LM1875 Amplifier Watts

[Suraj143]

Hello guys, yes the manufacture recommends to use a sealed enclosure.

I did experiments over last two weeks.When it is sealed the sound is no good, no bass at all.So I made a hole, after the sound was good.

I also seen in another forum one guy telling this sub needs a ported cabinet he also faced to the same scenario.

I have another sub box which is 1.21 Cu/Ft & just connected this woofer & did experiments.The sound is worst no volume no bass at all.

This woofer needs a small enclosure with ported 0.6 to 0.75 Cu/Ft this works nicely.

 

[audioguru]

Its power rating is 40W in a sealed enclosure. The air in the sealed enclosure stops the voice coil from too much excursion at low frequencies (smashing against the magnet frame).

In a ported enclosure there is nothing to limit the excursion of the voice coil at frequencies below resonance. Therefore the power rating is less unless a circuit attenuates the low frequencies.

The woofer is very cheap so it has no detailed spec's. Its cone is aluminum so it has a high mass and probably has a high Q at resonance. It might sound like a "bongo drum" (one note bass).

 

[4pyros]

Hello guys, yes the manufacture recommends to use a sealed enclosure.

I did experiments over last two weeks.When it is sealed the sound is no good, no bass at all.So I made a hole, after the sound was good.

I also seen in another forum one guy telling this sub needs a ported cabinet he also faced to the same scenario.

I have another sub box which is 1.21 Cu/Ft & just connected this woofer & did experiments.The sound is worst no volume no bass at all.

This woofer needs a small enclosure with ported 0.6 to 0.75 Cu/Ft this works nicely.

How do you know if you dont even have a crossover?
Without a crossover its just a speaker not a sub.

 

[audioguru]

How do you know if you dont even have a crossover?
Without a crossover its just a speaker not a sub.

The cheap woofer has a heavy aluminum cone so it has poor high frequency response. Maybe it doesn't need a crossover.
Have you heard foreign "music" from over there? It has no deep bass.

 

[Suraj143]

Guys I have a low pass subwoofer filter using UC4558 opamp. This will goto LM1875 Amp.No need cross overs.

 

[audioguru]

Guys I have a low pass subwoofer filter using UC4558 opamp. This will goto LM1875 Amp. No need cross overs.

Then it might be half of a sub-woofer crossover. The other missing half is high-pass filters to prevent the woofers from trying to produce very low frequencies.

 

[Suraj143]

Nice.

I removed the satellite speakers & connect only the subwoofer & checked the system.Bass is fine but I can hear the voice too from the subwoofer. I mean a little amount.

Note that I have three LM1875. Two of them for satellites & the other LM1875 with UC 4558 to subwoofer.I use 3A transformer 12-0-12 still.

 

[audioguru]

Then your speaker system has two satellite speakers for stereo high frequencies and one woofer for mono low frequencies. No sub-woofer.
My computer speakers are like that.

 

[Suraj143]

Hi audioguru I have a subwoofer which you call as a woofer.I don't know why you so negative on my subwoofer

Then I wonder what you say on ready made subwoofer systems which is available on market.Most of them have below 25W subs.Ex: Altech lansing VS4121 19W RMS, Sonic gear ENZO 500 25W RMS etc......

 

[audioguru]

Hi audioguru I have a subwoofer which you call as a woofer.I don't know why you so negative on my subwoofer

Wikipedia says:
"A subwoofer (or "sub") is a woofer, or a complete loudspeaker, which is dedicated to the reproduction of low-pitched audio frequencies known as bass. The typical frequency range for a subwoofer is about 20–200 Hz for consumer products.
The most common subwoofer driver sizes used for sound reinforcement are 10", 12", 15" and 18" models.

Woofer is the term commonly used for a loudspeaker driver designed to produce low frequency sounds, typically from around 40 hertz up to about a kilohertz or higher."

Mere use of the term "subwoofer" is no guarantee of good or extended bass performance. Many multimedia "subwoofers" might better be termed "bass drivers" as they are too small to produce deep bass."

Your woofer is too small to be a sub-woofer and is spec'd to go down to only 40Hz (like an ordinary woofer).

Then I wonder what you say on ready made subwoofer systems which is available on market.Most of them have below 25W subs.Ex: Altech lansing VS4121 19W RMS, Sonic gear ENZO 500 25W RMS etc......

They are little low power computer speakers.

 

[4pyros]

Guys I have a low pass subwoofer filter using UC4558 opamp. This will goto LM1875 Amp.No need cross overs.

Bass is fine but I can hear the voice too from the subwoofer.

Then your low pass is not working right.

 

[4pyros]

I have a subwoofer which you call as a woofer

No you have a speaker that could be a woofer or a subwoofer depending on how its set up.
Right now its just a woofer if you can hear voice thru it.
With a true subwoofer you would never hear frequency's that high.

 

[audioguru]

Voices heard from a subwoofer?
This is a big world. In some countries men sound like men and, you know, in other countries men sound the same as women.

Many articles about human voices in Google say "adult male 85 to 155 Hz, adult female from 165 to 255 Hz" so of course a subwoofer can produce the low frequencies of most adult male voices.

 

[ChrisP58]

Guys I have a low pass subwoofer filter using UC4558 opamp. This will goto LM1875 Amp.No need cross overs.

What is the roll off frequency of the filter?

What is the roll off rate?

 

[Suraj143]

What is the roll off frequency of the filter?

What is the roll off rate?

Very good question.Actually I don't know the roll off frequency.

Audioguru & ChrisP & 4Pyros

Here is the subwoofer filter circuit.Please fine tune it to fit to my design to get maximum performance from my design
Here is the circuit.

 

[audioguru]

Your filter is missing an extremely important capacitor so it is not a lowpass filter. Instead its low frequency response is flat then it has a +42dB peak at 30kHz.

 

[Suraj143]

Oops sorry audioguru I really missed that capacitor.But its a drawing mistake, in the pcb I have a 104 (0.1uF) capacitor.But you have used 110nF........?

Is my circuit ok?What about using TL072 instead of cheap UC4558?

I really like to thank you for the support you giving

 

[audioguru]

Oops sorry audioguru I really missed that capacitor.But its a drawing mistake, in the pcb I have a 104 (0.1uF) capacitor.But you have used 110nF........?

The difference is so small that you will not hear it and I can barely measure the difference.

What about using TL072 instead of cheap UC4558?

You can trust a TL072 made by an American manufacturer. I used over 10,000 of them (I used the TL074 quad opamp) for a product and every one passed a strict test.
I don't know if you can trust a UC4558 made by a Chinese manufacturer.
Texas Instruments still make the very old uA4558. It is low noise and has a 35kHz bandwidth good enough for audio.

I really like to thank you for the support you giving

You are welcome and I am glad to help you.

 

[Suraj143]

You can trust a TL072 made by an American manufacturer. I used over 10,000 of them (I used the TL074 quad opamp) for a product and every one passed a strict test.

Very nice to hear Most people say TL072 has more bass than uc4558.

In my pcb I have two of 4558 IC's.I'll replace them with TL072.

Still my 18V transformer is not winded yet.I'll get that in the weekend to test my system.

 

[Suraj143]

I have a small problem the cut off frequency will be around 100-107Hz.What will be the lower end?Is this frequency range is suitable for small subwoofer system like 25W?

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