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Learn something about sub enclosures from a Chevy pickup?

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Learn something about sub enclosures from a Chevy pickup?

Postby 1961TC4ME » Wed Jun 14, 2017 2:34 pm

Hi all,

O.K., now here's some outside of the box (no pun intended) thinking for you to ponder. I have a Chevrolet Double Cab Silverado, see here for reference >> https://www.google.com/imgres?imgurl=ht ... jwSC-J2ABA
Basically, it's a 4 door pickup. One of the very Annoying features of most newer cars and trucks is that the cabs are so air tight that when you roll down certain windows at speed you get a very audible low pulsing wind shudder in the cab, to the point it rattles not only your ears but your entire body, much the same you would feel and hear on the very lowest notes of an organ. Today was one of those warmer mornings on my way to work where the question was, should I turn on the AC, or roll down a few windows and enjoy the outdoors? I tried a few different windows down combinations as I drove along and when both back windows are down about half way at speed I get that very audible wind shudder, so I figured I'd do some experimenting as I drove along, but yes I also kept my eyes on the road (hey, at least I wasn't texting!). :mrgreen: :lol:

One thing I was curious to see was depending on the speed I was traveling if the pitch would go up or down along with the given speed. Sure enough it did! The faster I went the pitch went up, at 70 mph it was a very intense higher pitched shudder, to the point my ears couldn't take it, the pitch being probably around a 32' middle C give or take, the slower I went the pitch went down and at about 40 MPH it was down at what I would estimate to be at or near very near the lowest 32' notes and was more subtle but still with a pretty good shake to things, I figured probably because of the lower frequency and it getting close to dropping off the audible spectrum.

This got me thinking, yes, in subs it's all about air movement, but the general theory also seems to be we will also need a certain sized space for that air to move in or it's going to be very difficult at best to produce these very low notes as is usually the case, even with my 15" sub I still struggle to reach the very lowest notes, but it's in a very small roughly 2' x 2' box. My Chevy pickup seemed to debunk this needing a large space theory to an extent and it got me to thinking about box design as the difference maker where we could duplicate this 'windows down' situation. Could the success of a sub be dependent on not only how air enters the box but also how it also enters or exits the box or a chamber within the box? I know there are ported and folded horn boxes out there of various designs and sizes, I don't know which are better than others but it seems it would be interesting to build a box where there is a driver at the front like a traditional box (this would be the wind speed and force at speed) and have it driven towards another box that would act like a pick up cab with the back windows down. Then the question is since we're really not working with a conventional design so to speak and likely no way to calculate things, how big would the box have to be, would bigger be better, etc., etc? I'm thinking a box with a 15" driver probably wouldn't need to be much larger that say 4' x 4'? Maybe even smaller?

Thoughts, ideas on this crazy one? :wink:

Marc
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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Wed Jun 14, 2017 3:20 pm

By Jove Marc, you've got it!!! All you have to do is open your living room windows and get your house to move 40 to 70 mph!!! :D The cavitation would be TREMENDOUS. Wait.... maybe, disastrous? :roll:

O.K. Marc, now that I've thought about it for a minute, my suggestion would be "Don't Try This At Home!" :wink:

~S

p.s. Subwoofers can move a lot of air, but not as much as a Silverado!
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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Wed Jun 14, 2017 3:24 pm

Alright, now that I got my giggles out, I HAVE been kinda looking at open baffle subs. They don't use a box at all, and have no resulting coloring. Some folks are using 6 to 8 drivers on either side of the room! Now that would move a lot of air!!!

~S
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Re: Learn something about sub enclosures from a Chevy pickup

Postby 1961TC4ME » Wed Jun 14, 2017 3:30 pm

scottherbert wrote:By Jove Marc, you've got it!!! All you have to do is open your living room windows and get your house to move 40 to 70 mph!!! :D The cavitation would be TREMENDOUS. Wait.... maybe, disastrous? :roll:

O.K. Marc, now that I've thought about it for a minute, my suggestion would be "Don't Try This At Home!" :wink:

~S

p.s. Subwoofers can move a lot of air, but not as much as a Silverado!


