Hello,
I'm building a dipole subwoofer for use strictly below 80 Hz, crossed 4th order. Drivers used are the AV15 15" aluminum subwoofer built by TC Sounds, 2 per side. EQ is a Behringer DEQ2496. Active crossover is a Rane AC23B.
Are there any compromises in using Linkwitz w-frame as seen here:
http://www.linkwitzlab.com/images/graphics/d_woof1.gif
as compared to a U-frame? I know the cavity resonance is much lower, and that reduces the useable frequency response, but that's not a problem in my application. My main issue with the design, and I'm not sure if this carries over in reality, is that both woofers are firing at a physical barrier directly in front/behind them that is parallel to the woofer, ie: perpendicular to the direction of the sound pressure.
Does this cause any problems? Is a U-frame superior in any noticeable way? The main reason I'd like to use the Linkwitz style box is:
1) the even-order distortion cancellation
2) the force-reduction due to mounting the woofers against each other (in terms of pressures applied)
3) achieving a smaller total size as compared to a U frame containing 15" drivers. A U frame with two 15" spaced as closely together as is reasonable is probably at least 35" x 18" (H x W) whereas a W-frame can be perhaps 20" x 20", which is much preferable.
Alternately, there is this configuration:
http://www.mfk-projects.com/images/dipole2.gif
But it wouldn't allow for the even-order distortion reduction, or the force cancellation. Again, worth it?
Just want to make sure before I take the plunge...
thanks in advance,
-Tal
I'm building a dipole subwoofer for use strictly below 80 Hz, crossed 4th order. Drivers used are the AV15 15" aluminum subwoofer built by TC Sounds, 2 per side. EQ is a Behringer DEQ2496. Active crossover is a Rane AC23B.
Are there any compromises in using Linkwitz w-frame as seen here:
http://www.linkwitzlab.com/images/graphics/d_woof1.gif
as compared to a U-frame? I know the cavity resonance is much lower, and that reduces the useable frequency response, but that's not a problem in my application. My main issue with the design, and I'm not sure if this carries over in reality, is that both woofers are firing at a physical barrier directly in front/behind them that is parallel to the woofer, ie: perpendicular to the direction of the sound pressure.
Does this cause any problems? Is a U-frame superior in any noticeable way? The main reason I'd like to use the Linkwitz style box is:
1) the even-order distortion cancellation
2) the force-reduction due to mounting the woofers against each other (in terms of pressures applied)
3) achieving a smaller total size as compared to a U frame containing 15" drivers. A U frame with two 15" spaced as closely together as is reasonable is probably at least 35" x 18" (H x W) whereas a W-frame can be perhaps 20" x 20", which is much preferable.
Alternately, there is this configuration:
http://www.mfk-projects.com/images/dipole2.gif
But it wouldn't allow for the even-order distortion reduction, or the force cancellation. Again, worth it?
Just want to make sure before I take the plunge...
thanks in advance,
-Tal
Tal,
The dipole configuration on Monte Kay's web page would indeed allow for even-order distortion reduction. The wiring of the drivers would be such that one cone would be moving towards its magnet and the other cone away from its magnet. There is also still force cancellation at work, although it's not a full 180 degrees in direction as in the "W"-baffle concept.
The cavity resonance freqquency from a W-frame configuration would generally be above 200Hz for typical dimensions. That would seem to be well above your area of possible usage.
I like the W-frame configuration primarily because of the force cancellation aspect. This will impart significantly less vibration and buzz into listening room floor construction than the alternative. Of course, if you listening room floor is a slab this won't be an issue.
Your project sounds viable to me and it sounds like fun.
Cheers,
Davey.
The dipole configuration on Monte Kay's web page would indeed allow for even-order distortion reduction. The wiring of the drivers would be such that one cone would be moving towards its magnet and the other cone away from its magnet. There is also still force cancellation at work, although it's not a full 180 degrees in direction as in the "W"-baffle concept.
The cavity resonance freqquency from a W-frame configuration would generally be above 200Hz for typical dimensions. That would seem to be well above your area of possible usage.
