Re: What is a "line out" output for?
Hadn't heard of Phil Jones Bass. The Double Four is very intriguing; a 9-pound bass amp that's actually useful on a gig. But, I'm very skeptical of the response pattern of a couple of 4-inch woofers.
The biggest determinant of volume from a rig is not actually wattage, it's the sensitivity of the speakers. Sensitivity provides a baseline for all that power; it's how loud the speakers are when fed 1W of power, as measured from 1 meter away. You can have a 5000W rig, but if your speakers only have 80dB sensitivity, this monster rig will have the same volume, all other things being equal, as a 50w rig with 100dB sensitivity speakers. Now, sensitivity itself is only measured from one reference frequency, usually 1kHz. So, manufacturers can game the system by designing speakers with a resonant peak of 1kHz and crappy response at every other frequency. So, another key indicator is the full frequency response curve; this will tell you how much sensitivity the speaker retains, or even gains, at frequencies other than the reference frequency.
Unfortunately, a lot of instrument speaker manufacturers, even expensive brand names (like PJB), don't make this information readily available. Sometimes I've even struggled to find sensitivity ratings and resonant peak information, much less a full frequency response graph. The Double Four's manual is no help here.
I don't know about the 4" drivers, but based on my experience with the 5" drivers, I'd give them the benefit of the doubt.
My first experience with Phil Jones was at a TalkBass get-together in Seattle 3-4 years ago. Someone brought a briefcase amp, which has two 5" speakers. I grabbed a bass and plugged it in, without really paying attention to the bass I was plugging in. (The point of the get-togethers is to meet other bass players, show off stuff you have that is less than common, and try other people's stuff.) When I started playing, something didn't sound right.
As it turned out, the bass was a Knuckle Quake, a 39.5" scale bass that was
tuned an octave low. I was immediately in love with the bass, but the most remarkable thing about that moment was that
the speakers didn't puke. Later, I and others plugged a normally tuned bass into it, and it sounded phenomenal! I had no idea speakers that small could not only produce bass, but produce it well.
The briefcase immediately went on my short list, and I finally got one a few weeks ago. But before that, about a year or so ago, I got a Phil Jones suitcase amp (4x5), and later got a 6B (6x5) neo cab. Now, I use a 250W micro head through the cab for gigs, and I get all the volume and clarity I could want from a rig that is compact and light and convenient. It wouldn't work if you had to take a bus to practice or a gig, but it will fit nicely into any car.
Back on topic... I wouldn't hesitate to use the line out on my amp to feed the main board, or feed another amp. But I'd prefer to use the pre-amp out, if there's a choice.
