Light weight cabinet build

[TheDuff]

Yeah, I'm worried I'll have maker bias, but do plan to attempt objective measurements on the result. I'm getting kind of excited about building it this weekend.

Great.

I myself do not have any experience doing the kind of testing and measurements that you are able to do.

I can see where being able to measure these values is valuable. Better than just the ears or guessing.

Then there is that insideous designers bias.

 

[agedhorse]

Designer’s bias is very real. The less qualified the designer, the more likely the bias IME.

 

[6thplanet]

So, just placed on the cone? I'm a bit concerned about using anything sticky on the cone.

Just lay the roll on the cone, your not sticking anything to it.

 

[41hzthunder]

Just lay the roll on the cone, your not sticking anything to it.

Couldn't do this. The aluminum dustcap is 4" and the tape roll has a smaller hole. I don't want a dented dustcap, so I got some picture putty that didn't leave any residue to add 1/2 the expected mms. I'm still, running some tests, but Fs is consistently 30Hz. That's more in line with the K140 kit. I'm still skeptical though. QES and QTS are higher than the E-140 numbers, so that's also pointing to a K cone. I read that the tests should be run with the driver vertical rather than laying on the magnet structure. I want to try that and will limit this to 1 more hour of testing. When checking DC resistance with the driver sitting on the magnet I kept getting 5.7-5.8. It was acting microphonic. When I put it face down, so the cone would be less likely to move, I got 5.5 (spec) every time. Little things do make a difference. At some point I just have to accept numbers and move on to building.

 

[agedhorse]

It must NOT rest on the magnet, this will block the rear vent, resulting is incorrect data.

IIRC, the K and E cones are the same part even if they have different part numbers. The Q numbers are determined by many factors other than the cone. Be careful not to draw conclusions here.

 

[41hzthunder]

It must NOT rest on the magnet, this will block the rear vent, resulting is incorrect data.

IIRC, the K and E cones are the same part even if they have different part numbers. The Q numbers are determined by many factors other than the cone. Be careful not to draw conclusions here.

I had it on blocks, so the vent wasn't blocked. I did get a few vertical tests done. I'm getting Qms of 3.3-3.4, Qts .372 and Qes of .419, so a little off. Fs is very consistent at 30-30.2. Mms is 104.2-106.73. Vas is a little high 299.54-310. It may just be that I can't be more precise with the equipment I've got or that I need better skills. At this point, it seems like a rational basis to believe its a K kit in the driver. Although, I could be wrong.

 

[agedhorse]

If it’s an aftermarket kit, and there’s no good way to know without destroying the soft parts, then is could have different specs too. For example, if the cone or soft parts moving mass is higher, it can skew the other parameters. Same if the spider has a different spring constant.

This is the danger of making assumptions, there’s no real way to know what’s an accurate assumption and what’s not.

Just design your box around what you have, though I would run the tests with the driver in its normal operating orientation since there will be asymmetry with the cone facing up. That could be part of the difference.

 

[41hzthunder]

If it’s an aftermarket kit, and there’s no good way to know without destroying the soft parts, then is could have different specs too. For example, if the cone or soft parts moving mass is higher, it can skew the other parameters. Same if the spider has a different spring constant.

This is the danger of making assumptions, there’s no real way to know what’s an accurate assumption and what’s not.

Just design your box around what you have, though I would run the tests with the driver in its normal operating orientation since there will be asymmetry with the cone facing up. That could be part of the difference.

I think I could drive myself nuts chasing this. The parameters derived from free air are very close to spec, but the added mass ones are the issue. Could be user error, the motor has weekened over time, or a combination of things. If it is an aftermarket, its a damn good copy. Just moving forward now.

 

[agedhorse]

I think I could drive myself nuts chasing this. The parameters derived from free air are very close to spec, but the added mass ones are the issue. Could be user error, the motor has weekened over time, or a combination of things. If it is an aftermarket, its a damn good copy. Just moving forward now.

Impossible to know.

 

[41hzthunder]

Made some progress on the box. Got the 6 panels squared and cut to dimensions. Stacked the parts together to see how it looks for size. Played with the baffle layout. I want to plan for a possible horn or mid driver addition, even if I don't put one in. There's not a lot of space on the baffle. I will remove a lot of wood to get the driver in and vents. Triangle vents are likely my best option, but they will present issues for the grill frame. I don't like open vents with no covering. Tomorrow I'll get the rabbet cuts done and cut the baffle holes. Here's a couple pictures of the box and one of the cone markings.

 

[41hzthunder]

Over the weekend I was able to make some progress. The cabinet weighs about 21 lbs at this point and the K-140 weighs 15.5 lbs, so about 36.5 lbs without hardware, tolex and potentially, a mid driver or horn. Its encouraging. The target was 45 lbs or less.

I don't know if I'll add a mid driver or horn, but before assembly I routed a hole for the Faital Pro driver to a depth of 3/8" that can be completed later. It was never going to be easier to use a hole cutting jig than before assembly. I also cut the parts for a sealed chamber for a mid driver and think its best to install that before tuning. I may never use it, but its there and ready.

Bassbox has been getting a workout, checking tunings and adjustments to the internal volume of the cabinet. At some point, the numbers won't tell me anything new. At that point, its a matter installing the driver, testing, and adjusting.