I like the W-frame configuration primarily because of the force cancellation aspect. This will impart significantly less vibration and buzz into listening room floor construction than the alternative. Of course, if you listening room floor is a slab this won't be an issue.
Your project sounds viable to me and it sounds like fun.
Cheers,
Davey.
Tal,
before delving into force cancellation et al. you should think about the main difference between U- and W/H-frames:
While H-frames are true dipoles and W-frames come close, the U-frame is by definition a cardioid, but no dipole!
Both have different advantages/shortcomings mainly with regard to room response.
So I recommend to find out first, if you want/need a dipole or a cardioid subwoofer.
Rudolf
before delving into force cancellation et al. you should think about the main difference between U- and W/H-frames:
While H-frames are true dipoles and W-frames come close, the U-frame is by definition a cardioid, but no dipole!
Both have different advantages/shortcomings mainly with regard to room response.
So I recommend to find out first, if you want/need a dipole or a cardioid subwoofer.
Rudolf
sglkev,
The H-frame setup won't yield any more output than the W-frame. The drivers excursion and Sd are the limiting factors in SPL capability.
If you need more output your best bet would be to build an additional two woofers and stack on top of the originals. That will give you a full 6db more output. The original Madisound drivers are no longer available unfortunately, but there are some alternatives.
An example stacked setup is shown at the bottom of this page:
http://www.linkwitzlab.com/woofer3.htm
Davey.
The H-frame setup won't yield any more output than the W-frame. The drivers excursion and Sd are the limiting factors in SPL capability.
If you need more output your best bet would be to build an additional two woofers and stack on top of the originals. That will give you a full 6db more output. The original Madisound drivers are no longer available unfortunately, but there are some alternatives.
An example stacked setup is shown at the bottom of this page:
http://www.linkwitzlab.com/woofer3.htm
Davey.
dipole vs. cardioid
hello,
In regards to that discussion, I'm mainly interested in a velocity-source vs. pressure source subwoofer. Additionally, as I don't have too much room to play with, a cardioid may perform better when closer to the wall.
But the main thing I'm going for (as I think all implementations will sound fantastic) is a compact box, within reason.
thanks,
-tal
hello,
In regards to that discussion, I'm mainly interested in a velocity-source vs. pressure source subwoofer. Additionally, as I don't have too much room to play with, a cardioid may perform better when closer to the wall.
But the main thing I'm going for (as I think all implementations will sound fantastic) is a compact box, within reason.
thanks,
-tal
Re: dipole vs. cardioid
I would go for a U-frame. Some reasons:
For the same output the U-frame builds half as deep as the equivalent H-frame.
If you need the sub closer than 1 m to the front wall, the U-frame will profit from a wall gain, the dipole will not. Worse: the dipole will suffer from early reflections, that cancel much bass energy.
Tal,taloyd said:
I would go for a U-frame. Some reasons:
For the same output the U-frame builds half as deep as the equivalent H-frame.
If you need the sub closer than 1 m to the front wall, the U-frame will profit from a wall gain, the dipole will not. Worse: the dipole will suffer from early reflections, that cancel much bass energy.
Here is my take on this:
1. A cardoid "subwoofer", U frame or not, acts much like normal "omni" design above about 50 Hz. This could give you a bit more "punch" in the cavity resonance region. Around 50 Hz to about 25-20 Hz the cardoid acts like a cardoid. Below this region the cardoid starts transitioning to dipole radiation.
2. Dipole "subwoofer", suffers from reduced spl across its bandwidth whereas a cardoid is about 5-6 db louder in its cardoid and omni operation region.
3. Both designs operating in free-air are velocity type as opposed to pressure type designs - which should help considerably with linear decay.
4. Proper rear wave dampening of either an H or U frame will give not only a cardoid character (as mentioned in #1), but will also effect system compliance - lowering the impeadance "bump" of the driver's fs (..like an aperiodic box). This, and the velocity character, is probably the most benefical aspect of this design at least in the freq. range you desire. Doing so allows greater amplifier control over the driver at and near fs.
