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Subs for open ended Theater - Page 2

post #31 of 45
1/28/13 at 2:37pm
Quote:
Originally Posted by LTD02 View Post

"Additionally it should be noted that for the first 18miliseconds or so, it is physically impossible to pressurize a room (at any frequency) because the speed of sound (although fast) is not instant, it typically takes 36 to 50ms to start taking affect, up to a max of about 1/4 of a second. A trivial fact, but I just thought I'd state it.
There is a special-case to that where that is not true, and that is in hyper-sonic waves, but that's a totally unrelated topic to speakers"

if the room is small relative to the size of the wavelength (i.e. in the pressure vessel zone where the long dim. <1/2 lambda) the speed of sound increases dramatically. this came up when a guy tried to create a double bass array, but it didn't work as expected. then i read about this effect from some physics professors in europe. i don't think i have the reference handy. a trivial fact, but interesting none the less.
I'd say both those conjectures are incorrect. To visualize how a wave pressurizes a room with no lag, blow into a straw, with your hand blocking the open end. There is no lag between when you apply pressure at one end and feel it at the other; that's a basic principle of fluid dynamics. As for the speed of sound increase, I'd say that's someone trying to explain a measured cabin gain while not understanding the mechanics behind it. Geddes would have a field day with him. biggrin.gif
Edited by Bill Fitzmaurice - 1/28/13 at 2:43pm
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post #32 of 45
1/28/13 at 4:00pm
Quote:
Originally Posted by Gomdaf View Post

Would like to keep pricing under under 2k. Any thoughts or a direction I should persue based on this scenario?

Consider an 8 driver quasi-IB with the false wall. 4 manifolds, each manifold containing 2 opposed 15", the four manifolds placed at the 1/4 width and height dimensions of the wall, EQ to taste.
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post #33 of 45
1/28/13 at 4:46pm
Thread Starter 
@PNC Thanks for the input but if you typed that in chinese it would have had the same impact on me smile.gif I'm trying for a simple approach, this is my first project

@nograveconcern Why do you think the sealed is the wrong enclosure here? I'll check out the THT LP you mentioned for a read. I already know i'll end up thinking its cool, pondering it, and then once again doing nothing for a week because i can't make up my friggen mind.

These are my thoughts for now, given that they are going behind a screenwall with around 19" depth and trying to keep it simple:

Enclosure size of 17D x 23.5H x 23.5W by my calculations using 3/4" MDF that gives me an internal volume of 4.34 cu ft. Subtract out the sub volume and bracing and should come in around 4?? I'm not sure on that but if someone knows please chime in.

I did have a couple of questions. I'm going to recess the driver and double up on the front baffle for a total of 1.5". So can I just cut two separate holes for the woofer, one slightly bigger that the other to recess the driver and then glue them together? Is that what peaple do? Heres the mounting info for the Dayton 18 HO:

Overall Outside Diameter

18.17"

Baffle Cutout Diameter

16.69"

Depth

8.94"

# Mounting Holes
8

So would I then cut one hole to about 18.2", cut the other hole in the second baffle board to 16.69" and glue them on top of each other?

Then i would assume i just put the gasket in, and screw her down??

Like I said, first time noob here, just working out some of the details.

Concerning the Amp...any thoughts on the nu3000dsp vs the ep4000? I've mentioned i have an Onkyo5009 with XT32. Will the dsp in the NU3000 help to level two 18's out better than the Onkyo? If theres no gain here, i'd probably just go with the EP4000 and call it a day. I'm just wondering if it will help me get a flatter response or improved SQ down to 18hz

Please feel free to point out anything i've miscaclulated or anything i should do differently. once again, my room is about 2800 cu ft and is open ended.

Thanks!
Phil
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post #34 of 45
1/29/13 at 5:23am
Quote:
Originally Posted by Gomdaf View Post

@PNC Thanks for the input but if you typed that in chinese it would have had the same impact on me smile.gif I'm trying for a simple approach, this is my first project

@nograveconcern Why do you think the sealed is the wrong enclosure here? I'll check out the THT LP you mentioned for a read. I already know i'll end up thinking its cool, pondering it, and then once again doing nothing for a week because i can't make up my friggen mind.


That was directed at RLthx who wants only one sub, only needs to get down to 20hz, and has space behind the screen wall. For you, with a goal of a simple first project with room to grow later, a sealed build will be ideal.

These are my thoughts for now, given that they are going behind a screenwall with around 19" depth and trying to keep it simple:

Enclosure size of 17D x 23.5H x 23.5W by my calculations using 3/4" MDF that gives me an internal volume of 4.34 cu ft. Subtract out the sub volume and bracing and should come in around 4?? I'm not sure on that but if someone knows please chime in.

I did have a couple of questions. I'm going to recess the driver and double up on the front baffle for a total of 1.5". So can I just cut two separate holes for the woofer, one slightly bigger that the other to recess the driver and then glue them together? Is that what peaple do? Heres the mounting info for the Dayton 18 HO:

Overall Outside Diameter

18.17"

Baffle Cutout Diameter

16.69"

Depth

8.94"

# Mounting Holes
8

So would I then cut one hole to about 18.2", cut the other hole in the second baffle board to 16.69" and glue them on top of each other?

Then i would assume i just put the gasket in, and screw her down??

Yes, that's how it's done. wink.gif

Like I said, first time noob here, just working out some of the details.

Concerning the Amp...any thoughts on the nu3000dsp vs the ep4000? I've mentioned i have an Onkyo5009 with XT32. Will the dsp in the NU3000 help to level two 18's out better than the Onkyo? If theres no gain here, i'd probably just go with the EP4000 and call it a day. I'm just wondering if it will help me get a flatter response or improved SQ down to 18hz

Please feel free to point out anything i've miscaclulated or anything i should do differently. once again, my room is about 2800 cu ft and is open ended.

