New Home for the BG Ribbons - Part 27

[Johnloudb]

Okay, I'm sure you're right. I knew the BG used 350Hz quasi LR4, I just have this thing for 1st order crossovers. Our little Thiels were 1st order, of course. And our current speakers Nelson/Reed 804Bs have a dual slope crossover. Then there's the Duntech (1st Order) which I used go listen to on occasion at a local Hi-Fi store. My favorite speakers have been 1st order. Don't know what, if anything the 1st order crossover contributed.

I'm sure I'll get a quick lesson in crossover design once get this speaker together. I'll probably try a dual slope crossover at 500Hz and see how that sounds, and then compare to an LR4, or such.

[Dennis H]

Nobody builds 1st order acoustic crossovers, even Dunlavy. The best they can do is '1st order for a while.' Somewhere in the stopband, the driver's natural rolloff is going to take over and it won't be 1st order anymore. That said, 'for a while' may be good enough if the XO frequencies are close enough to each other.

[Johnloudb]

Yeah, I'm not sure what qualifies as "First Order." Dunlavy once said that to achieve sound resembling the actual event required a first order crossover and +/-2dB frequency response. I'd like to keep it first order at least an octave, but of course there's other considerations like comb filtering that might mess up my plans.

[ThomasW]

Good topic for a separate thread.

[chasw98]

Instead of digging a trench (which I won't even ask SWMBO about) what do you think of the idea of using 3 to 6 inch tall sawhorses to hold the array close to the ground? I can get a couple of sets of sawhorse brackets for about $12 and cut up some 2 X 4's to make a sawhorse that is 4 inches tall by 24 inches wide and lay the array on that. Then suspend the microphone from the air at a distance of 1 to 4 meters. Do you think it is worth the time?

[ThomasW]

Do you think it is worth the time?

Not really....... :B

From Whittaker's research we know it's problematic getting good line array measurements even in 'ideal' conditions like the huge gym he used.

We know from single driver testing the Nomex drivers are very good. We know the same about the Neo series.

At this point the only tests of 'consequence' are those used to setup the system in the listening room. We know from your first tests of the midwoofer line those plots looked 'goofy' compared to tests of a 'normal' loudspeaker.

So I think we should focus on finding a testing method that gives usable in-room data for dialing in the system. Whether that's a function of working with the gating or some other variable should be the focus of our attention.

[chasw98]

Yes, after refreshing myself with Whittaker's findings I saw that he 'interpolated' FR graphs because of all the jaggies in the measurements. He took his best guess and only identified really out of whack anomalies that didn't look like they belonged in the graph. I have a plan for a pair of baffles that is fairly fiinalized in my head and partly on paper. It will be 21" wide by 84" tall with a 65" by 9" inset for the Neo8's and Neo3's. I am going to start fabrication this weekend.

[Hank]

Chuck, you're progressing! Will your 65 x 9 insert be plexiglas? Do you plan to surface mount it, or route an inset deep enough for the plexi and mounted Neo's to drop into the inset so that the Neo's faces will be flush with the surrounding MDF? I've been thinking about an inset and then using a perimeter gasket to mount a plexi or aluminum insert onto so that it's isolated from any MDF baffle vibes. Looking again at the material thickness that "well nuts" are designed for, you could attach the Neo's to the plexi with "well nuts" and not have to gasket-mount the plexi. Dennis recommended well nuts for isolation in post #108. Thanks for that, Dennis - I don't remember seeing well nuts before.

[chasw98]

Chuck, you're progressing! Will your 65 x 9 insert be plexiglas? Do you plan to surface mount it, or route an inset deep enough for the plexi and mounted Neo's to drop into the inset so that the Neo's faces will be flush with the surrounding MDF?

The only choices I see are 1/4" oak from big orange, 1/4" masonite, 1/4" aluminum, and 1/4" plexiglass. I will probably try setting up the 3's and 8's in the 1/4" oak as a dry run, but I found a local supply house that will cut the plexiglass to a nominal 65 X 10 for $30 each. Seems reasonable. Aluminum would be very nice to try to use but I don't have the capability to machine it at home and I wonder if that surface might not resonate or ring possibly. Cost is not prohibitive with aluminum from our suppliers.

