Carl got a nice 15" quad voice coil sub driver from hometheaterdoc, and matching 1000W plate amp. Since I have the table saw and clamps, we're gonna make the box ourselves, to fit his special application. This is a single sub to fit under the upper platform at the rear of the room. There is ~11" space under the platform. This is just for theater use, to get those nuclear blasts and dino footprints just right. Not high end audio, which will have their own custom subs built in a separate thread.
Any help, advice, suggestions are most welcome!!
Thanks
Rich
I asked Shane Sangster, The Home Theater Doc, for some advice on building the box and received this response. Thanks Shane!!
"I prefer sealed and this driver will work either way.... obviously more output via ported, but it can still shake the walls with it sealed.
This driver moves a LOT of air. So you need to build a tough box. I used double and triple MDF for my sub cabinets. Front panel was 2.5" thick on my designs, but a lot of that was due to wanting to recess the driver a bit. box within a box with sand is a bit overboard. If the walls are thick enough and you use enough braces, that should be fine. not to say it wouldn't be better to go to the extremes. I'm just not sure it will help enough to offset the effort involved.
You'll likely want a bit bigger than 3.6 cubic feet... when you do the T/S parameter measurements on the actual drivers, the Vas is much higher than spec.... and Qts is higher as well which allows you to go bigger to get leaner less boomy bottom end. The plate amp does have a boost circuit for 25Hz which comes in handy.
You're going to wire it so it's a 5.6 ohm hookup (i.e. all voice coils in series with one another). That will work best with his plate amp.
--------------------------
Shane Sangster
The Home Theater Doctor "
We should characterize the driver with the Woofer Tester to make sure the Thiele Small specs are correct. But in the end, if we go with a sealed box, they are less critical, as long as the minimum volume of 34 liters is met.
I did some simple simulations with the published driver specs and WinISD speaker software (http://www.linearteam.dk/). 60liters is near the point of diminishing returns on bass extension. Carl likes optimizing to the point of diminishing returns, so that will be the target area for volume. Driver specs are not likely to vary too much from the specs, and Volume is the only variable with a sealed box, so hopefully that part will be fairly straightforward. But that's why I'm seeking advice and corrections for my assumptions... and just to have some fun sharing...
I'm thinking of making a flattish box under the platform, big enough footprint to give the 60liters we need while staying low enough to fit under there. The driver points out to atmosphere at the rear of the platform, tilted back 45 degrees to fit it in the 11" space under the platform. The sub box will not contact the platform above, unless someone thinks it doesn't matter. I am going on audio dogma here thinking we wanna isolate the vibrating box from the seating platform, but maybe some mechanical linkage would be even scarier. :D Mounting the plate amp on the vertical surface of the platform next to the sub hole. Cover the hole with some acoustic fabric.
Here's the spec sheet for the driver:
TC Sounds 3000 QVC (http://parkwestlake.com/nopw/rich/carl/carlssubdriver.pdf)
My webhost is uploading slow today. If it's still slow later, we can host it on AN.
Thanks
Hiya Rich,
I agree with your choice in using a sealed enclosure since you've got the boost at 25hz. Not knowing what that amp is, it might not take kindly to the huge impedance bump at the speakers F and tuning point in a vented enclosure. You'll likely get better quality bass with the sealed enclosure. If you've got access to Woofer Tester or some other driver measuring program, you will be surprised at how much the published TS parameters differ from how the driver actually measures. If you do have access to measurement software, be sure to break the driver in with a 20hz signal for a few hours first before you measure it.
If I understand this right, Shane is recommending a little bigger than 100L and you are thinking 60L for a 15" sealed?
Usually it is easier to reduce the volume of a box, if it is too small you end up doing this :duh .
Lin :)
Sealed enclosure is a must.
After that.....the sky is the limit. When I built my two sealed Rythmik subs I followed Brian's plan which (thankfully) don't call for anything too crazy and the end result speaks for itself. Everybody to this day who hears them, offers me money for them.
I should mention that I did not go nuts with the box's. Good old 3/4in MDF all the way around with the same being used for all the internal bracing. I get zero box vibration.
