Eminence Surround/Atmos Speaker Build
Ok, I'm about to order everything to make 4 surround speakers using the d220ti with beta 10cx. Because it's a sealed box, should I line the interior with acoustic treatment or not ?
So im thinking this is next project to fill out theater room. How important is timbre matching as im leaning toward the jbl d220ti to match front stage kl650s. Originally I was thinking extending these down to make shallow towers with feet as I have mounting issues in room for accurate surround placement. The kl650s I built 37 inch tall these I was thinking 43 inches tall for dispersion as eventually we'll be adding additional row of seating for post covid movie watching. I have some in ceiling 6in polks that I'm running in surround for now but want to build these and switch those polks to atmos when we upgrade avr and eventually swap those for 2 more of these. I didn't hear or read how efficient these are? Im guessing the 90 to 100 watts my avr has should be plenty as it's driving the kl650?
Wow. I just realized while adding items to PE project list that the 10" is eminence. So timbre matching dilemma. Match the sub to compression driver or compression driver to front stage.
Don't forget the PE discount code offered up on last night's Sound Advice live stream, good til the end of March, code ADVICE. $10 off order of $100 or more.
Honestly I ended up using the Eminence compression driver combo as my center channel with the THX for a while and had no issues. In fact, I really enjoyed it. If it was me, I would probably use the Eminence, but really that is up to you. Honestly, you won't go wrong either way.
Im thinking about taking 3.0" off the bottom depth and adding it to top which should maintain volume of box right? Im thinking about mounting these upside down which would allow me to place one under my window along my side wall of theater room.
@lionhrt9 - because of the angle of the box (being more narrow at the bottom than the top), you would need to add LESS length at the top than the amount taken off at the bottom. What you are trying to solve for is the reduction of volume (meaning space) to the added volume at the top. This is solving for irregular sized objects. To do this, you can basically break it into two rectangles, one is the box whose area is fully there, then the other is how much extra height the top has over the bottom edge (remember to use internal volume, meaning internal edge lengths, to figure out the box volume). You then solve for the amount of volume you would take off by removing 3" from the bottom of the enclosure (and adjust the run of the vent if it is effected). From there, you have to solve for the amount of inches to add to the top of the box (make a rectangle from the internal squared off edge, come close to how much you need, then use the angle of the front slanted plane to continue out to a square or rectangle, with that volume divided by 2). When that equals the amount of volume you removed from the bottom, then you would have the right amount.
I know it seems like a lot, but that is the easiest algebraic and non-trig or non-calc way I know to estimate the volume quickly.
Another way might be to switch around the front panel to have the speaker closer to the bottom, unless bracing is involved or the vent is such that it cannot be moved.
I don't know enough about the set, so am just trying to give as best an answer as I can.
I hope that may have helped in discussing the idea of angling the front of a set. If that wasn't the question, sorry for wasting your time. lol.
@ajc9988 thanks man. It provides excellent insight to exactly what I'm talking about. Plus I don't want to spend the time building them just to find out the math/geometry is wrong. Thanks for the write up!
@lionhrt9 - are you using a pre-made kit or doing a design based on the kit? How familiar are you with Sketchup or a CAD program?
If starting from scratch, I'd first calculate the needed volume for the speaker using WinISD. After that, add whatever volume for damping materials. Then, after figuring how you want to brace the structure, then calculate the volume of the bracing, along with finding out how much volume any vent or port will consume. Add up all the volumes you can (for the vent, you will later have to add volume for the wood structure of the vent after you figure out how you will snake it inside the cabinet, but that can wait unless doing a simple run in and along the back, as snaking inside will mean calculating the length of wood for each turn, etc., and that can take a bit, but isn't too hard). Then, figure out what angle you want the front panel to be angled.
Go into sketchup, then create a triangle with the angle you want, then pull it up. Do the same with a rectangle. Add the volumes together to get a rough idea of your dimensions and see if the volumes are close (if you didn't plan the vent run yet, then it may be getting close to time to do that; whereas if you did already plan the vent run and the volume of the material for the vent, you need to get it more precise).
Now, if running the vent along the top (largest side of the slant, with the bottom meaning the shortest wall that is a rectangle), then you can run it straight to the back, then down the back, but be aware of the mounting depth of your selected driver, as you do not want it to be interfered with on the would for the vent or for the back wall. Because it is at an angle, you need to figure out where the bottom part of the driver magnet will be once placed in the cabinet to check for interference that would prevent putting it in. This complicates making sure depth is right, but not insurmountable.
If instead you want to snake the port along the top, you might want to just make hard 90s as it snakes to not have to deal with the angle along the front which can complicate figuring out how the sloping angle can effect the waves and frequency of the port tuning, which can effect the final sound of the finished product. So you will, in effect, be sealing off little triangles in the top between the hard right and the front slope until the vent is done wrapping. If you do this, you will have to subtract the area of those triangles that are sealed off from the rest of the structure (or you can do a winding with steps to not fully seal those off, thereby not having to subtract the volume of that from the internal volume).
So this is my approach. Find the volume of everything. Start to plan internal structures of the box. Once the internal structures are roughly planned, finalize volume calculations to figure out size. Then use the volume to decide width (with checking baffle diffraction for location of driver on the baffle, etc.) to start also figuring out the height of the baffle. At that point, with this design, you will have the hypotenuse of the triangle. If you then know the angle you want the front face, you can figure out the volume of that triangle, along with figuring out the long bottom edge of the triangle, which is the height of the rectangle part. Since you know the width and now have the height, you just have to solve for the depth for the remaining amount of volume left to be apportioned.
Once you know the volume of both pieces, you then draw up how you envisioned the run for the vent port and make sure the lengths of the boards are roughly correct.
Then go back to the start and double check all your formulas for finding volumes for inside are correct (in part as a sanity check, in part for any design changes). Then, if it is not correct, change the design by tweaking as needed. If it is correct, you have your box.
I know that is probably a lot, but should give a decent explanation how to work on non-standard boxes. It's not perfect, but it should give you a framework to figure it out. Keep us posted on your journey and results! It sounds like a fun project!
Edit: Also just thought of there needing to be mention there can be some effects of having one edge of the port exiting longer than the other. Likely de minimus, but this does effect air flow, and since sound waves travel through air, there may be some effects. I do not know if this will be significant for putting the port above the driver, but I doubt it. But, for those scientists that love to do flow modeling of water or air, please feel free to model this and tell us of the effects.
Edit 2: and if you are doing a custom design made for your house, specifically, you can figure out how high you plan to hang it on the wall versus the height of your ears while seated. You then know the short arm of the triangle and the long arm (not Hypotenuse). That means you can figure out the angle you need the speaker to be at to reach you directly. If you do this to find the angle of the speaker, you can make a custom system that will have a really nice sweet spot. Otherwise you could use 30 deg to generally do it. Just a thought how to kick up a notch to aim it.
Otherwise, you could also build a box, generally, then come up with a mounting mechanism to a swivel arm (like you have for TVs or monitors), which can be used to aim the speaker however you want without trying to do all the math I mentioned above.
Multiple solutions, same problem, speaker attacked to wall at downward angle to give a good dolby atmos experience.