IB makeover..........

**Rodny Alvarez** · **04-02-07, 11:13 PM**

I'm back!!

The port has a resonance pass 60Hz, when I was inside of the box and you talk or scream can here a weird noise with a little echo, I think is the PVC pipe, change the crossover to 60Hz and it goes away!, I'm going to try Dynamat on the port to see if it kills the resonance, anybody with the same problem ??

If there is something else you guys want me to do before the other IB is gone let me know, I'll be glad to give it a shot

Haven't work on the other side, the plan is to work on it Saturday

**collo** · **04-03-07, 12:08 AM**

Hi Rodney,

since this is the last chance for an A-B comparison, I thought I would chime in with a request.

I know that in the past there has been a vast amount of discussion about the audibility of group delay at low frequencies. Your setup would allow a simple comparison without all the theorising.

Would it be possible for you to compare a few DVD sequences that have well defined transients in the range where the port is contributing to the output. This would be gunshots (eg Open Range) and assorted doors slamming and objects dropping (eg LOTR)

It would be interesting to know if the ported system is any less defined than the IB for this type of material.

regards
Collo

**SteveCallas** · **04-03-07, 12:51 AM**

I think in previous measurements of Open Range the gunshots weren't really all that low, so I don't know if that would be a good scene to use, but I could be mistaken. I think the low end favorites like Incredibles, WotW, and MI:3 with plenty of infrasonics would still be the best bets.

EDIT: Here it is. I think the bulk of the effect from this scene is actually higher up in frequency.

Quote:

Rodny wrote:

The port has a resonance pass 60Hz, when I was inside of the box and you talk or scream can here a weird noise with a little echo, I think is the PVC pipe, change the crossover to 60Hz and it goes away!, I'm going to try Dynamat on the port to see if it kills the resonance, anybody with the same problem ??

Hmm, cardboard sonotube is a naturally more damped material than pvc, I'm thinking that would play a role. To fix the issue with the pvc though, I'm thinking you would want to add more mass to the port. Strips of cloth dipped in plaster of paris and then warpped around the port perhaps?

**brucek** · **04-03-07, 08:12 AM**

Quote:

when I was inside of the box and you talk or scream

Quote:

anybody with the same problem ??

I'll bet not..............

**Sonnie** · **04-03-07, 10:46 AM**

Yeah... how often do you know people who can actually crawl inside their subwoofer box? With the size of these ports growing to massive diameters it won't be long before we have to put a grille cover over the port to protect kids from having access to inside the box. I can hear momma calling little Johnny now... "Where are you hiding little Johnny?" Or maybe the cat finds a new home.

Anyway... how exactly would you determine "group delay".... how do you view it?

**SteveCallas** · **04-03-07, 11:54 AM**

I believe he is referring to the shallower rolloff of a sealed as compared the the sharper rolloff of a ported below tuning - no measurements needed besides FR. In my opinion, it's about as much of a non issue as you can get when you take all aspects of performance into consideration in this range, easily trumped by a variety of other issues, but some folks (not you collo

) need some excuse to hold on to.

**collo** · **04-03-07, 05:33 PM**

The extra output of a ported system comes from exciting a resonance over the working range of the port.

I've always suspected that such a system may take several cycles to build to full excitation, and possibly delay over several cycles. If so, this may lead to sharp transients being less well reproduced in a ported system.

I was interested to see if there was any evidence of this happening in Rodny's ported IB.

I used the term "group delay" as this is visible in WinISD when you compare ported vs sealed. I think it actually emcompasses more than just the phenomenon I described, and I'm not sure how one would measure it.

I certainly don't see this as greatly diminishing the benefits of a ported sub (I've built a few...), but opportunities for an A-B test don't come along very often.

**SteveCallas** · **04-03-07, 06:39 PM**

Quote:

collo wrote:

I've always suspected that such a system may take several cycles to build to full excitation, and possibly delay over several cycles. If so, this may lead to sharp transients being less well reproduced in a ported system.