I would however not go overly big with the box as bigger doesn't always mean better.
Thanks to everyone for the help with this, especially Rich. I've been a bit overwhelmed with work and finishing the basement. As of today I have full electricity.. including all lights... pix to come on the basement thread...
Seems like sealed is the way to go. I'm now living nearby to the Hometheaterdoc so hopefully I can swing by and nab the measurement stuff soon. Carpet comes in a couple of weeks so, I'd like to have the platforms built prior to that... In order to build the platforms, I need the final outside dimensions of the sub. (Everything in this project requires multiple steps ahead thinking.)
Thanks again and looking forward to getting the max out of this sub setup. It's not cheap gear and I don't expect it to be adequate just for boom-boom stuff. I'll be watching live concerts on DVD as well... so it has to do some music right as well.
-Carl
Carl/Rich,
Would it be possible to build a test box (or two) first?
If you make one large box with an adjustable inside wall you should be able to get an idea how the different sizes will sound.
Lin
That's not a bad idea, Lin.. but that would make the project a little longer. To me, it's worth making this sub the best we can on the first try.. and not so much on perfecting it over time. Basically, I'm way too impatient for your thoughtful suggestion. ;)
Actually, if you know what you have to work with, you can cut a few additional 'ends' that will fit inside the cabinet so you can gradually decrease the cabinet volume. That's easy enough to do with a test box. Not sure if you have time though with your schedule and carpet coming in 2 weeks.
Bryan
Thanks for the great ideas everyone.
60 liters is only a guess, based on simulation with Qtc of .707. With boost at 25Hz I think 34L would be good enough and as tight and controlled as theoretically possible. Of course 100L goes lower with smaller Qtc, but it also requires much more bracing to stop wall flex and flubbies. 60L seemed to be at the sweet spot of added low freq extension for minimum volume. 100L is less than 1dB louder at 30Hz.
The cabinet must be a big square pancake, fitting around the framework for the seating platform above, so there is a limit to the cabinet size. With Two layers of MDF top and bottom, and fitting inside a 11" height space, that leaves 8" box interior height. Which requires 5.3 square feet of floorspace for 100L box, not including internal braces. We have the space for that, so we could do 100l if necessary.
Either way the volume is a variable to achieve desired system Q, so we have to measure Vas of the driver to know what we really have. We could do a movable wall but coming from engineering background I rather know before hammertime what is correct. To adjust volume I think it would be even easier to put some bricks in there to increase Q if we overshoot the volume.
What about stuffing for internal resonance control? Deflex would be a few hundred bucks, as would blackhole. There are some cheaper versions of blackhole type covering, I gotta lookup the link I got from from JoshK. Or we could go old school, and stuff it with cotton absorbent for reasonable price and we already have that in the plan for treatments so there will be extra lying around. Loudspeaker cookbook only comments on stuffing, usually 1/2 full of stuffing is best in his measurements. Maybe line the interior walls with the 5" thick recycled cotton bat?
Carl, what is the brand/model of the amp? I am confident that it is more than up to the task. Shane says it is a freaking brute and we will be at 5.6ohm on the driver, coils in series.
Carl when does the MDF show up? I have this Thursday-Friday off.
MDF will be at my house Thursday... If I have all my work done, I should be able to get it to you then or Friday. I'll bring the sub and amp as well... It's all boxed up at the moment.
This is the amp: http://www.madisound.com/catalog/product_info.php\?manufacturers_id=137&products_id=372
-C
plate amp is a 1000 watt Keiga ICE Power based unit from madisound.
