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mathman

Building a cab impedance questions

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So, I think I messed up slightly, read too quickly for some things.  So, asking for advice where to go.  This is a cheap cabinet plan.  I built a homemade cabinet last summer and put single 8 inch from and old amp and the 6 inch Celestion that came with the cheap Footnote amp I bought from parts express as a simple project.

The Monoprice tube amp I bought has a Celestion 8-15 that sounds pretty good once it is getting broken in.  I got a decent price on two of them and another of the 6 inch Celestion's.  Planned to wire the two 8 inches together as an external cab and the two 6 inches together for the footnote amp.  

I misread and thought I could wire two 8 ohm speakers together for 8 ohm.  It seems I read wrong. doh.

So, couple of questions.  It seems the amp can handle 16 ohm.  What is different about the sound as a 16 ohm cabinet.

The 6 inch speakers are 4 ohm.  Any way to wire all four together that would be better?

Thanks, total noob here but am starting to read more tonite.

Any ideas?

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As far as saying what an impedance mis-match sounds like, hard to say. Some purposely do this for tone reasons, maybe from just trying it or it just happened.  Here are practical considerations -

  1. Amps provide maximum power transfer when the speaker load is matched. Loudness. Tube amps may have an impedance selector, like Marshall. Usually means separate windings in the output transformer.
  2. if the speaker impedance is higher than the amp spec, less power goes to the speaker.  Output section of amp should be safe against blowing out.
  3. If the speaker impedance is lower than the amp spec, you get more than rated power from the output section. May be a chance to blow amp, especially at high settings.

Boogie amps (maybe some others) can tolerate a slight mismatch. For an 8 ohm rated amp, a 4 ohm speaker load can be tolerated. A 2 ohm load might be a problem. Some PA , solid state, amps tolerate a wide load range and develop max output power at low ohm load.

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Posted (edited)

Two words: Ohm's Law.

There's tons of websites and message boards online that discuss speaker impedance, and how Ohm's Law can help you figure the total impedance of speakers.  Keep in mind that separate speaker enclosures (or speakers wired together, that is) will have a separate impedance from another speaker enclosure, and once you figure out what the impedance is for one multi-speaker cabinet separately, then you have to do the same for the other, THEN figure out what the impedance is when you use the cabinets combined TOGETHER with one amp.  Of course, it's math, but it wouldn't hurt to get a second or even third opinion from someone else once who's familiar with these concepts once you've figured it out.

Here's one website that looks promising, but there's TONS of similar webpages out there too, just Google 'em.

http://www.prestonelectronics.com/audio/Impedance.htm

Lotsa YooToob videos going over speaker impedance and guitar amps out there as well:

Old Blackface Fenders (maybe Fenders older than mid-60's make, too) were known for being tolerant of impedance mismatches...most of the BF tube combos and all of the BF tube heads had an extra speaker/auxiliary jack around the back of the chassis, and Fender actually did sell extension speaker cabs for combos in the '60's, too (they were single 1x12", and roughly Deluxe Reverb sized, from what I've seen...of course, the heads had their own matching speaker cabs).  They simply were just plugged in.  I don't know about other amp manufacturers though, and I'm not sure about Mesa/Boogies, either.  Good luck!

Edited by crunchee
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Does the amp have 2 "separate" speaker outs?.. if not you're stuck with 16 ohms or 2 ohms

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From the picture I could find of your Monoprice amp it looks like it has one output good for anywhere between 8 and 16 ohms. If that is the case (as opposed to having two separate outputs one of the meant for 8 ohms and the other meant for 16 ohms) then you want the combined impedance of your speakers to be 8 ohms for maximum volume. 

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1 hour ago, crunchee said:

Two words: Ohm's Law.

There's tons of websites and message boards online that discuss speaker impedance, and how Ohm's Law can help you figure the total impedance of speakers.  Keep in mind that separate speaker enclosures (or speakers wired together, that is) will have a separate impedance from another speaker enclosure, and once you figure out what the impedance is for one multi-speaker cabinet separately, then you have to do the same for the other, THEN figure out what the impedance is when you use the cabinets combined TOGETHER with one amp.  Of course, it's math, but it wouldn't hurt to get a second or even third opinion from someone else once who's familiar with these concepts once you've figured it out.

