Does Sonotube + 2 Shivas = Bass Nirvana? (1 Viewer)

[Poul]

With Dan and Stan posting in the same thread...I feel like I should be paying to read this stuff, wonderful exchange of viewpoints!

It’s easy to make Dan educate us for free: just mention Shiva in any question about bass… I hope Dan will continue to do that!
BTW, I’m not suggesting Isobarik design with Shiva, not until I build Shiva sub anyway: I hope Shiva has Xmax long enough to avoid distortions alone.
About putting tube within a box: I’ve done this with smaller speakers, and later found the same technique in LDC; I filled an empty space (corners) between tube and box with sand, and it improved sound significantly. However, this will probably have positive effect only for mid frequencies. It cannot harm anyway.
Dan,
do you agree that Isobarik design - as I drew it above - will reduce THD? Drivers are close enough...
------------------
The reality is poor imitation of art.

 

[Tom Vodhanel]

I posted...
****He wants to put a SHIVA at each end of a large sonotube(i think)...whether he decides to wire tham out of phase hasn't been decided, nor is it extremely important IMO***
Poul responds....
>Well, if he wires them in phase, he needs twice a volume; if he wires them out of phase, he needs half a volume…I personally find 4 times difference in volume kind of important… <
You're still mistaking the original design for an *isobarik*...it's not...not in ANY sense of the word.
If Phil wanted, if could have them both facing in the
same direction(top driver facing into the enclosure, bottom driver facing out of the enclosure for instance), wired out of phase...and POSSIBLY reduce *non linear issues* with the drivers themselves. OR, he could have both the top and the bottom driver facing OUT of the enclosure, wired IN PHASE.
Either way, the required enclosure volume remains the same.
>>>Not quite. The best Isobarik constraction IMHO is “Face-to-face”, so they don’t need their own enclosure, like that:

 

[Phil Olson]

Tom,
This is what I'm wrestling with. If DD specifies 115 dB max for LFE and assuming that I use the 40 Hz crossover for the other channels, (steering below 40 to the LFE), how much SPL do I really need? I know that you covered this some time ago, but I forgot.
Like most people, I typically listen at about -10 dB. Listening at reference levels would blast me out of the room. I will, however, be adding some absorbtion treatments to deaden the room, (my RT60 is about 1.1 now and I'd like to bring it down to .3-.35), so I may listen more towards reference level when that's done.
I'll probably take the pool table out of the room, so I will have room for the 4-Shiva/30" Sonotube, but I don't want to spend more than I need if it'll never be used. On the other hand, If I build something that hits reference levels with the above crossover settings, then I never have to worry about LFE again.
Does all this make sense?
Phil

 

[Tom Vodhanel]

>>>Tom,
This is what I'm wrestling with. If DD specifies 115 dB max for LFE and assuming that I use the 40 Hz crossover for the other channels, (steering below 40 to the LFE), how much SPL do I really need? I know that you covered this some time ago, but I forgot.

 

[Phil Olson]

Tom,
The room is 14.375 X 8 X ~27.5. The 27.5 is not quite accurate because:
Mid Level, (kitchen, etc.)
___________ ______
| | |Wet |
| Bathroom| |Bar |
| | ______
| | |
|_________| |
| |
Lower level rear wall
The rear wall is the bathroom, then a small hall that is open to the next level, (from 4' up), then a wet bar under the stairs to the upper level. The ~27.5 is to the bathroom wall, the 4' high wall between it and the wet bar is ~34' while the wet bar is about ~29'.
There is a 6' french door behind the speakers on the front wall as well as two 3.5H X 6W windows on one side wall and three 5' openings along the other side wall.
If I built the large, (30" Sono), sub it would have to go into the corner just in front of the bathroom, (where there are built-in book shelves for my DVD collection. The corner by the wet bar is one of the 5' openings that leads to the mid level, and the two front corners aren't big enough.
I could put it where the pool table is now, just behind the seating area. But then it would not be corner loaded. I really wish I could start over with a new room. Ah well, next house!
Phil

 

[Phil Olson]

Boy, that drawing disn't turn out at all, did it! I guess I'll have to break down and figure out how to post drawings on the forum now.
What I meant to show on the above drawing was that the bathroom is about 7' wide, then there is a hall about 3' wide then there is a wet bar also about 3' wide.
Phil

 

[Tom Vodhanel]

>>>The room is 14.375 X 8 X ~27.5. The 27.5 is not quite accurate because:>>I could put it where the pool table is now, just behind the seating area. But then it would not be corner loaded.

 

[Phil Olson]

Tom,
Cool! I guess I'll try lugging one of the Snells around the room next Friday when I'm off. The pool table stays for now but the sub can sit below it just for this test.
Phil

 

[Phil Olson]

Tom,
Cool! I guess I'll try lugging one of the Snells around the room next Friday when I'm off. The pool table stays for now but the sub can sit below it just for this test.
By the way, does each driver give 3 dB more output. If I calculate right, then one Shiva is 87.7 dB @ 1W,1m(per data sheet) or about 114 dB at 600W/1m. So 2 Shivas would be 117 dB @ 1200W,1m(600W each) and 4 Shivas would be 123 dB @2400W,1m(again 600W each). This wouldn't of course include room gain, right?
Phil

 

[Tom Vodhanel]

>>>By the way, does each driver give 3 dB more output. If I calculate right, then one Shiva is 87.7 dB @ 1W,1m(per data sheet) or about 114 dB at 600W/1m.>> and 4 Shivas would be 123 dB @2400W,1m(again 600W each). This wouldn't of course include room gain, right?
Phil

