Basschat easy-build lockdown cab project

[stevie]

Thiele Small parameters of the Pulse 10 checked and they're in line with the manufacturer's published data, bearing in mind the temperatures and the fact that the driver's still not fully run in. I also ran a free-air impedance curve and there are no nasty surprises. First main resonance is at just over 2kHz, which isn't unusual.

When I have the cabinet, I'll be able to compare the modelled LF response with the actual measured response.

 

[Phil Starr]

Cabinet is complete in it's basic form. It weighs just 5kg and I've noticed that Jewsons where i bought the ply are advertising it now as poplar cored, when i bought it it was sold as Baltic birch though it looks like a generic hardwood on the outer veneers. the Chinese are making 'poplar' cored Eucalyptus skinned ply at the moment which is what I suspect this actually is. Anyway poplar cored is a nice bonus as the cab is extraordinarily light and i didn't pay a fortune for the ply. It has some voids which is a nuisance but It's tough to find a source of really good ply at the moment without going to specialist suppliers. It's good enough and 5kg is a very pleasant surprise. Photo's soon

[stevie]

That's interesting. What I haven't mentioned is that builders have the option of making a tweeterless version, or building in two stages and adding the compression driver later. So a cab built from this plywood with just the 10-inch driver should weigh between 8 and 9kg, depending largely on the weight of the grille.

[JohnDaBass]

15 minutes ago, stevie said:

That's interesting. What I haven't mentioned is that builders have the option of making a tweeterless version, or building in two stages and adding the compression driver later. So a cab built from this plywood with just the 10-inch driver should weigh between 8 and 9kg, depending largely on the weight of the grille.

I'm considering the tweeteless combo cab having an added section above to accommodate a Harley Benton Block 300 amp. That could possibly be a small combo around 12kgs.

[RichardH]

Stevie, talking of grilles, would one of the off the shelf 10" round grilles do the trick (might not be the prettiest, but just thinking of those who want to do a tweeterless version at minimal cost). I should also say that Blue Aran do sell metal grill sheet, but I think the sizes are large and will be expensive if you just want a single speaker with masses left over.

[Chienmortbb]

8 minutes ago, RichardH said:

Stevie, talking of grilles, would one of the off the shelf 10" round grilles do the trick (might not be the prettiest, but just thinking of those who want to do a tweeterless version at minimal cost). I should also say that Blue Aran do sell metal grill sheet, but I think the sizes are large and will be expensive if you just want a single speaker with masses left over.

Some of us used a UK supplier on EBay for the grilles for the BC112 Mk3 cabs and they were made ti size an quite reasonable. I will try to find the details,

 

Here you go, you can get steel or aluminium. Alluminium is much lighter but does not take finish so well. https://www.ebay.co.uk/str/sgsmetals/Perforated-Sheet/_i.html?_storecat=7064986013

Edited February 18, 2021 by Chienmortbb

[symcbass]

Small cab suitable for my smaller gigs with upright bass? Following with great interest! Thanks for all the updates so far. 

[RichardH]

54 minutes ago, Chienmortbb said:

Some of us used a UK supplier on EBay for the grilles for the BC112 Mk3 cabs and they were made ti size an quite reasonable. I will try to find the details,

 

Here you go, you can get steel or aluminium. Alluminium is much lighter but does not take finish so well. https://www.ebay.co.uk/str/sgsmetals/Perforated-Sheet/_i.html?_storecat=7064986013

The prices are more reasonable than I thought. I imagine using an etch primer on the aluminium would give a better chance of a decent finish. I see that Hammerite do a direct to galvanised paint that claims to work with aluminium, too.

[Paul S]

Daft question #1. 

Would it work to mount this into an aluminium flight case if there was an appropriate size?

 

[JohnDaBass]

Just now, Paul S said:

Daft question #1. 

Would it work to mount this into an aluminium flight case if there was an appropriate size?

 

Daft Answer #1.

It would probably be easier to buy the aluminium sheet, corners and edging and "clad" the outside of the cabinet rather than painting with Tuff Cab. 

[Paul S]

1 hour ago, JohnDaBass said:

Daft Answer #1.

It would probably be easier to buy the aluminium sheet, corners and edging and "clad" the outside of the cabinet rather than painting with Tuff Cab. 

Thanks for that.  I was actually thinking of a ready made enclosure to save my pitiful DIY skills being tested any further than they need be. ... 🥴

[stevie]

4 hours ago, RichardH said:

Stevie, talking of grilles, would one of the off the shelf 10" round grilles do the trick (might not be the prettiest, but just thinking of those who want to do a tweeterless version at minimal cost). I should also say that Blue Aran do sell metal grill sheet, but I think the sizes are large and will be expensive if you just want a single speaker with masses left over.

One of those grilles would work fine. It's a cheap solution and protects the cone, but does look a bit home made. The round grilles made from punched metal, i.e. with small, round holes, look a lot better (if you can find them) but are more expensive.

There's enough space on the baffle to fit a picture frame for a cloth grille. Then there are the metal grilles from Ebay mentioned above. I had real problems getting the etch primer to stick on the aluminium one - I tried two different brands. Although heavier, steel grilles are easier to finish with the type of spray paint that goes straight onto metal (Hammerite, Platikote and the German discounters' specials when they're available).

Edited February 18, 2021 by stevie

[stevie]

3 hours ago, Paul S said:

Daft question #1. 

Would it work to mount this into an aluminium flight case if there was an appropriate size?

 

You'd have to watch for vibration and air leaks. Otherwise, it might be worth a try.

[stevie]

4 hours ago, JohnDaBass said:

I'm considering the tweeteless combo cab having an added section above to accommodate a Harley Benton Block 300 amp. That could possibly be a small combo around 12kgs.

