It is currently Tue Mar 17, 2020 4:08 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 27 posts ]  Go to page Previous  1, 2
Go to page Previous  1, 2
Author Message
Post subject:
Posted: Mon Sep 06, 2010 10:32 am
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sat May 08, 2010 4:31 am
Posts: 411
Location: France
Shimmilou

The impedance (ohms) is the ratio of V (ac(fx)) / I (ac(fx)), where V =voltage, I = current, ac = alternative signal at x frequency.

For a simple coil Z(f) = R + jLW where R (ohm) equal to serial resistor, and L = inductance (Henry), j is quadrature vector (complex number), W =2*pi*f. As the impedance increases linearly with the frequency, the model is not enough to represent the speaker.

Usualy for a speaker, you have to consider the complete RLC circuit with a coupling with mechanic spring-masse-amortizor (cab). Then 2 differential equations with mutual coupling describes in first order the speaker (It is like a transformer --> electric current to acoustic waves).

Consequently, for the amplifier the ratio V/I (complex), the impedance, is considered and fit with curves given by speaker makers.

_________________
Tissan '52 Tele RI & Washburn Hawk 1980, Epiphone Casino MIK, Blues Deluxe RI & VOX ...


Last edited by Tissan on Mon Sep 06, 2010 1:52 pm, edited 1 time in total.

Top
Profile
Fender Play Winter Sale 2020
Post subject:
Posted: Mon Sep 06, 2010 11:31 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Tissan, this seems well beyond the purview of the discussion as regards the original poster's question. And as much as I admire your theoretical prowess (easily superior to my own -- I'd have to look all this "merde" up), most of the forum members will usually tune out "techno-babble" such as this. Personally though, I appreciate the refresher lesson.

:mrgreen:

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Impedance
Posted: Mon Sep 06, 2010 12:00 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Hi Tissan,

Yes, I think that Retroverbial is right, nice info, but too complex. It is nice to have referesher courses. :) You seem to be showing how to figure the impedance at a given point in time, or "instantaneous" impedance if you will. I guess that you could make a speaker response curve with the formulas that you used. But, you are right, I'm talking inductive reactance of the speaker, instead of figuring the exact impedance. I think that you will find that the C is negligible, but you forgot to include it in your formula anyway.

But, you didn't catch my mistake! I said that for a coil X sub L = 1 divided by 2(pi)FL, when it is actually just 2(pi)FL. The capacitor, X sub C is 1 divided by 2(pi)FC. I said that my memory hasn't completely failed, just slipping a little. ;)

But, that's what we have all been talking about, impedance in an AC circuit, resistance for DC, and impedance is calculated, resistance is measured.

_________________
---> "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.


Top
Profile
Post subject:
Posted: Mon Sep 06, 2010 1:45 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Mon Apr 21, 2008 1:37 am
Posts: 597
Location: Australia
:lol: :lol: :lol: Nerd Fight, Nerd Fight....... :P :P :P


Top
Profile
Post subject:
Posted: Mon Sep 06, 2010 2:05 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Sat May 08, 2010 4:31 am
Posts: 411
Location: France
Shimmilou,

That's why I wrote LW=L*2*pi*f in
(Z(f) = R + jLW ) to remind you formula 8) And after RLC stand for Resistor-Inductor-Capacitor circuit.
Impedance can be also measured ; maintaining I constant by an AC current source, the voltage is proportionnal to the impedance.
It is not so different of an Ohmeter where the current through the load is proportional to the resistor, remember galvanometer.

Anyway, we are here not for physics (and I don't want to be borring), but to share our "love" for fender sound.

When I'm home, what I prefer is to play with my tele on my BDRI.

There is no fight, I wanted to push Shimmilou to react against his formula.

At last, I really appreciate comments from Shimmilou and others ...

8) 8) 8) 8) 8) 8) 8) 8) 8)

Sorry to have pertubated the initial request :oops:

_________________
Tissan '52 Tele RI & Washburn Hawk 1980, Epiphone Casino MIK, Blues Deluxe RI & VOX ...


Last edited by Tissan on Mon Sep 06, 2010 2:38 pm, edited 1 time in total.

Top
Profile
Post subject:
Posted: Mon Sep 06, 2010 2:21 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Mon Dec 07, 2009 11:33 am
Posts: 419
Location: WNY Just south of nowhere, but just North of somewhere
WOW, now I'm lost. So back to the original question. Anyone have a Blues Jr NOS that they are running a ext. cab? And what type/model(2x12 or 4x12) and speaker manufacturer?
And how does it sound compared to the stock 12 inch Jenson.

