Goodmans Magnum K2 project

[RMutt]

I am rebuilding the above but hoping to use Wharefedale Super 12's as the bass drivers. A couple of questions. Were the speakers designed to use a mirror offset of the drivers? What are the crossover frequencies of this speaker. Thanks.

[aquapiranha]

Hi, Here is a pic of the pair I had, there are more on my photobucket page if you want to have a look. HTH, Steve..

http://i205.photobucket.com/albums/bb256/aquapiranha/Goodmans%20Magnum%20-K/Photo0031.jpg

more..

http://s205.photobucket.com/albums/bb256/aquapiranha/Goodmans%20Magnum%20-K/

[RMutt]

Thanks Steve. Very different looking speakers to mine. All the drivers are different. The backs of mine are completely sealed so access is only from the front through the hole made when the big driver is removed. First problem using the Wharfedale driver is that it mounts from the back of the baffle where the Goodmans mounts from the front.

[RMutt]

A couple more questions if anyone can help. I put the Wharfedale drivers in the Goodmans enclosure and appear to have made a speaker with incredible mid-range. The bass though is nowhere near as prodigious as I imagined it would be given the driver and the size of the enclosure. Would porting help(the enclosure is sealed) and if so how do I go about this? Also, if the crossover has deteriorated over time how would this manifest itself in terms of the sound? Thanks.

[Reid Malenfant]

Hi Andrew, in all honesty you can't just go dumping a driver into any old enclosure & expect great bass, or even clean bass come to that ;)

What you need to do is find out the driver parameters, as these will (given a bit of experimentation) tell you what you'll expect from an enclosure of a certain volume. Without knowing the driver parameters (Fs, Qts & Vas as i minimum) it's all guesswork as you have just discovered.

You may be able to port the speaker, but again to get anything like a decent flat response you'll need to know those parameters & the volume of the enclosure itself ;) There are more things to take into account than that in actual fact, i'm just breaking things down to be as simplistic as you can get :doh:

On the crossover question you'd probably end up with a slightly veiled treble & possibly midrange if it's a three way design due to capacitors deteriorating over time.

[RMutt]

Thanks Mark. When I bought them the Goodmans came with their bass drivers but they were damaged. Somewhat naively, it would seem, I thought I could drop in the Wharfedale drivers that I had hanging around and the crossover would do the rest. The Wharfedale seems to have a higher frequency range than the original which manifests itself as a 'brighter' sound. None of it has cost me a great deal so I am happy to keep experimenting and I appear to be learning all the time.

[Reid Malenfant]

Hi, is the super 12 a dual cone speaker? Something rings a bell here, also what is the driver surround? Is it felt or some kind of fabric half roll?

When i say dual cone, does it have what looks like a second smaller unsupported cone connected to near the centre of the 12" cone...

[RMutt]

Hi-ya, They were re-coned in about 1990 and have not been used much since. No they do not have the inner whizzer is it? The surround looks like foam. They were originally a full range but that may have been altered. They were 15 ohms but written on by hand is 8 ohms.

[Reid Malenfant]

Hi Andrew, ok, maybe you might be able to contact those that reconed them & ask for the driver specs? Otherwise you are going to need some test equipment to figure out the specifications for yourself :doh:

Yes, sorry, i forgot about the Wharfedale drivers with foam surrounds, if I remember right though they were kind of an open cell foam & flat, not in a half roll shape which is more common these days? :scratch: Well the original foam surrounds were at any rate :eyebrows:

Yes, you'd be right - whizzer cone ;)

[RMutt]

The Wharfedales were lent to me as a stop gap when my 'bought' speakers broke. They were in a big home made enclosure with a port. I hardly used them because ironically the high frequency was missing. Anyway I can keep them now so I thought I would try to build them into something. The surround is indeed a half roll shape.

[Reid Malenfant]

Curiouser & curiouser :eyebrows: All the Wharfedale drivers i have seen (standard drivers from back in the day) like the super 8 etc had green felt surrounds or some kind of grey open cell foam which was flat. Only the cloth surround drivers had a half roll, though i may be missing out a good deal of Wharfedale driver production :doh:

I don't know it all as i'm not old enough :lol: It means you are in a minefield, you need to know the exact parameters of the drivers you have there to have a hope in hell of getting some kind of enclosure approximately correct.

