Bass guitar cabinet (K-140, 2461, 2301, 3101, 3.5 cu ft)

[McDuff]

Well I had a bit of a result today... you know the sort of thing: chatting with someone you've just met in a social situation and when you mention that "my son plays a bit of bass quitar" you're told they used to play bass and they have an old bass cabinet in their garage you're welcome to if you're willing to pick it up.

It's almost always unusable junk, right? Just something else to be carted away on the next trip to the dump...

Well not this time! This time, whilst the cabinet was very battered and at the end of its life, the main speaker looked pretty decent and the badge said "JBL Professional Series Model 2901". I did not recognise the tweeter but it looked like a serious piece of iron too... Could I have lucked out? Maybe so... I got out of there quick before they could have second thoughts!

The cabinet is pretty much beyond help, but the K-140 looked OK until I gently pushed on the cone to see if it made any nasty noises and discovered it wouldn't budge much... on removing the speaker it was obvious why: someone had shoved a series of foam strips between the basket and the cone (see attached). I was surprised that the K-140 did not have a serial number.

The high frequency diver turned out to be a 2461 driver with a 2301 horn and lens. This looked OK also althought the horn has come a little loose - I assume I can just tighten that up. The 2461 is marked as 16 ohm (the K-140 is 8 ohms) though I have not checked that with a meter.

The whole lot was wired up with a 3101 passive crossover.

The cabinet is around 3.5 cu ft (21" x 27.5" x 10.5") with two ports 4" ID and 2" long. No cleats but several edge-attached chipboard battens to stop flexing.

The owner claimed it was quite a box in its day, which I can well believe as they are clearly good components.

I have not powered anything up yet.

I would be very interested in any comments on the appropriateness of these drivers for the role of a Bass guitar cabinet. Any pointers to suitable cabinet designs would be great as I'd like to build a new cabinet to give these drivers a second life. I have not been able to find info on the 3101 yet. Does the impedance of the 2461 make sense with this crossover?

What I would most welcome is some insight into why the K-140 was treated in such a brutal manner! I'd also love to know what is the best way for me to proceed - is it safe to just remove the foam and power the whole lot up? Does this treatment mean that a recone is inevitable?

[57BELAIRE]

Sort of reminds me of the 4627 Cabaret Series (K145 and 2901 Power Pack).

These components are more suited for keyboard and p.a. than bass.

I'd sell the power pack and buy another matching 15 and build/buy a
suitable cab....and above all...REMOVE THAT FOAM !

[boputnam]

It seems an odd configuration for a bass cabinet, but whatever.

I don't understand the intent of the foam - certainly remove that and fire them up. See what you got! Any "damage" done by it cannot be undone. As to whether a recone is required, that would take some sweeps...

[vettedrummer]

We have a bass guitar speaker that is loaded with two JBL 140's. The size of the cabinet is 15 3/4" deep x 23 3/4 "wide x 36" high. On the inside the cabinet is divided into two separate compartments. The back is solid. It's a copy of a Vox cabinet, but made a bit deeper (11 3/4 to 15 3/4) to deliver deeper bass. Works great in this size. Cheers, Frank

[Mike Caldwell]

I'm going to take a guess at the foam stuffed around the speaker. Doing a real quick cabinet calculation it looks like the tuning would be around 58hz. I would say someone was driving the cabinet too hard well below the cut off frequency and heard the speaker bottoming out so the foam was their idea of a fix even though it would not do too much for any forward movement of the cone!!!!!! If that was the case the cone condition may be questionable. A proper high pass filter is always recommended.

Mike Caldwell

[McDuff]

Thanks for those comments - very helpful indeed!

I removed the foam strips, which were keeping the cone 10 mm or so forward biased. It's a guess but based on the degree of breakdown of the foam I'd guess it had been there for a long time - maybe 10 years.

After the foam was removed it was still biased forward and after a few days of leaving the speaker facing upwards this relaxed back to about 5 mm or so. I assume that's pretty clear evidence that the surround at least needs replacing. Now gentle pressure on the cone results in a slight scraping feeling - I think it's coming from the suspension rather than the voicecoil scraping in the gap.

I'm going to leave it a little longer and then try powering it up to see what happens. Boputnam: you mention some sweeps - are you meaning just manually sweeping an oscillator to see if something rattles and buzzes, or did you mean some sort of semi-formal test of the frequency response?

A couple of comments there on using a pair of K-140s, so I may need to keep an eye open for another.

If I end up having to recone, any suggestion as to who I should get the kit from? I'm in Australia. There seems to be a huge price range. As I've not done a recone I'm tempted to do it on the cheap this time and maybe redo it properly in a few years - is this flawed thinking?

Cheers, Dieter.

[subwoof]

Since you don't have a lot invested, some "unorthodox" attempts to correct this should be attempted before shelling out the 200+ for a recone job..

You can do a oscillator / amplifier sweep with this at anytime without worry unless you are going for the full power test..:o) The range is specified here for the later E series which is identical except for power:

http://www.jblproservice.com/pdf/Dis.../E140-8-16.pdf

If you have access to one, use an oscillator that can do 1-10 hertz so you can see the cone move in slow motion to find "tics" that are caused by dirt buildup, sticky glue and surround cracks.

I suggest putting the cone into the "in" position for a few days ( put a 4" dia food can over the dustcap to shield it and pile on a few small pillows ) and then let it return to it's original position ( if possible ). The cloth surrounds are very hard to put a permanent "offset" to BUT the spiders are easy to stretch. If the spiders still are offset after all this, there is a solvent that some people have used to "tighten" it but you will need to really search this site for that particular thread.

Do a library search on this site for the "manual" that came with the K series speakers and it will have all kinds of useful box configurations.

The 2901 power pack is an excellent choice if you want to use this cabinet for PA, keyboard or steel / slide guitar. It will be too bright for lead though. Use a DPDT switch so the 15 runs full range for bass guitar use.

This was a stock CABARET cabinet but the E145 was a heavy bastard and the D/K140 was a lot more back friendly.

sub