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12v bike trailer system (help needed)

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Goegon View Drop Down
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    Posted: 27 July 2019 at 4:17pm
Hello,

I am planning on building a small 12 v soundsystem that can run a night on a car battery. It will be mounted on a trailer on a bicycle. (maybe I'll need a tandem because i think total weight will be quite a lot) It will be my first rig i build and after a week of researching I'm still quite in the dark. Bear in mind i still don't fully understand everything i need to know.

So far i was thinking of using a Tham18, a SMT212 and 2 tweeters (Beyma CP22), i guess i wil need a 3 way crossover to divide the 3 boxes (if someone has recomendations regarding this, happy to hear). And as far as i understand I'll need an amp for my sub and then like a 2 channel amp, 1 for the 12" drivers and 1 for the tweeters? Again if someone knows affordable D class amps that would fit here, i'd love to know.

All of the drivers i chose (the cabinet's recommended drivers basically) have a sensitivity above 90 Db so that should be okay right?
Yet if i put the RMS of just the subwoofer in a calculator it says i can run it 0.42 hours with a car battery. :s my guess is i just don't know enough about wattage use Tongue

What else would i need to make this system function? I'm talking bout all the little stuff no one talks about but are just as essential.

I hope someone here can help me out a bit  ^^

Thanks!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 27 July 2019 at 7:17pm
First I doubt whether even a Tham 18 will keep up with a 2x12 mid top. Go for a single 12 + HF. Then to save weight just use 1 amp, 1 side for bass and the other for mid/top. Use a passive crossover in the mid/top.

Having saved the expense and weight of an amp and 1/2 the 2x12, Spend the saving on neo drivers (that will save your legs).

To save even more weight you might consider a Cubo 15 instead of the Tham 18. This will play slightly higher allowing you to use a decent 10" in the mid/top cab. Likewise the 10" will play a little higher so you can use a smaller/lighter/cheaper HF.


Edited by markie - 27 July 2019 at 7:19pm
If it's got wheels or tits it's gonna cost a fortune
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Post Options Post Options   Thanks (1) Thanks(1)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 27 July 2019 at 8:27pm
You won’t be driving the sub with anywhere near it’s RMS (or more likely, AES) rating for any considerable length of time. 1/8th of that is more likely, up to 1/4 if you really push it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 27 July 2019 at 9:56pm
Originally posted by markie markie wrote:

First I doubt whether even a Tham 18 will keep up with a 2x12 mid top. Go for a single 12 + HF. Then to save weight just use 1 amp, 1 side for bass and the other for mid/top. Use a passive crossover in the mid/top.

Having saved the expense and weight of an amp and 1/2 the 2x12, Spend the saving on neo drivers (that will save your legs).

To save even more weight you might consider a Cubo 15 instead of the Tham 18. This will play slightly higher allowing you to use a decent 10" in the mid/top cab. Likewise the 10" will play a little higher so you can use a smaller/lighter/cheaper HF.


Thanks a lot for the recomendations, makes way more sense indeed! :)


Originally posted by toastyghost toastyghost wrote:

You won’t be driving the sub with anywhere near it’s RMS (or more likely, AES) rating for any considerable length of time. 1/8th of that is more likely, up to 1/4 if you really push it.


Okay, after another google search i realize i misinterpreted the term RMS, thanks for clearing that up. :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote imageoven Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 1:15am
You don't want to use a car starter battery, they are designed for lots of current quickly, whereas you need fairly low current for a long time. Read up about leisure batteries (last much longer). Then read up about the various Lithium batteries (much lighter but more expensive and with other more complex issues)
Keep pushing on, things are gonna get better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SamV Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 2:05am
You want class D amps, I'd use a minidsp + chip amps at around 36v. More expensive but maximises efficiency. But then just getting a car amp and a 120ah battery will sort you for the night anyways at loud enough volumes. Start with a leisure battery, think about lithium later, there's a bit of a learning curve to doing it safely. But if you do really want to go that way you can get decent units built for electric bikes for under a grand.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 12:35pm
First off, great idea :) Bike trailer rigs rock!

You're pretty brave to be considering a THAM18 bin - those things are really big! Have you thought about how it will ride on the trailer?

