Scrappy, a lightweight 8” cab built from scrap

[6thplanet]

Cool build! Should be a solid cab.

 

[ThisBass]

For driver Qts equal to ~0.7 I'd build a sealed cab rather than ported.

If I was in OP's shoes, I'd likely seal the port opening

 

[Razman]

Please post in the Janky Rigs of Doom thread when completed!

 

[mizedog]

For driver Qts equal to ~0.7 I'd build a sealed cab rather than ported.

If I was in OP's shoes, I'd likely seal the port opening

Thank you,
Caclulating in the Efficiency Bandwidth Product (EBP) of 61.25, my hope was to squeeze out a little more low end extension than a small sealed cab would get. Otherwise, I would need a huge cab, which would eliminate the light weight aspect I hoped to achieve (thinking of my daughter carrying It).

Here's what looks like a dismal response from a similarly size cab.

Maybe this will end up as firewood. Not sure yet.

 

[agedhorse]

Shorten the port about 20%

 

[mizedog]

OK, sounds like raising the FB to about 49hz, which would require less cone excursion than the 45hz I had modeled to. It would mean a mild bump from 55-110 hz. I'm learning.

 

[ThisBass]

OK, sounds like raising the FB to about 49hz, which would require less cone excursion than the 45hz I had modeled to. It would mean a mild bump from 55-110 hz. I'm learning.

I mild bump isn't all that bad.
Most of the time, especially for MI cabinets, a flat response was not neccessarily always wanted.

Regarding ported vers. sealed. Try to compare the sound of your cab when you block the port (respectively sealed cab), then go with the variant you like best.
Btw. it may be helpfull to evaluate the sound of the cab (sealed vers. ported) when you try to play some percussive/dynamical stuff on your bass guitar

 

[agedhorse]

OK, sounds like raising the FB to about 49hz, which would require less cone excursion than the 45hz I had modeled to. It would mean a mild bump from 55-110 hz. I'm learning.

Yes, this is ok

 

[ThisBass]

OK, sounds like raising the FB to about 49hz, which would require less cone excursion than the 45hz I had modeled to. It would mean a mild bump from 55-110 hz. I'm learning.

I'd suggest something in the range of 50..55Hz versus 45Hz.
From all what I can see this would help to improve damping at some content (and also help to reduce group delay).
It also helps to provide a "more musical" roll off shape vers. Fb 45Hz

edit:
furthermore a shortened port (better relationship of length vers. diameter) helps to damp unwanted port resonance.

 

[mizedog]

Wow, thank you so much.
I may screw on the top tonight and take a listen. Then, reduce the port length to the ~49hz point, then go further if needed.

 

[ThisBass]

Wow, thank you so much.
I may screw on the top tonight and take a listen. Then, reduce the port length to the ~49hz point, then go further if needed.

Although I suggested something in range of 50..55Hz.
Once you start with something ~49Hz take care with every piece of length you further cut off. Once the port is too short in length to meet your taste of sound, then it's too short, and a pain in the ass.

 

[6thplanet]

Your internal brace/port mount is a nice idea, but didn't allow for further tuning. Also note you'll be taking an inch off to make any discernable difference in tuning frequency.

 

[mizedog]

Sorry for the delay in progress. My daughters were in a really bad car accident last week, and I've been spending time at the hospital, and taking care of them at home. Right now, it's a full time job.
I've decided to simplify the design of the top. Instead of recessing a handle on top, I'll put the strap handle on the back. I've already drilled a hole for the jack on the top, and hope to get it wired up tonight for a test run. Sorry, no fancy aluminum.
I've got practice next week for a new group in a friend's basement. Having a light weight cab will really make the load in/out easier; especially on my new, bionic left knee!

 

[abarson]

So sorry to hear about your daughter. Take care of her, the rest of the world can wait.

 

[mizedog]

Thank you a arson.

 

[mizedog]

I was able clamp down the top, and give it a whirl (no foam lining yet). With the full length of tube, the lows were soft, and used a ton of cone excursion (as warned about). I cut off enough to bring the port length down to about 4.6", and it seemed to help. This driver is very bright (no surprise there). I added a little more cab bracing, and will add some foam. I'll also play with plugging the port as suggested.
To use this as is, I would have to drop the highs, and some mids. But, I think it will be usable for the quiet church, practice setting.
Please excuse my sloppy playing. It was late, and I haven't picked up a bass in a few weeks, and it was late.

 

[Lo-E]

Regardless of how this little cab project turns out, I hope your daughters are okay.

 

[mizedog]

Thank you Lo-E. Family is definitely the priority.

 

[6thplanet]

From the recording, doesn't sound to bad. Is that with the shortened port?

 

[mizedog]

Post #36 is the shortened port, higher tuning to about 50-52hz.

This one is the long port, tuned to 45hz (prior to being cut down).