Funny little W2-1767S....

[HareBrained]

Re: Funny little W2-1767S....

To be honest, Hare- It modeled better vented than with a PR.

I can get 69Hz out of it...

I had already thought of it before you mentioned it though.

Later,
Wolf

I guess we're going to disagree on this, and who thought of it. Half an octave more extension but it goes uncontrolled at 70Hz. How are you going to control that without adding components, active or passive? How much power can the vented alignment take without any over-excursion? The PR alignment is ideal for a near-field 2.1 system and it doesn't need any HP filter on the W2. Just my opinion.

[spasticteapot]

Re: Funny little W2-1767S....

I'd be interested in using a pair of those in "pods" for an automotive system. It would save a lot of time and hassle.

[Wolf]

Re: Funny little W2-1767S....

I guess we're going to disagree on this, and who thought of it. Half an octave more extension but it goes uncontrolled at 70Hz. How are you going to control that without adding components, active or passive? How much power can the vented alignment take without any over-excursion? The PR alignment is ideal for a near-field 2.1 system and it doesn't need any HP filter on the W2. Just my opinion.

There's only a half-mm difference in Xmax in my PR/Vented models, and you think the PR model would be fine without a HP filter? Then the vented should be fine as well. Most vented models have rising Xmax below the tuning anyway, and are not complaining about it in real-world applications I've heard.

My Sophomores have a huge increase in Xmax below tuning, and it doesn't require a HP filter either. Neither do the Overnight Sensations.

Granted- those are 4" designs, and this is a 2", but given that the W2-803SM was fine in a TL to about 60 Hz without trouble or HP filter, I would think one with 3x the Xmax will be just fine.

Oh- and just because I don't mention it online doesn't mean I didn't already consider it, but you take the rights on your dual-PR model if you want. I always intended on a single.

Later,
Wolf

[HareBrained]

Re: Funny little W2-1767S....

There's only a half-mm difference in Xmax in my PR/Vented models, and you think the PR model would be fine without a HP filter? Then the vented should be fine as well. Most vented models have rising Xmax below the tuning anyway, and are not complaining about it in real-world applications I've heard.

My mistake, I reversed the PR and driver excursions. You're right, the vented is no "worse" from that standpoint.

[Wolf]

Update! Name is official- 'Microtonnes'...

A very small cataclysmic nuclear explosion- that is the idea here!

Tentative almost to scale drawing:


Positions/BS:



Well- the vented will work, or at least that is my attempt from here further. The ports will angle the direction up a smidge for better listener position targeting. Baffles will likely be 1/4" plexiglass.

The xover is simulated but just a guess, so we'll err on the side of caution here. 6 parts, all of the smallish and cheap variety. It was easier to get a SXO to work between the 2, in the way they blended at the rolloffs, or at least it was for me. :rolleyes:

Simulation:


Xover schematic:


I know I know- the sensitivity is only 78dB +/-2.5dB or so. The 90dB output is still probable, but about all these could do on paper. That said- they could most likely be miniscule Sats for HT, PC speakers, or another nearfield setup of some sort. I did figure 2dB of BSC, being that they would probably be wall-mounted, or sit on a table or desk in front of you. I also wanted to protect the drivers a bit and keep them happier should you want a bit more on the volume dial.

The dips in the W2 response are the port resonances, and I did add them to the plot. For such a cheap build- I dont think I'll stress them, but had to see the effects they contributed.

The main issue of concern is probably the tweeter's Fs becoming quite ugly as it stands. If it sounds half-way decent as it is modeled, I won't press it further. I really don't want to jack up the cost on parts, but I have all of these on hand to try it out. I know the acoustic phase is only aligned around the broad xover range, but this is a simple build. It would be really hard to make that align better without using more parts.

As to xover position, I think I may embed the parts in the bottom panel, recessed into the surface. This will keep them out of the cabinet volume that is so preciously required, and the circuit will be easy to wire and out of the way. The rear panel will probably be removable, as I have to mount the 13-1761 from the rear with an M4.

Well- that's it for now!
Wolf

[Wolf]

Cut these out last weekend...

Well- at least the panels.
Short story- They're about the size of a coke can or even smaller.
I cut 2x about 14" long half-1.5" diameter PVC pieces to cut and assemble on the boxes as planned. I used aluminum angle-iron to draw a straight line, made a 90 degree channel and clamped it to the bandsaw, and ran the PVC through making both cuts at once. If you have a short jigsaw blade, cutting the line would take 2 passes for those without a bandsaw. I'll probably use biscuits for everything but the rear and flush baffles. The inner baffle for mounting will be biscuited, and I'll flush trim any excess before placing the flush baffle on top of it.

Changes to original cabinet picture-

*cabinet exit for port will be 2x 3/4" holes instead of a semicircle. That's easier, and same volume.
*double thick 3/16" hardboard for baffle and easy flush mounting.
*drivers rotated -90 degrees to keep tweeter from blocking port exit.
*slotted-in hardboard (1/8") to cover xover cavity underneath, and assist with glue up and bracing.
*slotted in 13-1761 tweeter mounting point (at this point). I will probably leave a hole on the rear baffle (and cover when not removing driver) or keep it removable to make mounting the 13- easier. I could just use terminal cups and remove them to mount the tweeter... Contemplating a CPVC channel for the 13- tweeter to reside inside, but probably too hard to do easily. This is a cheap and easy build afterall...



