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post #301 of 609 Old 04-23-2013, 06:11 PM - Thread Starter
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Originally Posted by HopefulFred View Post

Was that measured at your prime seat? looks pretty good! wink.gif

I would have said that ported was not the way to get lower extension. I would have said that most ported designs require HPF around 20(ish) Hz to avoid over-excursion of the cone at low frequencies. not true?

No, not listening position.. That was in my living room.. mic at about 3 feet. That was my first try with REW.

I'm still working on the subs.. I think generally you are correct, but working with the drivers in my price range it doesn't seem to make a large difference. The ported boxes are flat to 20 and then roll off (HPF at about 15). When I model them sealed they roll off more gradually, but start at about 50Hz. By the time they hit 15Hz they are down about 15dB; down about 25dB at 10Hz.

So yes (if I am doing this correctly), they have a bit more SPL below 15Hz, but not much. I assue when you get into the larger (18,21) drivers, it looks a lot different. That, or I am doing something wrong in WinISD.

Tim
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post #302 of 609 Old 04-23-2013, 06:15 PM
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I think you just need more power.

(that's a general truism, but I mean specifically to get more extension from sealed boxes.)
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post #303 of 609 Old 04-23-2013, 06:27 PM - Thread Starter
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I agree, but the excursion is going past Xmax when I do that. I wonder if I am entering something incorrectly.

I am looking at it now and they are all pretty much in the ballpark at 15Hz. At 10Hz sealed has 10dB over the ported boxes, but it is still down over 20dBs.. Maybe that is the nature of the beast. With room gain it may look better.

Tim
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post #304 of 609 Old 04-24-2013, 08:34 AM
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Im lost.... What exactly are you comparing?

You should high pass the horns within a db or two of where they unload to prevent bad noises and/or mechanical damage to the drivers.

Same for ported @ tuning freq

~12db/oct butterworth generally is good

properly designed Sealed = No high pass and uses acoustic rolloff of box to control excursion.

So yes that should give an advantage @10Hz to a sealed alignment but you need a ton of excursion to amount to anything that low and to compensate for lost sensitivity above the horn/ported tuning.

Generally speaking:

1 ported = 2 sealed ABOVE TUNING(everything equal)

Below tuning sealed has slight advantage bit you need lots of displacement to get meaningful 10Hz content and then generally EQ down the Midbass for a flat response......

Does that help?
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post #305 of 609 Old 04-24-2013, 08:55 AM
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I re-read back to see and I'm still a little confused....

But it looks like your using a lilmike F20 That should be highpassed at least 12db/oct(maybe steeper) no lower than 18Hz without asking in lilmike's thread and depending on power used.

For the F20 or any other ported horn Design "tuned" to 20Hz forget any meaningful output below tuning. Its gonna drop like a rock.

Now if your looking at options

Horns = greatest output above "tuning" with possible response peaks which may need EQ, Largest.

Ported = High output above tuning Larger than sealed.

Sealed = Lowest output in the Midrange but extended LF response. Smallest. Need Multiples for displacement requrements to meet SPL needs.
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post #306 of 609 Old 04-24-2013, 12:25 PM - Thread Starter
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Thanks for the input, Nick. I think I am saying the same thing, just not familiar with the lingo.

Yes, the horn for sure will be HP at 20Hz. I am thrilled with the F-20, it's just about flat to 20, which I think is exactly what Mike said in post #1 of his thread.

Right now I'm trying to figure out what to do for the rest of my subs. I have 2x MFW-15 and was playing around with what to do with them. They'll work pretty well in a horn, ported or sealed so I was plotting them in winisd to try and get a direction. I had originally planned on 2x Tuba HTLP, but I am now leaning away from that.

Sealed or ported the MFW's seem pretty much the same.. with some exception. Ported they're pretty flat, but really drop off below 20Hz. Sealed they start rolling off (gradually) at 50Hz, but put out more once you get below 15Hz.

Right now (meaning at this hour) I am thinking of dual opposed sealed in about 7 cu.ft.

Tim

edited to remove tuning in a sealed box.. duh
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post #307 of 609 Old 04-24-2013, 03:29 PM - Thread Starter
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OKay.. so here's where I'm at. I've modeled a few different way, and assuming the data was entered correctly:



Here you can see the same driver modeled a few different ways (green is 2 drivers)

I highpassed them all at 12Hz and manipulated the signal to bring them all to max excursion (or a wee bit over), and here are the SPLs:



Looking strictly under 20Hz you can see what I am talking about. By the way, the chances of me actually building an 18 cu.ft. enclosure are slim to none smile.gif

Tim
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post #308 of 609 Old 04-24-2013, 03:44 PM
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Why not build 2 more F20s?

