Hi
These Aura Cougar NSW1 drivers are very small and have a high X-max of 4.5mm.
What would be a suitable passive radiator for them to be used with 2 of them in a small enclosure?
The reason I am asking this is because on the product page, there is a suggestion by one guy that if used with a Peerless 3.5 inch PR, it will tune it too low and this may damage the driver. They say this because they dont have an "appropriate" sized PR.
So effectively what is the efficient way to determine the passive radiator suitable, not just for this driver but for any other driver.
Thanks.
These Aura Cougar NSW1 drivers are very small and have a high X-max of 4.5mm.
What would be a suitable passive radiator for them to be used with 2 of them in a small enclosure?
The reason I am asking this is because on the product page, there is a suggestion by one guy that if used with a Peerless 3.5 inch PR, it will tune it too low and this may damage the driver. They say this because they dont have an "appropriate" sized PR.
So effectively what is the efficient way to determine the passive radiator suitable, not just for this driver but for any other driver.
Thanks.
They have a Q of 0.7, which is rather high for a ported or passive radiator design. I would not use either. If you need more bass, cross to a small woofer.
If you search for passive radiator tuning on this forum I have answered your other question many times.
If you search for passive radiator tuning on this forum I have answered your other question many times.
Hi
Thanks. The reason for this one was that I was not able to ascertain if PR would be suitable or not, and how to validate and determine the correct size. Since you now mentioned that Qt is high, I now know one parameter. But I guess the exact value would remain attached to other parameters, right?
Thanks. The reason for this one was that I was not able to ascertain if PR would be suitable or not, and how to validate and determine the correct size. Since you now mentioned that Qt is high, I now know one parameter. But I guess the exact value would remain attached to other parameters, right?
You should look for drivers that have T/S params designed and optimized for a vented design. In designing boxes for PR's the PR effectively substitutes as the vent. You need to use software to design your bass reflex box and play with different drivers to see which one is capable of getting the SPL level and bass extension you desire as a bass reflex desig first. Use WinISD if you haven't downloaded that already and try to design a BR box. Now take that driver and box volume and design a PR around it vs using the vent. There are other ways to do this but I know Akabak can do this very easily.
For TS params needed for a vented box, look for low to moderate Qts of say 0.3 to 0.45, and look for large xmax. This is tough to find on a small 3 in or smaller driver so you may have to live with larger Qts. It is not that it can't be done, just that it is not ideal as the volume will be larger and you may get a bass peak at the response "knee". PR's can be made from any normal driver by running it without hooking up the leads and adding mass to tune it. With regards to over-excursion on the main driver, the software is needed to check xmax and max drive levels and you have to stay within those levels when operating.
For TS params needed for a vented box, look for low to moderate Qts of say 0.3 to 0.45, and look for large xmax. This is tough to find on a small 3 in or smaller driver so you may have to live with larger Qts. It is not that it can't be done, just that it is not ideal as the volume will be larger and you may get a bass peak at the response "knee". PR's can be made from any normal driver by running it without hooking up the leads and adding mass to tune it. With regards to over-excursion on the main driver, the software is needed to check xmax and max drive levels and you have to stay within those levels when operating.
Thanks. That was valuable.
I am not justifying myself, but WinISD somehow refused to run on my Windows 7. So only way to find some detail about drivers was resorting to questions on forums.
So actually are there any handy formulas, so I can work with and find the answer for this driver?(And for other drivers too)
Thanks.
I am not justifying myself, but WinISD somehow refused to run on my Windows 7. So only way to find some detail about drivers was resorting to questions on forums.
So actually are there any handy formulas, so I can work with and find the answer for this driver?(And for other drivers too)
Thanks.