Yet it appears there are so many drivers you could search for a year & a day & still get it wrong :mental:

All i can suggest i you somehow measure the parameters yourself. Not an easy thing if you don't have the equipment or knowledge, sorry :(

[Rare Bird]

Andrew which version 'K2's are they two tweeters or one?

[RMutt]

Mark. Sorry we may be at cross purposes. They do have green felt to seal them against baffle, when talking about the surround I mean the edge of the cone which is a half round foam affair, my terminology is obviously flawed.

Poor. They have one tweeter, top right. Were left and right speakers the same with a top right tweeter, mid to the left and bass below?

[Rare Bird]

Poor. They have one tweeter, top right. Were left and right speakers the same with a top right tweeter, mid to the left and bass below?

Poor :lol:

They are indeed K Mk.II then, yes tweeter to the right both sides. They should have really good Bass responce.. around 30Hz-20kHz responce

[RMutt]

Thanks for that. The bass response I am getting is nothing like that I imagine. Do you know the specs for the original driver as I may go down a more direct replacement type route.

[Rare Bird]

I don't.. ive heard K.II with small transistor amp, the bass responce should be very good, if your not getting it from the original enclosures something wrong! Or is it i'm not reading your posts properly :scratch:

[RMutt]

I have now abandoned the idea of using the Wharfedale Super 12 for the bass unit, it is patently not suitable. Bearing in mind I am on a tight budget I would like opinions on my plan B. I am hoping to replace all the drive units over time. Starting with the bass, I am hoping to use modern drivers from somewhere like Wilmslow Audio. Is it feasible to replace one driver at a time for better quality items, maybe even the crossover as well and achieve a good sounding speaker? As anyone gone down this route? Is it possible that by replacing for better and better items over time you can create a constantly upgradeable speaker?

[Macca]

If it were me I'd forget about using the Magnum cabs as the basis for a new speaker. there is nothing special about them. What about using the Wharfedale drivers as the starting point for a full range speaker? They are a full rnage driver, correct? Get the drive unit parameters and calculate and build an optimum size enclosure for them, maybe add a super tweeter. Hard to go wrong with that approach and no need to muck about with crossovers.

[RMutt]

Thanks Martin. That sort of cabinet is actually what they came out of originally. I still have them and they are a little too big. I never really liked the sound but adding the tweeters might have helped. I wonder whether the original tonal quality was lost when they were re-coned.

[Macca]

Thanks Martin. That sort of cabinet is actually what they came out of originally. I still have them and they are a little too big. I never really liked the sound but adding the tweeters might have helped. I wonder whether the original tonal quality was lost when they were re-coned.

I wouldn't have thought so but it is possible I suppose. The sound of big paper cones is not to everyone's taste though, so it could be they are just not for you.

[RMutt]

I have decided to plough on with this project so more help required please. Obviously I'm a novice so please be patient but the whole thing only stands at £35 so far and I continue to learn. I have managed to resurrect the original 12" drivers and now want to replace the capacitors. I have established the values at 4uf(2 per speaker) and 10uf(1 per speaker). Is there anything else I need to consider? The 12" driver appears to take its signal direct from the amp, is this usually the case? If it does not have any filtering does its frequency range stop at the point where the mid takes over? Does anyone know the cross over frequencies? Thanks.

[Macca]

It's usual to have an inductor in front of the bass driver to roll it off at higher frequenciesbut plenty of speaker designs don't bother and run the bass all the way up so if there is nothing in front of the bass driver that must be the design intention. It will be running into break up at higher frequncies but in practical terms this won't make a huge amount of diference to what you hear at the listening position although technically it is not ideal.

If you have all the drivers working now and have replaced the caps with new ones of the same value then that should be job done. You could consider replacing the internal cable with something better as I am guesing it is just bell wire on speakers that old, generic 79 strand will do if you don't want to get fancy, quid-a- metre stuff from Maplins, say.

You could also look at the internal damping and wadding - my preference is to rip it all out and replace with Deflex panels on all internal surfaces which cleans up the sound and gets rid of that 'woolliness' but I am not sure that Deflex is still commerially available and it was never cheap.