forget about blackhole or things of that nature. For the range of frequency this is being used, it really isn't worth the investment. I'm not saying it won't have an effect, just not enough of an effect to offset the cost involved. Build a sturdier box. I like using different thicknesses of MDF and HDF glued together to help with vibration and tuning. You can get 1, 1.25, 1.5, and 2 inch thick MDF in addition to the standard .75 inch stuff you find everywhere. The stuff at Home Depot is not really that great. I get mine at Raleigh Hardwoods over on the east side of town. They stock a couple thicknesses. This stuff is heavy, Rich... so make sure Carl is helping you. A circular saw to trim pieces down before final cuts on the table saw is your friend :)
I've built at least 150+ boxes over the years. The best ones used good bracing and different thickness materials moreso than what was stuffed in them. Depending on the cavity sizes, some acousta-stuff or insulation does tone things down a bit as far as cavity echo...... you don't have to spend a fortune. An overbuilt box is cheaper to do because the relative cost of MDF is a lot lower than the alternatives that are for sale out there to fix resonances, etc.. Full range speaker boxes are a completely different ballgame than a subwoofer. For subs, a good design, a good driver, and adequate clean power (I hate ice amps for full range, but do like what they do for subwoofer duty. The BASH based units are also pretty good for the money) put in a well built box and it's not rocket science to get good sound. The thing that usually limits commercial subwoofers is that the costs of packaging and shipping don't permit them to build an adequate box for their stuff and keep the price affordable. I even had to keep my box sizes down to do more than meet WAF factors (which were the major contributing factor to why I kept the box size to ~3.25 cubic feet with this driver in the 15 others I've built and installed here in the area).... a 40 pound plate amp, 50 pound driver, and 150 pound box made it a bit difficult to carry by myself to an install :) I finished installing plate amp and driver in the box onsite more times than I can count :) I couldn't go much bigger or I couldn't carry the darn thing by myself.
I personally like bass from a sealed box that has a Q ~0.50-0.55. It's a bit lean for a lot of folks... but the speed, attack, and quick decay are appealing to me. I'm not sure you want that for full time home theater, but you'll notice it on concert DVDs. I'd stick closer to .7 for more universal appeal...
I found the software CD for the woofer tester 2 unit I have. I'm pretty sure I know what group of boxes the actual measurement unit is hiding in. I'll try to dig it out tonight or tomorrow. I still have a sea of boxes to get through. This past weekend was a bit of a write off as we're still trying to find all the new furniture we're sticking in the place to fill it up..... had a bit of a blow-up over changing plans as to which rooms will house audio gear.... the acoustics are so terrible in most rooms, I'm claiming different rooms just because they will be a bit easier to try and tame things down a bit... which did *not* go over well.... tell me again why I need to live with someone else???? I have a feeling I'll be visiting Carl a lot when I want to hear what a real room should sound like :)
Quote from: hometheaterdoc on March 17, 2009, 10:32:42 AM
I found the software CD for the woofer tester 2 unit I have. I'm pretty sure I know what group of boxes the actual measurement unit is hiding in. I'll try to dig it out tonight or tomorrow.
Slightly off topic... You might want to contact Smith & Larson who are the folks who make the Woofer Tester 2. They have new software which is a free upgrade and it's much improved over the original versions. They ask that you contact them to get a login to download the software but it's worth the effort.
Their site is www.woofertester.com (http://www.woofertester.com)
Thanks Shane, I know about that real MDF. I prefer the lightweight soft powdery shit from Brazil (homedepot) because it is so much lighter. But it burns up blades and router bits. Carl has already bought the MDF from BuilderSupply. We'll see how that looks. I need a new blade too. That Trek speaker killed my blade.
You are correct about the box resonance. The pass band is 20-50Hz. Double thickness MDF's resonance will be way higher than 100Hz, so it will not resonate. So we are only concerned with flexing under internal pressure, which will be significant. Bracing and wall thickness will minimize that. Maybe some angle steel or just vertical 2x4 braces screwed in. The side walls will only be 8inches tall, so they are no problem.
Using factory driver specs:
Qtc .5 = 90 liters
Qtc .55 = 65 liters
Qtc .71 = 34 liters
SPL at 25Hz
Q .5 = -9.64 dB.
Q .55 = -10.18 dB
Q .71= -12.48 dB
So of the boost switch gives 10dB we are all set. Just pick the Q to taste.
An interesting FAQ for subs. http://www.diysubwoofers.org/faq.htm
Carl is planning to build a pair of dual driver OB servo subs to place next to the main speakers for music. So deep bass for music will be very accurate. In that sense, would you recommend higher Q?
