Ok here it is, i made a box with internal dimensions 18" x 18" x 22.5", i forget the cu. footage offhand but it is almost 4 i think. anyways, i have a dayton DVC 15" driver and 2 old mtx terminators 15" speakers as the PR's. I have already added over a kilogram to the speakers and the freq response is nowhere near the expected values. winisd said i should be 3db down at around 28 hertz with 1000 grams on the PR's. i have more than that on the PR's (not much more) and the response is crazy. it is 101db at63hz, then it is 96db @ 44hz and it keeps going down from there. should i shell out the big bucks and pay for the dayton PR's? should i stuff the box with some dacron or fiberglass? I already spent almost 200 bucks on the box alone so i can't scrap it. With the mtx's, i crank up the volume and it makes wierd noises, i just think it is because i didn't put all the screws in, but i know it doesn't have all the excursion the dayton has. pleeze help, i am up to my neck in this project, wallet is running empty. I will delay this project as long as it takes i guess. the box without the speakers weighs in at 100lbs by the way/ i am proud of it. I will make a thread about the project at some point. Thanks
Mike
Mike
The MTX Terminators you use as Drone Cones, (Passive Radiators), have weight on them to begin with.
I hope your weights are removable.
Have you tried making the Drone Cones lighter?
Reason I am asking is that if you tune either a vented box or a Passive Radiator box too low, it will begin to take on the frequency response of a Closed Box, which means less output in the bass range.
That sounds like what is happening here.
Try putting 600 g on the Passive Radiators and see what your output is there.
An 18" by 18" by 22.5" box is 4.2 Ft³, or 119.3 liters, if any Metric folks want to join in. 🙂
I hope your weights are removable.
Have you tried making the Drone Cones lighter?
Reason I am asking is that if you tune either a vented box or a Passive Radiator box too low, it will begin to take on the frequency response of a Closed Box, which means less output in the bass range.
That sounds like what is happening here.
Try putting 600 g on the Passive Radiators and see what your output is there.
An 18" by 18" by 22.5" box is 4.2 Ft³, or 119.3 liters, if any Metric folks want to join in. 🙂
I just looked up the mmd, (moving mass) of some MTX 15 inch subs, and that particular model had 125 grams on it.
If your MTX's have similar weight, then you are starting out with 250 grams on the Passive Radiators already.
Add over 1000 g and it looks like you are going too low.
Incidentally, do you know how to measure speaker impedance? You should have lowest impedance at the frequency you wish to tune the box to, that goes for a Passive Radiator or a vented box. Measuring impedance-cheap and easy to do-will tell you what your box is tuned to. All it requires is a cheap multimeter that measure AC voltage-which most people have handy, (or can borrow).
If your MTX's have similar weight, then you are starting out with 250 grams on the Passive Radiators already.
Add over 1000 g and it looks like you are going too low.
Incidentally, do you know how to measure speaker impedance? You should have lowest impedance at the frequency you wish to tune the box to, that goes for a Passive Radiator or a vented box. Measuring impedance-cheap and easy to do-will tell you what your box is tuned to. All it requires is a cheap multimeter that measure AC voltage-which most people have handy, (or can borrow).
First thing, how did you measure the speakers and what environment are they in? This makes a big difference, as LF measurements are difficult.
The easiest way to determine the amount of mass you need is to calculate the port length needed for a port with the area of your PR.
in a ~120L box, tuned to ~20Hz, you would need a port ~10.4 meters long.
The mass of air in this would be 1.8kg., so you will need about 650-700 grams on each PR, after subtracting off the existing mass of the cones.
The easiest way to determine the amount of mass you need is to calculate the port length needed for a port with the area of your PR.
in a ~120L box, tuned to ~20Hz, you would need a port ~10.4 meters long.
The mass of air in this would be 1.8kg., so you will need about 650-700 grams on each PR, after subtracting off the existing mass of the cones.
I started off by having no weight on the PR's, then i took a freq response with my radio shack spl meter, i did it outside with a test disc i made on my own about 4 inches from the cone. i used the correction values i found on the internet. then i took another freq response after adding 9 ounces each, the freq response seemed a little more extended, only by a few hz though. so i added another 9 ounces on it and took another freq response, another few hz added to the graph i made. so i went out and bought a 16 oz weight and added that too, so now the weight ADDED to the cones is over 2 LBS each. i took another freq response, and only a few more hz were added.
