The Once and Future Theater - Page 35 - AVS Forum
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post #1021 of 1195 Old 04-01-2014, 06:06 PM - Thread Starter
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Yeah, well... I wouldn't test it deliberately - not with the irreplaceable Sherbourn that I splurged for.

It's better now. smile.gif

Incidentally, does anyone know with confidence how the Sherbourn amp would behave if driven too hard (into too low an impedance) or overheated?

Edit: the owner's manual says don't drive anything under 4 ohms or you might "cause the amplifier to overheat, shut down, blow the line fuse, or trip your circuit breaker." I suppose that's the whole story. Sounds like I couldn't do any permanent damage... but I still won't be trying it.
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post #1022 of 1195 Old 04-01-2014, 10:21 PM
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Did you actually run the sub connected this way, or was this a near miss?

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post #1023 of 1195 Old 04-02-2014, 06:29 AM - Thread Starter
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I ran it that way for about two minutes - I don't think I even listened to a whole song. This morning I'm at the house with it running 4 ohm, happily shaking the floor upstairs from the basement. (not in a sealed isolated room, just out in the rest of the basement - so shaking the floor is to be expected)

What's weird, and I can't wrap my head around is what I perceived, but can't verify - that the excursion and output was super-high set to 1 ohm. Today the sound is more balanced (AVR trim 0), but the other day I was like "look at that cone jump!"

Let me explain. I know that at lower impedance, the amp has to put out more power for the same voltage (voltage same, lower impedance, higher current draw - just ohm's law) What's weird was that I had in my head that the excursion was directly related to voltage, not power. Same signal should mean same voltage - but I guess excursion is related to power, not voltage? Whatever... it's better now.
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post #1024 of 1195 Old 04-02-2014, 08:35 AM
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Steady progress and good job on resisting that temptation to hang the projector! smile.gif
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post #1025 of 1195 Old 04-02-2014, 09:13 AM - Thread Starter
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Hey thanks, Bryan. I'm just going to keep plugging away when I can. I appreciate the interest (from all of you!).

Don't worry about hanging a projector - I'm a LONG way from that, and there will be plenty of anticipation and lead-up to that.
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post #1026 of 1195 Old 04-02-2014, 11:23 AM
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post #1027 of 1195 Old 04-02-2014, 11:57 AM - Thread Starter
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The driver in question (Dayton UM15-22 Purchased from Parts Express) has two voice coils. Each one is 2 ohms. So if you wire the two voice coils in parallel, the net impedance is only 1 ohm. If you wire the two voice coils in series, the net impedance is 4 ohms.

For series (4 ohm): The positive signal comes into the cabinet and runs to the positive post of one of the coils. The signal runs through that coil and out the negative post, and then to the positive post of the other coil. After the signal passes through the second coil, the negative lead connects back to the amp.

For parallel (1 ohm): The positive signal comes into the cabinet and splits to run to both positive posts. The signal runs through each coil and then the two negative leads are joined to run back to the amp.

When I wired it initially, I took a short length of 10AWG cable (two conductor) and soldered banana plugs onto the ends (4 twist-lock banana plugs). I ran the signal cable into the cabinet and connected into the side of the binding posts of one of the coils. Then I used the short jumper I made to connect the two coils together: positive to positive and negative to negative. This accomplishes the parallel wiring (1 ohm). To change it to 4 ohm, I disconnected the jumper and tore it in half (to make two single jumpers from the one tandem). I connected the single jumper from the negative post on one coil to the positive post on the other coil, then the signal wires to and from the amp are connected to the remaining open posts.

Pictures would help here. You can find them around. A google image search is useful: https://www.google.com/search?q=dual+voice+coil+wiring+diagram
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post #1028 of 1195 Old 04-02-2014, 09:50 PM
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Quote:
Originally Posted by HopefulFred View Post

The driver in question (Dayton UM15-22 Purchased from Parts Express) has two voice coils. Each one is 2 ohms. So if you wire the two voice coils in parallel, the net impedance is only 1 ohm. If you wire the two voice coils in series, the net impedance is 4 ohms.

For series (4 ohm): The positive signal comes into the cabinet and runs to the positive post of one of the coils. The signal runs through that coil and out the negative post, and then to the positive post of the other coil. After the signal passes through the second coil, the negative lead connects back to the amp.

For parallel (1 ohm): The positive signal comes into the cabinet and splits to run to both positive posts. The signal runs through each coil and then the two negative leads are joined to run back to the amp.

