RL-p15 Passive Radiator Design

[Mike Cason]

I've been asked to post a build thread of my passive radiator design in this forum to help others who may be considering a design using the passive radiator.

My goal was to have a clean low end without having the port chuffing, huffing, noise, or resonance that can be associated with a ported design. I didn't mind spending the extra bucks for the passives to reach this goal.

I originally built a 5 cu. ft. box for the Titanics from Dayton and Parts Express, so due to the hard work and expense, I kept the box and used it for my project. The tuning frequency tests out at 23 hz. with a Granite Audio Test CD, which isn't shabby at all. These subs reach lower than 23 hz, so Michael Murray's organ music, concert DVDs, and movies are so lifelike! You think you are at the concert!

I've never heard anything that comes close to my build quality, and I've been to many high end audio stores to audition their goods. I used to own a Legacy Point One and mine are so much cleaner.

I've stacked or "co-located" the subwoofers, and I'm getting a 6 db overall gain in output. I've had to crank down all of my internal Rotel settings and gains on the amps as this corner loading and placement has made a dramatic increase in bass output. The QSC amps are running much cooler and I have turned the gains down about 30%. I have a much less chance of blowing the drivers due to the decreased power required by the drivers now.

With the dual subs and my room gain, these subs are extremely clean, low, and efficient. Music and movies are reproduced so well. If I had it to do over again, I would build larger cabinets. I would use two 18" passives with each 15" driver and load them heavy to get the lowest tuning frequency I could. CSS out of Canada sells 18" passives built by John Janowitz at Acoustic Elegance. Use WinIsd or get someone to help you determine what you will need before you start. I don't think I could handle a lower or better bass than these are producing for me.

I'm using two RLP-15's with dual 2 ohm coils, and 4 Parts Express 295-194 15" passive radiators loaded to 1100 grams. The finished cabinet is 1.25 thick particle board with Pionite laminate. These subs weigh in 235 lbs each. All four coils are wired in series, an 8 ohm load to the QSC 1450 amps bridged, delivering between 750 to 900 watts depending on the load and frequencies I'm sending to each sub.

Here is the graph that Mike P. did for me with WinIsd. The purple line shows my speaker with the dual drivers and passives in a 5 cu ft box tuned to 23.5 hz. The green line shows a 8.5 cu ft box with dual drivers (RLP-15"s) and a ported design tuned to 17hz. I'm posting a picture of one of my finished subs without the grills, as well as both of them stacked.

I have more photos and detailed information about the build if you would visit my Photobucket link in my signature.


Thanks,
Mike Cason

[Geoff St. Germain]

An interesting note about the co-location ala the THX recommendation. I was actually reading up about THX a couple of days ago and I noticed that they recommended that when using two subwoofers they should be placed in the middle of opposing walls. When using 4 they should each be in the middle of their own wall.

http://www.thx.com/home/setup/speakers/sub.html

[John N]

Looks like your ready to hold a concert (for your neighbors 3 blocks away!)

Did you build the frame or braces first or did you build the sides first?

I would like to build or have John Janowitz at Acoustic Elegance build a 15/dual 18 passive sub. (one to start with second later)

Nice build!!

[Warmon]

Really nice job...they look great!..

[Mike Cason]

Geoff,
I've spent days reading on placement and a poster had mentioned that THX recommends the co-locating of dual subs due to cancellations. Not all posters are correct. I do beleive this poster was referring to an auditorium or movie theater setup. I did read your link as well.

In an ideal home theater with the commercially built subs, which are usually low quality, placing 4 of them in the center of the walls around the room would appear to work fine. Most home theaters don't have subwoofers this large, cabable of the tremendous amounts of power and low end frequency waves so they couldn't possibly be set up around the room due to cancellations.

I tried to locate them in different places and the co-location worked out perfect as I'm seeing a 6 db gain in output. Before, when I turned both of them on, located on opposing walls, the bass diminished. Turning off one of the amps actually improved the bass with just the corner loaded sub. It's fairly obvious I can't center place them at the TV location in my set up due to the large TV I have, as shown in the THX link.

John N,
I built the cabinet first, then the frames. I used a drill press and a level to get an exact hole through the frames, the laid the frames on the sides and front of the cabinet. I then used the same drill bit and found the location where the snap in grill cups needed to be drilled and made a starter hole. There are many details of my build which can be found at my Photobucket link shown in my signature below. Feel free to browse the links to get a better idea of how I did everything.

I don't think John is going to have time to help you build a speaker. He has Dr. Bass (ex Klipsch guy) working with him now and they are sourcing passive radiators for large manufacturers and I don't even think his online store is open yet. He does offer misc drivers left over in stock for sale. He is designing a passive radiator that can be adjusted from the front after it's installed. Quite a concept! I may be a year before it's available. He's also working on a new line of drivers comparable to the AV series. I'll stick to Soundsplinter's!

