Celestion G12T-75 Guitar Amp speakers

[Yellow]

Hi

I have a friend at work who has asked me about implementing 4 x 12" Celestion G12T-75 drivers, into a DIY cabinet. He has a guitar amplifier, so the system will be a passive one.
I have had a look at some Marshall Amps on the net that use the G12T-75, and the cabinet seems to be about 175 litres in volume.

However, I have seen guitar amps that have "open-backs" like some head-phones.
I honestly know very little about implementing such drivers into a cabinet, and was hoping that there may be some fellow World Audio/World Design people who can give me a few tips - better still, a cabinet design spec.

Some questions I have:

1. Should these drivers be used in a closed-baffle or open-backed cabinet.
2. Should the drivers be wired up as two parallel pairs (what impedance does a guitar amp like? 8ohms, 16ohms or more?)
3. What sort of cabinet materials are best
4. Is bracing and BAF wadding used in guitar amps, or are they just basic open boxes
5. Should angles/deflectors be considered to break up standing-waves as in hi-fi speakers
6. Is any kind of "inductor" used before the drivers to roll-off the top end, or is the natural response of the driver used in a cabinet by itself (these drivers work up to about 5kHz)

If anyone can guide and advise, I would be very grateful.

Regards,

Neil.

[vitalstates]

Hi yellow

I think I have what you want.......I've got 4 jpg pages here, can I mail them to you(about 250k each)?

Regards

Ed

[James D]

No simple answer to this. I design and build guitar amps and cabs for various friends and musicians and the one thing I have learnt is there is no right or wrong way to do this - it various according to what the player plays and where he plays it and what is the tone in his head that he is after...

So they can be used in an open backed cabinet, a closed back cabinet, a half open and half closed cabinet, an aperiodic caninet , even but rarely a bass resonance cabinet...

ANd you can connect the drivers in series in parallel or in series parallel pairs - they sound different in each combination mainly because they load the amp in a different way each time - so this is very amp dependent as to what you can do and should do.

One thing I will say is that a cab with four G12-75 drivers is going to be loud!!!! So unless he is going to use it in a large hall then this is the wrong answer for his needs... But try telling 99% of guitarists that until they try it

If you can find out what his amp is, what his guitar is, what music he plays and where he intends to play it - then we can give some options and advice on how to proceed.

ciao

James

[Yellow]

Ed, James,

Thanks for your responses.
Ed, I would very much appreciate your 4 jpg pages. Either email or PM me. And James, I'll find out a bit more info tomorrow or Tuesday when I'm back at work.

Cheers,

Neil.

[vitalstates]

Hi Neil

I have pages from the old eminence manual, which has details of many stage cabs. Can you send me your email address so that I can mail you with attachments.

Regards

Ed

[Stratmangler]

Hi

i know from personal experience that the Marshall closed back 4x12 cabs tend to throw sound forward - at about 10 feet from the cab you get full level, which is WAY too loud for most normal applications.

Open back cabs tend to energise the air in a more local fashion (to the amp).

There are also tonal differences to be had by cabinet type, as has been mentioned.

Your friend could do himself a favour and sell the G12-75's and get some of the old style Celestion greenbacks - the speakers are less efficient, although still capable of deafening levels.

Couple the amp/speaker rig with something like the Marshall power brake and he should get the tone that he wants without having to deafen everyone in the room.

Regards
Chris