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Dirty-South Blues Harp forum: wail on! >
Speaker ohm's question
Speaker ohm's question
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paul45
65 posts
Apr 15, 2011
1:27 PM
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This may be a stupid question but here goes..... If you have an amp that allows you to use a 4,8 or 16 ohm speaker whats the differance in performance??
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Ant138
894 posts
Apr 15, 2011
1:31 PM
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That's a good question Paul and I've wondered about the very same thing ever since I've had my Epiphone valve jr.
I'll be very interested to hear the answer if anyone has one:o)
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http://www.youtube.com/user/fiendant?feature=mhum
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markdc70
66 posts
Apr 15, 2011
1:40 PM
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I once read somewhere that if you have a multi-tap output transformer, you don't use all of the windings unless you use the highest ohm connection. The higher number of windings gives you more/better harmonics and bass response. These are "facts" that got put into my head, I'm sure, from the internet, so I may be way off base here. Any amp guru's care to confirm/shoot down my opinions? There seem to be a few guys on here that really know thier stuff about amps.
Last Edited by on Apr 15, 2011 1:41 PM
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5F6H
632 posts
Apr 15, 2011
2:04 PM
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Firstly use the speaker that sounds best...it's not likely that you will find the same model in all impedances.
markdc70 is right, using the whole secondary winding should be more efficient, because OTs are wound differently ...a 16ohm OT with a 4 & 8ohm tap will be different to a similar OT wound specifically for the lower impedances. BUT...we're harp players and for best efficiency we want more amps than volts to push the speaker (50W isn't always just 50W, ratio of volts vs. amps makes a difference), for guitar it's not so critical as a lack of acoustic feedback makes this point largely moot. So I would say don't be afraid of using the lower impedance taps...in fact, I usually do.
So let's take a 50W amp. 50W into 16ohms equates to 28 volts at the speaker at 1.76 Amps. 50W into 2ohms equates to 10volts but at 5 Amps. This is why I'd always suggest rewiring a Blues Deville to 2 ohms & wiring up the white, 2ohm speaker tap, rather than the stock 8ohms.
All things being equal (similar speaker motor, cone material, magnet etc) higher impedances will give a thicker, bassier tone...perhaps erring on the "stodgy" side at times? Lower impedances will give a livelier, faster transients, brighter, airier tone.
All these assume a matched load (16ohm speaker on a 16ohm tap & a 2ohm speaker load on a 2ohm tap). The world isn't perfect, so if you have 4x4ohm speakers you are better off wiring them for 4ohms or 16ohms as you probably won't find a 1ohm OT...& even if you did, it would eat tubes. So once again I say use the speakers you like the sound of best, if you can wire them in parallel or series-parallel/parallel-series do so, rather than all in series.
Classic Fender OTs (on amps with parallel Ext Spker jacks) are tolerant to a 100% mismatch (either halving, or doubling of the rated speaker load) but for safety's sake it's always best to check before mismatching...don't assume that off-brand amps are as tolerant as Fenders, because many were constructed with a degree of mismatch to start with!
Never reduce the speaker load on a 2ohm BF/SF Super Reverb, or a Concert amp (Brown or Black 60's model), or a 2.67ohm Brown 3x10 Bandmaster.
Also be aware that a tube operates over a range of impedances & where the speaker load sits in that range affects the sound...but to play with impedances means knowing or determining your output transformer's "turns ratio", don't guess, go by manufacturer's recommendation if in doubt. A speaker's impedance rises with frequency response, harp doesn't usually drive the amp as hard as guitar, so often a doubling of speaker load (16ohms speaker on a 8ohm tap for instance) USUALLY is safe...but like I said, mismatch at your peril.
Last Edited by on Apr 15, 2011 3:14 PM
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tookatooka
2292 posts
Apr 15, 2011
3:00 PM
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@5F6H. Bravo! Take a bow. What brilliant information. Thanks for that. I don't need the info right now but it is something I have thought about in the past and never really knew why.
This is a great forum for golden nuggets like that. Thankyou Sir.
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Jim Rumbaugh
481 posts
Apr 15, 2011
3:55 PM
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my 2 cents, in simple terms.
when the amp impedance matches the speaker impedance, you get the most sound.
If the speaker impedance is too high, the speaker will not draw the power out of the amp. If it's too low, you're kinda puttin' a short circuit on the amp.
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intermediate level (+) player per the Adam Gussow Scale, Started playing 2001
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rharley5652
463 posts
Apr 16, 2011
12:40 AM
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@ paul ,.
its all in here:
Ever Have a question about speakers, but haven't been able to get an answer?
Are there any sonic differences or benefits of series over parallel wiring or vice versa?
how to wire speakers to obtain 2, 4, 8, & 16 Ohm loads.
http://www.webervst.com/sptalk.html
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Simply Unique Kustom Mic's By Rharley
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lumpy wafflesquirt
341 posts
Apr 16, 2011
12:42 AM
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it's like mics.
on mics match the impedance to the input impedance of the amp.
with speakers match the impedance to the output of the amp.
simples
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"Come on Brackett let's get changed"
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