new subwoofer king?

[robertcharles]

By the way, this project was not initially supposed to be this complex. At first, I was going to just build a 15-20 cubic foot box for 4 15 inch woofer I had just laying around. Well, after 5 or more years of "um uh well maybe um", it evolved into what you see above, and 2 crown Itech 8000's- of which I have no idea if I need all that power. However, that is another story. Anyhow, the configuration of the drivers had to be like they are because of placement and size constraint. Also, the Passive radiators were taken into consideration in order to eliminate rocking. I went through many different configuations, and this one seemed to be the most ergonomic, efficient and visually pleasing to me. I hope it all works out and they perform admirably. I tried not to cut corners once I got going, so hopefully, functionality will be high.

I'm hoping for mid january as a finish date. We will see.

[Ricci]

It's a quarter wavelength cancellation, Peavey writes about it in a slightly different application, although it is still applicable. It also applies to the cabinet dimensions in that you can only get the drivers so close to the walls of your room...
http://www.peavey.com/support/technotes/soundsystems/boundarycancellation.cfm

54Hz has a wavelength of 1132/52 = 21ft. One quarter of that is 63inches.
(speed of sound divided by the frequency is the wavelength)

I have found that it is more audible than room modes because you pretty much always have the null present - same with early reflections. Room modes can have phase rotations greater then 360, which would mean the cancelling effect is delayed - so you get a smearing/ringing of something that is there part of the time.

Also, the 54Hz null is going to come with nulls at 108Hz and 162Hz. You will see +6dB spikes at about 72Hz and 144Hz - just basic comb-filtering. You also get your first standing wave happening at 216Hz and every harmonic above that, which even with a perfect low pass filter can be triggerred by harmonic distortions and is then attenuated by its ability to transmit out of the cabinet, and it modulates the impedance on the active driver too.

Btw, bracing and what not looks very small to the wavelengths we're talking about, so it really doesn't affect these natural cabinet behaviors very much. You have to get dramatic and redirect the waves - think of it like pouring water through the bracing...it just keeps on flowing. If you've got a larger baffle, it'll deflect and wrap around. If you've got a really large baffle, it'll splash and then get the majority of its momentum redirected.

As far as the VC slamming the plate - that's what happens with a very linear suspension. Also, moving the back plate will reduce your Bl slightly and it will also just push the mode of failure onto something else. My bet is that the spider is the next weakest link. While bottoming against the back plate is scary as all get out, I think it's one of the least damaging failure modes....as long as you don't hit it so hard as to deform the VC former or windings. I guess the problem is that the source material that will cause you to hit the backplate don't occur very often, so you can't tell when you're just barely touching it. Putting filters in place to prevent this from happening is really the best approach - and if you get creative, you can make sliding filters with variable rolloff so that you're limited to peak excursion at all frequencies and amplitudes. This also has the benefit of dramatically reducing intermod distortion caused by low frequency signals that aren't perceivable, yet tax the driver real hard.

Btw, all cabinets have the above effects that I've mentioned. The trick is to get these effects out of the passband so that you don't trigger them. Large cabinets are absolutely required for deep efficient bass, but you gotta lower the HF corner with the lower LF corner.

One other side comment...I wouldn't be writing about all this if I didn't think it was audible. I've done some measuring and listening of my own and strongly believe that there is an audible correlation. The problem is that it is very difficult to do an A/B.

I understand what you mean about the wave traveling like water, I thought that if you break up the path substantially and reduce the area that corresponds to exactly one wavelength that it will diminish the strength of the resonance or null ( not eliminate)? The water still flows around everything and finds a way to get to the other cabinet wall of course but some of it will have to travel further around the bracing and partitions so that it will no longer correspond to 54hz right, somewhat dispersing the null? I have only a very basic knowledge of how wavelengths and acoustics work but I thought that the null would occur at the half wave (108hz or thereabouts) and not 1/4? I musta been confused there. Regardless if this is the case that it would be in the 54hz area (1/4wave), why don't more people see this kind of thing in their FR response, impedence plots, etc with large subwoofers and cabinets? I'm just wondering how big of a problem it is? I have no evidence of it at all in my large cabinet, with sine sweeps, close mic, room response, regular listening, impedence traces, you name it unless it's very small. Wouldn't every cabinet have a problem with this in the bass/ lower midrange?