Integrating sealed with a horn can be tricky. Phase shift introduced by the high pass can(often) causes cancellation below 20hz. IOW they might not play well together...,

For meaningful <20hz output in your gonna need more than 2- 15s.

Im not tryin to debunk you man, just dont want you to be disappointed/frustrated.
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post #309 of 609 Old 04-24-2013, 03:59 PM - Thread Starter
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Quote:
Originally Posted by NicksHitachi View Post

Why not build 2 more F20s?

Integrating sealed with a horn can be tricky. Phase shift introduced by the high pass can(often) causes cancellation below 20hz. IOW they might not play well together...,

For meaningful <20hz output in your gonna need more than 2- 15s.

Im not tryin to debunk you man, just dont want you to be disappointed/frustrated.

Nah, no debunking going on. I knew that to be the case (why else buy an 18 or 21 if you could use 15's), but certainly I could tell by the graphs that it wasn't gonna work out. I was trying to see what I could squeek out of them, which apparently is not much sub 20 (probably a no brainer to those sub gurus).

As for the F-20s.. space. And weight. Mostly weight. I had planned for 2 F-20s on the stage but at final measurement I have 1" to space *and* I have to lift it 3 feet in the air to get it over the bottom of the screen framing (poor planning on my part) *and* I have to squeeze my 3 stentorians in there. I am wondering if I will actually use the F-20 I built.

The DVC385-88 ported build I made models way better. Yeah, I gotta HP it at 15Hz, but it beats the MFW no question. It looks like I may be back to building horns for the MFWs,probably the THTLP. Up front either two F-20s or two of the ported DVC385's I built.

Besides, I like the F-20 in my living room smile.gif (shh don't tell the wife).

Tim
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post #310 of 609 Old 04-24-2013, 04:10 PM
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You've got room for 8cuft vented boxes? The red trace looks pretty good to me, but I understand the interest in infrasonics, which is one of reasons I'm leaning towards sealed.

What's the volume on the sealed box (yellow trace)?

What kind of SPL are you expecting out of the F-20s? I would have thought two should get you reference (115dB at LP) pretty easily. If that's the case, extras are for smoothing, not SPL, right - so max output is not so important? Nick knows better than me, I'm sure, but I've heard and read Geddes say basically as much. In fact, what I understand from Geddes is that you could (should?) build and EQ your filler subs basically to operate only in the bands that need smoothing. I don't know anything about the LF phase relationships Nick is talking about, but I would think your amp will have a phase dial on it - yes?

(edit: I didn't get to see your previous post before I started writing - output may be more important if the F-20s don't get worked in.)
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post #311 of 609 Old 04-24-2013, 04:29 PM - Thread Starter
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Quote:
Originally Posted by HopefulFred View Post

You've got room for 8cuft vented boxes? The red trace looks pretty good to me, but I understand the interest in infrasonics, which is one of reasons I'm leaning towards sealed.

What's the volume on the sealed box (yellow trace)?

What kind of SPL are you expecting out of the F-20s? I would have thought two should get you reference (115dB at LP) pretty easily. If that's the case, extras are for smoothing, not SPL, right - so max output is not so important? Nick knows better than me, I'm sure, but I've heard and read Geddes say basically as much. In fact, what I understand from Geddes is that you could (should?) build and EQ your filler subs basically to operate only in the bands that need smoothing. I don't know anything about the LF phase relationships Nick is talking about, but I would think your amp will have a phase dial on it - yes?

(edit: I didn't get to see your previous post before I started writing - output may be more important if the F-20s don't get worked in.)

The yellow trace was about 4cu.ft IIRC. Just looking at the graphs I think the MFW would be best suited for a horn. I can best them with the DVC385-88 that I already have, so it doesn't make sense to use them in another configuration.

If the F20 fit where I needed it, it's a no brainer.. it's awesome and the measurements show it does exactly what Mike said it would. But I need a smaller package. I can lay two THTLP down on top of each other and they will fit nicely in the rear of the theater. I would use two ported boxes tuned to 15Hz in about 7 cu.ft in the front that would dig a little deeper than the horns.

I wish I had a little more room.. but with the stage being 1" wider than the F20 it would take a lot to get it in there without damaging something. It may still happen.. just keeping all avenues open at the moment.

Tim
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post #312 of 609 Old 04-24-2013, 06:30 PM - Thread Starter
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Okay, so you guys motivated me to finish up the sub I had in the basement. As built it is 7.36 cu.ft. tuned to 17.5Hz:



It's the same driver, just different enclosures. Measurements taken at the same session-- same room (subs are next to each other), same settings, set the mic at 3' from the port.





