help with a SIMPLE 36v7a battery powered class D portable sound system

[tcmtech]

Dang. You have me in a tough spot now. You are in the middle of my love for obnoxiously loud music and overall dislike for cyclists.

I guess I will have to think about this for a while.

 

[budget minded]

for what it's worth, i only intend to blast music at cycling events, parades, tailgate parties and downtown on club nights. if i'm just cruising, i'll keep it down to a sane level.

everything is back to square one now though anyways. the extra wide schwinn trailer i planned on buying is gone and no longer stocked. i really liked it not only because of the width, but because it's "roll bars" mounted inside the frame instead of on tabs that stick up so i could make a true flatbed instead of having to raise one an inch and a half or more to clear the tabs.

at this point, i'm thinking about revisiting my "ultimate plan" and do the whole thing in "hempglass" and maybe even double the number of subs to 8. it's either that, or probably going with smaller 10" cabs and a wonkier design with a raised bed. i'm thinking about custom fabbing more as i know of a place where i can use all kinds of powertools now.

 

[budget minded]

The Battery University shows the mAh graph of a "light duty" Panasonic 18650 Lithium ion cell rated at 3200mAh. Its capacity is more than its rating at C/5, is the same as its capacity at C/2 and is 0.7 times its rating at 2c.
a Panasonic "heavy duty" 18650 cell is shown with a rating of 1950mAh. Its capacity is almost the same as its rating at any discharge up to 10C.

yes, it's a very nice capacity battery for it's size, but is way to expensive at a minimum $6 each from what i could find. getting enough of them to run a high power system into the hundreds of dollars.

i'm back to square 1 now as the schwinn bike trailer with a 28 1/2"+ wide wheelbase is no longer available. most trailers i've seen, ignoring ones over $200 are generally less than 24" wide between wheels making them too narrow even for 10" boxes. because of that, i'm considering my original dream plan of custom fabbing with fiberglass which will be lighter than wood, and now that i'm entertaining the idea of going in that direction again, 8 subs at 4 per side is doable, and maybe even using deep cycle car batteries and a 12v system might be an option because of the weight savings going with fiberglass. i WISH you could get high capacity li-ion and li-poly cells for around $2 each

 

[audioguru]

Why do you need more than one sub-woofer? Most sound systems have a single mono sub-woofer because we cannot hear the originating direction of low frequencies below about 180Hz.

 

[budget minded]

because every time you double the amount of drivers, you get a free 3dB boost equivalent to doubling amplifier power and increasing efficiency. using 8 subs will give me a 9dB boost, or make the 30w amp i'll be starting with act like a 240w amp. that will make whatever battery juice i have go a lot further.

doubling the drivers will also make using cheaper woofers that don't dig as deep in the bass a better option. the 4x goldwood woofers i intended to use in the 1.23 cubic foot boxes are $70 each, but at $18-$20 each, i can get a lot more cheap woofers to compensate for less bass extension and even save money. when i originally planned the system, i could only carry 4 x 12s is 2 boxes, so i sought to squeeze every 20 Hz dB i could out of that space, but i can create much more air volume with fiberglass as well as house more woofers.

finally, a lot of subs gives the system more eye candy value. i don't think ANY bike system has used that many subs... YET.

if i ever cruise a tailgate party, i'll be "competing" with megawatt car & truck systems for dancers

i haven't been to one, but i do know a lot of locals have portable PAs they bring to parks so i wouldn't be surprised to see a system like that at a football game here

 

[audioguru]

Your adding is not correct. If you have two speakers, each producing 30W then the sound level is +3dB only if the amplifier output power is 60W, not 30W. One speaker with 60W will produce the same sound level. No fee lunch.
Two 8 ohm speakers in parallel (connected to one amplifier) produce a 4 ohm load that needs double the current from the amplifier and battery. Eight 8 ohm speakers connected to one amplifier produce a 1 ohm load that is almost a dead short and requires 8 times the current from the amplifier and battery. Most amplifiers will curl up and die when feeding a load that is 1 ohm.

Cheap woofers sound like "one note bass" due to their uncontrolled high resonant frequency. Cheap old "boom boxes" produced one note bass. No deep low frequencies.

