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I had an epiphany recently in my never ending search for the perfect tone. I have 7-8 amps and have played/owned just about every amp imaginable (boutique, standards, mods, etc.) In my 5 watt champ clone, I use a very old 10" Jensen that came out of an old B-3 speaker cabinet. It's 8 ohms, so it matches most of my various amps. I decided to try on on one of my favorite 25 watt amps that has absolute killer tone at about 7-8, but is so loud that it blows the windows out of almost any small to medium size venue. I plugged it into here and I got fantastic tone and about a 40% decrease in volume (to my ears).

I have a very good Weber attenuater and works well, but I always detect a slight loss of tone. So---my question. Outside of damaging the speaker, am I putting any of my 25, 40 or 60 watt amps at risk by using this inefficient speaker to decrease my volume?

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Changing out speakers is a good way to balance tone and volume, there are some caveats, though.

  • The speaker/cabinet should be able to dissipate at least as much power as the rated power output of the amp.
  • The speaker/cabinet should have a nominal impedance at least as large as the rated output impedance of the amp.

It might not make sense to focus on the actual size of the speaker. Speaker size does affect efficiency (and tone), but you can find less efficient speakers at larger sizes. Also, it might make more sense to focus on entire speaker cabinets, and not just the drivers themselves (it's not clear from your question whether you're already doing this, so I decided to just mention it).

Here's what you can look for in a speaker cabinet to be able to turn the amp up higher without increasing the volume as much:

  • Higher impedance: If your amp has an 8 Ohm output impedance rating, then find a 16 Ohm cabinet, if you can. If your amp has a 4 Ohm output impedance, I would go for an 8 Ohm cabinet - not 16 - just to be safe. Doing this will cut the total power output for a given volume setting about in half.
  • Lower sensitivity: Perhaps this is obvious. 3 dB less sensitivity at 1W/1m for a cabinet is a noticeable difference in volume, if you can find it. Even a couple dB is worth it. A 6 dB drop would a huge difference.
  • Power handling: Again, make sure if you have a 25 Watt amp that your speaker cabinet can dissipate at least 25 Watts (probably not a problem at that rating). Remember if the cabinet is double the impedance of your amp, then you can actually go a bit lower than the rating. For example, if you have an 8 Ohm 25 Watt amp, you can get away with a 16 Ohm 20 Watt cabinet, because the actual power into 16 Ohms would be more like 12 - 18 Watts.

You might find that a 16 Ohm 12" driver in a close-backed cabinet both sounds great and is somewhat quieter.

  • Todd, thanks for the great answer. The speaker is 8 ohm like my amps, so I'm assuming it has adequate impedance. Now, though it's rated 8, when I test the poles of the speaker on the meter it bounces around from 6.8 to 7.7---which is about normal with 8 ohm speakers in my experience. I actually have 2 of these speakers, but putting both in the cab would, I believe, resist only as a 4 ohm speaker so that doesn't help, So, unless I blow the speaker, I assume I'm ok and that my risk there would be a damaged transformer. right? – Gator May 17 at 18:23
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    @Gator It depends how you wire the speakers. If you wire them in series then the impedance will add to 16 Ohm. If you wire them in parallel then they will coming in a more complicated way that will result in a 4 ohm load, as you say. – Todd Wilcox May 17 at 19:39

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