I have the equipment to take a impedence chart but i didn't even think of that. I am still dumbfounded. so it is looking like the most accurate wa to find out if the box is tuned correctly would be an impedence graph instead of a freq response then.
BTW the weights are kinda removable, the speakers are not the greatest so if i mess up the cone tearing off weights it is no big deal.
I have the equipment to take a impedence chart but i didn't even think of that. I am still dumbfounded. so it is looking like the most accurate wa to find out if the box is tuned correctly would be an impedence graph instead of a freq response then.
BTW the weights are kinda removable, the speakers are not the greatest so if i mess up the cone tearing off weights it is no big deal.
Close miked measurements will not get you a frequency response curve for the whole system. You will get a response for the woofer only, without the contribution from the PR's. A close miked response _will_ tell you where the tuning frequency is, because there will be a notch (a very sharp dip with little or no output) in the woofer close miked SPL at the tuning frequency. This notch is much more accurate indication of tuning than the impedance curve.
Looking back at the parameters of the woofer, a 120L enclosure is rather small for that woofer, although box design also depends on how you will connect the woofer to the amp. Are the coils in series or parallel or ?
I suggest you measure the parameters and model with something a little more powerful than WinISD.
Looking back at the parameters of the woofer, a 120L enclosure is rather small for that woofer, although box design also depends on how you will connect the woofer to the amp. Are the coils in series or parallel or ?
I suggest you measure the parameters and model with something a little more powerful than WinISD.
why didn't i think of that! genius, pure genius! 
i could measure the response of the PR's and superimpose it on the graph of the driver's response. Eureka! The voice coils are paralell. I was trying for as small a box as possible due to WAF. I dismantled my 9 cu ft. sonotube subwoofer for this little endeavour, i am going to keep it because you never know when you need a 9 cu. ft. tube of cardboard. what software would you suggest that is more powerful than winisd, that is affordable or free as my budget is TIGHT! just lost my job, well kinda, outta the military finally. 
mike
Okay i measured the freq response of one of the PR's and it pretty much filled in most of the area where the driver was going Kaput, but the PR is putting out about 13 db less than the driver, is there a way to measure bothe the PR's, or maybe add them together? they are on different sides of the box. and how do i add 80 db plus 80db? would it be 83db? i know it isn't 160, i am not very good at math.
mike
mike
First, you have two Drone Cones and one is 13 dB down from the woofer. That relationship should change with frequency.
Second, the two Drone Cones put out 6 dB more than each individually. So the Drone Cones are 7 dB down. If the highest the Drone Cones get compared to the woofer is that, then something is amiss. At the resonance frequency, the output of the Drone Cones should be considerably higher than the woofer.
The guess here is, you still probably are tuned too low.
Second, the two Drone Cones put out 6 dB more than each individually. So the Drone Cones are 7 dB down. If the highest the Drone Cones get compared to the woofer is that, then something is amiss. At the resonance frequency, the output of the Drone Cones should be considerably higher than the woofer.
The guess here is, you still probably are tuned too low.
Speekergeek:
I might have a problem with your selection of woofer.
I looked up the woofer at the Parts Express website. It said nothing of a symmetric magnetic field, extended pole piece, Faraday ring, shorting ring, or reduced second order distortion because of magnetic linearities.
A woofer in a Vented or Passive Radiator system, when driven just moderately hard, will actually leave it's midpoint and go all the way to end of it's travel, reducing output and producing awful distortion-actually clipping the waveform in half!
Here is an explanation:
http://www.diyaudio.com/forums/showthread.php?threadid=4524&highlight=
Unless a manufacturer tells you that it has a symmetrical magnetic field, or shorting ring, it probably does not have it on the woofer.
However, I think there is a chance that this woofer might have the symmetrical field. That is because this woofer sure looks like Parts Express' version of the Adire Tempest. The construction is similar, the Thiele-Small parameters are similar, even the language the two companies use to describe the woofer is similar.
Interestingly, even Adire does not speak of a symmetrical field except in the Tempest White Paper, where it is mentioned in the pole piece section. Most companies with symmetrical fields tell you right off.
The price of this woofer is only $15 less than a Tempest. Unless it has a symmetrical field, I would trade it in for a Tempest-much better value.
