Puzzle: Subwoofer vs Amplifier

[Dinesh Priyasad]

I'm a newbie just registered to the forum, cos I'm a finder of the reality of sound...

Unfortunately, here in Sri Lanka, it's quite a bit difficult to find a branded subwoofer driver, where audioholics are almost nowhere to standardize the quality of sound and where lots of myths have been created by many of sound equipment sellers, not only as their marketing strategies, but also due to their lack of knowledge in sound... So, I bought a pair of unbranded (named J AUDIO, a Chinese one) 8" bouble-coil & double-magnet of 8 ohms 300-450 watts as mentioned (though ridiculous for an 8") for just 30 bucks... Plus, I wanted to spend a little money on them, cos my intention was only to experiment my own design of a subwoofer enclosure (to see how it works)...

Thereafter, I asked a veteran technician (a professional amplifier maker) to build a two channel subwoofer amplifier for those I bought and installed separately in the two enclosures built to my design... What makes the story interesting is that, he told me he'd make it with an original STK 4191, which is a stereo IC, capable of delivering 50 watts RMS per channel (including a low-pass filter to extract bass), and when I questioned about its sufficiency for those I bought, he answered a 50 watts RMS would clip them at high volumes and could even blow them up at the max volume...

Now, the puzzle for me is that, I've got many resources under the topic "subwoofers" from the Internet and found most of the subwoofers are powered with amplifiers of 200/300/400/500 watts RMS, but at the same time, I gotta know that even a musical concert can be powered with a 500-1000 watts RMS amplifier...

Ah, forgot to say, you'd ask me about my usage, well, they're just for my home entertainment (a living room of 30' x 30'), but I need a thundering bass to enjoy...

Please help me in solving the puzzle and, btw, I hope this thread, in future, would be a great help for those like me who are curious about the wattage of amplifiers...

Note, here I meant nothing about that bullshit PMPO, a trap of the salesman to hunt down the poor customer, though technically makes no sense at all...

Thanks...

 

[rojo]

I'm a newbie just registered to the forum, cos I'm a finder of the reality of sound...

Unfortunately, here in Sri Lanka, it's quite a bit difficult to find a branded subwoofer driver, where audioholics are almost nowhere to standardize the quality of sound and where lots of myths have been created by many of sound equipment sellers, not only as their marketing strategies, but also due to their lack of knowledge in sound... So, I bought a pair of unbranded (named J AUDIO, a Chinese one) 8" bouble-coil & double-magnet of 8 ohms 300-450 watts as mentioned (though ridiculous for an 8") for just 30 bucks... Plus, I wanted to spend a little money on them, cos my intention was only to experiment my own design of a subwoofer enclosure (to see how it works)...

Thereafter, I asked a veteran technician (a professional amplifier maker) to build a two channel subwoofer amplifier for those I bought and installed separately in the two enclosures built to my design... What makes the story interesting is that, he told me he'd make it with an original STK 4191, which is a stereo IC, capable of delivering 50 watts RMS per channel (including a low-pass filter to extract bass), and when I questioned about its sufficiency for those I bought, he answered a 50 watts RMS would clip them at high volumes and could even blow them up at the max volume...

Now, the puzzle for me is that, I've got many resources under the topic "subwoofers" from the Internet and found most of the subwoofers are powered with amplifiers of 200/300/400/500 watts RMS, but at the same time, I gotta know that even a musical concert can be powered with a 500-1000 watts RMS amplifier...

Ah, forgot to say, you'd ask me about my usage, well, they're just for my home entertainment (a living room of 30' x 30'), but I need a thundering bass to enjoy...

Please help me in solving the puzzle and, btw, I hope this thread, in future, would be a great help for those like me who are curious about the wattage of amplifiers...

Note, here I meant nothing about that bullshit PMPO, a trap of the salesman to hunt down the poor customer, though technically makes no sense at all...

Thanks...

Hi Dinesh, and welcome!

If this is your sub driver, its rated RMS power handling is only 80 watts. If your amp builder were to build you an 80WPC RMS amp you'd only get maybe 1.5 dB additional output at the same distortion level as the 50 watt amp you've commissioned.

The real problem is that that driver is intended for car audio. It would probably make an OK mid bass module in a home theater, but it's not going to play low. More frustrating, there are no parameters published for it anywhere that I see. That makes it impossible to build a properly tuned box for it unless you can measure its parameters with special equipment (the Dayton Audio DATS v2 for example).

If that's not your driver, can you show us a link to your driver? Is there a page somewhere that describes its T/S parameters?

 

[Verdinut]

If you need thunderous bass to enjoy, you need at least one 15 inch subwoofer and preferably two, considering the size of your listening room.

