Technical question about speakers

[bodan]

I am researching for a speaker cab project. I'm trying to find the best 15" to 18" speakers for bass guitar within a 100 to 300 dollar range.

Basically, I am looking for speakers that have the broadest frequency range, highest Xmax, and highest sensitivity.

My question is this: Why would a given bass speaker have a frequency response range of 37kHz - 4.7kHz, yet have a recommended crossover of 500Hz? (these are tech specs from a 18 Sound High Output Low frequency speaker)

[billfitzmaurice]

Originally Posted by bodan

Why would a given bass speaker have a frequency response range of 37kHz - 4.7kHz, yet have a recommended crossover of 500Hz? (these are tech specs from a 18 Sound High Output Low frequency speaker)

Dispersion. What counts is off-axis response, not on-axis, which often runs two or three octaves higher than off.

[silky smoove]

Originally Posted by bodan

My question is this: Why would a given bass speaker have a frequency response range of 37kHz - 4.7kHz, yet have a recommended crossover of 500Hz? (these are tech specs from a 18 Sound High Output Low frequency speaker)

Saying 37hz - 4.7khz doesn't tell the whole story. You'd need to look at an SPL chart for the given speaker in a specific sized enclosure with a specific port tuning to see just how much content is produced at a given frequency. I'm guessing that the speaker in question has a drastic rolloff from 500hz to 4.7khz, or possibly some really nasty peaks right above 500hz that they're trying to get you to avoid.

There isn't really any single speaker that will produce that wide of a frequency range by itself. If there is it's likely to cost an arm and a leg. 2 and 3 way designs exist for a reason.

[bodan]

Same subject, different question.

I am looking at the specs for a Legend-cb15. I am noticing that a small sealed enclosure at 250w has really stable cone displacement for frequencies below 50hz (as does a large vented enclosure at 100w). However, when 275w is applied to the small enclosure, cone displacement goes through the roof below 50hz (as does pretty much any vented cab above 100w).

How exactly do these relationships correlate when looking at amplifier wattage? I was under the impression that you want a good bit of headroom in your wattage so you don't get damaging spikes. How would you achieve headroom if cone excursion at lower frequencies happens long before you reach the wattage rating of the speaker?

[billfitzmaurice]

Originally Posted by bodan

How would you achieve headroom if cone excursion at lower frequencies happens long before you reach the wattage rating of the speaker?

Use a driver with longer excursion capability.

[bodan]

I suppose that's one option, but I thought 4.8 Xmax was decent for most bass drivers....?

[rpsands]

High pass your input signal at 30-70hz depending on your application. I've experimented with a shallow 70hz high pass (12db), a steep 50hz, and a steep 30hz, and the steep 50hz is my preference for bass guitar (I play a 5 string).

24db/oct @ 50hz ought to do it.

In Winisd you can easily apply a 24db/octave low end shelving @ 50hz and see what it does to your displacement figures.

[bodan]

WinISD (beta) doesn't have this particular driver to choose. Any other recommended programs?

[billfitzmaurice]

Originally Posted by bodan

I thought 4.8 Xmax was decent for most bass drivers....?

It is. Now you know why the thermal power rating of drivers means so little.