My "sub" works bad

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Grandma´s_SUB

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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 :xeye: ).
*Can you give me some opinion?What is wrong here?Construction of the box?

Thanks!
Dean
 

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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!
 
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...
 
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)

🙄
 
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.
 
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 said:
If this woofer is useless why factory sells it?
Click to expand...

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.
 
Everybody is right.

The Qts is enormous. Are you sure you have it right? If so, the speaker would want to be mounted in a wall or ceiling - or a really gigantic box. And I mean gigantic as in you could live in it. Even then you would have a big bump in the low bass region.

You should be hearing too much bass (around 40Hz), not too little. Either the speaker or the amp is not working right.
 
We assume that the builder is trying to get the "bass sound" with his midwoofers turned on as well. If he just turns on the sub and uses a cutoff of 100 hz, he's probably just going to get what might sound like nothing to him. He's also comparing it to those Logitech stuff that probably has cutoffs in the 200 range.

Furthermore, he's building a box that peaks fairly low depending on program material and not in the higher midbass region like many "PC" speakers. Most newbies thinks that a peaked midbass is a strong low bass. If he has program material with only strong midbass, it might sound thin. In fact what a seasoned builder might say sounds flat might sound bass shy to many newbies.

My guess anyways.
 
Ot

Neal Armstrong actually said, "One small step for man..." He intended to say, "One small step for a man..." but he was, well, perhaps a little excited. The real mystery is not why he blew his line, but rather, why, with so much time to think about it, he couldn't come up with something better to say in the first place.

Now back to your regularly scheduled bulletin board.
 
Since you know how to build an amplifier, I suggest to measure by yourself the T/S parameters of this woofer after 24 hours of break-in.

I've never seen a Qts that high.

Good luck!
 
Qts 1.363, yes that's high but not something I haven't seen before in dirt cheap woofers. These kind of drivers are crying out for mild Linkwitz Transform or EAS/ELF use in small rooms where they won't be driven hard.
 
I also have doubts that the values in the data sheet are
alright......
I would assume that the drivers resonance frequency is much higher than stated in the data sheet.
If you feel that entire T/S parameter measurement is to complicated, then you should at least check the resonance frequency of the driver
without box. Simply drive the driver with a sine wave, sweep the
frequency and measure the current through the driver. At resonance frequency the current will have its minimum, because of the impedance maximum.
Next simple measurement would be to find the resonance frequency of
the diver, when mounted in the box....
This will give you rough idea about the real behavoiur of the sub.
Never trust a data sheet of no name drivers!
Richie already said: ....crying for a LT....
If you are able to measure the T/S parameters then you can turn the
entire behaviour of the sub by a linkwitz transform to any wish.

Good Luck
Markus
 
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