Loudspeakers - how do we compare?

[Steve Browning]

An interesting comment from a very knowledgeable source, on a different thread, prompts this next question.

The was along the lines of 'a 250watt rms speaker with an xmax of 4mm is not going to be any louder than a 150watt rms speaker with the same xmax. This is logical as a 10" cone moving 4mm is going to shift the same amount of air as a different 10" cone moving the same distance.

Does that make the xmax a more important comparison that mere rms handling? Doubtless this will set off a long thread about characteristics etc but the previous question was a brilliant thread and the knowledge gained was significant. I am hoping the experts can indulge me once more.

The question on what happens (electronically) when I turn up the treble control can wait for now.

[Lfalex v1.1]

If that were all there was to it, then yes.

However, I'd guess that other variables (system sensitivity and whether or not the enclosure is ported (and if that targets excursion control over ultimate low-end output)) would also alter driver behaviour.

To wit; its no good having the available xmax to shift a lot of air if you end up needing so much power to achieve it that you fry the voice coils. Power handling is still of some importance.

Edited September 18, 2020 by Lfalex v1.1

[Steve Browning]

10 minutes ago, Lfalex v1.1 said:

If that were all there was to it, then yes.

However, I'd guess that other variables (system sensitivity and whether or not the enclosure is ported (and if that targets excursion control over ultimate low-end output)) would also alter driver behaviour.

To wit; its no good having the available xmax to shift a lot of air if you end up needing so much power to achieve it that you fry the voice coils. Power handling is still of some importance.

I don't doubt it but the previous topic gave rise to some fascinating discussion and I am hoping this will do the same and prove informative. The question is posed simplistically in order to generate the most information and allow a greater understanding by those of us troglodytes that don't really know this stuff. 

[Bill Fitzmaurice]

The main advantage to higher power handling when not accompanied with a commensurate increase in xmax is resistance to abuse. Xmax tends to be more important as far as maximum low frequency output is concerned. That said, there are a lot of other factors that are significant as well. When you use software modeling software to see exactly what a driver will do you don't compare two or three specifications, you compare sixteen or more. 

[Lfalex v1.1]

At a slight tangent to Bill's post, concentrating mainly on old school low Xmax drivers' performance explains many of the older bass cab form factors.

Low Xmax? reasonable power handling per driver? Stick 8 of them in a box and you have potentially huge power handling,  good sensitivity, and the ability to shift a lot of air due to the sheer driven area of the 8 cones, in spite of the low Xmax.

Modern enclosures are heading back the other way, with fewer drivers, but similar or better performance and smaller,  lighter enclosures.

[Bill Fitzmaurice]

Low xmax is why the Fridge was invented. It was loaded with guitar drivers that had around 1mm xmax. Today there are tens with 8mm xmax, so one of those could equal the low frequency output of a '69 SVT. The trade offs for very long xmax tend to be lower sensitivity and reduced midrange response, so all things considered a pair of modern tens with 4 to 5 mm xmax would be the better option. I use tens with 8mm xmax, but only in subwoofers.

Edited September 18, 2020 by Bill Fitzmaurice