When I wired it initially, I took a short length of 10AWG cable (two conductor) and soldered banana plugs onto the ends (4 twist-lock banana plugs). I ran the signal cable into the cabinet and connected into the side of the binding posts of one of the coils. Then I used the short jumper I made to connect the two coils together: positive to positive and negative to negative. This accomplishes the parallel wiring (1 ohm). To change it to 4 ohm, I disconnected the jumper and tore it in half (to make two single jumpers from the one tandem). I connected the single jumper from the negative post on one coil to the positive post on the other coil, then the signal wires to and from the amp are connected to the remaining open posts.

Pictures would help here. You can find them around. A google image search is useful: https://www.google.com/search?q=dual+voice+coil+wiring+diagram

Having dual voice coils can be a great advantage. My UXL's are just 4ohm and figured running 4 with two Peavey ipr2 7500's. But a respected AVS DIY member told me to forget that idea and run all four on just one 7500. Supposedly amp can run safely in 2ohms but resistance in wire due to long runs worries me. Modeled and sure enough........running at 2 ohms in parallel the four UXL's are only down a db in output. Good call and will save $700-$800 in not buying another amp. But I do worry about clipping...........
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post #1029 of 1195 Old 04-05-2014, 05:36 PM - Thread Starter
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So, I was trying to keep this under my hat a little, since it's not settled and I have enough parallel projects going on around here (in this thread) that I didn't want to distract, but I need a little feedback.

I'm looking at DIYSoundgroup's Volt series - the V10 sealed coaxial speaker - for surrounds. I want to build them so that they maintain a low profile (fit close to the wall) and maybe have a little extra style. The flat pack recommended is a simple cube, but it's sold separately, so I'll just build my own to meet my needs. Here's what I'm thinking, from two angles - let me know if you can't tell what you're looking at.




Obviously, the joinery will be more complicated than simple flat packs. I'll have to be careful about clamping and various jigs and measurements to get it to fit together tightly. I've been thinking about it for a day or two, and it seems to me that I should be able to get the joint between the angled side panel and the baffle if I cut the end/edge of the side panel so that it wraps around the baffle a little. Is this foolish entirely?



Would MDF or plywood be preferred?
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post #1030 of 1195 Old 04-05-2014, 07:08 PM
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How did you decide on coaxials?

Any reason not to just miter the baffle and the side panel?

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post #1031 of 1195 Old 04-05-2014, 07:17 PM
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I am guessing he chose the coax because the ability to get the box size down - and also the wider dispersion pattern than a waveguide speaker lends itself well to a surround application. Plus the tweeter and the driver at centered with each other so it takes up less space than a traditional tweeter + woofer design or MTM which with some creativity could be awesome in a column design. Fred stole my idea I think.

What speakers did you build for LCR again ?

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post #1032 of 1195 Old 04-05-2014, 07:19 PM
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Or if you want to get fancier and if the angle works out, you could use a lock miter joint like this for example:

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/graphics2/TM75-7lockmtr0911.pdf
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post #1033 of 1195 Old 04-05-2014, 07:56 PM - Thread Starter
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Quote:
Originally Posted by J_P_A View Post

How did you decide on coaxials?

Any reason not to just miter the baffle and the side panel?
I haven't formally decided on coaxials yet, but actually Mike (Michael? sorry, not sure) has summarized the advantages I'd like to take advantage of. Of course, other designs have their own advantages as well - and I'm not interested in fitting them in columns, so that's not an advantage for me. Also, the point source nature of it seems like a smart choice for what amounts to nearfield listening for people on the edges of the seating - away from the sweet spot.
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I am guessing he chose the coax because the ability to get the box size down - and also the wider dispersion pattern than a waveguide speaker lends itself well to a surround application. Plus the tweeter and the driver at centered with each other so it takes up less space than a traditional tweeter + woofer design or MTM which with some creativity could be awesome in a column design. Fred stole my idea I think.

What speakers did you build for LCR again ?
I built the (NLA) Cheap Thrills - a B. Waslo design.

Quote:
Originally Posted by xjagox View Post

Or if you want to get fancier and if the angle works out, you could use a lock miter joint like this for example:

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/graphics2/TM75-7lockmtr0911.pdf
The lock miter joint was something I considered, and I may yet. As you noted, the angle is the limitation.

