NTNs Build

[Soundslike]

Edit: After finishing this thread and contemplating what I had written, I realized that it might give the impression that I'm urging builders to recess their drivers, and/or utilize rabbeted joints. I don't want to give that impression at all -- I personally like the rabbeted joints, for reasons I explain further on in this thread, but I recognize that they're not necessary and might be difficult if you're not equipped to make them. The same goes for the flush mounted drivers. Surface mounted drivers look perfectly fine, and are likely the best choice for newer builders when anything other than round drivers are used. If you're inclined to strive for simplicity, no one should ever be critical of that approach. The sooner you get to hear these, the better.
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Second Edit: If a drawing would be helpful, you will find one at, or near, the end of this string.
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A while back, I noticed all the interest in the Techtalk forum over Chris Roemer's Nano Neos, and the NTNs. After reading through what has to be the world record length string (35 pages and 693 posts as of this writing), I was intrigued by all the glowing reports, the low build cost, and the enthusiasm of the people who were building them. You can read the string yourself by clicking here.

So, as I've found myself doing more and more, I decided to build a set even though I wasn't exactly sure what I'd end up using them for. They've been done for a while now, and I know you hear this a lot, but they really did exceed my expectations. Even though everything I'd heard about them was highly complimentary, I'd have to say the rave reviews aren't in the least exaggerated.

When I first started on the NTN's I had several other speaker projects going at the same time. That naturally slowed my progress on the NTN's considerably. At that time, I planned to do as others have done -- post any comments I might have about building the NTN's on Chris Roemer's string (the link can be found above). I did make a number of posts, but before too long it occurred to me that what I was writing wasn't likely to be discovered by anyone who is contemplating building the NTN's, at least not without a quite a bit of effort. So, I've decided to create this build string to pass along my NTN experience, in the hope that at least some builders will find it helpful. I'll be copying and pasting some of my earlier posts from Chris' string.

My NTN's will be finished in high-gloss piano-like black. I will also recess the drivers although many have said that there isn't much point in doing that. I figured it couldn't be too difficult and started to scheme about how I'd make a template to use with a router bushing to duplicate the outer shape of the driver. I liked the challenge it presented but it was tougher than I thought -- more about that later. Here's how they turned out:

[MLS]

Re: NTNs Build

Nice work. Those look great. I built the Neos and I still enjoy listening to them and surprised at what they can do with so little.

[Soundslike]

Re: NTNs Build

I followed the usual process of cutting the necessary panels from a large sheet of 3/4" MDF -- first cutting pieces to a manageable size with a circular saw and panel guide, and then squaring them up to final dimensions on a table saw. I used the standard dimensions, if there is any such thing with this design. One of the appealing aspects of this design is the variety of different over-all shapes used by different builders, but I opted to go with the 28" by 6" by 9-1/2" dimensions. I won't bore everyone with the details of cutting the panels -- most already know how it's done -- but for anyone who's curious, the process is described in more detail in the build-strings that can be reached by clicking on the links below my signature.

I decided to follow Chris' advice and utilize rabbeted joints. In fact, I used rabbets on the other builds I was doing along with the NTNs. I've used bu*t joints, both with and without screws, and biscuit joinery on previous builds -- I'd say the rabbeted joints are easily the best method. You end up with easier glue-up/assembly, a more accurate result, and a stronger build.

But, there is one disadvantage to a rabbeted joint if the baffle is to be a different material or color than the rest of the box. if you use rabbeted joints all around, including the baffle, and you're going to veneer your speakers, you'll want to oversize the baffle and trim it to size, after veneering the top, sides and back, so as to achieve a perfect match where the baffle meets the box. That will make it necessary to cut the baffle rabbet widths wider than the others, which will introduce additional complexity, and resetting the saw. The other problem is that the baffle will appear to be a mere 3/8" thick if it is rabetted. Of course, these minor issues can be avoided either by utilizing a removable baffle, or by reverting to a bu*t joint on the baffle.

In the following drawing you can see the type of rabbet joint I used. There are other ways of course, but this method allows you to make the same 3/8 X 3/8 rabbet all all edges. Rabbets can be cut with a router, or with a table saw using only the blade (A & B), or with the table saw using a dado blade (C). The end result is shown in diagram D.

[Soundslike]

Re: NTNs Build

Thanks MLS; they are great aren't they....

Continuing with the build:

After cutting the rabbets, I next laid out the locations for the drivers and the port, on the baffle. As I've said in other build strings, I think it's best to draw the cutouts accurately on the baffles, before cutting any openings. Doing that can save you a lot of grief from mistakes down the road. Problems such as incorrect spacing or location should be much more apparent when you can see exactly what you're going to end up with, using the current layout. I'll have to admit that many of my builds bear the marks of impending errors -- scribbled out lines and erasures hint of disasters avoided.