I've been thinking about an inset and then using a perimeter gasket to mount a plexi or aluminum insert onto so that it's isolated from any MDF baffle vibes. Looking again at the material thickness that "well nuts" are designed for, you could attach the Neo's to the plexi with "well nuts" and not have to gasket-mount the plexi. Dennis recommended well nuts for isolation in post #108. Thanks for that, Dennis - I don't remember seeing well nuts before.

I have also been thinking and wondering about a gasket or some means of isolation for either the plexiglass insert or the Neos. My first question is; "Is it really neccesary?". The second would be; "What are the audible benefits of isolating the Neos or the plexiglas from the main baffle?". I am not sure it is worth the trouble to do. But I am open to ideas.

Dennis is a smart man. Great suggestion for using well nuts. I will have to look into price and availability. You would need approx. 192 pieces for all the Neos I am planning on using. I just did a quick check for a well nut that would fit into a 1/4" thick panel and use a 6-32 or 8-32 thread and I am not sure they exist. I could only find 10-32 and up. Maybe the well nuts could be adapted to isolating the plexiglas from the MDF baffle instead.

I should get some work done on stage 2 this weekend. It would be interesting to get a second panel 'mocked' up and actually hear a sampling of what a stereo pair will do.

Any thoughts on what type of passive crossover to use between the mids and highs?

Chuck

PS - I just checked again at McMaster Carr and you can get a well nut that will hold a 10-32 screw and will work in a .312 to .643 material thickness range. Part number 93495A190 at McMaster. Price is $7.59 for 10 pieces. Might hold the 1/4" plexiglass in an inset that had 1/2" thickness just fine.

[ThomasW]

I can't imagine any audible benefit going with plex, so use it if you want to pay a premium for looks.

I'd isolate the panel rather than messing with dozens and dozens of Well-nuts.

[chasw98]

I can't imagine any audible benefit going with plex, so use it if you want to pay a premium for looks.

What would you use instead? I can get the 2 pieces of 66" by 10" plex for around $60 cut and ready to go. I have tried masonite and it just doesn't work that well for dozens of screw holes that are near the edges. I have not tried 1/4" oak yet or luan maybe. What else is left besides aluminum or plexiglass?

[ThomasW]

Dozens of holes drilled close to the edges of plex are going to want to crack...

IMO tempered Masonite is great stuff, but an alu strip would work...

As we've discussed I'd use an adhesive to hold them in place. There's not enough mechanical force at work here to require the use of mechanical fasteners.

[SoneNelson]

on your friends measuring in a trench idea... what about measuring your array in a hallway vertically or horizontally to simulate the idea of a trench. maybe some combination of narrow hallway opening into a room or fake plywood walls.

[chasw98]

Here is a sketchup image of the array. I am starting to lay it out and make sawdust. Any thoughts, opinions, glaring screw ups?



I have not committed to the scallops at the top yet.

[chasw98]

on your friends measuring in a trench idea... what about measuring your array in a hallway vertically or horizontally to simulate the idea of a trench. maybe some combination of narrow hallway opening into a room or fake plywood walls.

I think that would work but you would need the plane of the baffle to be at the plane of the hallway where it met the room rather than halfway down the hall.

Chuck

[ThomasW]

Looks good to me.... :T

[JonMarsh]

Hey, I like scallops! Will these be au gratin?

[chasw98]

Hey, I like scallops! Will these be au gratin?

Ho dee ho, ho ,ho!!! :B

[chasw98]

And phase 2 begins. I have gotten the inset cutout done and cut some 5 mm Luan for testing. I will layout and mount up the Neo8's and Neo3's in the inset next. Then take the second piece of MDF and cut it out and do a roundover around the inset so there is a lot of room for the planar's to breathe. And then route for the woofers. But this gives you an idea. I built a template to do the routing for the baffle so the second or third one will go much quicker.

