Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"







I didn't expect it to take as much time as this did. Not even "finished" yet and I probably have a full 8 hours of labor per speaker all together here. All the little details add up. However, I'm really happy with the results. The removable baffles are very useful and I'm probably going to leave the crossover just wire nutted up for awhile so I can make changes if I want to.

The crossovers are basically just held in place with the dampening material which is this semi-stiff poly stuff I found at an upholstery supply house in the scrap bins. (they gave me what would easily have costed $25 to buy the same "quantity" at a hobby store for just $10). I don't have any acoustic reason that I chose this particular material to use as the internal dampening. It's just something I found and decided I wanted to try because it seemed like it would be easy to work with. Turns out it's very handy because it holds a shape like foam (springy/spongy behavior) but also sort of "clings" to the wood grain and itself such that all I had to do was lodge the pieces in there and it all holds itself in place. I can make adjustments to the amount of stuffing easily with this and the crossover is actually held snugly enough by this stuff "pinching" it into place that I can invert the speakers without anything moving.

Against my initial judgement and out of haste I did not use any sort of gasket material anywhere. Everything is precise enough and the fastening methods strong enough (tweeter is 5-screw, woofer is held on by socket drive 10-32 machine screws into T-nuts, front baffle has 6X 10-32 socket drive screws with wide washers, rear has 4 of the same) that everything sealed up nicely without.

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Forgot about the holiday so the sub exchange is still waiting on my being able to get a-hold of PE. Hopefully I'll remember to call them first thing in the morning.

[SirNickity]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Well?? How's it sound? :-) That's awesome you had all five available for audition at once. Hope it worked out OK...

I know what you mean about details. I'm usually in such a rush to hear a creation that it will sit without gaskets or cosmetic stuff for half a year before I get around to doing anything about it. By then, I'm either happy with the design or not. I guess it does save me the trouble of finishing a build that I don't like.

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

They sound pretty good so far. Without the sub they are being run full range, and thus, are not really operating in their intended application.

There is some usable extension to 60hz (below tuning), and even with Audyssey EQing up the bottom end (~+4dB 60hz) to try to makeup for the lack of low end response, they manage to sound very effortless at drive levels that would start to make many small speakers complain. With audyssey turned off and everything set flat they sound pretty good also, albeit, with sharply falling response below ~70hz, thin.

Looking at the amount of correction that audyssey is applying suggests that they are indeed fairly flat. The areas that audyssey is boosting are areas that simulation suggested dips in, and the areas it is pulling back are areas that simulation showed would be a little hot, so I feel overall quite good about the accuracy of my unusual procedure for simulating the complete speaker. Also, Audyssey set the speaker levels down about 3.5dB, which suggests to me that these speakers are indeed very efficient. (I'm guessing the system adjusts the speaker level so that "0db" on the volume control matches a reference level at the listening position or something, but I'm not entirely sure).


Wife and I watched "Star Trek" (one of my favorite movies) last night, and I understood a few passages of dialogue that had always eluded me in the past. I mentioned this and my Wife agreed that it was the first time she had understood a few pieces of dialogue as well and she is normally VERY good at understanding dialogue. The warp jump "boing" sound was, like a natural firework, executed without any noticeable compression. Even with the speakers run full range with the low end EQed up there was no problem. Mind you, we were NOT listening anywhere near reference levels. (Probably rarely ever will, but the design goal was still important to me).

For cinema speakers, these are a good compromise for being able to play loud and clean enough. however I believe they could be better for general "hifi" with some crossover adjustments. My biggest disappointment, and this is something I sort of expected after pulling the trigger on that crossover design (wider crossover region centered ~2K), is the lack of that hifi-point-source disappearing act that some speakers pull off really well. These don't "hide" themselves as well as I believe would be possible with a lower narrower xover region. I am tempted to go ahead and work up a slight modification to this crossover. I can probably re-use most of the same parts, and just swap a couple and add a component to move the crossover down a bit and tighten up the region (raise the "Q" of the circuits).

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Talked to PE this morning (Tuesday) about the UM10. Man this is a great company!

They have already shipped the replacement, and have sent me a prepaid return shipping label for UPS. VERY impressive service! I'll get the return unit on the brown truck as soon as possible.

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Eric

[SirNickity]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

That's a very well written review. Keep us posted.

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

I have already received the replacement sub!

I picked up screws and more plywood, will be working on the sub over the weekend. Pictures will be coming soon.

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Horn SUB!!!

