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Old 7th December 2005, 05:00 PM   #1
chops is offline chops  United States
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Exclamation Hey everyone, I'm back with a new big project!!!

Some of you might remember me from the infamous thread I started almost two years ago, and it's still going strong!....

My first Dipole Subwoofer!!!

Anyway, I'm in the search of a totally new custom subwoofer system for my home theater. Something that I have never dabbled with before.... multi passive radiators.

The dipoles that I built were great, but they were too large for my room and did not allow me to place my main channels in their proper postions for optimum imaging and soundstaging. Same thing goes for the SVS PB12-ISD/2 sub that I bought about a year ago, and sold almost 6 months ago.

My main priority with my system remains 2-channel sound quality, hence this new subwoofer system can not interfere with the placement for the main speakers (Definitive Technology BP10B). I am now running a front projection video system (InFocus ScreenPlay 4800) with an 8' wide x 4' tall screen on the front wall. I have since also moved all of the stereo equipment over to the side wall so the front area is more roomy and allows me to place the main speakers perfectly so that they completely disappear when listening to music or watching movies. I also have a fairly large center channel (Def Tech C/L/R 200) sitting on an amp stand under the center of the screen. And for right now, I'm using my brother's little Sony SA-WX700 which does an amazingly good job. It sits just to the right of the center channel, also under the screen.

Here's a page on my site about the theater. The pics are a little old, but you get the idea. I plan on finishing off the wall with black cloth and a theater style curtain and some track lighting.

http://chops.tzo.com/theatre.htm

Anyway, on with the project at hand...

My plans are to have the subwoofer system in a total of 3 peices that will attatch together to create a single unit looking like a "stage" under the screen. I want to make the enclosures out of 3/4" or 1" MDF, then have a friend of mine do an outer shell out of hardwood to give it a nice furniture finish. It will be bowed out towards the middle where an integrated center channel shelf and sub amp shelf (QSC RMX 1850HD) will reside. And the final touch with be a 3 peice removable grill with black grill cloth, also bowed out to the contour of the entire unit.

Please look at this picture as it is what I have in my mind for this project.
http://chops.tzo.com/IMG_0215.jpg

Now for the technical side of it.... I already have one Dayton 15" DVC sub from a previous system and I want to buy another one along with a total of four Dayton 15" Passive Radiators (PR's). This will make up the entire subwoofer system consisting of one 15" DVC and two 15" PR's per enclosure on either side of the center channel and sub amp. I will be running the mono LFE output of my reciever to the amp which will be running in stereo mode, with the signal Y-ed off at the amp inputs to run the subs off of each channel of the amp at 4 ohms which will give me 600 watts to each sub. My goals are to have a system that can reproduce bass down to about the 15-16Hz range and can reach a pretty decent SPL, and also be smooth, quick and musical. I don't need ear-splitting volume levels like 120dB at 15Hz or anything like that, but I still want to hear and feel the effects of those 15Hz tones in music and movies if they are there.

Since I have NEVER had any experience with passive radiators before, I am once again asking for the great and powerfull help of you guys. I know a lot of you know too much for your own good and need to share your awsome knowledge with me!

According to Parts Express, they say if you run PR's, you either have to use (say 12" drivers just for the sake of explaining this) two 12" PR's with a single 12" driver OR a single larger 15" PR with that 12" driver to do it any good.

Since I'm going to be running 15" drivers anyway, I'm assuming I'll have to also run two 15" PR's for each one. And depending on what size MDF I can get, I'll probably have somewhere around 8.5 - 9 cubic ft of enclosure airs pace to play with, maybe a little more if needed. The width and height are locked, so if I need a little more air space, I can always extend the enclosure forward more if need be.

Now my question is, I need you swell guys to work me up some kind of enclosure dimentions, SPL numbers and rough guess as to what kind of freq resp and curve I can get out of this system?!?! I know a lot of you have computer models, software and equations that can figure this stuff out in a matter of a few key strokes.

Many many thanks in advance to you all for your help on this!
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Old 7th December 2005, 05:14 PM   #2
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Personally I donít like the sound of PR based subwoofers, but thatís just me. However, a enclosure like that (dual purpose) while being great for utility seldom work very well in a real room as you will probably need to move it around to find the best SQ spot and that might not work so well for the equipment you plan to put in it. I assume the shelves are for audio equipment, if not never mind.

If your looking for great SQ for music why not consider an IB?
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Old 7th December 2005, 06:40 PM   #3
chops is offline chops  United States
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Quote:
Originally posted by kingdaddy
Personally I donít like the sound of PR based subwoofers, but thatís just me. However, a enclosure like that (dual purpose) while being great for utility seldom work very well in a real room as you will probably need to move it around to find the best SQ spot and that might not work so well for the equipment you plan to put in it. I assume the shelves are for audio equipment, if not never mind.

If your looking for great SQ for music why not consider an IB?
I have actually heard a couple of PR systems before (not this large of scale however), and I liked the sound of them. Plus, they give you the benefits of a ported system without the port noise and 4 foot long ports.

IB is not an option for this room. I have two bedrooms on one side, two cement walls on the other side, and not much of an attic up above.