Loud bass reproduction means big air volume displacement and the total cone area is among the most important factors for this to happen. Also, the amplifier driving the subwoofer(s) should have a power rating close to that of their acceptable power handling for reliable performance.

Preferably, the sub(s) should be installed in a ported cabinet for better bass response, better efficiency and less distortion than in a closed box. In fact, you would need some adequate knowledge about speaker building to be able to build the appropriate cabinet(s). The laws of physics are not flexible and you have to abide by them to arrive at successful loudspeaker building.

 

[Dinesh Priyasad]

First to say, thanks a lot for your reply...

If this is your sub driver, its rated RMS power handling is only 80 watts. If your amp builder were to build you an 80WPC RMS amp you'd only get maybe 1.5 dB additional output at the same distortion level as the 50 watt amp you've commissioned.

Ah, exactly the same... So, how could you find its rated power handling as 80 watts RMS, cos it's mentioned on the sticker wrapped around its magnet as 300-450 watts, and that's all I could find about its wattage...? I mean, did you test the same with the equipment you linked here, or how did you, cos I need to make sure if it's truly 80 watts RMS...?

Yeah, I once read about how wattage deals with senstivity (dB), so I know there's no much increase in dB occur between 50 watts & 80 watts... But, isn't it further okay to build my amplifier using STK 4191 IC, which ouputs 50 watts (per channel)...?

The real problem is that that driver is intended for car audio. It would probably make an OK mid bass module in a home theater, but it's not going to play low. More frustrating, there are no parameters published for it anywhere that I see. That makes it impossible to build a properly tuned box for it unless you can measure its parameters with special equipment (the Dayton Audio DATS v2 for example).

Next, the T/S parameters, well, neither I could find on the Internet nor is mentioned in its package, cos they come to Sri Lanka in wholesale boxes... Of course, that's why I initally told you, this is just experimental, and if my design wins, I'd never ever use them again, but, for now, I have to, cos I can't throw them away either...

 

[Dinesh Priyasad]

Thanking you for the reply...

If you need thunderous bass to enjoy, you need at least one 15 inch subwoofer and preferably two, considering the size of your listening room.

Totally agree with you... But, this is experimental... If my design wins, I'll definitely build two subwoofers with branded 15"s... That's for sure...

Loud bass reproduction means big air volume displacement and the total cone area is among the most important factors for this to happen. Also, the amplifier driving the subwoofer(s) should have a power rating close to that of their acceptable power rating for reliable performance.

Let's say I want those two 8"s to vibrate my small bedroom of 10' x 10'... Is that possible using a 100 watts (50 x 2) amplifier...?

Preferably, the sub(s) should be installed in a ported cabinet for better bass response, better efficiency and less distortion than in a closed box. In fact, you would need some adequate knowledge about speaker building to be able to build the approp.riate cabinet(s). The laws of physics are not flexible and you have to abide by them to arrive at successful loudspeaker building.

Actually, I'm not an audioholic with a great amount of knowledge in physics of sound, but I'm curious about how my design would be... It's kind of a mixture of both the bandpass and the transmission line, not explicitly, but implicitly... So, may I send you a sketch of my design...?

 

[Verdinut]

Unfortunately, I won't be able to help you with your project.
I suggest that you, as a first step, get hold of a good book on speaker building. One such book is "Designing, Building, and Testing Your Own Speaker System" by David B. Weems, which you probably can get through eBay at a very cheap cost.
In addition, in order to succeed with your project, I agree with Rojo's recommendation of getting a Dayton DATS v2 Speaker Testing Computer Interface, to enable you to measure the Thiele/Small parameters of your 8 inch transducers. Without a good information base, even with the best book on the topic, it's almost impossible to arrive at acceptable results.
With the help of a well documented book on speaker cabinet building and appropriate speaker testing equipment, you should be closer to your aim of obtaining interesting results.

Finally, if you want to obtain better results with less trial and error, I would suggest that you also get a speaker enclosure building software to configure the appropriate box size configuration etc. One of them is the Harristech BassBox software.

 

[Dinesh Priyasad]

Unfortunately, I won't be able to help you with your project.
I suggest that you, as a first step, get hold of a good book on speaker building. One such book is "Designing, Building, and Testing Your Own Speaker System" by David B. Weems, which you probably can get through eBay at a very cheap cost.
In addition, in order to succeed with your project, I agree with Rojo's recommendation of getting a Dayton DATS v2 Speaker Testing Computer Interface, to enable you to measure the Thiele/Small parameters of your 8 inch transducers. Without a good information base, even with the best book on the topic, it's almost impossible to arrive at acceptable results.
With the help of a well documented book on speaker cabinet building and appropriate speaker testing equipment, you should be closer to your aim of obtaining interesting results.

Finally, if you want to obtain better results with less trial and error, I would suggest that you also get a speaker enclosure building software to configure the appropriate box size configuration etc. One of them is the Harristech BassBox software.

