Need help designing serious bass solution for a big theater..horns vs ported or both? - Page 12 - AVS Forum | Home Theater Discussions And Reviews

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post #331 of 505 Old 08-01-2014, 09:00 PM
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good to know. I went back and measured the model so in the case of the f20, plan/drawing => hornresp => measurement all very well.


I've monkeyed around with the various t/s specs to try to recreate the effect observed and I can't.


I've monkeyed around with the various par/exp/con settings and they are confirmed not to be the problem.


The actual build was done quite well. I followed along pretty closely and have pretty high confidence that it was built according to the plan.


Another other thing that I can think of is how I measured around the bends/turns. I simply measure using straight lines through the center of the horn. Maybe that overshoots the actual result by a bit and more in the case where there are larger bends toward the mouth. I don't think that would result in a 50% difference though, maybe 10%.


Last, as has been discussed, may be that below a certain tuning point, the size of the horn (specifically the mouth) must increase at a certain rate or something comes undone. This can be seen in the acoustic impedance increasing as tuning is lowered, but then dropping rapidly almost as though it goes off some sort of cliff. I thought it looked fine on the Submaximus, but now I see that a small increase results in significant drop.


BTW, the danley dts-10, at least as I modeled it in hornresp some time ago, appeared to have a corner target around 15hz, but the actual build came in lower, something like 11hz, and it is another longer narrow low tuned horn. honestly, I had forgotten about that when drawing up maximus.


maybe it matters where the bends occur too. perhaps bends closer to the throat don't have as much of an effect as bends closer to the mouth.


fwiw.

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post #332 of 505 Old 08-01-2014, 09:11 PM
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Quote:
Originally Posted by diy speaker guy View Post
Here's what Lilmike said about that.

"Original F-20 was powered by a BASH 300, with a modded highpass (flat to 20). I have measured it to confirm this."


If the original measured flat to 20 hz it was flat well below the low knee so it wasn't an issue. BUT the measurement I showed here was not the one done with the plate amp anyway, it was measured by Lilmike, F20 with the Ultimax driver driven by a Inuke 3000. I picked the sim and measurement (Ultimax) specifically because I had a feeling you would bring up the plate amp again even though Lilmike said it wasn't an issue. (Edit - that's not a poke at you, I just wanted to make sure this perceived issue was not going to be an issue here. /edit)

Here's the post the Ultimax horn w/ Inuke came from.

Lilmike's Cinema F-20

Both the original measurement (with original driver and plate amp) and the Ultimax version driven with the Inuke are simmed and measurements shown in my horn folding thread. By comparing the two it's clear the plate amp wasn't an issue.

Anyway, I think the discrepancy in ALL these horns is due to a bunch of factors, folding and bends included, but I don't think 180 degree bends SPECIFICALLY can be blamed for the effects seen in Submaximus or any other horn.
The primary reason for the discrepancy in most of the box horns is failure to account for the pressure loss or impeadance of the fold's, fluid mechanics says the 90 degree fold needs to have 1.41 times larger cross section than the pipe to eliminate pressure loss, twice that for a 180 fold. Secondary but still important is the loss from box its self. Nearly impossible to build a perfectly rigid one, which the model assumes.

Speaking of boxes I would encourage you to at this point start thinking out of the box and first study the acoustic properties of the room you are planning to build, It would be very cost effective to design/build the optimized spaced rather than multiple subs/watts/boxes. Simple adjustments to your layout can save you $$$ in the # of speakers and watts and boxes you build.
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post #333 of 505 Old 08-01-2014, 10:39 PM
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Originally Posted by LTD02 View Post
good to know. I went back and measured the model so in the case of the f20, plan/drawing => hornresp => measurement all very well.


I've monkeyed around with the various t/s specs to try to recreate the effect observed and I can't.


I've monkeyed around with the various par/exp/con settings and they are confirmed not to be the problem.


The actual build was done quite well. I followed along pretty closely and have pretty high confidence that it was built according to the plan.


Another other thing that I can think of is how I measured around the bends/turns. I simply measure using straight lines through the center of the horn. Maybe that overshoots the actual result by a bit and more in the case where there are larger bends toward the mouth. I don't think that would result in a 50% difference though, maybe 10%.


