DIY Angle Cab - what would you load it with?

[thoward]

Evening all
(Apologies for the rambling post, if you are skip reading move to the bit in bold)
I am just looking for some thoughts on something I am considering building-

I started out with an old Trace Elliot BLX150 combo. It's a strange little unit with a 130W head, a 10" speaker and a little diffusion slot. It's deep but it isn't punchy. I was playing pub gigs and the bass wasn't always amplified, so I took the head out of the combo amp, built a single 15" ported cab (with an Eminence 15" - no tweeter - not certain on the Eminence model as it was 10 years ago - maybe a Kappa Pro 15?), and made a wooden sleeve to make a head out of the amp section of the combo which sat on top.

Now however I'm playing at home and practicing, and maybe with groups like dance bands etc, and whatever we do is properly amplified, DI'd and monitored, so I don't need a 15" cab, and I'd like it to be a bit more compact, and to reduce stage spill I'd quite like an angled cab.

I'm considering using the top of the Trace old combo (I know it's low power and old hat, but I'm kind of attached to it now) and making a small, compact angled combo cab, casing the head as well, with something really small and punchy like 2x8 or 2x10, or maybe 1x12 or 1x10? What would you be building, and how much should I pay attention to cab resonance etc (I did make some 12" & tweeter PA cabs about 10 years ago as well, and drew it all up on WinISD etc - but this was for full range response, what are reasonable responses for a bass cab?) and how much is just judgement and drivers for something which sound is so subjective?

 

[thoward]

To make this a bit clearer I've drawn up a quick sketch of what the angle cab might look like.
I've got three images, one is the head (it's a really shabby cab build..), and two of the kind of size of the combo. I haven't drawn the front of the combo and obviously the size will adjust according to the drivers, and the size of box needed for the drivers..

What would you think of loading it with and sealed / ported box or what kind of design would you be thinking for a small practice/small gigging amp like this?
I'm thinking more of an amp for an orchestra / theatre band pit rather than pub/club gigs

Obvious configurations that would fit would be 1x12, 1x10, 2x10
Further afield - would 2x8 be too small? 1x15 probably too heavy.

 

[T_Bone_TL]

Assuming you don't want to just load up the 10 from the old combo...? That would be the frugal first choice, since you seem to have moved away from the reasons you stopped using it and went to the 1x15, so it (with an optimized & angled box) might do just fine...

I'd lean to the 1x15 and a lightweight box, but that's my personal preference.

 

[thoward]

I don't actually know what the 1x10 in the original combo is - I supposed it must be a decent enough driver but I never considered it. That said I've got the original combo wrapped up and stored so I can turn it back to original if I ever want to sell it, and I'm not too worried about being frugal. I don't want to pay silly money for a driver but can spend sensible money.
By lightweight how would you make it lightweight? Lightweight driver or say 15mm instead of 18mm material?

 

[Rune Bivrin]

By lightweight how would you make it lightweight? Lightweight driver or say 15mm instead of 18mm material?

No reason to even use 15 mm material. I've used 9 mm ply with ample bracing for horn subs. 12 mm baltic birch ply is standard fare. Add an Eminence KappaLite 3012HO, DeltaLite II 2512 or BassLite 2012 and you have a very useful home combo that is easily moved when vacuuming.

I'm about to start on much the same with an Ashdown Little Giant 1000 amp and a DeltaLite II 2510 I've got stashed away (or maybe two). It'll be a tiny bit overpowered...

 

[thoward]

I'd be a bit worried about going down as thin as 9mm but in guess it depends on the overall size of the panels. I guess you need battening with 9mm though that you wouldn't need with 18.

You'd go with single 12 then? If I could reduce that height how would 2x8 compare?

 

[Rune Bivrin]

I'd be a bit worried about going down as thin as 9mm but in guess it depends on the overall size of the panels. I guess you need battening with 9mm though that you wouldn't need with 18.

You'd go with single 12 then? If I could reduce that height how would 2x8 compare?

9 mm is quite OK provided you brace sufficiently. Which is something you should always do anyway. Lack of bracing due to the complexity when mass producing is why commercial cabs generally go the "thick as a brick" route. That and the sad fact that a lot of people associate heavy with quality.

But for a smallish cab the gains going from 12 to 9 mm is very small. But you'd still need bracing.