I have used Parts Express, and they are a good outfit with good products. I have a hunch they may have built in a symmetrical magnetic field, and forgot to mention it. Hard to believe that they would make such a long throw woofer without using one.
But I would definitely call their toll free help line tomorrow to find out. Ask about a symmetrical magnetic field, an extended, (not vented), pole piece, or a shorting ring. Make sure you get someone who is not "winging it" on the other end-someone who knows what you are talking about.
Otherwise, I would not use this woofer. It is expensive, and for the money you should get one with a symmetrical magnetic field. Otherwise, you will get high distortion at the lowest bass ranges.
I might have a problem with your selection of woofer.
I looked up the woofer at the Parts Express website. It said nothing of a symmetric magnetic field, extended pole piece, Faraday ring, shorting ring, or reduced second order distortion because of magnetic linearities.
A woofer in a Vented or Passive Radiator system, when driven just moderately hard, will actually leave it's midpoint and go all the way to end of it's travel, reducing output and producing awful distortion-actually clipping the waveform in half!
Here is an explanation:
http://www.diyaudio.com/forums/showthread.php?threadid=4524&highlight=
Unless a manufacturer tells you that it has a symmetrical magnetic field, or shorting ring, it probably does not have it on the woofer.
However, I think there is a chance that this woofer might have the symmetrical field. That is because this woofer sure looks like Parts Express' version of the Adire Tempest. The construction is similar, the Thiele-Small parameters are similar, even the language the two companies use to describe the woofer is similar.
Interestingly, even Adire does not speak of a symmetrical field except in the Tempest White Paper, where it is mentioned in the pole piece section. Most companies with symmetrical fields tell you right off.
The price of this woofer is only $15 less than a Tempest. Unless it has a symmetrical field, I would trade it in for a Tempest-much better value.
I have used Parts Express, and they are a good outfit with good products. I have a hunch they may have built in a symmetrical magnetic field, and forgot to mention it. Hard to believe that they would make such a long throw woofer without using one.
But I would definitely call their toll free help line tomorrow to find out. Ask about a symmetrical magnetic field, an extended, (not vented), pole piece, or a shorting ring. Make sure you get someone who is not "winging it" on the other end-someone who knows what you are talking about.
Otherwise, I would not use this woofer. It is expensive, and for the money you should get one with a symmetrical magnetic field. Otherwise, you will get high distortion at the lowest bass ranges.
I didn't really understand alot of that last post, although i did check out the link and i can say i did notice that when the excursion of the woofer was high that it tended to "migrate" and stay a certain amount out from its normal position. i was curious so i turned the phase switch and saw it move in and out. i just set it halfway. As for too much weight, i took off 18 oz of weight earlier. I am still puzzled on how to accuratly measure the freq response.
Speekergeek:
The effect is greatest near the tuning frequency.
You don't even know what frequency the speaker is tuned now, so you don't know if the "suck-in" will come into effect.
As you move your frequency generator down the frequency scale, as your frequency approaches resonance, the cone gets displaced to the extreme of it's travel. It can only move in one direction from that point. It therefore cuts off half the waveform. I've seen it, and it is very significant.
With this price, I would insist on a symmetrical magnetic field. It really shouldn't have much to do with the phase adjustment on your sub amp, I wouldn't think.
I suggest you call Parts Express. Ask about extened pole piece or Faraday ring.
The effect is greatest near the tuning frequency.
You don't even know what frequency the speaker is tuned now, so you don't know if the "suck-in" will come into effect.
As you move your frequency generator down the frequency scale, as your frequency approaches resonance, the cone gets displaced to the extreme of it's travel. It can only move in one direction from that point. It therefore cuts off half the waveform. I've seen it, and it is very significant.
With this price, I would insist on a symmetrical magnetic field. It really shouldn't have much to do with the phase adjustment on your sub amp, I wouldn't think.
I suggest you call Parts Express. Ask about extened pole piece or Faraday ring.