Last, as has been discussed, may be that below a certain tuning point, the size of the horn (specifically the mouth) must increase at a certain rate or something comes undone. This can be seen in the acoustic impedance increasing as tuning is lowered, but then dropping rapidly almost as though it goes off some sort of cliff. I thought it looked fine on the Submaximus, but now I see that a small increase results in significant drop.


BTW, the danley dts-10, at least as I modeled it in hornresp some time ago, appeared to have a corner target around 15hz, but the actual build came in lower, something like 11hz, and it is another longer narrow low tuned horn. honestly, I had forgotten about that when drawing up maximus.


maybe it matters where the bends occur too. perhaps bends closer to the throat don't have as much of an effect as bends closer to the mouth.


fwiw.
I peeked in on the thread periodically but wasn't following closely. I did notice that Max pointed out that the sim was a lot closer to the measurement when the segments were switched to PAR. And there are other questions too. Was the volume occupied by bracing included in the sim? Were the t/s parameters measured? Was the build completely accurate to fractions of an inch? Was the throat aspect ratio high? You don't need to answer any of these questions but they show that there are some things not accounted for. Then there's losses in the enclosure, folding method (centerline vs advanced centerline vs others), internal reflections, even ambient temperature and barometric pressure have an effect on measurements. These things all add up and result in a measurement that doesn't exactly match the sim.

As far as I'm concerned we can do the best we can and try to minimize errors and things that we know will have an effect on measurements. But there will still be discrepancies. We can have ideas about where the discrepancies were introduced but if it can't be proved it's just a theory. And until we get a folding program based on fluid dynamics a lot of things will remain unproven. Since some horns measure higher than sim'ed and some measure lower I don't think there is a workable theory to explain what's going on but since these examples come in within a couple hz of the sim I'm not too worried about it.

In the case of the DTS-10 (and the TH-SPUD), there is stuffing in the throat and mouth area. This rounds off all the peaks, including the lowest frequency peak. Rounding off that peak at tuning will lower the q of the resonance and make the low corner look a bit lower in frequency than if it was unstuffed and undamped. I've never seen a dimensioned diagram of the DTS-10 so I've never simulated it, not sure if the stuffing is enough to cause the discrepancy you saw or not, but that gets you in the right ballpark at least.
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post #334 of 505 Old 08-01-2014, 10:48 PM
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Originally Posted by Cortga View Post
The primary reason for the discrepancy in most of the box horns is failure to account for the pressure loss or impeadance of the fold's, fluid mechanics says the 90 degree fold needs to have 1.41 times larger cross section than the pipe to eliminate pressure loss, twice that for a 180 fold.
Fluid dynamics is one way to look at the issue but I'm not sure how you could use it to do a fold. I'm also not sure the 180 degree bend part is right, a 180 is just two 90 degree bends. But then again I'm not a fluid dynamics engineer.

Soho54 spent a lot of time on engineering and reverse engineering folds, he pointed out some common errors that people make and he also presented the advanced centerline method, which is (IMO) the current state of the art in folding for the layperson. He was also working on his model for a "different (more advanced) way to model a horn. What you do is model the straight sections as waveguides/ducts only, and the bends are modeled as base forces of mass/resistance/compliance, and not waveguide/duct elements." This isn't a new concept but it's very advanced, you won't see anyone around here talking about it.

Here's a link to my advanced centerline folding thread. It's got a bunch of info, a lot of it came from Soho54's contributions.
Horn Folding - a brief study of the centerline vs advanced centerline method
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post #335 of 505 Old 08-01-2014, 10:54 PM
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here is the par vs exp hornresp model. doesn't seem like that is it.


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post #336 of 505 Old 08-01-2014, 11:27 PM
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here is the par vs exp hornresp model. doesn't seem like that is it.
It clearly doesn't explain everything but it does look closer to the measurement. A bit less damped and the low corner is maybe very slightly lower.