Eye candy? Your bike is a bicycle, isn't it? There is a 3-wheel bike in my neighbourhood with hundreds of bright blue LEDs along its frame and it looks great. It makes no sounds.
When I was little my uncle gave me one of the first transistor radios ever made. It was eye candy to my friends. One friend bought a "better" cheap portable radio that had "12 Transistors" embossed on its cover. We looked inside mine and saw 6 transistors. Inside his cheap radio there were the same 6 transistors in the circuit then 6 more transistors connected together in a circle but not connected to the circuit.
My daughter bought a cheap calculator that said on it "dual power solar and battery". Its solar panel was a photo of a solar panel and it looked like a real one.

 

[schmitt trigger]

i'm guessing that a buck converter (didn't do my homework there) is a sort of potentiometer for voltage compensation judging by the context of that reply.

A buck converter is a voltage REGULATOR circuit, which converts from a higher to a lower voltage.
Contrary to linear regulators, it does its task with very high efficiency. The better converters offer efficiency better than 90%.

 

[schmitt trigger]

BM;
I would assume that the humongous "Fantasma" setup you show in the image, must be powered from an external gasoline generator. At least 3 Kw.

The best ones, like the ones made by Honda are surprisingly quiet.

 

[tcmtech]

I would assume that the humongous "Fantasma" setup you show in the image, must be powered from an external gasoline generator. At least 3 Kw.

Actually, it's powered by photoshop.

If it was real and a basic competition system it would be more like 40 - 50 KW minimum.

 

[bountyhunter]

I would think it would be more cost/size/weight effective to focus on building efficient speakers than try to over muscle it with a huge amp that will eat a lot of battery power. I have no idea what the design objectives of the system are, but you should be able to build a very loud system with 25 - 50W for mains and 50- 75W for the woofer. Unless the objective is to deafen people standing a hundred yards away.

 

[budget minded]

No, a potentiometer is a resistor that throws away power by producing heat. A buck converter converts a high voltage to a lower voltage with only a small loss of power.

actually, the answer is YES... a buck converter controls the "volume" of voltage. you have to understand i don't know any electronics terminology so to me, altering voltage levels is the same as altering wattage, if that's what a potentiometer even does. it's the lowering of an electrical attribute... close enough... for me anyways.

i'm getting confused here... you say 6 cells will last 15 minutes, but 7 cells will last almost 6 hours. that doesn't make ANY sense that one extra battery would increase capacity 20fold.

i don't get either how half a dozen 3v li-ons would only last 15 minutes with 2x efficient class D when 10 low efficiency D cells would power a low efficiency class A/B 50wpc boombox for at least a few hours.

back to the amps vs volts issue, you never answered my question. which wiring configuration for a SET number of batteries is preferable... highest voltage with less amps or highest amperage with less volts? or, it doesn't make a difference?

Actually, it's powered by photoshop.

oh no. such systems are very real and extremely popular in latin america, though i'm not sure EXACTLY what the right keyword is for them. fantasma seems to yield the most search results. the pic i posted was of a "typical" pickup truck folding system, but they range all the way up to stadium filling big rig trailer systems. if you follow enough links at youtube looking for bicycle sound systems, eventually you'll start finding videos of a ton of those "som" systems

I would think it would be more cost/size/weight effective to focus on building efficient speakers than try to over muscle it with a huge amp that will eat a lot of battery power.

exactly! that's what i'm trying my best to do, but there are limitations to what you can fit on a bicycle trailer unless you're willing to go all out and invest in a cu$tom frame.

i THINK i've found the original trailer i wanted to use again online... a schwinn trailblazer. (i think)

it has one of the widest wheelbases available, uses REAL wheels that can take higher pressures without blowing your tires off the rims, 20" wheels that would make the trailer more or less level with my recumbent's 20" rear wheel, and recessed "roll bar mounts" so you can build a flatbed directly on the frame which is lightweight aluminum. i'll probably end up paying $50 more than i want for it, but it does everything i need it to, but i'm still not ruling out DIY fiberglass depending on how expensive it is. parts express has some really nice looking 88dB $20 woofers with inverted dustcaps i'd like to use. whatever i do, i'm going to have to hang the subs off the back for better weight distribution. i tried to buy a $50 local trailer that the seller never got back to me on when i left a message the day he listed it only to find out he sold it the next day. used trailers are very hard to come by here.

if i can get one of those, i'll go back to my original "easy to build" design with 2 x 4 @ 12" subs plan with all of the electronics mounted on the underside of the trailer. if i'm going back to a 4 sub layout, then i'll probably be using the $70 each goldwoods that put the most dB out at 20Hz for those boxes. i MIGHT have to permanently mount the subs to the frame. i never heard back from the aluminum fabricator i tried to get a ballpark quote on to build a pair of side panels. i THINK i'd only have 1/2" width TOTAL (1/4" per side) to work with, so wood is out of the question.

