70's Fender silverface re-cabb'ed for single 15"

Phil Halton · Post by **Phil Halton** » 7 Jan 2009 8:40 am

I've come across a 72 Fender silverface that was converted to a 15" speaker configuration. Well, I'm circling and feeling for my wallet. Before I jump on this, I was wondering how the 15" speaker might affect the overall sound of the amp as opposed to the origional 212 configuration? I'll be using it at low volume mostly, and thought the speaker might be a factor at low levels. Would it be a significant factor for this amp? As far as I understand, its a peavey 15" black widow--dont' know the ohm number.

David Doggett · Post by **David Doggett** » 7 Jan 2009 9:56 am

I have a Dual Showman head (same as a Twin chassis) that I play with either 2x12 Jensens or one or two 1x15 JBL cabs. The 15s have a deeper voice that give a thicker tone that I prefer for country, jazz and classical music. The 12s give a thinner tone that cuts through the mix better for loud blues and rock. To me these different voices cannot be completely compensated by adjusting the amp tone controls. The different size speakers have different responses that in effect change the mid points of the amp tone stacks, at least that's the way I explain it to myself.

If you use a single 15 in a Twin combo cab, for optimum volume and clean headroom, be sure the speaker impedance matches the amp (4 ohms).

Donny Hinson · Post by **Donny Hinson** » 7 Jan 2009 12:29 pm

What david said.

Except...the amp will tolerate an 8 ohm speaker (with just a slight power loss). I played one with an 8-ohm D130 for about 3 years.

Tony Prior · Post by **Tony Prior** » 7 Jan 2009 12:59 pm

I had a D130 in my 68 Silver Face Twin for probably 20 years. Never noticed any gain loss even though it was there. This was an awesome amp , what a goof I was for selling it. But at the time I stopped playing out for several years. Even sold my D10 Pro-III.

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Mike Schwartzman · Post by **Mike Schwartzman** » 7 Jan 2009 1:57 pm

There's a fellow around here that builds custom cabs for old Fenders. Several years back he built me a single 15" cab that would accomodate an early 70's Bandmaster Reverb chassis. That amp is a little less than half the wattage of a Twin Reverb. 2 power tubes instead of 4, and a tube rectifier rather than the Twin's solid state rectifier. I put a Weber 15" 4 ohm speaker in there.

It does not have the headroom to play it out at a gig (maybe for a blues gig or similar)...but it has lovely tone on pedal steel at home and I wouldn't hesitate to record with it. If I ever got a hold of a SF Twin I would do the same thing with it. I imagine it would be a terrific gigging amp, but I'd probably need a better back than I have to lift it.

Roger Edgington · Post by **Roger Edgington** » 8 Jan 2009 12:04 pm

I still have a pre cbs black twin with a D 130. It's good but mine needs new caps and stuff and it's heavy.

Tim Whitlock · Post by **Tim Whitlock** » 8 Jan 2009 3:29 pm

The original question seemed to be regarding whether a single 15 would perform better or worse than 2 12's at low volume. I don't think the size of the speaker in itself would matter as much as the tonal character of the speaker. I found that my JBL D-130F sounds thin and lifeless at low volume, but really bloomed and filled out at higher volume levels (5 or higher on my Twin). Conversely, the Weber Neo 15 I recently installed sounds better at low to medium volume levels, but doesn't handle gig volume as well. I think the best solution is to see if you can try the amp out under your normal playing conditions, before committing to buy.

Darryl Logue · Post by **Darryl Logue** » 8 Jan 2009 6:44 pm

I regularly use a 69 Twin with two 12" E.V. 417. It is a tighter more focused sound. I have used reissue Fender and Peavey four 10" I like those also. One consideration is the amount of cone surface. 15"=15". Two 12's=24" Four 10's= 40". I think it makes a difference.When Fender went to the master volume circuit they changed the cabinets, plywood with rabbit joints and a dado glued in baffel. These especialy the heavy twin tend to come apart. I have repaired and rebuilt many of these they can be difficult. Later 90's ? flakeboard I salvage the hardware throw the cabinet away and start over.

John Groover McDuffie · Post by **John Groover McDuffie** » 8 Jan 2009 10:41 pm

Actually when comparing speaker surface you need to use the relative areas of the cone, not the diameter.
area = pi * (radius)(radius) so to compare area you need to compare the square of the radius.
(all dimensions below are nominal, ie. the cone of a 15" speaker (for example) isn't a full 15" in diameter)

so:

15"spkr: r=7.5"...7.5*7.5=56.25...area=pi*56.25"
12"spkr: r=6"...6*6=36...area=pi*36"
10"spkr: r=5"...5*5=25...area=pi*25"
2x12 relative area is then pi*72
2x10 relative area is then pi*50

So 1x15 and 2x10 have about the same surface area, but the 10s probably have a faster attack and tighter bass. Hence the mighty SVT. (6x6550s doesn't hurt, either!)

John Groover McDuffie · Post by **John Groover McDuffie** » 8 Jan 2009 10:46 pm

So funny you should mention the cabinets.I am restoring a 1x15 Twin cabinet right now. It seems to a very good conversion of a dadoed style into a removeable, screwed-into-cleats style baffle board. The sides and corners all feel very solid.

David Doggett · Post by **David Doggett** » 9 Jan 2009 9:00 am

I'm sort of thinking out loud here, but it seems like the number of speakers has no effect on much except power handling ability. As far as voice or tone goes, two 12s sound the same as one. Two 12s can handle more power than the same single 12, but you have to feed more power to them to get that. Feeding 100 watts into two 12s, each one only sees 50 watts. There is still only 100 watts for volume. Yes, there is more speaker area to move air, but each speaker is only getting half the power, so there is not necessarily more air actually moved, and there might not be much volume change.

This assumes the same impedance load, which means if the one 12 is 8 ohms, the two 12s should be 16 ohms each, in parallel for 8 ohms total. If you compare two 8 ohm speakers in parallel (4 ohm total load), to one 8 ohm speaker, then the lower impedance setup will produce more volume. But that's an unfair comparison. At the same output wattage, two 8 ohm speakers will not necessarily be louder than one 4 ohm.

So it seems to be all about power handling. Two 50 watt speakers can handle more power than one. But this may have some effect on tone, because lower wattage speakers are more flexible, and some would consider them to sound better than higher wattage speakers. So four 25 watt speakers in a 4x12 cab might sound better than one 100 watt speaker.

It just seems like to me this is all a bit more complicated than just comparing speaker areas.

David Doggett · Post by **David Doggett** » 9 Jan 2009 9:01 am

Sorry, double post.

Marc Jenkins · Post by **Marc Jenkins** » 9 Jan 2009 9:45 am

David Doggett wrote:As far as voice or tone goes, two 12s sound the same as one.

2 speakers in an amp will have phase discrepancies; Daniel Lanois, for example, notoriously dislikes recording an amp with 2 speakers. It's probably small beans on a stage with other musicians, of course.

Darryl Logue · Post by **Darryl Logue** » 9 Jan 2009 1:28 pm

John, Thanks for the technical info. To me it seems a one 12" or one 15" are somewhat directional. Two 12" or four 10" spread the sound more. I like d130's allot.If someone is replaceing a baffle that has been modified it is much easier to unscrew the old style than remove a glued in one. Most everything I get in the shop is road worn used and abused. Even the finger jointed pine ones fail. I think recording a miked amp verses playing live can be a totaly different rig. Thats all.