Where to get 4 off 12 inch speakers in the UK?

You want four 60 watt 12" speakers for 30 quid each? Chinese junk from CPC maybe, the aluminium coned ones aren't too bad for £19 + vat each, but you`ll struggle to find 16 ohms off the shelf, so you`ll have to wire them in series/parallel for 8 ohms Next up is Eminence Alpha 12 at £30 + vat, again you`ll not easily get 16 ohms.

Celestion do the G12T @ 75 watts in 16 ohms. A natural choice as a 4 x

Hth

Ron(UK)

The message from "N Cook" contains these words:

Rapid Electronics of Colchester (of whom I have no commercial connection) sell 12" 200w speakers for about £20:00 plus VAT. I have used several of them in situations similar to yours.

On Tue, 02 Jan 2007 10:24:10 +0000, N Cook Has Frothed:

Saw someone on Ebay blowing out 12" OEM Celestion copies supposedly made in the USA. These started at $19 US each.

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I see a rock and a hard place coming up. I would replace the 4 16 ohmers with 2 8 ohmer 100 watts and selector switch bypassed, but for the same 4 bottle, 120W amp would that be the same oomph, as they term it. ? Although amp and cab are Crate make they obviously were not made as a matched pair as amp has 16/8 ohm output setting and cab is 4 / 16 ohm setting. I suspect they'd been running for some time as I received them , amp set at 16 ohm and cab set as 4 ohm , so they certainly won't be getting the same oomph as amp at 16ohms and cab at 16 ohms. Is there a way of perhaps saving stressing output matching transformer in the case of the speaker load going open circuit? eg a high watt 50 ohm resistor in parallel with each speaker of the serised

Providing the speaker load matches the amplifier, you should get the same output, but the apparent volume depends on the sensitivity of the speakers - most of these so called 'high power speakers are notoriously insensitive. 'Classic' guitar speakers such as the Celestion G12H etc, were/are very sensitive and have corrugated cones designed to 'trash out' at high volume without destroying the speaker.

Some of the Selmer amps had a high wattage resistor across the output jacks to help in absorbing some of the energy in the case of a loudspeaker cable becoming unplugged. That`s probably the safest way to go.

Before you put too much money into this cabinet, do you realise that you can buy a Behringer 400 watt 4x12 for little over £200, or much less if you shop around?

Ron(UK)

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I'll probably recommend 4x 8 ohms permanently wired as seriese / parallel 8 ohm and amp switched to 8 ohm with some 50 ohm Rs, at least if they switch amp to 16 ohms won't cause problems other than lower output. That is 2 seriesed in parallel with 2 seriesed for best failure mode outcome

Buying new box comes up against sentiment, it won't have a gaudy big "gold" logo saying CRATE on the front , the word crate means just shipping crate in USA presumably does not have the connotation of "heap of junk" as it does in the UK

Two things spring to mind here. The first is to just ask the owner what exactly he does ( or wants to do ) with the setup. If he is looking to find some very high output 'sweet-spot' sound from the rig, then you will need to be concerned about output level, impedance matching, and the overall sound you are going to get from replacement drivers. It is also important to know the instrument that's going to be played through it, and how. It's no good having a set of stiffly suspended lead guitar speakers, if it's going to have a bass guitar put through it. Likewise, a Yamaha organ at afternoon tea dances, is a world away from a synthesiser at a rock concert. I have these conversations all the time with musicians, and they can be a fickle lot, so best to understand what's needed right from the off.

The second thing to remember is that speaker impedance is by no means an absolute. It is a figure quoted for a particular speaker with a particular set of test drive characteristics, and is especially sensitive to frequency. If the owner is never intending winding the rig right up to full power, then

In theory, both conditions will result in a deviation from the 'ideal' sound, and I'm sure that there are audiophiles on some of the audio groups, who would tell you that such a mis-match is a cardinal sin, and that they would be able to hear it, but trust me - you, I or the average modern musician, would not hear anything untoward. So the bottom line is yes, by all means be aware of the *potential* problems, but don't worry yourself into an early grave about them. Equipment mismatches in the rock musician world, is the norm rather than exception ( well, perhaps not quite, but you take my point ...). Talk to the owner !

