Cardboard / Foamboard for 12v high-efficiency / low-cost sub?

[biggerbyfar]

I have an 8" dvc JL-Audio sub which worked nicely in a sealed box in my (now deceased) car.

I'm thinking of using it for a low-power, high-efficiency speaker setup running on a little 12v battery. I already have 4x full-range speakers (6" infinitys, also from said car) in a foamboard box, running on a tiny class-D amp (a 41hz.com "Amp6" 25w x 2) . That box runs great - pretty loud, and can run flat-out for over three hours from a small 12v 5Ah sealed lead-acid that as big as the palm of my hand. Now I wanted to evolve it a little, so I have a 4x50w Class-D "AMP9-Basic" also from 41hz, with a view to run the top box from two channels, and the bass end from the other two channels.

The 8" driver I have isn't very efficient, but it is imho a quality driver, and worked really really well in the car. I don't really want to spend-out on another driver. I'm wondering it a can bodge some kind of horn design from cardboard or, more likely, foamboard?. I was looking at the 'punisher' design, but it seems too big for this 8" driver, and my requirements. Does anyone have a design, or can I just factor the punisher design down to say 60% ? Will it be worthwhile at this size? It doesn't really have to be that robust, or look good, it's more of an experiment in getting the best PA sound that will run from a relatively tiny battery!

The most interesting post I've found is Cardboard Speakers! and in particular this picture http://www.diyaudio.com/forums/attac...amp=1098731075 although there's no further talk about the content of the pic.

Thanks!

[djk]

I think the foam-board will be 'invisible' at bass frequencies.

[biggerbyfar]

Does that happen when the sidewalls flutter with the sound rather than channel it? If the sidewalls are stiff, will that alone stop this happening?

[Ivo]

Hi.

I built a backloaded bass horn out of soft fiberboard. It goes under different names in different countries, we use it as floorboards to go under laminate or wood floors. It comes in green and brown here. It's fairly light and a bit brittle. I know it's also used as isolation material under roofing etc.

I used it because it was specified in the original plans. It worked really well, the bass came out strong and dynamic. It clearly wasn't invisible to the bass waves. It does have very low energy storage, so while the panels vibrate somewhat, they resonate less. I think some SPL was lost, but the sound was very clean. I built horns out of thick MDF as well, they had more issues. I bet a long cycle of revisions and evaluations of those designs could have smoothed that out, but the basic fiberboard horn was already really good.

I have heard good stories about people playing with cardboard speakers. Eventually they start building in wood, but the cardboard speakers often already work according to simulations etc. I don't see why you should start with cardboard.

I'm looking at Polyurethane boards, the foam is pressed between two sheets of paper. It looks less messy to work with than the fiberboard, but I'm wondering if it will work as well. It's a foam and does not consist of fibers, so I'm wondering if the energy storage/absorption will be the same/as good. If you decide to try out, please report!

Ivo

[djk]

The horn that is proposed is a bass horn.

You are not going to get much horn gain from cardboard or foam at low frequencties.

A Klipschorn is a good example.

Modern construction with sheetrock over 2' on center studs gives poor bass compared with plaster and lath over 16" on center studs, and a basement room has much better bass than the best above grade room.

2" of structural foam helped stiffen sone 200hz horns made from 5/16" fiberglass, but the same horn made from 3/4" plywood sounded better.

My experience is that nothing is as good as the computed simulation, and lightweight materials are not even close.