As for living with another person, I used to remember why, but it's been so long I forgot. Now I live with 4. :?
I have WT2 software, but it is a year old. I am registered so I'll try to download it. Thanks Mike!
Here is the plot of the driver with factory specs at Qtc = .55 (65liters)
[attachment deleted by admin based on 2 year limit]
Can the flooring surface of the platform lie directly on top of the box, or should there be a gap for vibration isolation? I guess it's whether you want to feel it in your feet. I think that would be annoying?
6 square feet (2x3') footprint will give about 100L volume inside a 1.5" wall thickness box. So framer spacing of 2 feet should be enough, with 2 square foot extra unobstructed space inside that framing bay if we need it, which we will need for the extra volume we wasted by tilting the driver to fit.
To be on the safe side, make a center framing bay with studs spaced 26" on center, the bay is centered on the length of the platform. I'll send you a dwg Carl.
Realistically, you're not going to prevent feeling some of the vibrations if you're sitting on the platform.
Personally, if it were me, and the driver will tolerate it, I'd build a 1/4 wave pipe from 2 of the cavities. Talk about fast and tight...
Bryan
It's the last row in the theater, I won't be sitting on it anyway.. So, no big whoop to me. That's essentially the 'make out couch' so a little vibration from underneath may be nice. ;)
Quote from: bpape on March 17, 2009, 12:44:14 PM
Personally, if it were me, and the driver will tolerate it, I'd build a 1/4 wave pipe from 2 of the cavities. Talk about fast and tight...
Great idea Bryan!
Like this, but folded into thirds to fit:
(http://homepage.mac.com/planet10/TLS/projects/exolinear/images/planB.gif)
The exit opens at the 1/4 wavelength you desire to boost. There will also be a minor null at a higher frequency.
http://www.t-linespeakers.org/projects/exolinear/rhinos.html
I have quarter wave simulator, but many brain cells would die in the effort.
(http://homepage.mac.com/planet10/TLS/projects/exolinear/images/rhinoB.jpg)
Actually, I think you generally would prefer to have the pipe length be at the free air resonance of the driver so the backwave helps to damp it. The one problem is that it can tend to want to unload below the tuning so I'm not sure it's optimal for HT usage - but it'd be outstanding for music and concert vids. According to their specs, that's around 22hz.
The other option to extend response and avoid chuffing is to use a passive radiator. Their doc shows tuning the PR from 10-25Hz. If you tuned it low and used the boost in the amp just above 20, you could likely have some serious extension relatively smooth into the teens.
Bryan
Yes, that's cool. The T/L is too complex for the schedule and the patience of the client anyway. I like the tall pillars though.
I'll check the out doc about PR. Thanks
Quote from: mgalusha on March 17, 2009, 11:46:23 AM
Quote from: hometheaterdoc on March 17, 2009, 10:32:42 AM
I found the software CD for the woofer tester 2 unit I have. I'm pretty sure I know what group of boxes the actual measurement unit is hiding in. I'll try to dig it out tonight or tomorrow.
Slightly off topic... You might want to contact Smith & Larson who are the folks who make the Woofer Tester 2. They have new software which is a free upgrade and it's much improved over the original versions. They ask that you contact them to get a login to download the software but it's worth the effort.
Their site is www.woofertester.com (http://www.woofertester.com)
Cool, I'll have to update my software.
Thanks Mike :beer:
Just a quick link for an easy calculator for volume adjustments for bracing.
http://www.hometheatershack.com/forums/enclosure-volume-calculator/
Bryan
Cool, thanks Bry
Just wanted to say thanks to both Rich and Shane.. Shane dropped off the woofer tester and a sack o' nickels and I took mdf and the sub to Rich this afternoon. We got started on testing and had a nice visit.
Thanks again, I'd be very lost without your help.
-Carl
You're welcome! Least I can do for all the help you've given me.
WT2 is working fine, thanks Shane. I'll post the results when I have run it a few times for confidence.
This driver is humongous. I'll post a picture later. Welded steel box would be appropriate for this beast.
