Originally Posted by BassThatHz View Post
Even if you only used 8 PA-460's, that would 32.5% load at 162.5w x 8 or 1300w, that's well under 20A rms and still less than 40% stress (and the PA's are WAY WAY cheaper... cheap enough to have a few spares on hand for just-in-case.)

16 PA's can do 126db all day long (and the breaker won't trip), the 6 UM's will smoke within minutes (and/or the breaker might trip constantly until it dies too, and the amplifier will also NOT be happy with sinewaves at 100% load).

I'd stick with 16 PA-460's @ 600w to keep the excursion and heat and power reasonable. My 2 cents.

As far as making them dual opposed, you definitely want to do that to reduce vibs, just screw the boxes together with small pieces of scrap wood.
I assume your are talking about the VBSS boxes with 16 drivers like I posted above. These boxes are a lot smaller than the Martys and would be easier to handle. The exhibition will be up for 3 months so smoking in 5 minutes is not an option. Would you recommend using a Dayton plate amp or rack amp to power all the subs?

8 PA-460's is attractive vs 16 but if I will really notice the difference with 16 then I could go with that. Even if 10 is better that is fine. 16 is a lot of boxes to make.

Do I make the standard size VBSS? Or do I change the port tube size to tune it to 10 - 15 hz?

Thank you.
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post #65 of 113 Old 01-21-2019, 07:09 PM - Thread Starter
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Originally Posted by BassThatHz View Post
3 months at 8 hours a day continuously I would imagine?
It will have a cycle, so the big DB and low hz will only happen sometimes. There will be a sequence of led illumination and then the infrasonic cycle. Breaks will happen in between.

Should I just use 8 subs? Are 16 too much? It is a 130000 cu ft room with openings to other rooms of similar size, (museum)

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post #66 of 113 Old 01-21-2019, 08:11 PM
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Originally Posted by subbuilds View Post
It is a 130000 cu ft room
That's boeing hanger size. I'd definitely go with 16 given the room size.
I was doing 40cuft boxes, PER cone (think 3.5ftx3.5ftx3.5ft or 17"x48"x96" using full sheets.)
You can do smaller boxes but the performance will suffer greatly.

1200w into 16 PA-460's in 20cuft boxes tuned to 14hz (75w x 16).


Sixteen 33"x33"x33" boxes, each outputting this much at 75watts:


The dimensions don't matter, only the total volume of the box and total volume of the port matter (that said: port area matters for chuffing avoidance.)

20cuft is basically the size of a large dual-door fridge, so 16 large-fridge sized boxes.
It's a lot of space and wood.

You could of course start with just a few and scale it up until happy or until you run out of space or money.
Low bass is expensive and big, we warned you...

That's just the physics of it.

There is no way to get loud ULF without astronomical driver costs in smaller boxes, or astronomical large amounts of wood and cheaper drivers. It gets even worse when you try to sustain that SPL for all day for months on end without smoke...

Also keep in mind that 1 bad driver or amp in a series-wired system will mute the whole system until replaced.

So in that case, multiple amps might be the way to go.

Like 4 of these, with 2 460's on each channel in parallel, dual 4-ohm, that way if 1 amp blows, you still have 3 others making bass, or if 1 channel blows you still have 7 more channels making bass, or if one driver cooks you still have 15 making bass.
https://www.parts-express.com/behrin...fier--248-7010

Using 8 plate-amps is too expensive or not enough power by the looks of things. You need a solid 300w @ 4-ohm x 8 (~150w per pair as per above with 3db of headroom to keep the amps from overheating).
At 300w x2 the nx1k meets that requirement without getting too expensive.
The NX's do have fans in them, about as loud as a projector. So 4 projectors worth of fan noise.

16 460's is a single 2-ohm load, dual series-parallel, or a dual 4-ohm load. SpeakerPower doing 1200w @ 2ohm... if it dies the SPL goes from 126db to 0db. As all your eggs are in one basket.
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post #67 of 113 Old 01-21-2019, 08:19 PM
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Quote:
Originally Posted by subbuilds View Post
8 PA-460's is attractive vs 16 but if I will really notice the difference with 16 then I could go with that. Even if 10 is better that is fine. 16 is a lot of boxes to make.
Going from 8 to 16 in this case will only gain you 3db. You gain 3db by doubling the amp power, so going from 100w to 200w for instance. You can also gain 3db by keeping the amp power constant and doubling the drivers (so 2 to 4, etc). So going from 8 to 10 will be a small difference.
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post #68 of 113 Old 01-21-2019, 08:37 PM
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Want to add 6dB (the equivalent of doubling the subs and power)? Cut the distance in half. That's some serious low hanging fruit here.

