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Author Topic: Speaker impedance matching  (Read 6318 times)

joecool85

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Speaker impedance matching
« on: May 17, 2011, 12:38:54 PM »
If you have an amp that puts out the most power at 4 ohms and you want to use a single speaker that is rated at 8 ohms, is it possible to attach a 1:2 ratio transformer to the speaker and put full wattage (minus any loses from the transformer) to the 8 ohm speaker?
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Minion

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Re: Speaker impedance matching
« Reply #1 on: May 17, 2011, 07:59:30 PM »
Nope , you don"t get something for nothing ....... If you want to use an 8 ohm speaker and have it as loud as when you use a 4 ohm speaker then get a more sensitive speaker ..... an 8 ohm speaker that is 3db more sensitive than your 4 ohm speaker will be just as loud as your 4 ohm and 6db more sensitive will be twice as loud as the 4 ohm .......

Cheers

J M Fahey

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Re: Speaker impedance matching
« Reply #2 on: May 18, 2011, 06:06:08 AM »
If you use a matching transformer, yes, you will, but said transformer will be almost impossible to find and if custom wound will cost way more than the correct speaker.
But don't worry, *many* excellent speakers can be found in 4 ohm impedance.

JayFett

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Re: Speaker impedance matching
« Reply #3 on: May 18, 2011, 02:58:43 PM »
Just use two 8-ohm speakers in parallel... the best of both worlds... LOUDER, bigger sound stage.
I don't recall seeing any of my favorite guitar speakers (Celestion or Eminence) offered in 4-ohm.
It is usually only 8-ohm, and occasionally 16-ohm.

If you are designing a boutique SS amp to sell, then including an 'accepted' speaker(s) is almost
part of the requirement.

joecool85

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Re: Speaker impedance matching
« Reply #4 on: May 18, 2011, 04:11:56 PM »
Love the nickname, JayFett.  And I'm not building an amp but considering building a cab that I could use to plug into my K20-X and also maybe use for testing amps later.  Ideally I would like something like an Eminence 1058 or 1258 but in 4 ohm.  If I do it I will probably end up just using two speakers, but it would be nice to use one for keeping not only the cost but the weight down.  I might try two 8" speakers...still light and small and the Webers are $25 each, so it would come in at least than a single 1058 even.  But then I wonder if I am doing that, would it make sense to put an 8ohm in my amp and then have a 1x8" cab to plug into that would be in parallel so it would be 4 ohms to the amp or would I build a 2 x 8" cab at 4 ohms and just unplug the internal speaker when I use it...hmmm.  Decisions, decisions.  I wonder what 2 x 8" would sound like.
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
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J M Fahey

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Re: Speaker impedance matching
« Reply #5 on: November 06, 2011, 04:45:57 PM »
Jensen MODs are excellent, have good price, and most can be had in 4 ohms.

Enzo

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Re: Speaker impedance matching
« Reply #6 on: November 07, 2011, 07:10:38 PM »
And aside from the good advice already given, remember that the reduction in power between the 8 ohm and 4 ohm speakers is only going to be 3 decibels if the speakers are otherwise the same.  Not really much of a drop.


And if you just MUST do this, Peavey made a 2/1 auto-transformer for the output of their 400G power amp board to do exactly what you propose, get full 4 ohm power into an 8 ohm load.  The part number was DG117, which is probably now a 70500117, in the newer parts number system.  You could call Peavey parts and ask if it is still available, and if so at what price.  I would guess under $50 if they still have them.

Peavey also makes/made the "Automatch" universal matching autotransformer.  It did the above job, plus could match to 70.7v systems and a lot of other things.  Probably way more transormer than you are looking for.

Dimi Pana

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Re: Speaker impedance matching
« Reply #7 on: November 08, 2011, 12:46:24 AM »
Very interesting thread, I wish more will contribute. Funny thing is I was recently looking at this --> http://www.tubesandmore.com website while researching on cabinet speakers.

I have a parallel question to what you're discussing here.

