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Old 04-11-07, 01:07 AM   #21
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Coby
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Line arrays....would love to do one; definately not in the plans for this problem. If I can do it as a twoway I can come up on the budget per speaker, since I won't have the additional $100 to $200 per speaker it'd cost for the amplification (minimum). I'll look and try to find some drivers that could work.

Remember, one of my firmest criteria is the form factor...picture three big center channels across the front, and similiar drivers for the sides and rear (but those can be oriented more vertically. I'm picturing using aluminum tube...like a 20" long 12" diameter for the woofer chamber. (I know...resonant...that'll be addressed). I've got access to a waterjet table and full CNC mills and lathes, and possibly a complete carbon fiber shop (need to talk to the shop manager and see what kind of access I can get).

Here's a couple of pics (if I can get the posting a pic part right):

btw, the enclosure1.zip is not a zip. rename the extension from 'zip' to 'edrw', then you can view it with eDrawings (there's a viewer available on the web for free). It's a pretty handy li'l tool.

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Last edited by cobyh; 04-11-07 at 01:15 AM.. Reason: pics

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Old 04-11-07, 01:26 AM   #22
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Coby
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Here's some shots of the room. Don't mind the mess; all the electronics just got relocated and the new PJ went in. Most of the electronics will be housed in the basement, so amps with fans on them are no worries. You can see part of the reason I need some oomph...it's a huge area to fill, and I took the shots from inside the dining area, which isn't shown, as well as the pass through kitchen.

Note the area between the screen and the halfwall. That's thankfully about ear level when seated. I have to fit my drivers there. The chamber can go behind it, either on it's side, or behind the screen pointing upwards, or downwards...there's some options.

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Last edited by cobyh; 04-11-07 at 01:28 AM.. Reason: forgot sumphin'

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Old 04-11-07, 02:46 PM   #23
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Ah, I'm glad you brought that up, though I think you might be looking at his example of a circular baffle, where right now this has no baffle other than the edge of the driver itself. I can emulate the spherical transition pretty easily with this, without changing the enclosure design at all. That was an informative site; I'd bookmarked it some time ago, with respect to baffle effect. It's part of what is driving this design concept.

RE: art....I'm not about art. I'm really a function over form kinda guy; these will likely offend the sensibilities of a few folks. I'm just hoping my wife'll buy into them.

One advantage of this type of enclosure design lies in the fact you decouple the baffle design from the enclosure. As is, there is no baffle. The case that produces the most ripple is a circular baffle; these don't have any baffle to speak of; just the driver's edge itself, and the effect from the other drivers in close proximity as well as the effects from the screen above and the halfwall below. However, with this design, you can change the baffle out at will, since it's separate from the enclosure. Picture a baffle with a star pattern centered on each driver, or some organic shapes....I can make several of them and then test to determine it's effect on the FR. , we can even tailor the FR curve acoustically, at least on paper, by swapping out various baffle designs. They'll attach to a ring around the driver tubes; flush mount, change a coupla screws and Bob's your uncle. Material can be changed for the baffle as well, since with access to a waterjet table, I can quickly cut out complex designs in just about anything (except MDF...those don't like water too much. Go figger..)

If I have some extra time tonight I'll model up what I'm talking about so it's more apparent. I'm expecting a much smoother curve than from a rectangular baffle, since a cylindrical housing is nearly ideal, but I'm betting it'll change quite a bit once it's in place. Another consideration I had was building one continuious baffle across all three front speakers (LCR) and mounting the screen onto it so it's flush, and fairly flush with that halfwall below. Then I have one baffle that's 9 feet long and 10 feet high or thereabouts, and contigious with the floor on the bottom and within inches of the angled ceiling on the top. I'm a bit scared of how that'd sound; that's basically an inwall application.

Some other advantages of this enclosure design are
1. Less in the way of standing waves
2. Much lighter weight to acheive the same rigidity
3. Very little in the way of panels that are acting as transducers
4. Easier for fabrication (at least for my situation)
5. Can be made very durable


I've been looking at 2 WR125ST's as a midrange, crossing over around 2800 with an XT19, with a 10" woofer to handle 60 to 400-500. Two 8" woofs might be a better choice but a single woof simplifies construction and affords more configurational options for the wall mounting of the other 4 speakers (surrounds, r,l,rears)
Thoughts on that? I'm concerned about getting them to the 110db mark cleanly, but I need to start modeling drivers and see what at least looks good on paper.