Some pictures of the progress before the cabinet is glued up.

 

[6thplanet]

Coming along nicely

 

[41hzthunder]

Its been a few days and I was able to get the driver in and get some data. First, with the the K-140 in and most of the hardware on, the cabinet as shown in the pictures, weighs 38.5 pounds. No tolex or grill, so weight will go up a bit. Second, the handles should have been 1-2 inches closer to the front, as the driver is a big part of the weight. Its not bad to carry, but would have been better balanced.

The box is tuned to 60 hz according to the impedance sweeps run on it. This was my target per the attached Amplitude Response graph. There were adjustments to the box volume, port size and length that got me to this. I'm pretty confident the final internal volume is 3.46 cubic feet. The sweeps, my measuring, and the modeling all agree.

When playing through the cabinet the volume is pretty even though all octaves, except when I get to F# on the E string. F#, F and E just seem a little less full. This is puzzling because I should have a slight increase in output on these notes. To get to 60 hz tuning, the ports are only the length of the baffle thickness. Again, this was puzzling to me. When I reviewed my modeling it seems I misunderstood the area field as the sum of all vents, not the area of each. So, yeah, wrong. I had decreased the size of the ports slightly to make the baffle layout work better and expected the vents to be longer. The program was saying add about 3 inches and that seemed possible since the vents were smaller. However, I had to remove the internal vent parts that were temporarily mounted to get to 60 hz tuning.

I'm wondering if the shallow depth of the vents is less efficient and not loading in a way that gives the low end boost for those last 3 notes. Also wondering if adding a third vent would make sense. The port length would go up to 2.9 inches, not a huge difference, but would give them some air/volume.

.

 

[41hzthunder]

I expected I would have to make adjustments to the cabinet while getting the tuning dialed in.

After more modeling in Bassbox today, adding a third port and trying a little higher tuning for the cabinet, I came up with the plot below. The results were really promising reducing the -7 db dip to -4 and increasing the 82 hz SPL to +1 db. The peak of the SPL bump occurs below the 2nd harmonic of the open E, but it does raise the E. F3 is 59.26 hz. Hopefully, this will give me a fuller open E tone. It just looks like a better outcome. However, that result is only possible if the box is tuned to 65 hz. The current port configuration can't do that, so its time to add a 3rd port in the upper left corner. The ports will be 1.69 inches deep, not a lot deeper than where I'm at, but some. Hoping its enough to improve the port function. The new port should be in before noon tomorrow.

 

[41hzthunder]

Okay! This project is in the end zone for now. The cabinet is under 40 lbs and should remain there when the aluminum grill is added. If a second driver is added, it will get up to 43 lbs.

I got the third port added and nailed the tuning! I'm happy to report that the week F#, F and E are now full and solid where they should be. The part of the port behind the baffle is attached with screws, which makes it easy to lengthen (or shorten) the port. The picture is a little distorted, but all three ports are the same size and shape.

In a couple weeks I'll post the completed cabinet with the grill and finish. A sound clip too!

At this point, I need to thank everyone that helped me understand the design issues and technical stuff. Definitely wouldn't have gotten here without the help. In particular, I want to thank agedhorse for his generosity with his time. There are several senior member on TB that are generous with their time and never get enough thanks.

Lessons learned:
1. This took a lot of time and if I didn't already have the wood, driver and a lot of free time, this might not have happened.
2. Research drivers, the tone you want and let the modeling software dictate box size and tuning.
3. Building without the abilty/equipment to test and verify results will likely put you somewhere other than where you wanted to be.
4. Know your limitations and stay within them, or take the time to learn the needed skills.
5. Your result may differ from your initial vision. That's okay.
6. Enjoy the ride!

I'll spend a couple weeks playing through the cabinet and determine if more high end is needed.

 

[Stylee Mousse]

I love those JBLs! Warms me cockles to see one in play.

I think you will enjoy it.

Nice cab also!

 

[JimChjones]

Good work.

 

[6thplanet]

Looking forward to seeing the finished product.

 

[41hzthunder]

Okay, took a little time, but here's the final look.

I decided to go with epoxy and paint for the finish. It was partly for the aesthetic and partly because I had the materials on hand. The sequence was 2 coats of epoxy sanded smooth, white primer sanded smooth, 2 coats of Ocean Mist, and one coat of matte clear. My wife volunteered to sew a cover for it, so it will be protected during transport. Its a custom speaker and I just thought why not do something custom for a finish.

The sound does seem very even through the registers. Yes, that's subjective and I'm working on a way to measure it objectively. Mentally, I'm geared to look for flaws more than admire my work. I'm always looking for things that can be improved. If I did it again, I probably wouldn't use the triangle ports because it made building the frame for the grill more complicated. Aside from that, higher frequencies still have me wondering. I'm very split on whether I need to add a driver for above 2.5k hz There's some high frequencies I would like, but they probably wouldn't matter in a mix. I would also have to figure out how to build an appropriate high pass filter and LPAD circuit. Perhaps in the future.

The cabinet works well with my '89 Fender Jazz Bass Special (MIJ), Fender Precision, and Rickenbacker 4003s. Each has a unique sound, but all are good. IMHO.

 

[6thplanet]

I dig it! Any reason you didn't paint the baffle black?