 

[bountyhunter]

back to the amps vs volts issue, you never answered my question. which wiring configuration for a SET number of batteries is preferable... highest voltage with less amps or highest amperage with less volts? or, it doesn't make a difference?

Impossible to answer without knowing system objectives. I assume that this is for some kind of medium fidelity earth shaker for popular music. The amount of voltage you need for your power supplies is highly dependent on dynamic range of the music material. You can easily double or triple your average SPL level for the system (for a given set of supply rails) by compressing the dynamic range and for most popular music, you won't hear the difference. For "rap" music, you can do anything you want without making it sound worse than it already does.

Point is, in your design, voltage rails come at a high price of battery cost, size and weight so you should identify all options and optimize the rails for your speaker and system.

 

[audioguru]

i'm getting confused here... you say 6 cells will last 15 minutes, but 7 cells will last almost 6 hours. that doesn't make ANY sense that one extra battery would increase capacity 20fold.
I don't get either how half a dozen 3v li-ons would only last 15 minutes with 2x efficient class D when 10 low efficiency D cells would power a low efficiency class A/B 50wpc boombox for at least a few hours.

In post #19 you mentioned Panasonic AAA Li-Ion cells that are tiny and have a capacity of only about 0.8A. They average 3.7V during a discharge so six of them produce about 22.5V at 3.2A (60 Watts of audio plus 12 Watts of heat) for 1/4 hour at full blast!. Then I said, "Luckily the average power of loud music is about 1/10th the maximum so the battery will last for 100 minutes when playing loud music." A D cell has a capacity that is 4Ah or 8Ah (10 times as much as an AAA cell) because it is MUCH bigger and heavier than an AAA cell so of course it lasts longer. A battery with 4Ah or 5Ah 18650 Lithium cells will play loud music for almost 6 hours because they are also much larger than AAA cells.

back to the amps vs volts issue, you never answered my question. which wiring configuration for a SET number of batteries is preferable... highest voltage with less amps or highest amperage with less volts? or, it doesn't make a difference?

The datasheet for the TDA7492 amplifier IC says with a 25V supply it provides 30 watts to two 8 ohm speakers and heats with 12W for a total of 72W. Six 3.7V Lithium cells produce about 22.5V which is almost 25V then the amplifier maximum power is about 49W of audio and 11W of heat. You can reduce the voltage then the current and power will also be reduced.

such systems are very real and extremely popular in latin America

Here in Canada we cannot believe you have high power bicycle sound systems.

 

[tcmtech]

Here in Canada we cannot believe you have high power bicycle sound systems.

It's not just a Canadian disbelief. I'm American and I'm having a heck of a time reconciling my love of building obnoxiously loud sound systems on wheels with one being tethered to what I consider the lowliest of transportation methods only fit for children.

It's like finding out the Statue of Liberty was a gift from Nazi Germany or that Canadian Maple syrup actually comes from North Korea. I feel conflicted and cheated.

 

[bountyhunter]

Here in Canada we cannot believe you have high power bicycle sound systems.

Here in the Bay Area we have a monthly assault on road laws and common decency called "Critical Mass" where bicycle riders "underscore" their belief that they own the road and infuriate drivers by creating huge swarms of bikes that block roads, ride through red lights and stop signs, etc. The last time I had the misfortune to get caught in one of those messes, the biker "bringing up the rear" was some kind of trailer thing with a booming sound system.... did I mention her two year old kid was riding in the thing as well?

https://en.wikipedia.org/wiki/Critical_Mass_(cycling)

 

[budget minded]

A typical D Cell can provide 12,000 mAhours.

hmmm... i didn't realize they had that much more capacity over AAA cells. and to think, radio shack cheats the daylights out of people stuffing AAA nimhs into D cell cases! i figured that larger batteries have to have higher capacity simply because of their mass. that's why in my early research into li-ion cells, i concentrated on the larger size, but even some of those are only rated at 800 mah.

