TIP31 feeding about 25 leds (audiorhytm circuit)

[Johanx2]

Guys, I am moving soon, and wont complicate too much with the enclosure for now, so I think that the dedicated bass chamber of my enclosure, it's going to be sealed, 1 cubit feet for 8" driver, and filled it with one pound of poly-fill. Have you heard the miracles can do with sealed enclosures? will put 1 pound, which it is the recommended quantity I have read.

Few pages back, I showed the picture design of the enclosure, some did not like it, even me, well, I actually like if compared to having two loud speakers very close each one together, specially if they don't show a form of angle, which I believe it does not help too much for a stereophonic sound effect. Is I mentioned before, my enclosure form its a vertical rectangule, I will go with that form for the saving space feature, (it won't take too much of your floor, but that wont mean that this thing will not sound amazing, it will!

So what I did with the upper chamber (for mids and highs, bass chamber is isolated), what I did, was to... well see the picture below...

So now everything is at the front, and just for now, I think I am very happy with it, not sure if because I am the designer... but I believe its a good idea for the vertical factor with stereo sound, don't you think? I will need to play with angles, not a problem for my circular saw, I have not table saw, but I did a 48x48 platform using some 2x8 lumber, very heavy thing, so I put on the board, and clamp a big aluminum ruler to guide the circular saw, just as accurate you want.

God! that little chinese device slams that subwoofer on 4 ohms, surely it can handle an even more powerful subwoofer and linked on 2ohms, which is when it really kick with power.

The picture shown below, it's not showing the bass ring, the leds, and few more things I am still not done with them, that will be another nice thing I liked, thanks to Bet! and everybody.

 

[Audioguru]

The Thiel-Small specifications of a speaker determines whether it should have a sealed or vented enclosure, the size of the enclosure and the size of the port tube.
All half-decent woofers have detailed Thiel-Small specifications in their datasheet and usually the manufacturer has a recommended enclosure design shown.

Your Pyle car woofer is probably model PM8 which is a woofer for a car. Its resonance is much too high for it to be a home woofer and is useless at subwoofer frequencies. A sealed enclosure increases the resonant frequency.

Stereo is sounds coming from two locations apart from each other. Your speaker with left and right in the same enclosure will produce only mono so why bother with two mid-highs speakers?

You might be destroying the woofer if the amplifier is slamming it. A woofer power rating is when it is mounted in its recommended enclosure because the air in the enclosure supports it.

Here are the spec's I found for the Pyle PM8 car woofer:

- - - Updated - - -

The internet has many articles about loudspeaker design.
Here is one:

 

[Johanx2]

Stereo is sounds coming from two locations apart from each other. Your speaker with left and right in the same enclosure will produce only mono so why bother with two mid-highs speakers?

Well, I know that it won't be a stereo sound in all sense, but I think I am helping a little by doing this, imagine the waves that each loudspeaker spreads on its own angle, filling a room, it can be more notorious when getting some distance from enclosure, and even close, aside, anyway putting small loudspeaker (5.25") gives me the chance to save some inches to the high of enclosure, so if I can put a pair, it obviously be louder, without increasing the total enclosure high size.

The subwoofer is the PLPW8D, data sheet says that its 200w rated, and supports sealed enclosure, 0.88 CF for both sealed or ported, it will be mounted in 1 CF, which I think its still more than suitable, with this and the poly fill in, I expect to have a nice sound. If it blows, whats the problem? its obtained experience and can later buy another one with better specs.

Wanna take a look at the data sheet?

What I am concern its about the 5.25" loudspeakers getting about 50w each one, they are marked as 200w rated as well, things that I won't believe until see them mounted and in action.

 

[D.A.(Tony)Stewart]

Note 10 cu ft required.

 

[Audioguru]

The Pyle PLPW8D woofer is not listed on Pyle's website so maybe it is obsolete.
The resonant frequency is 46.2Hz in a huge infinite baffle but a 1 cubic foot enclosure will raise it and it will boom at maybe 80Hz and cutoff lower frequencies.

Pyle's Suggested Enclosure Parameters shows a tiny enclosure and an F3 a little lower than the 46.2Hz free air resonant frequency so there must be a peak at maybe 60Hz then lower frequencies are reduced but 45Hz is at -3db. The peak makes it sound "boomy" and the cutoff is for a woofer, not a subwoofer.

I entered the speaker parameters into an enclosure design program at DIYaudio.com and it shows a 1.63 cu ft sealed enclosure for this speaker produces a flat response (no peak) and -3dB at 55.6Hz so there will be no deep bass.

 

[c_mitra]

Stereo is sounds coming from two locations apart from each other. Your speaker with left and right in the same enclosure will produce only mono so why bother with two mid-highs speakers?:

Not quite accurate. Stereophonic sound is similar to stereoscopic vision.

Because we have two eyes and they are located physically separate, they see the same object from a slightly different angle. The brain reconstructs the slightly different views into a one three dimensional view- the image formed on the retina is two dimensional. If you see with one eye closed, you will lose all perceptions of depth- the third dimension. If you see how the GPS works, this is not much different.