I'll usually layout the driver mounting holes at the same time. Doing so makes it much easier to get the driver holes well aligned with the vertical and horizontal on the baffle, since you can easily use a compass and a decent combination square before assembly. I drill 1/8" holes, using a drill press to transfer the exact locations to the back side.

The following photo shows one of many attempts to produce a usable template that could be used to make recesses for flush mounting the driver. To produce a good template, you have to be able to accurately draw the exact outline of the driver. Fair enough...., but to accurately draw the outline you'll need a variety of measurements or dimensions that are not provided.



This photo is labeled to show the measurements needed to accurately reproduce the driver shape. Most of them are not provided, which leaves you to either attempt your own measurements, or trace the outline directly on the template -- which of course means that you'll also have to enlarge the outline to account for the size of the router bushing.

[Soundslike]

Re: NTNs Build

I finally achieved a satisfactory result using the following process.

Select a piece of 1/4" hardboard and sand it smooth, if necessary. If time permits, apply a coat of something like varnish, lacquer, or shellac, to bind the surface better. A rough surface will cause you to draw jerky, irregular lines. If the surface is the least bit flaky, small bits will come off while you are sanding or filing the template to shape, leaving you with a vague line, and guessing how far to cut.

Draw a perfect square (I used 6" X 6"), and lay out diagonal lines corner to corner.

Find the center using the diagonal lines and draw arcs in the four corners to designate the outermost point of the mounting tabs (you're making marks to show the outermost tip of the tabs, not the final shape).

Draw a horizontal and vertical line through the center and well past the edges. These lines will be used later to align the template with the baffle.

Draw arcs at 0, 90, 180, and 270 degrees to define the outer edges of the driver's primary shape.

draw a circle for a cutout the size you will use on the baffle (I used 3-3/4"). Cut the hole.

Place the driver in the hole and align the mounting holes with the diagonal lines. Be precise. Mark the locations of mounting holes on the pattern. A transfer punch is a great tool to have in this situation.

Drill the mounting holes, and attach the driver to the template with screws.

Use a utility knife to trim away any gasket material that may be protruding form beneath the driver frame. At least one attempt to produce an accurate template was ruined because I didn't notice that a protruding gasket was causing me to stray with my pen.

Using a fine-point pen, carefully trace the outline of the driver frame being careful to keep the pen at the same angle all the way around. This line won't be used, but you may find it helpful later on.

With the driver still mounted on the template, draw the outline of the enlarged shape (to account for the difference between the pattern and where the router will actually cut - in my case, 3/32") all the way around. I find the best method is to make a spacer that can be placed against the driver frame. The spacer will allow you to consistently make accurate parallel lines and marks to define what few straight edges there are on the driver, and to designate the tops of the arcs. At this point, you should be sure to check the arcs defining the primary shape at 0, 90, 180, and 270 degrees.

Two tough tasks remain -- drawing the arcs that define the top of the mounting tabs, and determining where the straight lines begin and end, and where the various arcs begin. I'm pretty sure a student of geometry could tell us how to find the radius and center points of the arcs, but I was left to experimentation. I cut a variety of arcs from thin non-corrugated cardboard, until I found the necessary size. Once the arc radius was determined, I used a compass and the intersection of the diagonal lines and the outer marks drawn earlier, as a pivot point from which to mark the center for the tab arc radius.

Once the outline was defined, I cut most of the center out with a sabre-saw, and sanded/filed to the final shape. I'm fortunate to have a spindle sander, but simple sanding drums could be used effectively.

At this point, I should admit that it took repeated attempts to arrive at a usable process. Looking around at discarded pieces of hardboard and MDF littering the shop area, I found the remains of at least six attempts that produced unsatisfactory results.

Eventually, through sheer persistence, I was able to produce the close fitting template you see below. Note that only the top template is used (on the left as viewed in the photo) and that I've made notations on each of the templates indicating the method I used to produce them (I should say, how I laid them out). You'll also notice that a rail has been attached on either side to maintain alignment with the baffle. Centering the template is accomplished by aligning the perpendicular center lines on both the template and the baffle. My Porter Cable router is shown with the bit and bushing.



In this next photo, we see the rebate cut with the router. I intentionally made it deeper than it needed to be to provide room for gasket tape, and for a plastic laminate trim piece I intended to use to cover the rather plain looking pin cushion frame (more on that idea later). The gasket furnished with the ND 105-4's is probably adequate for surface mounting on a smooth surface, but questionable if surface mounted since there could be irregularities in the rebates.