I fully admit I don't have the answers and I don't have time to fully reverse engineer the horn from the plans to verify the accuracy of the fold to make sure the sim matches the plans. I just don't think the answer is as easy as 180 degree bends, especially considering the F20 example. I appreciate your ideas about why the F20 doesn't comply with your theory, and your efforts into trying to figure it out but I don't think the theory is correct and I don't even know how it could even be proved or disproved. And I'm really not sure why you are not happy with the way your design turned out, it's only a couple hz off at the low corner (and a bit lower in spl at the low corner because of that) but it seems like a good horn and a perfectly acceptable result. The peaks are ~evenly spaced and not too high in amplitude, there's no problem nulls, there's a reasonable amount of gain compared to a ported box and you got a nice wide bandwidth. Overall it seems like a win to me.
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post #337 of 505 Old 08-02-2014, 04:04 AM
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So you are still advocating going with a low tuned ported sub system ?
I advocate experiencing <10Hz capability before deciding that it is not worth pursuing, whether that be with transducers or sealed/IB subs. If you are planning to visit notnyt, PM bossobass and see if he could demo his setup for you. Bosso has extension down to ~3Hz. Notnyt uses crowson transducers to fill in under 15Hz. Depending on room resonances, one setup could be more efficacious than the other in transmitting the energy in the soundtrack to you.

JSS
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post #338 of 505 Old 08-02-2014, 06:32 AM - Thread Starter
 
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I'm pretty sold on not needing single digits, and realistically I'm not seeing how I get it without sacrificing SPL. I'd add transducers too. But usable output at 10hz is as low as I need.
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post #339 of 505 Old 08-02-2014, 08:50 AM
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You might want to think about the room gain profile as in my experience when a system has a flat response outdoors and if the room has a lot of gain then the bump in the response below 30Hz will be EQed down unless you prefer that bump. Also to me it still doesn't sound right with EQ compared to a system that compliments the room gain profile better. I also believe that a systems native response plays a part in the sound of a system, particularly as you approach its limits where systems tend to revert to their natural response.

A FLH approach with enough displacement will mean that your system functions as a sealed system below the knee and you can EQ it flat if desired as long as you are careful about the excursion limits just like a sealed system, you loose the output on the top end but this also often the same as with a sealed system when EQ is used to flatten the response. With FLHs you just loose more output up top if EQed flat but you can switch back to high output mode if you are in the mood for insanity and use the flattish response (if so desired) for normal listening/viewing where the system is within limits at lower levels. The falling response of an undersized FLH can in some cases compliment room gain quite well similar to a sealed system. This was kind of my thinking when I suggested multiple Alpines over the UXL so that you gain displacement which will help in your goals of "usable output" at 10Hz. In a way you can think of FLHs as a sealed sub with a lot more to give above the knee.

I know you mentioned that you don't prefer a flavor but I think that everyone does, some investigation with your current existing subs and a DSP/measurement system will give you great insights to your preferences, IMO. Tailoring your sub system to this is of great importance for achieving a system that is subjectively good. If however you are looking for a system that tries to be as "accurate" as possible from an objective view then the numbers hold great value and should be pursued. Others have already mentioned the importance of the room,treatments,measurements and of course integration, none of this should be overlooked obviously as it all functions together.
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post #340 of 505 Old 08-02-2014, 09:02 AM - Thread Starter
 
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I think I'd like to design the subs in theory to be as flat as possible or have the best extension characteristics and if room gain ends up boosting additionally I'd be happy with that. It's a lot easier to apply a little cut than it is to try to boost something that's not there.

I also think my room gain will be a lot less than most basement theaters. I am on the second floor, in a big space. Too big to get that boost people get in the meat of the bass band. My gain might be a little under 20hz, but it won't be anything to write home about considering the dimensions and 8000 cubic feet of space being filled.

I also know that I generally prefer a house curve. Flat is cool, I'll have a setting for perfection but I suspect I'll actually use the house curve more often. Boosting the lower regions is fun and exciting.