 

[Jeff Mitchell]

Poul,
If you look in Vance Dickason's book or in David Weems' book they have very clear illustrations on what an ISobarik design is. What phil was considering is like the M&K push pull design. Iso barik loading according to Weems is where the front driver is acting as if it were on an infinite baffle and the second driver is placed directly behind it with only a tube connecting the front of the second driver with the back of the first. I can't do a drawing here but I've got it sitting in front of me. yes isobariks do have smaller volume per se, but pushpulls have the same volume as standard compound designs.
Jeff

 

[DanWiggins]

Tom asks

 

[Nick Streit]

Wow! I just e-mailed Tom and then I found this thread. I plan on using an 18" tube with a driver and a port at each end. Since I am using a Hsu amp that has an eq boost at 17 HZ, I can go a little smaller (6.5 ft2 for two drivers), and tune a little higher (roll off before eq boost starts at about 28 Hz). The problem is I don't have room for a 12" driver and a 4" flared port (flare is actually over 7") on an 18" endcap. Are you 18" dual driver sub guys planning on using a straight unflared 4" plumbers PVC pipe? Are you worried about port noise? Anyone think I should skip the Hsu alignment and make a big sub and let the 17 Hz eq boost do scary things to my driver?
Nick

 

[Tom Vodhanel]

>>>Wow! I just e-mailed Tom and then I found this thread. I plan on using an 18" tube with a driver and a port at each end. Since I am using a Hsu amp that has an eq boost at 17 HZ, I can go a little smaller (6.5 ft2 for two drivers), and tune a little higher (roll off before eq boost starts at about 28 Hz).Anyone think I should skip the Hsu alignment and make a big sub and let the 17 Hz eq boost do scary things to my driver?

 

[Phil Olson]

So I was playing around with WinISP tonight and came up with the following numbers for Dan's EBS design:
Box 330L + 2 Shivas@3L or 6L + 2 4"X18" [email protected] or 9.4L = 345.4L.
This would w equate to a 24" sono ~4' high or a 30" sono ~2.5' high.
This would give me 117 dB @ 20 Hz anechoic right?
If I used the 15" PR, (with the 30" sono), would I need one or two?
On the other hand, I could put 6 Shivas in the same box, closed, drive it with 3600 watts and kick everyone's ass. Is that even feasible with Sonotubes, or would they shread instantly?

 

[Tom Vodhanel]

>>>This would give me 117 dB @ 20 Hz anechoic right?>If I used the 15" PR, (with the 30" sono), would I need one or two?

 

[Phil Olson]

Tom,
I was just kidding about the 6 Shivas, it was late and I was getting a little punchy. I see that Mike Knapp is going to build the same beast. What would you recommend for port size/length/material? I assume that I got everything else right?
Phil

 

[DanWiggins]

Poul typed:
>
Hey, I'll talk about acoustics anytime - don't even need to bring Shiva up...
>
Well, I wouldn't MIND if you did isobarik; after all, it would double the number of drivers you'd buy, and that won't hurt my feelings...
But, actually, you really won't gain from an isobarik pair in any acoustic output sense. The ONLY thing you gain is a smaller box. That's it. Two Shivas mounted "normally" would require a box 4 times as big. But you'd have the same acoustic output.
>
I don't think you'd get any THD reduction. The reason is that the internal driver's acoustic output is completely masked by the external driver. The external driver "sees", ideally, and infinite air load. The only way you would get THD cancellations is if the air chamber between the two drivers is:
1. large, compared to the wavelength
2. not a steady volume (i.e.: the drivers aren't moving together)
In both the cases, you will get a little reduction in THD *AT CERTAIN FREQUENCIES*. At othersm though, you'll get an increase.
Overall, isobarik operation is really only good whn you have to shoehorn a driver into a tiny space. And even then, I'd avoid it, because of the extra cost. Better to find a driver that will work in your given volume...
Dan Wiggins
President
Avatar Audio

 

[Tom Vodhanel]

>>>Tom,
I was just kidding about the 6 Shivas, it was late and I was getting a little punchy.>> What would you recommend for port size/length/material? I assume that I got everything else right?

 

[Phil Olson]

Tom,
2 Shiva's
24" Sonotube 46" long
2 3/4" ends for internal 44.5" Sonotube
This would leave 11.65 cu ft or 329.9 Liters
Subtracting 6 Liters for the two drivers leaves 323.9 Liters
Subtracting 9.4 Liters for the vent leaves 314.5 Liters
Adding some stuffing, I figure the net would 'look' like 330 Liters, (up about 5%), to the woofs.
Tuned to 16.5 Hz
A question on vents. By my calculations:
The 9.4 Liters for vents would be for 2 4" X 18", (4.5" OD), with a vent mach of .12
If I went to a single 6", (6.5" OD), vent it would be 19.2" long but the vent mach would be .22 and it would take up 10.4 Liters
If I went to a single 8", (8.5" OD), vent it would be 36" long and the vent mach would be back down to .12 It would take up 33.5 Liters
It would seem that 2 4" vents would be optimum so...
Where am I going wrong in my calculations? Am I missing something?
For the amp I would temporarily use a Bryston 4B which can put out 800 Watts. That should tell me whether or not I need to buy a Mackie.
Phil
P.S. For strength I would add a second endcap on each side, but out of the tube, (1 in - 1 out per side).
By the way I did the above calculations using WinSID. In addition, just for I did some modeling. If I did the model right, it would take 4 Shiva's at twice the enclosure size, (660 Liters) and twice the amp power for a closed design to equal the ported 330 Liter 2 Shiva design.