Nay, good sir, for I am a knave [emoji90]
I hadn't planned to, and I am not set up for REW right now, perhaps a few days when fall semester is done (about 1 more week). I will certainly take some when & if I do any EQ for them. For the matter, I am not one who collects much data like our illustrious Patrick Bateman. Usually I don't even know the accepted ways to measure. And the final disgrace: my microphone is not calibrated 🙁
I wish my engineering skills were the equal of my writing skills ("competent"). On the other hand I have that flame of tinkering (Grandpa had it too although he apparently never did anything electronic). For the Polluto, taking it as an example, I am also good at making unproven assertions 🙂
Can a good frequency response be expected from a cheap driver which is only rated 100 Hz - 10 K Hz? Listening 90 degrees off axis? In a large "Florida room" (living room) that has a sloping ceiling and other asymmetries?
I do know enough about physics and acoustics (see? I have learnt something here), that I know basically how a resonant tube (transmission line) works. With the Polluto: disadvantage: adding a port (at least at bottom) makes it less of the ideal point source. Advantage: since the line is stuffed, it filters out the higher frequencies and also allows the power of gravity to pull the bass notes, which are heavier, down the tube and flow out the rear port [emoji12]
I hadn't planned to, and I am not set up for REW right now, perhaps a few days when fall semester is done (about 1 more week). I will certainly take some when & if I do any EQ for them. For the matter, I am not one who collects much data like our illustrious Patrick Bateman. Usually I don't even know the accepted ways to measure. And the final disgrace: my microphone is not calibrated 🙁
I wish my engineering skills were the equal of my writing skills ("competent"). On the other hand I have that flame of tinkering (Grandpa had it too although he apparently never did anything electronic). For the Polluto, taking it as an example, I am also good at making unproven assertions 🙂
Can a good frequency response be expected from a cheap driver which is only rated 100 Hz - 10 K Hz? Listening 90 degrees off axis? In a large "Florida room" (living room) that has a sloping ceiling and other asymmetries?
I do know enough about physics and acoustics (see? I have learnt something here), that I know basically how a resonant tube (transmission line) works. With the Polluto: disadvantage: adding a port (at least at bottom) makes it less of the ideal point source. Advantage: since the line is stuffed, it filters out the higher frequencies and also allows the power of gravity to pull the bass notes, which are heavier, down the tube and flow out the rear port [emoji12]
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Some data. With DEQ2496 and pink noise, there is a suck out of about 8 db at 2500, 3150; then an even bigger peak around 5000. Perhaps my whizzer? Photo of current iteration (deterioration?)
An externally hosted image should be here but it was not working when we last tested it.
Thank you for your interest! I am the McGuyver of this board 🙂 Taking items of little value, assembling them into a noise maker of even less value 🙄
This project is easy enough and at least one of my fans has asked about measurements. I do have basic RTA (REW + mic) and could run some tests. I "should have" (and could on the next build and/or tear-downs of current prototypes) at least run a FR sweep for each unit.
This project is easy enough and at least one of my fans has asked about measurements. I do have basic RTA (REW + mic) and could run some tests. I "should have" (and could on the next build and/or tear-downs of current prototypes) at least run a FR sweep for each unit.
Improvised whizzer wrenched from cone, Ijit fidgets...
Not content with ok-sounding speakers, I decided two days was enough for the improvised whizzer and twisted one off. I thought I'd damaged the cone (a good guess since the sound was audibly distorted afterwards...). On the 2nd one, I was more careful and Gorilla Glue notwithstanding, I was able to snap off the second light bulb cover, er, whizzer. 🙂
Amazingly, both speakers work with no audible or bad distortion (from a quick sine sweep).
So next tweaker idea is: what to use for a real phase plug? I've read a few discussions today, that suggest at best a DIY phase plug won't make much difference, but is more likely to make matters worse. So??? I am working with a sub-$10 driver here that's already been through hell, so why not play some more with it? So off to Lowe's to see what ready-made cone-like objects are on offer (having learnt here that cabinet knobs, curtain rods parts, etc. may work).
One silly idea: with the dust cap off, could one make a "co-axial" reflex speaker? Why not? The port is in the center of the diaphragm 🙂
Not content with ok-sounding speakers, I decided two days was enough for the improvised whizzer and twisted one off. I thought I'd damaged the cone (a good guess since the sound was audibly distorted afterwards...). On the 2nd one, I was more careful and Gorilla Glue notwithstanding, I was able to snap off the second light bulb cover, er, whizzer. 🙂
Amazingly, both speakers work with no audible or bad distortion (from a quick sine sweep).
