DR ext cab problem

onstage76 · August 15th, 2006, 07:54 AM

Hi guys.

Am about to pull the trigger on a '68 SFDR (drip tray). I believe these come with an ext "out". My question is this - what is the best ohmage for an ext cab for my new DR? If there is an impedence mismatch with an extra cab - will that ruin the amp? - but then how can this be bad if fender actually built the amp with the ext socket??? I'm confused

Do people notice their DRs running bad with extension cabs? I have an 8ohm cab I would love to use if this is the correct thing (2x16ohm weber chicagos wired in parallel).

Thanks for your help. If I get positive responses this amp will be mine within the week

GuitarGuerrilla · August 15th, 2006, 10:07 AM

8 ohms for the extension cab and 8 ohms for the built-in speaker. Technically, there is an impedance mismatch, but it falls within Fender's operating parameters for that amp. I ran my '68 with an ext speaker with no problem. sounds great, too!

bongo · August 15th, 2006, 06:09 PM

In the same vein, I have a 1x12 cabinet with a 16ohm Vintage 30.
Any reason not to use it with my 65 DRRI ?

GuitarGuerrilla · August 15th, 2006, 07:24 PM

As far as the amp is concerned, you should have no problem.

There will be an imbalance in the power sent to the speakers, but since the amp only puts out around 20 watts, it is highly unlikely that you could hurt the combo speaker (which is a C12K or an Eminence gold back, I think. Both rated for much more output).

One thing to be aware of is that if you use a different speaker model in the ext. cab than is in the combo, there may be a difference in volume between the two speakers. This is not so much because of the impedance difference, but because different speakers will output differing sound levels if the efficiency of the speakers is very different.

Nothing will be hurt by this, and you just might enjoy the sound! I generally try to use the same model speaker in the extension cab as is in the combo. Don't know if I'd like a V-30 mixed with a C12K or gold back eminence.

Tremo · August 15th, 2006, 08:01 PM

If you're going to use an ext speaker along with the internal speaker, make sure they are in phase or the low end will take a big hit.

jjmantele · August 15th, 2006, 09:35 PM

No Problem. I moved the feet on my '71 so it would mate with the 4x10.

onstage76 · August 16th, 2006, 09:05 AM

Tremo said "If you're going to use an ext speaker along with the internal speaker, make sure they are in phase or the low end will take a big hit".

What does this mean?

jhundt · August 16th, 2006, 12:05 PM

if the combo speaker and the cabinet speaker are out of phase, the cones will be moving in opposite directions - that is to say that one cone will be moving forward while the other moves backward. The sound waves then cancel each other out, and this is particularly noticeable in the bass frequencies. If you ever hooked up your home stereo speakers out-of-phase, or your car-stereo speakers, you would right away notice that the bass is almost completely gone. If you've never had this problem you should try it sometime, just reverse the speaker leads on on of your stereo boxes and hear how efficiently phase cancellation removes low frequencies. It won't hurt your speakers, it just messes up the sound.

onstage76 · August 17th, 2006, 12:22 AM

so how do you make sure your speakers are in phase?

GuitarGuerrilla · August 17th, 2006, 12:43 AM

Well... You should be able to hear it. Sounds weird. Lack of bottom.

But if you want to know for sure, get a nine volt battery. Disconnect the speaker wires. Using wire, attach the positive end of the battery the positive terminal. Touch the negative to the other speaker terminal. Which way did the speaker cone move?

Now do the same to the other speaker. If the cone moves the same way, you're good. If one moves the cone in and the other moves it out, connect the wires from the amp in reverse order on ONE of the speakers (or speaker systems, if working with a multi-speaker cab).

