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Basschat easy-build lockdown cab project


stevie

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Back on track, thanks for this John, it's really useful to have an independent personal opinion. I have to say that this pretty much matches my own experience. I also rolled off the bass a tad and found the cab perfectly adequate for rehearsals. the basic sound is just a lovely open honest sound of the bass but I also added a little compression (and grit also). The band loved it. I'd also pretty much agree with the assessment of it's capabilities, 100+ would be beyond it as would anything outdoors.

 

You'll find when you have two for PA it will sound a lot better than the single speaker. I do a lot of critical listening when testing speakers and listening in mono often shows up things you don't notice with a stereo pair and of course the imaging will do so much to the experience.

 

This little speaker has given me a little doubt as to what I'm doing next. I've got the parts to build the 12" BC Mark3. I've been using bits and bobs of prototypes I've been taking to gigs for years and I wanted to have a go-to set up for important gigs. I've been using a couple of Beyma 12 based BC Mark1's for years. This BC 110T is so much better than it has a right to be and is so portable I'm now thinking of just having a second. Then I'll have two speakers I just won't touch for gigs and I can experiment freely with whatever else I have. For £125 and less than a days work it's tempting. Just a question of which one to build next.

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Yes, with the BC12MkIII. However, that was a much more complex design with extensive bracing that benefited from being CNC'd (and encouraged quite a few forum members to build one who probably wouldn't have bothered). I'm not sure that CNC is the way to go with this cab though, because the assembly technique Phil developed simplifies the way the cab is put together. You just need to get the panels cut accurately, which many wood merchants will do for you at nominal cost. And then it almost assembles itself.

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What we are trying to do is to introduce people to all sorts of ways of building cabs and encouraging them to experiment. At the same time we want to offer designs that will be satisfying to own and will work first time.

 

We're also trying to give enough information that people can do their own adaptations. If somebody wanted to there is no reason not to build the 50l MK3 cab with the drivers and crossover Stevie designed  but using the 'easy build' technique. Or you could  build the cab we are discussing here with a circumference brace borrowed from the MK3, or indeed a rear port. If you keep the overall volume and the port dimensions the same you preserve the tuning so if you wanted a taller cab or one that matched your amp dimensions that's all possible.

 

Everything we do on here is creative commons, we're happy for people to build the cabs for their own use or to build one for a friend so long as it is done on a not for profit basis. If anyone wants to put together a small run of CNC flat pack kits for BassChatters on a not for profit basis that's good too from my point of view.

 

I'm not sure what the next project will be, I've got all sorts of plans but I need to clear some of my stinky poo out of the house to make some space. I'm also being reminded I have to fit a new bathroom :)

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this is a little off topic, but....

 

When tuning a round port, I can do the rice/frequency generator test and trim the overall length to suit what I need

 

When buidling a shelf ported cab, is there a trick to tuning? 

 

I could see adjusting the shelf to suit being a bit of a pain with a built cab (apart from building a prototype first and hacking it about a bit :))

 

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1 hour ago, carnabass said:

this is a little off topic, but....

 

When tuning a round port, I can do the rice/frequency generator test and trim the overall length to suit what I need

 

When buidling a shelf ported cab, is there a trick to tuning? 

 

I could see adjusting the shelf to suit being a bit of a pain with a built cab (apart from building a prototype first and hacking it about a bit :))

 

That's one of the reasons we use tube ports. It's a lot easier in the prototyping phase. Otherwise it's probably better to make the shelf undersized and add on rather than have to cut bits off. 

 

I prefer round ports anyway. The walls of any port are where there is resistance to air flow and where non-linear air flow starts to cut in. The way to have the least air in contact with the walls is to have a circular cross section. We also found that multiple small ports demonstrated earlier chuffing than a single large one. Not very scientific as it was a sample size of one but it was a very obvious effect.

 

Having said that other considerations come in to play. I often use whatever port material I have to hand, either plastic plumbing pipes or cardboard tunes from carpet warehouses.. Some designers have used triangular ports in corners. They'll experience more turbulence but it's a really convenient place to put them and the triangular bracing of the panels will be significant. Stevie really doesn't like chuffing so uses large ports for preference. I don't mind high port velocities on the basis of the absence of much fundamental coming from the pickups. It's hard to say any particular design choice is the 'one' as all speaker design is a matter of weighing gains in one area against compromises elsewhere.

 

We are really happy to go off topic, lots of people read the answers and learn stuff and it keeps us on our toes for the next design.

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32 minutes ago, Phil Starr said:

 Some designers have used triangular ports in corners. They'll experience more turbulence but it's a really convenient place to put them and the triangular bracing of the panels will be significant.

 

To put the tonal counterargument for triangular ports at the corner of the boxes, I'll defer to the prose of BFM:

 

Quote

Corner ports also sound better than round or slot ports, as their placement equalizes air pressure inside the cabinet, preventing cone rock at high levels

 

The way I read this you would get a similar effect putting round ports at each corner of your box. In a band context I doubt I would be able to tell the difference, but maybe others will be able to.

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5 hours ago, chyc said:

 

To put the tonal counterargument for triangular ports at the corner of the boxes, I'll defer to the prose of BFM:

 

 

The way I read this you would get a similar effect putting round ports at each corner of your box. In a band context I doubt I would be able to tell the difference, but maybe others will be able to.

According to Duke Le Jeune, a respected designer of bass cabinets, cone rock only occurs if the port is directly behind, but off centre, to the driver. In one of the threads in Talkbass he goes into detail about he got, and solved the problem of cone rock, with the help of Eminence's technical department.

 

This is opinion. Corner ports are a type of slot port and they break several of the conventions. Firstly as @Phil Starrhas already mentioned, @steviehas demonstrated  to me and @Phil Starrthat a single large round port is better than several small ones*. There is no good reason to suspect that this is not true of multiple corner ports. So why do people use slot or triangular/corner ports. Firstly they act as bracing and secondly they negate the need for an expensive moulded port**. Remember that the wood that creates the slot or corner port is effectively an offcut of the main cabinet panels or a much cheaper material.

 

*This was why the Mk3 version of the BC112 cabinet had one large port instead of four on the MK1.

** A part costing £1 at manufacture will probably end up £3-4 on retail price.

 

 

 

 

Edited by Chienmortbb
smelling cheque
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Slot and triangular ports do not have to be an issue, again when designed with this in mind. The pro audio industry has used both for decades without any problems being described.  The common theme is that designers using such ports design them so that they typically don't have an aspect ratio much over 1.5:1 depth to short leg dimension. These are products that have tens of thousands of pro touring shows under their belts, so there's no doubt that they have proven themselves many times over.

 

I have used both types of porting as well, and haven't experienced such difficulties either.

 

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I don’t think anyone has said that slot or triangular ports haven’t been used or that they are unusable. John was explaining the reasoning behind our choice of single round port for this cab. There are some practical benefits to using alternative shapes but, if your aim is to minimise port chuffing/distortion/compression, a round port performs better than any other shape because it allows for the most uniform flow of air through the port. On small, high power cabinets, a carefully optimised port can make a big difference.

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I hope people building their first cabs at home aren't being put off having a go at building by this :)

 

It's great to see a range of opinions though. You'll see different designers have differing opinions and the truth is many of us have 'go to' ideas we tend to repeat. The reality is that all speaker cab design is a matter of balancing differing concerns. In the case of port designs it is pretty much impossible to design a really compact high power cab with deep bass that won't have higher port velocities than you'd like. For high power, high excursion speakers you need a wider port to allow it to 'breathe'. Increasing port area for a particular tuning means the port needs to be longer and that both increases the volume of the port and takes it closer to the back of the cab. If you are aiming to have a compact cab then a port of several litres is obviously something to avoid.  so you have to compromise. Equally if you have a small cab then the places to put a large port are limited, more compromise.  Just look at the RCF PA cabs; generally recognised to be one of the best sounding units available at the moment. Every spare bit of space at the front is either port or speaker.

 

image.thumb.png.af902d72561c7c04da2c77c0b284c398.png

This is just the port of course, there are other tweaks and compromises to be made: weight, portability, target response and so on. then there are practical considerations like the cost of production for commercial designs and the availability of parts for the home builder. If you buy a cab then you are stuck with the compromises chosen for you, if you self build you can add your own tweaks or accept the tried and tested designs so you have a bit more choice.

 

You can see the difference in approach even in this cab. I designed the original box which had a 12" speaker and two smaller ports. That design choice was based upon having a lot of 68mm pipe to hand and the availability of a 68mm hole saw at a price home builders could afford. I check them but I'm not particularly concerned about port velocities as I rarely if ever find they are a problem with bass guitar. My design does chuff with test signals but has never made unpleasant noises with me at gigs (apart from my playing of course) even though it has a 12" driver with greater excursion and power handling. Stevie chose the most widely available and affordable ready made port and that won't exceed unacceptable port velocities under any conditions within the pass band. It's on the big side for a single 10 but it fits and it works. The tuning isn't an issue as that was done by measuring after the cab was built. 

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3 hours ago, agedhorse said:

Oooh, and it has both slots AND triangles too!  ;)

 

To be pedantic, they are all irregular quadrilaterals. 🙂

 

I'm sure the cunning selection of side dimensions so they are all unequal ensures smoother resonances in the 40-43Hz band, while enhancing the sprightliness of the 48Hz undertone.

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5 hours ago, agedhorse said:

Oooh, and it has both slots AND triangles too!  ;)

I am sorry for sending this thread off track so this will be my last contribution on posts (at least until the next time). Those RCF speakers are excellent as are many others without round ports. I would happily use those if supplied at a gig for FOH applications and I know a number of people on here and Talkbass use them for backline/monitoring successfully. However for this project the round port is both easiest to implement and gives the best result.

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