Here's one website that looks promising, but there's TONS of similar webpages out there too, just Google 'em.

http://www.prestonelectronics.com/audio/Impedance.htm

Lotsa YooToob videos going over speaker impedance and guitar amps out there as well:

Old Blackface Fenders (maybe Fenders older than mid-60's make, too) were known for being tolerant of impedance mismatches...most of the BF tube combos and all of the BF tube heads had an extra speaker/auxiliary jack around the back of the chassis, and Fender actually did sell extension speaker cabs for combos in the '60's, too (they were single 1x12", and roughly Deluxe Reverb sized, from what I've seen...of course, the heads had their own matching speaker cabs).  They simply were just plugged in.  I don't know about other amp manufacturers though, and I'm not sure about Mesa/Boogies, either.  Good luck!

Yes, lot's and some are contradictory.  Thanks!

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11 minutes ago, HAMERMAN said:

From the picture I could find of your Monoprice amp it looks like it has one output good for anywhere between 8 and 16 ohms. If that is the case (as opposed to having two separate outputs one of the meant for 8 ohms and the other meant for 16 ohms) then you want the combined impedance of your speakers to be 8 ohms for maximum volume. 

Yes it says 8 to 16 on the output so I am going to wire the two 8 inch in series to get 16 ohm. 

 

thanks all!

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1 minute ago, mathman said:

Yes, lot's and some are contradictory.  Thanks!

I know...that's why I don't use more than two speakers at a time!  Hope it helps anyway.

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If you know what your doing you can wire many 8 ohm speakers together and get 4ohms 8ohm or 16ohms using parallel and series wiring!! This explains it well:

 https://cie-wc.edu/Series_Parallel_9_14.pdf

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37 minutes ago, Dutchman said:

If you know what your doing you can wire many 8 ohm speakers together and get 4ohms 8ohm or 16ohms using parallel and series wiring!! This explains it well:

 https://cie-wc.edu/Series_Parallel_9_14.pdf

Thanks,  One day I may try something different.  For now, I am going to plan on the 16 ohm two speaker.  Once I get that going I will play more later!

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There are opinions out there also about sound differences between speakers wired in series vs. speakers wired in parallel, which was how I originally read your question.  I don't know if this is Eric Johnson territory or not, but it's something else to Google and investigate.  I haven't bothered, myself, because it would necessarily involve changing other variables too, and I can't figure out how I would isolate the series/parallel differences, if I were to notice any at all.

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On 7/3/2019 at 7:17 AM, crunchee said:

Two words: Ohm's Law.

There's tons of websites and message boards online that discuss speaker impedance, and how Ohm's Law can help you figure the total impedance of speakers.  Keep in mind that separate speaker enclosures (or speakers wired together, that is) will have a separate impedance from another speaker enclosure, and once you figure out what the impedance is for one multi-speaker cabinet separately, then you have to do the same for the other, THEN figure out what the impedance is when you use the cabinets combined TOGETHER with one amp.  Of course, it's math, but it wouldn't hurt to get a second or even third opinion from someone else once who's familiar with these concepts once you've figured it out.

Here's one website that looks promising, but there's TONS of similar webpages out there too, just Google 'em.

http://www.prestonelectronics.com/audio/Impedance.htm

Lotsa YooToob videos going over speaker impedance and guitar amps out there as well:

Old Blackface Fenders (maybe Fenders older than mid-60's make, too) were known for being tolerant of impedance mismatches...most of the BF tube combos and all of the BF tube heads had an extra speaker/auxiliary jack around the back of the chassis, and Fender actually did sell extension speaker cabs for combos in the '60's, too (they were single 1x12", and roughly Deluxe Reverb sized, from what I've seen...of course, the heads had their own matching speaker cabs).  They simply were just plugged in.  I don't know about other amp manufacturers though, and I'm not sure about Mesa/Boogies, either.  Good luck!

Side note endorsement:  Neil Preston is an extremely talented and no B.S. electronics expert.  He's a perfectionist about his work and is reasonably priced for what you are getting - a real, experienced expert.

He's serviced my MB and an nailed ugly L6 head repair.

Not affiliated in any way, just a happy customer - but Neil is a "no-brainer" choice for those of us near the Kansas City metro area.

Sorry for the brief  hi-Jack.

 

OK . . . . . Ohhhmmmm . . . . .  