The handy formulas, developed by Thiele-Small are kind of complex 2nd order differential equations and solutions. You can also do it with SPICE or any other circuit modeling program, as well as Mathcad, Matlab, etc. Basically, need a way to solve 2nd order differential equations.
http://en.wikipedia.org/wiki/Thiele/Small
Here is a way to do it with SPICE (which is freely available in various incarnations as it was developed under academia).
http://micka.de/org/en/download/spice-tsp_en.pdf
http://en.wikipedia.org/wiki/Thiele/Small
Here is a way to do it with SPICE (which is freely available in various incarnations as it was developed under academia).
http://micka.de/org/en/download/spice-tsp_en.pdf
I don't have the beta version up, but I do run the Pro Alpha version. Runs fine in W7, W8, W8.1. Set the compatibility mode to "XP Service Pack 2".
Bob
@xrk971
I did some testing and found that two Fountek FR58EX in a vented enclosure, 7x4x3 inch internal, with 1" diameter, 4" long port will tune the box to about 95 Hz.
Since I dont prefer a vent, can you help me with determining the appropriate passive, that will tune it to 80Hz.? How can I move from here.
Find me some passive radiators you are willing to use size wise. Need their TS params. Alternatively, find a driver that has long xmax that is about right size with fs as low as possible. We can add mass to it to turn into a PR.
Ummm... depending on how low in freq it is tuned, a good rule of thumb is to pick a PR that has minimum 2x the surface area for equal Xmax. The TS params of the PR are somewhat irrelevant, if they exist at all. Unless I misunderstood what was written. Another way to look at it is to use a PR that is at least 1 driver sizer up or two, two is better. So for a 5.25" driver a minimum 8" PR. A 10" would be larger but better.
The lower the tuning the more important the area of the PR and xmax of it becomes.
The lower the tuning the more important the area of the PR and xmax of it becomes.
If you are going to model the PR, there are still mechanical params like fs, Cms, Rms, Mms, Sd. Take for example the 3.5 inch Peerless:
Peerless 830878 3-1/2" Passive Radiator
http://www.parts-express.com/pedocs/specs/264-1060-peerless-830878-specifications.pdf
at $11 it might be something that can work here.
Peerless 830878 3-1/2" Passive Radiator
http://www.parts-express.com/pedocs/specs/264-1060-peerless-830878-specifications.pdf
at $11 it might be something that can work here.
Ok
So I found a two 2inch micro subwoofer with a high X-max and low Fs.
Tang Band W2-2040S 2" RBM Micro Subwoofer 4 Ohm
Tang Band W2-1625SA 2" Neodymium Subwoofer
As a sidenote I actually found an application where two Dayton Audio ND65-4 with that Peerless 3.5inch PR can be used in a small enclosure of 7x4x3 inch. But the prob is that its sensitivity is low. And somehow judging with the reviews, the sound is OK compared to what you will get from the Founteks. Moreover I believe Fountek is weather resistant(and not much cost). Thats a plus.
Thanks.
So I found a two 2inch micro subwoofer with a high X-max and low Fs.
Tang Band W2-2040S 2" RBM Micro Subwoofer 4 Ohm
Tang Band W2-1625SA 2" Neodymium Subwoofer
As a sidenote I actually found an application where two Dayton Audio ND65-4 with that Peerless 3.5inch PR can be used in a small enclosure of 7x4x3 inch. But the prob is that its sensitivity is low. And somehow judging with the reviews, the sound is OK compared to what you will get from the Founteks. Moreover I believe Fountek is weather resistant(and not much cost). Thats a plus.
Thanks.
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Have you worked out all the requirements for your design? You are going to have some trouble getting the tuning right in a passive radiator design that small.
I played around with the passive radiator calculator here:
mh-audio.nl - Home
Based on the pair of Fountek drivers you specified you will need a PR with an Sd of around 50-70 cm sq. The only small PR that I know of is the Peerless 830878, with a Sd of 50 cm sq.