Ilkka has measured this with a ported sub with port open and port plugged. The delay at tuning frequency is definitely not o the order of several cycles, see here. The difference he measured at tuning, where delay would be highest, was less than one cycle. As tuning frequency gets lower and lower, I see this being less and less of an issue due to sensitivity at infrasonic frequencies and the actual tactile effect. As an example to test, try playing a 10hz sine wave for only 0.5 seconds and see what kind of an effect you get out of it

I definitely agree with you on this opportunity though, it is about as ideal as it gets, and I'd encourage as much testing as can be stomached.

**collo** · **04-03-07, 09:54 PM**

Yeah, that was the thread I was remembering. I sat off it a bit and missed that little gem from Ilkka about the port getting up to speed quickly.

I just received a query from a bloke in England wanting some 10inch flared ports. If he procedes with an order, I'll have to make the molds.

Don't tell me that upgraditis is lurking again....muuuussst resist.......

**Rodny Alvarez** · **04-03-07, 10:06 PM**

OK..... so you guys want me to play some scenes with low bass (LFE) and see if there is any noticeable (transients)sound from the IB and LLT??
Steve!! you said to play a 10Hz sine wave for 1/2 of second or 5 seconds??
Which LOTR has the scene and what chapter??

Just want to make sure I'm doing it right!!:

**SteveCallas** · **04-03-07, 10:54 PM**

Quote:

Rodny wrote:

Steve!! you said to play a 10Hz sine wave for 1/2 of second or 5 seconds??
Which LOTR has the scene and what chapter??

Well I was saying it in jest to point out that differences in group delay at 10hz are essentially pointless, I didn't mean to actually test it. But I guess if you have a burning desire to actually test it, I can record you a 10hz sine wave that lasts 0.5 seconds (yes, 1/2 second) and send it to you.

The kind of testing I'd like to read more about would just be more of your impressions from watching movies with solid infrasonics and switching back and forth between the two bass systems. I'm convinced that people will prefer more headroom and linearity down low with a sharper rolloff as compared to less headroom with an earlier, shallower rolloff - it just makes sense based on the way we percieve infrasonics. But the more impressions you could provide one way or the other would be great

Have you tried MI:3 yet? Plenty of solid infrasonics in that one

**Sonnie** · **04-03-07, 11:06 PM**

From DrPainMD's Master List of DVDs with Bass thread:

"Lord of the Rings: Fellowship of the Rings" EE DTS-ES DD-EX
1. Ring drops, Chap 1 (0:03:49)
2. Sauron Explodes, Chap 1 (0:04:04)
3. Skeleton falls into well, Chap 8 (0:27:39)

"Lord of the Rings: The Two Towers" EE DTS-ES DD-EX
1. Gandalf falls, Chap 1 (0:02:48)
2. Black riders, Chap 14 (0:49:42)
3. Gandalf slays Balrog, Chap 15 (0:53:54)

"Lord of the Rings: Return of the King" EE DTS-ES DD-EX
1. Green light, Chap 11 (0:41:40)
2. Undead King, Chap 27 (1:27:22)
3. Shelob, Chap 33 (1:51:40)
4. Olephant charge, Chap 42 (2:12:48)
5. Mount Doom, Chap 53 (2:40:50)

"Mission Impossible III"
1. Menu
2. Explosive charge in your head, Chap 1
3. Standby to go Live, Chap 3
4. Phoenix, get to the LZ!, Chap 3
5. Apache flies through exploding van, Chap 4
6. Chap 11
7. Chap 17

**Rodny Alvarez** · **04-05-07, 11:36 PM**

I watched some of the scenes the Sonnie posted and some scenes the LLT had more information then the IB, I can hear more sounds when played the LLT, we switch back and fourth during the same scene and you can hear other things that you couldn't with the IB

My son was switching amps during the scene and even him said that the LLT sounded better.

