Sd msqM?

[Sguirrelfeather]

Ok, the search feature not working is getting annoying. lol Tried Google, and all I found were people asking the question...no answers.

On American Bass subs, they list the surface area in a format I am unfamiliar with: msqM I can theorize that the sqM is square meters. If I am right about that, what is the first m for? Certainly it isn't for milli, because a 12" with only 49 square millimeters is obviously wrong. lol Even in inches, I would expect the area to be between 90 and 100. I'm baffled. Anyone have any idea?

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[Papermaker85 5,000+ posts]

Measure the cone yourself. Most manufactures are outright wrong anyways.

 

[Papermaker85 5,000+ posts]

It should be mm is millimeter

Mm is megameters no way in hell is that accurate

I guess they just make **** up like they know better. American bass drivers arent impressive anyways.

 

[n2audio 5,000+ posts]

Honestly, i don't know what it is they're trying to communicate.

But to the best of my ability, it seems they've just put the decimal point in the wrong place on sq mm.

Figuring on a 1" surround you have a 10" diameter cone on the 12.

10" = 254 mm. For r^2*pi you have 127 * 127 * pi which is 50,670 sq mm vs a 51.07 spec.

If that's not it, I have no idea.

 

[trumpet 5,000+ posts]

Don't enter Sd. It isn't necessary.

 

[Sguirrelfeather]

Honestly, i don't know what it is they're trying to communicate.
But to the best of my ability, it seems they've just put the decimal point in the wrong place on sq mm.

Figuring on a 1" surround you have a 10" diameter cone on the 12.

10" = 254 mm. For r^2*pi you have 127 * 127 * pi which is 50,670 sq mm vs a 51.07 spec.

If that's not it, I have no idea.

That sounds about right. Closest explanation I've found so far! lol I have emailed their customer service folks, but so far no answer.

Don't enter Sd. It isn't necessary.

It is when designing a t-line enclosure.

 

[Papermaker85 5,000+ posts]

Honestly, i don't know what it is they're trying to communicate.
But to the best of my ability, it seems they've just put the decimal point in the wrong place on sq mm.

Figuring on a 1" surround you have a 10" diameter cone on the 12.

10" = 254 mm. For r^2*pi you have 127 * 127 * pi which is 50,670 sq mm vs a 51.07 spec.

If that's not it, I have no idea.

Thats not for a cone. Thats for a flat diaphragm.

 

[n2audio 5,000+ posts]

Thats not for a cone. Thats for a flat diaphragm.

I was referring to the speaker "cone". Not a geometric cone.

In my ~25 yrs of dabbling I've never know Sd to be calculated as actual CONE area.

Besides, for one, the minuscule difference in actual "cone" area vs circle is negligible, and two - I don't THINK the slight surface area increase matters anyway since it isn't normal to the direction of travel.

 

[Jeffdachef 5,000+ posts]

That sounds about right. Closest explanation I've found so far! lol I have emailed their customer service folks, but so far no answer.


It is when designing a t-line enclosure.

you need to measure man, that calculation doesnt work. SD is measured at the tip of the surround to the other tip of the surround so half the surround actually counts as cone area as well.

I'd recommend joining T line basshead on facebook, its a group full of T line enthusiasts, more than likely one of them will have the measurements you need for an american bass sub.

 

[Papermaker85 5,000+ posts]

I was referring to the speaker "cone". Not a geometric cone.
In my ~25 yrs of dabbling I've never know Sd to be calculated as actual CONE area.

Besides, for one, the minuscule difference in actual "cone" area vs circle is negligible, and two - I don't THINK the slight surface area increase matters anyway since it isn't normal to the direction of travel.

It affects every parameter that isn't electrical

Fs vas qms etc.

 

[Sguirrelfeather]

you need to measure man, that calculation doesnt work. SD is measured at the tip of the surround to the other tip of the surround so half the surround actually counts as cone area as well.

I'd recommend joining T line basshead on facebook, its a group full of T line enthusiasts, more than likely one of them will have the measurements you need for an american bass sub.

I'll check em out! I had planned on measuring, but for now I'm just doing a lot of research and theory so i can understand better. My next one will be built for me, but I still want to learn more and maybe start tinkering eventually.

 

[n2audio 5,000+ posts]

Thats not for a cone. Thats for a flat diaphragm.

For the record -- my assumption was correct. You do not use ConeA=pi * r(r + sqrt(h^2+r^2)) - pi * r^2.

Surface area of the geometric cone is NOT Sd. The phrase is "Effective Projected Surface Area". It is calculated with pi * r^2 using 1/3 of the thickness of the surround on both ends, 2/3 total.

(2/3 of the surround thickness + cone D) / 2 would give you the correct R.

 

[Papermaker85 5,000+ posts]

For the record -- my assumption was correct. You do not use ConeA=pi * r(r + sqrt(h^2+r^2)) - pi * r^2.Surface area of the geometric cone is NOT Sd. The phrase is "Effective Projected Surface Area". It is calculated with pi * r^2 using 1/3 of the thickness of the surround on both ends, 2/3 total.

(2/3 of the surround thickness + cone D) / 2 would give you the correct R.

again that is for a flat diaphragm. if the diaphragm isn't flat that isn't the correct surface area..also using the surround without understanding how is affects the actual displacement is pretty useless. very little of the surround contributes to actual displacement. more like 1/4.

you cannot find surface area of a convex cone by using the formula of a flat circle diaphragm. its not flat its a convex cone. its pretty common sense. nothing to argue. if it where a flat diapharghm you could use that forumla but its NOT. one look and you can see its not.. lol

fyi is pi*r*l this is for the lateral surface area..

 

[n2audio 5,000+ posts]

again that is for a flat diaphragm. if the diaphragm isn't flat that isn't the correct surface area..also using the surround without understanding how is affects the actual displacement is pretty useless. very little of the surround contributes to actual displacement. more like 1/4.

you cannot find surface area of a convex cone by using the formula of a flat circle diaphragm. its not flat its a convex cone. its pretty common sense. nothing to argue. if it where a flat diapharghm you could use that forumla but its NOT. one look and you can see its not.. lol

fyi is pi*r*l this is for the lateral surface area..

I replied to this specifically to clear up any confusion on the CORRECT method to derive SD. And unlike you, I took a few minutes to verify what I was pretty sure I knew.

There are thiele small measurement tutorials all over the place. I'm surprised you've never taken a few minutes to look at one.

I repeat... Sd is NOT surface area of the CONE. If that was the definition, then clearly yes, you'd need to use the formula for cone area to get it, but it's not. NONE of the sources I found mention that at ALL. It IS effective PISTON area. And that is "pretty common sense" if you can think beyond middle school geometry.

If what you are claiming were true we'd have spl subs with a very deep cones to maximize SD, but the "RADIATED AREA" would not be incresed so displacement would not be improved.

There is some argument to be had on 1/3 vs 1/2 the surround thickness. 1/3 makes more sense to me because as you approach the apex of the are it's going to be moving less and less.

Audioholic mentions this issue in post 16: http://www.caraudio.com/forums/general-discussion/497240-cone-area-relation-chart-2.html

 

[Papermaker85 5,000+ posts]

Its simple. Im telling you from testing. Do you know what the most difficult parameter to meausre is? Its VAS.

The diaphrams shape is directly related to tge formula you use to derive the actual pistons surface area.

Sd

Here is one link..

Understanding Loudspeaker Data | Eminence Speaker

Sd-this is the actyal surface area oonthe cone note te use of tge word cone..