Notice what GaryP has to say about rear-wave dampening here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80064&perpage=10&pagenumber=5
5. The H frame allows for non-linear 2nd order reduction (and the U doesn't). Note however that the Linkwitz H frame is compromised for both even AND odd order non-linear distortion. The "fix" to this is to "tightly" couple the drivers frames together, AND do NOT couple the H frame baffle to the drivers.
Notice what GaryP has to say about baffle vibration and non-linear odd order distortion here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80064&perpage=10&pagenumber=4
Though it was a U frame - an H frame will still have some of these problems if it isn't decoupled from the driver.
With particular emphasis on #4, AND that #5 can include #4 - I'd suggest an H* frame cardoid with the appropriate rear wave dampening. It should give you the best of everything with only a modest increase in H frame size (where the rear is slightly increased to allow room for a few spaced fiber partitions from some modest "batting").
*Note that you do not have to keep equal path lengths in this design, i.e. you might just as well "clip" the front extension of the H frame.
1. A cardoid "subwoofer", U frame or not, acts much like normal "omni" design above about 50 Hz. This could give you a bit more "punch" in the cavity resonance region. Around 50 Hz to about 25-20 Hz the cardoid acts like a cardoid. Below this region the cardoid starts transitioning to dipole radiation.
2. Dipole "subwoofer", suffers from reduced spl across its bandwidth whereas a cardoid is about 5-6 db louder in its cardoid and omni operation region.
3. Both designs operating in free-air are velocity type as opposed to pressure type designs - which should help considerably with linear decay.
4. Proper rear wave dampening of either an H or U frame will give not only a cardoid character (as mentioned in #1), but will also effect system compliance - lowering the impeadance "bump" of the driver's fs (..like an aperiodic box). This, and the velocity character, is probably the most benefical aspect of this design at least in the freq. range you desire. Doing so allows greater amplifier control over the driver at and near fs.
Notice what GaryP has to say about rear-wave dampening here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80064&perpage=10&pagenumber=5
5. The H frame allows for non-linear 2nd order reduction (and the U doesn't). Note however that the Linkwitz H frame is compromised for both even AND odd order non-linear distortion. The "fix" to this is to "tightly" couple the drivers frames together, AND do NOT couple the H frame baffle to the drivers.
Notice what GaryP has to say about baffle vibration and non-linear odd order distortion here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80064&perpage=10&pagenumber=4
Though it was a U frame - an H frame will still have some of these problems if it isn't decoupled from the driver.
With particular emphasis on #4, AND that #5 can include #4 - I'd suggest an H* frame cardoid with the appropriate rear wave dampening. It should give you the best of everything with only a modest increase in H frame size (where the rear is slightly increased to allow room for a few spaced fiber partitions from some modest "batting").
*Note that you do not have to keep equal path lengths in this design, i.e. you might just as well "clip" the front extension of the H frame.
I have a quick question. If I'm building Linkwitz W Frame with a different-sized woofer, should I scale it up or down depending on the woofer size I'm using, or should I just use his original dimensions? Also, is this design quite forgiving with different woofers that can be used?
Bumping a really old thread here, but I figured that's better than opening a new thread, as my question is in relation to the original post.
Bumping a really old thread here, but I figured that's better than opening a new thread, as my question is in relation to the original post.
Funny, are we assuming sticking a driver in a box is normal and we need to justify a dipole? Maybe a thread about the influence of boxes should be started.
Dipole discussions are always disembodied from rooms and ever-so-sophisticated comments are made about cardoid versus something else. What happens when a 50 Hz note hits a back wall a fraction of a wave-length away? Does theory goes out the window?
Better to think about managing back waves as the home reproduction issue, not just pure theory.
B.
Dipole discussions are always disembodied from rooms and ever-so-sophisticated comments are made about cardoid versus something else. What happens when a 50 Hz note hits a back wall a fraction of a wave-length away? Does theory goes out the window?
Better to think about managing back waves as the home reproduction issue, not just pure theory.
B.
Jonathan,
Yes, you'd probably need to scale the construction size based on the woofers you're using. Also, consider possible issues with installation/de-installation of the woofers. It can be a bit tricky and require some contortion skills, special tools and/or a removable panel maybe.
