SB Acoustics monitors build

[Wolf]

People have taped over the tweeter, or removed the faceplate, and just recut the woofer recess dimensions. Since you don't have a central pivot, you could install one in the driver mount holes from the rear, and locate center, and recut.

If you happen to have a spare tweeter face, or can print one, you can use that as a sacrificial template, and just pattern to the tweeter face.

Later,
Wolf

[danmarx]

I have never trimmed a tweeter faceplate but I have considered doing it often times but always chickened out in the end. If I were to do it however, I would probably opt for Wolf's method, where you basically install the tweeter and re-router the woofer. You could probably actually do this on a sacrificial baffle and just make sure to keep the center-to-center distances the same. Or if you did this in the actual enclosure, you'll have to create a central point for your router jig. Basically what Wolf was saying. I have done this, not to overlap a tweeter, but to flush mount a new pair of drives in an existing enclosure. I attached small blocks to a piece of MDF and glue it to the backside of the baffle, thus providing the crucial pivot point. From there routing is normal. Remove the blocks when complete. See pics below. This is just an example, not saying it's the best way to do it though!

[Wolf]

If you don't want to fight circular scratches, apply a layer of painter's tape over the baffle, or even contact paper to keep this at bay.
Wolf

[DeZZar]

Thanks for all the suggestions. I ended up trying the print and sand method and I think it turned out ok.

I printed a little plastic wheel the same size as the woofer and stuck sandpaper to it.


Then carefully positioned and scribed a line on the face of the tweeter. Put the sanding wheel in the drill press and slowly sanded up to the scribe line. It did a really good job - I didnt need to cut any material away beforehand.


Boxes are now all lined with a layer of felt and acoustic foam.

[DeZZar]

Driver cutouts completed as well...


And a quick test fit...


Here's the tweeter face in position. Just holding it with my fingers but when you line it up correctly it sits perfectly on the woofer without any gaps! Happy with that :D

Just need to repair that tiny little point of wood between the drivers that chipped off during routing despite being taped etc :'( (booo!)


So now these baffles will get glues down in place onto the boxes. They are slightly oversize to allow for trimming - and once trimmed I'll give them a round over before final sanding. Then I can clean the workshop up and move onto fine tuning the port and taking measurements!!

[Castlesteve1]

This is a great thread. Using the printer to make a sanding wheel was genius. Really nice work.

[scottvalentin]

Wow excellent work and that veneer is VERY nice looking. Thanks for sharing the process, nice job on the sanding wheel.

[DeZZar]

Thanks Scott!

I really like the veneer too but I haven't been able to get anymore of it unfortunately. Will definitely keep my eye out for it. In case you find some in the future, its Tasmanian Blackwood.

[mattk]

This is a great thread. Using the printer to make a sanding wheel was genius. Really nice work.

I've done something similar in the past with a piece of plywood I cut to the right diameter.

[danmarx]

The 3D printed sanding wheel was a great idea! I wouldn't have thought of that. Nice job, the fit looks perfect. As far as my router job, some tape over the baffle definitely would have prevented the rings. Also, making sure the screws on my Jasper jig were sub-flush would have helped as well. I refinished the whole speaker in the end any way. This build is looking great though. Can't wait to see some measurements.

[DeZZar]

As far as my router job, some tape over the baffle definitely would have prevented the rings.

It depends on the surface finish - I've had the tape start to roll up under the jig as its turning causing other issues and even with a smooth base I've had chips get caught and scratch the surface anyway - I try and make sure all the routing is out of the way as early as possible in the process well before any finishing. But - re-routing existing speakers will always be a bit of a challenge. A CNC would solve that! :P

[DeZZar]

Baffles glued on a couple coats of danish oil added for a little protection.


Ran the woofers in for a couple of hours and measured after cool down. For anyone curious, this is how my copies of the SB17NRX2C35-4 measure after a couple of hours break in:

Param	Spec Sheet	2Hr Break In	% Variance
Qes	0.41	0.501	+22%
Qms	4.49	4.551	+1%
Qts	0.37	0.451	+22%
Fs	36	39.67	+10%
Vas	27.6	25.21	-9%
Mms	13.9	13.9	0%
Cms	1.4	1.154	-18%
Rms	0.7	0.76389	+9%
Re	3.1	3.124	+1%
BL	4.9	4.65	-5%
F3 (Hz)	43.6	45.5	+4%

This is actually very good as I know from previous tests that Qes, Qms and Fs will all continue to drop out to around 24 hours break in. Vas will remain about the same.

This means the box tuning can remain the same as designed. It will yield a slightly higher f3 for now but this will settle closer to the intended f3 as the drivers continue to break in with use.

So onto port tuning. Initial test showed tuning was around 34hz. Target is 41, and I did leave the port a little long to start with. However, I also suspect the compound elbow in the port (on top of the fact its never usually what the software says) will play a part in the final length. I took a hacksaw to the port and chopped some off and it looks like we need to loose around 60mm to hit 41hz. Just printing a new elbow now to suit the new dimensions.


Here's a couple of shots with the drivers bolted in during port testing.

[jvphotog]

Love seeing your Ender at work. I just used my Ender5 to make some gaskets out of TPU for a Faital waveguide. Such an awesome tool... when it works!

[DeZZar]

Yeah still the best tool in the shop I'd say! I'll been wanting to try some TPU but they say the ender needs a few little upgrades to handle it well...

[invaderzim]

and the award for "Best Neighbor Ever" goes to..... DeZZar.

[Unbiasedsound]

I wish I was dezzar's neighbor. lol

[DeZZar]

Hey I would love to have neighbours into DIY! It'd be awesome! Not enough DIY'ers around these days!

[DeZZar]

I've done something similar in the past with a piece of plywood I cut to the right diameter.

I thought about that too with a scrap of MDF but it was getting late into the evening and I didn't want to make anymore noise with the router - so thought I'd set the printer going instead! But making a wooden wheel with a bandsaw or router circle jig is definitely a faster option!!

I can see this happening again in the future and its got me thinking about creating a jig that can take different sized outer rings to sand to different diameters...something more substantially centred on bearings that runs true.....hmmmm

[DeZZar]

Getting the measurements underway now. I've started with just the woofer/port near field because there is a barking dog next door that just wont shut up!! I suppose that gives new meaning to measuring the woofer....heh heh...

Anyway, good opportunity to compare the modelled box response with what we actually achieved and I'll run the far field later.

Here is the woofer and port nearfield with the port scaled and combined response (blue).



Looking over the data in a little more detail here is a normalized comparison of the winISD model vs the actual result. (I've normalized it all to the level at 200Hz).

I'm really happy with this and actually consider it to be pretty good alignment between the model and result. An extra bonus is that with the port tuning right on 40hz we've achieved further extension of F3 than predicted without sacrificing any magnitude in the preceding octave.

From an expected F3 of 45.5Hz we've got ourselves 42.3Hz. Not bad for a 6" woofer in 15L