Haha! I knew this one would get a few cross eyed chuckles! :lol: Like I say, at least I wasn't texting at the same time, not like I ever see that happen! NOOOOO, not ever! Yeah, right!

Marc
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Re: Learn something about sub enclosures from a Chevy pickup

Postby PhantomoftheOrgan » Wed Jun 14, 2017 5:14 pm

Hi Marc,
Google "rotary woofers". These might apply the method of sound production you experience in your truck. They are expensive, though. You might be able to invent something that would cost much less.

Infinite baffle type subs are looking more attractive now that a person can purchase economical power amps with hundreds of Watts output. Combined with an equalizer to boost the low pitches, I.B.s make sense to me. Then you don't have to worry about tuning the box. If you have an attic or basement to use as the other side of the baffle, the main concern is securing the drivers and everything in the room so they don't rattle.
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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Wed Jun 14, 2017 5:40 pm

Hey Phantom, IB subs are another way to go, the drivers have the same requirements as those for open baffle, but with open baffle you wouldn't need the other room. That's good for me, since I neither have attic, basement, nor another room! I did find an open baffle design called a ripole, wherein 2 woofers are placed facing each other in close proximity in a "W" open frame. It is supposed to lower the fs by roughly 10Hz and have a flat response as well. The drivers need not be expensive, and the frame is an easy build, so with a driver with an fs of say 25Hz, one could possibly build a sub capable of 15-16Hz, in a box about 18" square from 1 sheet of MDF and two $30 drivers plus an amp.

~S
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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Wed Jun 14, 2017 5:56 pm

Marc, these long subs like the Tuba Home Theater have the kind of space you're talking about inside of them, and can apparently get VERY low. The concern comes in considering speed of that distance, as well as coloration of the sound from the shape of the box! We, as organists, should be quite familiar with how changing the shape (cross sectional) of a pipe changes it's timbre. The same HAS to be true of a speaker BOX. It is for this reason that I am looking at open baffle speakers so seriously.

Open baffle fans rave about "uncolored" sound and a "live" sounding soundstage. That sounds great to me! Open baffle subs are said to be free of "boominess" and single note coloration that plague the less expensive subs that flood the market, and are less expensive than the high end ones.

Like I said, it's just something I'm looking into, and as I've said many,many times before, nothing,NOTHING starts more controversy than stating an opinion about speakers! :roll:

~S
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Re: Learn something about sub enclosures from a Chevy pickup

Postby Eric Sagmuller » Wed Jun 14, 2017 8:44 pm

I had seriously considered IB subs at first. But was put off with putting a hole in my floor, ceiling, or wherever. Also I found the drivers are easy to destroy at very low frequencies, as there is no air cushion to keep them in check. Hence the need of many large drivers.

I would be surprised if open baffle subs would work well at very low frequencies, as the two waves would tend to cancel each other.

I am very happy with my subs and don't feel they color the sound. Of course they are quite large, so they don't need to be driven very hard to get plenty of pedal.

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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Wed Jun 14, 2017 10:51 pm

Eric Sagmuller wrote:I had seriously considered IB subs at first. But was put off with putting a hole in my floor, ceiling, or wherever. Also I found the drivers are easy to destroy at very low frequencies, as there is no air cushion to keep them in check. Hence the need of many large drivers.

I would be surprised if open baffle subs would work well at very low frequencies, as the two waves would tend to cancel each other.

I am very happy with my subs and don't feel they color the sound. Of course they are quite large, so they don't need to be driven very hard to get plenty of pedal.

Eric


Good points Eric! As I understand it, The drivers used for both IB and OB installations need to meet certain criteria to withstand the forces they are subject to, without an air cushion. Among them are a high Q factor and (I believe) limited Xmax.