Thanks!
Phil
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post #35 of 45
1/29/13 at 7:10pm
Thread Starter 
Quote:
Originally Posted by Gomdaf View Post


Concerning the Amp...any thoughts on the nu3000dsp vs the ep4000? I've mentioned i have an Onkyo5009 with XT32. Will the dsp in the NU3000 help to level two 18's out better than the Onkyo? If theres no gain here, i'd probably just go with the EP4000 and call it a day. I'm just wondering if it will help me get a flatter response or improved SQ down to 18hz

Please feel free to point out anything i've miscaclulated or anything i should do differently. once again, my room is about 2800 cu ft and is open ended.

Thanks!
Phil

Can anybody comment on the above remarks between these two amps for running two Dayton 18HO's?

Also, do either of these amps have any safeguards against blowing the driver?
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post #36 of 45
1/30/13 at 5:06am
Quote:
Originally Posted by Gomdaf View Post

Can anybody comment on the above remarks between these two amps for running two Dayton 18HO's?

Also, do either of these amps have any safeguards against blowing the driver?

In a sealed box the enclosure protects against blowing the driver, however the DSP iNukes have HPF and limiters if you want to use them.
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post #37 of 45
1/30/13 at 6:29am
Quote:
Originally Posted by nograveconcern View Post

In a sealed box the enclosure protects against blowing the driver
Not really. A sealed box limits excursion, so you're less likely to suffer mechanical failure. But when you limit excursion you also reduce sensitivity and therefore output, which one might compensate for with more power, making it more likely to damage the driver via over powering. The only way to positively eliminate the threat of driver damage is to use a brickwall limiter to limit the amp output voltage to the driver Pe or displacement limit, whichever is the lower, and to high-pass.
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post #38 of 45
1/30/13 at 7:31am
+1 what Bill said.
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post #39 of 45
2/21/13 at 5:17pm
Thread Starter 
Started rolling on this project. Tradeshows and sales meetings bogging me down lately! I'll try and post some picks later but here's where I'm at and a few questions.

Just got two Dayton 18 HO's today smile.gif
I've started box construction (4 cu ft) and have done all except baffles

I'm going with gluing 2 3/4" thick pieces together and a recess for the driver. Questions:

What glue should I use to laminate the two together? I've used PL on all the joints, I thought maybe the expanding properties of PL might not be so good for this.

Should i cut the baffle holes first and then glue together or glue together and then cut and router? Is there a preffered method? Obviously one cut out is larger than the other for the recess.I have a plunge router and circle cut jig.

Lastly...for sealing the inside joints should I scrape away the excess PL and then re-apply a bead of PL or would caulk be better?

Thanks in advance!

Phil
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post #40 of 45
2/23/13 at 6:35am
Cut the baffle holes first just makes sure they will line up. You can use pl to glue the baffles as long as its clamped good which you have to do anyway. No reason to buy different glue for it. If you have good squeeze out your joints will be sealed. No need for extra. What I do is, put a plastic sandwich baggy or latex glove on my hand and smooth down the inside joint bead of pl.

Not sure how you plan to finish these, but Diysoundgroup.com has flat packs for these drivers now. Would make things a lot easier.
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post #41 of 45
2/23/13 at 1:26pm
Quote:
Originally Posted by Gomdaf View Post


What glue should I use to laminate the two together? I've used PL on all the joints, I thought maybe the expanding properties of PL might not be so good for this.

I used wood glue but it's because I had it and PL and I hate using PL anymore than I have to as it's not as easy to work with and clean up. PL will work perfectly fine though as Brian mentioned.
Quote:
Should i cut the baffle holes first and then glue together or glue together and then cut and router? Is there a preffered method? Obviously one cut out is larger than the other for the recess.I have a plunge router and circle cut jig.

If you have a flush trim bit that is easiest. Cut the inner baffle and then cut the outer a hair bit larger on all sides, to allow a little margin of error. Measure dead center as you did on the first one and them glue them together. You can then trim the excess.
Quote:
Lastly...for sealing the inside joints should I scrape away the excess PL and then re-apply a bead of PL or would caulk be better?

I've used both and each work equally well. No need to scrape anything away, just lay a nice bead over the top and be done with it. smile.gif
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post #42 of 45
2/23/13 at 3:13pm
Thread Starter 
Thanks! I do have a flush trim bit. I'll give it a shot
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post #43 of 45
2/27/13 at 6:05pm
Thread Starter 
What screws should I use to mount these bad boys? Is it a bad idea to just use #10 wood screws? Or should I go the Hurricane Nut route? If so, what size? 10 - 32? It scares the crap out of me at this point in the game to go drilling quarter inch holes around my baffle recess lol.. I used a piece of 3/4" birch ply for the inner baffle figuring it would be better to screw into than mdf. Any suggestions or tips for mounting hardware would be appreciated
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post #44 of 45
2/27/13 at 9:28pm
I can't speak for 18's but I've always used course drywall screws which are as long as the thickness of your front baffle. I would imagine you'd be fine as long as you're not going in and out of the holes no more than 6 times or so. If you predrill each hole with a bit smaller than the inside thread diameter of your svrews I can't see why you would have any problems. There's more than enough screws in these speakers to hold them in tight. I think the key to screwing them in is to use a hand screw driver rather than a drill so way you can go slow and steady and not over torque the threads and end up stripping the holes.
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post #45 of 45
2/28/13 at 7:03am
I use hex head sheet metal screws all the way through the baffle. They have full length threads and good head grip so less chance of slipping a point through a surround.
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