LORT Return of the King, mount Doom, chap 53 definitely there was more sounds when we played the LLT, this is not on all the scenes some scenes it was hard to tell the difference.

MI III, standby to go live and phoenix get to the LZ chap 3, the LLT outperform the IB

on this scene you can feel the blades going right by your head, it just sounded and felt better with the LLT

Open Range the gun shots, again the LLT move my pants more then the IB, specially with the double barrel shotgun

I dint hear any port noise or anything weird coming from the LLT, or the IB,........... I did heard something coming from the IB when we played a BASS CD that I used at work on car stereos, both of the amps set the same way and no EQ , it sounded like the IB bottom out,( made a clack noise ) the LLT did not made the noise!
The scene "Irene" from Black hawk down, its louder with the LLT and you can feel it more

I'm not very good explaining things

so if there is something the you want o need to hear............. I guess you better come on down and tested yourself!!

**collo** · **04-06-07, 04:31 AM**

Well thanks for that Rodny,

your results will set the cat amongst the pigeons!

Would you say that, apart from being louder, the ported design was as detailed as the IB?

Collo

**Chrisbee** · **04-06-07, 05:43 AM**

Still clutching at very large straws here...

What about the large mass of air in that huge port?

Wouldn't it tend to continue oscillating for far longer than in the dinky little ports used on commercial subs?

**Sonnie** · **04-06-07, 11:00 AM**

I'd say those are fairly convincing results... hearing is believing! I believe I'm happy I ultimately went with LLT...

**SteveCallas** · **04-06-07, 06:14 PM**

Thanks for the additional impressions Rodny, that kinda seals the deal as far as I am concerned. Measurements show a substantial improvement and subjective impressions point to a uniform preference. I bet it's almost scary to consider what you'll have on your hands when you convert the second IB to a LLT

**Rodny Alvarez** · **04-06-07, 07:31 PM**

Quote:

collo wrote:

Would you say that, apart from being louder, the ported design was as detailed as the IB?
Collo

In my opinion YES!! and some scenes even better!!

I've had my IB for a while now, it sounded good, but after listening to the SLLT is just mo better

,in the scenes with the low bass you can feel it and hear it better, like the scene when the ring drops, the thump its scary

.
I'm happy with the results

, cant wait to finish the other side, the wood is cut already all I need to do is put it together

, the only thing is the acoustical material, just cant make up my mind on what to use and I want some damping material as well, something like Dynamat or Hushmat.

**collo** · **04-07-07, 12:40 AM**

Thanks for that Rodny!

It's rare that these opportunities come along, and I'm sure your results will be discussed for quite some time yet!

I find myself looking at my room containing the manifolds. Maybe a cheap door with a few 10inch ports through it.......certainly 6dB more headroom @ 20hz would be nice.

A 12 driver IB was supposed to cure me, but it's funny how the urge continues........

**Wayne A. Pflughaupt** · **04-07-07, 03:23 PM**

How does cabinet rigidity fit in with SLLT and LLT designs? It seems a daunting task to make something as large as Rodny’s as rigid as a good manufactured sub is. I’m going to hazard a guess that since the internal volume is so great, and a ported design, it doesn’t exert the same pressure on the cabinet that you have with a smaller sub?

I’m sure glad I caught this thread before embarking on the IB I was contemplating! I certainly like the idea of isolating the backwave from the rest of the house. Not to mention, you can insulate the outside of the box, to help protect it from extreme temperature changes of an attic – something I’ve been concerned about an IB here in Houston.

Regards,
Wayne

**Sonnie** · **04-07-07, 04:30 PM**

Use serious bracing... that's what I did, although my panels were no where near the size of Rodny's. He mounted his to the rafters and top side of the ceiling joist... so he had 2 x 6 or 2 x 4 bracing for all but one side and he braced it pretty well. Maybe he can share some pics of it. You can brace a large panel with a couple of 2 x 4's and it should be just as rigid any sub... the bigger the panel... the bigger and more braces you use.

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