My "sub" works bad

[Grandma´s_SUB]

I bought my first woofer(driver) for 25Euro of "Noname" company.
"It should be good for first DIY sub", I said.For that price it has expected Q parameters(look at the graph).So I put a speaker in 120L sealed box,but there is no bass at all(friend´s logitech speakers for 50Euro play better ).
*Can you give me some opinion?What is wrong here?Construction of the box?

Thanks!
Dean

[mike.e]

1. Your assumption may not reflect reality. The response attached would give boomy kick drum bass atleast

2. There could be a variety of problems with current unit

3. Buy something that many others have here,such as Adireaudio units and a plate amp,and problem solved

Cheers!

[richie00boy]

I agree that's one hell of a boomy curve, but before spending more money let's look deeper into what you are doing. How are you deriving the signal for the sub? It may be that you simply haven't got your filter right. Your amplifier could be at fault. Just for starters...

[Grandma´s_SUB]

Ok.I made 100W amp from tda 7294 chip.For filtering I use active filter 12db octave-variable;about 100hz(I try variabling,but there was no diffirence at bass-except,that mids were cut off)

[richie00boy]

Have you tried the sub with another amp, a bought amp? I think your chip amp could be the problem.

[sam9]

Yup. I suspect the IC. At least try with another, prefereably much more powerful, amp and compare.

Re the TDA 7294:

-----The manufacturer's literature calls it a 100W unit. That's pure balooney unless you like 10% THD (and that's THD of the solid state variety). 50W is closer.

-----If you are really trying to run it at 100W, you are pushing it way up the thermal dissapation curve (see datasheet). Unless you have a sufficiently large heatsink to deal with that the chips protection circuits may be restricting the power available

---You didn't show the circuit elements surrounding the chip. If you are just cloning the application notes, I think one or more of the examples in there roll off HF a bit at the input (a high-pass filter) probably to save the chip from attempting to be used beyond it's capabilities.

---I think 100W (let alone a more realistic and listenable 50W) is pretty skimpy for a sub woofer anyway. Again this can be veruified by borrowing a higher power (200W?) amp and trying that with you speaker.


It may very well be that the fault likes with the loudspeaker after all, but I think you need to resolve the amplifier question first so that you can narrow the problem.

[Bill Fitzpatrick]

What do you expect? You have a high Q woofer in a box that pushes the Q even higher. Not only will you have exaggerated upper bass but the low bass will all but evaporate. The woofer is useless.

[Grandma´s_SUB]

If this woofer is useless why factory sells it?Its 12" huh

http://www.6moons.com/audioreviews/norh/tda7294.pdf
*tda 7294 datasheet

http://www.svet-el.si/shopimages/14_v.jpg
*I made this,just mono version(I bought a kit)

Dean

[DcibeL]

Originally posted by Grandma´s_SUB
If this woofer is useless why factory sells it?

Because people will buy it. I mean, you bought it, didn't you? I'm just buggin'.

That amp you built there would put out 70W RMS per channel according to the 7294 datasheet. I would assume something like 50W RMS is more realistic. If you had a dual voice coil driver, the same input signal could be applied to both amplifiers and give you 50W to each coil, for a sum of 100W. I haven't tried using two separate amps to drive each coil of a DVC, so I don't know how well this would work. Two 7293 chips can be bridged to give 100W output, but you would need to use a different pcb from the one you have.

[DcibeL]

Woops, sorry I didn't read there that you built the mono version. My bad.