Another Goodmans Magnum project

A place for DIY project discussions.
Geoff.R.G
Posts: 1562
Joined: Thu Aug 11, 2016 2:46 pm
Location: Denham UK
Has thanked: 132 times
Been thanked: 476 times
Great Britain

Re: Another Goodmans Magnum project

Unread post by Geoff.R.G »

OK I can follow that, and it makes sense so what about some of the exotic cones like the Leak Sandwich bass?

User avatar
Dr Bunsen Honeydew
Posts: 30758
Joined: Wed Jul 11, 2012 7:26 pm
Location: Muppet Labs
Has thanked: 0
Been thanked: 48 times

Re: Another Goodmans Magnum project

Unread post by Dr Bunsen Honeydew »

Trying to make the piston more rigid, same with KEF B139.

Geoff.R.G
Posts: 1562
Joined: Thu Aug 11, 2016 2:46 pm
Location: Denham UK
Has thanked: 132 times
Been thanked: 476 times
Great Britain

Re: Another Goodmans Magnum project

Unread post by Geoff.R.G »

Dr Bunsen Honeydew wrote:Trying to make the piston more rigid, same with KEF B139.
Sorry, should have been more direct, does it really work or is it another way to deceive? I have a pair of Leak 2030s but they aren't accessible at the moment, I was happy with them for many years before I replaced them with some NAD floor standers, which I cannot find on the NAD site but that is another story.

User avatar
Dr Bunsen Honeydew
Posts: 30758
Joined: Wed Jul 11, 2012 7:26 pm
Location: Muppet Labs
Has thanked: 0
Been thanked: 48 times

Re: Another Goodmans Magnum project

Unread post by Dr Bunsen Honeydew »

Everything is a compromise, everything has a down side, everything needs to be seen by a designer as *your* balance. For me both the Sandwich and the solid block of polystyrene foam (KEF B139) are bad solutions. Energy becomes more stored and then released but changed, as all of these things become mechanical filters, but you have to try and avoid store and release / phase / musical timing problems. Neither the Sandwich or KEF B139 solutions have been used again by anyone else, where as the standard cone has swung from paper to polymers like Bextrene and back to polymer paper mixes and again good old paper on its own. Material has a sound, and Bextrene is a fine example, its mix of character end up adding a "quack" to the music. I dislike it, it is hard to work with to get rid of it, and it damages music. Bextrene probably gains more (because it is so bad) than other cones with the Doc Mods. But it needs a lot of doping. Well made paper cones have the least of a character or sound.

User avatar
Toontrev
Posts: 166
Joined: Mon Aug 22, 2016 12:48 pm
Location: Chester le Street
Has thanked: 31 times
Been thanked: 43 times

Re: Another Goodmans Magnum project

Unread post by Toontrev »

Fascinating stuff, many thanks for taking the time to offer a full explaination. Puts into perspective the comments and remarks I've read on the site about alternative designs and solutions.

User avatar
jayman67
Posts: 553
Joined: Fri Apr 01, 2016 6:28 pm
Location: brighton uk
Has thanked: 0
Been thanked: 0

Re: Another Goodmans Magnum project

Unread post by jayman67 »

very interesting doc,by the way the surrounds on my klh 23's are cloth and doped to make air tight,a way to tell if its sealed well is to push in on the bass driver it should spring back slowly.
they have very good bass,the tweeter i think lets it down a bit,i wonder if one of yours would work well?
Yamaha NS1000M speakers,Pioneer PLC-590 turntable,,Alphason HR-100S-MCS/Zeta tonearms,Denon 103sa cartridge ,Sony 700ES Amp,Sony X555ES CD Player, Nakamichi ca5 pre amp.

User avatar
Dr Bunsen Honeydew
Posts: 30758
Joined: Wed Jul 11, 2012 7:26 pm
Location: Muppet Labs
Has thanked: 0
Been thanked: 48 times

Re: Another Goodmans Magnum project

Unread post by Dr Bunsen Honeydew »

"a way to tell if its sealed well is to push in on the bass driver it should spring back slowly."

Who told you that, It is the opposite of the truth. What that is showing is an air leak. In a sealed cab the driver only goes back a little as the air pressure in the cab increases and on release it bounces back immediately.

User avatar
jayman67
Posts: 553
Joined: Fri Apr 01, 2016 6:28 pm
Location: brighton uk
Has thanked: 0
Been thanked: 0

Re: Another Goodmans Magnum project

Unread post by jayman67 »

pretty much the general consensus from all the so could experts from the yank forums and the classic speaker forum,i actually said in reply what you have just said but was told the opposite should be the case.
Yamaha NS1000M speakers,Pioneer PLC-590 turntable,,Alphason HR-100S-MCS/Zeta tonearms,Denon 103sa cartridge ,Sony 700ES Amp,Sony X555ES CD Player, Nakamichi ca5 pre amp.

User avatar
Dr Bunsen Honeydew
Posts: 30758
Joined: Wed Jul 11, 2012 7:26 pm
Location: Muppet Labs
Has thanked: 0
Been thanked: 48 times

Re: Another Goodmans Magnum project

Unread post by Dr Bunsen Honeydew »

Its nonsense. Just think about it. If the driver moves in then the air is being pushed out through a hole somewhere. You then let go of the driver and the air will slowly return under the pump of the driver re-centering. If the cabinet is air tight there will be strong resistance to the driver being pushed in, and when released the increased air pressure will bounce the driver out to its balance point immediately.

Typical of the eeediots who call themselves experts. There must be an awful lot of IB speaker out there with air leaks.

Geoff.R.G
Posts: 1562
Joined: Thu Aug 11, 2016 2:46 pm
Location: Denham UK
Has thanked: 132 times
Been thanked: 476 times
Great Britain

Re: Another Goodmans Magnum project

Unread post by Geoff.R.G »

Dr Bunsen Honeydew wrote:Typical of the eeediots who call themselves experts. There must be an awful lot of IB speaker out there with air leaks.
I would imagine that most leak, usually around the nasty plastic moulding the terminals, and sometimes the crossover, are attached to. I don't remember seeing many with gaskets to seal them and the connectors probably leak too, depending what they are.

Post Reply