still, if i could easily get 5 hours run time out of 8 x allegedly 2.5 mah nimhs (now energizers are only rated at 1.8 mah tops) pushing 10wpc, then getting a similar run time out of 2 x 11v 7a batteries just pushing 35wpc should be a piece of cake and then some with 3x+ the amp hour rating at twice the voltage. for now at least until i can afford to upgrade the system. just toying with the numbers in my head, adding a 3rd 35w channel for bass should still be a reasonable load on a pair of cheap lead acid batteries. there's a lot more capacity in those than 8 nimhs.

well as far as i'm concerned, MOTORISTS are the lowest form of life on the planet which, as traitors to mother earth, they are destroying and too stupid or selfish to care. a lot of the world's problems can be traced to social climbers. i don't climb, but i'll challenge a GROUP of pushy punks to dance. when they figure out that you are not impressed by their poop flinging show of force and have marked their "leader", they generally reveal what sniveling cowards they are. that's the mindset i'm fighting, and haters can't stand it that bike systems are in fact MUCH cooler than car systems. i defy ANY car system owner to claim they've had a hot 42DDD MILF run up to them and start humping their leg. never gonna happen.

now... where was i? oh yeah... back to the volts vs amps issue, i'll simplify it as much as possible. say, i wanted to use one of sure's 100wpc modules rated 15-36v and have half a dozen 11v 7a batteries. which is preferable for wiring them up series parallel, 22v 21a or 33v 14a? same number of batteries, one way favors voltage, one favors amp hours. either it doesn't make a difference, or one method is clearly better for run times, at least

as to critical mass, i support them in their fight against the internal combustion devil, but myself, i ride on the sidewalk to stay as far away from the unholy enemy as possible.

I assume that this is for some kind of medium fidelity earth shaker for popular music.

then you assume wrong. i'm placing sound quality as a priority of SPL. that's why i absolutely REFUSE to muddy my bass in the slightest with ports and will stick to sealed subs regardless of what i lose in bottom octave extension, BUT i'd also like to squeeze as many dB as i can out of the system too of course. serious dancing requires higher SPLs for sure, but even a "15 wpc 85dB" system is enough to make ladies wanna dance. i'm aiming higher, and will be going with a light show too when funds allow.

i also hate "popular music". it has no flavor, or in the case of rap music (i love REAL hip-hop but never liked rap, even BEFORE gangsta and the current crop of attitude spitting fidiots... more social climbing pests) no soul. i will play unpopular playful beats and mostly instrumentals, so pop music isn't an accurate description of what i'm doing which is pretty much going against the flow in every way possible from my perspective. (lousy music, cars & sloppy ported boom)

kinda like THIS...

but without the rap

more like THIS...

so many stoopid DJs spin attitudal music aimed at males without a clue to the lighter fare women prefer. ask most women what they like, and "easy listening" or some variation therein tops the list more than anything. i agree. music should be fun and not knuckle dragging celebrations by aholes that need to be beaten down to a pulp for their insolence. being in touch with my dancing feminine side is an advantage small thingy compensating coal stackers and butt buddy thugs can never match on the dance floor. i'm going with my strengths building this system.

for the record... anyone that claims to be OG & hip-hop is a lying IDIOT! REAL hip-hop is about getting OUT of gangs, dancing instead of fighting and there are rules of respect eg. you can NEVER touch an opponent in battle. call yourself OG, but i'm PRE-G

 

[audioguru]

i wanted to use one of sure's 100wpc modules rated 15-36v and have half a dozen 11v 7a batteries. Which is preferable for wiring them up series parallel, 22v 21a or 33v 14a? Same number of batteries, one way favors voltage, one favors amp hours. either it doesn't make a difference, or one method is clearly better for run times, at least

I have never seen an old lead-acid 12V/7Ah motorcycle battery. They are about 13.8V when fully charged so 3 in series make 41.4V which is higher than the 36V maximum allowed for the Sure amplifier. ST Micro make the IC and say that 44V is the maximum so 3 batteries in series should be fine. The 3 batteries will average 36V. If you use less than 36V then the maximum output power will be less, with a 24V power supply the output power with some noticeable clipping is about 33W per channel into 8 ohms.

