12" Cab Diary Continued

[funkle]

Here’s a grenade I’ll just throw into the mix. Probably merits a separate thread. But..

How much smaller could this cab be shrunk without compromising the low end too much? (But keeping the compression driver). I’m thinking about the Barefaced Super Midget style proportions...pretty tiny...very appealing...

(https://barefacedbass.com/product-range/Super-Midget.htm)

I know that shrinking the box will potentially affect driver output as well. But I’m just interested to know. 

[LukeFRC]

25 minutes ago, funkle said:

Here’s a grenade I’ll just throw into the mix. Probably merits a separate thread. But..

How much smaller could this cab be shrunk without compromising the low end too much? (But keeping the compression driver). I’m thinking about the Barefaced Super Midget style proportions...pretty tiny...very appealing...

(https://barefacedbass.com/product-range/Super-Midget.htm)

I know that shrinking the box will potentially affect driver output as well. But I’m just interested to know. 

My guess is there’s two problems with this... one shrinking it means you’re going to have to compromise things to get it ‘flat’ again - and also the front baffel is pretty crowded so I doubt those dimensions can shrink much (and if they did the Xover would need jiggling(?) and it’s only 26cm deep - loose much more and you will struggle having enough space behind the port that it doesn’t get affected by the back wall...

[funkle]

Good points. I’m less interested in ‘perfectly flat’...you shrink the cab and you get a little bass hump often which can be helpful. Or a hindrance, depending on your design preference. I’d be interested in knowing what ‘good enough’ is...tricky question. 

[LukeFRC]

5 minutes ago, funkle said:

Good points. I’m less interested in ‘perfectly flat’...you shrink the cab and you get a little bass hump often which can be helpful. Or a hindrance, depending on your design preference. I’d be interested in knowing what ‘good enough’ is...tricky question. 

You’ve a 125mm wide port ending only 110mm from the back wall... so not much wiggle room there the baffel if it went on a diet I think could only be made 50mm thinner and narrower maybe, if everything fitted... It’s hardly big gains there... maybe if you used the port on the side that would let it shrink down more... and you’re having to reengineer construction, baffel and so on. How much smaller would you want it? 

The previous version v2 had s smaller tweeter and different porting so maybe that would work? That used the Bayma driver though. 

[LukeFRC]

FYI to make the volume of the cab (based on exterior dims) the same as the barefaced compact it would need to be 16cm shorter.

That horn is 17.2cm high.... 

 

[RichardH]

I think you'd have to look at the design @Phil Starr demoed building - dimensions 35cmx45cmx23.6cm, (compared to the 45cm x 42cm x 28cm of the BF cab) but add a tweeter - maybe the one used in v1 of the cab - rather than a compression driver with horn. 

[stevie]

19 hours ago, funkle said:

Here’s a grenade I’ll just throw into the mix. Probably merits a separate thread. But..

How much smaller could this cab be shrunk without compromising the low end too much? (But keeping the compression driver).

Luke and Richard have more or less answered this question. My answer is: not much. You could reduce the volume by no more than 10 litres if you wanted to. You would lose a bit of bottom end but not a huge amount. Drop the size by any more and you'll lose the bottom end solidity. The Beyma SM212 will work in a slightly smaller box than the Faital - so you could in theory make that even smaller.

The problem is, of course, where can you shrink the cab? If you were to use a box pan grille, you could reduce the width of the cab marginally, as the baffle has been sized to accept a picture frame grille. You could also take about 30mm off the height (but no more) and still keep the horn. But as Luke has pointed out, you can't reduce the front-to-back depth because of the port. 

Personally, if I wanted a smaller cab than this one, I'd be looking at using a 10" driver. If you try to cram a 12" driver into too small a box it's easy to end up with a thin sounding cabinet. You then need to use two of them to get a decent sound.

 

[funkle]

Gotcha. Thanks everyone. Very informative discussion as usual!

[stevie]

If anyone reading this thread is going to the South West Bass Bash next month, you'll be able to try out the system I've been building here. I've also been promised a CNC kit of parts in time for the Bash. Fingers crossed that it happens.

[stevie]

It looks like the prototypes of our CNC kit will be ready tomorrow. I'll therefore be bringing them to the South West Bass Bash on Sunday. The crossover is now finished and I'll post a photo shortly along with the circuit diagram. Here are some measurements of the final system.

This is on axis:

[stevie]

Here's the 60-degree curve (30 degrees off axis).

And the 90 degree curve (45 degrees off axis).

[stevie]

Achieving a smooth response from above the cabinet was one of the design goals. However, I was surprised at the following measurement, which was taken from 4 feet in front of the cabinet with the mic at ear level, or about 5 ft. 7 inches. What this means in practice is that you will be able to clearly hear the pitch of what you are playing even when standing close to the cab. I'm fairly sure there isn't any other bass cab capable of doing this without being raised or tilted.

This is actually an older measurement, taken before the last modification to the crossover, which improved the phase tracking and filled in the slight dip you see here between 2 and 3kHz.