I've built a simple spreadsheet to look at some of the cabinet design options. I was told by mtg90 (Matt), who designed the crossover, that there would need to be about 6.5 inches of internal depth to the cabinet - or maybe a little more. The baffle for the 10" driver is 12" square, and 3/4" inches thick. The standard cabinet design for this speaker is a cube, 12" on each edge. So, I figured the easiest way to adjust the cabinet design was to maintain total volume and build from the same material (therefore maintaining internal volume - at least pretty closely considering changes in bracing or what have you). Given the overall layout I outlined in the sketch above, I stipulated that the baffle and back faces would be parallel (meaning no downward angle - they will fire straight out into the room), and built the sheet to determine the volumes of the various cabinets at two different depths. First I considered the minimum depth of 7.5 inches (I should go back and change this to 8, because 8 minus front 3/4" baffle and 3/4" back leaves the specified 6.5 inches internal depth - but I may build with 1/2" material instead of 3/4"), The sheet gives the volume of the enclosure and the angle of the side panels for a variety of back panel sizes. I also added a calculation for total volume (not angle) for a depth of 9 inches. Since a design goal is to make the overall depth as small as possible, this seemed like enough possibilities.

Here's a shot of a portion of the sheet - I have hidden many of the irrelevant columns used for intermediate calculations (though I forgot to hide a few of the useless ones). You can see that using the prefered minimum depth of 7.5 inches, a back panel of 18" by 18" gives me a total volume very close to target, but an angle of 38.7 degrees. I don't imagine I will find a good way to use a lock miter bit to make that angle joint.
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post #1034 of 1195 Old 04-05-2014, 08:05 PM
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Quote:
Originally Posted by HopefulFred View Post


Mike (Michael? sorry, not sure)

Either is fine biggrin.gif Most friends call me Mike, mom calls me Michael still tongue.gif

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post #1035 of 1195 Old 04-05-2014, 08:06 PM - Thread Starter
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Oh, I skipped J_P_A's question about the need for complicated joinery. The answer is that I want something that I can clamp lightly without brads. I don't want any fasteners in it. That seems like a silly stipulation, but it comes from mostly being worried that I'll try to use the brad nailer and eff it up.
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post #1036 of 1195 Old 04-05-2014, 08:21 PM
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Quote:
Originally Posted by HopefulFred View Post

Oh, I skipped J_P_A's question about the need for complicated joinery. The answer is that I want something that I can clamp lightly without brads. I don't want any fasteners in it. That seems like a silly stipulation, but it comes from mostly being worried that I'll try to use the brad nailer and eff it up.

As long as you can get it in place with moderate pressure something like gorilla wood glue or tight bond II should hold it no problem. Glue actually is stronger than wood in most cases. Using a router bit to increase the surface area and make it fit tight is a great idea I think. Seems easier to fit up, and stronger.

I love my cordless brad nailer though... I'd probably shoot it up if it was me biggrin.gif. I don't like shooting brads into 1/2" though, too easy to shoot out the side. 3/4" is thicker and safer.

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post #1037 of 1195 Old 04-05-2014, 08:30 PM
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Did you ask Matt Grant his opinion on modifying something like this ?
http://www.diysoundgroup.com/forum/index.php?PHPSESSID=49f7ef898d82f541105224c22e824ff5&topic=53.0

This might work well with your DNA 350 too.

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post #1038 of 1195 Old 04-05-2014, 08:43 PM - Thread Starter
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I haven't asked him about that - and I'm sure there are good modifications that could be made. I really was hoping for sealed - so I had thought I would do what Java did, here, especially since that's SEOS and DNA-350 (also NLA, but 360 is the same-ish they say) and the Delta 10A worked in a pretty small sealed box. The SEOS would be a good bit more money, and I've kinda become a little smitten with the coax idea. I'm going to keep reading and not commit just yet, hoping that the new coax designs Erich has coming down the pike might offer significant performance improvements at a budget I'm okay with.
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post #1039 of 1195 Old 04-05-2014, 08:54 PM
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I bet if you wanted to design a box and pick a driver MTG might help on the crossover. Sounds like a fun project. No reason you can't convert to sealed and save some enclosure volume. You should ask what he thinks about a driver choice for sealed surround speakers. Box design and modeling is the easy part. I'm too noob at crossovers though, and not sure I want to invest the effort to learn. I saw some 8" sealed in a slanted box based on the karma 8s but forgot who built them.