I sent parts express a nasty email. 
just kidding. before now i never even knew what a faraday ring was. thank you for opening my eyes. I am going to check out the tempest while i wait for a reply from parts express. I guess i still have a lot to learn about audio reproduction. I am thirsting for knowledge by the by. So you are saying either i should save up and buy a tempest and use their PR's (most likely). and either sell the dayton or build a sealed box for it? what do you think. I definitly don't want all the work and money i have put into this box to go to waste. should i put the project off until i get $$$ to buy a tempest. are you an adire audio representative? 😉
just kidding. before now i never even knew what a faraday ring was. thank you for opening my eyes. I am going to check out the tempest while i wait for a reply from parts express. I guess i still have a lot to learn about audio reproduction. I am thirsting for knowledge by the by. So you are saying either i should save up and buy a tempest and use their PR's (most likely). and either sell the dayton or build a sealed box for it? what do you think. I definitly don't want all the work and money i have put into this box to go to waste. should i put the project off until i get $$$ to buy a tempest. are you an adire audio representative? 😉Parts express emailed me ack and said the dayton dvc does not have a faraday ring or a bumped back plate 🙁 . that sucks. what good is this subwoofer without it? do i have to have these things to have a good subwoofer? I think i may be selling it on ebay soon and using Xmas money to buy a tempest...... or maybe a Timult!! ( laughes maniacally) and a parts express 1k watt sub amp. that is almost a grand right there, plus i would need better PR's, that is another 200 bucks right there. whew! expensive hobby this is!
Many use this driver with great success. Try a simple ported box. You don't even own any proper PRs, just some old drivers. Try again with the Dayton PRs that are designed to match the DVC 15".
BAM:
The "suck-out" problem exists in both the Vented Box and Passive Radiator Box.
A Drone Cone box works on the same principles as a Vented
box, and despite a slightly different response formula, is essentially identical with it. Build a box for a Vented enclosure, and you can stick a Passive Radiator in there and it will work if the correct weight is added.
In fact, the term Bass Reflex applies to both the Passive Radiator box and Vented box, but in practice people only apply it to the Vented Box.
The main difference between Passive Radiator and Vented is that the Passive Radiator has a resonance itself, below the box's resonant frequency, and this tends to steepen the cutoff slope, worsening the transient response of the system slightly.
The advantage of the Pssive Radiator is there is port noise, and on enclosures tuned extremely low, you don't have to build a port so large that a significant portion of the internal box volume is taken up by the port.
The "suck-out" problem exists in both the Vented Box and Passive Radiator Box.
A Drone Cone box works on the same principles as a Vented
box, and despite a slightly different response formula, is essentially identical with it. Build a box for a Vented enclosure, and you can stick a Passive Radiator in there and it will work if the correct weight is added.
In fact, the term Bass Reflex applies to both the Passive Radiator box and Vented box, but in practice people only apply it to the Vented Box.
The main difference between Passive Radiator and Vented is that the Passive Radiator has a resonance itself, below the box's resonant frequency, and this tends to steepen the cutoff slope, worsening the transient response of the system slightly.
The advantage of the Pssive Radiator is there is port noise, and on enclosures tuned extremely low, you don't have to build a port so large that a significant portion of the internal box volume is taken up by the port.
Speekergeek:
I took the liberty of calling up Parts Express this morning to ask about the same thing you did.
First, I asked abouut a symmetrical magnetic filed, to prevent the cone from going to the end of it's travel. I asked the tech if he knew what I was talking about. "No", he said.
The tech assured me that he owned this model and there were no magnetic nonlinearities. But the tech admitted that he used this in a sealed box. Although I have read of this phenomenon occurring in a sealed box, I have never observed it in one-only a vented box.
However, the tech told me that the woofer has a shorting ring? "Are you sure?" I asked. "Do you have the spec sheet or whatever that specifically says so? Because neither your online nor print catalog mentions it", I said.
"Well, with an excursion like that, it should", the tech said. However, he said nothing that indicated specifically that he knew that for a fact. He repeated that he saw no magnetic irregularities in his home system. But of course, that was a sealed box.
In other words, I really got no assurances from Parts Express Tech Support that the woofer had that shorting ring.
To be honest, I was somewhat surprised that the tech mentioned a ring. In theParts Express top-of-the-line Titanic, 10 and 12 inch, they achieve magnetic symmetry not with a shorting ring, but with an extended pole piece.
Moreover, the woofer strikes me as a clone of the Adire Tempest, (I have no connection with Adire-in fact, I never used one of their products in a box, I just know from others here that the Shiva and Tempest are good products). Anyway, the Tempest has an extended pole piece, though you have to go to their White Paper and look for the evidence of that.