_________________
Image


Top
Profile
Post subject:
Posted: Mon Sep 06, 2010 2:50 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Tissan wrote:
Shimmilou,

Anyway, we are here not for physics (and I don't want to be borring), but to share our "love" for fender sound.

When I'm home, what I prefer is to play with my tele on my BDRI.

There is no fight, I wanted to push Shimmilou to react against his formula.

At last, I really appreciate comments from Shimmilou and others ...

8) 8) 8) 8) 8) 8) 8) 8) 8)


Absolutely! I like to discuss things, and sometimes we can get carried away. :lol: After all, we are talking "nominal" value for the speaker anyway. :wink:

In between posts, I am trying my Tele with my new C600, comparing it to my modified C600. I like 'em both!

newwt wrote:
WOW, now I'm lost. So back to the original question. Anyone have a Blues Jr NOS that they are running a ext. cab? And what type/model(2x12 or 4x12) and speaker manufacturer?
And how does it sound compared to the stock 12 inch Jenson.


My Fender 1x12 cab with a Celestion G12P-80 speaker is supposed to be delivered the day after tomorrow, I will definitely try it with the BJr, as well as the HRDlx and the C600. I will post my thoughts about it after trying it out. :) Sorry we got side tracked from your original post.

_________________
---> "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.


Top
Profile
Post subject:
Posted: Mon Sep 06, 2010 3:33 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Mon Dec 07, 2009 11:33 am
Posts: 419
Location: WNY Just south of nowhere, but just North of somewhere
newwt wrote:
WOW, now I'm lost. So back to the original question. Anyone have a Blues Jr NOS that they are running a ext. cab? And what type/model(2x12 or 4x12) and speaker manufacturer?
And how does it sound compared to the stock 12 inch Jenson.


My Fender 1x12 cab with a Celestion G12P-80 speaker is supposed to be delivered the day after tomorrow, I will definitely try it with the BJr, as well as the HRDlx and the C600. I will post my thoughts about it after trying it out. :) Sorry we got side tracked from your original post.[/quote]

Cool, and now for something completly different, I have a Line 6 with (2)
12 inch 50 watt 8 ohm speakers. can I bypass the amp and just use these speakers and the cab as the ext. cab ? And if yes how do I wire it ?

_________________
Image


Top
Profile
Post subject: BJr extension speaker
Posted: Mon Sep 06, 2010 4:03 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
newwt, if both speakers are 8 ohms, they may be wired together for 4 ohms total. I'm not familiar with Line 6 amps, but typically if there are 2 speakers at 8 ohms each, they will be wired in parallel for 4 ohms total (they could be in series for 16 ohms, but I doubt it). See what the Line 6 manual says, if anything, about the speaker wiring. If each speaker is 8 ohms, you could use one speaker from the Line 6 amp, just unplug the 2 speaker terminals from one of the line 6 amp speakers, and unplug the speaker terminals of the BJr and hook up the Line 6 speaker to it. Make sure to mark the polarity of the wires before disconnecting. I use a piece of tape to mark the + wire(red terminal). That is, if the wire is long enough to reach. I made an extension wire for that very reason, to hook my C600 amp to the speaker in my Deluxe. I cut a 6 foot speaker cable in half and put spade lugs on one end. It is a little effort, but would work for testing comparisons. :)

_________________
---> "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.


Top
Profile
Post subject:
Posted: Wed Sep 08, 2010 4:24 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Mon Dec 07, 2009 11:33 am
Posts: 419
Location: WNY Just south of nowhere, but just North of somewhere
OK, new question time.
I have a chance to pick up a Marshal 412 cab. with (4) 8 ohm speakers, if I wire it as (2) sets of speakers,(in series) each set will be 16 ohms.
So at that point I run out from the amp/ in to 1st set of 2 speakers, out from those and in to the 2nd set that should be (2) seperate cabs at 16 ohm each, which should be 8 ohm stereo. YES or NO ????

Please advise

_________________
Image


Top
Profile
Post subject: BJr ext cab
Posted: Wed Sep 08, 2010 7:00 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
newwt wrote:
OK, new question time.
I have a chance to pick up a Marshal 412 cab. with (4) 8 ohm speakers, if I wire it as (2) sets of speakers,(in series) each set will be 16 ohms.
So at that point I run out from the amp/ in to 1st set of 2 speakers, out from those and in to the 2nd set that should be (2) seperate cabs at 16 ohm each, which should be 8 ohm stereo. YES or NO ????