Sounds like an interesting project. You could probably keep the cab the same size, as the few litres that the amp would take up won't be a problem. You'd just have to alter the port length slightly.

[Phil Starr]

3 hours ago, Paul S said:

Daft question #1. 

Would it work to mount this into an aluminium flight case if there was an appropriate size?

 

From the point of view of the speaker cabinet design the crucial thing is the volume, You'd want the same internal volume and space to fit the speaker(s) and port. Any volume that is substantially different would need a different tuning port. The cab we are building is of 12mm ply, anything thinner/less rigid is pushing towards the point where quite extensive bracing will be needed. This cab itself will be improved by bracing and we will no doubt discuss that later, once the basic design is finalised. At that point the success of the cab would depend upon the exact structure of the flight case. If you love that look then  go for it, but I think you'd have to be prepared to do some mods or get it custom made.

[JohnDaBass]

Phil, @Phil Starr

What are the draft dimensions of the prototype cab?

[Phil Starr]

The dimensions of the box are the same as the 'Easy Build' cab. Easy 12" cab build - Amps and Cabs - Basschat. Obviously the baffle (front panel) cutouts are different. We moved the 10" down as low as possible to leave space on the panel to include the port and the horn. You can get the size of the horn and port from Blue Aran's website and the 10" pulse from Celestion if you want to crack on with a build. We will put up a complete drawing once we have the prototype working and tested.

Edited February 18, 2021 by Phil Starr

[Phil Starr]

Just winging it's way to Stevie for the next stage.

 

[Mottlefeeder]

On 18/02/2021 at 11:41, RichardH said:

The prices are more reasonable than I thought. I imagine using an etch primer on the aluminium would give a better chance of a decent finish. I see that Hammerite do a direct to galvanised paint that claims to work with aluminium, too.

If you have the option of buying a pre-coated grill, I would seriously consider it. When you spray a grill, you spray from the front, and 70 % of your paint goes through to the newspaper behind. Then you spray at an angle so you don't miss the edges of the holes, and 70% of your paint goes through the holes... I reckon I spent £10-15 on paint for the last grill I painted.

David

[Jack]

On 18/02/2021 at 18:18, Phil Starr said:

The dimensions of the box are the same as the 'Easy Build' cab. Easy 12" cab build - Amps and Cabs - Basschat. Obviously the baffle (front panel) cutouts are different. We moved the 10" down as low as possible to leave space on the panel to include the port and the horn. You can get the size of the horn and port from Blue Aran's website and the 10" pulse from Celestion if you want to crack on with a build. We will put up a complete drawing once we have the prototype working and tested.

If the dimensions are the same then what is the advantage of the newer 10"? Is it purely a cost thing?

[Phil Starr]

The original cab was designed to do a particular job and has a tailored low end to suit smaller venues/rooms. The 10 is going to have a smoother response and is being designed as a full range speaker with a horn. The 30l cab is a deliberately small cab for a 12 but is a decent size for a 10. It is only the box that is the same, they are two different speakers aimed at achieving different things.

[Mottlefeeder]

On 18/02/2021 at 10:45, Chienmortbb said:

Some of us used a UK supplier on EBay for the grilles for the BC112 Mk3 cabs and they were made ti size an quite reasonable. I will try to find the details,

 

Here you go, you can get steel or aluminium. Alluminium is much lighter but does not take finish so well. https://www.ebay.co.uk/str/sgsmetals/Perforated-Sheet/_i.html?_storecat=7064986013

I have used this supplier for several cab grills and have been very happy with the results (he also offers a powder coating service) - 

http://www.speakergrills.co.uk

David

[martyy]

I'll be following this with interest. @Phil Starr mentions that the cab is being designed to be full range - does that mean that the cab could potentially double up as a PA speaker?

[stevie]

That question opens up a big can of worms, @martyy. Yes, at a pinch, you could use it as a PA speaker. However, cabs used for bass guitar normally take into account the extra bass response you get from using the cab on the ground. So it will sound bass-light when used on a pole in the air and you'd need to eq it accordingly.

The design goals of this project are not the same as a PA speaker, where the midrange is the focus of your attention. Remember also that this is a budget project. The Basschat Mk III cab was designed with no compromises in the midrange (expensive compression driver, low crossover frequency, good system power response) and works really well as a floor monitor or a PA speaker (in the latter case with the necessary LF eq). In fact, before lockdown, a group of us  compared it with an active RCF cab and agreed that its reproduction of voice  was superior.

I'll be testing the finished design using all kinds of material, including full range audio - and I'll report back.

Edited February 24, 2021 by stevie

[stevie]

I've been a bit busy with work recently, which is slowing the project up, but I managed to fit the drivers to Phil's cab and measure the in-cab impedance of the bass driver this morning.

The tuning frequency with our 100mm diameter x 120mm port is around 58Hz. We need to get it lower and I've already planned for that. Those of you familiar with WinISD might like to enter the parameters of the Celestion Pulse 10 to see what's happening.

The impedance curve is a useful troubleshooting tool, which tells you a lot more than just the load the driver is placing on the amp. Notice the bump just above 2kHz, which was there when I measured the impedance in free air. That's the main breakup point of the cone. There's likely to be some irregularity in the response here, depending on how well the manufacturer has managed to damp the resonance - if at all.

There's also a faint bump at about 350Hz. That's caused by the vertical standing wave inside the cab. It looks better than I'm used to. The most interesting - and unusual - bump is at 60Hz. I have a good idea what that is but will have to troubleshoot it.

Any suggestions?

Edited February 26, 2021 by stevie