Measuring my ZRT's

[djn04]

So I bought a measurement mic, a DBX, and a Blue Icicle mic pre and ran them through Fuzzmeasure.

Here are the results.



They seem pretty similar to Zaph's measurements except for the dip around 100hz

http://www.zaphaudio.com/ZRT.html

Any ideas what would cause this? Could it be the room, differences in measurement technique or something else?

Also my cabinet design is slightly different. I used the Madisound baffles but my cabinets are 10" wide not the 9" called for in the design.

[JonMarsh]

What was the gating length you used and the window type? This looks rather smoothed- which is OK for understanding the general trends.

Normally in room measurements with gate over 4-5 msec will certainly show effects from room acoustics, including floor bounce, wall bounce, etc. The upper end rise is indicative of uncontrolled high frequency diffraction effects - including the behavior of the 6620 and similar SS models (I know, I have some)

[djn04]

What was the gating length you used and the window type? This looks rather smoothed- which is OK for understanding the general trends.

Normally in room measurements with gate over 4-5 msec will certainly show effects from room acoustics, including floor bounce, wall bounce, etc. The upper end rise is indicative of uncontrolled high frequency diffraction effects - including the behavior of the 6620 and similar SS models (I know, I have some)

I think this graph was a 1000ms sweep or it might have been 100ms. Regardless of length, I tried from 10-1000ms, I got the same dip in the graph. I'm not sure what you mean by window type but the frequency was the default from 1hz-Nyquist (I have no idea what Nyquist means). The graph has 1/3 octave smoothing, which is the highest setting. The lower settings obviously had less smoothing but the same dip was present.

I'm new to the measuring thing so I'm not entirely sure what I'm looking at but I do appreciate the help everyone here provides.

[Dave Bullet]

There is excessive smoothing - something like 1/6th or even 1/8th would be better.

As it stands, I'd say you have nothing to worry about. A speaker that measures +/-2dB is great in my book. The peak over 10Khz could be a mic calibration issue. Which mic are you using and is it calibrated?

A wider cabinet will change baffle step (lower it). This means the as built speaker will have a little more baffle step compensation than designed for. The change isn't hugely significant and shouldn't account for the 100Hz area.

I'd measure your room and distance from speaker to the boundaries. Convert this to a frequency measurement and see if any two line up.

Alternatively, move your speakers around in all planes (x,y and z), remeasuring to see what changes to highlight the contribution (placement and boundary effects, floor bounce etc..). Even closing doors to the room may have an effect (room pressure effects).

[djn04]

One other thought I had was whether it could be a result of not enough stuffing in the bottom of the enclosure. John calls for heavy stuffing at the bottom of the enclosure to reduce the lengthwise pressure node at 140Hz.



The above is John's measurement without enough stuffing.

My graph seems to have the the bump starting at around 140hz but it continues past the point in John's graph. I thought I put a good amount of stuffing in the bottom. Anymore and I would really be packing it in there.

Just a thought?

[evilskillit]

That measurement looks pretty good. Tho changing the baffle width by a whole inch is a pretty big no-no. It looks like you got away with it without any problems but it could attribute to deviations between your design and his.

[fjhuerta]

Isn't it a floor bounce issue?

Also, I noticed your mic isn't calibrated -the top end is far too hot.