I'd disagree about the VC slamming being safer issue, at least as far as TC's cones are concerned. I like a suspension limited design better. If the dual spiders and surround plus possibly the motor all start limiting at the same time it should be less damage prone than if you just allow the VC to slam the back plate full force which is what seems to happen if you are not careful, since the LMS is so linear. The cones on these are pretty easy to dent and actually seem a bit fragile to me compared to a heavy paper cone, or CF. If the extra VC clearance was built into the LMS driver it could have been accounted for in the design. It's a minor nitpick and you have to be driving the heck out of one to even have to worry about this but there's always that what if scenario.

[DrWho]

Regardless if this is the case that it would be in the 54hz area (1/4wave), why don't more people see this kind of thing in their FR response, impedence plots, etc with large subwoofers and cabinets? I'm just wondering how big of a problem it is? I have no evidence of it at all in my large cabinet, with sine sweeps, close mic, room response, regular listening, impedence traces, you name it unless it's very small. Wouldn't every cabinet have a problem with this in the bass/ lower midrange?

I've never seen an instance where it wasn't measureable. It'll show up as a narrow dip that brings the response down at least 20dB or so. My laptop's harddrive bit the dust, otherwise I would just post a whole slew of outdoor ground planes that I remember showed this quite clearly. It happens in full range speaker cabs too (in fact, that's what most of my measurements were from).

If you're not seeing any signs of it in your measurements, then all I can say is that you're probably not measuring it properly. That happens all the time though, which is why I cringe at posts where people essentially say "look at my pretty line". I much prefer the approach that starts with hearing an audible problem and then using measurements to find and quantify the problem that way the fix can be qualified.

[Ricci]

So you are saying that every speaker will have this 20db deep null in the fr? How narrow are we talking about? What about all of the individuals who take measurements all of the time professionally? Can you show me an example of what to look for?

[DrWho]

So you are saying that every speaker will have this 20db deep null in the fr?

Depends on the polar response of the rear wave and the specifics of the rear volume.

Give
me some time and I'll come up with some real world measurements.
Actually, below is a screenshot from Hornresp that calculates it for
one dimension - I almsot forgot it had this ability. I went ahead and put in 63" (160cm)...I think I said 50-some Hz for the first null and this is showing 100-some Hz? I gotta scratch my head on this one...

[DrWho]

And then here it is when the distance is short enough to not be a major problem:

[DrWho]

And then here's a real world ground plane measurement of a TC LMS-5400, with a cabinet dimension of ~30"

I took this measurement last summer in Indy. The length and width of the box were similar but not identical, which is why this dip is wider than normal.

[Ricci]

Thats where I was confused too. You know a lot more than I do about this stuff, but I thought that 54hz sounded too low and 100-110hz sounded more reasonable. So it seems to be the half wave that causes the null? That makes sense to me just visualizing things.I'll go back and look at some of my measurements. Recently I talked to Collo about box notes and the same thing is apparent in his program. Boxnotes would say that the primary resonance issue would be 54hz but when measured it would be twice that.

[robertcharles]

Here is the granite templates. Granite is ordered and should be here in 2 weeks, so they say.

[John Warren]

You have to give granite/wood bonds some freedom to accommodate expansion (for example, dollups of silicone adhesive in countertop assy or no glue at all).

Also, I know from experience that using epoxy adhesive on granite tile to MDF causes cracks and bond fractures in the MDF.

How are you going to glue the granite to the cabinets?

[robertcharles]

It's going to be bolted to the top and bottom and siliconed to each panel. The tops and bottoms are oak ply not mdf. Remember, the boxes are laminated with oak and mdf. It Is a trial and error situation. Any thoughts?