Yesterday afternoon, we had a pair of Chinooks strafe our house in formation. They flew directly over my back yard at about 500 feet. There is no sound like that, 12 blades beating a 4 rotor chorus of supersonic shock waves at 11Hz. I wonder if this sub can do that? I would pay to see that again.
Shane suggested that I break in the new driver before measuring it. I was thinking about what signal to use. A disco song would have some bass, but nothing to put the sweat on this driver. So I used SoundForge to create a custom torture track.
At first I created a track of pink noise low passed at 80Hz. It did not seem to be very loud. I boosted it to clipping, but RMS was not very strong. I needed more energy down low. My daughter liked the noise sound though, she came up to me while I was editing it and said "I hear something weird in my bedroom."
I decided to use a 20Hz sine wav mixed 100% with 33Hz sine. I put the 20 in left channel and 33 in the right to get some overtones from interference. Combined the channels to mono, then convert mono back to stereo, I saved both forms if anybody wants it we can upload it to this server. It is one minute long, so you can put it on repeat.
I will try to setup my 80W AudioSource amp into bridged mode and run the mono track on the driver for a while. The surround seems very soft and pliable to me. Spider is pretty tough though.
The waveform looks like this:
[attachment deleted by admin based on 2 year limit]
That curve kind of reminds me 'Kilroy was here'.. ha. Glad we've got time for break-in. The platform is built. I have the ability to remove the solid plywood top to route wires and such. The plate amp has a home in the back corner.
Total space is 24" W x 50" L x 11.3". I'm not sure why it's not 11.5... but it isn't. I feel short-changed. ;)
I did some basic right-triangle math to figure out if we'd still have enough room and we 'should'. But I don't know how to figure out how the magnet comes into play in the dimensions. Using a combination of a2 + b2 = c2 and sinA = a/c.. I can figure the hypotenuse by the angle of the triangle.. but.. those are straight lines. By my calculation we have 15.56" of room from the middle front of the plane of the driver to the middle rear at a 45* angle.
But, when you put that big circle around the bass of the driver, I'm not exactly sure how to factor that... but it could get very tight.. It might have to be a 40* angle... and it could be less than that... I have plenty of room to notch out the plywood on the top as needed. But at a 45, I don't think it'll fit in an 11" high box if my fuzzy Math is right.
-C
I'll check it with CAD once I start on the design. It's OK to tilt back farther. We can point it down. I went to borg (Big Orange) today to get baffle screws and router bit. I will assemble it with glue and 1.25" staples. I will laminate the MDF walls together with glue and staples while standing on it. If the're room I'll make the baffle 3 layers thick, two layers for the rest. With supports inside. Weather should be nicer later this week. So I will try to get the design done by then.
Thanks! This week is all rain.. :( If you get the design done this week, I can come over for a full day next week to put it together.
-C
The client who shall remain anonymous (eh-HEM!) wired the voice coils in parallel, giving my poor little AudioSource amp a punishing .35Ohm load. It is remarkable that the amp played at all, and it played pretty damn loud. I had the volume up to 75% on the Sonos and it ran that way for 10 minutes, but it did get very hot. I turned up the volume to 90 and it blew the thermal protection after a couple seconds, no harm. Shane helped me figure it out. Rewired in series for 5.6ohm impedance, the excursion at same volume level doubled and no heat from the amp. I played a godallmighty house shaking organ track through it at same volume setting I would use in my system and the driver cone only moved about 1/2"p>p. Running the torture test track on it at same volume setting makes it move >1". Turning up the volume it will go farther and farther with no bottoming. This thing is SICK! I better use some extra staples.
Shane thinks a few hours of play will be enough to loosen it up enough. I should be able to do that tomorrow.
:duh I'm the dumb client.. :duh
I blame the manufacturer for making me think. ;)
Wow - 20Hz on an amp into 0.35 ohms! That's amazing that it played at all.
Bryan
I should listen to it again now after that serious "burn in". You know it's done when you can smell the resistors. :lol: It's a good little amp. It's my emergency spare when all else fails. "bluisana" (AN) recommended it to me.