[chasw98]

Just thought I would post (bump) this thread back to the first page. I have finished routing and cutting the inlay for the mid's and hi's using the 1/4" Luan. I have picked up the plexiglass to make the real thing and started routing and drilling it out last night. I have also acquired the 1/8" flat bar aluminum for the back of the inlay. I am going very slowly and carefully with the plexiglass because of what I learned doing the mockup with the Luan wood. I don't want to make a tragic/expensive mistake. So far, so good. Pictures at 11.

Chuck

[JonMarsh]

Where's the scallops and the au gratin? :W

[chasw98]

Where's the scallops and the au gratin?

If this keeps up, one of us is buying dinner at RMAF!



Here is how you hold .0025" tolerance using common garden variety objects from around the house.

Custom Dust control....



Precision Mobile Drill Press



One of a kind router table/fence!

[JonMarsh]

Improvising jigs and fixtures is a time honored tradition in some quarters...

[Hank]

Oh, yeah, baby!

[Johnloudb]

Oh, Yeah .... Baby! Show us more, you know what we like. :yeah:

[JonMarsh]

Fixture Porn? Perfect idea for a Friday... :B

The only thing that could compare would be tool porn...








Yeah, dinner will be on me at RMAF, Chuck!

[Johnloudb]

Fixture Porn? Perfect idea for a Friday... :B

The only thing that could compare would be tool porn...

Yep, It's all good! :yeah:

[Hank]

Chuck, a quickie between meetings:
Regarding attaching the plexi into the inset, you could use 3M double sided foam tape - quick and would isolate it from the MDF. Secondary benefit: revenue for my company :B
I'm bad.
bye

[chasw98]

Chuck, a quickie between meetings:
Regarding attaching the plexi into the inset, you could use 3M double sided foam tape - quick and would isolate it from the MDF. Secondary benefit: revenue for my company :B
I'm bad.
bye

But does it have the holding power to last a long time in hot and cold environments? And does it look good?

We need an adhesives engineer with some answers! :rofl: ;x(

While you brought the subject of adhesives up...... What can we use to mount the Neo3's and Neo8's to the plexiglass or whatever we pick to mount them on? I have started drilling and tapping holes and I will have no hearing left by the time I finish drilling and tapping 192 holes. They will work real well but it sure is tedious!

And how about a part number and availability for this double sided tape if you want us to use it?

PS - I was actually in home depot looking for some double sided and all I could find was carpet tape so I gave up.

[ThomasW]

It's a specialty item not something usually sold in a big box store. I've never seen any color other than white

http://www.uline.com/BL_6015/3M-Double-Sided-Foam-Tape

The strength is limited to that of the foam between the layers of adhesive.

I'm still shilling for black polyurethane caulk.... :B

[Johnloudb]

That 3M tape does hold really good. I've been gradually peeling it off our open ceiling (for 14 years) where I once put up some sound absorbers. I admit I haven't been really aggressive about getting it off.

It does tend to yellow a bit over time. Not terrible but, if you'll see it through the plexiglass ....

[Amphiprion]

Chuck, a quickie between meetings:
Regarding attaching the plexi into the inset, you could use 3M double sided foam tape - quick and would isolate it from the MDF. Secondary benefit: revenue for my company
I'm bad.
bye

So you have time to pimp your company, but not send out poker invites? You better hurry, I might go out and get a job one of these days

Oh and the double sided foam tape is indeed strong. It held the phone on my cubicle wall in place for many months.

[Johnloudb]

I have cats! And, when I needed tape to hold my Lineup R44 speaker to the speaker stand, did I just trust any tape? No Sir! I used 3M Double Sided Foam Tape. This stuff is strong and forms a bond that lasts. Only one 2.5" piece of tape did the job. For over a year now 3M has secured my speaker, while my cats regularly jump on my speaker to get on top the TV. It's still holding strong!

Image not available

Need tape? Don't walk, run to your local 3M retailer.

[chasw98]

It's a specialty item not something usually sold in a big box store. I've never seen any color other than white

http://www.uline.com/BL_6015/3M-Double-Sided-Foam-Tape

The strength is limited to that of the foam between the layers of adhesive.

