how do manufacturers determine frequency response?

[pkgum]

how do manufacturers determine frequency response?

[AudioFreak]

of an individual driver or of a speaker?

[pkgum]

of a speaker (subwoofer)

Example...Say that Velodyne says that its top subwoofer has a frequency response of xxHz - xxxHz

How did they come up with xxHz -xxxHz?

[ThomasW]

How did they come up with xxHz -xxxHz?

They measure it.

[JoeBob]

I do believe he wants to know if they use the f3 values, or whatever. I unfortunately don't know the answer, just think you misunderstood his question. Although I am curious myself.

[pkgum]

joebob is right..I want to know how they DETERMINE the figures

plz don't post obvious or stupid answers

[argo]

Risking to post obvious or stupid answer

It differs from manufacturer to manufacturer. Some measure, some calculate. Some tell -3dB, another -6dB and more often -10dB bass cutoff point. Many of them are just plain lying.

Argo

[sandro]

just decide if some of the following is stupid....

- They have BIG anechoic room and measure the output
- by simulating the curve via software or calculations
- measuring the sub in different rooms to provide a 'real' figure
- asking their marketing dept. about what to print
and many more

Seriously, you did not asked an easy question: I guess that an universally recognized standard for low freq measurements is not existing, and each manufacturer uses the method they believe is best (some really influenced by mkt considerations and some honestly believing their way is the right one)

bye
sandro

[pkgum]

Just be confident when posting the answers....


The "obvious and stupid" part was just referring to VERY obvious answers like Thomas W's answer, "they measure it'

Everybody knows that...DUH

It was a misunderstanding anyway

[alaskanaudio]

pkgum,

I would suspect that most manufactures measure the response of woofers or sub-woofers in a similar mannor that I do. This method has been described in quite a number of publications and can be quite accurate.

The method involves taking SPL measurements with a calibrated measurement microphone very close to the cone of the woofer. A distance of 1/4 inch away is good.

An automated frequency sweep is done over the frequency range of interest and the woofer is driven hard enough to provide a reasonable listening level. Care is taken not to drive the woofer hard enough to slam the cone into the microphone at the woofer or enclosure resonant frequencies. A automated level measurement is done as the frequency sweep is done and the results recorded by software.

The measured SPL level is then be adjusted mathematically to any desired distance from the woofer cone. This method avoids nearly all reflections that a room may produce and gives good reliable results.

Computer programs do all of this very nicely. I use LinearX LMS and its calibrated microphones for doing this.

http://www.linearx.com/products/anal...LMS/LMS_01.htm

When a woofer has a port the same measurement is also done from right in front of the port without making any system level changes. The output from the port is then added mathematically and to the primary woofer output to get the overall extended low frequency response plot. The ratio of the woofer cone area and the mouth area of the port are taken into consideration when the math is crunching the numbers to adjust the relative effective SPL levels between the two.

It is almost impossible to measure a woofers response in any other way in the average room and prehaps even a very large almost dead room. Thus a lot of money can be saved by using the close in measurement method. No special room is required.

Putting a woofer closer to a wall or corner will increase the lows substantially, as will placing a woofer in a vehicle. Thus a flat measured response may not give a flat response when a woofer is in actual use.

If you do not have a copy of the Loudspeaker Design Cookbook, by Vance Dickason I would suggest picking up the latest version. It explains a lot and is extremely useful for anyone doing speaker building or measurement work.

http://www.audioxpress.com/bksprods/books/bkaa60.htm

I Hope all this helps.


John Fassotte
Alaskan Audio