Placement shouldn't be an issue as I have had very very good results with other subwoofers towards the center of the front wall before. In fact, the best bass response in this room has some front subs in this location.

And the shelves (there will be two of them), the top one will be angled up slightly for the center channel and the bottom one will be for the QSC amp.

All I'm really looking for are what the enclosure dimentions have to be (cubic air space) to get one 15" DVC driver and two 15" PR's to reproduce decent quality bass down to about a solid 15Hz.
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Old 7th December 2005, 09:11 PM   #4
chops is offline chops  United States
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Alright, I've done a little bit of playing around on WinISD and have come up with this so far....

Enclosure size - 8.0 CF
Tuning Freq - 16Hz
Port Dia - 6"
Port Length - 32"
Group Delay - 18.29ms @ 20Hz

Apparently the group delay is supposed to be under the approximate audibility thresholds for that frequency and up. At least according to this review from Hometheaterhifi.com...

http://www.hometheaterhifi.com/volum...er-4-2005.html

Mine at those same freq's are:

27Hz - 10.59ms
33Hz - 7.44ms
49Hz - 3.62ms
87Hz - 1.18ms

I guess that's not too bad. They are considerably lower than the ones in the review.

Also, the sub should be down -9dB from 80Hz to 15Hz, but this is also without the effects of room gain, so that should help in the finished product. My room seems to be very good at reinforcing frequencies below 25hz or so.

Anyway, I have the port diameter and length, but I do not know how to calculate the mass and volume of the port. At this point, that part is over my head. However, I do plan on learning on how to figure these kind of things out eventually.

So if anyone would like to take a jab at this, please feel free to speak up.
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Old 7th December 2005, 09:27 PM   #5
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I've heard it said that most people who say they've never heard a passive radiator sub that they like have never heard a passive radiator system done right. I'm fairly inclined to agree - my AE Speakers AV12 woofer in 3 cubic feet with two 15" passive radiators has a sound approximating a sealed sub with most music program, and then starts to sound like a vented box when the program material ventures nearer to the tuning frequency.
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Old 7th December 2005, 09:31 PM   #6
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Calculate the volume of your port, then mutilpy that volume by the density of air.
I found a density of 1.25kg/Cubic meter.

Pi R^2 times the length times the density. Make sure your distances are in meters. That number is how much your PR should weigh. Then you can have fun tuning it exactly how you want it.
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Old 7th December 2005, 09:39 PM   #7
chops is offline chops  United States
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Quote:
Originally posted by tade
Calculate the volume of your port, then mutilpy that volume by the density of air.
I found a density of 1.25kg/Cubic meter.

Pi R^2 times the length times the density. Make sure your distances are in meters. That number is how much your PR should weigh. Then you can have fun tuning it exactly how you want it.
That's just it. I don't know how to do any of that.

How do you calculate the volume? What is the density of air?

Pi R^2?! Stupid question, but what's that and what does it mean?

Don't get me wrong, I'm not totally out in left field. I know that Pi = 3.14159265. But as far as the "R^2" is concerned, I'm not too sure about. Sorry.
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Old 7th December 2005, 10:11 PM   #8
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I did not think that last post though.
I am sorry but the actually calculations will prove to be much more complex. Ill hand this off to someone with experience.
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Old 7th December 2005, 10:43 PM   #9
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Hi Chops,

Welcome back.

I do like the sound of a PR system, but what I've found is that it can get tricky unless you have all three drivers on the same baffle. I did a single 15 with dual 15 drones in a three chamber "coffin", woofer in the middle. That sounded good.

The first cabinet, a cube type cabinet didn't sound good because the driver was firing out the front and the drones out the sides. Even when I corner loaded or turned it woofer down or both for that matter, I wasn't happy. Might be something to consider.

As far as box size, I'll have to let those who have used that woofer help. Seems awfully big though. Sure you need 15Hz?
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Old 7th December 2005, 11:07 PM   #10
chops is offline chops  United States
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Quote:
Originally posted by Cal Weldon
Hi Chops,

Welcome back.

I do like the sound of a PR system, but what I've found is that it can get tricky unless you have all three drivers on the same baffle. I did a single 15 with dual 15 drones in a three chamber "coffin", woofer in the middle. That sounded good.

The first cabinet, a cube type cabinet didn't sound good because the driver was firing out the front and the drones out the sides. Even when I corner loaded or turned it woofer down or both for that matter, I wasn't happy. Might be something to consider.

As far as box size, I'll have to let those who have used that woofer help. Seems awfully big though. Sure you need 15Hz?
Hi Cal, thanks for the warm welcome back!

I was kind of thinking the same thing about the driver and PRs being on the same baffle. Unfortunately, the limitted space in my room won't allow for it. Also, I guess I could also go with a 20Hz tune, just as long as I get some usable output down to 15-16Hz. That SVS sub I had spoiled me with plenty of sub-20Hz rumble, which I had tuned to 16Hz BTW.

If you looked at that drawing I made, the cone on the side of the enclosure is the driver. However, I have been thinking and I could be wrong, but is it possible that the inner most PR might move less than the one closest to the driver because of the greater distance?

If this is the case, I was also thinking of moving the driver to the back of the enclosure in the middle of the rear baffle so it will be placed in between the two PRs on the front baffle. Does that make sense?
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