So next tweaker idea is: what to use for a real phase plug? I've read a few discussions today, that suggest at best a DIY phase plug won't make much difference, but is more likely to make matters worse. So??? I am working with a sub-$10 driver here that's already been through hell, so why not play some more with it? So off to Lowe's to see what ready-made cone-like objects are on offer (having learnt here that cabinet knobs, curtain rods parts, etc. may work).
One silly idea: with the dust cap off, could one make a "co-axial" reflex speaker? Why not? The port is in the center of the diaphragm 🙂
Thank you for your interest! I am the McGuyver of this board
Taking items of little value, assembling them into a noise maker of even less value
I dunno, man.. I'm right behind ya..
From a console stereo cut in half with a chain saw to these beauties, using cardboard boxes and some spray paint..
I dunno, man.. I'm right behind ya..
From a console stereo cut in half with a chain saw to these beauties, using cardboard boxes and some spray paint..
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Chain saw? Even I haven't used anything greater than my jigsaw 🙂 It gives me unhealthy ideas with what to do with a beat-up old 1946 ? Philco console radio someone gave me.
I would like to hear your opinon on your cardboard speakers: did you use any kind of damping on the panels? I have dabbled in this (earlier project was using two sturdy kitty litter boxes to make a "boombox" sized unit. Yours look bigger, but it's hard to judge the scale. Using cardboard (or more popular, foam board) has been a popular alternative material on this board for some time.
I would like to hear your opinon on your cardboard speakers: did you use any kind of damping on the panels? I have dabbled in this (earlier project was using two sturdy kitty litter boxes to make a "boombox" sized unit. Yours look bigger, but it's hard to judge the scale. Using cardboard (or more popular, foam board) has been a popular alternative material on this board for some time.
I spent a good hour hunting around Lowe's this evening, in search of the elusive pre-shaped phase plug. I had bought a 7/8" dowel, resigning myself to whittle or otherwise shape a pair, when in plumbing I found a pair of $0.65 each, "3/4 poly insert plug". They fit fine, perhaps too short but appears to stay in with super-glue. I mean really, using a ferrous piece to take advantage of the magnet and make it removable? That is for the timid (or people with expensive FR's). Now I will be able to glue on a golf ball or whatever the next tweak turns out to be 🙂
Do yourself a favor and buy a pair of Vifa TC9FD's for $12 ea. Perfect for these types of projects (high Qts) and they sound great.
The chain saw was used as a size management tool. All I wanted was the speakers and the whole thing was too big to fit in the Subaru..
Those are 12" alnico magnet speakers with 2" paper tweets mounted in an 18"x18" box from Walmart, lined internally with pieces of a mattress pad that I picked up at Family Dollar. They sounded better OB after I used a razor knife and cut the back of the box off. I gave them to a friend for his garage..
I'm treadin' on thin ice, being this is the full range thread but as for cardboard, there is something magic about it if you can control the resonant thing..
Those are 12" alnico magnet speakers with 2" paper tweets mounted in an 18"x18" box from Walmart, lined internally with pieces of a mattress pad that I picked up at Family Dollar. They sounded better OB after I used a razor knife and cut the back of the box off. I gave them to a friend for his garage..
I'm treadin' on thin ice, being this is the full range thread but as for cardboard, there is something magic about it if you can control the resonant thing..
Try this to reduce cardboard resonance.
http://www.diyaudio.com/forums/multi-way/265957-damping-sheets-constrained-layer-damping.html#post4144674
xrk971: thanks for the Vifa TC9FD suggestion; I looked at the Vifa line on Parts Express and the driver you cite is the most popular. One of the trials of this hobby is "analysis paralysis", in this case, the mind-boggling number of potential drivers. For now, I am quite content to experiment with the current set of drivers. If I were going to build a better model, I would seriously shop for a suitable fullrange and probably a 6" or 8" since tubes are available to match those diameters.