Thanking for your reply, I appreciate the way you advised me... Actually, you should have a proper knowledge in designing subwoofer enclosures, cos it all comes to BASS in the end, so you can't play games with it...

 

[lovinthehd]

How did you design a sub enclosure without the T/S parameters?

 

[Dinesh Priyasad]

How did you design a sub enclosure without the T/S parameters?

The problem is that, I could find no info about the drivers I bought, so I thought to build the enclosure considering only the driver size (I know I'm wrong)...

 

[Dinesh Priyasad]

Okay, generally asking (may be a little silly), are two 8 inches subwoofers hitting 100 watts RMS of bass together enough to entertain in a 30 feet x 30 feet room (not to shake it but to feel it)...?

 

[lovinthehd]

The problem is that, I could find no info about the drivers I bought, so I thought to build the enclosure considering only the driver size (I know I'm wrong)...

Hard to know what your amp requirements would be without knowing at least the sensitivity specs let alone what type/size of box to take advantage of the drivers' capabilities. In any case for a huge room like you've got, not too likely two 8" drivers are going to do it...but what box type/size did you make?

 

[Dinesh Priyasad]

Hard to know what your amp requirements would be without knowing at least the sensitivity specs let alone what type/size of box to take advantage of the drivers' capabilities. In any case for a huge room like you've got, not too likely two 8" drivers are going to do it...but what box type/size did you make?

So, here's a simple sketch of my own subwoofer enclosure design, a mere combination of the bandpass and the transmission line... Actually, I forgot to say, I planned the design as a theory, not specially for those 8"s, but generally for all driver sizes...

Now, here, I center my sub into a 10" x 10" board (that's driver size + 2") and position in the middle of the enclosure, seperating two 10" x 10" x 10" rooms... Then, the port comes, a 1" high (fixed, no matter what the driver size is) and 10" wide (the same width the room takes, so for the port, it's not the height, but the width increases/decreases as the driver size gets larger/smaller)... At the runtime, primarily, air comes out of the front (the cone) and the back (the magnet) of the driver moves freely inside the rooms (this is what I call "free motion"), secondarily, air gets pressure as going through the port, considering the shape of the port, as you see, the back air takes an S shaped turn and the front air takes a U shaped turn (this is what I call "compression"'), and finally comes out of the port hole... That's it... Looks a bit awkward...?
View attachment 20984

 

[MrBoat]

Your best bet would be just to order a known, reputable subwoofer driver/amp with choices of already known cabinet configurations and just buy it regardless of the cost and get it over with. It's worth it just for 'not' enabling the predator sales industry. If your living room is 30' x 30', have internet access, surely you must have some resources.

The only bargains in audio are buying used, reputable gear from honest people, and building things yourself with reputable parts and information.

The driver/amp you present here would not be suitable for much more than a computer desk, or some other near field scenario with the performance you expect. My computer speakers/sub are 40 watts.

 

[Dinesh Priyasad]

Your best bet would be just to order a known, reputable subwoofer driver/amp with choices of already known cabinet configurations and just buy it regardless of the cost and get it over with. It's worth it just for 'not' enabling the predator sales industry. If your living room is 30' x 30', have internet access, surely you must have some resources.

The only bargains in audio are buying used, reputable gear from honest people, and building things yourself with reputable parts and information.

The driver/amp you present here would not be suitable for much more than a computer desk, or some other near field scenario with the performance you expect. My computer speakers/sub are 40 watts.

I mean, that's the size of the living room of the house I'm currently residing at, but my house to which I'm going back by the of this year, is much smaller in size comparatively, so I think two subwoofers hitting 100 watts of bass would be quite enough to entertain in my small bedroom of 10' x 10' x 10' there...

Agree with you on the fact you said about getting branded stuff... Sad to say, our country is being covered up with those Chinese crap, that we can hardly find an item with its specs atleast, so we're like blindfolded...

 

[MrBoat]

I mean, that's the size of the living room of the house I'm currently residing at, but my house to which I'm going back by the of this year, is much smaller in size comparatively, so I think two subwoofers hitting 100 watts of bass would be quite enough to entertain in my small bedroom of 10' x 10' x 10' there...

Agree with you on the fact you said about getting branded stuff... Sad to say, our country is being covered up with those Chinese crap, that we can hardly find an item with its specs atleast, so we're like blindfolded...

Our country is being overtaken by Chinese crap as well. It hides even in domestic products. Some of it is pretty good, if it is made to a higher spec by another more reputable company just outsourcing the labor to there.

 

[Dinesh Priyasad]

Our country is being overtaken by Chinese crap as well. It hides even in domestic products. Some of it is pretty good, if it is made to a higher spec by another more reputable company just outsourcing the labor to there.

True...