I guess you can do it a couple ways. One is a house curve EQ setting or whatever in the DSP. Another is keep the flat profile or the calibrated settings and just boost the sub out gain to run a little HOT. Either gets you about the same result. I do expect that I'll be able to with the flick of a switch go from perfectly flat calibrated setting to a house curve. I think the house curve is fun sometimes.
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post #341 of 505 Old 08-02-2014, 11:32 AM
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Originally Posted by maxmercy View Post
I advocate experiencing <10Hz capability before deciding that it is not worth pursuing, whether that be with transducers or sealed/IB subs. If you are planning to visit notnyt, PM bossobass and see if he could demo his setup for you. Bosso has extension down to ~3Hz. Notnyt uses crowson transducers to fill in under 15Hz. Depending on room resonances, one setup could be more efficacious than the other in transmitting the energy in the soundtrack to you.

JSS
The ported system is -3 at like 10hz. I don't use the crowsons just to fill in under that, they add huge tactile feedback lost to the slab. At the risk of sounding like a salesman, they're really really good and add so much to the experience. Even with music.
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post #342 of 505 Old 08-02-2014, 12:21 PM
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The ported system is -3 at like 10hz. I don't use the crowsons just to fill in under that, they add huge tactile feedback lost to the slab. At the risk of sounding like a salesman, they're really really good and add so much to the experience. Even with music.
Not,
My ported 21" cube is a foot to my left , not under my seat. It has completely changed the tactile sensation of 18-50 hz. Especially at mid level SPL. Is the reason people want crowson is too hide the sub ?
I use the sub beside me as a end table.
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post #343 of 505 Old 08-02-2014, 12:23 PM
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Not,
My ported 21" cube is a foot to my left , not under my seat. It has completely changed the tactile sensation of 18-50 hz. Especially at mid level SPL. Is the reason people want crowson is too hide the sub ?
I use the sub beside me as a end table.
they add more tactile feedback. especially when on a slab. and they can be run down to very low frequency.
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post #344 of 505 Old 08-02-2014, 01:31 PM
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The ported system is -3 at like 10hz. I don't use the crowsons just to fill in under that, they add huge tactile feedback lost to the slab. At the risk of sounding like a salesman, they're really really good and add so much to the experience. Even with music.
They are on the wish list.

JSS
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post #345 of 505 Old 08-02-2014, 01:55 PM
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The ported system is -3 at like 10hz. I don't use the crowsons just to fill in under that, they add huge tactile feedback lost to the slab. At the risk of sounding like a salesman, they're really really good and add so much to the experience. Even with music.
at what number of subs are crowson's a cost-effective upgrade?
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post #346 of 505 Old 08-02-2014, 01:57 PM
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at what number of subs are crowson's a cost-effective upgrade?
depends on the room. for me, they're a must have now, along with subs
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The ported system is -3 at like 10hz.
That and you have so much freakin head room that making 10db "flat" isn't that much of a problem if it actually mattered.
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post #348 of 505 Old 08-02-2014, 02:01 PM - Thread Starter
 
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They are on the wish list.

JSS
+1. But I'll have to wait.
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post #349 of 505 Old 08-02-2014, 02:02 PM
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That and you have so much freakin head room that making 10db "flat" isn't that much of a problem if it actually mattered.
sure it is, you can't boost ported below tune. drivers unload and excursion sky rockets
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The ported system is -3 at like 10hz. I don't use the crowsons just to fill in under that, they add huge tactile feedback lost to the slab. At the risk of sounding like a salesman, they're really really good and add so much to the experience. Even with music.
I'd be curious to hear what they add to the musical experience if you don't mind sharing.
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post #351 of 505 Old 08-02-2014, 04:58 PM
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I'd be curious to hear what they add to the musical experience if you don't mind
if you've ever been in a car with a loud system, it provides a lot of the same tactile feedback
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if you've ever been in a car with a loud system, it provides a lot of the same tactile feedback
I have, thanks that was a good example and provided perspective.

Does it help with "punch" (think kick drum)? Often punch can be enhanced by transmission through seating.
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post #353 of 505 Old 08-02-2014, 05:04 PM
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yep
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post #354 of 505 Old 08-02-2014, 08:12 PM - Thread Starter
 
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Anyone ever go to a system that was single digit capable and then play with a hard high pass filter and compare?

Popalock you ever high pass your system at like 15hz and compare it ?
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post #355 of 505 Old 08-03-2014, 05:28 AM
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Anyone ever go to a system that was single digit capable and then play with a hard high pass filter and compare?