Yep....My neighbors have come a knocking when the house gets rockin....SRV, Austin City Limits....

Thanks Warmon.....It's taken 5 years, lots of rebuilds and failures, followed by a quite happy DIY'er. Let's don't discuss expenditures for the R & D with the teardowns and rebuilds. My 28 year old son brings his freinds over to demo new videos and music DVD's, my fav.

[Geoff St. Germain]

I don't think that the output has much to do with cancellations. Cancellations will occur regardless of whether you're using a pair of 10" subwoofers or arrays of 18" subwoofers.

Regardless, I was just clarifying the THX standard.

[John N]

Mike Cason wrote:

Geoff,
.

I don't think John is going to have time to help you build a speaker. He has Dr. Bass (ex Klipsch guy) working with him now and they are sourcing passive radiators for large manufacturers and I don't even think his online store is open yet. He does offer misc drivers left over in stock for sale. He is designing a passive radiator that can be adjusted from the front after it's installed. Quite a concept! I may be a year before it's available. He's also working on a new line of drivers comparable to the AV series. I'll stick to Soundsplinter's!

.

He will still build custom subs and speakers . He does answer questions on his forum but it may take a few days. http://www.aespeakers.com/phpbb2/

I'm in this hobby more for music DVD 's also

[Mike Cason]

John,

Mr. Janowitz is a brilliant man and really know his business. I'm glad he's able to still do some build outs. His shop was down for a while, so I haven't kept up too much with him. I glance at his site from time to time.

Those 4-12" TD-S Lambda mid-woofer drivers shown in my mains came from him before he bought out Nick McKinney's inventory in Florida.

Have fun,
Mike

[Mike Cason]

Testing time guys & gals....

Last evening I had a few hours to really put this stacked mass of drivers to the test and it passed with A+'s....

I cranked the gains to max on the amps (750 to 900 watts per sub cabinet). I pulled the stacked subwoofers about two feet from the inside corner of the walls to help with the radiation of the sound waves for optimal room gain.

I started out with a Telarc SACD of Michael Murray's Dupre-Franck-Widor organ music performance at St. Sulpice, France. I followed that with Eugene Ormandy's Philadelphia Orchesta with Michael Murray at the Organ at Syphony Hall, Boston, another Telarc SACD. The organ's low end is one of the lowest in the musical instrument scale and cranked up, my pants, shirt, and everything that wasn't glued or nailed down shook, and was as clean as it could be expected. I went on to Frederick Fennell with the Cleveland Symphonic Winds. This SACD has a lot of march music and kettle drums. I wasn't disappointed with this one either. Very clean and crisp. The kettle drums sounded like they were in the living room.

I could have listened to it all night but had another one of my favs to check out......

How about Joe Satriani's Live in San Francisco...a small change in music format. I like most music except, rap, country(except for a couple of artists), and the new dance pop culture.

This is a two disc DVD set and I was again blown away with my low end and SPL. His performance was really cookin on disc one, and when we got to the fifth song, Borg Sex, the living room blew apart. It was an awe-inspiring "actual" reproduction of the concert. There are tons of low end bass in this song, and it went into a few other rifts with extremely low and clean bass.

I had to jump up and grab my rat shack SPL meter and at the subs, I was pegging about 118 db and in the center of the living room at the seating area, with the combined speaker arrangement I was listening to 120 dbs of pure clean music. My main Rotel amp/processer is a 100 watt high current model and it was set to 72 on the gain with more headroom. It goes up to 81 or 91 wide open. I also had the two QSC 1450 sub amps bridged and maxed out and never clipped, and a cheap KLH 100 watt amp for the center back B & W DM 303's.

With the Joe Satriani, and Michael Murray's performance, the bass was so good I don't know if you could have felt a transducer under your chair at the levels I was listening.

If I ever take on another subwoofer project, I'll again sacrifice the extra hundreds of dollars for the passive radiator design. It has it's own clean sound without the port noises I spoke of at the beginning of this thread and they deliver as promised.

Many, many thanks to Michael Grynick and his efforts to work with TC Sounds to produce such a fine performing driver with excellent follow up tech support and prompt emails.
Mike

[mrstampe]

Wow!! Excellent build thread, outstanding finished product and great review!!! I can't wait to listen to this setup -- luckily Mike lives just down the road from me!

[Mike P.]

It's good to hear that you're happy with it, Mike. Let us know how it sounds with a movie.

[Mike Cason]

Mike,

Prision Break, 24, Stargate Atlantis, U571, Independance Day, the Spiderman series, the Jurassic Park series, and The Abyss, special edition movies all have been fantastic with just the first subwoofer. Movie impacts and explosions have been superior and sometimes scarry if you didn't know they were coming. I'll post again after watching one with the dual sub setup.

