two 8"s in a box...

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Hi all

I'm (in the process of) making a subwoofer using two of these 8" drivers.

I decided to set up a new thread here because of the actual specs of these drivers... and the price (£16)

T/S parameters are...

Fs - 33Hz
Qts - 0.3528
Qes - 0.3964
Qms - 3.21
Vas - 56.8L
Sd - 0.0216
Re - 11.6
Vd - 64.93cm^3
Xmax - 3mm
Le - 0.59mH
8 ohm/coil
60W rms/coil
100W rms peak, with no damage
88.94 dB/W/m

I put these into winISD before buying the driver, got some very nice results...

Link to buy some is...

http://cpc.farnell.com/LS00415/audio-video-tv/product.us0?sku=unbranded-55-1455

See what you think

Will post more on the sub I'm making later on...
 
Yeah - they're the same ones...

I really like them... there's decent low-end frequency response, and the higher end rolls off nicely

I'm planning on using 2 of them is a 42L cube, sealed with Linkwitz, to go to -3dB @28Hz

It says 3mm Xmax, but even after that there is only a little distortion.

I dare say there are better drivers out there, but not for that price.
 
14.11dB

loses 1db per Hz down after that.

Sounds good in some bigger boxes - had to put bottles of water in to reduce int. volume to 21L/driver.

pics of the spreadsheet attatched.

red line = correction
Green = overall output
Blue = pre-corrected output.

For the driver size, and the simplicity, and the price, the speed and low-end bass guitar bits are damn good.
 

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Interesting to note here - you can achieve v.high mid-bass SPLs using relatively small drivers...

Use harmonics (2nd, 3rd, to around 11th) and your brain fills in the fundamental.

I am fiddling with this concept to get huge SPLs without much Xmax being used...

Not what I'm after, though... may use it as an add-on later.
 
Hi,
do you realise that you are sending 25.7times the power to the pair of 8s compared to a flat signal sent to the remainder of the system. That's what +14.1dB of LF gain does.
Your total bass power handling is 120W.
Divide by 25.7 and that gives the maximum equivalent power you will send to the satellites. I would not be happy with a maximum power of 4.7W into my satellites. That's only +6.7dB of overhead above an average level of 1W. I look for at least +20dB of overhead to reduce the number of transients that get clipped.

My advice, investigate what can be achieved with +10dB of LF gain.
 
No, you forget. The quoted power handling already takes into account both coils. Also it's a max rating, in reality probably 50-60 RMS.

What you are proposing is about 99% identical to my first major sub-woofer project, a good many years ago now. Build it, but don't think you will get any serious SPL from it. Your theory about the harmonics giving you extra apparent SPL is wrong, it just sounds like a cheap sub being thrashed.
 
I hope to do the same - I'm only 15 years old, so this sub was designed to go low, not loud, as SWMBO just cuts my room out on the fusebox if the music "accidentally" gets too loud.

This isn't for a living room HT system - it's for a room 3mx3.5m

Thanks for the encouragement etc.



PS To double check - http://mcmelectronics.com/product/55-1455 says the same - 60W rms per coil.

PPS - As I am 15, my budget is also quite small (compared to most people here) - £100, so I got some cheap drivers, and decided to make something reasonable out of them.
 
According to Dad (who's usually with me when the music gets too loud, cheering me on), this sub is only a small, test version of the full thing.

I think he's thinking 12" or more for the final piece.

This could get interesting, but I think it will happen much later on...

And I know what you mean by abused.

I sometimes have a few friends over after school (parents work full-time, so they get home at 5, and i get home at 3-15). And there's always one who yells "crank it up", so, I turn it up a bit, then there's the usual yell of "louder", until the whole thing is distorting like crazy, and the electricity meter is spinning.

Those kind of volumes only last until someone smells an amp cooking.

Which doesn't matter, because I got the amp from school, for free, and they have 4 more "broken" ones.
 
Yeah - this is my 2nd project.

The first went horribly wrong when I decided to go down the PA speaker route.

SWMBO wasn't pleased

Neither was I, as I wanted to do a 178L box, ended up with a 28L box

The first would have gone flat to 40Hz, and really loud, the 2nd was rubbish.

Nevermind, eh?

Only cost me £30 to have a good mess around.

But this time, I drew up all the graphs, different type of cabinets, decided on sealed + Linkwitz, as it was one of the smallest designs.
 
Hi chris661,all,

A last minute suggestion:

Why not build a stuffed T-TQWT (Tapped-( folded) Tapered Quarter Wave Tube) using the two suggested drivers.
Only one internal divider and two bracings is needed.

See the submitted picture 1(1) of a HR simulation.

Folding technique and the placing of the port, example:
My sons T-TQWT (BP-TQWT) is described here:

http://www.diyaudio.com/forums/showthread.php?postid=1653128#post1653128

And pictures at:
http://www.diyaudio.com/forums/showthread.php?postid=1658457#post1658457

http://www.diyaudio.com/forums/showthread.php?postid=1757771#post1757771

b

1(1)
 

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