In a PR design the moving mass substitutes for the mass of air in the port. A 3 inch cone is approximately the same as a 3 inch port. In order to tune the PR to 95 Hz you need a light cone. The Peerless PR is much too heavy for this application, at 38.5 grams it is more than 30 grams too heavy. You will end up with tuning of around 40 Hz. An alternative is to find a small speaker with a lighter cone and use that as your PR. The Tymphany/Peerless 830855 appears to be very close to what you need, but there may be others that I don't know about.
PR designs roll off quicker than ported designs and have a "notch" in the response at the Fs of the PR (different from the tuning frequency). Ideally you want a very low Fs. The 830855 has the right moving mass for your application, but an Fs of about 63 Hz, which isn't very low.
Going a bit larger for the PR will help. As you increase the PR diameter you need to increase the PR mass to maintain the same tuning frequency. And that extra mass lowers the Fs. At an Sd of 50 cm sq. in your 1.4 liter box you need 6.8 grams of moving mass for 95-Hz tuning. But if you increase the PR size to 87 cm sq. (a 5.25-inch woofer) you need 21 grams of moving mass. This means adding approximately 10 or 12 grams to the typical woofer of that size, but it also allows you to fine-tune it and lowers the notch frequency too.
But if you are going to purchase a 4-inch or 5-in woofer then why not use it as a woofer? Is box size an issue? Those Fountek 2-inchers can move more air than most speakers their size, but could use some help.
I played around with the passive radiator calculator here:
mh-audio.nl - Home
Based on the pair of Fountek drivers you specified you will need a PR with an Sd of around 50-70 cm sq. The only small PR that I know of is the Peerless 830878, with a Sd of 50 cm sq.
In a PR design the moving mass substitutes for the mass of air in the port. A 3 inch cone is approximately the same as a 3 inch port. In order to tune the PR to 95 Hz you need a light cone. The Peerless PR is much too heavy for this application, at 38.5 grams it is more than 30 grams too heavy. You will end up with tuning of around 40 Hz. An alternative is to find a small speaker with a lighter cone and use that as your PR. The Tymphany/Peerless 830855 appears to be very close to what you need, but there may be others that I don't know about.
PR designs roll off quicker than ported designs and have a "notch" in the response at the Fs of the PR (different from the tuning frequency). Ideally you want a very low Fs. The 830855 has the right moving mass for your application, but an Fs of about 63 Hz, which isn't very low.
Going a bit larger for the PR will help. As you increase the PR diameter you need to increase the PR mass to maintain the same tuning frequency. And that extra mass lowers the Fs. At an Sd of 50 cm sq. in your 1.4 liter box you need 6.8 grams of moving mass for 95-Hz tuning. But if you increase the PR size to 87 cm sq. (a 5.25-inch woofer) you need 21 grams of moving mass. This means adding approximately 10 or 12 grams to the typical woofer of that size, but it also allows you to fine-tune it and lowers the notch frequency too.
But if you are going to purchase a 4-inch or 5-in woofer then why not use it as a woofer? Is box size an issue? Those Fountek 2-inchers can move more air than most speakers their size, but could use some help.
Well the original question was about finding/using a PR.
Now, what is the question, designing a speaker? To do that you have to define what ur trying to do more fully.
Any dirt cheap larger speaker with the magnet removed and maybe the pole piece cut away with a hole saw (to permit greater rearward excursion) that also has a suitable Xmax and construction will make a good enough PR.
All small wide range speakers tend to be low sensitivity...
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stevebogus, what "notch" is this? don't think I have come across this before. Afaik the Fs of the PR in the box is the center or max output point of what is a pretty smooth curved response.
Now, what is the question, designing a speaker? To do that you have to define what ur trying to do more fully.
Any dirt cheap larger speaker with the magnet removed and maybe the pole piece cut away with a hole saw (to permit greater rearward excursion) that also has a suitable Xmax and construction will make a good enough PR.
All small wide range speakers tend to be low sensitivity...
-----------
stevebogus, what "notch" is this? don't think I have come across this before. Afaik the Fs of the PR in the box is the center or max output point of what is a pretty smooth curved response.
