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Old 28th October 2002, 05:52 AM   #1
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Location: Meyerton, South Africa
Question Newbie building speaker box. Help.

Hi

First I would like to say I live in South Africa and money is tight. So I can`t buy $100 subs.

With that said I can go on. I have a Eurotec 12" sub. On its box it says:

Max input power = 1000W
Transient response = 25-2000hz
Nominal impendance = Dual 4 ohm
Max continuous music power = 500W
Fs = 30hz
Qts = 0.8066
Qes = 0.9173
Qms = 6.6801
Vas = 82L
Efficieney (1w/1m) 89dB

I have entered the numbers in LSPcad but it say it needs more parameters.

What do I do now? Can I work out the other numbers it wants with the qts/qes/qms?

Thanks
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Old 28th October 2002, 04:27 PM   #2
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Hey, good to see some more South African people on board. I can gladly give help you offline (just click on my handle and use the e-mail facility).

That woofer is at best 250W and with such a high Qts is not likely to make a good candidate for either a sealed box or a vented box. What is your budget, what is its intended use (ie size of room, music, HT) and how big may it be (directly related to efficiency/extension). Usually it is better to consider the needed performance and then try and look for a useful implementation.

Anyone want to pitch in with some good links on speaker modelling?
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Old 28th October 2002, 05:20 PM   #3
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Location: Palo Alto, CA
I've just brached into speaker building and started using "speaker workshop". Its free (for now....) and I've found it to be great all around. I've seen complaints thats its too difficult to figure out and use, but considering all that it does and the price (or lack there of) Its hard to beat. It took me the better part of a weekend to figure it all out, it could take more or less depending on you base level of knowledge. The site's forum is very responsive to folk's questions and problems. The only caveat is that there are a few sound cards that won't work, but since the software's free, there's no risk to trying.

For about $10-30 US you can build a jig to attach to a PC soundcard and measure the full T/S parmeters and impedence for a driver, then model a sealed or proted box response. This is a good place to start and may be all you need it to do.

For another ~30 to 50 US you can add (build) a mike and preamp.
This allows freq. response measurements, crossover modelling and optimization. All within one package.

The link is:

www.speakerworkshop.com

Once there,
search Wallins jig for the jig instructions
and look over the Speaker project example for aa walkthrough

Best of luck,

Pete Kunz
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Old 28th October 2002, 05:59 PM   #4
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Quote:
Originally posted by mgoedeke
Hey, good to see some more South African people on board. I can gladly give help you offline (just click on my handle and use the e-mail facility).

That woofer is at best 250W and with such a high Qts is not likely to make a good candidate for either a sealed box or a vented box. What is your budget, what is its intended use (ie size of room, music, HT) and how big may it be (directly related to efficiency/extension). Usually it is better to consider the needed performance and then try and look for a useful implementation.

Anyone want to pitch in with some good links on speaker modelling?
Hi, it is good to see South Africans here.

By 250W do you mean rms? And if that is so must I use two 125w rms amps because it is dual voice coil?

I am looking to spend not more than R200 ($15) on the basic box excluding the covering etc. I want to use it in a 6x6.5m room and sometimes in a 4x9m room. I want to use it for music and movies. The box can be about 60x60x60cm or in old speak 2x2x2 foot.

Edit: I have put the sub in a cardboard box just to see how it plays. It pushes a lot of air but there are not bass. A real wooden box would give it good bass right?

pjkunz: I will look into the link you gave me.
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Old 28th October 2002, 06:22 PM   #5
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Default Ultra-Frugalphile

I use Speaker Workshop as well and it is great, but not for subwoofer design (excpt for measuring speakers for which it is invaluable). Over here in SA sourcing drivers is a big problem and I believe in Meyerton that might be even more of a problem. A friend of mine (originally from Meyerton, his dad own a gym there) built a 220l 12 Pioneer bandpass sub which kicks some serious butt (with all the usual caveats about bandpass boxes). The problem with almost all cheap car woofers in SA is that they usually have a Qts of around 0.7 1 which rules them out for hi-fi subwoofers. I take it you have already bought this sub, so a sealed box might be your ticket. It will not take 25 watts cleanly, never mind 125 x 2.

Perhaps you can give us your current equipment list and then one could see what is a good place to get you started. Nothing wrong with being cheap (au contraire, frugalphilia lives) and it is amazing how far some gainclones and Passive Line Level crossovers can take you.

R200 is really pushing it, even more so if that is to include a box (usually you can budget about that amount for the wood and even that is really cheap). Usually a 6,5 driver goes for such money (and that isnt even the imported stuff). If you say that size isnt that much of a problem (that is a BIG box), you can always build a big Bass-Reflex cabinet with a cheap 15 (found something nice for just shy of R400), which would land you in trouble with the neighbours and parents. Perhaps you would do better with a 6,5 bass mid and 1 tweeter floor standers which could give you 40 Hz and those rooms arent too big.

Private mail me and I will gladly guide you through such a project or even just give advice. Perhaps you should state the size room, music, others, but usually a sub or a simple 2-way makes for a good first project.
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Old 28th October 2002, 06:51 PM   #6
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Default Re: Newbie building speaker box. Help.

Quote:
Originally posted by intelceleronman
Fs = 30hz
Qts = 0.8066
Vas = 82L
Those are the only numbers you really need to do basic box-size calculations.