In the last few days I wound up changing the design a bit.... As it would turn out. The horn end is a bit larger than previously planned. The result is basically a transition to higher SPL and less low end extension. The 1W sensitivity from 40-80hz is now about the same as my mains, ~91-92dB range. This should make for a very good dynamic match to the mains. The last (lowest) acoustic impedance spike of this horn is right about 30hz now, with useful loading to ~25hz. (20hz is acoustically unloaded for all intents and purposes, so this falls short of what many people would consider a requirement for a HT sub, but I think I can live without the last few hz there). If I decide I want the extension back, the solution is actually pretty easy.. I can pull the thing apart and "trim off" about 2" from the rear, re-position that last vertical baffle, then "trim off" about 2-3" from the bottom as well. Shrinking the last segments of the horn would buy back the extension at the cost of some efficiency. This way I can try this design out first. It's easier to cut something smaller than larger ;)







This is my first horn sub build and I am again astounded at the enormous amount of work it takes to complete one of these. If you have ever made a horn sub; hats off to you sir! these are a LOT of work. Like my other speakers, it has been brought in for a test run. "Finish" will be later...

I intend to make a cover baffle from another layer of the same ply such that the only "visible" thing from the front is the driver surround and cone, the mounting flange will be hidden. At that time I will finish flush-trimming the horn-end and then give the "aesthetic" cover baffle's horn-end hole a round-over.

Currently it's still missing a lot of the details internally and will be taken apart later on to install corner treatments on all bends (all outside corners are just square right now). Nothing has been glued at this time. Screws about every 3 inches and everything is a pretty snug fit. I'd like to maybe try a gasket forming material, rather than glue for this build, so that I could get an even more "firm" and "sealed" fit everywhere than without, but with the ability to pull the unit apart. I need to do some research to this end as I'm concerned that many gasket making materials would act more like glue on wood, (unsure). I also intend to cram some more wood into the chamber area to tighten it down some more. I *may* install a brace down the middle of the first "segment" of the horn there to both firm up the front baffle and to effectively increase the compression ratio even slightly higher. (currently it's about 3.5:1). So yea, there's a lot more work to be done.



The horn is sitting out in the middle of the dang room just for hookup and testing (seems to work fine!)... I need to move some furniture around to get it against a wall. After spending about 15 hours today working on this I wasn't inclined to move furniture.

[richard t]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

NIce Job. Especially on the dados.

[Derekj]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Nice build! I like the natural finish on that plywood. Would look sharp with just a clear finish that's for sure.

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Yea for $38 a sheet this stuff is not bad looking at all. The sub-sides will probably be painted black at some point because there are just too many screws to do anything else. As much as I like the light wood look all the furniture we wound up with is pretty dark finish, so that will probably wind up setting the "tone" for the direction of the stains/paints.

I made a last minute decision on the screws for the sub.. I was originally planning on some heavy long screws, like #8-10 deck screws with torx or square drive... then realized that perhaps I would be better off in the long run with a larger number of smaller "finishing" screws. This proved to be a good move. I didn't split or damage the plywood anywhere with a screw. The screws I used are a #6 cabinet/trim type "finishing" screw. Fairly short, ~1-5/8". Stronger than typical black "drywall" screws with a slightly smaller head, didn't break any of them. With proper pilot and through-drilling these grabbed very well and the heads sink below the surface easily without countersinking the cut. I can puddy and sand up the screw holes before painting and be in pretty good shape I think.

[Sidi]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

I have the same lamps you do... coworker gave them to me. Lol.

[Cajun Jeff]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

In regards to the "Chinese pine" construction material.

I recently built about 24' worth of upper cabinets in my workshop and garage. I used pre finished Chinese birch plywood. 3/4" for carcass and 1/4" for backs. It was natural color with a durable and slick clear poly finish. I used alder for the face frames.

I was very pleased with this ply as I worked with it. Dedicated plywood blades for the saws produced slick cuts!

[SirNickity]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Awesome. I've built a few horn subs now. Yeah, they take forever, but they sound so good.

How did it go with the mirrored dados? I did that on a recent build. Had to widen a few of them due to not-quite-perfect alignment. I'm sure it was a combination of measurement error on the dados, and the inside panels not being perfectly perpendicular. CNC would sure make things easier!

Maybe it's just the scale of the picture, but that seems pretty small for a 10. Are you really getting to 25Hz with that?

My personal opinion... 30Hz is the highest I ever want a sub rolling off. The lower the better. Every time I hear someone say "ehhh... for music, 40Hz is plenty", no way. At least, not if you like electronic music -- and not just dubstep. I have a horn that rolls off sharply below 40. It sounds fantastic down to that point, but I frequently miss that last bit on bottom. I could probably live with 25Hz though. ;)

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Yea the dado jointing was sort of messy... It was a learning experience as I went along so to say the least, if I were going back to do it again I would have done it differently..

