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Leaving the backside open (Read 11638 times)
gexter
Ex Member



Re: Leaving the backside open
Reply #15 - 01/12/06 at 05:59:15
 
I thought that the one side vented idea was kinda cool. But I think that if it is not flat on the carpet on the floor whats the use. But its still a idea. I would not try it that way so maybe I should have said that in the beginning.

My orignal post says it all  (Hmmm   how do ya figure that?
IMHO of course.) then I thought I was being an a55  shooting the idea down.  

I was running my 5 1/4 flat on the floor on some thin carpet with a 20 lb plate on it. thats the way it work best. it's in a holiday trailer and gives a good illusion of bass for the kids. ( rattles the hell out of everything)
They use it and like it because I don't and I don't want to play with it anymore.

That would not work at all in my house!. My toy WO32 is set up just like 60 mentioned a couple times. mouth firing into the floor 4" up and thats how it works the best for the room. I would have not even thought of that unless 60 would have mentioned it. I screwed with that design and I like it. its my favorite build and most fun.

I admit that I don't play around and experiment anymore. I read though all these formulas and ready made plans.
I am reading another book right now and I got so bored I checked in here to be accused of using crack. ( thats more fun than the book)

Now its not nearly as much fun as " what happens it I do this...... oh that sucks what about this... mmm better...why?" Trying it in differant ways is always fun and then sooner or later you hit the wall of physics.

I would not argue with the Dawg either and a whole host of others. Well ok ya I would argue but thats for entertainment value not because I think I am right.  ;)


Smiley





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DirtDawg
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Re: Leaving the backside open
Reply #16 - 01/12/06 at 06:48:47
 
Fellas, groovy fellas,

The kRaK remark was a meager attempt at humor and once again it fell thru the cracks and became total goofyness. I was only crackin' on ya, without realizing there was some sensitivity to the subject. If I ever come up with a way to crack you guys up I'll be happy, but I hope no one has a burr in their crack tomorrow. Gotta get crackin' here. Those kids get up at the crack of dawn.
Cheesy Cheesy Cheesy
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« Last Edit: 01/12/06 at 06:49:32 by DirtDawg »  
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Jet-Lee
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Re: Leaving the backside open
Reply #17 - 01/12/06 at 14:54:57
 
LOL, that crack comment was kinda funny to me. I thought DD wanted some.

I still, though, don't understand why my idea wouldn't work only doing it to one side.

A floor is concrete/wood, padding, carpet. Why can't you make a floor, with padding and carpet, and just attach it to the box. You would just flip the box over on top of your "floor" so that your not compressing everything too much to cancel the varo-vent, but not too little to make it too much, but it's set just the same as if it was in your living room. The you secure the "floor" to the box with brackets to keep it at it's pressure and still be mobile.

You could then stand it on end with the mouth facing down about 4" and have the varo-vent effect along with the great sounding down-firing of the horn.
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Hellion
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Re: Leaving the backside open
Reply #18 - 01/12/06 at 16:59:22
 
Yeah what's wrong with securing the "floor" to the box?
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J_Rock
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Re: Leaving the backside open
Reply #19 - 01/12/06 at 20:40:27
 
I can understand if you didn't read my post, but when you ask what people think and I already stated I think it would work similarly if done only on one side...
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Jet-Lee
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Re: Leaving the backside open
Reply #20 - 01/12/06 at 20:55:33
 
I just realized, while reading, all your doing by laying the open WO or WO32 on the carpet, is making it a variation of an aperiodic box.

An aperiodic membrane is aka a variovent.

Now, why is it that you absolutely have to vent an aperiodic enclosure into a seperate sealed volume, and not just out into thin air? I don't understand that part, since it works just fine with a WO/WO32.

J_Rock, don't mean to argue, but I was rather confused by both yours and DD's posts. You both say that it wont work, but it could.....confusing to me.
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« Last Edit: 01/12/06 at 20:58:13 by Jet-Lee »  
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DirtDawg
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Re: Leaving the backside open
Reply #21 - 01/12/06 at 21:34:54
 
I'm not saying that covering the top and bottom sides of a WO32 with carpet or some other acoustically absorbent material will not work. As long as the seal is good and the panel is rigid, it works. If you feel the need to absorb certain frequencies that might hit the top or bottom, there are better things than carpet to use for that.

Treating the inside of a cabinet with absorbent materials will not create an aperiodic enclosure or a vario-vent. The whole reason to leave the bottom off and couple your cabinet directly to the carpeted floor is to extend one side of the port/vent/horn to almost infinity (almost!).

The other (top) side will still be operating at the same specification, but the side that is down will appear longer to the pressure exiting the cab and continue to load or resist that pressure wave as it enters the room. That will give you a better coupling into the air in the room. The added benefit is that the internal pressure will also enhance the coupling to the floor, since the floor is subjected to all the pressures inside the cabinet.

It's not complicated, it's just difficult to explain.

If you want an aperiodic cabinet, the main thing to remember is that it is merely a tuned vent cabinet which has a resistive port. You do not need 2 chambers to achieve this. I think that idea came from looking at pictures on that car audio site where the trunk seems to be drawn as if it was more important than it really is. The resistive port will help to smooth out the impedance peak at Fs in a much smaller box at a loss of total output. OK so, just add more power to the smaller cabinet!

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Jet-Lee
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Re: Leaving the backside open
Reply #22 - 01/12/06 at 21:47:23
 
Everything I've read has stated that with an aperiodic box, the volume that the aperiodic membrane vents to needs to be completely sealed from the volume that the cone of the speaker plays to. I still do not understand why, and no one explains it.