I would suggest downsizing your plans a bit. Most bike rigs have a 12 or 15 inch bass bin and 8 or 10 inch mid-tops. You've got to consider getting the thing through standard 600mm doorways, and not having it so tall that it tips over when you try to go round a corner! Difficult with an 18" bin. It's less of a problem for it to be extra long, than to be tall or wide. 

The Carryfreedom "Bamboo" trailer design is pretty good, and easy to make. You can change the size to suit what you're putting on it. Or, consider a monocoque design - ie the wheels and towing arm are attached directly to the bass bin, which forms the structure of the trailer. 

You will want to be able to have the mid-tops "down" for transport and "up" for playing out. You can do this with top-hat fittings and two different lengths of 38mm pole, or you could have the mid-top on a hinged or telescopic pole that can move up and down, and lock in place.

Pioneer and Alpine make good Class D amplifiers. Or the other option is to buy amplifier and power supply modules from eBay, or a supplier like Wondom (aka Sure Electronics). This can work out a little cheaper but you then have to make a box for them (or mount them inside your speakers....) and wire them up, provide a volume control, crossover etc....

Don't get carried away with your power requirements. Sure you will probably end up using a bass driver that can handle 1000 watts. But 150 watts of real power is actually plenty to get such a driver pumping and - assuming an efficient design like a tapped horn - can easily get you to SPL's of over 110dB at 1 metre. You absolutely don't need a 1000 watt amp (and a REAL 1000 watt 12v amp will be huge, expensive and difficult to find)

If you have about 300 watts of real power from your amp, and it is about 70% efficient (a generous figure) you will be pulling an average of about 4.5 amps from your battery, so a 75Ah leisure battery should last about 16 hours (based on a figure of 12.5% average vs peak power) But you generally don't want to run your battery all the way flat, so expect about 8 hours of full-beans continuous use - more if you play at lower volume.

If you get an amp without such functions built-in, you'll need some kind of processor or crossover too - a lot of people use the MiniDSP. They are pretty cool because they power up from 5-24v, they come prebuilt and ready to work and you can change your system configuration quickly, but they have some disadvantages - they cost quite a bit, there's no limiters or compressors in them, and the output level is disappointingly low, so in a lot of cases you need a set of gain boosters between the DSP and the amps. Also consider the FreeDSP and Wondom JAB boards (all use the same Analog Devices ADAU1701 chip.)

I've had good success using analogue line-level crossover modules, eg there is a good board from XKitz that powers from a single +12v supply and can be easily configured to the frequencies you want. Or there is a guy called KMTech who does nice 3 and 4 way boards but you do need to arrange a +15/0/-15v supply for them. Again there's small modules you can buy on eBay that do just that. The analogue boards can't be adjusted on the fly of course, but offer superior input/output level capability and lower cost than the DSP solution.

Good luck with it bro! Would love to see some pics when she's ready ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 1:15pm
Thanks a bunch for your input studio45.

Yeah i realised quite soon after i wrote this that 18" is quite a bit too large ^^ Now i'm thinking of building a tham15, and then just buying a decent full range 8" or 10" speaker since it looks like there's models out there that are quite decent for a price you couldn't build your own with. Was thinking of something like a turbosound iP82.  maybe add a tweeter or two.
Edit: Or instead of a turbosound i will go with one medium quality 10" woofer and 2 tweeters in a self build box, looks like more fun to me.

Prices of somewhat sturdy bike trailers are way to high in my eyes so i think i will weld one myself at a friend's workshop, the bamboo design is interesting but i don't know if i would trust it completely with expensive gear on it.  A monocoque design could prove useful too.

I'll have to do some digging to find an amp that suits me. Since I'm very new to all of this I'm gonna look for one that has build in crossovers, volume control etc. The less I do the less i can do wrong LOL
Edit: I'm going to try to figure out how to build an amp and crossover that fits this project, will be less expensive, better optimised and i will learn more like this.