Positioning the tweeter under the midrange as shown....most alignments I've seen have it above the mid. I've seen some that have it below. I'm assuming there's some effect, possibly directing the HF at a slight downward angle if I did it as shown? (from the boundry reinforcement of the driver above it). Is that correct?


Last edited by cobyh; 04-11-07 at 02:56 PM.. Reason: clarifying

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Old 04-11-07, 02:50 PM   #24
ssabin
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Coby,
d I am in a similar boat as yourself, although I don't expect to make up my mind on anything soon. I have too many other honey-do projects to complete before I get to play with building speakers.

I too am amazed at the lack of active designs that have been published for the DIY.

I am currently looking hard at implementing an active crossover for one of the TMWW 3-way designs using Dayton RS drivers at HTGUIDE, or doing my own active crossover on a GR-Research AV3, which is a 2.5-way speaker. Some the RS designs on HTGUIDE give you the individual driver crossover functions, so all you have to do is implement those!

After reading a ton about this, it appears that the biggest sonic benefit in going active is in separating the woofers from the rest of the speaker, and an active between the mid and tweeter doesn't buy much over a passive corssover. However, if you are going active anyways, especially if you are going to build your crossover with discrete opamps (my plan), you might as well do the whole thing.

I keep waiting for a GR-Research design that uses the new M-165X driver in a 3-way design. Perhaps I'll just email Danny there, explain what I'm planning on doing, and see what he suggests. He's great about that sort of thing from what I've read.

At any rate, good luck in your quest, and I look forward to reading about what you end up with. The only difference between the two of us is in our speaker size limitations - I intend on building 7 towers, with the center tower being perhaps smaller to fit underneath a future screen. I'm curious to see how well this works out, and how easy it is to implement a good design, or at least a new implementation of an existing proven design.


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Old 04-11-07, 05:11 PM   #25
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
Active designs don't really need to be published because they are so flexible. You can mismatch
drivers on purpose and still come out sweet. Everything I do is all active, it's too easy to get
great sound if you know how to turn knobs and use your ears
Today 2:50 PM

I suppose that's true. But it wouldn't take that much work to write down someone's optimal settings for their crossover design. Discrete implementation would be very cheap too. The entire design cycle would be much quicker than for a passive crossover as well.

If I ever get to the point where I'm going to build 7 identical tower speakers, I will undoubtedly buy a 2496, or whatever the rage at that point in time. But hopefully, I'll be able to use that to translate the optimal crossover settings into a discrete Op-amp design that can be replicated less expensively. Maybe I'm really in a minority by wanting to do DIY active AND build my own boards and amps!

Well, if I ever get there, I'll be certain to document the journey - there has to be someone like me around!


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Old 04-11-07, 07:31 PM   #26
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
thylantyr wrote: View Post
110dB[c] spl goal. From what distance? What frequency range?
It's easy to hit higher SPL from those 1m reference points but harder to do
from a greater listening distance. It's easy to hit those numbers with bass,
but it becomes harder to reach playing midrange and even harder with
tweeters.


SPL aside, look into getting 1" dome tweeters as they will have more ability.
Isn't the XT19 a 3/4" dome? If so, go bigger.
Sorry, I thought it was obvious; I meant 1 meter away, and full frequency of course. The one meter measurement is the only one that gets published with any consistancy; it would be a bit hard for manufacturers or other DIY'ers to publish numbers of spl levels experienced in my Lazyboy, and I don't think my wife would like the constant stream of people coming into the house bearing drivers to do that test.

I disagree with the comment disregarding the 3/4" dome tweeters. They fit my criteria better; the dispersion is more uniform and they're more effective crossed over higher than you like. If I remember right, the XT19 is around 91db efficient, crossed over at 2,500, and with my crossover being a tad higher than that, I doubt it'll be more stressed than that test case.

Anyhow, I'll see if I can round up a couple for the test speaker and see what it sounds like. What else is out there that's similiar to the CSS WR125? A bit more efficiency would be nice, but the distortion and off axis performance looks great.


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Old 04-11-07, 08:00 PM   #27
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
ssabin wrote: View Post
I suppose that's true. But it wouldn't take that much work to write down someone's optimal settings for their crossover design. Discrete implementation would be very cheap too. The entire design cycle would be much quicker than for a passive crossover as well.

If I ever get to the point where I'm going to build 7 identical tower speakers, I will undoubtedly buy a 2496, or whatever the rage at that point in time. But hopefully, I'll be able to use that to translate the optimal crossover settings into a discrete Op-amp design that can be replicated less expensively. Maybe I'm really in a minority by wanting to do DIY active AND build my own boards and amps!