Can you build the boxes there? That's going to be the easiest way to build HUGE boxes. Cut them up when the 3 months are up.

With such a huge space forget about room gain. Luckily, I posted earlier in the thread that with 6 ported boxes you should hit 120dB @ 15Hz @ 3m away with no room gain. If you're wondering if you can hear 15Hz @ 120dB, ask my wife
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post #69 of 113 Old 01-21-2019, 08:41 PM
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Quote:
Originally Posted by CrusherW9 View Post
Going from 8 to 16 in this case will only gain you 3db. You gain 3db by doubling the amp power, so going from 100w to 200w for instance. You can also gain 3db by keeping the amp power constant and doubling the drivers (so 2 to 4, etc). So going from 8 to 10 will be a small difference.
It's actually MUCH worse than that, not only are you doubling the power but you are cutting the coil-area in half and increasing the excursion by 40% by cutting the cone-area in half. That increases the distortion considerably, in this case 3db is a big deal.

Trying to gain back the 3db with doubling the power makes the excursion increase to 80% and the heat per coil to shoot up like 4x. Again that 3db is a big deal.

Just going from 16 down to 8 and cutting the power in half, reduces the SPL/headroom by 6db. That's not desirable either.

The PA-460's don't have tonnes of excursion, you need to keep it as low as possible.

Imagine how hot a 100w bulb gets, you need to keep the power and heat and excursion as low as possible, otherwise it will smoke or sound distorted.

Excursion and Power are your enemy, not your friend. They both cause problems.

To keep the breaker from popping you need to keep it at 1200w or half power for a SpeakerPower 2400, also to keep the amp cool.

Drop the box size from 40cuft to 20cuft and 2400w to 1200w renders the chart I just posted prior.
A 3db loss for the power and a few more db loss for the smaller box.
75w per PA-460 is a 15% load, manageable but the 40cuft and 600w figure is more-ideal.

Low bass is challenging in every regard when your budget and power is restricted,
even more taxing when requiring loud bass-all-day in a hanger-sized room without smoke.
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post #70 of 113 Old 01-21-2019, 09:23 PM
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Originally Posted by aron7awol View Post
Luckily, I posted earlier in the thread that with 6 ported boxes you should hit 120dB @ 15Hz @ 3m away with no room gain. If you're wondering if you can hear 15Hz @ 120dB, ask my wife
Yes 119.7db @ 3m with 6000watts rms though... (1000w per cone, lots of heat! Won't last long! )
But the OP only has 2400w, so 115.8db @ 3m (400w per cone), and that's STILL stressing his amp and breaker to clipped/tripping levels.

16 PA-460's each in a 20cuft 14hz tuned box does 116.7db @ 3m @ 1200w (75w per cone).
16 PA-460's each in a 40cuft 14hz tuned box does 117.5db @ 3m @ 600w (37.5w per cone, no heat all-day ).

The PA-460 doesn't like small boxes, that's the only downside of using that woofer.
16 $200 B&C-18's would be better than the PA-460 in smaller boxes, but more $$$, still cheaper than 16 UM-18's (in even smaller boxes)...

You can use less wood and use expensive drivers, or use huge amounts of wood and use dirt cheap drivers.
No free lunch.

Heat is still a BIG problem with lower cone quantities and/or less efficient drivers.
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post #71 of 113 Old 01-21-2019, 09:43 PM
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Originally Posted by subbuilds View Post
It will have a cycle, so the big DB and low hz will only happen sometimes. There will be a sequence of led illumination and then the infrasonic cycle. Breaks will happen in between.



Should I just use 8 subs? Are 16 too much? It is a 130000 cu ft room with openings to other rooms of similar size, (museum)
Is it 13,000 cuft or 130,000 cuft? Based on the room images you showed earlier I'm thinking 13,000 cuft?

