Design challenge - backpack bass amp

[DaveK]

I have a bit of a design challenge and could really use help from all the DIYers here. I need a bass guitar amp that is backpackable by a teenage girl. My daughter plays electric bass in her high school marching band and they have a couple parades coming up. She needs something battery powered that she can carry while marching and playing bass.

My first thought is something like the Phil Jones Briefcase bass amp, but lighter and maybe with speakers on both sides. How does the briefcase get decent bass sound out of 5" speakers and what BFM design might be similar? SLA Pro?

[old_bassist]

With respect, can you consider something on a four-wheeled wagon instead of in a backpack?

The bassist has to move a lot of air to keep up with a crash and bang unit

[Benj Ross]

A jack 10 lite would come in 8 lbs lighter than the pj. Breifcase not sure what your options are for battery powered amps though

Benj

[Gregory East]

How robust is she?

With strong legs, a back to back pair of J10, with my busking power pack of deer hunting battery, lepai 12v amp, sansamp pedal for preamp. For keeping up with brass an upgrade on the amp would be the go.

Extra jack plugs in the bottom, battery etc low for balance, nice solid bass hanging from amp pack for counterweight. She better start training and have good arch support.

[DaveK]

Her band director was not happy with the wagon idea so we're trying to come up with a backpack amp instead.

I think the Jack 10 is a little bulky for a backpack so I'm hoping for something slimmer. If possible, I'd also like the speakers to fire out the sides of the amp to cover both sides of the parade route.

If we can figure out a BFM-based cab design, I think I can build it a lot lighter than the PJ briefcase by using the BFM Lite approach (thin ply and lots of bracing).

[Gregory East]

1 up, one down, facing opposite directions, best I can come up with. Line array types give away the horn loading and add more weight in drivers.

Since when did they have electric bass in a matching band anyway? I thought Sousaphone was the American bass horn for walkabout?

[Bill Fitzmaurice]

I thought Sousaphone was the American bass horn for walkabout?

+1. We have a member who did a cart, using a DR250 and T48 as I recall, powered by an QSC amp and a pair of 12v batteries. It was successfully used with a marching band on the football field. As for electric bass and a backpack, Hoffman's Iron Law combined with no boundary loading renders the notion ill advised. It would work for a sidewalk performer, but it won't reach sousaphone levels.

[Doug Hart]

Hoffman's Iron Law combined with no boundary loading renders the notion ill advised. It would work for a sidewalk performer, but it won't reach sousaphone levels.

+1
Ain't gonna happen. Cart it your only option if you want it to be heard.
Trust me, I've been down this road (I'm an assistant HS band director)

[LouC]

One of my builds went to a high school bass player. They wanted to do the same thing. I think they tried a wireless pickup on the bass guitar, and put the amp & boxes on the sideline. Don't know how successful that was. They finally decided to leave the bass player on the sideline.

[jswingchun]

I think they tried a wireless pickup on the bass guitar, and put the amp & boxes on the sideline.

That's was my first thought when I read this. A Line 6 G50 Digital Wireless has a line of site range of 200 feet, the G90 does 300 feet.

[mattaudio]

I like the wireless idea. So this is for parades? You'd have to enlist someone to walk along the side of the band with some sort of rolling amp. I'm thinking you could build some sort of frame around some Titans to boundary load them to the ground like this: http://billfitzmaurice.com/images/Placement/Free.jpg

[DaveK]

Thanks for all the input so far. Sousaphone/tuba is the standard low end voice for a marching band, but she plays string bass and does not want to learn tuba. Her band director, like most, is a master at working with what he has.

For field show season we did use wireless to a stationary PA on the sidelines, but that will not work for parades.

Bill, how does the PJ Briefcase get decent bass from 5" speakers? Is it boundary loading, a really big rear chamber relative to the speaker size, psychoacoustic tricks, or something else?

Doug, what bass options did you try? Is it possible to sacrifice low-end extension to get enough SPL in the low-midrange to match a trombone or baritone?

[wounded horse]

Thanks for all the input so far. Sousaphone/tuba is the standard low end voice for a marching band, but she plays string bass and does not want to learn tuba. Her band director, like most, is a master at working with what he has.

For field show season we did use wireless to a stationary PA on the sidelines, but that will not work for parades.

Bill, how does the PJ Briefcase get decent bass from 5" speakers? Is it boundary loading, a really big rear chamber relative to the speaker size, psychoacoustic tricks, or something else?

Doug, what bass options did you try? Is it possible to sacrifice low-end extension to get enough SPL in the low-midrange to match a trombone or baritone?

I wouldn't think it does get decent bass from a 5" speaker and out in the open you ain't got a chance. All that brass makes a lot of noise. Take that sousaphone, it has a nice long horn path and needs someone with serious lungpower to get heard.

[Studarl]

The way I see it there are 2 ways to get high sensitivity either using many drivers ala line array or using a high efficiency cab.

Our old bassist used to have a 2x15 ampeg cab with one 15" facing out the back of the cab and one out the front, presumably wired push pull which to be fair did always have a huge amount of grunt!

If you had say 4x8" drivers 2 facing the rear, 2 facing the front the same layout could be achieved as the briefcase in your picture.

However it would likely be a heavy option, especially if they are 100W units!

I think a lot of the phil jones stuff like the EA stuff is transmission line.

Stu

[Bill Fitzmaurice]

Bill, how does the PJ Briefcase get decent bass from 5" speakers?

It doesn't. It has adequate extension and output for an indoor coffee house gig, but it can hardly compete with a brass band outdoors.