Jims 3 way speaker build

[jimbones]

I started measurements with zma with drivers in box. In orfder going down is Mid, Woofer and Tweeter. frd measurements next.
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[jimbones]

OK some frd measurements of the midrange On axis and 30 degrees off axis 1/24th smoothing.on and off axis looks the same

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[jimbones]

SB34 woofer ​
SB34 Off axis 30 degrees

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SB34 On Axis
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[jimbones]

Now the tweeter
On Axis

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Off Axis
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Impulse
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[jimbones]

OK so i have a problem I can see the .frd file saved in my folder. However when I am using XSim I try yo import it and it doesnt see it????

[a4eaudio]

Make sure they aren't *.txt or worse *.frd.txt
I know I have saved from something (Word, notepad, Excel, not sure) and it added .txt even though I had named the file .frd.
Also, I don't have file extensions hidden so I could see this, but if you have extensions hidden it doesn't show what is behind the period and won't be obvious.
Hopefully it is something like this, because it's an easy fix.

[a4eaudio]

Regarding zma plots from DATS. A lot of people prefer the grey background (which you can set in preferences) but I can see your plots fine on my PC (I saw them earlier on my phone and that was harder).

Have you measured all of your drivers. i.e., both woofers, both mids, both tweeters? That little spike at 150Hz on the woofer looks a little "off" to me - it could be a resonance peak or something. Hopefully someone more knowledgeable than me can chime in. If it measures that way on both of your woofers, then it is almost surely cabinet related. If it measures on only one, it is specific to ONE of your drivers. I had something similar recently and I went to my box modeling program (WinISD) and in the Vent section it had the port resonance and that was exactly where I had a little spike. In my case, though, it was quite a bit higher in frequency.

[jimbones]

Regarding zma plots from DATS. A lot of people prefer the grey background (which you can set in preferences) but I can see your plots fine on my PC (I saw them earlier on my phone and that was harder). I will set the background. However these are jpgs. I can not see the .frd while in XSIM.

Have you measured all of your drivers. i.e., both woofers, both mids, both tweeters? That little spike at 150Hz on the woofer looks a little "off" to me - it could be a resonance peak or something. Hopefully someone more knowledgeable than me can chime in. If it measures that way on both of your woofers, then it is almost surely cabinet related. If it measures on only one, it is specific to ONE of your drivers. I had something similar recently and I went to my box modeling program (WinISD) and in the Vent section it had the port resonance and that was exactly where I had a little spike. In my case, though, it was quite a bit higher in frequency.

I only measured one speaker set of 3 drivers. I have the wires exiting the port and the port is not glued to the flare yet, only pressed fit.

comments embedded

[Wolf]

Honestly, the midrange FR is exactly the same. They are the same plot, so you have not posted it's off axis.

As to the woofers, it looks like a DCR alignment like you have a 2 chamber box vented both out and between. I would make sure you don't have a brace or stuffing at least partially blocking one part of the volume into another.

It's just too low to be a port upper resonance.

Wolf

[jimbones]

I think I have a screw hole unfilled as I have to install another threaded insert and bolt. Would that do it?

[Wolf]

Doubtful, not tuned low enough to do that.

[jimbones]

Wolf here is a pic of the rear of the cabinet. Note no port installed on this one yet. Maybe the opening of the port on the speakers I am measuring is too close to rear panels? 3 inch?

[jimbones]

Wolf I have another suspicion. The enclosure for the mid comes close to the sides of the cabinet and there is a volume of air above it almost acting like a separate enclosure??? See diagram of overhead view Note that the yellow area represents unobstructed air flow. There are two "winglets" that attach to the sides of the cabinet for support and add rigidity. I have 2 questions: Is the mid enclosure too large? and will removing the wings provide more unobstructed airflow to correct that peak in the zma plot and does it matter? Much thanks.

[rpb]

Is it possible that the area behind the mid enclosure is acting like a port with the air chamber above the woofer? For a temporary test, I'd fill the top airspace with some foam, or dense fiberglass, and remeasure. Also, the impulse shows a bump at 1msec. Is the woofer raised 4' off the floor for measurements? If it's near the floor, you should get it higher.

[jimbones]

ha ha it aint getting higher off the ground. It must weigh a 100 lbs and I had back surgery lol. I will have to make compromises. I just want to make sure i am not chasing something that may not be all that critical.

[rpb]

Do you have some large coils, and caps on hand?

If you do, take a close mic measurement of the woofer. Then add a trial and error filter, and measure close mic again to see if the roll-off is 12dB, and at what frequency it has dropped 6dB. Adjust the filter as needed. Or.... Make an frd from the close mic, and sim a low-pass filter.

[gregrueff]

It’s an enclosure resonance/ standing wave.
Add stuffing or padding to the walls and run your impedance sweep again.
You can figure out which dimension it is by where you damp the modes.

Cheers,

[jimbones]

I damped the side walls only. Now that you remind me, I once read that standing waves occur in tall speaker cabinets. I did not damp the underside of the top of the cabinet.

[jimbones]

Bizarre thing I noticed. I decided for the hell of it i would measure once again the Fr of the woofer. The impulse response is inverted compared to yesterday and I did not change the set up. How can that happen? Yesterday it was positive going today it is negative going.

[DeZZar]

It’s an enclosure resonance/ standing wave.

​​​​​​Definately. What's the tallest unbroken dimension in the box? I.e that rear unobstructed height? Look for dimensions around 1200mm and 600mm. Worst case you have multiples of both internally. I would add several inches of acoustic stuffing top and bottom of the box.

[DeZZar]

Box tuning also looks to be around 38-39Hz.

I wouldn't adjust this just yet as you will need to add more stuffing to deal with box resonances. However, in a target 70L enclosure with an SB34NRXL performing to spec, you are likely not getting the expected magnitude response - bit of a hump up at 50hz and sharper roll off (bit of a knee) - could give you some undesirable boom - or it could be insignificant.

F3 is negligibly different but if you're aiming for some accuracy here your port length will need some fine tuning - just do it after all internal materials are in place and measure both impedance of the woofer and frequency response, nearfield, of both woofer and port (combine appropriately), just so you can see both where the tuning is and how its impacting the bass performance before tuning port length.