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Loudspeaker impedance question.


StewartB

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Folks, this question has probably been answered before, and I did do a bit of googling before asking.

 

I have acquired a new solid state amp - Hiwatt (Maxwatt G50) which runs a Hiwatt branded 50 watt / 4 ohm speaker (I measured the speaker at 4.3Ohm).

 

The printing on the speaker - "RKT50" makes me think this is actually a Hiwatt branded Celestion Rocket 50 of 4 ohm impedance.

 

The amp has an external "speaker out" which is labelled "4 to 8 Ohm". Anyway, the question is whether changing the origignal speaker to a Texas Heat 8 ohm (which I have in my stock of spare parts) would reduce the apparent volume or loudness of the amp? My research tells me that an 8 ohm may drop the output by maybe 3 dbl or so. I guess I need to experiment to get a resolution, but thought maybe someone more experienced in amps would know the definitive answer? Comments appreciated.

 

StewartB

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Typically, I don't think you will hear that much difference, as you will just turn the amp up. There will be more of a difference in the speaker than the ohms that you will hear. I would suspect that given a choice you might think it would sound better if you had a texas heat of 4 ohms because that is how they designed it, but that is only a guess.

That said, adding impedance is better than subtracting. It should be perfectly safe as you will only be driving the amp a little harder into the speaker. The danger of using less impedance is the possibility of overheating the output transformer. Since the amp you have has an external speaker jack and no impedance switch, that should tell you it was designed to handle more of an impedance load.

 

Why not try it and see how it sounds? It may or may not be what you like.

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Typically, I don't think you will hear that much difference, as you will just turn the amp up. There will be more of a difference in the speaker than the ohms that you will hear. I would suspect that given a choice you might think it would sound better if you had a texas heat of 4 ohms because that is how they designed it, but that is only a guess.

That said, adding impedance is better than subtracting. It should be perfectly safe as you will only be driving the amp a little harder into the speaker. The danger of using less impedance is the possibility of overheating the output transformer. Since the amp you have has an external speaker jack and no impedance switch, that should tell you it was designed to handle more of an impedance load.

 

Why not try it and see how it sounds? It may or may not be what you like.

 

Thanks stein. I will swap them over and do an A/B test. I had the Texas Heat in another amp and liked the sound, so that was part of the reason for changing. I'll let my ears be the judge. Thanks again,

 

Stewart

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FYI - Speakers have manufacturers codes just like potentiometers and many other electronic components.

 

If you ever wonder who ACTUALLY made a speaker and you can find the code on the speaker (usually number with a two to four digit prefix separated by a "dash" from the other numbers) it can be internet researched, or post it here (I have a fairly comprehensive list).

 

For example:

A speaker, regardless of whether its says "Gibson" on it or "Fender" (or whatever), with a code prefix of 220 was made by Jensen.

One with 465 is an Oxford, 285 = Rola, 67 = Eminence, just to name a few.

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"...adding impedance is better than subtracting..."

 

I don't think that's necessarily true for solid state amps.

 

But a higher impedance speaker will result in lower nominal output from the amp.

 

You may not hear the difference though, depending upon the efficiency of the speakers in question.

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"...adding impedance is better than subtracting..."

 

I don't think that's necessarily true for solid state amps.

 

But a higher impedance speaker will result in lower nominal output from the amp.

 

You may not hear the difference though, depending upon the efficiency of the speakers in question.

 

Thanks. I will do the swap this weekend and see what it sounds like. I think the existing speaker has an SPL of about 95 whereas the Texas Heat specs say 99. Possibly the higher efficiency of the Texas Heat will make the sound levels about the same.

 

Thanks to all offering advice. Appreciated.

 

Stewart

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