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post #72 of 113 Old 01-21-2019, 09:58 PM
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6 UM-18's each in 33.33cuft 14hz tuned, does 114.8db @ 15hz @ 3m @ 1200w (200w per cone, 20% load).

That's still more heat per cone, less db's, and more money on drivers, but MUCH less money spent on wood and less floor space and transportation costs, easier to build too.

Would it handle 200w of ULF all-day? Your guess is as good as mine. I'm thinking it would, but who knows 100% for-sure until it is attempted.
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post #73 of 113 Old 01-22-2019, 04:41 AM
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I don't have time, but just for kicks, how big would a bandpass box be, and how much increase in efficiency could the OP expect? 40 cu ft boxes are enormous! I can't help but think you could play around with a bandpass box and get there for less wood and less power...

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post #74 of 113 Old 01-22-2019, 05:44 AM - Thread Starter
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Quote:
Originally Posted by BassThatHz View Post
That's boeing hanger size.

Quote:
Originally Posted by Pradeep2 View Post
Is it 13,000 cuft or 130,000 cuft? Based on the room images you showed earlier I'm thinking 13,000 cuft?


Sorry, typo. It is 13,000 cu . 26' x 37' with 14' ceilings.
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post #75 of 113 Old 01-22-2019, 06:12 AM
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Quote:
Originally Posted by subbuilds View Post
Sorry, typo. It is 13,000 cu . 26' x 37' with 14' ceilings.


Like I and @BassThatHz said, pro-audio speakers are designed to take a lot of stress. The PA460 I believe is the better way to go. But yes that is a lot of wood to make a lot of enclosures. @BassThatHz , if I understand you correctly, 16x 20cuft enclosures tuned to 14Hz would still get the OP to around 116dB. That should be a viable solution for a 13000cuft room, correct?


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post #76 of 113 Old 01-22-2019, 07:09 AM - Thread Starter
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Quote:
Originally Posted by BassThatHz View Post
6 UM-18's each in 33.33cuft 14hz tuned, does 114.8db @ 15hz @ 3m @ 1200w (200w per cone, 20% load).

That's still more heat per cone, less db's, and more money on drivers, but MUCH less money spent on wood and less floor space and transportation costs, easier to build too.

Would it handle 200w of ULF all-day? Your guess is as good as mine. I'm thinking it would, but who knows 100% for-sure until it is attempted.
With reasonable use of plywood I could not get a 33cuft box. I could get a 28cuft box from ~6 sheets of plywood. After taking out the port, driver, and braces it comes in at 28cuft. I posted and image.

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Originally Posted by Purenv View Post
Like I and @BassThatHz said, pro-audio speakers are designed to take a lot of stress. The PA460 I believe is the better way to go. But yes that is a lot of wood to make a lot of enclosures. @BassThatHz , if I understand you correctly, 16x 20cuft enclosures tuned to 14Hz would still get the OP to around 116dB. That should be a viable solution for a 13000cuft room, correct?
Since I am now talking about 36 sheets of plywood, I am going to have to limit the number of boxes to 6. Also, that is about how many will fit in the room as well as budget.

Remaining decisions:
  • PA460 vs UM-18?
  • How to tune 2'x2'x8' box to 14/15hz?
  • Multiple amps as @BassThatHz suggested or 1?

(Regular size Full Marty included for scale reference)





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post #77 of 113 Old 01-22-2019, 08:02 AM
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Originally Posted by BassThatHz View Post
Yes 119.7db @ 3m with 6000watts rms though... (1000w per cone, lots of heat! Won't last long! )
But the OP only has 2400w, so 115.8db @ 3m (400w per cone), and that's STILL stressing his amp and breaker to clipped/tripping levels.
No, my estimate was based on 2400W, not 6000W:

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Quick and dirty model of 6 ported UM18s in 20cf each tuned @ 15Hz getting 400W of power each produces 120-125dB @ 15Hz @ 3m away assuming wall/corner boundary reinforcement and no room gain.
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post #78 of 113 Old 01-22-2019, 08:12 AM
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I think BTH's numbers are more accurate than mine. I don't quite remember, but I don't think I factored in the 2400w total power available in my UM18 vs PA460 graph/details I posted earlier. Sorry about that.
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post #79 of 113 Old 01-22-2019, 08:21 AM
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Did another quick comparison...