Those particular W-frame woofers evolved from the Audio Artistry speaker systems that Linkwitz designed back in the 1990's. At that time the Madisound woofers were selected for a variety of reasons. I suggest to read the entire portion/links of Linkwitzlab.com on this to understand the trade-offs required for driver selection.
Dipole Woofer
Generally, SL believed in using woofers that were fairly close to Qts = 0.5, but not above it. Good/long excursion capability, low distortion, and minimal aerodynamic noise when operating.
Dave.
Yes, you'd probably need to scale the construction size based on the woofers you're using. Also, consider possible issues with installation/de-installation of the woofers. It can be a bit tricky and require some contortion skills, special tools and/or a removable panel maybe.
Those particular W-frame woofers evolved from the Audio Artistry speaker systems that Linkwitz designed back in the 1990's. At that time the Madisound woofers were selected for a variety of reasons. I suggest to read the entire portion/links of Linkwitzlab.com on this to understand the trade-offs required for driver selection.
Dipole Woofer
Generally, SL believed in using woofers that were fairly close to Qts = 0.5, but not above it. Good/long excursion capability, low distortion, and minimal aerodynamic noise when operating.
Dave.
I wonder how critical the dimensions are. This is from the relevant Linkwitz article.
"As I indicated in FAQ4 I have been trying to find a large excursion 12" driver that would give me twice the useable volume displacement as the 1252DVC or X6100 for 6 dB more acoustic output at about the same level of non-linear distortion. The cabinet size should increase only marginally and the cost of the driver should not more than double.
I have come to the conclusion that it is not possible to obtain this. What is possible, though, are lower distortion at the same displacement, and about 3 dB more useable output at twice the cost and in a 2.5" wider cabinet than for the 1252DVC or X6100."
"As I indicated in FAQ4 I have been trying to find a large excursion 12" driver that would give me twice the useable volume displacement as the 1252DVC or X6100 for 6 dB more acoustic output at about the same level of non-linear distortion. The cabinet size should increase only marginally and the cost of the driver should not more than double.
I have come to the conclusion that it is not possible to obtain this. What is possible, though, are lower distortion at the same displacement, and about 3 dB more useable output at twice the cost and in a 2.5" wider cabinet than for the 1252DVC or X6100."
Dave, thank you. Noted on your suggestion to look at installing/removing the drivers. Qts of 0.5 or less might work in my favor in this case. Hopefully I can get something going. If I do, I'll report back in this thread.
Thanks again.
Hi Jonathan,
I'm currently running W-Frames using a pair of 10" high-QTS (1.12ish) woofers and am still able to achieve deep, musical bass. The Linkwitz site was great help in designing them for me, but if you're looking for similar concepts or really in-depth explanation of the theory of operation for them, you should look for slot-loaded open baffle and ripole concepts. I'll link my original thread where I got some excellent advice:
Dipole Bass Recomendations
You're right to worry about cavity resonances, but I didn't run into any real problems with my 10" woofers up until about 200Hz with a 12 dB/oct slope, so you should be fine with your 15" setup at 80 Hz with LR4 slopes.
Hope that helps you out!
I'm currently running W-Frames using a pair of 10" high-QTS (1.12ish) woofers and am still able to achieve deep, musical bass. The Linkwitz site was great help in designing them for me, but if you're looking for similar concepts or really in-depth explanation of the theory of operation for them, you should look for slot-loaded open baffle and ripole concepts. I'll link my original thread where I got some excellent advice:
Dipole Bass Recomendations
You're right to worry about cavity resonances, but I didn't run into any real problems with my 10" woofers up until about 200Hz with a 12 dB/oct slope, so you should be fine with your 15" setup at 80 Hz with LR4 slopes.
Hope that helps you out!
Hi there, thank you very much for sharing. I have checked the thread that you linked. Sorry it seems the reference about cavity resonances and 15" woofers are the original poster's questions. I have a small Pioneer woofer that I'm trying to find a use for, so it's a really humble project
Thanks again.- Status
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