Passive Radiator?

 

New member
Username: Gonzaga_92

Post Number: 1
Registered: Jan-11
Well I will start off to say I have built a sub for my computer. The box is 16x16x17.(h x w x l) I have a 12" STRIKE 450w RMS subwoofer in the box already, currently side firing(right side) and a built in amp(120v / 240w @ 4ohms)

Currently the box is bass reflex ( two 2-1/4" ports on the back under the amp. I want to add a passive radiator to the opposite(left) side of the box. (and block/remove the ports)

The sub sounds good most of the time, but when it's pushed hard, especially around 25-15hz, the ports "chuff" and whistle. Are the ports just too small for the driver? Or is my amp just not able to power the driver properly?

Would using a real radiator have much more effect than using the identical driver unhooked as a "radiator" in its place? A buddy of mine is using a 12" driver with another 12" driver as a radiator in his truck and it sounds really good, although his box is 4 feet wide and 2 feet tall/deep.(and 60 lbs haha)

I know radiators are adjustable/tuneable with weights, but finding a good one where I am could prove to be a problem. I would have to order one off ebay. I was looking at a CSS 12" radiator, anyone have experience with one of these?

Equipment used -
Kenwood VR-405 receiver
Sound Dynamics main speakers
Custom 12" sub
PC (via. optical)
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15832
Registered: May-04
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How'd you come by the equations and instructions for the enclosure you're now using? Did you follow some sort of formula supplied by a designer or did you just kinda wing it and build what you thought might work?

Ports tend to make noise, it's one of the most common objections to a simple vented enclosure. You can influence the degree of noise by placement and configuration of the port. If you've placed the port in a high velocity area of the baffle, you'll have more noise than if you can move the port to another location. Front vs rear vs bottom firing ports also make a difference in perceived noise. Flaring the port also makes for lower noise product. Once again, did you have any proper guidelines for constructing this enclosure or did you just make it up as you went along?

Staying with the configuration you have you might try a bit of mass at the internal edge of each port to offer a bit of restriction to the velocity/noise without drastically altering the port volume. A layer of polyfill placed at the entrance to the ports is where I'd start, support the material so it doesn't shift position over time. If you care to experiment before you open the cabinbet, just stuff a bit of polyfill into the port and listen for any improvement in noise while not affecting the bass response of the system. The fit in the port should be rather loose as too much material pushed in too tightly will change the type of enclosure the driver sees and will ultimately affect the "alignment" of the enclosure. If you think a bit of restriction in the port is good, then take the driver out and work at the material from the inside.

Otherwise, call both PartsExpress and Madisound. They both sell "real raditators" and can advise you on the best route to take with a new enclosure design.


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New member
Username: Gonzaga_92

BC Canada

Post Number: 2
Registered: Jan-11
I used the manufacturers recommended box dimensions for the sub driver used. I also went off the approximate size of my other similar subs (Focal 800v and Mission 700ASi)

I was going to go with a bigger enclosure, but "wife-friendly" meant I had to use a box no bigger than our current subs.

I might just buy the identical 10" driver to the 12 I have and use the amp to power the ten, and the ten to power the 12. is this a good idea? The ten inch is closer to the power of my amp @ 300w RMS as I know that under powering, especially with subs is a bad idea.

I was reading up on radiators and according to the internet you are supposed to use one size up from the driver used( a 10 for an 8, a 12 for a 10 and so on) The problem here is, a 15" wont fit in my cabinet, thus leaning me towards getting the ten. Bad Idea or not? thanks
 

New member
Username: Gonzaga_92

BC Canada

Post Number: 3
Registered: Jan-11
One more thing, the sub is on the computer so will be used for 99% music
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15835
Registered: May-04
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The approximate size of another subwoofer has nothing to do with the appropriate volume of the enclosure for this subwoofer driver. The dimensions the manufacturer suggested should be what you followed. If you deviated from those dimensions, then you screwed with the final product. Bigger is not better, bigger means you've changed the alignment of the driver/enclosure. This will result is subpar sound quality.


It sounds an awful lot like you're not yet the best at DIY speakers. The physics of matching drivers to enclosures and drivers to passive radiatiors if fairly well structured and if you're thinking you've got a better idea than the driver manufactuer, then you're probably wrong. So, yeah, starting to buy more drivers when you still have no good idea how to make them work well in an enclosure is a "bad idea".

Call the retailer who sold you the driver and consult with them or call Parts Express or Madisound for some assistance. Or, start over from scratch and follow the instructions given for the proper box with the proper location and volume for the ports for this driver.


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New member
Username: Gonzaga_92

BC Canada

Post Number: 6
Registered: Jan-11
I don't need your lip, I just wanted to know what you think would sound the best. I am on a budget, and don't need a perfect sub. otherwise I would have bought another Focal. so Ignore everything else I said, and answer this question please.

Will a radiator make a SIGNIFICANT improvement over a driver in its place?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15840
Registered: May-04
.

I don't need your attitude. I've answered the question as I think it should be answered.
 

Gold Member
Username: Superjazzyjames

Post Number: 1319
Registered: Oct-10
Gonzaga, my advice to you is this: Don't do what I did. While Jan is very knowledgeable, it's apparent that some people, you and me included, need some time to get used to his approach. So, rather than get into a big ugly fight, I would suggest you just read what he wrote, don't let what you find offensive bother you and just think about the rest of his advice. Otherwise, be prepared because other members of this forum WILL defend him and rather fiercely so. Just some friendly advice.
 

New member
Username: Gonzaga_92

BC Canada

Post Number: 7
Registered: Jan-11
Sry Jan, didn't mean to be too rude, just hate when people belittle me.

I talked to a guy on parts-express and he recommended getting two Dayton 12" radiators. At only 20$ a piece (and with shipping to Canada) I am going to get two and run them both. I'll put up some pictures when I receive them and get them installed.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15846
Registered: May-04
.

I didn't belittle you, fella. I said, "If you deviated from those dimensions, then you screwed with the final product", and, "It sounds an awful lot like you're not yet the best at DIY speakers".

You're not "the best" at this time and you shouldn't be making assumptions which lead to poor results. Everyone learns to perform proper diy the same way, it is a process. Experience is (hopefully) knowledge. Most of us screw up a few projects due to trying to do something we don't fully know how to accomplish. If you keep at it and you follow instructions until you have a better grasp of how it all fits together, you'll succeed if you pay attention to what's in front of you. If all you want is to have a finished diy that does as advertised, follow instructions - they are there for a reason. If you truly want to learn about speaker design and construction, learn what you need to learn so you can make those assumptions which will be a further learning experience. Then learn from your mistakes and your accomplishments.

It's a process that we all go through. Don't be insulted if someone tells you you don't understand something. Don't be afraid or too proud to ask what it is you don't yet know or understand. Find out what it is you need to understand and then apply it to a project or your overall view of audio.

Good luck with the project.


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