You are right Carl, this driver is just too damn big. Here are some options to mount it.
If you can do a 4" bump up for total height 16" at the baffle then we can mount it vertical with no tilt. The bump can be a foot wide and 2 feet long. If your couch will have 4" clearance under it than that will be the easiest. Tilting the driver 25 degrees lowers the max height to 15", but adds build complexity. Removing the driver for maintenance or tuning the volume will be easier with vertical mount than diagonal.
You could also mount it facing up into the couch above. The whole driver including the roll surround would be recessed below the top surface so you could cover it with steel grid, cloth, etc. But the platform needs to be decoupled from the driver baffle (imo) and the driver needs to be protected from debris and stepping from above, it is more vulnerable facing up.
Any opinions on which is better?
richidoo,your experiences loosening up the suspension on Carl's subwoofer reminded me of what happened when I first took delivery of my loudspeakers. They have two Dayton Titanic MKII subwoofer drivers per speaker and the efficiency is 96dB1w/m.. The fallout from the combination of high efficiency
and two 350w rms subwoofer drivers per side was that for 3 months I looked at the speakers and wondered where the bass was. I finally got a brainstorm and realized that I was not breaking in the speakers with maybe 10
watts on crescendos when I played the system loudly. I did something similar to break in my speakers, I hit them with 20Hz sinewaves at -20dB and hit about 110dB continous for a half an hour. It took three "treatments" to loosen up the drivers and get the output below 70Hz. to match up with the rest of the spectrum. This being a vented system, the port was doing most of the work below 30Hz which didn't help it break in,the drivers were still only moving about a half inch at 110dB. That insane sub you guys are building will certainly work better from the get go with the driver already loosened up. You won't risk damage to your foundation trying to break in in after it is assembled. It looks like there is no good reason that the sub shouldn't work as well for music as it would for home theater,that is one incredible looking driver.
Scotty
I measured the couch and I only have 3.5" of clearance there.. I took some photos of the platform yesterday but I got sidetracked (as always) and now can't find the camera.
I was thinking of putting the platform on gliders to adjust the seating anyway.. I could just leave those gliders in long-term. Just a thought. That would add at least .5" to the whole platform.
-C
Thank Scotty. It is kinda scary to see that 15" cone moving in and out that far, that fast. I showed my 8yo, told him if there was a box around it, it would sound like a giant bomb exploding. Oooooo 8)
Carl, After talking with you yesterday I think we have decided to build the sub box with driver vertical, with tall baffle sloping down to meet box. The couch may have to be a few inches away from the rear edge of the platform. If you can specify how many inches the bottom edge of the couch can be moved forward of the rear edge of the platform would help me design the top angle of the sub box. You suggested 6 inches yesterday, that is enough to accomodate your 3.5" couch height if the couch is moved in 6". I will try to minimize how far in it must be moved. The thickness of the MDF is the limiting factor there.
I'd like the couch to be on the back edge.. so, I'll raise the couch a half-inch, no big whoop. ;) BTW, that's a scrap of wood across the back for structural rigidity whilst moving it around.
Here are some photos:
[attachment deleted by admin based on 2 year limit]
What is that smaller hole photo #004?
I'll get the top surface of the box down as quick as possible, then you can fiddle the box/couch/platform together.
Q test results:
Re 5.090 ohms
Fs 24.666 Hz
Qes 0.4135
Qms 7.0802
Qts 0.3907
Le 5.049 mH @1k
Still to do Vas test.
Looks great, thank for doing the testing, Rich. I'm not sure how to repay you for the work you're doing but let me know what works for you..
The other cutout is for the plate amp. There is a little tiny hole on the step for the power and signal cables.
-C
Cool, that amp is big too!
The Vas test is not working well. It runs and runs for hours not making headway. I have anice 60g stack of coins in the cone, but the tester seems stuck. It keeps flashing "Vas: Fiding Zmax::Search", and then never rises above 1Hz. Drive is 100%, voice coils in series. Any ideas to try?
Thanks
Please comment on this design. This is about as compact as I can make it. Air can move behind the cone into the volume easily when driver is rotated 45 degees. One 2x4 brace vertical in the center.