Please advise


I think that you have the concept right! Both 16 ohms connected together with jacks and speaker cables would give you 8 ohms, you would not have stereo though, you only have one signal. You need a stereo effects pedal, with two outputs and/or just two amps, with each amp plugged into each cab input. I think that you mentioned before about a "stereo" cab, with each input as 8 ohms? If each input is 8 ohms, and you connect them together with a jack, it will be 4 ohms, no stereo. But, just double check that each "set" of two speakers are 16 ohm as you say (I am not familiar with Marshall cabs). I think that typically in a 4x10 cab, internally each set of two 8 ohm speakers will be wired in parallel for 4 ohms, then the two sets are wired in series with each other to give 8 ohms total for the cabinet. But there are many configurations for 4x12 cabs, so just make sure what yours is. I believe that two speakers are not generally wired in series for various reasons, namely the balance between the two speakers, but there is nothing wrong with trying it that way if you want.

If your cab speakers are wired so that each set is 16 ohms, then you are definitely on the right path. :)

I also got to test the BJr with my new Fender 1x12 ext cab with Celestion speaker. The new cab speaker was much more warm and mellow, with more low end and less volume when compared to the stock BJr speaker. The stock speaker was brighter and crisper, and seemed to have better response and was more "snappy" or tight in the mids and was louder than the cab. I guess that part of the sound difference is the closed back enclosure. I am sure that an open back ext cab would sound more trebley and louder.

Overall, I'd say that in this case, I prefer the stock speaker sound to that of the ext cab. But I really got this cab to use with the HRDlx and C600 amps anyway, so I have some more fun,.... errr,... I mean some more serious work left to do. :D

_________________
---> "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.


Top
Profile
Post subject: Re: BJr ext cab
Posted: Wed Sep 08, 2010 8:05 pm
Offline
Aspiring Musician
Aspiring Musician
User avatar

Joined: Mon Dec 07, 2009 11:33 am
Posts: 419
Location: WNY Just south of nowhere, but just North of somewhere
shimmilou wrote:
newwt wrote:
OK, new question time.
I have a chance to pick up a Marshal 412 cab. with (4) 8 ohm speakers, if I wire it as (2) sets of speakers,(in series) each set will be 16 ohms.
So at that point I run out from the amp/ in to 1st set of 2 speakers, out from those and in to the 2nd set that should be (2) seperate cabs at 16 ohm each, which should be 8 ohm stereo. YES or NO ????

Please advise


I think that you have the concept right! Both 16 ohms connected together with jacks and speaker cables would give you 8 ohms, you would not have stereo though, you only have one signal. You need a stereo effects pedal, with two outputs and/or just two amps, with each amp plugged into each cab input. I think that you mentioned before about a "stereo" cab, with each input as 8 ohms? If each input is 8 ohms, and you connect them together with a jack, it will be 4 ohms, no stereo. But, just double check that each "set" of two speakers are 16 ohm as you say (I am not familiar with Marshall cabs). I think that typically in a 4x10 cab, internally each set of two 8 ohm speakers will be wired in parallel for 4 ohms, then the two sets are wired in series with each other to give 8 ohms total for the cabinet. But there are many configurations for 4x12 cabs, so just make sure what yours is. I believe that two speakers are not generally wired in series for various reasons, namely the balance between the two speakers, but there is nothing wrong with trying it that way if you want.

If your cab speakers are wired so that each set is 16 ohms, then you are definitely on the right path. :)

I also got to test the BJr with my new Fender 1x12 ext cab with Celestion speaker. The new cab speaker was much more warm and mellow, with more low end and less volume when compared to the stock BJr speaker. The stock speaker was brighter and crisper, and seemed to have better response and was more "snappy" or tight in the mids and was louder than the cab. I guess that part of the sound difference is the closed back enclosure. I am sure that an open back ext cab would sound more trebley and louder.

Overall, I'd say that in this case, I prefer the stock speaker sound to that of the ext cab. But I really got this cab to use with the HRDlx and C600 amps anyway, so I have some more fun,.... errr,... I mean some more serious work left to do. :D



OK, atleast I'm on the right track now. I was thinking of either building two
of these,or one as a 412 configuration but with isolating the four speakers
into (2) sets of speakers
[/img]Image

Or maybe just use the Marshall 412 the way it is. (8 ohm setup)

_________________
Image


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 27 posts ]  Go to page Previous  1, 2
Go to page Previous  1, 2

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: