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Bigwan

So I bought a heap...

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So I've bought a cab on the cheap. My sometime band are toying with the idea of taking up a share of a rented rehearsal space where we leave our own gear, rather than the gear-supplied-charged-by-the-hour variety. So I need an appropriate rig - something butt ugly, heavy as a really heavy thing, difficult to move, but with a reasonable sound. Hence this cab, which cost me the princely sum of £50...

It started life as a laney B215, about 20 years old I'd guess, but its had a challenging paper round. It's now loaded with 2 different peavey black widow drivers, a 1515KADT and a 1515KA in separate chambers. I doubt the cab was re-tuned when these were fitted. Each chamber has 2 4" ports fitted. The jack plate on the rear has had 2 of the original old connectors removed (XLRs by the look of them) and the plate is not sealed off from the top speaker chamber. The speaker grill has been off and on A LOT in its lifetime and is held on by 4" long drywall screws driven in at extreme angles. The baffle is pretty chewed up from where the grill used to be attached... And from the time before that... And the time before that... Some of these are bound to have gone through to the speakers chambers. 

Despite all that, it actually sounds quite good (at least as good as half the charged-by-the hour rigs I've used this past year). Loud, punchy and articulate... But there's a mild, farty distortion on almost every note when I dig in even moderately. I could possibly live with it in a band context, but it would annoy me a bit. 

The question is, given the description above, could there be an easy/cheap fix, beyond a glug of petrol and a match? Would a badly tuned and leaky cab distort? 

Help me Obiwan Kenobi, etc. 

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2 hours ago, Bigwan said:

. But there's a mild, farty distortion on almost every note when I dig in even moderately. I could possibly live with it in a band context, but it would annoy me a bit. 

The question is, given the description above, could there be an easy/cheap fix, beyond a glug of petrol and a match? Would a badly tuned and leaky cab distort? 

Help me Obiwan Kenobi, etc. 

You might want to check how well the speaker cones are glued to the chassis.  Check of they are loose, can be lifted with up from the chassis. For about 25 years I used a Peavey bass combo (bought new) fitted with BW speaker.  At the 25 year point the combo became very 'farty' in a gig.  It transpired that the paper cone was no longer glued to the chassis in any serious way.  It is fixable with  an appropriate glue e.g. Evostik, PVA, copydex, thixofix.  Do it sonner rather than later, I damaged mine terminally. Also check if the speakers have some 'foam' in the magnet as a 'dust trap'.  In mine this had disintegrated with age. 

 

Equally well it could just be a loose speaker, check they are well screwed against the baffle, it could also just be a vibrating panel.  Vibrating panels can be cheaply fixed with cross bracing using cut down broom handle glued in.  See Bill's post https://www.talkbass.com/threads/adding-bracing-to-a-cabinet.876201/

 

Edited by 3below
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All good advice from 3below.

Any leaks in the cab will produce the kind of noise you're describing. So my first port of call would be the input panel. If there are any gaps (from your description it looks like there are) seal them, and make sure all the jack sockets have a jack in them - not just the one you're using.

I'd also suggest you get someone to play the bass (low E is always good) while you crawl around the cab trying to locate exactly where the noise if coming from.

The good thing about having separate chambers is that you can use the drivers individually. So if you find you have a faulty driver, just disconnect it and use the good one.

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On 28/12/2019 at 21:58, 3below said:

You might want to check how well the speaker cones are glued to the chassis.  Check of they are loose, can be lifted with up from the chassis. For about 25 years I used a Peavey bass combo (bought new) fitted with BW speaker.  At the 25 year point the combo became very 'farty' in a gig.  It transpired that the paper cone was no longer glued to the chassis in any serious way.  It is fixable with  an appropriate glue e.g. Evostik, PVA, copydex, thixofix.  Do it sonner rather than later, I damaged mine terminally. Also check if the speakers have some 'foam' in the magnet as a 'dust trap'.  In mine this had disintegrated with age. 

 

Equally well it could just be a loose speaker, check they are well screwed against the baffle, it could also just be a vibrating panel.  Vibrating panels can be cheaply fixed with cross bracing using cut down broom handle glued in.  See Bill's post https://www.talkbass.com/threads/adding-bracing-to-a-cabinet.876201/

 

Good call on the foam. Having never experienced BWs before I was unaware of this issue. But that was certainly one of the problems. I've removed the magnets, cleaned out the remaining foam and dust, cleaned the melted goo off the voice coil/mylar former and cleared as much as I can get out of the air gap in the magnet. 

I'm awaiting fresh mounting screws, t-nuts and gasket tape before remounting the speakers. This'll give me some time to work on the sealing of the cab and jack plate and investigate the correct tuning of the chambers.

I found a comment on the other forum from greenboy (of fearless/fearful renown) that the 1505KADT is NOT suitable for bass... So we'll have to see how it works out... I'm reluctant to spend any more on "the heap" so replacement drivers are out of the question! 

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2 hours ago, Bigwan said:

I found a comment on the other forum from greenboy (of fearless/fearful renown) that the 1505KADT is NOT suitable for bass... So we'll have to see how it works out... I'm reluctant to spend any more on "the heap" so replacement drivers are out of the question! 

Use it.  If it self destructs wait until a cheap s/h 15" appears on this chapel.   I replaced my done for BW with a £25 'Fender' 15" bought in this parish.  It was better than before, very unscientific approach, no T/S parameters, measuring cab volume, no changing port length and/or size, just luck :)

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So does anyone know the difference between a 1505KA and a 1505KADT? The peavey literature I can find seems to suggest they are one and the same, but physically these 2 drivers are different, the basket of the KADT being about an inch deeper than the KA. @3below @stevie @Bill Fitzmaurice

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1502DT is the usual 'bass guitar' BW - they often crop up cheap on here.. The specs are a bit JBL 140-ish if I remember correctly..

Hope you solve the flapping.

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On 29/12/2019 at 11:37, stevie said:

I'd also suggest you get someone to play the bass (low E is always good) while you crawl around the cab trying to locate exactly where the noise if coming from.

 

I did this on an old Hartke VX215 which had started to sound raspy, got my mate to play bass through it while I put pressure on each side of the cab until it sounded normal. Had a look inside to see what would be separating from where, put a few screws in it (cut a square U shape out of the carpet and glued it back over the screw) and it held up for another year of gigging until I sold it. Was still trucking on when the buyer sold it on eBay years later, think he even made a profit on it!

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Quickly plugging numbers into WINISD gives a tuning frequency of 50Hz for the 1505KADT using the existing ports. I haven't taken into account the volume of the ports or the volume displaced by the driver yet so we're very ballpark there and it seems a little high to me already...

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FWIW, I bought a 2 X 15" Hartke cab once really cheap as it sounded rough. Turned out after a good search that the input jack was tarnished and dull and not making good contact with the plug when inserted.

A tickle with wire wool and contact cleaner and it was rattling pub windows.

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55 minutes ago, Chienmortbb said:

If you do want a new driver, the Beyma 15CVM2 is not too expensive (£52ish) without modelling in WinISD looks to have a decent spec https://www.bluearan.co.uk/index.php?id=BMA615CVM28&browsemode=manufacturer h

From my limited knowledge that's a pretty tidy looking driver for the price. I'll bookmark that one as a "just-in-case". Xmax of 7mm and quite a wide frequency response.

The chambers of this cab are a little small (89 litres or 3 cubic feet, it's quite compact for a 2x15) so tuning is always going to be higher than ideal, but if I forget about fundamental frequencies (bah, who needs 'em), and high pass to 45/50Hz somewhere in the chain then all will be well... I think... 

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