Edited April 4, 2019 by stevie

[stevie]

Finally, here is the RTA measurement of the cab standing on the floor in my garage. It is the average of about 12 points in space and gives a good idea of how the cab will sound in a room. The rolloff at high frequencies is normal for this type of measurement.

 

Edited April 4, 2019 by stevie

[funkle]

2 hours ago, stevie said:

Achieving a smooth response from above the cabinet was one of the design goals. However, I was surprised at the following measurement, which was taken from 4 feet in front of the cabinet with the mic at ear level, or about 5 ft. 7 inches. What this means in practice is that you will be able to clearly hear the pitch of what you are playing even when standing close to the cab. I'm fairly sure there isn't any other bass cab capable of doing this without being raised or tilted.

Phenomenal graphs. I can’t wait to build one. 

I do think one cab, the Big Baby 2, that Alex makes, would be able to match the performance here...in terms of audibility above or near to the cab without having to tilt it or raise it. It has a less expensive compression driver and a nice waveguide. But I can’t think of many other bass cabs that will do that. Maybe the Audiokinesis models as well - the Thunderchild, Hathor, and Changeling. Those have some unusual techniques to allow audibility above the cab.

It is stellar work though! I’m stoked. 

[stevie]

Thanks Funkle. Much appreciated.

I thought I'd go and re-measure from above the cab, as it really is quite impressive now. Remember this is from nearly six feet above the cab. Here you are:

 

It's possible that one of the Audiokinesis models could do something similar, I agree. I saw that Duke has used a 90 x 90 horn on one of his models. The reason the response of this cab doesn't collapse at higher frequencies is because I've turned the horn round so that the 90-degree dispersion is directed towards the player's ears - and because the crossover point is relatively low. The Barefaced model can't do this because its crossover point is much higher (and it doesn't have a constant directivity horn). The ideal crossover point for our system would actually be around 1.5kHz, but that would take a more expensive compression driver and a larger horn. 

The measurement below shows what happens when you listen to a 12" driver with no tweeter from the same position. The Basschat cab is in green and a 12" bass guitar driver (with an on-axis response beyond 3kHz) is in red. It shows why you cannot hear your bass clearly when you stand close to a normal bass cab on the floor. That 1 to 3kHz region is really important for intelligibility.

 

Edited April 4, 2019 by stevie

[funkle]

Gotcha. Absolutely fascinating. I’m really stoked now! Fingers crossed for the CNC pack debut...

😎

[Chienmortbb]

Well the CNC cab was at the bash and was impressive. It was a prototype and the are a few things to iron out but I was impressed. The rigidity of the construction with no glue was surprising. When I say surprising, I mean surprisingly good. 

Edited April 8, 2019 by Chienmortbb
Add clarity

[stevie]

Here is a photo of the crossover in the cab at the SW Bass Bash. This is the one I was originally going to include with the kit.

 

After the Bash, I spent half a day revisiting the crossover design and  "revoicing" the cabinet to reduce the 2kHz to 6kHz region slightly. I and one or two of those present at the shootout heard a slight excess in that area.

As luck would have it, I managed to simplify the crossover somewhat in the process.  As soon as I have built another one up, I'll post another photo. It will basically be the same build quality but with fewer parts.

 

 

Edited April 13, 2019 by stevie

[stevie]

CNC cabinet assembly photos coming this afternoon. Watch this space.....

[LukeFRC]

19 minutes ago, stevie said:

CNC cabinet assembly photos coming this afternoon. Watch this space.....

Looking forward to it!

[stevie]

Here we go.

To assemble a cab you'll need:

Tube of PVA glue. I recommend the UHU PVA, which sets in an hour. If you want to build this cab really quickly, use their ultra-fast setting glue, which sets in ten minutes. It’s expensive though. Perhaps better to take your time and enjoy the creative process. You can easily build this cab in a day, but most of the time is spent waiting for the glue to dry.

Hammer. Soft-faced is best, but any will do as long as you use a scrap piece of wood when hammering on the face of the plywood, although the poplar we’re using has a much tougher surface than most.

½” brush to brush the glue into the rebates.

Also recommended:

Set of long clamps. Three clamps as shown in the photos are about £15 delivered from Ebay. These will be used to pull panels together, if required, so that they mate flush. They are definitely worth it, but you could get away with using weights and gaffa tape, or weights and woodscrews.

Drill. All the holes you need are predrilled, but if you’d like to fit t-nuts for the bass driver or the carrying handle, you’ll need to open up the holes a bit. The holes  provided  are fine if you want to use wood screws. I'd recommend t-nuts for the bass driver and four for the handle, but because of the light weight of the cab and the bass driver, normal woodscrews will be fine.

Start with the back panel.

 

Edited April 13, 2019 by stevie

[stevie]

For (my) convenience, these photos show a dry run without any glue. You can see that the back panel is rebated to take all the braces. Insert the main figure-of-eight brace into the recess. Tap it into place with your hammer.

[stevie]

All the panels are a very snug fit. You therefore need to tap them into place with your hammer. It is advisable to use a piece of scrap wood between the poplar ply and your hammer. You should end up with a joint like this.

 

[stevie]

Now fit the two vertical braces as shown. A quick tap with the hammer is all you need.

[stevie]

Now fit the second brace.