Oh, and one more piece of eye candy...

IMG_1679.JPG

Tim
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post #313 of 609 Old 04-25-2013, 08:30 AM
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Very cool. Thats the fastest sub build I ever saw!!! eek.gif

Wheres the pikchers!!!!

I understand space contraints for sure. Those look like they would play very nice. If your needing output, ported is the way to go imo.

Also FWIW the MFW is for all intents and purposes the same driver as the Dayton DVC 15. They model nearly identical so consider them interchangeable. If you need more spl just pickup more DVCs when they on sale. biggrin.gif

How much power are you feeding the MFW in ~7cubes?
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post #314 of 609 Old 04-25-2013, 10:16 AM - Thread Starter
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Quote:
Originally Posted by NicksHitachi View Post

Very cool. Thats the fastest sub build I ever saw!!! eek.gif

Wheres the pikchers!!!!

I understand space contraints for sure. Those look like they would play very nice. If your needing output, ported is the way to go imo.

Also FWIW the MFW is for all intents and purposes the same driver as the Dayton DVC 15. They model nearly identical so consider them interchangeable. If you need more spl just pickup more DVCs when they on sale. biggrin.gif

How much power are you feeding the MFW in ~7cubes?

Haha, when you read the thread on that ported sub (link in my sig) you will find that the build was anything but "fast" biggrin.gif When I model the MFW vs the DVC the DVC does seem to do better in the 20Hz region. Of course I am just looking at the lines on a graph.. They may be negligible in reality.

The only amp I have atm is a BKa-1000, so I am feeding them plenty. Not sure how to determine what I am actually giving them-- can I figure it out with a DMM?

All I can say is at ~22Hz the difference between the F-20 and ported box is like night and day. The F-20 rocks the place.. the ported is nothing special. It really makes me want to go with the two F-20s but I just realized they might not fit at all due to the screen frame. Need to really buckle down and draft the screen wall to figure out how to make this work.

The ported box is sized to slip right in under the screen, but the output is clearly not the same as the F20. I thought it would perform a tad better than the F20 at sub-20Hz.. but they are surprisingly similar.

I posted about the Kicker C154 in the DIY forum.. this seems like another cheap alternative. Not quite as good as the DVC, but man it's real close. Wait, why am I looking at more subs?

What I really want s to fill in the low end (sub-20) but I guess I'm talking bigger speaker and bigger dollars to make that happen. Also seems like it is going to create a bigger EQ issue.



Tim
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post #315 of 609 Old 04-26-2013, 05:08 AM - Thread Starter
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Micro-update. I've been ordering (and boxes have been arriving) the finishing details. Don't make the mistake I did: you get close to the end and start thinking "all I need is carpet and seats" and don't account for all of the little finishing details.

I thought, "I just need 3 doors, that's about $350". Then you add hinges (got 4x4 black ball bearing for the theater door), latches, thresholds, seals.. man it's a lot more than $350.

Cables, banana plugs, plates, speakon connectors.. yeah that's easily another $100.

By the way, the door slabs came in.. I went to pick them up, took a deep breath, bent at the knees, picked one up.. then put it back down. Employee said "what's the matter". "That is not a 1-3/4" thick door". Yep, they sent 1-3/8. So I am waiting for replacement slabs.. Hopefully today.

Frankly if you're setting a budget, I'd add $1000 for the stuff you don't think about until you need it.

I'm hoping the black DMD fabric will come today so I can get the columns finished up (also waiting for panel retainers...). I haven't ordered the red fabric yet. GOM is pricey and I won't need it until the very last minute as it will only be on the wall-hung absorber panels. I'm looking at my panel design to see if there is a way I can reduce the yardage (and $$$).

Tim
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post #316 of 609 Old 04-26-2013, 05:20 AM
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Tim,

 

I couldn't agree more - carpet is NOT the last expense.  I was telling my wife that the carpet should be the last big purchase, but then I started looking at my list of things I need to finish and quickly realized I'm not even close.

 

  • smoke detector
  • zwave thermostat
  • zwave switches
  • step lights
  • cables
  • shelves for rack

 

I hope she doesn't notice the flow of boxes arriving hasn't slowed.

 

 

With that said - you are almost there!!  It looks like you will cross the finish line before me.

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post #317 of 609 Old 04-26-2013, 05:29 AM
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Quote:
Originally Posted by Mr.Tim View Post

Frankly if you're setting a budget, I'd add $1000 for the stuff you don't think about until you need it.