6 x UM18 in 28cf tuned @ 15Hz @ 400W each (total 168cf and 2400W)

16 x PA460 in 10.5cf tuned @ 15Hz @ 150W each (total 168cf and 2400W)

The second option is ~4dB louder @ 15Hz.
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post #80 of 113 Old 01-22-2019, 08:23 AM
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Well when this art project is finished I want to see a link to a high quality recording of what this was like to experience first hand!! Have you done anything like this before or have any other projects that you are using for inspiration that are on YouTube or anything?
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post #81 of 113 Old 01-22-2019, 08:51 AM - Thread Starter
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Quote:
Originally Posted by aron7awol View Post
Did another quick comparison...

6 x UM18 in 28cf tuned @ 15Hz @ 400W each (total 168cf and 2400W)

16 x PA460 in 10.5cf tuned @ 15Hz @ 150W each (total 168cf and 2400W)

The second option is ~4dB louder @ 15Hz.
This might be due to my misunderstanding of amplifiers but I would not have 2400w continuous available on a single 20amp circuit. At a safe 80% load it is 1920w. Of course it can have brief bursts up to 2400w.

Is driving the UM18's @ 400W going to be too hard on them?

Above @BassThatHz mentioned that there was some concern even at 200w with ULF. They will not be running continuously for 8hrs a day but would do 1-2 minute bursts of ULF throughout the day.

If I used 6 PA460 instead of 6 UM18's to save $600 I assume the performance would drop significantly. If the difference is not much saving is good.

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Well when this art project is finished I want to see a link to a high quality recording of what this was like to experience first hand!!
Of course, opens this summer and will post video. Inspiration is from thinking about sound and how to explore and extreme version of it to give new sensations for visitors to the gallery other than just a visual experience. Hopefully this makes it a "felt" experience as well.
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I redesigned the box to turn the speaker to the side so the boxes can be placed back to back in a dual opposed position. The port is kept facing out into the room so the sound is felt out there the most.

I don't know how tall to make the port inside the box. How is this calculated?

Do you think I need more bracing than I have?

Can I put the cabinets close to each other in the space? Currently they are shown with 1.5' spacing.






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post #83 of 113 Old 01-22-2019, 10:01 AM
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Quote:
Originally Posted by subbuilds View Post
If I used 6 PA460 instead of 6 UM18's to save $600 I assume the performance would drop significantly. If the difference is not much saving is good.
There would be a large drop off. Going for the cheaper PA460s must be made up for in quantity.
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Mains: Fusion-15 LR, Custom Tapered Ported Volt-6 Center, Ported Volt-10 Surrounds, Custom 45°/45° Double-Angled Ported Volt-6 Atmos
Subs: The Two Towers (HT18 32cf 11.5Hz x 2), UM18 4cf x 2, Crowson MAs x 4
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post #84 of 113 Old 01-22-2019, 11:06 AM - Thread Starter
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Quote:
Originally Posted by aron7awol View Post
There would be a large drop off. Going for the cheaper PA460s must be made up for in quantity.
Thanks, that makes an easy decision. I will go with the UM18's.
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post #85 of 113 Old 01-22-2019, 01:28 PM
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Before you go high wild on you boxes, a sheet of MDF weighs near 80 lbs... I have to have to people to move my Johnny-sized subs, even without the driver. Remember this only has to make 15-30hz notes. Seems like you could come up with a solution that would use a smaller box, else these are going to be a real pain to move! 1/2 ton truck could carry just 2 if then at a time...

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post #86 of 113 Old 01-22-2019, 02:48 PM
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Just as an experiment, I modeled using WinISD:

UM18 ported in 26cf tuned @ 15Hz

UM18 4th order bandpass with a 4cf sealed chamber and 22cf ported chamber tuned to 16Hz (this gave me slightly more output @ 15Hz than 15Hz tune)

I fed both the same power (400W) and the ported box beat it by ~1dB.

Granted, this is the first 4th-order bandpass I've ever modeled, but I have plenty of experience with WinISD so I'm confidently I did it correctly, and I experimented with different sizes of the chambers and tunes.