I can't speak for the drivers; for home use you shouldn't really need that much. You'd probably get good mileage out of 2 Beta 8 drivers too. Or even 1.

Small, loud, deep. Pick any two.

 

[thoward]

I'd say getting a deep sound is more important than pure volume. When I say home playing I might use it outside of home, but most work I am involved in now is cabaret style / lounge style where I'm more likely to need monitoring than proper level.
How would you go about designing the cab, ports (if any) and bracing for the cab? Would you have internal battening on a 9mm ply cab then? This would be a job for the top sleeve where the amp section is- I guess that would still have to be strong enough to be self supporting. Compact is a priority but weight isn't a massive issue

 

[Philonius]

This recent thread featured a cheap-but-good 12" driver:

http://www.talkbass.com/threads/ano...mall-and-cheap-22-pounds-that-pounds.1095329/

I thought about taking this basic concept; driver, box size, port dimensions, and re-working it into a kick back design like you are considering. It seems it would be easy enough for someone who knew what they were doing. I wasn't sure exactly how one would reconfigure the port dimension with a change in box layout. Easy enough perhaps? If I felt confident enough I wasn't going to screw up the tuning, it would be a very tempting project.

 

[T_Bone_TL]

I wasn't sure exactly how one would reconfigure the port dimension with a change in box layout.

Step one, keep the area and length of the port the same. Step 2, reinforced by many a TB DIY build, make the port shelf in sections, and don't glue it all in place until after you test the box tuning, so you can make final adjustments ["the sugar (or rice) test."]

As for lightweight, thinner wood and more bracing (not just or even mostly "ribs" - a lot of it is poles/rods/columns/dowels/broomsticks right across the cabinet) or following Zac and Pete and a few others down the composite (fiberglass/XPS) route, which seems to have worked well and held up well for them, despite some "running the heck away" that seems to have happened on the commercial cab front. I've been away from TB for several months, and sometime in there I gather there might have been some sort of fecal matter storm involving commercial composite cabs, based on some of the composite-hostile comments I've seen recently. AFAICT, Zac and Pete still seem happy with their home-made ones a good many years on, so I have hope that mine will turn out OK if I get it done that way.

 

[Philonius]

^ When reconfiguring a cab's dimensions, and aiming to keep the internal volume the same, is the area within the port considered as part of the cabinet volume or not? Not sure if it would necessarily change, just want to be clear on the concept.

 

[T_Bone_TL]

My understanding (having read up quite a bit while dithering on actually getting started with my build) is that the port is "not" considered part of the box - if internal, it (like the speaker cone/magnet/bracing) is deducted from the overall internal volume.

I sometimes amuse myself with visions of external cab ports rising from the top like exhaust pipes (but it would be annoying to carry, or need to be easily broken down for transport.)

 

[thoward]

Sounds like chimney stacks..

I've drawn up the cab with 2x Eminence Beta 8s (for some reason I like the idea of 2x8 rather than a 12, and I can't fit 2x10 in that cab at the moment


It's approx 31L cab, and tuned with that port to around 58Hz (it's a 23cm port 43cmx3cm, so equivalent area to 12cm diameter port according to my maths - I'm a bit restricted at the moment as I am totally Mac-based at work and home so can only use the online version of WinISD, so it's a bit long winded)

I'm not sure what type of response I should be looking for? It's a terrible way of working, but there is a graphic on the amp so I can change the tonality somewhat.

I also looked at some Neo drivers that are about the same price as the Eminence and have a slightly more interesting curve:



But the drivers are a bit of an unknown - the supplier seems to rate them (they are a pretty trusted supplier in the UK as well) but they look a bit weedy:

http://www.bluearan.co.uk/index.php?id=PAUE8200N

What are anyone's initial thoughts? I could tune the cab a bit - at the moment I worked backwards from the dimensions rather than really tuning the cab for the speakers.

 

[T_Bone_TL]

I like the first curve better of those two.

@fdeck's program is a bit quicker and highly portable, but you have to scroll through the results to see some of the calculated parameters. Well worth a whirl. Invalid Link Removed

Having accepted that "flat down to 41" is not needed, not normal, and hard as heck to get, I'm trying to keep the -3db point below 82 Hz to catch the first harmonic of the low E, which neither of those manages; but the second one has major falloff well above that before it hits the sharp knee. On a practical note (and it may just be the drawing, of course) I'd fair the corner (round off the sharp edges) on the bent port. Based on current reading, with some added construction complexity admitted as a fault with this idea, I'd also consider two ports, at half the size, one below the left driver and one above the right driver - supposed to help with cooling air flow.

