Tiny 12 litre subwoofer making 15Hz and 600ccm? - Page 2 - diyAudio
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Old 2nd January 2004, 03:29 AM   #11
usekgb is offline usekgb  United States
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That driver looks almast exactly the same as the Eminence LAB12 driver. I have four LAB12's in my shop, and I plan on putting two of them in a 1 ft^3 box and doing a linkwitz transform to it. This box will be driven by one side of a crown MA2400. I should be able to get an f3 of around 15-18 Hz. Any comments?

Cheers,
Zach
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Old 2nd January 2004, 05:59 AM   #12
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Quote:
I have four LAB12's in my shop, and I plan on putting two of them in a 1 ft^3 box and doing a linkwitz transform to it. This box will be driven by one side of a crown MA2400. I should be able to get an f3 of around 15-18 Hz. Any comments?
if you enjoy
1) high distortion
2) low output
3) inefficient operation

Then build it

Model it in winisd pro from www.linearteam.dk
get the winisd patch,which will make it 0.7,use LT filter,and see excursion for yourself

It isnt my cup of tea


I just treid a shiva in 20litres. runs out of excursion with 32watts with an LT

Cheers!
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Old 2nd January 2004, 03:52 PM   #13
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@mikee
.."running out of excursion" sounds like you tried it with a vented box, which is the default setting. They typically run that way if driven below their tuning frequency.

It tried my 11 Dynaudio 15W-75 in a closed 12l box. I recommend this URPS principle for closed cabinets only.
The program states results that match really good with my measurements.

Fres: 159Hz , my measurement 158Hz
Qtc: 1,144, my measurement 1,12
max. power for linear operation at 30 Hz: 702W
My measurement 780W (Well, excursion during operation is not easy to measure.....)

Thanks for the link to the "linear people"!
The program seems to give quite reasonable results.


@usekgb:
...doing a linkwitz transform to it.....
If you are not using the system in the area of the resonance frequency,
then the filter type (linkwitz or butteworth or tschebycheff or else) is
not so important, because at a certain margin from the roll off (at least one octave) they all give the same steepness.
But if run the system also in the area of the resonance frequency, then the filter
characteristic must match to your box. I do not think that two Eminence LAB 12
in a 11l box will give a linkwitz characteristic.....

2 speakers with an Vas of 125l ==> together 250l...
....pressing them into a 1 ft^3 (around 11l ??) closed cabinet..
Damn that's excessive!
You may end up in a resonance frequency somewhere around 110Hz.
But with speakers which would naturally have 22Hz!
You plan 2 speakers with 8Ohms, parallel.. ending up at 4Ohms?
One chanel of the crown, 800W?
Probably underpowered for what such a consruction would need.
For 13mm excursion 30Hz you would probably needmore than 10kW.
(Excursion is a square root function of power)
On the other side I have doubts that this speaker with large diaphragma,
but small voice coil whould not show heavy bending of the diaphragma itself.
And the voice coils would probably also not be able to handle the really required
power for full diaphragma excursion. In this ultra small cabins the required power at low frequencies
is very high, while excursion is relatively small.....so the self ventilation is poor compared to
the applied power!
I am not convinced that this design would be succesful.
Also please be aware if your filter does not really compensate the low frequency defeat of the closed cabinet, then it will sound like a telephone...


The Dynaudio ESOTECs have a diameter of 145mm (less than 6") and a voice coil of 75mm (about 3").....
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Old 2nd January 2004, 03:58 PM   #14
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Quote:
.."running out of excursion" sounds like you tried it with a vented box, which is the default setting
no,sealed box.

It just seems like 'what is the worst way to use a woofer?'
= LT!

it just doesnt agree with my ideas

Cheers

my horn at its RMS rating and 45hz....
Attached Images
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Old 2nd January 2004, 04:53 PM   #15
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Hi Zach!

Uhhps I messed up when calculating 1ft^3 into litres.....
1ft^3 is around 25l...30, not 11l.....
OK, that is still very small, but some
chance that you will get it working.
But you will probably operate the system also at its resonance frequency. This requires for a good matching of the filter characteristics......
...difficult project!

Do you have some more details about
your filters for equalizing/compensating the low frequency attenuation of the box?

Cheers!
Markus
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Old 2nd January 2004, 05:16 PM   #16
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Hi Mikee!
..yes, this are different worlds!

In fact I like horns. They are very efficient. But horns for low frequencies are large.
The horn area must grow very slowly for this......

Also vented designs are more efficient than a closed cabinet. But you can only run them above their tuning frequency. Below that they will defeat by 4th or 6th order (sealed only 2nd order).
If you design vented cabinates for low frequencies you will also end up in a large design....