I'm still shilling for black polyurethane caulk.... :B

Holy Gigabucks! $63 a roll! And you have to buy 2 rolls at a time! And you said plexiglass was $pendy!

So where do I find black polyurethane caulk?

Where's Hank?

[ThomasW]

So where do I find black polyurethane caulk?

Home center stores

[Johnloudb]

Chuck, that really doesn't help Hank. :roll:

Ace is the Place! This might also work for you.

Permatex - Black Silicone Sealant

[chasw98]

Chuck, that really doesn't help Hank. :roll:

Ace is the Place! This might also work for you.

Permatex - Black Silicone Sealant

I am not sure that the Permatex is the same as the polyurethane caulk Thomas is singing hosanna's for. Chemistry is not my forte.

[chasw98]

Chuck, a quickie between meetings:
Regarding attaching the plexi into the inset, you could use 3M double sided foam tape - quick and would isolate it from the MDF. Secondary benefit: revenue for my company :B
I'm bad.
bye

My company is designing a new product and it might require some very strong double sided foam tape. I wonder who I would talk to at 3M about getting, oh maybe, 1 inch wide, 30 feet long of 3M 4004 for a sample for the engineers at work? :T

[ThomasW]

Glue and damp.....

http://www.house-painting-info.com/polyurethane-caulk.html

[Hank]

John: THANKS for buying 3M stuff!
Chuck: It's strong enough. Adhesives is one of our core technologies. Aircraft are held together with our specialty adhesives - stronger and cheaper than rivets. Our Very High Bond DS tapes are used by auto mfgrs to attach emblems to cars and trucks.
If you're worried about the white color of the consumer tapes, here's a black one (and, it's $21.97/roll): http://www.shop3m.com/70006210838.html
I looked for 4004 but couldn't find it quickly. I'll try again later. What a coincidence that 30 ft is about what you'll need for your speakers :W
Gotta go before Thomas catches me blathering about tape...

[chasw98]

What a coincidence that 30 ft is about what you'll need for your speakers :W

Got to get up early to get one by Hank, doncha'. :B

[chasw98]

Hank, will the 4496 you pointed to in your post be strong enough to do the job of holding the plexiglass with the drivers mounted to it in the wooden MDF frame? It is very easy to drill and countersink holes but the possible decoupling gives the tape an added advantage!

[CraigJ]

Chuck,

Dennis or someone else may have already mentioned this, Monte Kay used RTV to hold his 40 2" Aura drivers in place for his speakers. From Monte's web site, "To mount the 2" Aura drivers I just glued them in place with RTV. The 6" drivers are compressed between foam tape gaskets and rubber grommets. As you can see in one of the construction photos the grommets simply go between the driver flange and an aluminum bar that holds everything in place. This actually worked out quite well!"



Good luck,

Craig

[ThomasW]

Gotta go before Thomas catches me blathering about tape...

That's right where's my whip?...... :B

Nothing wrong with double sided tape. I use it for lots of stuff, but don't see it as a 'structural' adhesive.

I've used polyurethane caulk to seal concrete expansion joints in the driveway and patio. It's amazing to me given the very high UV environment with huge temperature swings we have in Colo, that it sticks to anything and remains flexible for years and years...

[chasw98]

Chuck,

Dennis or someone else may have already mentioned this, Monte Kay used RTV to hold his 40 2" Aura drivers in place for his speakers.
Craig

Craig:
I read that when I first started down this path. I don't like gluing stuff on speakers. Thomas and I have a gentlemans agreement not to discuss/argue the benefits/disasters of hot glue, RTV, squeezable muck, or whatever. I am old school and am looking for a mechanical way to mount but I am also too lazy and don't have the precision tools to drill and tap 100 plus 4-40 holes (and they all have to be just right or you start over) in plexiglasss and aluminum. So I may have to give this round to Thomas and his amazing polyurethane stuff. I am going to test some this weekend.

But I did like the way Monte used the grommets and aluminum to hold the woofers in place! :T