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Any Rules For Mixing Cabinets?

#221
DaveAceofBass said:
When the amp "sees" two 8 ohm cabs (4 ohms total), the power is not necessarily distributed evenly 50/50 between both cabs. It depends on the speaker configuration and sensitivity of the cabs.
Click to expand...

The math I am familiar with says that only the impedance curves, and whether the cabs are connected in series or parallel (and they're virtually always in parallel), matter, as far as determining power distribution. So there can be minor differences in power distribution between two "8 ohm" cabs, but they are explained by the impedance curves.

I do not see how either the speaker configuration or the sensitivity of the cabs would make any difference in how the power is distributed.

Can you explain it to me?
 
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#222
DukeLeJeune said:
The math I am familiar with says that only the impedance curves, and whether the cabs are connected in series or parallel (and they're virtually always in parallel), matter, as far as determining power distribution. So there can be minor differences in power distribution between two "8 ohm" cabs, but they are explained by the impedance curves.

I do not see how either the speaker configuration or the sensitivity of the cabs would make any difference in how the power is distributed.

Can you explain it to me?
Click to expand...
just when you think the dead horse was buried someone digs it up...

I predict crickets.
 
#223
Yup, inductive reactance, add a bit of capacitive reactance and good old linear R to taste. For the SPL for a given freq. add cab response and driver sensitivity (SPL) and stir well. Like it or not, there is some L, R, and C in every circuit made by man, even a copper trace on a circuit board.
 
#224
DukeLeJeune said:
The math I am familiar with says that only the impedance curves, and whether the cabs are connected in series or parallel (and they're virtually always in parallel), matter, as far as determining power distribution. So there can be minor differences in power distribution between two "8 ohm" cabs, but they are explained by the impedance curves.

I do not see how either the speaker configuration or the sensitivity of the cabs would make any difference in how the power is distributed.

Can you explain it to me?
Click to expand...

Duke, you are not asking me, and I believe you know much more than I, but I believe there is a bit of semantics involved. Sensitivity, as you know, is proportional to SPL. SPL is power in the form of air motion. The other power, wattage, and it's consumption is also present as you noted, and XL (2piFL), the largest factor in Z vs. freq., goes up with freq., so if there is much variance of XL, there will be much variance in Z. I think variance in Z betwen two cabs would most likely be seen with a single driver in one cab and several in another, resulting in total Z for one cab being off compared to the other. Or we're all nuts :D

If only everything was rated in horse power, we could all get along better :D

Sorry if there are discrepancies, I am well medicated now, in attempt to sleep tonight.
 
#225
BadExample (love your moniker!), can you give me an example (I'll settle for a bad one!) illustrating what you are describing? I don't see how the power distribution would be anything other than what the impedance curves predict. Yes the power distribution relationship can change with frequency due to the reactive components of the impedances, but that is already predicted by the impedance curves (both phase and magnitude) of the cabs.

Thanks!
 
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#226
OK, here is a bad example attempt:

If one cab has an SPL of 90 db @ 1watt/1meter and the other has an SPL rating of 100 db @1 watt/1 meter, the more sensitive would produce 10 db more sound pressure, a form of power.

The Z, yes, predictable if you know what the curve is, or the value of L and make your own curve.

My opinion is that the unknowns will be more a factor. Stuff the average Joe doesn't know or care about. The end goal is to get the plucked string to vibrate the eardrum just right, and there is a lot of stuff in between.

My medication is fully soaked in and I am about to pass out now... I feel my head wobbling about. In the 70's the good stuff came from your friends and your friends friends. Now it comes from your doctor.
 
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#227
BadExample said:
OK, here is a bad example attempt:

If one cab has an SPL of 90 db @ 1watt/1meter and the other has an SPL rating of 100 db @1 watt/1 meter, the more sensitive would produce 10 db more sound pressure, a form of power.
Click to expand...

That has nothing do with the subject though, which is power distribution in the voice coils. Link Removed
 
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#228
BadExample said:
If one cab has an SPL of 90 db @ 1watt/1meter and the other has an SPL rating of 100 db @1 watt/1 meter, the more sensitive would produce 10 db more sound pressure, a form of power.
Click to expand...

Passinwind said:
That has nothing do with the subject though, which is power distribution in the voice coils. Link Removed
Click to expand...

I see what you mean, BadExample, and maybe our difference is actually semantic after all.

