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Multi-Way Conventional loudspeakers with crossovers

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Old 27th September 2016, 07:57 PM   #171
bwaslo is offline bwaslo  United States
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Default Appearance with different panel thicknesses

I'm leaning toward re-designing the sealed version to use half-inch (12mm) ply instead of 3/4" nominal ply (19mm). That would be one fewer size of pre-veneered (or not) ply to obtain, would allow for a little more internal volume for the box, and I think looks a little better, too.
Click the image to open in full size.

I don't think the wall stiffness will be affected much because of the rather narrow sizes of the top, bottom, and side panels, and the use of internal braces and stiffeners in general. The front panel construction would be the same, as that has to be done for the different layers needed on that.

I'm also making the cabinet 1" deeper, to allow for optional use of larger/deeper HF drivers (even though it looks like maybe the DFM-2535R00-08 will stay around, after all - they are on sale at Parts Express till the 30th, by the way, might be worth getting a few while they're cheap).
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Old 27th September 2016, 11:06 PM   #172
bwaslo is offline bwaslo  United States
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Default The Tymphany HF CD is no longer "discontinued"

The people at Parts Express convinced Tymphany to continue production and availability of the DFM-2535R00-08!

It turns out the driver they were going to replace it with was both (1) different and (2) more expensive, so not really a good replacement. Apparently it was selling well enough at PE and PE has enough influence to convince the manufacturer to keep it active. (thanks l, Parts Express)
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Old 28th September 2016, 12:55 AM   #173
sphykik is offline sphykik  United States
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That's great news! Glad to see the project continue as-is.

I've been getting parts together over the last few days, and furiously selling things on Craigslist to fund them. A banjo is next All of the drivers are ordered and shipped, and the waveguides are on their way as of this afternoon.

I'm visiting the lumber yard tomorrow with a friend and his truck. I was going to ask you about using all 3/4" plywood, but now will just buy 1/2"!

Time to start reading up on the crossover. I have plenty of experience soldering cables and laptop parts, but my electronics knowledge is not advanced. Got a TPA3116 amp on the way, to play with and potentially mod. Reading up on the MiniDSP 2x4HD also.

I don't quite understand how impedance works at the input of the amp, and I'm trying to figure out if I should use the miniDSP before or after the preamp. I'd like to use my TV as a switcher and go optical out to the miniDSP. But using the DSP as a "receiver" seems somewhat impractical (no visual indicator of volume, use of IR remote control changes volume 3-4db per click). Anyways, all problems for later down the road, but any input is appreciated.

Looking forward to making sawdust over these next few weeks. Thanks for the consistent updates!
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Old 28th September 2016, 04:39 PM   #174
Phantom250 is offline Phantom250  United States
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Bill, that's great to hear regarding the Tymphany CD. I already have some, ordered just in case they did go out of stock.
I have a question regarding the use of two mid ranges, would that help to increase the overall efficiency or would there be more to it?

Thanks for all your great work.
John
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Old 28th September 2016, 05:16 PM   #175
bwaslo is offline bwaslo  United States
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Hi Sphykik,

(can I assume that there's a great story behind that name?)

Quote:
Originally Posted by sphykik View Post
I'm visiting the lumber yard tomorrow with a friend and his truck. I was going to ask you about using all 3/4" plywood, but now will just buy 1/2"!
That would be a good plan, if you are building sealed versions. If you are going after cosmetics, look for hardwood pre-veneered ply -- I'm partial to "red oak", but there are usually several types available. Get some iron-on veneer edge tape, too.

I've been working up clean drawings for the 'sealed', and since you are already getting lumber, attached are what I came up with (so far) for cutting plans on the plywood panels. It might help. I should have the rest of the drawings up sometime today or tomorrow.

Quote:
Originally Posted by sphykik View Post
Time to start reading up on the crossover. I have plenty of experience soldering cables and laptop parts, but my electronics knowledge is not advanced.
There's not too much you need to learn, just how to solder parts and try to keep inductors away from each other.

Quote:
Originally Posted by sphykik View Post
I don't quite understand how impedance works at the input of the amp, and I'm trying to figure out if I should use the miniDSP before or after the preamp. I'd like to use my TV as a switcher and go optical out to the miniDSP. But using the DSP as a "receiver" seems somewhat impractical (no visual indicator of volume, use of IR remote control changes volume 3-4db per click). Anyways, all problems for later down the road, but any input is appreciated.
The output impedance of the 2x4HD should be ok with about any amplifier or receiver input, it is pretty low. In the living room here, I drive optically from a TV (which is connected to a media center box via HDMI) to the miniDSP 2x4HD, and from the miniDSP right into power amps (I'm using two ICEPower 200ASC modules at the moment).

