Bass outdoors?

[chico1st]

Hi there I am designing a loudspeaker for my bike and I am a little concerned about bass. If I am outside, will the bass travel very far or will it get lost since there is no containment like in a house.

when im riding I would like my nearest neighbour to be able to hear the music well say 10 ft radius.

I guess my question is in that situation, is there a point in pursueing bass? I can make more "efficient" speakers if i dont bother with bass.
If bass in this situation is pointless where should I draw the line? 300 Hz?


NOTE: I am using a generator on my wheel and I only make 3W.

[Frank Berry]

You're not going to have any significant bass with only 3 watts available from your generator.
I would concentrate on something that will provide good audio down to about 100Hz.
Even so, your power is very limited and most of the power will go into producing the lower frequencies. A cladd "D" amplifier would be a good choice since it's the most efficient.

[Frank Berry]

... and you'll probably need a battery to keep the amplifier running when your tires aren't going fast enough to produce the required voltage.

[sreten]

Hi,

Note that 3W average power output from the generator to charging a battery
to drive an amplifier, should be enough to drive a 15-30W amplifier with music.

rgds, sreten.

[Bigun]

You might find something of interest here (low power amplifier, supplemented with solar cell power supply): The Boominator - another stab at the ultimate party machine

[head_unit]

Originally Posted by chico1st

...will the bass travel very far or will it get lost since there is no containment like in a house...

The bass will actually travel farther than high frequencies. But I know what you mean by "lost" i.e. since it has so much room to expand it will not be concentrated like in a home or in a car which is correct. The walls of one corner of an infinitely large room would "squeeze" the bass into 1/8 of the directionality compared to out on your bike. If I'm recalling correctly, each time you cut the space in half, the pressure doubles, and the SPL goes up 6 dB. So that bicycle will lose 18 dB at -very- low frequencies compared to the room.

Another problem was pointed out in an Audio Engineering Society paper by Louis Fielder who was at Dolby at the time. It is well known that human hearing is insensitive to bass (Google "Fletcher Munson"). He then extended that to say, essentially, "if you can't generate enough SPL at a certain low frequency, then you won't hear it and are wasting your time."

So yeah, on your bike you might as well not bother with low bass.

This actually sounds like a good application for one of those DSP "bass extending" technologies. They operate from another oddity of hearing: you will "hear" the bass fundamental if all the overtones are correct. I think Audyssey ABX is one such system; I just can't remember the others. If you want to pursue that, a different thread is in order. A non-DSP application of that was some tiny KEF 4" woofer speakers which reproduced jazz bass amazingly well, presumably because although the lowest bass notes were not audible, everything else was "right" and the brain filled in the difference.

I'd make your amp with a simple ADJUSTABLE 1st order highpass filter to cut out the very low bass and concentrate the amp power where it is useful. Please note that according to research I did, a steeper filter will NOT improve available amp power although it can reduce excursion. That's because though the filter is less below cutoff, it filters more above cutoff compared to steeper filters.

Don't go nuts and make some 100 Hz ported box, or use a steeper highpass filter. Due to severe corruption in the time domain, you will mess up the overtones and completely lose that "hearing the missing fundamental" effect. Maybe a 60 Hz port in a design with a very shallow slope, but really I would avoid porting in this application.

Originally Posted by chico1st

NOTE: I am using a generator on my wheel and I only make 3W.

Other folks here know better, but for typical amp designs you would need to reduce that down a lot. Now, if you had a "topping off" type of high frequency switching power supply, that could help. Class D/T definitely at this low power, if you want to maximize SPL.

The above comment about 15-30 watts...not normally. It's true if you could feed 3W CONTINUOUS then you could get bigger peaks, BUT BUT BUT you need an unusual amp design like the monster Rockford, which has very large energy storage isolated from the power supply and just topped off by the power supply.

[GM]

Based on doing some motorcycle systems, limiting them to a telephone's ~300-3 kHz BW with a ~5.25-6" nominal driver for some directivity, so something like this and maybe high pass it: BOSS BRS52 5-1/4" Dual Cone Replacement Speaker | Parts-Express.com

GM

[sreten]

Originally Posted by head_unit

The above comment about 15-30 watts...not normally. It's true if you could feed 3W CONTINUOUS then you could get bigger peaks, BUT BUT BUT you need an unusual amp design like the monster Rockford, which has very large energy storage isolated from the power supply and just topped off by the power supply.

Hi,

No. The average power level of an amplifier when clipping with music is a lot less
than the same clipping level when tested with sine waves, who listens to them ?
(At any level music spends ~ 80% of the time below ~ 20% of the peak voltage.)

Nothing unusual about the amplifier is needed, the difficulty here is the
variability of the power supply, which suggests a switching supply that
is very tolerant of input voltage levels for the same output, driving a
battery, which is essential for for when you are not moving.
The essential design problem is the power supply, not the amplifier.

rgds, sreten.

[sreten]

Hi,

About the F&M curves, low bass is utterly pointless, but reasonable
levels at 10 feet or so IMO imply around 150Hz or so to me for efficiency,
and a fairly peaking vented alignment, ameliorated by the inevitable baffle
step for all small speaker enclosures.
FWIW the DSP apects for low bass are IMO pointless, the DSP can only
suggest a lower fundamental, might be useful in HT, but here the correct
harmonic series is already on the recording for the fundamental.

rgds, sreten.

[zottinger]

Originally Posted by sreten

Nothing unusual about the amplifier is needed, the difficulty here is the
variability of the power supply, which suggests a switching supply that
is very tolerant of input voltage levels for the same output, driving a
battery, which is essential for for when you are not moving.
The essential design problem is the power supply, not the amplifier.

rgds, sreten.

I'm assuming we're talking about bikes as in bicycle not motorcycle.
I totally agree about the power supply being the bigger problem than the amp since the output of a dynamo varies a lot.
However there are many tested diy designs for such power supplys, for example here:
News - Aktuelles zur Homepage des Rad-Forum-Ladegeräts: Forumslader (site is in german, the plans are at least partly in English
http://forumslader.de/fileadmin/user...dlicht2010.pdf