Say you have to chose between a single speaker or a combination of 2 (or more) speakers to achieve the desired Ω resistance for your amp. If -for example- a 2X8" combination has -almost- the same (cone) area as a 1x12", or to make the question more ..."provocative",  if a 4x4" has exactly the same area as a 1x8", why the 1x12" would be the choice of most people. Is it the better bass response of the larger 12" speaker or what?

I am not sure how I come up with these questions, probably because for the last few days I've been sick as a dog and have too much free time just lying in bed fighting this nasty cold. :'(

 

Evil_Food

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Re: Speaker impedance matching
« Reply #8 on: November 08, 2011, 04:49:13 AM »
Quote
why the 1x12" would be the choice of most people

What people choose is very subjective and rarely related to anything tangible. I've come to the conclusion that most people define sound with very ambiguous terms, which in my mind brings only confusion. I haven't got a different way to describe it though, so I guess we'll have to manage somehow.

I would assume it's the bass response, since that's the benefit of a larger speaker. If you look at the frequency response of jensen mod speakers http://jensentone.com/mod_index.php and compare the mod6-15 and mod12-110, the lower cut-off frequency isn't that much different in the 12", but the impedance peak is more prominent. Since valve amp (and some ss) gain depends on speaker impedance, the gain around peak is higher for the 12".

Also I would expect the 12 inch to be louder, but you can find large speakers with 90db spl.

Don't forget the large speaker looks cooler ;)

And here in the UK the smallest speaker I could find was the 6" jensen (everything else is 8 inch minimum and I don't think it would be much different in the US).

phatt

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Re: Speaker impedance matching
« Reply #9 on: November 08, 2011, 09:50:03 AM »
Hi Evil F,
           It's not just the cone size as there are many factors involved.

A lot has been discussed here; http://www.ssguitar.com/index.php?topic=1968.0

Voice coil *Diameter* plays a big roll.
If you are going to compare different sized cones you need to consider how VC Dia effects the sonic result.

In General;

Smaller Dia cones have smaller VC Dia and this can lead to the peaking effect. Some early guitar speakers are sort after for that quirky effect.

Take the same size speaker but with bigger VC and the sound will be flatter over a wider freq range.

A speaker cone of X Diameter can only cover about 3 octaves anyway and a larger VC
is more able to hold the cone in suspension over that given range.

Now add magnet types and a list a mile long of all the other paremeters that also add to the end result,, and and and. LOL

For more indepth,,Try this;
http://www.lenardaudio.com/

Click on *Site Map* Down the bottom you will find quite a bit of indepth stuff on guitar amps and speakers.
(I believe those pages are still up)
This chap Specializes in Theatre Sound Systems these days but built some big Austrailian Guitar Amp rigs in years past,, Valves of course.

Cheers, Phil.

Evil_Food

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Re: Speaker impedance matching
« Reply #10 on: November 08, 2011, 11:36:33 AM »
Thanks phatt, quite like the website. I think this link in particular http://www.lenardaudio.com/education/13_guitar_amps_3.html should be a "Read before you post" as it will save a lot of explanations.

Loudthud

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Re: Speaker impedance matching
« Reply #11 on: November 22, 2011, 09:49:39 PM »
Weber sells a couple of impedance matching autoformers, the WZC-50 and WZC-100. They have several taps including some oddball impedances like 5.3 ohms for those 3x12 cabinets. Down near the bottom of the page at: http://taweber.powweb.com/store/magnetic.htm
« Last Edit: December 07, 2011, 08:39:55 PM by Loudthud »

joecool85

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Re: Speaker impedance matching
« Reply #12 on: November 23, 2011, 09:34:44 AM »
Weber sells a couple of impedance matching autoformers, the WZC-50 and WZC-100. They have several taps including some odball impedances like 5.3 ohms for those 3x12 cabinets. Down near the bottom of the page at: http://taweber.powweb.com/store/magnetic.htm

Neat!  I figured you could use a transformer but hadn't been able to find one.  Thanks!
Life is what you make it.
Still rockin' the Dean Markley K-20X
"New" amp: Fender Frontman 25 DSP (FM25DSP)
thatraymond.com

 

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