Sons of JBL:Part 1:18" Version of JBL 4520

So, the bitzo's design is very flat, saul has very one note-ish caracter, levyte shows that 10 cm throat is the maximum for keepin the flatiness
Bitzo, I would go from 3,6 to 5-7 cm to keep it musical.

bitzo wrote: so the throat limit I guess...would be around half of SD?

IMHO, is not that simple or scientific. There are some factors regarding scoops, software/sims cannot predict, and only experience reveals.

There are drivers that perform with tight throat/tight expansion, and others only with larger throat looser initial expansion. See the list I provided earlier in the thread.

Once you arrive at throat gap that will work, altering size alters scoop characteristics.
Little or no difference in initial sections of graph, even with throats of much varying size, clearly indicates inability of software to perceive this.
Maybe close scrutiny/comparison of V18-1000 vs V18-1200 could reveal what constitutes small/chamber tight compression friendly driver, as oposed to medium chamber/loose compression driver.

Unfortunately large soundsystems out there dont understand this, and are discovering the expensive way, that replacing 1850 with any random driver, in tight compression scoop, does'nt always work out.

I'm slowly starting to get the point.
could you post some "medium chamber/loose compression driver parameters please? I can't find v1200 specs anymore.
what do you mean for initial sections? lowend? Sorry to teasing you but I'm starting to get some concepts remained a mystery for a long time. smiley20

bitzo wrote: I'm slowly starting to get the point.
could you post some "medium chamber/loose compression driver parameters please? I can't find v1200 specs anymore.
what do you mean for initial sections? lowend? Sorry to teasing you but I'm starting to get some concepts remained a mystery for a long time. smiley20

Would expect 40-60hz graphs for the different throat sizes to be wildly varying.

[attachment=0:3ri6erpv]<!-- ia0 -->v18-1200_spec.jpg<!-- ia0 -->[/attachment:3ri6erpv]

much obbliged.....
so I guess... high qts driver with high qms and large vas (like pd186) works good in small chamber/throat scoop, low qts driver with low qms tight vas (like pd1850) works also good, but need different expansion rate. More "slow" I suppose.
So more stiff driver, low qms, high qts, large vas (like v18-1200 ) works better in large chamber/throat.

so I guess b&c 18tbx100, rcf lf18x400 , fane 18xb are in the first category.
v18-1000, b&c18nw100, rcf lf18n451 in second category.
Maybe bms 18n840 is in the third category, ehmm.... :think: is there someone with a large experience with bms drivers ? smiley17

v1200 aint stiff compared to a PD1850

ok isn't stiff but....is a correct interpretation of t/s param in your opininon? or I miss something

bitzo wrote: ok isn't stiff but....is a correct interpretation of t/s param in your opininon? or I miss something

www.speakerplans.com/index.php?id=faq1

Qms: Driver mechanical Q

Qms is the mechanical Q of the speaker and only takes the speaker's mechanical properties into consideration. It is a measurement of the control coming from the speaker's mechanical suspension, which is made up of the surround and spider.

The total driver Q is Qts and is derived from the electrical Q (Qes) and the mechanical Q (Qms).

Qts is defined as 1/Qts = 1/Qes + 1/Qms

Qms is calculated

Fs sqrt(Rc)
Qms =

---

f2 - f1

Drivers with a very high mechanical Q can sound more open, cleaner and have a better dynamic range. This is because they have less loss. The surround is more flexible, the spider is better constructed, they have better air flow and usually have higher sensitivity. So a high mechanical Q is a very good indicator of energy storage behaviour.

So Qts is just a product of Qms and Qes and an understanding of what they are is important when designing a loudspeaker system. Qts, Vas and fs are all that is needed to determine the box size, but when you get to a very advanced stage of designing, its parameters like Qes and Qms which become the foundation of what you do.

BL: Driver motor strength.

The higher the value the stronger the motor. Given in tesla meters. Drivers with high BL values of around 30 or more have the ability to control their cones very accurately. These drivers will almost certainly have very large magnets and will weigh a lot. Note also that drivers with high BL values will normally have a low Qts value. Drivers with a low BL value of 20 or less will be less able to control their cones. These drivers will not feel as tight as those with higher BL’s. They will also normally have higher Qts values of over 0.28 and while at home in ported or bandpass cabinets I call these drivers mud motors because of there slow and heavy sound with a less than perfect transient response.

Vas: Volume of air equal to the driver compliance.

This can be thought of as how stiff the movement of the cone is. The value is given in litres or cu inches. There are a lot of variables that determine the Vas, so you can’t really say that high values of Vas mean a certain thing or are better. A single or double suspension spider will affect Vas, so does the size of the cone. The temperature of the air and also the humidity will affect Vas and so it is one of the hardest parameters to evaluate.

JR.junior wrote: So, the bitzo's design is very flat, saul has very one note-ish caracter, levyte shows that 10 cm throat is the maximum for keepin the flatiness
Bitzo, I would go from 3,6 to 5-7 cm to keep it musical.

sorry but what is a one note-ish character? How could you find it from a sim?

bitzo wrote:

JR.junior wrote: So, the bitzo's design is very flat, saul has very one note-ish caracter, levyte shows that 10 cm throat is the maximum for keepin the flatiness
Bitzo, I would go from 3,6 to 5-7 cm to keep it musical.

sorry but what is a one note-ish character? How could you find it from a sim?

With regards to scoops, sim's are limited in their usefulness, have said this before..

Have a look at various 18" scoop plans, and one thing you will see is, scoop throats are never smaller than a certain size, regardless of what sims say.

To get an understanding you have to hear various designs with different drivers, and or prototype some of your ideas to teach yourself.

Example... Turbomax 1500, Void V18-1200 rubbish in ASS S118.. PD1850, V18-1000 excellent.

Sim/HR can't tell you this, driver qts is a start, but not conclusive on it's own.