Similarly our two ears receive the same sound with a delay because of the physical separation. The brain interprets this delay and computes the direction for the source of sound. For simple sources, it is very good at it.

Just like you can add reverberation artificially in software, you can also superimpose the same sound with a delay and put it out through one speaker and it will sound stereo. However, this difficult to do with several different sources at the same time. Many 5 speaker (or 7 speaker) surround sound systems work like that- they really do not have 5 or 7 independent sound sources. It just creates an illusion.

Just like a ventriloquist.

 

[Johanx2]

The Pyle PLPW8D woofer is not listed on Pyle's website so maybe it is obsolete.
The resonant frequency is 46.2Hz in a huge infinite baffle but a 1 cubic foot enclosure will raise it and it will boom at maybe 80Hz and cutoff lower frequencies.

Pyle's Suggested Enclosure Parameters shows a tiny enclosure and an F3 a little lower than the 46.2Hz free air resonant frequency so there must be a peak at maybe 60Hz then lower frequencies are reduced but 45Hz is at -3db. The peak makes it sound "boomy" and the cutoff is for a woofer, not a subwoofer.

I entered the speaker parameters into an enclosure design program at DIYaudio.com and it shows a 1.63 cu ft sealed enclosure for this speaker produces a flat response (no peak) and -3dB at 55.6Hz so there will be no deep bass.

Thanks for the data, then this is good scenario to try the polyfill fiber and see what can it do. As I mentioned before, can I have read some users talking about it, and they said that it really made impressive improves lowering the frequency. This is going to be good experiment, I always wondered how many hz can that simple thing low down or see how true it is. Nothing stop me to later mount and screw a better sub, that time having some experience that this thing will give me.

Have you tried polyfill before?

 

[c_mitra]

I entered the speaker parameters into an enclosure design program at DIYaudio.com and it shows a 1.63 cu ft sealed enclosure for this speaker produces a flat response (no peak) and -3dB at 55.6Hz so there will be no deep bass.

It may be better to place the speaker at the center of the largest face (by that I mean the face with the largest value of side1+side2). Putting the speaker near the bottom edge is perhaps not so wise.

 

[Audioguru]

Many years ago I also tried polyfill in a speaker to cause the sound waves in an enclosure to become heat waves which travel slower and reduce (a little) the resonant frequency of a speaker in a sealed enclosure. It reduced 60Hz with no polyfill to 57Hz with polyfill which measures a little better but the difference cannot be heard. But a speaker sounds much better when the internal echoing sounds of its enclosure are absorbed.

Your woofer resonates at 46.2Hz with no enclosure but a good 8" subwoofer speaker resonates at 30Hz or less. A low frequency is produced with a heavy cone and loose but accurate suspension. The heavy cone reduces sensitivity so the magnet must be stronger to raise the sensitivity back to normal. Your small sealed enclosure will cause a resonant peak at an upper bass frequency which is no good but some people like it.

 

[c_mitra]

But a speaker sounds much better when the internal echoing sounds of its enclosure are absorbed..

This is the key. You will have additional nuisance in the form of standing waves (fortunately they form with high frequencies where the lambda is smaller)

 

[Johanx2]

I have been comparing the specs of few 8" drivers on an enclosure calculator (I am understanding many things now), I found that there is not big difference in final enclosure hz with another brands with similar or a bit more price, like pyramid, pioneer, planet audio, I still have to try the data of some more brands, but what I concluded, its that, I need a ported enclosure of at least 1.5 cF if I want something good in the range of power I need (I need it around no more than 100w) and 8" woofer. Maybe there are in the market 8" subs with a lot less of hz, of course more expensive and pointing to big powers (even 400w), for that reason I pointed to pyle, and maybe next time to pyramid. I modified the design of my enclosure and increased its height in order to make it 1.5 cF, which with the proper port will throw around 34hz, which I believe its ok for this application I am making.

Please I have not understood something. Audioguru, You told me that domestic subwoofer drivers are usually lower in hz instead of audio car, how can I get one of them in the future? can you throw me some data? Thanks.

 

[Audioguru]

I picked an inexpensive ($25.27US) 8" woofer from Parts Express and put it in the DIYaudio enclosure calculator. its maximum allowed power is only 60W but its performance is pretty good since its resonance is at 30.3Hz. A sealed 0.88 cubic ft enclosure produces a flat response down to 51Hz. A 1.64 cubic ft ported enclosure produces bass down to 29.2Hz:

 

[Johanx2]

I picked an inexpensive ($25.27US) 8" woofer from Parts Express and put it in the DIYaudio enclosure calculator. its maximum allowed power is only 60W but its performance is pretty good since its resonance is at 30.3Hz. A sealed 0.88 cubic ft enclosure produces a flat response down to 51Hz. A 1.64 cubic ft ported enclosure produces bass down to 29.2Hz:

I see, take a look at this:
https://www.parts-express.com/dayton-audio-sd215a-88-8-dvc-subwoofer--295-484

This is 80w, and 31hz response, I needed something like this at first instance then, I was ignoring that factor since the beginning, price its similar to those cheap car audio subs.

