Impedance Question

[jwatts]

Can I estimate the frequency response of a loudspeaker by using a plot of its impedance?

 

[soongsc]

No.

 

[Cal Weldon]

The high end will be tough to guage but if you have the impedance graph, you can tell the resonant frequency and have a good idea how low it can go as not too many drivers are much good below it.

 

[jwatts]

Measurements

What is the best way to determine it? Can I calculate somehow from the woofers Thielle Small parameters?

 

[Cal Weldon]

Why don't you post what you know about the driver and we'll see what we can do.

 

[jwatts]

10 Inch Sub

I was asked to find the Thielle Small parameters and properties of a subwoofer for a friend of mine. All I need is the frequency response. The parameters I have found so far are listed below. I can set up and do a near field frequency response measurement but if I could just calc it somehow it would make my life easier.


Fs(Hz) = 33.79
Qms = 5.2537
Qes=.4616
Qts=.4883
Vas(ft^3)=.83
Bl(N/A)=7.82
Efficiency(%)=.09
Rvc(Ohms)=1.79
Le(uH)=652.19
Xmax(In) Peak to Peak = 1.17
Sensitivity 85 db@1w/1m
SdIn^2) = 51.84
Vd(ft^3) = .035
Inverted Cone Volume(ft^3) = .047
Magnet and Cone Volume(ft^3) = .092
Mounting hole ID 9-1/4(In)
Mounting depth 8 inches (In)
Continuous power 500 watts RMS
80 oz double stacked magnets

 

[ocool_15]

your frequency response of a sub(any speaker) will be dependent on the enclosure. You can get an idea of its response <~300hz from the T/s parameters but measuring a speaker with a mic will be most accurate when done properly.

 

[jwatts]

Low End

How about the low end? What is the lowest possible frequency this sub can produce? Can I get that from these parameters or impedance curve.

 

[ocool_15]

fs is an indication. get WinISD(free!) and check how it performs, you will have cabin gain to add to the low end. This looks like a car sub that is not optimized for sealed or ported specifically.

F3 is when output power has dropped down to half and it used most often

 

[soongsc]

There are three basic things that limit the low end Fo, driver area(size), and Xmax. The LinkWitz Lab site has a maximum SPL calculatorwhich is convenient.

 

[jwatts]

The Sub

The manufacture actually handed these to me and said tell what they can do. Can you find the parameters? Should we put them in production and so I am playing with them. It is a car sub. That massive Xmax is killing my port lengths. The minimum port diameter is calculated at 7.2 inches and is super long in a SBB4 or QB3. The Vb is .7 ft^3 in a SBB4 but The vents are super long. I am trying to talk the manufacture into making me some passive radiators for them. You could build a good sub in a small package with a PR instead of a port. I have looked at other manufactures making similar subs but the boxes are over twice the volume I would use and the ports are not quite as large in diameter as what I calc but I suspect the large volume and shorter diameter ports are just to keep box size down. It appears to be the trend these days. I am actually writing the owners manual for them and I am done except the frequency response.