I was talking about power distribution to the cabs (not SPL from the cabs), as Passinwind said, as I think that's more likely to be a primary concern to anyone pairing dissimilar cabs because of the possibility of sending too much power into one of the cabs and damaging it.
 
#229
DukeLeJeune said:
The math I am familiar with says that only the impedance curves, and whether the cabs are connected in series or parallel (and they're virtually always in parallel), matter, as far as determining power distribution. So there can be minor differences in power distribution between two "8 ohm" cabs, but they are explained by the impedance curves.

I do not see how either the speaker configuration or the sensitivity of the cabs would make any difference in how the power is distributed.

Can you explain it to me?
Click to expand...
I agree that if there is any difference it will be slight but, as you know, the impedance of a speaker cabinet varies with the frequency of the signal. Is it possible that factors such as reactance in a particular cab and its drivers might result in a slightly different impedance from that of a different cab during operation?
 
#233
Passinwind said:
That has nothing do with the subject though, which is power distribution in the voice coils. Link Removed
Click to expand...

Yes sir, I was stepping in to hopefully prevent a big fist fight between The Duke (like he ever says anything that could offend anyone - joking... No unrest) and another fella, pointing out the other fella was talking about power vs. sensitivity. I'm not really opinionated on the mixing of cabs. I'm not the sharpest hammer in the toolbox, so I hereby step out of the debate.

MVE said:
It's the same as mixing two different salad dressings, "it MIGHT taste good....but it PROBABLY WON'T"
Click to expand...

Why I smoke my veggies and mix my drinks.
 
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#235
BassmanPaul said:
Sorry Dave but if the impedances are the same the power split is equal.The speaker configuration and cabinet sensitivity might equate to different volume levels coming out of the boxes but the power used is equal.
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They are not resistors, Look at the impedance at say 80hz. One may be double the other.
That is if you can find any measurements of any bass cabinet.
 
#238
Indeed there can be noticeable difference which depends on frequency spectrum.
it's not unusual that the average Impdance increases with boost of lows (EQ adjustment).

The measurement to proof the Impedance versus spectrum dependency is rather simple.
Take a pink noise and do a measurement for Urms and Irms and then calculate Z=Urms/Irms.

Then boost the low end by +12 dB and measure Urms and Irms and calculate Z.
There should be a very remarkable increase for Z

The measurement proof is also possible with a bass guitar for low notes like E0 but measurement is somewhat delicate due to lots of level deviations (dynamic) with a "real" bass guitar signal.

My 4 Ohm 212 ported cab bahaves like a 7 Ohm while my sealed 4 Ohm cab stays rather robust with around resulting 5 Ohm.

Consecuently it means that rated nominal Impedance of a cab isn't a steady number nothing at all.
The average (or nominal) Z can easily double it's manufacturer rated number, deepending on EQ adjustment and notes played on the instrument.
And consequently it also means that tube amplifiers sometimes don't work well with ported cabs, depending on "personal" EQ adjustment preference AND distinct impedance curve of the ported cab. As usual, it all depends.
 
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#240
ThisBass said:
Indeed there can be noticeable difference which depends on frequency spectrum.
it's not unusual that the average Impdance increases with boost of lows (EQ adjustment).

The measurement to proof the Impedance versus spectrum dependency is rather simple.
Take a pink noise and do a measurement for Urms and Irms and then calculate Z=Urms/Irms.

Then boost the low end by +12 dB and measure Urms and Irms and calculate Z.
There should be a very remarkable increase for Z

The measurement proof is also possible with a bass guitar for low notes like E0 but measurement is somewhat delicate due to lots of level deviations (dynamic) with a "real" bass guitar signal.

My 4 Ohm 212 ported cab bahaves like a 7 Ohm while my sealed 4 Ohm cab stays rather robust with around resulting 5 Ohm.

Consecuently it means that rated nominal Impedance of a cab isn't a steady number nothing at all.
The average (or nominal) Z can easily double it's manufacturer rated number, deepending on EQ adjustment and notes played on the instrument.
And consequently it also means that tube amplifiers sometimes don't work well with ported cabs, depending on "personal" EQ adjustment preference AND distinct impedance curve of the ported cab. As usual, it all depends.
Click to expand...

Curious, will this work to measure the inductance of a cab: How to Measure Inductance ??? I think the article is written with a single inductor in mind.
 
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