Thanks,
Mike

[Mike Cason]

Woooo....movie review time as requested......

I have a several movies to choose from but I chose Independence Day to demo.

I initially put in the DVD for a simple test and was going to move on to a couple others, but I was so overwhelmed by the movie's performance with the second sub added to the system, I watched the whole thing over again. I didn't see the need to demo others to give you the report on movie reproduction results.

It exceeded my expectations and delivered me two hours of the finest movie experience I've ever heard. My living room isn't even treated for home theater use, other than the carpet. Yep, I'm sold on the PR design!

I've emailed Dan Marx over the years due to his expertise in the audio field with various projects. He had some interesting information for me regarding the tuning frequency of the 23hz of my subs. I couldn't beleive after Mike P. modeled my sub in WinIsd that my tuning was only 23.5hz because they get so much lower than that and are so clean. Using the visual test, I tested them at 23hz, actual.

For those of you who are trying to get your tuning hz down in the teens with large boxes and ports, you may want to take note of his recent email to me:

Quote: "I know what you mean about the majority of people lately bent on tuning in the teens. I'm not all that into it. Enclosure sizes are just to large for my tastes. Even a small (relatively speaking) sealed box with a modeled f3 of ~35 Hz can have usable extension all the way to 20 Hz in-room and sound fantastic to me. Room gain does wonders for subs. The simulated numbers, whether they be f3 or fb, don't mean much in terms of how the sub actually sounds to you. It's more just a metric to shoot for when designing the sub, and of course, most people use them for bragging rights. :-)"

http://www.danmarx.org/audioinnovation/

If you are contemplating building a good passive radiator subwoofer, don't worry about trying to acheive a mid teen hz box tuning because if you can get down in the low 20's, you will be very happy. As shown in the graph in the beginning of this thread, by using a lower tuned box (larger), you may even sacrifice some of your mid bass response.

I hope this thread will help those of you contemplating the use of passive radiators for your next project.

Mike

[vinculum]

Beautiful system, Mike. I've seen pictures of it floating around for some time. Glad you decided to share more information.

A couple questions. What frequency are you running your high pass filter? I assume at some point slightly below tune the passive radiators exceed their excursion capabilities. Have you ever bottom'ed the passive radiators?

I too have a passion for DVD concerts and am looking to build the best possible system for such. Learning all I can!

Thanx
Dr V

[Mike Cason]

Hi Dr. V,

Thanks for your thoughts and compliments on my system.

Electronic House magazine posted my system in October of '04 too.

I have my high pass filter set to cut off at 60 hz. I'm using a pair of Lambda TD12-s midwoofers in parallel in my mains and they are quite capable of handling 60 hz and up very well. My doubling of the the drivers in the mains gives me 6 db gain too. I don't want to muddy up the subs with unnecessary frequencies. They were designed to do just that.....handle the low end frequencies. I don't need an external equilizer either. I really like them crossed at 40hz, but my mains have to then carry the 40 to 60 hz frequencies and that takes away some of the sound quality of the mains due to the extra load.

As far as the passives, the golden rule/ratio is twice the passive displacement for each driver. I don't think I've ever bottomed out the passives yet and I've really hit them with a lot of SPL. My wife did blow a pair of RLP-15's when changing movies once while I had them way overpowered and had the gains set to full. I used to hit each driver with 1450 watts each. She switched to one of Jurrassic Park's most intense scenes by accident via Direct TV and I couldn't get from the bathroom to the remote in time to mute it. My passives survived unharmed. They are built by Eminence Loudspeaker Company who has been building pro and home audio drivers for many years. They are available through Parts Express.

Using Linkwitz's tuning CD and watching the movement of the passives down in the teens, I think the passives would reach a decent number below tuning before bottoming out. I've had the original sub in operation for 3 years now and I know they have really got down in the low hz because i used to hit them with that 1450 watts times two drivers with a variety of movies and music. I think that's why they sound so good.

I ran the freqs down to 10 during testing, but of course at low volume. At 10hz, the passives were moving so much they could have churned butter if I could have connected them up to a machine!

Golden rule number 2, don't overpower your drivers like I did. You have a nasty gremlin built into music and movies, and that is called subsonic frequencies, real killers! Even with filters, they can get to your drivers at high SPL, like a computer virus.

I'm using a sub box that I built in 2004 using the Dayton Titanics. It is so well built and looks so good, I didn't want to rebuild another box to accomodate the RLP's and was hoping for a good result, which I did indeed achieve. That's why I built a second one to match.

Doing it over again, I would model, or have someone model for you, a little larger box and instead of having two 15" passives for a single 15" driver, I would use two 18" passives that CSS is now offering per driver with more weighting than I have at 1100 grams per radiator.