Meanwhile, I now have two spare carpet tubes from Lowe's behind the big sofa 🙂
You asked for FR sweeps of the Polluto. In lieu of that, I gave you the EQ for the "whizzer" experiment above (yuk!) and this one, with the dust cap removed and a modest phase plug installed, a more Bose-901 driver like EQ:
1247 Hz 3/2 Oct -12.0 dB
597 Hz 3 Oct - 4.5 dB (on a DEQ2496)
Meanwhile, I now have two spare carpet tubes from Lowe's behind the big sofa 🙂
You asked for FR sweeps of the Polluto. In lieu of that, I gave you the EQ for the "whizzer" experiment above (yuk!) and this one, with the dust cap removed and a modest phase plug installed, a more Bose-901 driver like EQ:
1247 Hz 3/2 Oct -12.0 dB
597 Hz 3 Oct - 4.5 dB (on a DEQ2496)
No plots? The Vifa is very versatile and can work in many different types of alignments. I have designed and used it in things ranging from OB, BR, MLTL, BLH, FLH, DCR, sealed, etc. it's midrange smoothness for vocals is tough to beat and it doesn't beam like a 6 or 8in fullrange. I have bought probably 2 dozen of them - highly recommend for experimenting. Look at the index page on the foam core thread and you can see all the things I have made with it.
Maybe if I build a better pair.
Ijit is taking a break from "fool-range" speaker experimentation fora few days. Instead, he's tidying up his house (no small feat) with the help of a friend. Much of the mess is of course audio gear and projects. At least stuff will get re-sorted and dusted off. I've been browsing the full range drivers and there are so many to choose from. I still have one fresh driver left; one of the Polluto's is dying but not totally dead yet. More ideas for this project, some practical, some not:
1. Instead of an adhesive like Gorilla Glue, especially for a mock-up, perhaps instead use easily removable stickum (caulk?) for likely to be replaced parts like the expendible drivers 😉
2. If you're going to experiment with phase plugs, similar advice applies.
3. If you put the tube on a wooden board (base), and plan to make it a QW tube, can the port go on bottom? In that case, you need a hole in the board and some feet to elevate the board.
4. Possible decor: In better keeping with the name "Polluto", you could decorate the tube like a smokestack. Add a tiny blinking blue LED at top to simulate the aircraft warning light.
The "Polluto" is so easy and shows much promise for the idle experimenter 🙂
1. Instead of an adhesive like Gorilla Glue, especially for a mock-up, perhaps instead use easily removable stickum (caulk?) for likely to be replaced parts like the expendible drivers 😉
2. If you're going to experiment with phase plugs, similar advice applies.
3. If you put the tube on a wooden board (base), and plan to make it a QW tube, can the port go on bottom? In that case, you need a hole in the board and some feet to elevate the board.
4. Possible decor: In better keeping with the name "Polluto", you could decorate the tube like a smokestack. Add a tiny blinking blue LED at top to simulate the aircraft warning light.
The "Polluto" is so easy and shows much promise for the idle experimenter 🙂
A semi practical idea at least for myself who is the de facto Bose 901 pimp and procurer ahem I meant rebuilder here, is to make a pair of Pollutos with the aforementioned easy release for drivers, to test the often- buggy ancient CTS drivers that come with my new acquisitions.
Finally, some sweeps!
OK, I set up the pair of Pollutos and did one sweep (two per measurement) for unit A, B and with port open or closed. The sweeps are remarkably the same, leading me to wonder if the QW tube worth the trouble? Rather than bore you, I inclose a link to the REW file you may download and play with.
Remarkably flat (+/- 5?) between roughly 70-3000 Hz. Not bad for a cheap driver.
Usual disclaimers: ECM8000 not calibrated, done aoubt 3 feet from top of cylinder and 2 feet off tile floor. Data should compare well because mic and speakers were in essentially the same positions.
Index of /shared
Then download the file "12-20-14 Polluto Sweeps.mdat"
OK, I set up the pair of Pollutos and did one sweep (two per measurement) for unit A, B and with port open or closed. The sweeps are remarkably the same, leading me to wonder if the QW tube worth the trouble? Rather than bore you, I inclose a link to the REW file you may download and play with.
Remarkably flat (+/- 5?) between roughly 70-3000 Hz. Not bad for a cheap driver.
Usual disclaimers: ECM8000 not calibrated, done aoubt 3 feet from top of cylinder and 2 feet off tile floor. Data should compare well because mic and speakers were in essentially the same positions.
Index of /shared
Then download the file "12-20-14 Polluto Sweeps.mdat"
Plotting against us!
Why of course...since the responses are so similar, here is an average (50 - 3K Hz). The response peaks about 1.7 KHz and drops more or less evenly at about 7 dB/oct. If you want a different plot just ask. This set of measurements were done below axis of the speaker, at say -30 degrees to the horizontal so it is kind of not on axis 🙂
Why of course...since the responses are so similar, here is an average (50 - 3K Hz). The response peaks about 1.7 KHz and drops more or less evenly at about 7 dB/oct. If you want a different plot just ask. This set of measurements were done below axis of the speaker, at say -30 degrees to the horizontal so it is kind of not on axis 🙂
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