[attachment deleted by admin based on 2 year limit]
You need to update the drawing Rich, it should have BAM on the sub... BigAssedMother... :o
I think you're going to have a hard time like that. It's going to be pretty tough to get it braced and solid enough to not have that driver just shake it apart.
Bryan
Good Idea Mike. Finally it has a name!
Thanks Bryan. The largest unsupported span is about 12 inches, from vertical brace to rear corner, which are supported in two directions, so effective max unsupported span is about 9 inches. All surfaces are double ply MDF glued and stapled every 2 inches except right near baffle where 2 layers just won't fit and I made some 4" wide reliefs at the center of the driver. Do you have some suggestions how to improve the strength? I could easily add more vertical braces, in fact I had 4 in there, but I thought 6 inch max unsupported span was overkill. I was also thinking about using threaded rods to pretension the box, I could use a few of those without increasing the box size too much, but there is plenty of room to extend the length for more bracing. There isn't room for thicker top/bottom walls or anything more near the driver. Maybe a layer of FG on the seams, but that won't help much with stiffness. I was also thinking of epoxying on some 1/8 aluminum sheet in critical spots, if needed. Or even making the baffle from aluminum, but that's probably $200 for custom CNC. tia for any ideas
Rich
It's not the baffle itself that I'm concerned with. I'm worried about where the angle meets the top of the riser. The kind of force that driver is going to exert is just asking to sheer that angle right off. If the driver is capable of being mounted vertically (cone up), I'd likely just do that. Having seating on top of it won't stop much of anything at the very low frequencies. Or, is the depth from cone to back of magnet too big to mount that way?
Bryan
I'm not nuts about it pointing straight up. I think it'd be awesome for a few minutes, though. ;) It would be firing directly into someone's rear end...
I know low bass is considered omnidirectional but the bass won't be distributed evenly for the audience if one person is sitting on the sub and another person is 7' farther. There will be a distinct imbalance that will be impossible to cure doing that.
Pointing the sub to the rear of the room gives it a chance to pressurize the area behind the seats first.
I like the design as-is... It works for me and looks pretty rigid with the bracing you've proposed. Looking forward to putting it all together! :)
Quote from: bpape on March 28, 2009, 06:52:13 AM
It's not the baffle itself that I'm concerned with. I'm worried about where the angle meets the top of the riser. The kind of force that driver is going to exert is just asking to sheer that angle right off. If the driver is capable of being mounted vertically (cone up), I'd likely just do that. Having seating on top of it won't stop much of anything at the very low frequencies. Or, is the depth from cone to back of magnet too big to mount that way?
Bryan
Thanks Bryan, I see your concern. I weaved the edges together at the angle, and put that 2x4 beam in there to support the angle in the center. The angle is also woven into the side walls. But I could put an aluminum angle on the outside, spanning the width. Whatya think about that? You're worried about the flexing of the joint under pressure, right?
Vertical driver in a simple box would have been much easier, but the motor is 8 inch diameter, so angling the driver vertical makes the top of the motor about 13" off the ground, so none of the driver would fit under the deck. Tilted, I get about 2/3 under the deck. I agree it is gonna be a highly stressed structure. We'll have to see if we can break it after a few beers. I'll bring the ear protection. haha Then we can build another square box to go in the attached utility room.
Yeah - I'm worried about having anything other than a direct brace in the direction of the driver movement. Pushing at an angle like that I think it will eventually fail. Maybe a brace that's parallel to the driver axis that extends from the baffle at that angle all the way down to the joists on the floor?
Bryan
OK, I see what you mean. There is plenty of room either side of the driver, so it should be easy enough, and it will take some of the fore/aft vibration off that joint. Good idea, thanks
I bought a jigsaw for the subwoofer project, and I saw the platform today too. We decided to make a rectangular box and shoot it straight upward from the top of the platform. With Carl's Piegas solid down <40Hz, and OB subwoofers up front down to 25Hz, this sub will crossed in very low so it shouldn't matter which way it points. We'll brace the hell out of it, should be quite solid. We are supposed to knock it out next week. I hope to have the square parts cut ahead of time.
