Guitar speaker xmax

[RudeBoy]

Saturday's amusement.

I'm building a 1x12 closed back extension cabinet. The internal volume with the driver in it will be around 1.5 cu ft. I started playing with WinISD to get an idea of the characteristics I can expect of this cabinet when loaded with various drivers for which I have TS parameters. Eminence provides TS parameters for their guitar speaker line so I started with those. I also looked at a JBL E120.

The Eminence drivers are all modeled in a 1.5 cu ft closed cab.
The E120 is modeled in a 1 cu ft ported cab, tuned to 80 Hz.

• Red Fang, rated 50W, pink trace
• Cannabis Rex, rated 50W, yellow trace
• Black Mountain, rated 30W, orange trace
• Man O War, rated 120W, white trace
• Private Jack, rated 50W, purple trace
• Black Powder, rated 75W, blue trace
• JBL E120, rated 150W, green trace

The system response of all the Eminence drivers is pretty close, but look at the maximum power curves. That's the frequency and power at which the cone excursion is equal to xmax. If the cone excursion is exceeds xmax then farting out commences. All of the Eminence drivers exceed the xmax dimension at powers well below the driver's thermal rating and at frequencies well into the guitar range. Based on this data I would go with either the Private Jack or the JBL.

Still, I must be missing something because people do use these drivers, though I have seen reviews and reports of "farting out" on certain guitar forums when discussing some of these.

-- bradley

[Steve Conner]

When it comes to guitar speakers, just don't think too hard about the Thiele-Small parameters.

Celestion refuse to print any, and I've always suspected that the real reason is that many Celestions have a voice coil that's neither overhung nor underhung, but the same size as the magnetic gap. This leads to a speaker that works just fine, but its Xmax is zero and hence the other Thiele-Small parameters can't be measured accurately.

Moral of the story: Xmax is the maximum linear displacement, but the speaker may have a good deal of usable non-linear displacement on top of that before you hear any objectionable "farting".

In any case, guitar speakers are tuned for lots of midrange output at the expense of bass, and a guitar amp's output has most of its energy in the midrange and relatively little bass, so the Eminence speakers are probably fine. Unless you're one of those guys with lots of tattoos and a 7-string.

I built a ported cabinet for an EVM12L a while back: Index of /speaker

(Once I was happy with the performance, I went back and made a better looking one with the same internal volume.)

[black_labb]

keep in mind that the nonlinearity of the speakers also play a role in the sound low down. this is just the speaker cabinets effect on things, and guitar speakers are far from being linear. the jbl will probably be more linear than the rest (the speaker itself, not the speaker & cab combo)

guitar speakers only have short xmax, but this is part of the sound. when the amp is turned up you start to creep over the xmax and get some unlinear response (distortion). this is often desired in guitar amps. if you want a very clean sound at loud volumes then pay attention to the xmax graph, otherwise its not too much to worry about.