Mixing speaker sizes

[Wiggybass]

[quote name='stevie' timestamp='1349427084' post='1826085']
I'm afraid not. The only reason to change your 18 would have been to increase power handling (although even this is a bit moot). Otherwise, a 1 x 18 will work with a 4 x10 as well as another 4 x 10 – in many cases better, in fact, because 18s don't normally have an extended HF response and are thus less likely to cancel the mids/highs coming from your 4 x 10.
[/quote] Replacing a single 18 with a 4 x10 should make quite a bit more racket because it will shift a lot more air. If we assume that the whole surface of a cone driver is active in terms of direct air displacement (it isn't quite but let's keep this simple), then one 18" driver has a surface area of roughly 176.71". A single 10" has a radiating area of about 78.54" so four of them working together will have 4 x 78.54" = 316.16" bashing the air out.

Edited October 5, 2012 by Wiggybass

[Wiggybass]

[quote name='Mr. Foxen' timestamp='1349436871' post='1826257']
Also missed that impedance varies with frequency as well as phase, and fairly sure that can make fun with mismatched cabs too, picturing a ported cab with the big impedance peak at a frequency where the paired cab is not sensitive, resulting in more power going to the less sensitive cab at that frequency.
[/quote] Critical and excellent observation. Impedance varies [i]wildly[/i] with frequency, the main reason why impedances for both individual drivers and complete speaker cabs are usually stated as 'nominal'.

[alexclaber]

[quote name='Mr. Foxen' timestamp='1349436871' post='1826257']Also missed that impedance varies with frequency as well as phase, and fairly sure that can make fun with mismatched cabs too, picturing a ported cab with the big impedance peak at a frequency where the paired cab is not sensitive, resulting in more power going to the less sensitive cab at that frequency.[/quote]

This doesn't matter when cabs are connected in parallel.

Cone area alone doesn't tell you how much air a rig can move - you need to also consider cone excursion (and port area if that's a potential limitation).

[Roland Rock]

[quote name='Wiggybass' timestamp='1349437150' post='1826262']
Replacing a single 18 with a 4 x10 should make quite a bit more racket because it will shift a lot more air. If we assume that the whole surface of a cone driver is active in terms of direct air displacement (it isn't quite but let's keep this simple), then one 18" driver has a surface area of roughly 176.71". A single 10" has a radiating area of about 78.54" so four of them working together will have 4 x 78.54" = 316.16" bashing the air out.
[/quote]

A 15" has an area of 176, an 18" has an area of 254. Still, your point remains valid.

[Mr. Foxen]

[quote name='alexclaber' timestamp='1349437460' post='1826267']
This doesn't matter when cabs are connected in parallel.
[/quote]

How does it work with cabs paired, one sealed one ported, like this, are used together:

At around the frequency where the sealed cab has a impedance peak in the lows, does it mean that most of the power goes through the sealed cab with its lower impedance, and then be subject to the poor sensitivity of the cab that low, or do they behave the same individually as they would alone, because the voltage is still the same?

[stevie]

[quote name='Wiggybass' timestamp='1349437150' post='1826262']
Replacing a single 18 with a 4 x10 should make quite a bit more racket because it will shift a lot more air. If we assume that the whole surface of a cone driver is active in terms of direct air displacement (it isn't quite but let's keep this simple), then one 18" driver has a surface area of roughly 176.71". A single 10" has a radiating area of about 78.54" so four of them working together will have 4 x 78.54" = 316.16" bashing the air out.
[/quote]
Maybe. Maybe not. It depends on several things and radiating area is only part of it.

[Wiggybass]

[quote name='alexclaber' timestamp='1349437460' post='1826267']
This doesn't matter when cabs are connected in parallel.

Cone area alone doesn't tell you how much air a rig can move - you need to also consider cone excursion (and port area if that's a potential limitation).
[/quote] That's an interesting thought. Is there a linear correlation between increased excursion and equivalent increase in effective radiating area? My first thought would be that greater excursion would just push the same amount of air harder, not that it would move [i]more[/i] air, but I'm willing to learn!

[Wiggybass]

[quote name='Roland Rock' timestamp='1349437667' post='1826271']
A 15" has an area of 176, an 18" has an area of 254. Still, your point remains valid.
[/quote] Sorry, quite right - put the wrong numbers in this...http://www.mathsisfun.com/geometry/circle-area.html DOH!!!

[Wiggybass]

[quote name='stevie' timestamp='1349438071' post='1826282']
Maybe. Maybe not. It depends on several things and radiating area is only part of it.
[/quote] What are the others? Assuming equivalent amplifier power etc..

Edited October 5, 2012 by Wiggybass

[Roland Rock]

[quote name='Wiggybass' timestamp='1349438407' post='1826290']
What are the others? Assuming equivalent amplifier power etc..
[/quote]
[quote name='alexclaber' timestamp='1349437460' post='1826267']
Cone area alone doesn't tell you how much air a rig can move - you need to also consider cone excursion (and port area if that's a potential limitation).
[/quote]

[stevie]

[quote name='Wiggybass' timestamp='1349438407' post='1826290']
What are the others? Assuming equivalent amplifier power etc..
[/quote]
Alex already mentioned excursion, and it is worth adding that the average 18" PA driver has twice the excursion of the average 10" PA driver. But assuming equivalent amplifier power, the reference efficiency of the driver and the size of the cabinet (or the moving mass to air-load mass ratio).

[Wiggybass]

[quote name='stevie' timestamp='1349439823' post='1826329']
Alex already mentioned excursion, and it is worth adding that the average 18" PA driver has twice the excursion of the average 10" PA driver. But assuming equivalent amplifier power, the reference efficiency of the driver and the size of the cabinet (or the moving mass to air-load mass ratio).
[/quote] OK - So is there a linear correlation between increased excursion and equivalent increase in effective radiating area? My first thought would be that greater excursion would just push the same amount of air harder, not that it would move [i]more[/i] air...