The only challenge is making a thick walled box, while leaving an inch of clearance between bottom of box and back of motor for cooling air to the voice coils.
If need be, I can remove the carpet, subfloor, and my membrane stuff to get at least another 1.25" under the platform. Then the sub will rest directly on the concrete which I think might be better anyway for isolation purposes.
I'm not sure how much room is under the seats I'm getting but it should be at least a couple of inches.
Here's a link to the seats. (http://www.bostontables.com/p-52-7537-3-seat-black-leather-home-theater-seating.aspx) About 1:15 into the video you can see the back and it looks like there will be plenty of room to have some protrusion out of the top.
OK.. off to bed.. everyone have a great weekend... I'm excited about getting this sub built, Rich.. thanks again for all the help! :) :) :)
I redesigned the sub with Bryan's concerns and time considerations in mind. It's now rectangular and pointing straight up. The chair over it will be in great demand.
Since crossover will be very low ~40Hz, the chair above and the direction of pointing should have very little influence, at least on sonic performance elsewhere in the room. The person sitting in the chair above was always gonna get a little something extra for their ticket price.
Comments please? We plan to build it on Thursday.
Thanks
Rich
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Finally some reality behind one of these "Let's Build a..." projects! Feels good to finally make something again. We had a blast, and nobody got stapled.
The walls are 2 laters 3/4" MDF laminated with Titebond1, then Carl stood on the top while I stapled every 6 inches or so over the whole surface. He moved his foot for each staple, so there should should be few voids if any. We forgot to count blade kerf for one of the cuts, doing the fraction math by pencil on the board and making the same mistake 3x. funny!
After 6+ solid hours, the box is almost finished. Still left to do is mount driver with blind nuts, cap screws (and red loctite?) Then attach the top with glue, staples and screws to the support studs.
This box is absolutely solid, and huge... Can't wait to hear it.
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Way cool!!! Carl-in-a-box :rofl:.
What a great day, thanks so much to Rich for thinking it through and making it a fun project.
Without some planning this might've been a real disaster filled with stop and go head scratching. Instead we got it 90% complete in a day... and towards the end we were both smiling.. and 1 of us being somewhat silly.. as shown in the pix ;)..
The box seem solid and well-supported. I've never seen anyone build something so exacting out of wood. It has very tight tolerances throughout, especially for a garage-assembled project.
Thanks again and looking forward to hearing it soon... The projector won't be here mid-May so we have to wait a while.. I'm thinking it'll all be worth it. :)
Hell with the projector, we can just listen to the soundtracks!!! :drool:
Do you have Pearl Harbor?
Sub is all done!
I have a full weekend, but I'll bring it over next week. I hope it sounds good. You can experiment with stuffing, but it is big enough to not need any really, unless you hear some midrange ringing inside of it, then add a layer of hot water heater FG wrap on the floor.
It is heavy but solid. Probably 200 pounds all up.
Mmmmm. New toys to play with. :beer: :yay2:
Bryan
You need to fire that beast up in your living room. :)
It doesn't have a hole drilled for speaker wire yet. Carl wants that in a neat location TBD.
I'll need to get the sub up and running this week.. Seats and projector are getting ordered tomorrow or Tuesday and will be here next week.. So the platforms need to be finalized or there will be nowhere to put them. :o
I've been in work-mode like crazy this week... yesterday took a day off from everything... and so today it's back to the grind.. Things should calm down (a little) after a big meeting tomorrow... then I can get the platforms finished. :)
-C
Good to hear the progress. Which projector did you decide to buy?
Rob S.
I'll bring it over as soon as you are available. Tues or Weds? It will take two to lift it out of the van.
Looking forward to hearing sound in the cave.
This will be an exciting week. Thanks for all you've done, Rich.
I've decided sound quality takes priority over movie viewing so, the panel project will happen this month and the projector will have to wait another month. I've decided on the Panasonic AE-3000. That looks like the best for the money. The AE-2000 was what I would've bought a year ago. Those still get good reviews too.
-C