On the flip side, I'm waiting on the availbility and prices of the new VMP line of passive radiators that TC Sounds (now Audio Pulse) is offering. Their claim to fame is that they have passive radiators with a 40mm xmax with a 2000 gram capability and two of those 15" passives should work with most, if not all of the 15" high excursion drivers now available. You might even be able to get by with one, but the cabinet would walk all over the floor. You need opposing radiators to keep the cabinet stable.

http://www.audiopulse.com/products/p...-radiators/vmp

This would keep you from having to buy two of the more expensive and probably unnecessary 18" VMP units, or the ones from CSS. IMHO, the VMP is a much better passive than the CSS models. I've seen some close up photos of the construction details and read the specs of both units.

Once I get the availablity and pricing, I may change out my 8 passives with the VMPs. It would be a straight drop in replacement for mine. My acquaintence, Dan Marx with AudioInovations is running the numbers for me right now to see what they would do for me.

(If Mike P. reads this post, would you mind llooking at the VMP link and plug in some numbers for me if you still have my file? Dan Marx is using a different program and I would like to compare the different results.)

If I do decide to change them out to the VMPs, I may sell my passives as I still have the shipping boxes.

There's one more Golden Rule to remember. When using passive radiators, make sure your driver(s) have a Q (QTS) of .4 or lower. The RLP-15 dual 2 ohm is rated at .333 and the dual 4 ohm is .447 which should work fine. Higher Q drivers don't work well with passive radiators. High Q drivers need to be in sealed boxes.

Let me know if I can help answer any more questions you may have.

btw...Loggins and Messina came over last night with one of their latest DVDs. I let em rip! And for a second night in a row, I didn't get to bed till 11:30.(Wife is out of town). Utterly awesome performance by a couple of real legends and their 8 member band. I had front row seating! The gains were at 50% and that's all they needed!

Again, passive radiator systems don't suffer the effects of port noise or port resonance that some ported boxes have, and have a unique clean sound of their own. They also require smaller enclosures.

Good luck and have fun with your project!

Mike

[vinculum]

Mike, Thanks for your detailed response. Those Lambda drivers in your mains are supposed to be really nice for low midbass distortion. If i was building some mains, I'd definitely consider them for my project!

The high pass filter I was referring to is the "rumble" filter, which is normally set just below tuning . I believe you mistaken my question for the low pass filter which is between the bottom frequency response of the mains and upper frequency response of the subwoofer.

Remember, below tuning the passive radiators will move quite far, but the active driver is now unloaded and working completely out of phase with the passive radiators. Low level testing might make them look like they are packing quite a punch below tuning, but during normal playback levels this is a bad situation as excursion can get out of hand and any audible benefits are cancelled by the active drivers behavior. This is where the high pass filter helps to protect everything.

I'm not so sure the Audiopulse PRs would be better than the CSS models. From what I understand, the Audiopulse PRs have very stiff suspensions which is a no-no. Here is a good PR faq from Acoustic Elegance. http://www.aespeakers.com/phpbb2/vie....php?f=4&t=549

Also the metal cones can be damaged more easily than the flat MDF circle used in the CSS models. The CSS passives don't have these issues and are half the price. This may be most important thing, the CSS passives are actually available to purchase. Audiopulse is in a state of the unknown. They have never shipped any product that I'm aware of! That being said, if i had TC/AP active drivers I probably would seek to acquire passive radiators of the same company to keep suspension linearities the same. They are also easily adjustable, which is a bonus. Unfortunately they seem to be unattainable. I emailed them quite some time ago and never heard a response. I never really expected one either, but i tried.

Several prominent people are working on new PR designs as we speak. This year we should see more options to choose from. Always a good thing for builders!

Dr V

[Mike Cason]

The only other filters I'm using are on the amps. They are pro audio amps and don't have the options normally found on sub-mounted plate amps. I've got the low pass filters set at 30 hz to prevent overexcursion due to transient signals. (My options are 50 & 30 hz) Now that I've reduced the wattage from 1450 watts per driver at 4 ohms down to 800 to 900 watts with an 8 ohm load for both drivers in each cabinet, I may even turn them off.

After listening to a few more good movies and DVD concerts, I'm so pleased with the final results that I'm going to leave the current passives in there and enjoy what I've got. I've got so much clean bass and high SPL, it would be foolish to keep spending money on them. It's like a drug habit....once you get a taste, you just want more and more. There is a time to stop and appreciate what you really have.

I want to start on some custom surrounds to run in parallel with my in-ceiling Polk RC85-I's and have some left over drivers to start the project, so it's time to move on.

[Ricci]

You actually have the 30hz highpass engaged on your amps? That would definitely protect your stuff! You should look into getting a better filter. You should be much better off with a 20hz highpass. You are losing a lot of your useable low end right now.