Also, in talking with Parts Express a couple of years ago, the tech actually admitted that an earlier version of the 15" Dual Voice Coil subwoofer was made by Eminence, (they aren't supposed to admit that). Well, the Adire Shiva I am told is made by Eminence, and therefore I would presume the Tempest as well. This adds more weight to the theory that the Parts Express DVC 15" is a clone of the Tempest.
In addition, I would point out that in it's better PA speakers, Eminence is beginning to add an extended pole piece. Which means that an extended pole piece is becoming a normal feature of the Eminence line.
So I think there is a good chance your Parts Express 15" Dual Voice Coil Subwoofer has this extended pole piece, (Eminence calls it an "extended core"-same thing), which is an alternate method to achieve magnetic symmetry and prevent "suck-in".
I am considering sending an Email to Parts Express to ask about the extended pole piece specifically. You can, if you wish, as well.
Even if your woofer doesn't have a symmetrical magnetic field, it is already bought and should be finished in a couple of days. Let's tune it and see what happens. If it stays at the midpoint at resonance, then you have no problem. If not, why not return it?
One more thing-I mentioned that if you tuned the Passive Radiators too low, the speaker begins to take on the characterisitics of a Closed Box. Well, a Closed box will work well in a 4.3 Ft³ enclosure. I know you don't want to take the Passive Radiators out. But you can aadd extra weight to them so they get tuned so low that the entire enclosure resembles the output of a Closed Box. At that point, you won't need a symmetrical magnetic field, because Closed boxes tend to not require it, for some reason.
So all might not be lost. Don't give up on this woofer yet. 🙂
I took the liberty of calling up Parts Express this morning to ask about the same thing you did.
First, I asked abouut a symmetrical magnetic filed, to prevent the cone from going to the end of it's travel. I asked the tech if he knew what I was talking about. "No", he said.
The tech assured me that he owned this model and there were no magnetic nonlinearities. But the tech admitted that he used this in a sealed box. Although I have read of this phenomenon occurring in a sealed box, I have never observed it in one-only a vented box.
However, the tech told me that the woofer has a shorting ring? "Are you sure?" I asked. "Do you have the spec sheet or whatever that specifically says so? Because neither your online nor print catalog mentions it", I said.
"Well, with an excursion like that, it should", the tech said. However, he said nothing that indicated specifically that he knew that for a fact. He repeated that he saw no magnetic irregularities in his home system. But of course, that was a sealed box.
In other words, I really got no assurances from Parts Express Tech Support that the woofer had that shorting ring.
To be honest, I was somewhat surprised that the tech mentioned a ring. In theParts Express top-of-the-line Titanic, 10 and 12 inch, they achieve magnetic symmetry not with a shorting ring, but with an extended pole piece.
Moreover, the woofer strikes me as a clone of the Adire Tempest, (I have no connection with Adire-in fact, I never used one of their products in a box, I just know from others here that the Shiva and Tempest are good products). Anyway, the Tempest has an extended pole piece, though you have to go to their White Paper and look for the evidence of that.
Also, in talking with Parts Express a couple of years ago, the tech actually admitted that an earlier version of the 15" Dual Voice Coil subwoofer was made by Eminence, (they aren't supposed to admit that). Well, the Adire Shiva I am told is made by Eminence, and therefore I would presume the Tempest as well. This adds more weight to the theory that the Parts Express DVC 15" is a clone of the Tempest.
In addition, I would point out that in it's better PA speakers, Eminence is beginning to add an extended pole piece. Which means that an extended pole piece is becoming a normal feature of the Eminence line.
So I think there is a good chance your Parts Express 15" Dual Voice Coil Subwoofer has this extended pole piece, (Eminence calls it an "extended core"-same thing), which is an alternate method to achieve magnetic symmetry and prevent "suck-in".
I am considering sending an Email to Parts Express to ask about the extended pole piece specifically. You can, if you wish, as well.
Even if your woofer doesn't have a symmetrical magnetic field, it is already bought and should be finished in a couple of days. Let's tune it and see what happens. If it stays at the midpoint at resonance, then you have no problem. If not, why not return it?
