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Post subject: XD Superchamp extension speaker question
Posted: Wed Oct 20, 2010 7:43 am
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Location: Conway, Arkansas
guys
recently pulled the stock speaker out of my SC and installed a 50w 8 ohm Weber vintage 10". It sounds great , but I would still like a little more headroom,
I can mike it out but would like another option. I have a pro junior cabinet only that has a stock fender 10" 8 ohm 30 watt speaker , with a 1/4 input. I tried
"Y" ing out to connect the two speakers , and it seemed to work fine. Then I sent a question to Fender support , and they said I might damage the amp because of the total ohms, or something like that. I asked Weber the same question, and they said it would be ok. Anyone out there have any experience with this. By the way , I replaced all three tubes with Ruby , along with the
Weber speaker , and this amp sings!
thanks
Don


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Posted: Wed Oct 20, 2010 7:55 am
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Fender support speaketh the truth.

The SCXD was designed for an 8Ω speaker load. Adding a second speaker in the manner you describe cuts that impedance in half -- not conducive to the amp's longevity.

HTH

Arjay

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Posted: Wed Oct 20, 2010 1:44 pm
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Retroverbial wrote:
Fender support speaketh the truth.

The SCXD was designed for an 8Ω speaker load. Adding a second speaker in the manner you describe cuts that impedance in half -- not conducive to the amp's longevity.

HTH

Arjay


Ω = ohm
The amp is designed for a 8Ω speaker load.
Y'ing the connection would, indeed, cut that speaker load in half, thus
it would become 4Ω and that Ω load falls 4Ω's short of the amp's 8Ω load requirement.
If I am not mistaken,
Y'ing speakers this way is called "parallel" wiring.
I "THINK" if you wanted to run two speakers in parallel, you would want
a pair of 16Ω speakers which when wired in parallel, would cut the Ω load in half and thus would be doable to meet the amp's Ω requirement.

a four speaker setup
If Don wanted 4 speakers wired in parallel, he would need 4 32Ω speakers. Note: actually, I am speaking in reverse: If Don wanted to
hook up 4 speakers, he would need use 4 speakers which are rated at
32Ω and he would need to wire it parallel.
I think the only consideration following ohm load with running four speakers is that of watt ratings.
IF the speaker is rated at say 15 watts, then four would equal a total of
60 watts. An amp that is only capable of 15 watts is certainly not going to
blow a speaker when the combined speaker chain can handle up to 60 watts from the amplifier.
My question in this setup's regard concerns volume:
1) Would Don expect the perceived volume be noticeably, if not dramatically reduced when the vol. knob is turned all the way up?

2) Would he expect that he will never push any of those speakers to distortion. I am thinkin' this would be the case.

3) Would there be any potential for amp damage? I am thinking no, but tube longevity may be reduced because the amp is being required to use full juice just to maintain adequate volume levels.

2 speaker wired in series
If Don wired two 8Ω speakers in series, what are the pros and cons?
Does the amp still suffer from inadequate watt shortage that could equate to volume potential reduction if using the speakers he so cites?

Just thought I would toss this link in for reference.
http://jumbosunshade.com/swd01.htm


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Post subject: SCXD ext speaker impedance
Posted: Wed Oct 20, 2010 2:30 pm
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Hi dontkr,

Your amp can only produce X watts of power, no matter what the speaker impedance. It won't produce any more watts with a 4-ohm speaker(s), than it will with an 8-ohm speaker(s). The impedance matching is only about efficient transfer of that power, as much as possible to the speaker(s). You can use a 4-ohm speaker(s) with the 8-ohm amp, nothing wrong with that.

If you use a 4-ohm speaker(s) with an 8-ohm amp, you can quickly reach the amp's rated output watts with the volume knob much lower than with an 8-ohm speaker(s). Turning the volume up from that point, with a 4-ohm speaker, the amp becomes less efficient, and might result in more unwanted distortion. It would be like running the amp at full power all of the time, and that is where the potential problem is, max heat and max distortion can shorten the life. There is good distortion and bad. This is why it is just usually best to match the impedance of the amp and speaker(s). :)

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Post subject: Re: SCXD ext speaker impedance
Posted: Wed Oct 20, 2010 3:29 pm
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shimmilou wrote:
Hi dontkr,

Your amp can only produce X watts of power, no matter what the speaker impedance. It won't produce any more watts with a 4-ohm speaker(s), than it will with an 8-ohm speaker(s). The impedance matching is only about efficient transfer of that power, as much as possible to the speaker(s). You can use a 4-ohm speaker(s) with the 8-ohm amp, nothing wrong with that.

If you use a 4-ohm speaker(s) with an 8-ohm amp, you can quickly reach the amp's rated output watts with the volume knob much lower than with an 8-ohm speaker(s). Turning the volume up from that point, with a 4-ohm speaker, the amp becomes less efficient, and might result in more unwanted distortion. It would be like running the amp at full power all of the time, and that is where the potential problem is, max heat and max distortion can shorten the life. There is good distortion and bad. This is why it is just usually best to match the impedance of the amp and speaker(s). :)


Shim,
I just want to clarify that I am curious about an amp with X watts powering X number of speakers that are rated at X watts - Would having more speakers divide the amount of amp watts per speaker? (ie 15w divided by four = 3.75) Drivers require a certain absolute minimum amount of watts to even move the cone, don't they?
That's what I was alluding to if you read my reply to arjay.
However, what you said about the lesser 4 ohm answers another speculative question I was going to ask earlier but refrained from doing so.
With what you said, combined with a bit of what I had said I have another question:
ohms matching and aside, IF you wanted to obtain speaker distortion, would you want a speaker that is rated just above the amp's max watt capability? (Don't know if this is associated with "headroom" or not)
Assuming the amp is turned up full vol. and tube distortion is occuring with speaker distortion also in full bloom. Back off the volumn a slight, speaker distortion tapers off to clean and peak tube distortion begins to peak.
Is that how that works or supposed to work on top shelf holy grail amps?


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Post subject: Re: SCXD ext speaker impedance
Posted: Wed Oct 20, 2010 5:26 pm
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Twinhit wrote:
Shim,
I just want to clarify that I am curious about an amp with X watts powering X number of speakers that are rated at X watts - Would having more speakers divide the amount of amp watts per speaker?


Yes, a 20 watt amp, with 4 speakers, each speaker gets about 5 watts.

Twinhit wrote:
...ohms matching and aside, IF you wanted to obtain speaker distortion, would you want a speaker that is rated just above the amp's max watt capability? (Don't know if this is associated with "headroom" or not)


Well, you want the speaker to have more wattage than the amp can produce, to prevent unwanted distortion, which is bad for amp and speaker. When you say headroom, to me that means clean sound at high volume, very late breakup (no distortion). So, a 15 watt amp driving a 30 watt speaker would give more headroom. But, it also has to do with speaker sensitivity rating, cone design and other factors for breakup and perceived volume.

Twinhit wrote:
Assuming the amp is turned up full vol. and tube distortion is occurring with speaker distortion also in full bloom. Back off the volume a slight, speaker distortion tapers off to clean and peak tube distortion begins to peak. Is that how that works or supposed to work on top shelf holy grail amps?


I couldn't have said it better, the "sweet spot". Some players like to reach the breakup (good distortion) early, at lower volumes. They might run their bias hotter, or select a different speaker that is made for early breakup. The distortion that you will get from overloading the speakers, is bad distortion, doesn't sound good, so you want plenty of watts in the speaker. :)

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---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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