With a 36V power supply the amplifier produces 40W per channel into 8 ohms just before clipping or 60W per channel with some noticeable clipping. 80W per channel is with horrible distortion. Your kind of music has an average output power that is about 20% of the maximum continuous power. Then with 60W per channel as the maximum, 12W per channel is the average which is 24W for both channels. The amplifier is 90% efficient (plus idle current plus the fan) so maybe its total average power input is 36W. Then its average current is 36W/36V= 1A. The 7Ah batteries can supply 0.7A for 10 hours or 1A for maybe 5 hours. Use two sets of 3 batteries with the 36V sets in parallel for the amplifier to play all day or all night.

RAP is not music. Instead it is an African person reading a book out loud in a nasal monotone with a strong beat in the background.

 

[tcmtech]

well as far as i'm concerned, MOTORISTS are the lowest form of life on the planet which, as traitors to mother earth, they are destroying and too stupid or selfish to care. a lot of the world's problems can be traced to social climbers. i don't climb, but i'll challenge a GROUP of pushy punks to dance. when they figure out that you are not impressed by their poop flinging show of force and have marked their "leader", they generally reveal what sniveling cowards they are. that's the mindset i'm fighting, and haters can't stand it that bike systems are in fact MUCH cooler than car systems. i defy ANY car system owner to claim they've had a hot 42DDD MILF run up to them and start humping their leg. never gonna happen.

Well have you considered that us vehicle owners are how you get all of your stuff you need to live delivered to you through the stores you shop at? Unless you're living 100% on your own garden and handcrafted everything you own with your bare hands from nature's raw materials someone's vehicle plays a very critical role in your existence.

And to be honest, as a vehicle owner who used to have the over the top sound system in high school through college (twice) plus used to work as a pro DJ I got a lot more than one good leg hump for my work.

So yea when you can haul upwards of 14,000 pounds of payload and pass the 1000 watts at the speakers power level on your bicycle and can get tail from it anytime you want all while making over $60K a year doing it come brag to me. Until then stay on the sidewalk where you belong.

And as far as the environment goes, well, How many trees have you planted? I just knocked out ~150 over the last two days (~350 to go in the next week) and have done close to 10,000 in my lifetime.

If you want to laugh at me go ahead. My ego can take it. I did the vehicles loud music and pretty girls thing until it got old and I grew up.

 

[bountyhunter]

RAP is not music.

Amen. It may be relevant socio economic commentary on the life and times of America, but it definitely IS NOT music/

Funny. Trying to describe music to today's generation is like trying to describe the color azure to a blind man. I remember pulling my car off the road so I could listen to the radio the first time I heard Carlos santana rip away on the lead in to Black magic Woman. I still remember the first time I heard Eric Clapton tearing it up on his Fender Stratocaster when he played White Room and Sunshine of Your Love. And Led Zepplin created a whole new sound and Hendrix made music so powerful that it left people's brains frozen. The Door's had songs so hauntingly beautiful they transcended time. And of course there was the Who and the Stones and many others. I can only assume all the good music has been done because all we get now is pre packaged garbage.

And this generation thinks some moron screaming profanity into a microphone is music.

 

[bountyhunter]

well as far as i'm concerned, MOTORISTS are the lowest form of life on the planet which, as traitors to mother earth, they are destroying and too stupid or selfish to care.

OK. Well just remember: average bicycle's mass about 15 pounds, average car about 4000 pounds.

as to critical mass, i support them in their fight against the internal combustion devil, but myself, i ride on the sidewalk to stay as far away from the unholy enemy as possible.

It might interest you to know that in most places riding a bicycle on the sidewalk is illegal..... not to mention dangerous. Those annoying people keep trying to use the SIDEWALK as a place to walk.

i'm placing sound quality as a priority of SPL. that's why i absolutely REFUSE to muddy my bass in the slightest with ports and will stick to sealed subs regardless of what i lose in bottom octave extension, BUT i'd also like to squeeze as many dB as i can out of the system too of course.

Well, with acoustic suspension design (no port) and an enclosure of thast size you'll probably have a lower -3dB corner of about 60 Hz or more so your "sub woofer" won't be subbing much.

hmmm... i didn't realize they had that much more capacity over AAA cells. and to think, radio shack cheats the daylights out of people stuffing AAA nimhs into D cell cases!

Wow. I believe you'll find the smaller cells molded into larger D cases are "sub C" which are many times larger than AAA. The Radio Shack ones I had were rated 1600 mA-Hr. And Harbor Freight sells similar cells so it's not just a radio Shack conspiracy.