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bandpass subs for outdoor 12v class-D system

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nsh View Drop Down
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    Posted: 01 August 2016 at 10:42am
Hi!

Bought a pair of Hz International's SB600 dual-voicecoil 6th order bandpass subwoofers http://www.hzsoundsystems.com/legacy-products/sb600-dual-sub/ mainly on a whim because i'm stupid and impulsive and terrible with money, but I have a hunch they might make for good outdoor subs with a bit of tinkering.

They have a pretty reasonable sensitivity [103dB] and max-SPL [125dB], though I'm not sure in what space [pi pi/2 pi/4] they are modelled at.

I have a few questions on how to make the most of them outdoors.

1. Can I rely on the internal channel crossovers of a class-D car amp like the Bassface 4.1 or Pioneer GM-D8604
 or is it worth adding an active crossover / minidsp?

2. Has anyone used these and can advise on crossover points? I have a few options for coverage, including having a kick box to meet the mid-tops, but that adds amplifier and crossover complexity so if they can extend to match with some 12" midtop cabs without losing much of the bandpass gain advantage, that'd be sweet.

3. I presume that there's no benefit to driving the voice coils separately, and they should be run parallel/mono? Again is there much benefit to actively blending the L/R bass signals before amplification?

4. Coupling? Vents together side by side?

Any other thoughts or suggestions welcomed.

Thanks,
-nsh

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nsh View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nsh Quote  Post ReplyReply Direct Link To This Post Posted: 01 August 2016 at 1:33pm
Actually, I think they're 4th order BPs rathe than 6th. Would have to have a third port somewhere to be 6th order.
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Hemisphere View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 04 August 2016 at 7:28pm
There's no reason why a built-in crossover wouldn't work. Might not provide the best quality and tweaking crossover frequency from 35 to 3,500Hz with a screwdriver is never going to be very accurate. If you bought an amp with a crossover anyway you could always buy a separate one and switch the built in one off if it wasn't good enough.

Orientation of the vents will almost certainly make absolutely no difference (and will absolutely certainly make almost no difference).  Close together and as close to the ground as possible is a safe bet but if you find it advantageous to align them in any other way for some reason I wouldn't worry about it.

The spec sheet looks incredibly optimistic for the size of box. 30-250Hz and 103dB/watt in a cabinet not much bigger than a 15" full range cabinet? I know there is wizardry to be had with bandpass alignments but I can't see how it would stretch that far.


Extending the crossover frequency up high won't diminish the efficiency of the box in any way but it may well sound awful and certainly will be far from flat towards the upper end of the specified response. If the box really does have anything like 103dB/watt (which can really only be a 2pi measurement/calculation, no way is it 4pi and only a seriously dodgy company would quote their sensitivity in 1pi or less without some indication of this), then it's bound to have at least one large peak and drop off significantly outside of that peak.

I guess you'd want to sum the L+R bass frequencies to mono to minimise risks of cancellation or muddiness in recordings where the left and right channel signals are different. Similarly if you just run the left or right bass channel you'll be missing loads of content. Putting stereo bass signals into a single speaker is definitely a bad idea.

It looks like a really interesting box though and for everything I've said I'm sure it will be a great option for 12v outdoor bass. Lightweight plastic enclosure will probably have it's limits for sound quality on bass, but it does make it portable. Everything is a compromise with mobile 12v anyway.

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