My questions pertain to bass guitar amplification.
I understand that impedance is measured in Ohms and that the lower the
number the lower the resistance.  Most bass rigs cite specs based on 4
ohms and 8 ohms.  Is there any advantage to using speaker cabinets
with a
lower or higher ohm rating?

Also, when playing electric bass in small settings or with unamplified
instruments, is it better to turn down the volume on the bass, itself,
or to turn down the amplifier volume.  I know some bassists who
generally keep the master volume on their instrument at full volume
and make adjustments at the Head.  Simply, which method provides the
best and fullest tone?

Hi rover3d:

Thank you for your question!

You usually won't have to worry about the impedance on a speaker
cabinet for regular uses.

Basically, impedance is important because with too low of a resistance
in your speaker cabinets, you might risk overloading your stereo
amplifier. If your speaker cabinets have too high of a resistance, you
won't be getting the full wattage you paid from your amplifier.

The actual math is simple, but for most purposes, you won't need to
worry about it too much. To see how much wattage is actually used by
your cabinets, you use the following formula:

Actual Wattage In Use = 
(Rated Impedance of Amplifier / Total Impedance of Speaker Cabinets) X
Rated Wattage of Amplifier

So for example, let's say you have a stereo amplifier rated at 800
watt at 2 ohms, and some 8 ohm speaker cabinets. See below for an
illustration:
http://www.modernrecording.com/articles/soundav/link13.html

If you were to hook up only one of your 8 ohm speaker cabinets to your
amplifier, then obviously the total impedance of your speaker cabinets
in this case is 8 ohms. Using the above formula, the actual wattage in
use would be (2 ohms / 8 ohms) X 800 Watts = 200 Watts, which is well
below the rated 800 watts of your amplifier.

Here's where things get tricky though. Let's say you want to hook up
three more 8 ohm speaker cabinets to the same amplifier, so we now
have four 8 ohm speaker cabinets hooked up. The tricky thing about
impedance is that when you have more than one speaker cabinet, you
DON'T multiply the impedance of one speaker cabinet by the total
number of speaker cabinets to find the total impedance, as you might
expect. Instead, to find the total impedance, you DIVIDE the impedance
of one speaker cabinet by the total number hooked up. So when you have
four 8 ohm speaker cabinets hooked up to one stereo amplifier, you
have a total impedance of (8 ohms / 4 ) = 2 ohms (NOT 8 X 4 = 32
ohms!).

So now, with our new four speaker set up, using the formula above, the
total wattage being used is: (2 ohms / 2 ohms) X 800 Watts = 800
watts.

Since our stereo amp is rated at 800 watts, this setup is perfect.
Obviously, if we try to add another speaker cabinet to our setup, that
will further reduce the total impedance, and we risk overloading our
stereo amplifier (since lower total resistance means high wattage
used!).

All this might be confusing if this is the first time you've
encountered these ideas. Please feel free to ask for a clarification
if you're still confused. This site gives an alternate explanation of
these same principles:
http://www.modernrecording.com/articles/soundav/link13.html

For your question about the volume, it typically depends of the
quality of sound at the source, and quality of your amplifier, and the
quality of the wiring in your setup. For example, I would expect that
you can get very good sound quality in your guitar itself, then it
would be a great idea to keep the master volume on your instrument at
full volume. On the other hand, if your guitar doesn't handle high
amplitudes as well as it should, but you do have a pretty good
amplifier and excellent wiring, then it would be better to lower the
master volume on your instrument a bit, and compensate it with your
amplifier.


Google Search Strategy:
speaker cabinet impedance
://www.google.com/search?q=speaker+cabinet+impedance&hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&start=10&sa=N

I hope this helps! If you need any clarifications, please don't
hesitate to ask. I would be more than happy to assist you further!

Best Regards,
blader-ga

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Request for Answer Clarification by rover3d-ga on 17 Mar 2003 15:47 PST

Thanks for your efforts.  I'm more focused on the quality questions
than the math (which is interesting, however) since I am shopping for
a bass rig.  Your 2nd pargraph helped me understand the importance of
impedance, but I'm still confused if a lower resistance level on
speakers suggests they deliver better or worse sound?  Is a speaker
designed, spec'd and rated based on 4 ohms, cleaner than one based on
8?

As to the volume question, are you saying that the best rule of thumb
is to control the volume from the weakest quality link in the chain,
so if the bass is top quality but the amp is 2nd tier, keep the
instrument volume at max?  Isn't there a point of diminishing return
for any electronic device which would mean max volume is not the best
sound?

Appreciate any clarification you can offer.

R

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Clarification of Answer by blader-ga on 17 Mar 2003 16:33 PST

Hi again rover3d:

You asked:

"Your 2nd pargraph helped me understand the importance of
impedance, but I'm still confused if a lower resistance level on
speakers suggests they deliver better or worse sound?  Is a speaker
designed, spec'd and rated based on 4 ohms, cleaner than one based on
8?"

The impedance levels are given so that you can see if your setup is
appropriate for the power rating of your stereo amplifier. This is why
I outlined the math that you would use the calculate this. The
impedance number itself has absolutely NO affect on the quality of the
sound. Some other numbers in the speaker's specs tell about you the
quality of the speaker, such as frequency response, S/N ratio and THD.
There is a great guide to these terms here:
http://www.newsearching.com/speakers/speakers.html

You asked: 

"As to the volume question, are you saying that the best rule of thumb
is to control the volume from the weakest quality link in the chain,
so if the bass is top quality but the amp is 2nd tier, keep the
instrument volume at max?  Isn't there a point of diminishing return
for any electronic device which would mean max volume is not the best
sound?"

Yes, you are correct about the point of diminishing return. The
example I gave was a rather general answer and I agree that it could
have been more clear.

Specifically, what you are talking about is the S/N (sound to noise)
ratio of your components. A higher ratio means that there will be less
distortion and static noise at higher volumes than that of a low
ratio. Higher quality components have higher S/N ratios. There is no
real rule of thumb for this, as it would depend on the quality of the
components in your setup. In general, you would want to keep your
components at the highest volume possible without noticable distortion
or interference from the component itself.  This level will obviously
differ from setup to setup.

I hope this helps! If you have any more questions, please let me know!

Best Regards,
blader-ga

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Request for Answer Clarification by rover3d-ga on 17 Mar 2003 18:19 PST

Thank you.

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Clarification of Answer by blader-ga on 17 Mar 2003 22:07 PST

Thank you for your question, and the tip is much appreciated!

Best Regards,
blader-ga