Design my Sealed Tumult (1 Viewer)

[Dan Pawlowski]

My Tumult design

I decided to go for a sealed, critically damped design Qtc=.5
I will wire the Voice coils in series to obtain an Re=3.0 ohms and Le 4.2mH.

I have used WinISD and Unibox402 and I have conflicting results.
Now, from what I understand if the Vb=VAS = 160L then the Qtc=Qts=.358 correct??

With out using any absorption damping factors, WinISD states a box size of 170L for a Qtc=0.5???



Using Unibox, no fill, no leaks Qtc=0.5 requires a box size of approximately 160L??? Use the design by Vb and Q module
(I think there may be a gitch in the program)Yet, utilizing the standard design module the Vb = 132???

Add heavy fill and minimal leaks and the box size is 103L. (this makes sense)

Do either of these programs take into account the approx. volume displacement of the driver?? (I am guessing the Tumult displaces around 12L).


What volume of box is required if 100% damping is used??


Thanx

Dan

 

[Patrick Sun]

You just add the displacement from the Tumult to the final target internal volume. Shoot for 120 liters total (or more if you need to take into account internal bracing as well).

 

[Pete Mazz]

I'm getting more like 250 liters for a .5 Qtc using WinSpeakerz.

100% stuffing will increase apparant volume by ~25%.

Pete

 

[Dan Pawlowski]

I've emailed Adire Audio.

I will let you know what the magic number is.

Thanx anyways


Dan

 

[Brian Bunge]

Now that I have a laptop, I downloaded Unibox version 4 and it's giving me much different numbers from version 3. I still need to double-check that I have the exact same specs loaded into both versions. Also, it looks like version 4 doesn't give you the Qtc when you specify an internal volume instead of a target Qtc.

 

[Bob Reimer]

Dan,

Why don't you consider an LT circuit and a smaller box? Email me privately if you want to discuss this.

Regards
Bob

Creative Sound Solutions

 

[Dan Pawlowski]

The reason I would like Qtc = 0.5

From what I know about filters (and a speaker box with its driver is just a mechanical high pass filter) the optimum transient response will occur with a Q of 0.5 (Minimal ringing with a pulsed signal input). Yes, I can achieve this response with a smaller box and some electronics, but at what expense?? Will the driver inside a box set with a mechanical Qtc of 1 but altered electronically to Qtc=0.5 not ring (flabby bass)?? I truly do not know. I wish I did know. Does anybody know??

I believe that optimizing what I would call “the mechanical Q” to my desired 0.5 will result in the best possible transient response for this or any sub woofer. I am still researching my options….Actually, I plan on altering my crossover in my AVA250 to provide a bass boost (LT) with Q=.5 roll off too if required. I have quite figured this one out yet, but I will be looking at it soon.


Patrick,
For Qtc=0.5(Physical volume of enclosure minus speaker displacement volume)times 80% for stuffing absorption
I am using a sonotube for this first design so there is no bracing.
To give (132L – 12 L) 0.8 = 96L

In UniBox402 under the standard design column Vb=132L for Qtc=0.5 (if i trust that unibox is correct). So its looking like the subs box volume should be approximately 100L.


Thanks Bob, I am interested in your views and I will Email you but my heart is set on a 100L box or should it be 130L?.
But as I stated above I may be looking at a bass boost (LT) as well.

My big concern is that my initial Vb should be equal to a value between 132L to 137L. Or should it be equal to 160 to 170L???


Dan

 

[Jack Gilvey]

http://www.trueaudio.com/st_lkxfm.htm
http://sound.westhost.com/project71.htm
http://sound.westhost.com/linkwitz-transform.htm
http://www.trueaudio.com/basslst2.htm

 

[Dan Pawlowski]

Thanks Jack
Good article Fast Bass
"The lower the group delay IN THE PASS BAND, the faster the bass response".
This is achieved with a system Qtc=0.500 and a very low Fc.
Hence the LT to shift the Fc and if required change the system to Q=0.500. Correct??
Dan

 

[Brian Bunge]

Dan,

Yes, you are correct!

 

[Dan Pawlowski]

Update on the question:

What volume of box is required to yeild a Qtc=0.500??

I asked Tech Support at Adire and they gave me the following response.

"You want a net 5.75 cubic feet - after driver, box, and brace displacement"


5.75 cubic feet is about 163L

So i figure around +10 to 12L for driver displacement, no braceing in a sonotube, and stuffed with 6lbs of polyfill gives me .75(163+12) = 131L Physical Vb.

Dan

 

[Pete Mazz]

OOps! I had wrong params entered. WinSpeakerz is giving me 6 ft^3 now. Sorry for the misinfo....

Pete

 

[Javier_Huerta]

Pete, I'd think the Tempest displaces way less than 12 L. Maybe 4 liters... does anyone have the exact magic number?

 

[Pete Mazz]

I think the Tempest displaces 5 liters.

Dan is talking about the Tumult. Not sure on that puppy.

Pete

 

[Brian Bunge]

Dan,

The purpose of the polyfil is to absorb the backwave of the driver (keeping sound waves from bouncing around the enclosure and coming back through the driver) and to make the apparent internal volume larger. So you don't subtract the amount of volume the polyfil takes up. In actuality, it should make the driver sound as if it were in a larger enclosure. Using 6 lbs. of polyfil would give you up to a 25% increase in volume.

 

[Javier_Huerta]

How come I thought he was talking about a Tempest?!? I guess I was a bit tired. Sorry about that.

 

[Dan Pawlowski]

Brian:

you don't subtract the amount of volume the polyfil takes up.

If 6lbs of polyfill "fools" the driver into thinking it is in a 25% larger volumed box 1.25*(physical Vb), would the system Qtc not change as well (lower)?? And therefore a compansation is requried to keep my desired Qtc=0.500 and not be lowered to Qtc=0.480

Dan

 

[Brian Bunge]

Dan,

Yes, I'm sure. According to Unibox, you need a 136.7L enclosure heavily filled with polyfil to achieve a Qtc=.5.

 

[Dan Pawlowski]

Brian

I am not sure where the confusion is :

So you don't subtract the amount of volume the polyfil takes up.

I dont understand the above statement.

Dan

 

[Brian Bunge]

6lbs of fill Vb=131 for Qtc=0.500

A box difference of 25%

The difference is, with the first box, your total volume after bracing and the driver should be 163L. The second box should be 131L after the bracing and driver. The polyfil is not figured into the equation at all. The way you are describing it, you'd still build the 163L enclosure and stuff it with polyfil to get a Qtc=.5. What I'm saying is to build the 131L (or whatever) and stuff it for the same Qtc. If you stuff the 163L enclosure you'll have a lower Qtc. Adire's recommendation for 5.75ft^3 was assuming no polyfil.

Does that make any more sense?