The method that occurred to me part way through cutting the dados is as follows: Since most of the segments are parallel to edges of the panel, I set an edge-guide on the router, then performed the cut on both panels back to back with the edge guide locked to the same position. This combined with what was actually a fairly good layout with pencil on the panels to begin with, and some white knuckled sober driving for all of the angles (I didn't want to mess with trying to come up with jigs), and everything worked out fine. Also helps that I am using a 0.75" cutting tool and 0.700" thick ply ;)

Keep in mind that even if the dados are perfect, the sides aren't going to just slip on perfectly. There's too much other error that all adds up to panels that aren't "aligned" perfectly with the opposing panel. I removed the top and bottom of the box with the internal baffles all screws to one side of the box, so I could reach inside and "adjust" the panels to drop into the slots of the side I was trying to install. I eventually resorted to sitting on an end that was fitting and smacking the panel with my fist (precision adjustment fist) from one end to the other until it popped into place. I'm hoping that leaving everything screwed up in the current position will make things fit more comfortably when I take it apart for modifications later...

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This is a fairly good approximation of the current horn. There are MANY ways in hornresp to produce a rough simulation of the physical thing I have created and they all produce similar results (as they should). And YES, by all of what is "normal" for most horn designs, this is small for a 10" driver, however, I am compensating for size with displacement and amplification.







Note that while response is -6dB@30hz and -12dB@25hz, there is still substantial acoustic loading at 30hz (a displacement minima and horn resonance). The acoustic impedance at 25hz matches other minimas in the design, below that the acoustic resistance falls on it's face. The result of a relatively long "squashed" tapered line like this, is that the transition below the last resonance from loaded to unloaded is not as abrupt as in more "open" horns/lines, or in traditional reflex enclosures. In hornresp, the "departure-angle" of the simulated displacement coming out of the last minima can give some indication as to how much useful range there is below tuning in a design. Most often, acoustic loading is still present until predicted displacement rises above the next highest displacement maxima. The useful extension below tuning is ignored in most designs because it is so abrupt and narrow that it's not worth cliff-walking the edge.

I have run test tones. With room loading and poor human ears it sounds roughly "flat" to 30hz, 25hz is absolutely there but a bit quiet, 24, 23, 22, fades VERY fast.

....

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Watched a couple movies since getting the sub put into a better position and running audyssey through a full 8 position calibration. My "middle of the road" approach to BSC seems to have played out just fine. I see audyssey EQing DOWN the low frequency range on the center channel, and UP on most other channels. I believe I pinned down a middle ground well enough.

The system has the sort of effortless theatrical slam that we "expect" from a commercial theater, but with better extension on both ends of the spectrum. The bass digs plenty low but having experienced sub-30hz movie effects now I am developing a bit of an itch for "deeper" still. I'm going to leave the horn alone for now as anything lower would just **** off the neighbors. This thing shakes the walls and floors 2 stories up with only the first "signal" light on the crown flickering (~10W or less I'm assuming).

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I'm sold on the idea of using bass horns to extend the SPL of an otherwise low efficiency, high displacement driver. The UM10 doesn't fit what most people would call a "good" driver selection for a horn sub, but in my limited experience thus far I think this is a winner of a combo. Most bass horn designs seek a driver based on Qts and Fs. I was looking primarily at Vd and Vas, specifically for a driver with the highest possible Vd/Vas ratio.

I'm also sold on pro-sound midbass drivers. They sound "hifi" enough to me. I think once the dynamics are unleashed these may actually be "cleaner" than many hifi approaches. Matching EBP of the midbass to a desired passband seems to be a very good solution to maximizing the utility of the midbass selection. I look forward to using pro-sound drivers in future builds.

Eric

[mdocod]

Re: Build Log. Compact Home Cinema Speakers and Sub. Semi-Pro-Fi. "From The Ashes"

Starting to work on "finishing" a pair of them...




Sooo... The plan is something I have no experience with, and really have no clue if this is going to work out. I did crude version of what I would like to do on a test piece, and believe I can make this work...

Rustolium cabernet stain, flat black valspar interior paint (a basic primer/paint combo), and rustolium gloss. Using one of the nicer "blue" masking tapes to slap black trim on the cabinet.

The stain is the easy part, and I'm learning now that I really didn't even need to tape for it, the valspar would have covered it over no problem but oh well...

I sanded the "butts" with 120, 240, 500, and hit the flats with the 500 to clean up some discolorations from me touching them etc. I did some filling work here and there and learned a few important things about wood glue. I won't get into too much detail but if you are working on prepping a surface for painting/staining, don't use wood glue as a mechanism for filling in the low spots. It will cause more problems than it solves... I've since picked up some more traditional "wood filler" material that I will be using when I do the next "round" of speakers.

I just did my 3rd coat of black on the rims of the front baffle, and first coat on the boxes. This is going to be a long process of painting and sanding to get a "flat" enough result for the finish I want. I am going to run the gloss right over both the stain and flat black, which will (hopefully) turn the flat black glossy. The trouble is that, while a few imperfections on stained wood is no big deal, the black needs to be just about dead nuts perfect before I start to gloss this up if I want it to look any good. This is going to be tricky but I managed to get some more wind in my sails to deal with the long process when my Wife saw what I was doing. She is actually pretty excited about how they will look and thinks it's a great idea.

Eric