Well, since several years power amplifiers for low frequencies are no issue any more.
1kW...2kw... what ever you want!
But limited space in my appartment is an issue.....
That's the main reason for such URPS designs.

The price for small size is efficiency and distorsion. I agree.
But according my experience bass is suffering more from poor resonances of your room than from distorsion. And in this regard this design is very fortunate! You can adjust the damping and you have a small box which can be easily positioned an acustically reasonable place.
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Old 3rd January 2004, 12:30 AM   #17
usekgb is offline usekgb  United States
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Quote:
Originally posted by ChocoHolic
Hi Zach!

Uhhps I messed up when calculating 1ft^3 into litres.....
1ft^3 is around 25l...30, not 11l.....
OK, that is still very small, but some
chance that you will get it working.
But you will probably operate the system also at its resonance frequency. This requires for a good matching of the filter characteristics......
...difficult project!

Do you have some more details about
your filters for equalizing/compensating the low frequency attenuation of the box?

Cheers!
Markus
Basically, I'm just playing around with ideas I haven't tried before. I originally planned on doing this with one driver, but I don't think I will be able to get enough SPL out of just one. Thus.........Why not go overboard and put in two? Anyway, I haven't run all of the number yet, but here is what I have so far: According to WinISD, two Eminence LAB12's in a 1 ft^3 (28.3 liter) box gives me a 6 db down point of 44 HZ and a Qtc of 1.19. Now, I put this in to the Linkwitz tables, and if I want a f(p) of 15 Hz, I get a DC gain of 18.69. I understand that this is somewhat high, but still doable. Now, if I don't need this to go quite so low, I can get higher SPL's out of this system. If I go with an f(p) of 20 Hz, I get a DC gain of 13.7. This requires 4 time less power to get to the same SPL's, and only loses a few Hz on the bottom.

Now, using a larger box, I can really get some low end out of this system. Using a 2 ft^3 (56.6 liter) box, I get a 6db down point of 35 Hz and a Qtc of 0.88. If I put these numbers in to Linkwitz's tables, I get an f(p) of 15 Hz and a DC gain of 14.72. This is very doable without using an unreasonabley large enclosure.

As for horns, they are very efficient, but not my cup of tea. I think they are very useful when you need to project low frequencies over long distances, such as outdoor concerts, but they just don't seem to blossom without a large listening room.

I also use vented cabinets all the time. Unfortunately, a cabinet with two LAB12's requires about 7.5 ft^3! This is quite a bit bigger than I am able to put in my apartment.

The main reason I was thinking of the dual LAB12 in a sealed box was just to try something different and have some fun while doing it. As it is, 2 LAB12's in 3.5 ft^3 gives an f3 of about 40 Hz, which could easily be equalized to extend lower if desired. In fact, I am installing such a system this weekend at a local night club using 4 LAB12's, two per side. I am eager to see how it sounds.

Thanks for the input everybody. Please let me know if my reasoning is off somewhere, or if I am missing something obvious.

Cheers,
Zach
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Old 4th January 2004, 10:02 PM   #18
SlaitH is offline SlaitH  Sweden
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Interresting very interresting!!

Have you guys considered what to use for equalisation??

I'm building the Thor subwoofer on the Linkwitzlab site. I made a PCB for the EQ circuit. Not operational yet but i tried it with my multimeter and a sinus generator and I got the exact response that's on the site.
Now it remains to be seen if it applies when I put it to the test in my living room.

I will drive it with a bridged amp of the famous PA 300 from the elektor magazine, 600Watts that should do wouldn't you think??
I'm not at home at the moment so I can't do the modeling in any of the programs above.

Hell if it doesn't work out i'll just make the box smaller and put in a passive woofer and i'm set

but we'll just have to wait and see.

But I like your thoughts, thinking of the fact that companys like B&O, Sunfire and some other use the very same ideas.

So keep it up
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Old 5th January 2004, 12:05 AM   #19
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Quote:
600Watts that should do wouldn't you think??
if your EQing 20db....

to have the same SPL you need 20db more amplification available.

1
2
4
8
16
32
64
128 21db
256
512

you can input a few watts before using your 600watts rms and losing all your headroom..


Quote:
[horns]but they just don't seem to blossom without a large listening room.
Mine does.


Click the image to open in full size.

Cheers
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Old 5th January 2004, 12:31 AM   #20
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Default Linkwitz transform

Quote:
...doing a linkwitz transform to it.....
If you are not using the system in the area of the resonance frequency,
then the filter type (linkwitz or butteworth or tschebycheff or else) is
not so important, because at a certain margin from the roll off (at least one octave) they all give the same steepness.
The "Linkwitz transform" is a pole shifter and Q adjuster, not a standard highpass/lowpass filter.

http://linkwitzlab.com/filters.htm#9
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