The lack of volume indicator is an inconvenience, but a partial workaround is to set the TV's internal speakers to 'OFF' and program the miniDSP to use the same volUP and volDOWN remote codes that the TV uses. On my TV, that causes the on-screen indicator to still show the volume increasing/decreasing, though the TV doesn't make any sound itself. The miniDSP sees the codes and does the actual volume control. You don't really know the volume setting, but you can see that the remote is sending something out at least and what direction it is going. I haven't checked but I think the volume steps are less than 3dB (doesn't sound that course, seems kind of slow, actually).

Some people would tell you (and I would have even told you, too, till I actually tried it) that using "digital volume control" into the DAC (which is inside the miniDSP, right before its outputs) will lose resolution when below full volume. But I don't hear resolution being lost even at low volume, I think any loss is down below normal domestic room noise. I think it would depend on gain structure, and if your amp has about the typical gain level of ~26dB, you should probably be fine.
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File Type: pdf Sealed Box Panel Cuts.pdf (375.8 KB, 41 views)
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Old 28th September 2016, 05:25 PM   #176
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by Phantom250 View Post
I have a question regarding the use of two mid ranges, would that help to increase the overall efficiency or would there be more to it?
It wouldn't affect the efficiency in general, that would be set by the least efficient drivers in the system (which is almost always the woofers, and is in this system, too). Two midranges would allow for higher volume in the midrange before distortion, but again, given that the woofers would be more likely to run out of gas before even the one midrange would (assuming music signals), I don't really see the point.

But if you do want to go dual midranges, you'll need to change the crossover (both impedance and needed attenuation change - not difficult, but needing attention). Also, the baffle would need to be taller so that the extra midrange lump sticking out of the top of the waveguide has somewhere to fit behind.
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Old 28th September 2016, 05:43 PM   #177
bwaslo is offline bwaslo  United States
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BTW, I think I never got around to mentioning it, but the "Durham's Rock Hard Water Putty" worked very well for filling the volume between the driver and the waveguide. "Rock Hard", they aren't kidding, it's like a piece of ceramic.

The only down sides are that it takes adjusting to get the consistency right (add water -- too much!, so add more powder -- too much! so add more water....repeat...). And that it is kind of messy. The stuff is yellow and leaks down inside the waveguide, so you have to make sure to clean there with a wet rag before it hardens (which happens before long). After it hardened, I took a black felt-tip marker to blacken any of the yellow that showed through the midrange ports.
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File Type: jpg Durhams.jpg (64.4 KB, 549 views)
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Old 28th September 2016, 06:10 PM   #178
bwaslo is offline bwaslo  United States
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I forgot I did this last night

-- here's an "alternate" panel cutting plan for the half-inch ply, based on 24"x48" sheets. For those of us who are panel-size challenged (I can't get a 48"x96" or even a 48"x48" into a Honda FIT!).

Actually, this may be a better (better use of wood, easier to cut) plan even if you can transport larger panel sizes --

Click the image to open in full size.

-- so, disregard the first page in the just-posted pdf from this morning

Bill
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Old 29th September 2016, 10:26 AM   #179
SMathews is offline SMathews  United States
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Quote:
Originally Posted by bwaslo View Post
I use HornResponse to figure the midrange port sizes and lengths and to check whether their locations will work ok. Cut and try would make you go through drilling holes into a lot of SEOS15 horns to get it right! I don't model the tweeter response, though, since I know (have measured) how that works on an unmodified horn.
Thanks Bill. How about the "array effect of the woofers"? Is it possible to simulate it ?

Simmonds
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Old 29th September 2016, 05:25 PM   #180
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by SMathews View Post
How about the "array effect of the woofers"? Is it possible to simulate it ?

Simmonds
Hi Simmonds,

There are a couple of ways to do that. You could use PCD (using the same driver type for "woofer" and "tweeter", at same height, with varying horizontal offsets) and watch the off-axis response vs frequency. Or calculate what the relative delays will be due to different distances from drivers (via Pythagoras, from 8th grade geometry, and the speed of sound) when you are off at at some angle, then put those delays into XSim. You could even use a spreadsheet, calculating the sum of delayed sine waves. In any case, assume the drivers are omnidirectional (which they should be for the most part at lower frequencies, though really, aperture and baffle sizes will still have some effect-- but omni is good enough for approximating). You also have to know about where you want the array to start kicking in, since you want to blend into that from where the waveguide's directivity starts to drop out.

Then, put woofers and waveguide on a baffle and take measurements of waveguide and woofer array at several angles. Finally, design the crossover for flattest falling response at those horizontal angles from the baffle, consistent with what ranges the drivers can cover with decent overall response smoothness and power handling.

I also did the same process at first for vertical off-axis, but it turned out that the trick for that was to get the woofer apertures as close to the waveguide center as possible and then make sure that the phase responses of the woofers and midrange waveguide track each other though the crossover range. Most of the crossover design time was spent getting that phase tracking along with the requirements for horizontal off-axis responses.
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