More updates later...
Later,
Wolf

[Wolf]

Re: Box alignments... Another alternative...

Something told me that 2dB of BSC, and the rolloff at 60 might not be enough bass. So- I figured in another alignment for kicks. I mean- it should ba capable of a 'TB mini-sub' status, right? Heh...





The Xmax is a little more controlled before unloading, and you get another 5 Hz extension outta this tiny box. The peak will give it a bit more emphasis in the bass range, which is never bad for something this small. It rises to +6dB from the valley just above it in the FR, so it may sound a lot more full this way, and you'll hopefully not be thinking it still lacks bass. I know the 'bass presence' range is around the 100-120 Hz area, so I hope it still has a bass presence factor.

I realize the ports might be chuffing at this point too, but it is at 90dB level. Lower the knob a click or 2, and it becomes reasonable again. If you want more output, the stuffing will need increased a bit more than in this sim, and it'll be more like the original box alignment.

Thanks for looking...
Wolf

PS- that peak could be an evil dillemma....

[Starkiller4299]

Re: Funny little W2-1767S....

Neat design, Wolf! Ignoring that narrow band suckout (which the ear supposedly filters pretty well anyways) that's a pretty solid +/-2dB design for $50/pair, box included! I may have to build a pair or two--one to give away, one to keep :p.

[Wolf]

Re: Funny little W2-1767S....

Thanks for the compliment!

I did more work on the cabinets today, but I have yet to voice the xover, so please be patient to see if it sounds like I hope it should.

I also have to verify the port tuning as what the simulation calls for, and can't do that until construction is done.

I got the 'woofer' holes cut today, made the plexi crevice covers for the xover cavity and the corresponding slots to install it, figured out a method of xover connection to implement them underneath externally, set the actual pending angle to see how much room will be underneath for xover placement, and I'll be seeing how I can layout the xovers in the specified area later this evening.

Funny thing about this little booger project- It might be rather complicated to construct just because of the port. I would think an external slot port would also work, but the diffraction signature would change without the roundover from the port being there.

Anyway- I'm hopeful this will turn out pretty nicely.
Thanks,
Wolf

[Wolf]

That Acoustic Phase was really bothering me...

....and I finally took another look to see what I did wrong.
I had the Z-offset as a positive! :o

So- the schematic I just replaced the original file I uploaded with the correct one to avoid confusion. This thread has it right in all locations. All I had to do was reverse the polarity on the tweeter to get it to look fine, and it was in fact better aligned than before simmed.

Here's the corrected FR simulation response (much better!!):



I'm a lot happier with it's representation now, even if all that was wrong was the offset/polarity.

Later,
Wolf

[Taterworks]

Re: Funny little W2-1767S....

Hey Wolf,

The only thing I'd suggest before you start building is that you enlarge the inner opening of the port to probably 3 times what you have now. If that orifice creates any turbulence at all, it won't chuff -- it will whistle. The effective dimensions of the port will still be the dimensions of the pipe.

[Wolf]

Re: Funny little W2-1767S....

Hey Wolf,

The only thing I'd suggest before you start building is that you enlarge the inner opening of the port to probably 3 times what you have now. If that orifice creates any turbulence at all, it won't chuff -- it will whistle. The effective dimensions of the port will still be the dimensions of the pipe.

I thought about doing just that too...

I haven't started construction yet, but I have cut out the panels, minus baffles.
Later,
Wolf

[Wolf]

Update: Funny little W2-1767S....

I have the baffles assembled and cut out.

I increased the opening into the port, and it's now a penant-shape to maximize flow and not decrease structural integrity. 3/4" long rectangular section, and then the triangle below that. I'll update the drawing to show more detail later.

It turns out I need to make another set of 4x 4" x 4" x 1/8" hardboard panels. The ports are a tad wider than expected, and allow breathing room to the belly cavity where the xover will be. One panel worth of depth will fix that, as well as give me something the fronts and backs can screw to for assembly instead of edge-MDF.

I got PE 091-1160 jacks for connections since they are tiny like the project and still take 'nanners. I tried to find an acorn nut to go over the open end on the inside, but it seems to be a non-standard pitch thread. It seems to be either an M6 or 1/4-20, 1/4-28.

The tweeters will easily press-fit, but are a non-standard hole size. About 12mm diameter total. I won't be using the M4 screw mounts.

One goal was to not use the router on this project, and I have not. I have used the drill-press, bandsaw, table and miter-saws, and the Dremel.
The baffle is 2 layers of the 1/8" hardboard, with one for the through hole, and the other for the rebate. I used a 'tungsten wood-shaping bit' in the dremel to accomplish the rebates, and it was fairly easy to do.

Since the cavity is covered by plexi, I have to glue that in place now that the connections are made through it, and then I can start on the rest of the assembly.

I'll post pictures when I take some...

Later,
Wolf

[Taterworks]

Re: Update: Funny little W2-1767S....

I'll post pictures when I take some...

Later,
Wolf

Well, hurry up and take some!

[Wolf]

Re: Update: Funny little W2-1767S....

Well, hurry up and take some!

If my wife would quit running off with the camera I might...
I hope to post some later...
Wolf