But given the high Q of your woofer, the only suitable boxes are infinite baffles (ie mount it in the wall and use the room on the other side as the enclosure) or an aperiodic enclosure. Given you have specified max size and would like to move it from place-to-place we will have to just consider the aperiodic box. Fortuneatly the (crude) design algorithm is dead simple (but the results aren't).

Build as bid a box as you can get away with. Mount the driver on one side. Then as far away from it as you can, drill a number of holes that are about the same area as the woofers pistin area. Now you need to resistively damp these "ports". Foam blocks tightly mounted against the holes from the inside, or fiberglass insulation sandwiched between two screens are effective. You tune the box by changing the resistance in the port. Ideally you can tune by minimizing the impedance peak, but if you can't measure impedance you have to do it by ear.

The idea is to try to get the Q of the system as close as you can to the free-air Q, which will still be higher than ideal since it started out so high.

dave
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Old 28th October 2002, 07:36 PM   #7
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Default Re: Ultra-Frugalphile

Quote:
Originally posted by mgoedeke
I use Speaker Workshop as well and it is great, but not for subwoofer design (excpt for measuring speakers for which it is invaluable). Over here in SA sourcing drivers is a big problem and I believe in Meyerton that might be even more of a problem. A friend of mine (originally from Meyerton, his dad own a gym there) built a 220l 12 Pioneer bandpass sub which kicks some serious butt (with all the usual caveats about bandpass boxes). The problem with almost all cheap car woofers in SA is that they usually have a Qts of around 0.7 1 which rules them out for hi-fi subwoofers. I take it you have already bought this sub, so a sealed box might be your ticket. It will not take 25 watts cleanly, never mind 125 x 2.

Perhaps you can give us your current equipment list and then one could see what is a good place to get you started. Nothing wrong with being cheap (au contraire, frugalphilia lives) and it is amazing how far some gainclones and Passive Line Level crossovers can take you.

R200 is really pushing it, even more so if that is to include a box (usually you can budget about that amount for the wood and even that is really cheap). Usually a 6,5 driver goes for such money (and that isnt even the imported stuff). If you say that size isnt that much of a problem (that is a BIG box), you can always build a big Bass-Reflex cabinet with a cheap 15 (found something nice for just shy of R400), which would land you in trouble with the neighbours and parents. Perhaps you would do better with a 6,5 bass mid and 1 tweeter floor standers which could give you 40 Hz and those rooms arent too big.

Private mail me and I will gladly guide you through such a project or even just give advice. Perhaps you should state the size room, music, others, but usually a sub or a simple 2-way makes for a good first project.
Hi

I have bought the sub. It was R300. I am willing to spend R200 on the box only. I am not that cheap. I am willing to make a bigger box than what I have talked about. I can go up to 24"x30"x40" old speak or 60cmX75cmX100cm. Will that give it better deep bass?

I will also email you about this.

Thanks

intelceleronman
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Old 28th October 2002, 07:56 PM   #8
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Unfortunately using that sub in a bigger box will bring you a lower Q and lower the point where your roll off starts, but things quickly get out of hand for very little gain. A solution is the aperiodic box, but this is a lot of effort and not likely to give you much value. It is really a pity that these subwoofer drivers have such a high Qts, because otherwise one could port them (more output, less distortion, lower bass) and/or put them into a better sized box. Usually one looks at woofers with a Qts between 0.25 and 0.45 (arbitrary values, but close enough). Get yourself WinISD Pro (the alpha) from linearteam and try whether you cannot arrive at the other parameters with this program. That box you are now suggesting is HUGE and it would be a real pity to put such a 12 into a box which would be big even by 18 standards and require a lot of effort. Wood is getting expensive here (6 x 9 MDF 18mm is sheet is >R350 thesedays) and the box will easily go for more than R200. I will continue this offline.
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Old 28th October 2002, 08:01 PM   #9
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Default Re: Re: Ultra-Frugalphile

Quote:
Originally posted by intelceleronman
I can go up to 24"x30"x40" old speak or 60cmX75cmX100cm. Will that give it better deep bass?
The smaller the box, the higher the Q and the F3 point are pushed. Only an infinite size box will give you a Q = the Q of the speaker, but a much smaller box can approach it. So the bigger the box, the lower you will get. The idea behind aperiodic is that it damps the resonance, and makes the box appear somewhat bigger than it is.

If you model the speaker as a sealed box you will get an idea of where diminishing returns on the box size start to occur.

dave
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Old 28th October 2002, 08:37 PM   #10
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Default Ok, not that bad, but none the less

OK, modelling turns out not to paint as dark a picture is I initially thought. A 75l sealed box should be in order with an F3 of 33 Hz (not bad) but a 2 dB hump around 55 Hz. The low bass will not be excessive and car-audio people equate this to a tight bass. If you want to do this, you, Id say a 75l sealed box would be in order (could make a small corner table). To put things into perspective your average 8 bass-mid driver is capable of similar results in a smaller (ported) enclosure. Its not what you got but what you do with it.

Efficiency comes in at about 85 dB at 2.83V which is rather low for such a large box. Seeing that youve already bought this thing, Id say go for it. You could always try and sell it and go for the 15 idea (which Im planning to do soon, just two of them)


Good night.
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