With all that accomplished you should have some serious sounding speakers that will be be very different in presentation to the modern 'WAF Towers' - in a good way! Then you just need to think about stands and placement.

Hope that is some help:)

[RMutt]

Thanks for the info Macca. I have made new baffles that are stuck onto the front of the originals so the drivers now come out beyond the original 'picture frame'. I have also made the drivers into a mirror arrangement. They look quite neat although I say it myself. Just ordered capacitors so that is the next job. I have had to cut the connecting wires as the drivers fit from the front, so until I do the capacitors I can't hear them. I will replace the wires at the same time as you suggest.

[Macca]

Sounds good - Stick up some photos if you can

[RMutt]

http://i40.tinypic.com/2uqys6s.jpg

[RMutt]

You can see the big Wharfedale driver in the background. You can also see the damage to the Goodmans bass drivers and my somewhat amateurish repair. The cardboard cone has a plastic laminate that has started to become detached, you can see it best in the nearest speaker.

[Macca]

They look good - I see your additional front baffle as well :) - what a shame about the bass drivers - maybe you could find a doner pair cheap on the bay.

[RMutt]

All finished now and sound great. Changing the capacitors made a big difference. I'm still hoping to replace the bass drivers. Some Goodmans drivers from that era have paper cones and some, like mine, have the plastic coating. To be honest in all my searching I have not seen a picture of the coated ones where it is not coming away from the cone. Can someone help me with the chronology of this range? Did the paper only cones come first? Is the frequency response of the two types the same? Did the Magnum SL come after or before the K2? Do all the SL's have paper cones? Thanks.

[Alan]

SL's had all PVC covered cones, and as a complete speaker sounded nicer than the K2 to me, in spite of being a cheaper construction. If the separation is fairly minor it's nothing to worry about - I just checked in my garage to see if I still have a spare driver for you but I must have sold it in the end.

[RMutt]

http://i46.tinypic.com/16ktm2w.jpghttp://i45.tinypic.com/xcktig.jpgI finished these speakers some time ago and thought it was time to give an update as various threads came together in completing them. Thanks to all who contributed to threads such as the merits of soft dome midranges to making grilles and how they might affect the sound. Having completed the first incarnation of these speakersI found that at certain frequencies one of the original midranges was buzzing. I swapped both for another pair of Goodmans midranges I acquired second hand for £25. Unfortunately they turned out to be more sensitive than the originals and drowned out the bass. I fashioned a partial fix by rubbing silicone sealer into the paper cone. It stopped them sounding so harsh, but they were still too much for the rest of the speaker. I bought a pair of second hand soft dome Vifa D75MX-41-08 midranges for £70 that had the right sensitivity. I made rear chambers from the plastic cylinders that are used to cover bulk spindles of blank CD’s. These are almost exactly 1 litre. I lost some of the internal volume of the speaker in doing this but gained a little by removing the large piece of foam that Goodmans had stuffed inside and using instead thinner wadding. I found another pair of second hand Goodmans bass drivers for £65. The original tweeters blew during a party and I replaced them with new Vifa D27TG-35-06. I have made grilles by using quadrant to make a sort of picture frame affair that friction fits over the protruding baffle.
As you can see very little science has been used in making these speakers but they sound absolutely fantastic, much better than my Mordaunt Short MS815’s. Their biggest strengths are the overall scale of the music, mainly down to the 12” drivers, the amount of detail and clarity being of the ‘I’ve never heard that before’ type and the placing of instruments and voices in their precise positions. Bass is very clear and not at all boomy.
I’m using a Squeezebox Duet and Cambridge Audio CD transport through a Rega DAC into a Rega Mira.

[Alex_UK]

You've just reminded me I've got a pair of K2's in the garage I haven't even plugged in yet... I doubt I'll be going the whole hog like you have though! Nice one Andrew.

[DSJR]

What else have you in your garage Alex? If I'd known you had these I'd have INSISTED you'd brought them last week!!!!!

[Macca]

Looking good - and seemingly well worth the effort. Nice restoration.

[Alex_UK]

What else have you in your garage Alex?

Even I'm not sure what other little gems may be waiting to be discovered that I've bought and forgotten about! ;)