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Van PA system Build Advice

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Category: General
Forum Name: 12v Powered Systems
Forum Description: From Mini-rigs to ICE, all your low voltage audio needs here...
Printed Date: 10 August 2022 at 4:00am
Software Version: Web Wiz Forums 12.05 -

Topic: Van PA system Build Advice
Posted By: Motif
Subject: Van PA system Build Advice
Date Posted: 22 June 2020 at 11:39am
Hi guys, 

I’m planning on building a PA system to play parties out of the back of my van with. At the moment I have two qs500 mid tops as well as a qs250 (bought this very cheap before I found the qs500s). Now I had planned on buying two pioneer GM-D9701 amps to drive each of them.

I’ve now realised as they are rated to 500w rms at 4ohms would I be able to use just one and run the speakers in parallel? Is there a downside to this it seems like an obvious way to save money and space. 

Lastly I am considering whether the addiction of a sub is worth the extra effort, ideally I’d like something compact and relatively efficient (although from what I’ve read so far this may not be possible). I do however listen to lots of bass heavy music and love dubstep is there anything worthwhile that would compliment the setup in particular?

The whole system will run off a car battery ideally lithium if I can get the cash together. I know a generator would make this a lot easier however I am planning on building a bed and living space and in a perfect world would like to have the system in there at all times batteries makes this much easier.

Appreciate any tips or input


Edit: would consider using an inverter if that's a better option although from my understanding I would lose a lot of efficiency 

Posted By: Chris Grimshaw
Date Posted: 22 June 2020 at 1:41pm
This is important: if you're planning on having this stuff permanently installed while you're driving or whatever, seek the advice of your mechanic to make sure that everything is bolted down correctly, and will withstand a car crash.

I'm serious.

You don't want to hit something head-on, airbags deploy and for a split second, you're fine.
... and then the subwoofer flies into the back of your head. A skull won't ever win a fight with a high-velocity subwoofer, and it won't even be close.

Or the amplifier(s) or whatever. Make sure it's all physically secure. Big metal straps, bolted to the chassis, etc etc.

With that out the way, you'll be up against Hoffman's Iron Law for the bass: small, low, loud - pick any two. You can flex that a little if you throw some cash around. It's worth figuring out what sort of size box you can get away with - as an example, you could do a single-fold tapped horn which would provide a useful amount of output from a slim (but long) enclosure, laid down along the length of the van.


Quality sound from Sheffield

Posted By: Jo bg
Date Posted: 22 June 2020 at 2:12pm
excellent points about security!

isn't the pioneer 9701 strictly a subwoofer amp? 
i see you can finetune the lowpass up to 500hz, but you can't remove it entirely, or am I wrong?

i would use the 9704 2 channels in bridge per qs500, and ditch the 250

the qs 500 with 15 speakers should provide some bass allready, more so if you keep them close touching each other.

lots of bass means lower efficency, portable sysyem usually compromise on low extension, but it is your choice and some music needs lower bass than other.

Posted By: Motif
Date Posted: 22 June 2020 at 5:02pm
Cheers Chris I appreciate the thought I do have a plan to have them secured down through the ports in the bottom used for speaker poles and then strapped down. Cheers for the design suggestion I had considered something like that I may have to look around for plans as I believe designing it at the moment is beyond me. 

Thanks Jo for pointing that out not sure how I missed it and I was so close to ordering one of them. 

Still curious as to if I can run the speakers mono and in parallel to get more power out of them considering the amp is about to run speakers at 4 ohms? Or is there some important part of the equation I am missing. 

I guess I’m also interested in the potential benefits of running a sub or if I’m really better off just driving more power into the two mid tops.

Really appreciate the help so far cheers guys 

Posted By: Jo bg
Date Posted: 22 June 2020 at 5:55pm
if you run the four channel amp with 2 pairs bridged into 8 ohm loads you are running each channel at 4 ohms, it's ok.

consider some panels to fill the batteries, if you talk about hundreds watts oit means big batteries.

simply hook the speakers to any amplifier outside to get a feel if the bass is enough for you.

that size of speaker usually is meant to be used fullrange so may work.
if bass is not enough for you, welcome to the club.

Posted By: Jo bg
Date Posted: 22 June 2020 at 5:58pm
yes you could parallel the speakers and hang them to a mono amp.
only check that it is fullrange, not lowpassed for sub use.
an highpass from 30 to 50 hz, depending on how high you are willing to let some bass on the table, could double battery life.

Posted By: Jo bg
Date Posted: 22 June 2020 at 5:59pm
you could also use the 9704 with 2 channel bridged on a sub and 2 channel bridged on the tops in parallel.

Posted By: Motif
Date Posted: 23 June 2020 at 2:44pm
I think I may have to look at other amps as I'd like to be able to drive them to their full 500 watt RMS although I know it will be overkill for most situations!

Posted By: Jo bg
Date Posted: 23 June 2020 at 3:50pm
9704 bridged into two 8 ohm loads should give (with big full batteries) 520 W peak / 260 w rms into each speaker according to specs.
considering power compression and port compression 500watt rms would gain you max 2dB over 260. a very small difference, but battery will last half the time.

with portable system it's good to have big speakers like you have, not to squeeze every watt out of them, but because they have higher sensitivity (will be very loud with a smaller wattage, where smaller less efficent speakers would need more power to reach same level) so don't feel like you are wasting them.
I run a couple 15s on a portable system with 40watts total, they could take more than 2 kW peak, but the system gets very loud with few watts and battery lasts for days.

if 260 watt is not loud enough for you, 500 watts won't be either,
and I doubt that speaker would be very nice to listen to when pushed at it's limits.
and you will need a big battery bank, you could easily burn 10 A per hour, without counting lights, console, fan.
efficency is the name of the game, don't get lost in watts, you need at least a 5x increase to make a real difference… 10x increase to double the percieved volume.
Again, before spending money, can't you get hold of a 250 - 300 watt @8 ohm amplifier(that's very small in pa world), hook it to your speakers and get a feel of how loud it goes and how much bass you get.
a couple 15s with 500 watt behind them should move some air, and be quite heavy compared to many portable systems, so it could satisfy you.
if you expect Soundsystem kind of pressure, a sub is on order.

if you provide a pictures and dimensions of your van floor we can help more with sub options.

Posted By: Motif
Date Posted: 22 July 2020 at 8:28am
Hey Jo 

Can’t thank you enough for this I actually forgot about this thread as I got caught up at work recently. I really appreciate the depth of your reply and will definitely be going with that amp. I was actually just about to order a much more expensive one which went up to 500w rms but really I’ve pushed 150watts into a less efficient speaker and the volume already surprised me, definitely chasing numbers I didn't really have my head around. 

I think Il see how the system goes without a sub and consider building one down the line. 

Thanks again absolute life saver!

Posted By: Jo bg
Date Posted: 23 July 2020 at 9:15am
Good to hear. I hate to see people burn money.
That's not good for business sadlyLOL

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