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On 7/3/2019 at 7:26 AM, BoogieMKIIA said:

As far as saying what an impedance mis-match sounds like, hard to say. Some purposely do this for tone reasons, maybe from just trying it or it just happened.  Here are practical considerations -

  1. Amps provide maximum power transfer when the speaker load is matched. Loudness. Tube amps may have an impedance selector, like Marshall. Usually means separate windings in the output transformer.
  2. if the speaker impedance is higher than the amp spec, less power goes to the speaker.  Output section of amp should be safe against blowing out.
  3. If the speaker impedance is lower than the amp spec, you get more than rated power from the output section. May be a chance to blow amp, especially at high settings.

Boogie amps (maybe some others) can tolerate a slight mismatch. For an 8 ohm rated amp, a 4 ohm speaker load can be tolerated. A 2 ohm load might be a problem. Some PA , solid state, amps tolerate a wide load range and develop max output power at low ohm load.

Thanks.  This is a nice little amp but cheap. Wondering if it might not handle mismatched loads as well.  I also have two 4 ohm speakers so I may wire them to make an 8 ohm load and compare some.  This is just a fun cheap little project to start learning.

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Got the two 8 inch Celestion's in and wired as 16 ohm.  Sound great so far. Need to break them in.  The top two are 6 inch Eminence.  Going to connect them to the cheap Footnote amp I bought last summer.

IMG_1069.jpgIMG_1076.jpgIMG_1074.jpg

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Every time I read a thread like this or try to research how to hook up amps to the proper resistance, I come out dumber than before.  I've never fried a head, so I guess I'm doing OK.

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23 hours ago, tommy p said:

I've never fried a head, so I guess I'm doing OK.

I’ve found the voice coils in the speakers will fry b4 the transformer... I had a guy bring over an Egnator to show it to another guy at a jam at my house. He plugged it into a 1-12 8 ohm cab with a vintage greenback in it. Not sure how he had it set but the greeny let out a high frequency squeel and it was gone.... of course he didn’t offer to replace the speaker. Kinda pissed me off... I really didn’t like the Egnator either... to sterile... no harmonics... probly great for metal tho!!

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Oh look!  A dead horse!  I gotsta beat on it some!!  

Gonna try for some straight answers here...  First, you have two 8-ohm speakers and two four ohm speakers.  For the 8 ohms (or the 4's for that matter), any sonic difference between series and a parallel wiring is likely, as noted previously, somewhere in the province of Eric Johnson.  We mere mortals needn't worry our pretty little heads about it.  What is more important is the impedance match between the amp an the cab.  A tube amp with an impedance selector on it will put out the same amount of power at each of its impedance ratings provided the speaker load is matched.  OK, that's out of the way.

If I'm reading your intentions wrong, just stop me right here.................................

OK, what you want to do is take the 8's and wire them in series  = 16 ohms.  Then take the Eminence 6's (which punch way above their pay grade) and wire them in series too = 8 ohms.  Wire these two pairs in parallel and you get a combined impedance of 5.33 ohms.  If you care, see the magic formulae and incantations above.  Now then.  Having had a Footnote and the speaker (I actually have 4 of these speakers looking for a cabinet), I know that the Footnote was originally driving one of those 6's.  Ergo, a 4 ohm load.  Solid state amps generally don't mind an impedance mismatch to the up side even if they produce less power and this is a pretty minor mismatch.  Additional speaker cone area as well as cabinet design can more than overcome this.  So, you're cool with running the Footnote into all 4 speakers in this configuration.

Now, with the Monoprice:  tube amps, as a general rule, are more tolerant of an impedance mismatch to the down side than they are to the up side.  The exception I've found is with EL84 amps which I think has more to do with the output transformers.  Yours is a 6V6 and the output transformer looks pretty hefty.  Again, this is a fairly minor mismatch, so you should be just fine.

This is commonly called series/parallel wiring and most 4 x 12 cabs have been wired this way since Pete Townshend demanded them from Jim Marshall.  Take THAT, EJ... 🤣

 

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7 hours ago, tomteriffic said:

Oh look!  A dead horse!  I gotsta beat on it some!!  

<great info not copied>

Take THAT, EJ... 

 

dead-hamer_horse.gif

Awesome,  Just the idea of was looking for.  Does the volume you play the amp have any the load mismatch?  i.e. If I don't play at higher volumes am I less likely to blow something?

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Running any amp full-tilt for extended periods puts wear and tear on the thing even under optimal conditions.  On the Monoprice I don't know that it'd be all that harmful, but I'd still err on the side of caution (maybe 8 out of 10).  Still it isn't a bad mismatch so, no major worries.   As for the Footnote the mismatch is actually putting the thing further into its "comfort zone" so you'd have no worries about diming the thing.

 

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