Arfa

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I'm trying to work through the following , set as a hypothetical

An amp of 100 watts rating, set for 8 ohms powering one 100 watt , 8 ohm speaker in a box.. Then same amp powering 4 off of same speaker type wired to give 8 ohm overall in a cab. For the same volume setting of the amp then the same amount of audio out of each set up , its just the 4 way one will be able to go into peak overdrives much more comfortably, or is there other differences ?

For a start, four times the surface area of speaker cone, is going to shift four times the volume of air ... I guess this will likely increase the perceived volume level, for the same volume control setting in the same room. It would make an interesting experiment. I'm not sure that I see where you're coming from with the "peak overdrives" comment. Explain more please ??

Arfa

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assuming 2 series 8 ohm // 2 series 8 ohm and current I , voltage V applied to the single case then 0.5I and 0.5V for each in the 4 off case so power of .5I x .5V or 1/4 power in each or exactly the same as the single case , overall. assuming linear 1/x power in leads to 1/x audio power out, which is probably not the case, ie non-linear conversion

I don't know about overdriving as I'm not a muso but I assumed it was what many liked doing, taking it to 11 and all that.

"N Cook" wrote in message news:enh1tm$t0c$ snipped-for-privacy@inews.gazeta.pl...

Ah, OK, I see where you're coming from. 4 x 100 watt speakers, series'd and parallel'd to arrive back at 8 ohms makes a 400 watt 8 ohm cabinet, so driving in a 100 watts, results in a dissipation of only 25 watts in each speaker, right ? Seems a fair point.

As far as overdrive sound goes, this is normally achieved by deliberately overdriving an early stage of the amp, and once you've achieved the degree of overdrive sound that you want, it should remain just so over the full range of output power of the amp, as controlled by the master gain. So if you set up a Canned Heat " Let's Work Together " type sound ( this was probably actually done with an external fuzz pedal on the original record, but a similarly harsh distorted buzz saw sound can be created by preamp overdrive ), then you could take that same sound from a village hall to the National Indoor Arena, just by cranking the master. However, some musicians believe that there is a particular high power output point on any given amplifier, that generates a perfect sound ( for them ). This point is the 'sweet spot', and may be at a point where the output stage is being driven so hard that it is going into hard clipping. This sound cannot easily be transported between different sized venues, unless you interpose a power absorber between the amp, and the speaker cabinet. Such devices are commercially made, and readily available to the professional musician, and are usually adjustable, so allowing you to drive the amp at almost full output to hit your sweet spot, whilst attenuating the input to the cabinet down to village hall amounts. This is why it's important to check with the owner just what he wants to do with the rig, before making a decision on how to proceed.

Arfa

Something you should know about sound reinforcement speakers is that generally speaking it`s prudent, for instrument use, (guitar amps) to use speakers which can handle twice the amplifier power. For example, a

On the other hand, PA speakers should be provided with around twice their power handling, ie, a 400 rms watt speaker cab should be driven by an 800 rms watt amplifier. The amplifiers used for PA should never be driven into clipping, but when they are, that`s when things break!

In most cases when a speaker burns out, it`s because the amplifier driving it wasn't powerful enough to provide adequate volume without clipping.

Ron(UK)

Not responsible for any ensuing flame wars, as the above is often difficult to comprehend, and contentious ;)

As someone who is also involved in repairs of this equipment, I would have this down as good *practical* advice rather than anything particularly contentious - although I can see where you're coming from on that point. Basically, it reinforces all that I've said about driving amps to output stage clipping, and above all, the need to talk to the owner, to find out just what he needs the rig to do.

Arfa

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Is it not simply that if you drive an output to clipping then you are dumping full rail 60V or whatever DC on the speaker. If it stays for more than a few milliseconds driven to full high or low then that is enough to burn out the voice coil after its already hot from sustained high, but not clipping, normal AC.

Well it`s not technically DC, more of a square wave than a sine wave, so the peak lasts longer and the waveform contains up to twice the energy, but you are correct that it`s voice coil heating that`s the killer.

There are some handy papers on the Rane site covering what happens when amplifiers are driven into distortion btw.

Ron(UK)