Popalock you ever high pass your system at like 15hz and compare it ?

One JTR Orbit Shifter vs Three Power Sound Audio XS30s

I believe he is talking about his demo experience of popalock's system.

My experiences align with his observations.
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I've read a couple of threads in the past that were really good on the subject but I forget them now or which ones they are. The bottom line is that even if I wanted the single digits I'm not sure I can afford what it takes to get it. Decision being made for me in some ways there. I'd like as much ULF as I can get but it's the area that would be sacrificed first. I'm thinking with a tune of mid teens I won't be missing anything anyways.
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post #357 of 505 Old 08-03-2014, 09:39 AM
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Anyone ever go to a system that was single digit capable and then play with a hard high pass filter and compare?

Popalock you ever high pass your system at like 15hz and compare it ?

Yes he has - post 10.


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I've tested frequencies below 15Hz or so at desertdomes, gorilla83, carp, and popalocks. Tests using minidsp, dcx-2496 etc. Removing all frequencies above 14, 15 16Hz, 18hz... in my opinion if you don't boost the low frequencies with a strong house curve it just doesn't matter. And until it's fairly high dB (much higher than -10 or -15dB) you can't notice them anyway -----even in the most potent of movie clips (black hawk down, hulk, etc) all four of the rooms we tested this in are filled with multiple 15s or 18s.

Desertdome - eight 15" AE subwoofers in infinite baffle and J-River as LPF. Removed all frequencies above 14hz. Desertdome will tell you below about 14Hz doesn't matter to him. (Wooden main floor, old 1900's era built house)

Gorilla83 - tested with three submersive hp subs with a 18 hz HPF on and off - IIRC. Removed all frequencies below 18hz, played the same clip again with those frequencies. Two ported captivators in 15Hz tune had quite a bit more tactile feel on the same clips than the three submersives with no hpf. With hpf on or off the difference was like 5% at most with demos of the hulk using the three submersives. I wish we would have retested with a lpf at that meet since there were so many people there. --- or perhaps a 14 or 15hz HPF instead of a 18hz HPF. If I recall correctly - we were using a Behringer DCX-2496. (concrete slab of basement new house)

Carp - 8 SI sealed, played with a lot of LPF settings using minidsp. carp thinks nothing below about 14Hz matters even with 8 SI. (concrete slab of basement, modern house)

Popalock - played with a 14hz LPF with a minidsp and 16, 18" sealed SI subwoofers. The room shakes and certain precise spots do crazy things, but I wasn't even impressed with subsonic ULF even there. Apparently popalock wants more...he bought 16 more for a total of 32 eighteens. (concrete slab of basement, modern house)

For me ULF to 10 Hz or below is a forum novelty, nothing more. I feel a bit like the child in the emporers clothes story when people talk about chasing the super low ULF. If 16, 18" subwoofers in a 1500 cubic foot space at popalocks couldn't convince me if the merits of ULF, when testing with a LPF, I personally don't think it's worth pursuit.

Just my observations.
WOW! Excellent post and link. Thanks!
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post #359 of 505 Old 08-03-2014, 10:43 AM
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Originally Posted by Archaea View Post
I agree with your observations, superb post. The note about the emperors clothes story is particularly apt.
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I do appreciate someone who has heard a lot of things or been to a lot of GTG events, even if it's opinion it carries a lot of weight with me. That said, I do also feel like I "know" the majority of the posters here at regulars and respect them all, so I'm also appreciative of any and all the replies or advice I've been getting. Thanks to all for that.

Right now I'm still stuck, but that is ok. On one hand I can port low and do it all rather easily, and I can keep every sub ported. something like 4 UXL18 plus (8) infinity 1260 on the sides should be more than sufficient.

But before I make the final decision I think I need to fold a horn for the infinity, and test it side by side with one ported at 20hz and compare. That might be a fun experiment. Is there any good designs I could use to speed up this design process for those ? I just ordered 10 sheets of MDF for my wife's closet I'm building this week, secretly between me and you the project only takes about 7.5 sheet Shhhh... don't tell her. It's going to be accidental scraps so I might as well use it right ?
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