Measuring cabs to create sensitivity reponse charts

[Keryn O'Shea]

All the gear and no idea..
I'll play over the next couple of days.

This is where l had thought to place the cab, it's 50ft to the first tree, is it suitable?

[Bill Fitzmaurice]

50 feet to the nearest large wall is sufficient. 15 feet from a tree would do, unless it's a Sequoia.

[Keryn O'Shea]

I did a thing..

Does that woofer look average to you? Also is the 3-6k peak something to diagnose?

[Keryn O'Shea]

TLAP at 1.4v & 2.83v because it's a 4ohm cab, it was about to rain & I didn't research what to do before I started!

[Keryn O'Shea]

The Frankenshorties just because I was curious. 16ohm, 6.5" Jaycar Hifi woofer, 4xGT302.

[Seth]

Interesting results. Remind us again, which driver combination you have.



How did you go about setting everything up?

[Keryn O'Shea]

It's an "FS" brand 400w woofer, melded array. Set up was mic and cab on speaker stands, l set the amp to 2.83v at 500hz, then hit measure on REW.

[Bill Fitzmaurice]

That's not how it's done. You take two measurements. The first is ground plane, the cab on the ground, the mic a few inches above the ground two meters away. This gives you the half-space result below the baffle step frequency; add 6dB to get the 1 meter result. The second is with the cab on its back facing up, the mic suspended two meters above it. This gives the half-space result above the baffle step. Superimpose the two charts, splice them where they intersect in the lower midrange. Use 1/6 octave smoothing, as you can't hear with better resolution than that, and it gets rid of the minor peaks and valleys that are of no consequence.

[Keryn O'Shea]

.. You take 2 measurements..

Oh ok
I'll get back at it then

[Seth]

...baffle step frequency...

New phrase for me. Researching now.

[Bill Fitzmaurice]

It's where the radiation pattern narrows to 180 degrees. At and above that frequency the cab is in half-space with no boundaries present. Below that frequency boundaries must be present to get a half-space result, or it's full space. The only way to get a full spectrum half-space result with a single measurement is with the baffle walled in, with no other reflections. To do that you either need an anechoic chamber or you can put the cab face up outdoors in a pit, back-filled to have the baffle level with the ground. This is all moot if what you care about is in-room response, but if you want true apples to apples comparisons it has to be half-space, so you're only measuring the speaker and not the speaker plus the room.

[Seth]

It's where the radiation pattern narrows to 180 degrees....

Is that based on information gained in the measurement itself, calculated based on cab width, or something else?

[Bill Fitzmaurice]

The baffle dimensions, which is why it's called the baffle step. In the case of a horn it's the mouth dimensions.