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15" speaker replacement recommendation

Discussion in 'Amps and Cabs [BG]' started by andysvec, Aug 28, 2004.

  1. andysvec

    andysvec Supporting Member

    Hello all, I'm a newbie here with a quick question.
    I need a replacement speaker for my old trusty Randall RB100 combo amp (bought it new back in early 90s, just a plain 100watt low/mid/high/compressor with one 15. On the back there's two speaker out jacks that say 60watts to 8ohms, 100 to 4 ohms). I have lots of nicer gear (trace, swr, etc.) but find myself using this amp constantly because of it's portability and decent sound, the older I get I've noticed my goal is to make it from the car to the stage in one trip!
    Anyway, the original Jaguar speaker desinagrated a few years back, and I had a peavey black widow lying around I put in (much bigger magnet and power capability, but sounded fine). About a year later I started noticing some distortion with that one so I bought a speaker from musicians friend, think it was a fender 150watt (I figured maybe the peavey was too much speaker for the amp). This new one really distorted, so I put the black widow back in. I'm not real sure if it is the speaker or the amp, everything sounds great at low volumes but when cranking it up a bit I notice the distortion, not as bad with the black widow but terrible with the fender. The black widow did sound great for about a year, but was old also.
    So I guess there's two questions here:
    - is there any way to tell if it is something with the amp or the speaker thats causing the distortion?
    - if it is the speaker, any recommendations for a replacement? I've seen so many choices on partsexpress.com for replacements, and I think the new randalls have eminence legends, but even they have a few choices. I've tried a few different basses and I know it's not that, they all sound great through my 'real' rigs. But I'd like to keep this one in commision.
    Thanks for any input - AJ
  2. Yossarian


    Jun 24, 2004
    If the brand new fender speaker distorted too, I'd blame the amp. Or are you just pushing the amp too hard, or doing something wrong in installing the speaker maybe? However, I don't really know much about this sort of thing, so I'll just say if it comes to it, www.avatarspeakers.com has Eminence speakers and such for a nice price.
  3. andysvec

    andysvec Supporting Member

    thanks for the quick reply, this forum is great!
    the speaker replacement is pretty straightforward so I don't think I screwed that up. But it could be the amp, any way of knowing for sure?
    I wouldn't mind buying one last speaker for the thing either, but not quite sure what the right one would be to put in it.
  4. Yossarian


    Jun 24, 2004
    you could hook a different amp up to one of your distorted speakers, and see if they're still distorted. However, if the problem is that the amp is freaking out and blowing your speakers, I dont know how to figure that out. I don't know the details here, but you can get some tool that will measure the power output of your amp. If you can get your hands on... whatever that thing is... then you can see if your amp is putting out some crazy signal. Or you could take your amp in to some local tech guy, see if they can figure it out.
  5. Petebass


    Dec 22, 2002
    QLD Australia
    The reason your speaker transplants aren't working is because cab design isn't as simple shoving a speaker into a wooden rectangle. It's a lot more scientific than that.

    1) 15's ain't 15's. Put the wrong speaker in the wrong sized cab, and even a brilliant speaker will sound and perform like garbage. The speaker's Thielle Small Parameters determine the speakers ideal enclosure size, so there's no fudging it.

    2) Assuming you can find a speaker that is happy in the size of your enclosure, you'll have to re-tune the porting. See the ports that let the air escape from the cab? They're not random. They're designed to be a certain length and diameter and are therefore tuned to a certain frequency. It's a very important part of the design of a vented cab and has a huge effect on how the speaker will respond in the bottom end, both in sound and speaker cone excursion.

    The chances of finding a speaker that likes the same cab size and porting as your existing cab are virtually nil. Generally speaking, any speaker replacement will require the cab to be retuned.

    Usually it works out best to buy the exact same original speaker again, or get the damaged one reconed. Either that or abandon the concept of "one trip to the car" and instead, get a amp with more mumbo.

    But if you insist on replacing the speaker, post the cabinet dimensions here. The speaker guys will do the math and advise you of some speakers that might work.
  6. andysvec

    andysvec Supporting Member

    thanks for the info petebass. That's what I was thinking, that it has to be the original type or a specific replacement speaker. But it is a sealed cabinet, no ports, so I don't know if that makes any difference.
    I'll pull the black widow out today and measure the inside of the cabinet. Let me check if I still have the original speaker also, maybe reconing is the best option.
  7. Petebass


    Dec 22, 2002
    QLD Australia
    Huge difference. Chances are the speakers you've been transplanting have an EBP (Efficiency Bandwith Product) better suited to ported cabs. Which is why they've not performed well in a sealed cab.

    The good news is that sealed cabs are much more forgiving on the cab size. It's not as crutial as with ported cabs. It also means there will be no need for re-tuning.

    The bad news is that finding speakers that prefer sealed cabs can be difficult. There just isn't as many of them around.

    Post the cab dimensions anyway and we'll see what we can come up with alternatives to reconing the original.
  8. andysvec

    andysvec Supporting Member

    okay, I found my original speaker and I took out the other and measured the inside of the cabinet part of the combo, here's the dimensions of the inside of the cabinet:

    19 3/4" wide, 16" high, 8 1/2" deep - sealed cabinet
    (not big at all, I'm surprised it sounded so good at one time).

    The back of the head has two 8ohm speaker outs (with the internal speaker connecting to one of them), and says 60w at 8ohm, 100w at 4ohm.

    Here's the strange thing, the original 15" speaker is a 4ohm Jaguar RES-150. If it has a 4ohm internal, how could I hook up an external cabinet without dropping the total below 4ohms? Anyway, that's a moot point because this is just my mid size amp and I don't plan on using it with an external. But that was one of my problems also, I was putting 8 ohm replacements in there.

    So I guess what I need is just someone to look at the size box I listed above and my wattage (100w at 4ohm), and recommend a 4ohm replacement speaker. (If at all possible, one at partsexpress.com because they are one of the few that will ship USPS to me here on Guam).

    Thanks again for all the help on this!
  9. Petebass


    Dec 22, 2002
    QLD Australia
    As I thought. The only drivers on Bgavin's spreadsheet with a low enough EPB were all Hi-Fi type subs. That means they go quite low but will produce nowhere near the type of mid and high frequencies required to be a decent bass guitar speaker. They're designed to be used in conjuction with seperate mid and high freq speakers.

    Not only that, they're very inefficient, so you need to feed them a hellovalotta watts to get them up to gig volume. 100w won't produce much sound at all. Furthermore, they're predominantly 8 ohms speakers, so it's more like 60w.

    I'd normally send you to the re-coner at this point but before I do - I'm suspicious that the Jaguar spaker may not be original equipment on that amp. My next phone call would be to Randall to find out what the original driver should be. If it is the Jaguar, recone it. If not, buy the original speaker from Randall.
  10. andysvec

    andysvec Supporting Member

    know anyone online that does reconing?

    The jaguar is the original, I bought this amp new way back (1991?). Yeah, I think I'll contact Randall also and see if they have a suitable replacement. If not, recone.

  11. Forget about calling or writing to Randall (I´ve done it a lot). Send an e.mail and they don´t write back. Call them and they tell you this amp is not been made anymore and they can´t give you any information. What you can do is look for speakercompanies in the internet that recoment volumes for theyr speakers. Messure the inside of the cabinet you have and look for a speaker that fits in there. Good luck