Thanks,

Robert

[robertcharles]

Granite has arrived. Paint soon.

[robertcharles]

Primed and ready.

[Jay481985]

Looking good. When is the estimated time of completion?

[jacksonbart]

I prefer BurgerKing

[TheEAR]

Estimated time of completion ...ERROR, I tried to compute but got blue screens of death! []

After the 800lbs cabinets are filled with 240lbs of TC Sounds and connected to the iTech8000 amps. When the PLAY button ....BOUM.....huge earthquake and FOX news will be on location to report. No more roof to cover the house!!!

[darkside]

Yeah, those subs have certainly been a long time coming, but oh my word, I'm sure the time spent will be well worth it when they've finally got power to em'. I am so jealous []

[robertcharles]

a little progress

http://i228.photobucket.com/albums/ee292/robertcharles123/100_2497.jpg
http://i228.photobucket.com/albums/ee292/robertcharles123/100_2486.jpg

[michael hurd]

Cut and paste from the AVS forum...

Michael,



I currently have the cabs running from a qsc rmx 2450. I cannot imagine
having them running each on an itech 8000. I have to get some
measurements and calibration going. I have no idea what these things
are capable of. All I can say is that the cabs themselves do not budge
or rock or vibrate in any way- so that is good. Any thoughts about
power and output?







Thanks,



Robert

I never had an LFE channel hooked up before these new cabs. Now The movies are just cruising along and then ""BAM"" they just tear the place up. The house is not making any funny noises currently, but the filaments in the light bulbs are rattling like no tomorrow.

[robertcharles]

I give you "POTENTIA MAXIMUS".

POTENTIA MAXIMUS is a dual cabinet, opposed driver configuration LFE system. Each cabinet is 18.10

cubic feet internal volume with a system tuning of 14.4 Hz. This project was an evolution of LFE

design and implementation. It started as a small build utilizing existing drivers and amps and evolved

into The grandest system that I personally or physically could assemble. Each cabinet consists

of approximately 8.5 sheets of MDF and Oak Ply. I feel that the melding of these materials gives extremely

good build qualities. The ply adds strength and durability, while the MDF allows for superior machining and

it is extremely consistant and nondirectional in structure. Each cabinet including the grills weighs in at

approximately 1000 pounds. The drivers and PR's alone in each cabinet weigh roughly 225 pounds- a true heavyweight.

All of the panels are minimally 1.5" thick and the 2 baffles are each 2.25" thick. The granite was applied in the

same fashion as each panel. The entire surface was epoxied and the entire granite slab was bolted to the cabinet and

became part of the system. Thus, adding 1.25" of thickness to the top plate and the base. It also added over 245 pounds

to the system. With the drivers configured as they are, the cabinets take up the bare minimum of floor space,

and results in a cabinet that neither vibrates or rocks due to the movement of the PR's in the system.

Newton really had something with those laws of motion.

The system consists of:

1. 4- 18" TC Sounds LMS 5400 Active Drivers capable of delivering 32 liters of displacement
at 38 mm xmax.

2. 8- 18" TC Sounds Variable Mass Passive Radiators (VMP's) capable of delivering 76 liters
of displacement at 45 mm xmax.

3. 2- Crown ITech 8000 power amplifiers. Each amp is capable of delivering 8000 watts into an 8 ohm
bridged load on a 220 volt service.

4. 1- MIC2200

Special thanks is in order to the following people.

1. NEO Dan. Dan has been instrumental in the development and ultimate production of this system.

2. Michael Hurd Mike's knowledge of paint helped transform this behemoth into something special.

3. My parents My parents gave me an unobstructed place to assemble this project which would have not been
possible otherwise.

4. My Nephew Mike helped me in varying aspects of assembly and final assembly of both units. Helped greatly
Mike in mounting drivers and PR's.

5. My brother Mike helped me in assembly and moving. He also supplied many of the clamps used in assembly.
Mike

6. My brother Helped in assemblly of grills. Also responsible for designing and manufacturing the badges for
Barry each cabinet.