And don't forget about all the "soft" costs too....like beer to drink while working on the theater. That alone can be the cost of a projector throughout the course of a project! tongue.gif
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post #318 of 609 Old 04-26-2013, 08:12 AM
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Quote:
Originally Posted by TMcG View Post

Quote:
Originally Posted by Mr.Tim View Post

Frankly if you're setting a budget, I'd add $1000 for the stuff you don't think about until you need it.

And don't forget about all the "soft" costs too....like beer to drink while working on the theater. That alone can be the cost of a projector throughout the course of a project! tongue.gif

+1
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post #319 of 609 Old 04-27-2013, 06:06 PM - Thread Starter
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Well.. nothing that I needed for today actually came. Looks like everything is coming on Monday. No, hinges, so I couldn't hang the doors. No fabric, so I couldn't finish the columns.

I ended up just sputtering around doing miscellaneous things. I got my cables terminated in the AV closet:

IMG_1682.JPG

Soldered all the sub connections (wired for 6 subs + coax for a powered sub). I also finished up the HVAC in the AV closet.. you can see the return filter/grill below the speaker connections. That one is tied into the house HVAC system.. when the air handler is running that will draw air out of the closet. I also have a Panasonic inline fan on a thermostat that draws air from the top of the closet.

I made a lot of these (and have many more to do):

IMG_1686.JPG

I'll be using those whips to connect the subs to the wall plates and to connect the amp (which has speakons) to the speaker terminals in the AV closet (pictured above).

I wish they made a decent wall plate with speakons.. They are realllly nice and so much easier to terminate. I could only find plates in stainless so I went with the ubiquitous banana jacks everywhere. I probably should have made my own wall plates.

Tim
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post #320 of 609 Old 04-27-2013, 08:55 PM
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The good news here is that all those things would have been tacked onto the "oh yeah I still need to do that" list, and now you've gotten them out of the way. So that is a good day's work. smile.gif

And it's not too late to make your own speakon wall plates. wink.gif
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post #321 of 609 Old 04-28-2013, 05:03 AM - Thread Starter
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Quote:
Originally Posted by HopefulFred View Post

The good news here is that all those things would have been tacked onto the "oh yeah I still need to do that" list, and now you've gotten them out of the way. So that is a good day's work. smile.gif

And it's not too late to make your own speakon wall plates. wink.gif

You don't know how true that is, Fred. I dreaded getting in that little closet (I also had to reverse the supply and return piping on the HVAC) and finishing that up. Rightfully so-- my knees were killing me-- but I can cross that off the list.

There's a still a bit of wiring to do for the thermostat, smoke alarm and a few spares.. But not too bad.

I just realized I need 2 more panels for my columns.. But I'm out of 3/8" ply. Really don't want to spend $35 on another sheet for 32x48 of material.

I'm still undecided on subwoofers. I think I may have a plan to get 2 F-20's behind the screen. I measured it out, this is what it would be:

Left side of screen <|> 20" wide space to put left Stentorian in <|> F20 <|> 20" of space to put Center Stentorian in <|> F20 <|> 20" space to put right Stentorian in <|> Right edge of screen

So the questions I have are 1) what to I do about the giant wall of F20 and reflections? I treated the entire front wall.. but a lot of it is blocked by the F20s and 2) what issues, if any, do I have with only 20" of space for the Stentorians (the stens will be flush with the front of the F20's); am I getting into some type of baffle that I need to worry about?

Tim
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post #322 of 609 Old 04-28-2013, 06:27 AM - Thread Starter
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Caviats of this speaker arrangement??

Screen_Wall.png


Am I going to get any funk due to the F20's being so close??

Tim
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post #323 of 609 Old 04-28-2013, 07:20 AM
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Theoretically you could pickup some baffle reinforcement from the faces of the F20s. Even if you did though it would only likely yield a db or two gain in the lower FR. I dont believe it will affect the mains at all in an appreciable way. Any effect would be minimal and easily tamed with room EQ.

I would however treat the faces of the F20 also, they are now a big reflection point on front wall.

When placing pay attention to the position of the "mouths" and place them away from modal pressure minimas and maximas. Generally better with mouths down firing outwards. Measure and confirm.

Edit: Forgot to mention JDanforth has his pair of F20s on his front stage like this and i thought it worked great. I didnt measure anything abnormal in this config. Certainly less impact than other room effects.
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post #324 of 609 Old 04-28-2013, 07:39 AM
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I think Nick's right. The LF gain can be EQed out if it's a problem. The treatment they need is for HF reflections off the back of the screen - so whatever 1 or 2 inch treatment you've got on the wall should be continued onto the fronts of the boxes.