As for battery i currently have my eyes on this VRLA gel accu: https://www.accuserviceholland.nl/gel-12-100-vrla-lpcg-accu-12-volt-100-ah.html
As far as i understand you're allowed to drain it to 20% which means almost twice the party ^^

Right now the project is still in the mental phase, but after august I'm gonna start building it. Looking forward to it a lot, I'll definetly keep you updated with pics when the time is there :D


Edited by Goegon - 28 July 2019 at 4:04pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 2:00pm
I should add that you obviously don't build the trailer out of *bamboo*! I used 20x20mm square steel tube and a MIG welder. It is very strong. Old school/office desks are a good source of such tubes ;)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 28 July 2019 at 4:05pm
Okay that sounds way less wonky already xD
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goegon Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 1:28am
Oof, so after a lot of searching i think i settled on driver choice...
One Tham15 loaded with Kappa PRO LFA-2 15"
and one top cabinet loaded with Beyma 8BX 8" and Beyma CP25.
for the tops I'll use a miniDSP 2x4 and let them crossover at ±5,5Khz
can i use the same miniDSP for the sub aswell?
Edit: or should i be looking at 4 ohm drivers instead?

Apart from the drivers i think the chain will look something like this:
110 Ah Gel battery -> circuit breaker -> car head unit -> miniDSP -> amplifiers -> speakers

does all that look somewhat okay? Please share your thoughts.
As for amplifiers I'm still too confused about them to settle on some...

Here are the links to the speakers in case you want to see the specs:
http://www.bax-shop.bel/15-inch-luidsprekers/eminence-kappa-pro-15-lfa-2-luidspreker-15-inch - https://www.bax-shop.be/nl/15-inch-luidsprekers/eminence-kappa-pro-15-lfa-2-luidspreker-15-inch
http://www.bax-shop.bel/8-inch-luidsprekers/beyma-8bx-professionele-coaxiale-luidspreker - https://www.bax-shop.be/nl/8-inch-luidsprekers/beyma-8bx-professionele-coaxiale-luidspreker
https://www.bax-shop.bel/tweeters/beyma-cp25-professionele-compressie-tweeter - https://www.bax-shop.be/nl/tweeters/beyma-cp25-professionele-compressie-tweeter


Edited by Goegon - 29 July 2019 at 8:24am
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Post Options Post Options   Thanks (1) Thanks(1)   Quote slaz Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2019 at 11:45am
Originally posted by Goegon Goegon wrote:

Oof, so after a lot of searching i think i settled on driver choice...
One Tham15 loaded with Kappa PRO LFA-2 15"
and one top cabinet loaded with Beyma 8BX 8" and Beyma CP25.
for the tops I'll use a miniDSP 2x4 and let them crossover at ±5,5Khz
can i use the same miniDSP for the sub aswell?
Edit: or should i be looking at 4 ohm drivers instead?

Apart from the drivers i think the chain will look something like this:
110 Ah Gel battery -> circuit breaker -> car head unit -> miniDSP -> amplifiers -> speakers

does all that look somewhat okay? Please share your thoughts.
As for amplifiers I'm still too confused about them to settle on some...

Here are the links to the speakers in case you want to see the specs:


I'd agree with studio45's comments on just about everything .... here's a few of mine.

keep it simple as possible for a first-time setup.

Use a 12 or 15 bass box yes .... (i'd go for a good 12 myself) .... THAM 12 would be great.
But use e.g. 12mm ply and use some clever bracing to keep the weight down. Buy an off-the-shelf plastic mid-top (mebbe a EV ZX1 or similar) and use its built-in passive Xover.
Get a 4ch classD car amplifier (Pioneer, Alpine etc.) but use it as 4ch bridged into 2ch .... this gets you a good impedance match for 8 ohm drivers.
You can then use the ampifiers built-in Xover to cross between bass and mid-top. Ideally find an amp with variable HPF to suppress very low bass e..g below 50Hz (can make a big difference to battery life without sacrificing much subjective bass extension). It won't be as capable as a mini-DSP wrt Xover slopes etc. but _can_ still work quite well. DSP could be added later.

Construction-wise .... make sure to keep the CoG (centre-of-gravity) as low as possible.
Consider mounting some parts on the bike itself (e.g. amplifier, other bits of electronics).
Use a phone/tablet as music source ... a car-head unit will likely be too current-hungry.

When you've done principle contruction of the bulky stuff, take some time in quiet streets somwhere to practice handling the trailer - braking, emergency stops, evasive action in traffic, dodging pot-holes etc.
Don't underestimate the awkwardness of that amount of weight behind a bike .... it can take some getting used to.

REMEMBER....POLITICIANS AND DIAPERS SHOULD BE CHANGED OFTEN AND FOR THE SAME REASON
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