One more thing-I mentioned that if you tuned the Passive Radiators too low, the speaker begins to take on the characterisitics of a Closed Box. Well, a Closed box will work well in a 4.3 Ft³ enclosure. I know you don't want to take the Passive Radiators out. But you can aadd extra weight to them so they get tuned so low that the entire enclosure resembles the output of a Closed Box. At that point, you won't need a symmetrical magnetic field, because Closed boxes tend to not require it, for some reason.
So all might not be lost. Don't give up on this woofer yet. 🙂
WOW! 
you have really gone out of your way to help me. i very much appreciate it. You have much more knowledge about speakers than i do and you knew all the right questions to ask. i did send them an email but they probably just looked at the catalog for the answer. you did some sherlock holmes work. THX bigtime. back to the matter at hand, i have been recording the freq response in the backyard (which is about 9 feet by 25 feet with a 5 foot fence all around) I have put it in a corner and measured the response from 4 different points, i would turn the speaker 90 degrees and make a graph, i did that four times. should these combined give me a good idea of the general freq response? should i move the speaker out in the open field and do it, then in the house? that is a lot of lugging around a 100+ Lb subwoofer, i will have to put handles on it! i can hide it with the grill cloth. sadly i cannot return the sub as i bought it last year and have had it in another box for a long time, but it may not be a bad thing if the speaker is a tempest clone as you say.
would there be any tell-tale signs of a extended pole piece that i could tell without dismantling the speaker? I have read about DIY faraday rings wrapped around the speaker magnet, is this worth the trouble? i read that it was mostly for extending the upper freq response.
you have really gone out of your way to help me. i very much appreciate it. You have much more knowledge about speakers than i do and you knew all the right questions to ask. i did send them an email but they probably just looked at the catalog for the answer. you did some sherlock holmes work. THX bigtime. back to the matter at hand, i have been recording the freq response in the backyard (which is about 9 feet by 25 feet with a 5 foot fence all around) I have put it in a corner and measured the response from 4 different points, i would turn the speaker 90 degrees and make a graph, i did that four times. should these combined give me a good idea of the general freq response? should i move the speaker out in the open field and do it, then in the house? that is a lot of lugging around a 100+ Lb subwoofer, i will have to put handles on it! i can hide it with the grill cloth. sadly i cannot return the sub as i bought it last year and have had it in another box for a long time, but it may not be a bad thing if the speaker is a tempest clone as you say. would there be any tell-tale signs of a extended pole piece that i could tell without dismantling the speaker? I have read about DIY faraday rings wrapped around the speaker magnet, is this worth the trouble? i read that it was mostly for extending the upper freq response.
I really doh't know about telltale signs plainly visible for an extended pole piece.
Faraday ring aroudn the magnet? Don't know about that one. Which is not to say it won't work, only that I had not heard about it.
Sent an Email to Parts Express. However, my web-based Email isn't working right now-hope they don't miss Parts Express' answer.
Faraday ring aroudn the magnet? Don't know about that one. Which is not to say it won't work, only that I had not heard about it.
Sent an Email to Parts Express. However, my web-based Email isn't working right now-hope they don't miss Parts Express' answer.
PS: I really didn't do all this research just for you. I pick up this these things over time, such as the fact that the Shiva and the Tempest are good speakers and that they are made by Eminence, (well, the Shiva for sure-Tempest probably). And I called Eminence about extended pole pieces, ("cores") out of my own curiosity some months ago.
Symmetrical magnetic fields are something of a big point with me, ever since I saw the effects in a ported box of not having one. Really, with the ported box becoming more popular than the sealed, people should know about these things, and manufacturers should make every speaker with a symmetrical field. Even an extened core is just ¼" or less of pole piece material. How much can that cost?
I did make that 3 minute phone call to Parts Express on your behalf, true.
I think that every bit of knowledge on this board helps somebody, who helps somebody else, etc.
Symmetrical magnetic fields are something of a big point with me, ever since I saw the effects in a ported box of not having one. Really, with the ported box becoming more popular than the sealed, people should know about these things, and manufacturers should make every speaker with a symmetrical field. Even an extened core is just ¼" or less of pole piece material. How much can that cost?
I did make that 3 minute phone call to Parts Express on your behalf, true.
I think that every bit of knowledge on this board helps somebody, who helps somebody else, etc.
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