Bass outdoors?

chico1st

Member
2010-09-16 1:02 pm
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.
 
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.
 
...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.

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.
 
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.
 
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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.
 
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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/use...nsd/Download/Allgemein/12V-Standlicht2010.pdf
 

chico1st

Member
2010-09-16 1:02 pm
yes i mean pedal bike.

I was previously planning to just run everything through a 1-2 F cap, but an actual battery pack might be a better option. There are lots of lighting projects based off generators for bikes.

GM you posted this speaker as a suggestion that goes on motorcycles but it doesnt seem to be weather resistant at all. how do you deal with that you your builds?

HeadUnit, i agree with the 1st order filter but dont think i will use any complex DSP for now... simplicity... Maybe later. Yes I am planning to make a class d filter chip (they are all BGA from what ive seen :( )
Interesting info in the bass 'loss'


Srten: I hadnt thought about actually making a 15-30 W amp based on my 3 W input, what level do you think is more reasonable (15 or 30 W... or in between) would I need a large battery for this?

I was planning to either use 2 of these 3" drivers or 1 of these 6.5" drivers (WR65 on page 7). These speakers are water proof and that seems like a good idea since weather varies and i always ride my bike. The 3" speakers are made for use with a subwoofer so I imagine the bass is poor but I dont know how low it would go. Efficiency is big for me and the salesman said these are both ~88 dB

To summarize: I dont plan to port this (weather concerns) and I should limit my range to ~150Hz?
 
GM you posted this speaker as a suggestion that goes on motorcycles but it doesnt seem to be weather resistant at all. how do you deal with that you your builds?

To summarize: I dont plan to port this (weather concerns) and I should limit my range to ~150Hz?

It's a car audio driver made from weather resistant materials and of course needs a rear box, though it needs some venting to keep condensation under control. The occasional squirt of WD-40 doesn't hurt them either. For sure, submersible marine spec drivers will be best, but tend to be relatively expensive, inefficient.

The lower the LF gain BW for a given SPL, the more power required, so the actual point should be chosen by how much power you can easily generate with good speech intelligibility at low distortion. Where I live, the ambient noise level is high enough that a ~phone BW limited '70s era transistor FM radio w/headset must be turned up higher than I prefer, so it's going to need to be much louder with speakers out in the open and some distance away.

GM
 
Sreten: I hadnt thought about actually making a 15-30 W amp based on my 3 W input, what level do you think is more reasonable (15 or 30 W... or in between) would I need a large battery for this?

I was planning to either use 2 of these 3" drivers or 1 of these 6.5" drivers (WR65 on page 7). These speakers are water proof and that seems like a good idea since weather varies and i always ride my bike. The 3" speakers are made for use with a subwoofer so I imagine the bass is poor but I dont know how low it would go. Efficiency is big for me and the salesman said these are both ~88 dB

To summarize: I dont plan to port this (weather concerns) and I should limit my range to ~150Hz?

Hi,

Battery size depends on how long you want it to be able to run with
no charging input. TBH those speakers do seem just like car units,
which are fairly weather proof due to condensation etc in car doors.
I'd get cheap car speakers, if they conk out, get some more. I'd
expect the 6.5" drivers to be more efficient, 3" too small to me.
Generally the bigger it is, the more efficient it is (+ bigger box).

If going coaxials experiment with a resistor on the tweeter if the treble
sounds too hot. I do not know what powers Class D amplifiers come in
but assuming stereo anything > 10W per channel into 4ohm should
be fine. Larger powers will allow shorter term draining of the battery.
For mono you can double the above.
There is a BOSS 6.5" listed on PE.

Forget the large car type capacitor, switched mode charging
supply to a battery will be far more useful in the long run.

rgds, sreten.
 
Another thing
Assuming you are talking about a hub dynamo Your 3W output are really conservative. There are quite many people running 3 3W LEDs off a hub dynamo. If you check the graphs in the pdf I linked you get [email protected]@20km/h and that is the charging current at the battery.
Furthermore the circuit in the pdf uses shottky diodes as rectifiers, these aren't too efficient. There is a more efficient solution using 2 IRF7319 MOSFETS.
Some links about all that:
Get up to 12.8w from the shimano / SON dynamo hub | Bike Commuters
Very simple/cheap dynamo led light - CandlePowerForums
Dynamo LED Light Systems for Bicycles (electronic circuits)
daniel