 

[Johanx2]

Coming back to the simple vumeter comparator (LM311), so I should not connected to the amplifier output which is bridged (btl), unless I am using a separated power supply? Or should I connected to one of the loud speaker? this is something I did not understand at all. Some electronic parts have almost arrived, so I need this to be clear soon. Thanks.

 

[Audioguru]

Look at my post #124 again. Remove the stereo inputs and remove the input coupling capacitor that will damage or destroy the input of the comparator.
Since the amplifiers are bridged then the output voltage of each wire of a speaker swings down to +2V and up to +22V when the supply is 24V. Then the comparator can use the same +24V and 0V supply as the amplifier with no damage to its input.

 

[Johanx2]

Look at my post #124 again. Remove the stereo inputs and remove the input coupling capacitor that will damage or destroy the input of the comparator.
Since the amplifiers are bridged then the output voltage of each wire of a speaker swings down to +2V and up to +22V when the supply is 24V. Then the comparator can use the same +24V and 0V supply as the amplifier with no damage to its input.

You did not only remove that coupling capacitor, but only modified a resistor and pot value, reason? Also, is there a danger having that pot on a max or min ohm value setting? I supposed this is for gain, right? So I should start at max ohm value and adjusting the best setting for it.

Thanks.

 

[betwixt]

The comparator circuit can be connected in two ways:

1. The comparator circuit is connected at the input to the main amplifier:

In this scenario, the signal is 'single ended', it has a ground connection and a signal connection. You can connect the ground to 'GND' and the signal to the comparator input.

2. The comparator circuit is connected across the loudspeaker wires:

Because it is a bridge amplifier, BOTH the speaker wires carry signal, there is no 'ground'. The comparator works exactly the same, it is only concerned with what it sees across it's input but if the power source to the comparator/LEDs has it's own ground connection to the wall socket or elsewhere, it will be linked to one of the speaker wires through the circuit (GND connection). This is very likely to damage the amplifier.

The safest way to connect it, which works in all situations is through a small isolating transformer. This makes the comparator completely independent of the amplifier, it will make no difference at all if it is wired across the amplifier input or output and you can use a grounded power supply for the LEDS.

Brian.

 

[Johanx2]

Thanks betwixt, then I think I am simply going to connect it to one of the loudspeakers, which I believe that stereo sound, its not bridged. is not it? TPA3116

 

[Johanx2]

As you can see here, I am taking this very seriously, will put some leds around the woofer, in the front, which will be commanded by the comparator connected to one the of the loudspeaker terminals, so there I avoid what you mentioned can happen, but I am still thinking about what Audioguru said, that which such modifications can be easily connected to the subwoofer output, which is already mono with channels mixed, therefore it would be convenient as well in that sense going there.

I added a double baffle, it adds stiffness and can work some esthetics in the edges, like sawing the edges in diagonal or rounding them with a router.

I do not know guys, but this thing should be nice in the dark, and it will! I put 18 leds which are 10mm 3.4V@20ma, surely will throw good light winks when viewed in directly angle.

Yesterday I cutted some MDF, and will use 5/16 dowels at the edges, so I forget about splitting anything with screws, which is always happens, there are special screws, but I simply believe that MDF and screws are not compatible, you cannot trust an apparently good screws mdf, it can suddenly split in future time, I actually prefer box joints, but it requires more techniques, I am ok with dowels and good wood glue.

Surely this is not final design and will modified somethings like that aluminum rectangle for controls, maybe I will remove it and work the wood, so I can properly install the pots, which are the most annoying when mounting on wood, push buttons are so easy, just a 15mm circle cutting, and you are done. There in the front, at first instance I can say will have a latching push button for power, then the pots, and at the finish another latching butting deactivation the lights, which may be annoying On all the time.

 

[Audioguru]

Why don't you look at the datasheet of the TPA3116 stereo bridged class-D amplifier IC? Is says and shows that each wire of a speaker is driven from its bridged amplifiers then the voltage swing is from +2V to +22V which is perfect for my modified comparator circuit shown in my posts.

Of course I changed the position of the threshold pot (it has nothing to do with gain) and its series resistor and I changed the value of the series resistor because my modified circuit is designed to be fed from the modulated DC output of an amplifier. The DC output voltage of each of these amplifiers is at 12VDC which is half of the supply when there is no signal and it swings up and down with signal. The threshold control can be set for a low signal level or a high signal level and the polarity of it can be set for positive or negative going peaks.

Since the amplifier is a cheap no-name-brand Chinese one sold by ebay then you do not have a schematic or parts layout.
Where is the subwoofer amplifier input? Is it from the volume control, from the lowpass filter or from the stereo to mono combining?

The volume control of each amplifier is probably grounded and has the signal capacitor-coupled to it. If you connect the comparator circuit's input to the input of the volume control then its AC signal swings to a positive voltage and to a negative voltage but the negative voltage will damage or destroy the input of the comparator since it does not have a dual polarity supply. An inverting opamp can be added to have an AC signal input from the input of the volume control, a single positive supply voltage (the same supply that powers the amplifiers) and have a rectified output that can safely feed DC signals to the comparator.