Driver TS parameters for small BR enclosure...

[delphiplasma]

How important are they? I've spent a night experimenting with various different drivers in a 13 litre cabinet tuned to 35hz. The results of the frequency response is much the same.

JBL GTO804
FS=30hz
FB=45hz
BR=35hz
Cone=70hz

TangBand W5-1138MF
FS=55hz
FB=47hz
BR=45hz
Cone=65hz

Pioneer 6inch driver
FS=52hz
FB=45hz
BR=35hz
Cone=70hz

Elac 8inch
FS=20hz
FB=30hz
BR=20hz
Cone=70hz

CPC 6inch
FS=40hz
FB=58hz
BR=33hz
Cone=70hz

Why is the rolloff for all the drivers measured at the cone all around 70hz? And apart from the elac driver all the bass reflex measurments are around 35hz?
This is my first time with BR subs. I usually do sealed cabinets.

Please ask if further clarification is required

Help will be much appreciated.

Thanks

 

[Brian Steele]

How important are they? I've spent a night experimenting with various different drivers in a 13 litre cabinet tuned to 35hz. The results of the frequency response is much the same.

Something's not right there. If the cabinet is tuned to 35 Hz, then Fb will remain at 35 Hz, no matter what driver you put in it, unless the volume of the driver itself is large enough to noticeable reduce the net volume of the cabinet.

 

[sreten]

Hi, The FB I presume is F3, rgds, sreten.

Clearly defining the terms used would help.

 

[delphiplasma]

Hi,

Sorry, FB refers to the drive unit impedance, what the minimum electrical impedance is, the resonant frequency of the drive unit within the ported enclosure. I'm guessing 70hz is because the drive unit sees the enclousure as an IB below which the bass port takes over.
FS drive unit free air resonance as measured by myself
BR is the F3 measured from the Bass Reflex port
Cone is the F3 measured from the bass unit
As the TS parameters are so different I can only presume that the enclousure can only affect the bass output, without taking into account distortion.
I guess the Elac driver is the exception.

 

[delphiplasma]

I hope my previous post makes sense. The edit tool seems to have made the description worse.

 

[delphiplasma]

I guess TS parameters only really apply to sealed and large bass reflex enclosures?

 

[bjorno]

I guess TS parameters only really apply to sealed and large bass reflex enclosures?

Hi delphiplasma,

TS parameters are important, at least: fs.Qts,Vas and Vb for a Closed Box but for a BR you also need a suggestion for a value for fb.

From the sparse information you gave, I only tested one of the Drivers,the Tang-Band-W5-1138SMF (I've never heard of a W5-1138MF) in a BR:

Note: fc is the Closed Box cut-off frequency that only is equal to the value at the location of f-3dB if the Box Qtc is 0.707.

Qt (= Qtc) is the equivalent Q value for a BR that can be measured for Driver in a BR Box if the Port is Closed.

b 🙂

 

[delphiplasma]

Yes, TS parameters are important, well, at least what i use to think. However, and apologies for the sparse info on the other drive units, I cannot get my head around why out of all those drive units, of differing sizes, differing suspension compliances...etc, that the overall measurements of those differing drive unit are all very roughly the same. I can literally overlay each frequency curve measurements over each drive unit within the only constant being the enclosure.
The information bjorno provides is very comprehensive. However, we are looking at the driver as the constant and the box as a variable via software. What I was thinking is that the enclosure parameters are more important than the drive unit. I actually made physical measurements. So the question is why do all the differing drive units measure the same? Thanks

 

[sreten]

Hi,

Your measurements are all over the place with a fixed cabinet
and tuning. A simulator with the driver parameters will tell
you a lot more, even basic WinISD. You need Fs, Qts, Vas.

rgds, sreten.

 

[delphiplasma]

Thanks. With a fixed enclosure using different drivers with different TS Parameters I would expect to see my measurements all over the place. However, the measurements appear pretty consistent regardless of the drive unit TS parameters.
Inputting the TS parameters into WinISD will give me a ballpark of what measurements to expect. Although, some TS parameters specified by manufacturers have little to be desired. TangBand quote the 5inch Fs at 45hz; actual value is 55hz.
Maybe the measuring mic is too close? The mic is 3inches away from the centre of the cone and 3 inches from the centre of the bass reflex port.

 

[Sonce]

Maybe the measuring mic is too close? The mic is 3inches away from the centre of the cone and 3 inches from the centre of the bass reflex port.

On the contrary, measuring mic is too far away at 3 inches, it should be maximum at 1/8 inch from the center of the dust cap or from the center of the bass-reflex port.