Well, if I ever get there, I'll be certain to document the journey - there has to be someone like me around!
I think the other aspect is folks can find tons of material on passive designs from those in the know and basically ride their shoulders, whereas there's nowhere as much as on designs using active crossovers and that's intimidating. It's new (well, not really) and it's not readily apparent how easy it is, or how inexpensive. I don't think most folks would shirk at the idea of spending $70 to $100 a speaker for a good quality crossover, and you can do the DCX for that much these days. But they don't know that...Need pictures and screenshots and stories and cost analysis of finished projects and test results....there's just not much out there. You can help with that. :-)

I love the what if aspect of it....I want to hear for myself what the numbers mean; I want to change things and just listen. Good stuff...

Love your idea of building your digital active crossovers yourself. What kind of cost per speaker (threeway) do you envision?


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Old 04-11-07, 08:39 PM   #28
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
Love your idea of building your digital active crossovers yourself. What kind of cost per speaker (threeway) do you envision?

I'm thinking, $10-20 per speaker is attainable for the active crossover for a 3-way, depending on how much is needed. Probably a bit more if you have to also figure in a power supply per speaker for the amp and crossover, but that's more allocated cost, and depends how all the electronics get packaged.

I used to design Bessel filters for accelerometer data processing on combustion engines, and although I haven't done that in quite some time, it doesn't seem like it would take much to put together a cookbook of active filter designs using op amps all in a single Excel workbookl. Just plug in the target frequency and spit out the resitor and cap values. To keep it simple, just have seperate sheets for different types of designs (LR2, LR4, BW2, BW4, etc). Throw in an all pass stage and some baffle step compensation, and designing the thing would be pretty straightforward. Not only that, but 1% resistor tolerances make it easy to ensure the frequency points are right where you want them. The speaker designer could pluck out which stages are necessary and have a complete crossover done.

I still think you'd want a more flexible active crossover to get through the design stage, but once you're there, go discrete!


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Old 04-11-07, 10:11 PM   #29
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
thylantyr wrote: View Post
I still don't see your vision exactly. Your CAD drawing shows tweeter, ~ 5" midrange,
and dual ~ 7.5" woofers. Is the large tube airspace for the 7.5" drivers or is this another
isolated chamber for the 10" woofer(s)? If so, this is a 4 way module ?
Don't worry about the driver arrangement in the drawing; it was something created in about 10 minutes to give a general idea of the enclosure and a possible option, and to help you understand that a 6 foot tall tower of drivers won't fit here. Dual 8's, a 5" mid 'n a tweet under 3" for outer flange isn't what I'd hoped for...if I can do it with a single woofer and use a mid and tweet that have their own chamber, life's easier. But that'll be what it'll be. what part of the criteria are confusing? I can restate some of it...it's a 7 channel equal amplification, equal speaker system, direct radiating, +/- 3db from at least 80 to 18k hz (lower is nice, higher is probably entirely unecessary), low distortion (linear and non linear, harmonic, im), excellent! dispersion characteristics for a wide and clear soundstage, using active digital filtering and eq'ing, and able to produce the same tonal quality across all 7 units while conforming to at least two distinct packaging requirements (lcr vs the 4 onwall units). That leaves quite a bit up in the air, I know, but as decisions are made more will be nailed down. Part of the reason I'm leaning towards a threeway is dispersion related...much easier to have consistant dispersion characteristics with three sizes of transducers across that frequency range.

BTW, all of these speakers actually will be four way's....all will be rolled off to a LLT sonotube subwoofer using a single Avalanche 18" driver. But each individual unit will be a threeway on it's own.

Any of ya'll readers have any experience with the CSS WR125?


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Old 04-12-07, 09:18 AM   #30
ssabin
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Re: 7 speaker home theater DIY project with active crossover...would love discussion


Quote:
thylantyr wrote: View Post
If I gave you $250 to mimic a DCX in performance and build quality, it's hard to do.

The whole point is that once you are done using a 2496, you really don't need all of that flexibility. $250 is a lot to some folks for the crossover function for a pair of speakers. Most of use here are focusing on speakers pairs, but the OP and I are thinking about 7 identical speakers.

I'm not saying I am right and you are wrong, but despite the increasing value and power in modern DSPs, there is still a (shrinking??) place for DIY electronics too.


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