Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Cabinets-Speakers => Topic started by: g-man on June 13, 2016, 04:37:58 pm
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About half-way down this page is an explanation of how to determine the value of a series dropping resistor to attenuate a speaker. Though it says it's for a tweeter, it's true for any speaker.
http://techtalk.parts-express.com/forum/tech-talk-forum/15515-series-resistor-for-tweeter-attenuation (http://techtalk.parts-express.com/forum/tech-talk-forum/15515-series-resistor-for-tweeter-attenuation)
You may wish to consider an L-pad attenuator for the louder speaker. It's like a rheostat; is adjustable to taste like a pot; no math; and at any setting it preserves the ohm's rating of the speaker.
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A fixed resistance L-pad is fine, so long as you are correct about the dB drop you need. And, yes, use 8 Ohm's for that one speaker being attenuated.
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When I read this post, I thought you wanted to reduce the output of the cabinet, not to balance the cabinet. The simplest way I know to reduce a cabinet output, is to switch from from parallel to series, this will reduce the output, and therefore the volume.
I am curious at what frequency Weber is using to determine Z? Is he using the nominal impedance? Without further info, the Weber calculator is at best qualitative and not quantitative at all.
Are the speakers the same model and the same brand? Maybe you can find typical frequency data for the speakers, so you can use the Z (which is frequency dependent) To rubgoldberg this, and make it quantitative, there is quite a bit more work to do.
Maybe one of the gurus, will explain the weber L-pad e
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When I read this post, I thought you wanted to reduce the output of the cabinet, not to balance the cabinet.
g-man's post: The only problem is that one speaker is a bit louder (more efficient) than the other. I'm wondering [how to] to balance the output without harming the speaker or amp.
The following is off-topic:
The simplest way I know to reduce a cabinet output, is to switch from from parallel to series, this will reduce the output, and therefore the volume.
Yes, but it creates an impedance mismatch with the amp (unless there's a matching OT tap); though the impedance mismatch is probably tolerable.
I am curious at what frequency Weber is using to determine Z? Is he using the nominal impedance?
Yes, that's shown on the Weber Calc website. L-pad design assumes the nominal impedance of the speaker driver. This is good enough to obtain the specified amount of attenutuion.
An L-pad is a voltage divider. There are an infinite # of values for the series and shunt resisitors in a voltage divider, which will yield the desired voltage reduction. The L-pad uses certain specific resistor values, which together with the nominal speaker load rating, preserve that load as "seen" by the amp.
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When I read this post, I thought you wanted to reduce the output of the cabinet, not to balance the cabinet.
g-man's post: The only problem is that one speaker is a bit louder (more efficient) than the other. I'm wondering [how to] to balance the output without harming the speaker or amp.
Yes, but it creates an impedance mismatch with the amp (unless there's a matching OT tap); though the impedance mismatch is probably tolerable.
I am curious at what frequency Weber is using to determine Z? Is he using the nominal impedance?
Yes, that's shown on the Weber Calc website. L-pad design assumes the nominal impedance of the speaker driver. This is good enough to obtain the specified amount of attenutuion.
The title of this thread is "Adding series resistance to reduce output" My solution does that.
I do not disagree with the fact that an impedance mismatch is taking place. It won't hurt a 2 ohm or 4 ohm output to be hooked up to a 16 ohm nominal impedance. however, the reverse is not true. Misquoting association football "No harm no foul"
Thinking about the problem, Using the assumption, both speakers are the same model, same manufacturer, and same year, it could be dirty contacts/poor solder joint within the cabinet. You're not looking at a lot of difference in resistance at the connectors to get a detectable difference in speaker performance
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Using the assumption, both speakers are the same model, same manufacturer, and same year, it could be dirty contacts/poor solder joint within the cabinet.
Good point, about which g-man's 1st post is vague.
@g-man: are these two speakers the same model???
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Jjasilli, you points are well taken.
See how assumptions have gotten me into trouble.
At, the best, what we are looking at qualitative solutions