7. My friend Helped in many aspects of assembly and also responsible for helping move cabinets to my home.
Keith

8. My friend Helped in many aspects of assembly and moving cabinets to my home. Also helped apply granite to
Joe the cabinets.

9. Big Rob He is bigger than me! Helped to move cabinets to my home.

10.Bossobass Supplied magnets to me for grill application. Thanks!

11.Kyle Keating Helped with various technical aspects of design and assembly.

12. Ilkka Risannen Tested the LMS 5400's and shared his thoughts of the drivers with me and offered design assistance.

Thanks also goes to all at the AVS forum and the Home Theater Shack. Thanks for all the suggestions and assistance!!

I have been asked many times about how much did this system cost. I have gathered all of the numbers that I have and

here is the list to the best of my knowledge.

Total cost of build.

1. 4 - 18" LMS drivers $ 3600.00

2. 8 - 18" VMP's $ 2400.00

3. 2 - Crown ITech 8000's $ 6000.00

4. 1 - MIC2200 $ 100.00

5. 4 - granite slabs + finishing $ 1100.00

6. 2 - custom designed logos $ 3600.00

7. 12- sheets Oak Ply $ 540.00

8. 5 - sheets MDF $ 100.00

9. Paint, primer & supplies $ 500.00

10. Bolts, cap screws & washers $ 185.00

11. Grill cloth and materials $ 85.00

12. Tung oil finish and stain $ 110.00

13. 36 Pillows @ $4.50 $ 175.00

14. Internal wiring and connectors $ 15.00

15. Epoxy for granite application $ 32.00

16. Electrical upgrade $ 575.00

17. Inwall Speaker wire runs& Neutriks $ 225.00
and wall plates

--------------------------------------------------

Total material cost $19337.00

The big question seems to be, "Is the total system worth what I paid, let alone the time invested in it."

To this statement, I say, "Absolutely!" Of course I could have gone with much cheaper drivers or sealed or ported and

eliminated the PR's, and, I did not need the Itech amplifiers at all. I could have used MDF for the top and

the base instead of granite, I could have not had the badges made, I could have used canned spray paint, I

could have used cheap spandex for the grills-as a matter of fact, I could have eliminated all the grills entirely.

Instead of all of the I could haves, I can say "I did." I actually did this project as planned from beginning to

end with no compromises. I took my time and waited for the things to come together. I am very pleased with the results.

I have absolutely no regrets and the outcome was exactly as planned. Could I have achieved the same level of performance

using a different system that was more cost effective? I am sure I could have gotten a lot more drivers and a lot more amps

for less money, but on an apples to apples comparison, I would be hardpressed to beat this setup. I definitely think

I made the right choice as far as drivers goes. These things are absolutely phenomenal.

For me, the project was totally worth the effort. It has gained me many new friends, allowed me to utilize skills that I was

not sure I possessed, taught me many valuable lessons for later projects and allowed me to spend over 2 years working on a

hobby that I completely enjoy. The actual building process was as much fun as the listening and tweaking process.

Now, as far as "How does it sound?" All I can say to that is it has exceeded all of my expectations. The sound and

overall feel is phenomenal. The total output is extreme to say the least. Overkill? I say to this, "No!" I just consider

it as headroom. I like my system to sound powerful as it is cruising along. As a matter of fact, before this addition, I

was running things at 5 channels with no LFE. I loved the sound, and now it is just that much better for me. As far as bass

goes, I got what I was looking for. It is visceral- to say the least. Movies that we have seen many times before are now

even better. With test tones, I feel that the house is actually undulating back in forth- just like when you see the videos

of earthquakes. It feels like I am riding a boat in a real bad sea.

My plans are to get the system as complete as possible before having some sort of GTG, so that people more knowledgable

than me can give a totally non biased opinion of the LFE setup.

I thank all of you guys for the support and help in the last few years, and I hope to see and hear from any and all who wish

to know anything I can offer about this build.

Thanks,

Robert Pizzolato