[Soundslike]

Re: NTNs Build

In this next photo, we see the finished baffles with rebates for flush mounted drivers. Not much material left separating the tweeter from the woofers.

[tomzarbo]

Re: NTNs Build

Soundslike,

I really admire all the work you went through to get those buggers flush mounted. It really looks nice in the final pic, your planning and hard work paid off big time.

I own the neo nano's and I feel that the NTN's would be worthy of all the work you are doing to get the finished product so nice looking. I have all the parts for a set of NTN's and I plan on doing a super-nice cabinet build as you did.

Nice work!

TomZ

[Soundslike]

Re: NTNs Build

Thanks Tom; the NTN's are definitely worth the time and effort. As you know, Chris Roemer's original goal when he designed the Nano Neos, was to produce a high-value design capable of good performance at a very reasonable building cost. I think he succeeded admirably, and in fact, the end result no doubt exceeded even his expectations.

[Gracias]

Re: NTNs Build

Thanks for documenting your technique. The pin cushion frame design is my only complaint with this powerful little woofer and seeing it recessed I think the added work is easily justified. The compact design with all black drivers and a beautiful piano black finish is something you should be proud of.

Being too lazy to attempt recessing the frame, I rear mounted it and ever since have wondered how much of a sonic compromise the .5" difference in depth between tweeter and woofer created. If P.E. ever runs another sale I will try the NTN your way and put the question to rest. Thanks for leading the way.

Mark H.

[Soundslike]

Re: NTNs Build

Thanks for the compliment Gracias. That little pin cushion frame isn't particularly attractive -- I think it has an industrial look about it. I've wondered the same thing about rear mounting the drivers, perhaps with a rebate on the inside of the baffle so the acoustical center is closer to the front. Perhaps something like this:



That wouldn't leave much material to attach the frame to -- I'd probably back them up with an MDF ring on the backside.

[RDR75]

Re: NTNs Build

Thanks for the compliment Gracias. That little pin cushion frame isn't particularly attractive -- I think it has an industrial look about it. I've wondered the same thing about rear mounting the drivers, perhaps with a rebate on the inside of the baffle so the acoustical center is closer to the front. Perhaps something like this:



That wouldn't leave much material to attach the frame to -- I'd probably back them up with an MDF ring on the backside.

I was kind of think of something like that for the Tritrix I'm working on - when I received parts and saw the gasket material on the front of the Dayton DC130BS-4's - I thought it would look slick seeing less frame and more wood
I decided against it mainly because this is my first attempt and didn't want to deviate in too many ways from what is the prescibed building method...plus I already have enough uncertainties swirling around in my head - I didn't want to add another

...Congratulations on another top-notch build...it's always a pleasure reading your threads

[Soundslike]

Re: NTNs Build

In this next photo you can see how the driver fits in the rebate. The driver has accumulated a lot of shop dust during the long process of producing a template.



The following photo shows the plastic laminate trip piece I mentioned earlier. My original intention was to make these trim pieces to cover the black pin-cushion frames. However, after the enclosures were painted, I didn't care for the look and so I discarded the idea. The laminate I used was some I've had in my lumber pile for years -- it has a grainy leather look to it that didn't go too well with the overall look. I do think, however, that the idea is worth pursuing with a more suitable laminate. Perhaps one of the shiny metal types, or one with a carbon fiber look would work well. If I come across something that looks better I'll probably give it a try, just for the heck of it.

But, I think the idea described by Gracias (illustrated above) regarding rear mounting the drivers may be a simpler way to go, providing there's no compromise to be made acoustically. Making the trim pieces does require a lot of attention to detail, and you still end up with the somewhat odd outline of the driver. I've another idea in mind that I may describe in a drawing later on. Edit: forget the drawing..., post 15 by Chris features a treatment in the third photo that shows that what I had in mind has already been done. Very well done too...

[Wolf]

Looks like...

....another happy inductee into the:
"ROF Laboratories" audio society of ear-conjoined NTN builders

Chris and his company's plan is to take over the world of DIYers, and assimilate everyone into building at least one pair so they multiply and take over the world, and do it on the cheap. ;)

Heeheehee!
Wolf

[greywarden]

Re: NTNs Build

Don't look at the screen! Merely seeing and ntn or NeoNano build will force you into building one! :eek:

[Chris Roemer]

Re: NTNs Build

Don't look at the screen! Merely seeing and ntn or NeoNano build will force you into building one! :eek:

Really?

Take that, and that, and that, . . .