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post #1040 of 1195 Old 04-06-2014, 06:25 AM
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Wouldn't that be similar to their angled surround sound flat pack?

http://www.diysoundgroup.com/flat-packs-1/speaker-flat-packs/surround-flat-pack.html

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post #1041 of 1195 Old 04-06-2014, 07:35 AM - Thread Starter
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No, Joe - that's for pointing the speaker down into the listening area. I don't want to do that (much anyway), I want the cabinet to be shallower. That cabinet is shallower at the bottom, but only a little.
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post #1042 of 1195 Old 04-06-2014, 08:34 PM - Thread Starter
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Woodworking is fun, but let me tell you: if you work for hours at something and then test fit it and find that it doesn't fit... cue the sad trombone music.

In the interest of answering my own questions - specifically "Can the joinery like I suggested work? and "Is plywood or MDF preferred?" I decided to to see if I could build a mock-up of the speaker cabinet design I posted the other day.

I had both MDF and plywood scraps sufficient to make a small box, so I went for the plywood - figuring I'd be happier without the MDF dust. Having worked through most of the problems in constructing this unusual box, I feel confident that plywood is a very good choice.

So, the first thing to figure out was how to make the notch I wanted to join the slanted sides with the baffle. I've developed a couple tricks to doing it, but the heart of the technique is cutting partway through the panel with the piece laying flat on the table, then turning the piece vertical and running it over the same blade. To do that you should use a jig to hold the piece vertical and keep it tight against the fence. I built one last night and used it, but then it broke before I figured out the tricks to getting the notch sized right. It is all about where you put the fence, and there's no good way to measure. Anyway. I was able to get them cut pretty nicely, eventually:



The second thing to work through is the compound miter needed to fit the slanted panels to fit together. This is where I think I ran into trouble, but I think I can come up with a way to deal with it. I may need a tip or two.

I built this mock up without a back - I probably would have added one if it had come out better, and I will need to try again to figure out how to do it right, but I am not there yet.

Here's the pieces I made. The small square is the baffle in this scenario. You can see the rabbets I cut in the two slanted panels to make up for the fact that the baffle is recessed within the slanted panels, but mounts on top of the flat panels (you'll see better how they fit together in a later picture I think). I have to do that one kerf at a time - this is a simple operation I run here. I made all of these with only a table saw, using the built in bevel gauge, the miter gauge to feed through the pieces, and the fence - that's it. Ultimately, I didn't even measure anything (though I did on a few of the first iterations). Turns out patience and careful use of geometry are better allies than measurements, at least so far for me.




As I began to fit the pieces together, it seemed like they were going to fit nicely (of course I had been test fitting everything as I went, but not all of it together). Three sides and the baffle look pretty good.




But when you go to include the fourth side, the compound miter shows itself to be wrong...




So I ask you - is this reasonable proof of concept?

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post #1043 of 1195 Old 04-07-2014, 07:55 AM
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You are close enough biggrin.gif. Can't give up now. The plywood was a test. Now perfect it on those MDF scraps smile.gif

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post #1044 of 1195 Old 04-07-2014, 08:15 AM - Thread Starter
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Having slept on it, I see now that the cut I'm trying to make is the same as crown molding outside corner. I need to figure out how to do that with one cut with the stock flat against the table. Any tips?
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post #1045 of 1195 Old 04-07-2014, 08:19 AM
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With a little tweak to that side panel, that looks good to me. It would be nice if there was a router bit that would let you do this in one or two passes, but I don't know of one.

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post #1046 of 1195 Old 04-07-2014, 08:49 AM
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Jigs are your friend

Perfect world one of these, but DIY ones can be made



I also really like these over the dial on the table saw
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post #1047 of 1195 Old 04-07-2014, 09:38 AM - Thread Starter
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Those look nice, I'll look into them. Thanks.

But how do I figure the angles? It seems like numbers for crown molding are all based on the standard crown angles, but mine won't be that. Mine will be 38.7 if I stick with the 7.5" depth from the spreadsheet I posted earlier, but probably slightly different. Point is, I need to be able to calculate it, I think.
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post #1048 of 1195 Old 04-07-2014, 09:51 AM
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post #1049 of 1195 Old 04-07-2014, 10:09 AM - Thread Starter
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Man, oh man... I'll have to do some reading. Thanks for the links - my google-fu was failing me. Also, a quick look at the results of those calculators tells me I need to test the results, because getting differed numbers from all of them!
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post #1050 of 1195 Old 04-07-2014, 10:16 AM
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Ya calculating helps get you close but there are always tweaks when the actual cutting begins
Drawing it up in Sketch up I think will get you the closest and allow you to modify and measure the angles
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