Try one Dayton ND91-8 with two opposing Peerless 830878 passive radiators in a box volume of between 1.2 and 1.8 litres volume and be pleasantly surprised(around 60~70Hz tuning), its only about 83 dB for 1 watt so needs a bit of wick, you can use just the one passive but you have to remove the original weight and replace with something lighter (not worth the trouble) every time I crank them up in my workshop I am amazed at what they can do (within their limits)
That was immensely helpful!
So in essence while selecting a passive driver, both Sd and Mms are the reference.
Couple of queries from here-
1. How did you get to the desired Sd value? You suggested 50-70 cm sq. For Fountek it is 17.35 cm sq. Is it the ratio which is generally suggested, 2-3 times the active driver.
2. When the weight is determined by the port dia, tuning freq and encl. vol., how to ascertain if it will work well for the active driver, that is considering its X-max and other parameters.
yup. I am looking to get to a portable design. 0.03 to 0.04 ft3. Without some DSP magic, I know deep bass is not possible, so trying to get to atleast 80Hz using full range and passive only.
Thanks.
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I had tried those too. But used to get strange errors while filling up the driver params. So later I removed the program. I will now try to install it once again on my linux system using Wine. Will see if it works?
Determining if a driver, and one or more passive radiators in combination with it, are suitable for a particular project is a bit of an iterative task. I find that the following approach is practical:
Start with a particular driver that would like to use. The next step is to base the PR alignment on a vented alignment. In fact you can completely ignore the PR at this step. Try to determine a box volume and port that will work. Next you want to try and figure out which PR can be substituted for the port, so that the vented box becomes a PR. Then you can adjust the mass added to the PR to set the tuning to the same frequency as you had for the vented box.
You will find that not just any PR will work. Also, there are only so many PRs available to the DIYer, so you need to pick from these.
As someone mentioned the well known rule of thumb is that if the PR is of the same nominal diameter as the driven driver (e.g. woofer) then you should use two of them. This should really be restated in terms of total displacement, Sd*Xmax. In total the PRs should have at least TWICE the total displacement as the woofer. There really isn't any reason why one must use a PR with the same diameter as the woofer.
Using two PRs in the design and putting them on opposite sides of the enclosure is strongly recommended, since the force from the mass of each PR (which can be pretty significant) will cancel. Otherwise your enclosure may vibrate quite significantly around the tuning frequency when the PR is undergoing its highest excursion.
There are a couple of free programs that you can use to model PR systems. These include Unibox, and Woofer Box and Circuit Designer. I am sure that many other programs exist as well.
Start with a particular driver that would like to use. The next step is to base the PR alignment on a vented alignment. In fact you can completely ignore the PR at this step. Try to determine a box volume and port that will work. Next you want to try and figure out which PR can be substituted for the port, so that the vented box becomes a PR. Then you can adjust the mass added to the PR to set the tuning to the same frequency as you had for the vented box.
You will find that not just any PR will work. Also, there are only so many PRs available to the DIYer, so you need to pick from these.
As someone mentioned the well known rule of thumb is that if the PR is of the same nominal diameter as the driven driver (e.g. woofer) then you should use two of them. This should really be restated in terms of total displacement, Sd*Xmax. In total the PRs should have at least TWICE the total displacement as the woofer. There really isn't any reason why one must use a PR with the same diameter as the woofer.
Using two PRs in the design and putting them on opposite sides of the enclosure is strongly recommended, since the force from the mass of each PR (which can be pretty significant) will cancel. Otherwise your enclosure may vibrate quite significantly around the tuning frequency when the PR is undergoing its highest excursion.
There are a couple of free programs that you can use to model PR systems. These include Unibox, and Woofer Box and Circuit Designer. I am sure that many other programs exist as well.
Oh! 🙄 I've seen a number of posts (elsewhere) that indicate Wine doesn't play well with XP compatibility issues.
Bob
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