August 15th, 2006, 07:54 AM	#1 (permalink)
onstage76 TDPRI Member Join Date: May 2006 Location: melbourne australia Posts: 34	DR ext cab problem Hi guys. Am about to pull the trigger on a '68 SFDR (drip tray). I believe these come with an ext "out". My question is this - what is the best ohmage for an ext cab for my new DR? If there is an impedence mismatch with an extra cab - will that ruin the amp? - but then how can this be bad if fender actually built the amp with the ext socket??? I'm confused Do people notice their DRs running bad with extension cabs? I have an 8ohm cab I would love to use if this is the correct thing (2x16ohm weber chicagos wired in parallel). Thanks for your help. If I get positive responses this amp will be mine within the week

August 15th, 2006, 06:09 PM	#3 (permalink)
bongo Tele-Meister Join Date: Jan 2004 Location: hamden, ct Posts: 139	In the same vein, I have a 1x12 cabinet with a 16ohm Vintage 30. Any reason not to use it with my 65 DRRI ? __________________ all I need is just one more guitar :)

August 15th, 2006, 09:35 PM	#6 (permalink)
jjmantele Tele-Holic Join Date: Aug 2003 Location: New Jersey Posts: 850	No Problem. I moved the feet on my '71 so it would mate with the 4x10. __________________ JJman If it says "Vintage" on it -it isn't.

August 16th, 2006, 12:05 PM	#8 (permalink)
jhundt Friend of Leo's Join Date: Mar 2003 Location: Netherlands Age: 54 Posts: 2,989 9 Photos	out-of-phase speakers if the combo speaker and the cabinet speaker are out of phase, the cones will be moving in opposite directions - that is to say that one cone will be moving forward while the other moves backward. The sound waves then cancel each other out, and this is particularly noticeable in the bass frequencies. If you ever hooked up your home stereo speakers out-of-phase, or your car-stereo speakers, you would right away notice that the bass is almost completely gone. If you've never had this problem you should try it sometime, just reverse the speaker leads on on of your stereo boxes and hear how efficiently phase cancellation removes low frequencies. It won't hurt your speakers, it just messes up the sound.

August 15th, 2006, 10:07 AM	#2 (permalink)
GuitarGuerrilla TDPRI Member Join Date: Jul 2006 Location: USA Posts: 68 1 Photos	8 ohms for the extension cab and 8 ohms for the built-in speaker. Technically, there is an impedance mismatch, but it falls within Fender's operating parameters for that amp. I ran my '68 with an ext speaker with no problem. sounds great, too!

August 15th, 2006, 07:24 PM	#4 (permalink)
GuitarGuerrilla TDPRI Member Join Date: Jul 2006 Location: USA Posts: 68 1 Photos	As far as the amp is concerned, you should have no problem. There will be an imbalance in the power sent to the speakers, but since the amp only puts out around 20 watts, it is highly unlikely that you could hurt the combo speaker (which is a C12K or an Eminence gold back, I think. Both rated for much more output). One thing to be aware of is that if you use a different speaker model in the ext. cab than is in the combo, there may be a difference in volume between the two speakers. This is not so much because of the impedance difference, but because different speakers will output differing sound levels if the efficiency of the speakers is very different. Nothing will be hurt by this, and you just might enjoy the sound! I generally try to use the same model speaker in the extension cab as is in the combo. Don't know if I'd like a V-30 mixed with a C12K or gold back eminence.

August 15th, 2006, 08:01 PM	#5 (permalink)
Tremo Friend of Leo's Join Date: Mar 2003 Location: Silicon Valley, CA, USA Posts: 3,735	If you're going to use an ext speaker along with the internal speaker, make sure they are in phase or the low end will take a big hit.

August 16th, 2006, 09:05 AM	#7 (permalink)
onstage76 TDPRI Member Join Date: May 2006 Location: melbourne australia Posts: 34	Tremo said "If you're going to use an ext speaker along with the internal speaker, make sure they are in phase or the low end will take a big hit". What does this mean?

August 17th, 2006, 12:22 AM	#9 (permalink)
onstage76 TDPRI Member Join Date: May 2006 Location: melbourne australia Posts: 34	so how do you make sure your speakers are in phase?

August 17th, 2006, 12:43 AM	#10 (permalink)
GuitarGuerrilla TDPRI Member Join Date: Jul 2006 Location: USA Posts: 68 1 Photos	Well... You should be able to hear it. Sounds weird. Lack of bottom. But if you want to know for sure, get a nine volt battery. Disconnect the speaker wires. Using wire, attach the positive end of the battery the positive terminal. Touch the negative to the other speaker terminal. Which way did the speaker cone move? Now do the same to the other speaker. If the cone moves the same way, you're good. If one moves the cone in and the other moves it out, connect the wires from the amp in reverse order on ONE of the speakers (or speaker systems, if working with a multi-speaker cab).