Problem in my measurements - severe dips in the low end region...

[fjhuerta]

Hi all!

Lately I've been practicing measuring different speakers, to get an idea on how to do things "the right way". I've been fairly lucky, until yesterday.

I tried measuring a very slim column speaker with a Tang Band W4-657SB driver on top, at around 3 ft. off the ground (memo to myself - don't ever buy again a W4-657SB driver).

I measured the speaker in a room where I have some acoustical treatment. I took it at around 3 ft. distance from the source. I usually lift my speakers a bit higher (1 or 2 feet). Since this is a column speaker, I didn't do the same.

I got the 400 Hz dip.

I'm assuming this is a floor bounce issue. Am I right? Should I try lifting the column off the ground a few feet? Any other ideas would be greatly appreciated!

(BTW yes - that's the ragged response of a W4-657SB. It may be the worst performing driver I've ever tested - in my limited experience, of course).

[TacoD]

I also think it's the floor but it can also be a measuring artefact. What timewindow you're using?

[fjhuerta]

Hi taco,

I'm using an offset of 100 cm, an MLS length of 32768, a Sample Rate of 96KHz, and a length of 6 ms.

[cjd]

length of 6 ms.

ding

C

[fjhuerta]

ding

C

Is it too short?

If I go to, say, 12 ms I get far too much floor bounce. 20 ms is unusable.

2 ms gets rid of the floor bounce, but I suppose the measurements are pretty useless.

[ThomasW]

Don't blame the speaker when it's the room.

Do a measurement 1" or less from the center of the cone. Then compare that with your current one.

[fjhuerta]

Hi Thomas!

I'm not sure it's the room. Here's the measurements taken of another Tang Band speaker, the W4-1337S, in-baffle on a bookshelf speaker some 40 cms. higher than he W4-657-SB. I don't have any issues in the low end... that's why I'm confused!!!!

I also attached a pic of the TB-W4-657SB, neafield.

[ThomasW]

It's either the room/placement or a defective speaker. Unfortunately there's no FR plot on the PE website for comparison...

[fjhuerta]

TB's frequency response

Hi Thomas,

This is T-B's frequency response graph for the W4-657(SC).

It looks similar to mine - but I used a 30 dB window, and they use a 100 dB one. I can see the peaks and valleys in that graph too, only smoother.

For comparison, I included my own graph, smoothed and with a window of 100 dB. It's basically identical. what I don't understand is - why did I get that cancellation in bass?

[ThomasW]

What are the dimensions of your baffle?

[Jed]

To verify whether or not the driver is defective, measure one that you know isn't and see if you have that dip again. If so, you know there is something going wrong with your measuring technique. Which sound card are you using and is it able to work up to 96K sampling rate?