The standing waves do cancel each other out in an open baffle arrangement, requiring a careful baffle design. Sometimes just a wide board, or like the ripole I am looking at, as well as placement away from the rear reflecting surface raises the cancellation frequency to around 200 to 300Hz, which would be above where I would cross it over anyway.

As I always say, many views, I just looking into this, not trying to sell it. :)

~S
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Re: Learn something about sub enclosures from a Chevy pickup

Postby 1961TC4ME » Thu Jun 15, 2017 12:26 pm

This would be a top view. I'm thinking of a box along the lines of this, dimensions to be determined. I've seen some similar designs and in this idea the driver would be in front and there would be an additional ported chamber / box inside the outer box, the inner box acts as the resonator, kind of like my pickup cab with the windows down does. Next questions would be, should the outer box be sealed, or should it be ported, and where?
Image
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Re: Learn something about sub enclosures from a Chevy pickup

Postby scottherbert » Thu Jun 15, 2017 10:48 pm

Interesting concept, a resonator within a resonator. Kind of a resonator squared, so to speak. I don't know, but if you want to port the exterior box, assuming the interior box is representing the pickups cab, I suppose you could port it out the rear into the pickup box? :wink:

~S
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Re: Learn something about sub enclosures from a Chevy pickup

Postby Grant_Youngman » Fri Jun 16, 2017 11:00 am

1961TC4ME wrote:Hi all,
This got me thinking, yes, in subs it's all about air movement,
Thoughts, ideas on this crazy one? :wink:
Marc


Forget vibrating cones. You need one of these … :-)

http://www.rotarywoofer.com
Grant
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Re: Learn something about sub enclosures from a Chevy pickup

Postby organtechnology » Fri Jun 16, 2017 5:39 pm

Grant_Youngman wrote:
1961TC4ME wrote:Hi all,
This got me thinking, yes, in subs it's all about air movement,
Thoughts, ideas on this crazy one? :wink:
Marc


Forget vibrating cones. You need one of these … :-)

http://www.rotarywoofer.com


Do they make model aircraft with variable pitch props?
I think this would be a success except for the name "Thigpen" and the fact that the home must be reconstructed to accommodate the woofer ;)
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Re: Learn something about sub enclosures from a Chevy pickup

Postby magnaton » Fri Jun 16, 2017 9:09 pm

Grant_Youngman wrote:
1961TC4ME wrote:Hi all,
This got me thinking, yes, in subs it's all about air movement,
Thoughts, ideas on this crazy one? :wink:
Marc


Forget vibrating cones. You need one of these … :-)

http://www.rotarywoofer.com


There is a set of these installed in Trinity Church, Wall Street on their M&O digital organ.

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Re: Learn something about sub enclosures from a Chevy pickup

Postby dw154515 » Mon Jun 19, 2017 2:44 pm

Your driving experiments amused me because, I must admit, I have amused MYSELF doing the very same thing. In my fiance's Jeep Liberty, the "car cab as a sub box phenomenon" is just epic - to the point of it actually being down right irritating to the extent that I won't even drive that thing with the windows down. The relatively large volume of air in the cab oscillates with air passing through the open window(s), which is much the same as air flowing through a large Bourdon pipe; same principal, really.

On all of this subwoofer talk, I have to say, for people interested in getting the BEST BANG FOR YOUR BUCK, I can speak with absolute certainty about the benefits of the TubaHT by Bill Fitzmaurice. The 36"x36" folded horn is a BIG BOX - not all that much more or less than the reverberate space in the cab of your Silverado (or my fiance's Jeep Liberty). Not only that, but if you have a hallway, or 'chute' in any way shape or form that you can push the TubaHT into (facing backwards), or even with the mouth opening INTO a corner, you can use the walls/ceiling as extra horn "throat" and get even better results.

The TubaHT suffers a few limitations, and it IS a bit massive for a residential setup - unless you have sufficient space for such a big box - but the performance coefficient to cost is just AMAZING.
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