I'm not sure if I agree with Nick about orientation - not that you'll have much choice. I would try to position the acoustic centers 1/3 and 2/3 across the front wall. That should set up the standing waves to cancel out the width modes - basically producing a plane wave from the bottom of the front wall. It'll still couple to height modes and obviously length modes, but it should help seat-to-seat variation across each row of seats. (That may be the same thing Nick is recommending, but I don't think about it the same way he's talking about it.)
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post #325 of 609 Old 04-28-2013, 08:02 AM - Thread Starter
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Quote:
Originally Posted by NicksHitachi View Post

I would however treat the faces of the F20 also, they are now a big reflection point on front wall.

When placing pay attention to the position of the "mouths" and place them away from modal pressure minimas and maximas. Generally better with mouths down firing outwards. Measure and confirm.

Edit: Forgot to mention JDanforth has his pair of F20s on his front stage like this and i thought it worked great. I didnt measure anything abnormal in this config. Certainly less impact than other room effects.

The mouths can either face towards the side or the middle, which is to say towards each other or away from each other. I had assumed away from each other after reading a whitepaper by some guru whose name I can't recall (Geddes?)

Quote:
Originally Posted by HopefulFred View Post

I think Nick's right. The LF gain can be EQed out if it's a problem. The treatment they need is for HF reflections off the back of the screen - so whatever 1 or 2 inch treatment you've got on the wall should be continued onto the fronts of the boxes.

I'm not sure if I agree with Nick about orientation - not that you'll have much choice. I would try to position the acoustic centers 1/3 and 2/3 across the front wall. That should set up the standing waves to cancel out the width modes - basically producing a plane wave from the bottom of the front wall. It'll still couple to height modes and obviously length modes, but it should help seat-to-seat variation across each row of seats. (That may be the same thing Nick is recommending, but I don't think about it the same way he's talking about it.)

Okay, seems everybody agrees about the EQ-ability. The front wall is faced with 3-1/2" roxul spaced 1" off the wall.. I don't have anything 1" thick on hand for the front of the F20's. I can use something thicker, provided I put the F20 in first, then place the treatment on the F20 both above and below the bottom of the screen. Oh, my Kingdom for an inch of stage..

Could I put these diffusers on the front? Cheaper than other alternatives (eg an entire roll of linacoustic). I could use 2" OC703, but then I'd have to wrap it in fabric.

Thanks guys!

Tim
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post #326 of 609 Old 04-28-2013, 08:03 AM
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Yes^ HF is ab correct this is ideal. That puts both subs in the 3rd order HP region but with opposite polarity thus cancelling each other's modal excitation.

IDK if he can get to 1/3-2/3 looking at that diagram though...... Assuming he cant, he should avoid the 2nd and 4th order minimas and maximas as they couple constructively and obviously avoid the corners too (1st order).
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post #327 of 609 Old 04-28-2013, 08:18 AM
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Chances are that the foam stuff off eBay does not do what it should. I'd use the 2" OC703.
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post #328 of 609 Old 04-28-2013, 08:24 AM - Thread Starter
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Okay, I admit I have no idea what the minima and maximas are smile.gif I dimensioned the digram with 1/3 points and I also marked the 1/4 points. Positioning at 1/3 not possible. Can't even get close.



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post #329 of 609 Old 04-28-2013, 09:08 AM
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http://www.hunecke.de/en/calculators/room-eigenmodes.html

This image depicts the second order modal response in the x (width) dimension. As explained in the caption, the white areas are minimum pressure (nulls) and the dark areas are maxima (peaks). The minima are the 1/4 points. As Nick says, you want to avoid the 2nd and fourth order minima and maxima (though I think 4th order is sufficiently HF as not to matter). If the acoustic center of your F-20 lands at the 1/4 point, they will drive the 90Hz standing wave constructively, and 90Hz variation seat-to-seat (within each row) will be large and uncorrectable. (Note that 90.3 Hz is the center of the 2nd order width eigenmode based on a functional width of 3.81 meters. That frequency may change slightly in real construction as the walls are not infinitely rigid - flex in the walls will reduce the frequency some.)

I think you want to place the ports closest to the center - that is, place the F-20s as wide as possible, with the ports pointing toward one another. Nick?
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post #330 of 609 Old 04-28-2013, 09:47 AM - Thread Starter
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Ok, fumbling through this I pumped my dimensions into Fred's link:

Eigenmode%252020Hz.png

Eigenmode%252041Hz.png

Eigenmode%252045Hz.png

90.3 is just like yours. So I don't want it in the black nor in the white?

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