[alexclaber]

[quote name='Wiggybass' timestamp='1349438090' post='1826283']That's an interesting thought. Is there a linear correlation between increased excursion and equivalent increase in effective radiating area? My first thought would be that greater excursion would just push the same amount of air harder, not that it would move [i]more[/i] air, but I'm willing to learn![/quote]

http://barefacedbass.com/technical-information/Volume-displacement.htm

If you have a 2x12" cab and a 4x12" cab, both appropriately ported and both tuned to the same frequency, and the 2x12" has woofers with twice the Xmax of those woofers in the 4x12", then they'll both be able to produce the same amount of bottom (low frequency SPL). I don't know the numbers on the typical Marshall 4x12"s from the late '60s but I'd bet that our Big Baby 1x12" can produce as much true bottom, thanks to having easily three times the excursion and a ported rather than sealed cab.

As long as the difference in radiating area isn't enormous (like a single 8" vs an 8x10" - because you'd run into issues with acoustic coupling) then cabs with equal volume displacement (cone area x cone excursion) will have equal ability to produce low frequency sound.

[stevie]

The Marshall 4x12s from the late sixties didn't produce any true bottom.

[xgsjx]

A bit like comparing a Phil Jones Bass 21B to an 8x10 I suppose? The 21B has 21 5" drivers.
Or like how BFM's Titan subs can get great results from a single 12" driver that can beat a 2x15 sub?

[stevie]

You can't calculate radiating area accurately from the speaker diameter because the surround accounts for a larger proportion of the speaker diameter the smaller you go. PA 4x10s have around 15% more radiating area that 18s - not a huge difference - but in practice have much lower excursion capabilities. An 18" thus has the potential to move a lot more air than 4 x 10s. The fact that most people believe the opposite to be true is down to their respective efficiency in the midrange.

[xgsjx]

But then Bill's Titan 48 say's otherwise...



That's a 1x15 vs a 2x18.

[Mr. Foxen]

Horn loaded changes the deal, since the radiating area is the horn mouth, not the speaker cone.

[alexclaber]

[quote name='stevie' timestamp='1349440678' post='1826352']The Marshall 4x12s from the late sixties didn't produce any true bottom.
[/quote]

But like all sealed cabs, they can given appropriate EQ!

xgsjx, that's a 1W sensitivity plot - it's telling how how much air is being moved per watt but it isn't telling how anything about how many watts the cabs can handle cleanly and thus the max LF SPL available. With horn-loaded subs the volume displacement is effectively increased by the increased air pressure at the cone anyway - very different to bass cabs.

[alexclaber]

(Although there have been horn-loaded bass cabs, none of them exhibit loading down to low frequencies where volume displacement matters, so they're no better than sealed cabs down there...)

[stevie]

[quote name='xgsjx' timestamp='1349442584' post='1826395']
But then Bill's Titan 48 say's otherwise...



That's a 1x15 vs a 2x18.
[/quote]
That drawing doesn't say anything about 4x10s. All it says is how good Bill Fitzmaurice is with a felt pen.

[dincz]

[quote name='Wiggybass' timestamp='1349440152' post='1826339']My first thought would be that greater excursion would just push the same amount of air harder, not that it would move [i]more[/i] air...[/quote]

I guess the simple answer is that if you want to know how much air you're moving, you need to measure it in cubic inches rather than square inches. Displacement (i.e. volume of air) is the key, and that's a combination of cone area and excursion.

[Wiggybass]

[quote name='alexclaber' timestamp='1349442888' post='1826402']
But like all sealed cabs, they can given appropriate EQ!

xgsjx, that's a 1W sensitivity plot - it's telling how how much air is being moved per watt but it isn't telling how anything about how many watts the cabs can handle cleanly and thus the max LF SPL available. With horn-loaded subs the volume displacement is effectively increased by the increased air pressure at the cone anyway - very different to bass cabs.
[/quote] Is the T48 a horn-loaded cab, I'm not familiar with it? I know SB850s very well though, they are direct-radiating and were top of the tree in their day.

Edited October 5, 2012 by Wiggybass

[Wiggybass]

[quote name='stevie' timestamp='1349441382' post='1826375']
You can't calculate radiating area accurately from the speaker diameter because the surround accounts for a larger proportion of the speaker diameter the smaller you go. PA 4x10s have around 15% more radiating area that 18s - not a huge difference - but in practice have much lower excursion capabilities. An 18" thus has the potential to move a lot more air than 4 x 10s. The fact that most people believe the opposite to be true is down to their respective efficiency in the midrange.
[/quote] Yup, got it - good explanation, thanks.

[Wiggybass]

[quote name='alexclaber' timestamp='1349440319' post='1826344']
[url="http://barefacedbass.com/technical-information/Volume-displacement.htm"]http://barefacedbass...isplacement.htm[/url]

If you have a 2x12" cab and a 4x12" cab, both appropriately ported and both tuned to the same frequency, and the 2x12" has woofers with twice the Xmax of those woofers in the 4x12", then they'll both be able to produce the same amount of bottom (low frequency SPL). I don't know the numbers on the typical Marshall 4x12"s from the late '60s but I'd bet that our Big Baby 1x12" can produce as much true bottom, thanks to having easily three times the excursion and a ported rather than sealed cab.

As long as the difference in radiating area isn't enormous (like a single 8" vs an 8x10" - because you'd run into issues with acoustic coupling) then cabs with equal volume displacement (cone area x cone excursion) will have equal ability to produce low frequency sound.
[/quote] Alex, just for reference, from what frequency downwards do you consider 'true bottom' (oooerrr)? 160-ish?