I guess I'll never understand the vario-vent aspect of the WO/WO32.

I'm not sure you understand 100% what I mean with the carpet idea, I'm not "treating" the inside of the box. It's really just creating a false (portable) carpeted floor, and securing the WO/WO32 to it. It would be the same as taking your WO/WO32, securing it to your existing floor with angle brackets, then cutting out that square of floor. SO you have a portable vario-vented WO/WO32.
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« Last Edit: 01/12/06 at 21:51:06 by Jet-Lee »  
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DirtDawg
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Re: Leaving the backside open
Reply #23 - 01/12/06 at 23:11:51
 
[quote author=Jet-Lee  link=1136480094/15#22 date=1137102443]Everything I've read has stated that with an aperiodic box, the volume that the aperiodic membrane vents to needs to be completely sealed from the volume that the cone of the speaker plays to. I still do not understand why, and no one explains it. [/quote]
The actual resistance to the flow of air through the membrane is what damps the resonance of the driver. Generally, the common practice is to use a vent that is equal to the driver's area and a much too small cabinet volume and bring the tuning of the vent down to the desired range with layers of resistant material. You can also get there by using membrane material behind or in front of the driver, but it is a more difficult approach for the DIYer. The reason it is more desirable to use the membrane suspended in the cabinet or attached to the driver is that it's a more efficient way to damp the resonance.

Those are the most difficult to tune, because the air space between the driver and the resistive membrane is so small. A much easier plan for the dIYer without test equipment, is to use a resistive port design.

I'll try to find a site that explains it for you, written by someone who can actually write well.
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« Last Edit: 01/12/06 at 23:16:27 by DirtDawg »  
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DirtDawg
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Re: Leaving the backside open
Reply #24 - 01/12/06 at 23:14:10
 
[quote author=Jet-Lee  link=1136480094/15#22 date=1137102443]I guess I'll never understand the vario-vent aspect of the WO/WO32.

I'm not sure you understand 100% what I mean with the carpet idea, I'm not "treating" the inside of the box. It's really just creating a false (portable) carpeted floor, and securing the WO/WO32 to it. It would be the same as taking your WO/WO32, securing it to your existing floor with angle brackets, then cutting out that square of floor. SO you have a portable vario-vented WO/WO32. [/quote]

I think I do get it now, but the property of the floor that makes it magic is that it extends far past the sides of the box, extending the loading of the vent and that property is not easily made portable.   Smiley

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Jet-Lee
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Re: Leaving the backside open
Reply #25 - 01/13/06 at 00:21:06
 
So then the sound comes up through the carpet further away from the box? I think I understand that now.

A link about aperiodic would be greatly appreciated, thanks!
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DirtDawg
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Re: Leaving the backside open
Reply #26 - 01/13/06 at 00:32:28
 
Jet,

You gotta get carpet out of your head! It only helps to create a seal for the internal cabinet pressures, which can be substantial.

The benefit the floor offers is that of a plane, a large flat surface, in contact with the vent, which tends to extend the opening of the cabinet. Grin
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Hellion
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Re: Leaving the backside open
Reply #27 - 01/13/06 at 00:34:21
 
so the entire floor becomes loaded and is a part of the whole equation?  Okay so the venting isn't what makes the box have a lowered LF?  I'm confused...  What makes the whole upside down on the carpet arangement so appealing?

What about using an AP vent in the side of a wo32? would that cause the magic to happen too?  or what?  I suppose that what I really would like you to do is explain how the floor does it's magic.  Then once I have that in my wee little brain I will understand why this can't be mode portable.  I'm sorry, but I do not understand the whole thing and need a foundation of basics to build an understanding on.


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DirtDawg
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Re: Leaving the backside open
Reply #28 - 01/13/06 at 00:43:41
 
"Aperiodic box

   Essentially a poorly sealed box, an aperiodic box vents the inside of the box to the outside air via an "acoustic resistor". All other comments about sealed boxes generally apply. The purpose of an aperiodic design is to allow a smaller enclosure than would normally be possible. If you put a driver into a sealed box that's too small, it will exhibit high Q, causing a peak in its lower response and a high impedance peak. By letting the box leak air, both the response and impedance peaks are tamed. Aperiodic boxes should not be confused with ported boxes (discussed below). The essential difference is that a that the port in a ported box acts as a Helmholz resonator tuned to a specific frequency in order to enhance and extend the low frequency response. Aperiodic vent designs exhibit no such characteristic resonance and functions solely as an acoustic resistance. As with any other low frequency system, the smaller size is achieved at the cost of a somewhat higher F3 and a steeper 18 dB/octave roll off than a sealed system.
Aperiodic vents are sold primarily by Dynaudio (which calls them "Variovents") and Scan-Speak (which merely calls them a "flow resistor")."



Another definition.


More still


DIY Audio Forum. Read the last post. This guy has the same type EBS cab as I built 15 years ago and I now use in my HT system. He points out a critical concern about ABs in general.
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« Last Edit: 01/13/06 at 02:03:39 by DirtDawg »  
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Jet-Lee
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Re: Leaving the backside open
Reply #29 - 01/13/06 at 01:58:56
 
[quote author=DirtDawg  link=1136480094/15#26 date=1137112348]Jet,

You gotta get carpet out of your head! It only helps to create a seal for the internal cabinet pressures, which can be substantial.

The benefit the floor offers is that of a plane, a large flat surface, in contact with the vent, which tends to extend the opening of the cabinet. Grin [/quote]
I got it now. Thanks!
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« Last Edit: 01/13/06 at 01:59:06 by Jet-Lee »  
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