 

[thoward]

Do be honest I can't see cooling be a major issue there but I see what you are saying as with the only port being at the bottom there would be no airflow in at the top - it makes the grill across the two 8inches slightly harder though as it would have to cover the ports as well. I would quarter or half inch round all the edges depending on material thickness but I just haven't bothered to illustrate that on the drawing.

I'll look up the root frequency of that bottom E and make some more informed drawings - thanks for the frequencies you'd be aiming for.

The back story of this is I used to play as a teenager, but haven't picked my bass up for over a decade - I want to make a nice-ish custom amp to start again with. I'm a theatre technician by trade so have the electrical knowledge and can physically build the cabinet (hopefully) to a reasonable standard but the acoustic knowledge is my weakest area - also quite what you're aiming for - I know what the response for all sorts of PA systems should be but a bass amp is so subjective I don't know what kind of response we're actually aiming for.

 

[Jools4001]

You could reinvent the wheel or you could look at existing designs that have done all the hard work of speaker selection, cab design and tuning for you, such as Bill Fitzmaurice. There are several sizes of monitor plans available in both horn loaded and reflex designs. I built two of the Wedgehorn 8s as vocal monitors and they are great at what they do, but the beta 8s that are in them aren't capable of going much below 100hz in those enclosures so they don't do bass...apparently the larger 10" version can. If you're not wedded to monitor style cabs, there are also simplex and jack models that might appeal

 

[T_Bone_TL]

I would quarter or half inch round all the edges depending on material thickness but I just haven't bothered to illustrate that on the drawing.

I'll look up the root frequency of that bottom E and make some more informed drawings - thanks for the frequencies you'd be aiming for.

I was particularly thinking of the bend inside the port, but yes, I hardly expect you'd bother to show that on the drawing in any case. And if following the thread (22lb...) we are referring to, I'd really contemplate 1 12 .vs. 2 8's - speaker, box, etc already sorted out in that build, just keep the box volume the same when reshaping it. Per the builder, @Lowactnsatsfctn

According to WinISD, this cab should take 237watts before reaching Xmax, with an F3 of 62HZ.​

Which exceeds my current rough and ready go/no-go approach by a solid 20 Hz.

Not shockingly, you'll find that 41 Hz is the fundamental of the Low E on a normal 4-string bass.

Also, Xmax is usually the limiting factor in bass speakers/cabinets, rather than "power rating"

 

[thoward]

Okay, not a bad idea, you will have to excuse this but I plugged the numbers from that (specs of the driver and box dims & tuning into onlineISD as it's the easiest way for me to compare with the other two graphs)



It's not worlds apart though it is a good improvement - on both we've got -9 at 50Hz, whereas the 12inch B&C is +6db better at 70Hz plus, whereas the dual 8 is losing a lot of power (-6dB) from very high, as you say. I'm going to plug some more numbers and try some improvement.

Link to the 22lb box plotted with B&C in fdecks program - that is nice, still need to use ISDonline to calculate port length for tuning mind
Invalid Link Removed

 

[T_Bone_TL]

Without bothering to go look for myself, does online ISD have the ability to model all three on the same graph in different colors? Regular ISD does that, which can be handy for comparisons. I keep an antiquated PC laptop around just for WinISD (and I don't let that one on the internet anymore.) In any case, looks a lot better to me...

Given that you'd be driving this with a 130W head, no real worries on the cooling front, I suspect, so keeping the port simple is a perfectly reasonable approach (I suffer from over-optimization disease at times.)

 

[thoward]

Unfortunately it always draws in green, so I can draw all 3 but still only in green. I do have a virtual installation of XP on my mac at work so I will install WinISD on that when I get back on Tues.

I have got some nicer curves using 2x B&C 8inch drivers but it gets pricey as the drivers are around £120 a piece so the single 12" is more economical. I'm not sure why I'm hung up on dual drivers, it just seems more instinctively to shift more air, and I was considering low passing one of them to give coupling only at the bottom end, but I think I might be being a bit too complicated just for the sake of it.​