Does WinISD model a 4th-order bandpass accurately?
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Mains: Fusion-15 LR, Custom Tapered Ported Volt-6 Center, Ported Volt-10 Surrounds, Custom 45°/45° Double-Angled Ported Volt-6 Atmos
Subs: The Two Towers (HT18 32cf 11.5Hz x 2), UM18 4cf x 2, Crowson MAs x 4
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post #87 of 113 Old 01-22-2019, 03:10 PM - Thread Starter
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Quote:
Originally Posted by kennyandersen View Post
Before you go high wild on you boxes, a sheet of MDF weighs near 80 lbs... Seems like you could come up with a solution that would use a smaller box
I do plan to make the boxes out of plywood rather than MDF so that will save some weight but I am definitely trying to figure out how to make the boxes smaller with my power limitations.

I finally got WinISD up and running. I put in the info for the UM18's and believe I modeled the vented boxes correctly to represent a Full Marty which is 11cuft and the bigger 28cuft boxes I designed. To simulate the Marty's vents, I put in 3 square vents 3" tall and 7.5" wide. I made bigger vents for the 28cuft box so the air speed would be lower.

I put the signal power at 200w for each. The Marty is in red and the 28cu is in green.

It says the Marty does 105.782 db @ 15hz and the 28cuft box does 111.544 db @ 15hz. Am I modeling that correctly? EDIT Just realized I did not change the listening distance to 3m. The 3m distance graph is below.EDIT

105 db @ 200w seems pretty good or would I not feel that in the big room?

How do you add multiple boxes together in WinISD?

At least I answered the question on how long to make the vents, WinISD tells you.

Thank you for everyone's help so far. I am learning a lot and would not be able to do it without you.



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Quote:
Originally Posted by aron7awol View Post
Just as an experiment, I modeled using WinISD:
Thank you.

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post #88 of 113 Old 01-22-2019, 03:41 PM
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Quote:
Originally Posted by subbuilds View Post
105 db @ 200w seems pretty good or would I not feel that in the big room?

How do you add multiple boxes together in WinISD?
You might be happy with 105dB but given this whole thing is theoretical at this point including what your in-room performance will be and not knowing what you'll actually want for SPL it's best to optimize it as much as you can to give yourself room for error. More headroom will only be a good thing, as it will minimize power, heat, distortion, etc.

You can just add dB for multiple identical subs with identical power...

For 2 add 6dB
For 4 add 12dB
For 6 add 15.6dB
For 8 add 18.1dB
For 16 add 24.1dB
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Video: Sony 85" X900F @ 80" eyes-to-screen (49.4° viewing angle)
Audio: Denon AVR-X4400H 7.2.4 Atmos
Mains: Fusion-15 LR, Custom Tapered Ported Volt-6 Center, Ported Volt-10 Surrounds, Custom 45°/45° Double-Angled Ported Volt-6 Atmos
Subs: The Two Towers (HT18 32cf 11.5Hz x 2), UM18 4cf x 2, Crowson MAs x 4
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post #89 of 113 Old 01-22-2019, 03:51 PM - Thread Starter
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Quote:
Originally Posted by aron7awol View Post
You can just add dB for multiple identical subs with identical power...
Thank you, so simple.

I think I am going to get 1 driver and build a test box. I really don't have any big subwoofer experience so I think I need to hear a box to even begin to decide where the db need to be. I know it is cheaper to buy all 6 but can get the remaining 5 in 1 shot.

Now I need to pick an amp or multiple amps.
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post #90 of 113 Old 01-23-2019, 10:34 AM
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I hope you don't have a lobby selling snacks and drinks. Glasses will fall to the ground!
Did you ever take into consideration that probably the entire building is going to hear the 15-20hz sine waves from that room?
You'll also have to glue up like everything in that room, anything loose will rattle away.
Oh and I'd suggest filling the space above the first brace with polyfill and lining the chamber around the driver with acoustics foam (don't put any near the port).
This will smoothen the frequency response and lowers THD.
Also, I don't know if you mentioned it anywhere but I'd suggest getting a UMIK, an equalizer (which works down to 10Hz, i.e. miniDsp) and REW that room.
Rooms do all kind of wierd things. Just keep that in mind when you installed your subs and the frequency response isn't to your liking.
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