JustMLS first time advice.

[alexander91]

Hi. I've recently started a speaker project and have got a bit stuck at the measurement stage.

I'm using scanspeak drivers (8531G woofer and 6600 tweeter)

Anyway do my measurements look ok ?

Tweeter on axis


Woofer on axis


Woofer with mic at tweeter position.


Also how do I calibrate for impedance measurements ?

Thanks for any advice and help, its greatly appreciated.

[NyxOne]

Hi. I've recently started a speaker project and have got a bit stuck at the measurement stage.

I'm using scanspeak drivers (8531G woofer and 6600 tweeter)

Anyway do my measurements look ok ?

Also how do I calibrate for impedance measurements ?

Thanks for any advice and help, its greatly appreciated.

The phase of the tweeter look a bit off to me. It should almost looks like a flat line (play with the offset).

If your trying to model an xover with minimum phase measurement (tweeter on axis, woofer on axis + offset entered in justMLS) then the woofer phase also looks a bit off IMHO (but i might be wrong).

The bump/dip around 2000hz is a bit suspicious but I bet its diffraction. Is it a really slim baffle ?

I see you've done one mistake : choose CH1-2 and not CH1 when in 2 channel mode (left of the Export button).

Also, you might want to have a look at this thread : The Spassvogel MT

Impedance calibration is covered in the manual. Test your result with a resistor of know value to validate your calibration (might be a bit off because of the cables you use to get to the DUT, they have a resistance to).

Good luck and welcome aboard!
Chuck

[alexander91]

Could my protection capacitor be causing these strange results ?
And thanks for the link, was a very interesting read. Given me an inspiration boost

[5th element]

Your results aren't strange they look perfectly normal and you've set the gate correctly to filter the impulse response for useful data.

I wrote a guide on making loudspeaker measurements that can be found here.

http://www.mediafire.com/?i5fegsdgxwza5aj

When using a two channel measurement technique, one channel measures the output of the microphone and one channel measures the output of the 'amplifier'. In doing this it removes any response variations that the amplifier would cause. If you place the wire that measures the output of the amplifier after the protection cap it will measure this as the amplifiers response and correct for it accordingly.

[alexander91]

Thank you very much for that guide. I'm going to have a go with ARTA and compare to my justMLS results. Hopefully get on to crossover simulation in a few days.

Just a quick question, is it ok to use my probes I built for mls with ARTA ? The manual states I should use Zener diodes as well.

Should I measure impedance with the speaker mounted on the baffle ?

If I wanted to slant my baffle like JonW does (it looks cool and helped the phase alignment) should I measure with my test cabinet slanted ?

Thanks again.

[JonW]

Hi Alex,

I just responded to your PM at DIYaudio. (But I hang out here more.)

Your measurements look good to me. Post 444 in the Spassvogel thread has my measurements in the final cabinet:

http://www.htguide.com/forum/showthread.php4?t=25031&page=13&pp=35

They look very similar to yours. Not surprising given the similarity in drivers. Your tweeter response looks a little more wobbly than mine. I'll guess that yours is in a different looking cabinet and that's why. But it all looks great so far.

With regard to how to deal with the slanted baffle and LspCAD, pasted from my PM:
I think that what I did was just take the raw driver measurements in the slanted baffle. Then model everything in LspCAD without touching the angle in LspCAD. In other words, the raw measurements were from a slanted baffle, so there was no need to tell LspCAD anything about it. As far as the program thinks, the baffle is straight. And as far as I can tell, everything turned out well.

I think that if you take measurements from a straight baffle and then want to see what happens- in theory- if you slant the baffle, you can put the raw, straight baffle measurements into LspCAD and then dial in some slant in that part of the program. To see how the crossover output will change. But I didn't do that.

Does that make sense? I hope that it helps.

So now you've got to reveal what this project is. I like the driver choice.

I'll try to help where I can. I will be traveling Sunday-Tuesday so not much time in front of computers. I'll try to check in then but certainly will after I return. Good luck!

[5th element]

Just a quick question, is it ok to use my probes I built for mls with ARTA ? The manual states I should use Zener diodes as well.

The back to back zener diodes are there to protect the input of the sound card from any excessive voltage. Providing you are careful and keep the drive level down this should not be necessary. On the other hand sometimes you can create loud thumps etc by mistake and this could do some damage.

Should I measure impedance with the speaker mounted on the baffle ?


If I wanted to slant my baffle like JonW does (it looks cool and helped the phase alignment) should I measure with my test cabinet slanted ?

You should measure everything in the drivers final resting place, ie in the cabinets you intent to use them in. If your test cabinet does not have a slanted baffle, but is otherwise identical to the final cabinet, then by all means tilt the test cab back a little.

One thing to perhaps bare in mind is that slanting the cabinet back is normally done for visual reasons more then anything else. Yes, slanting it back will move the tweeter backwards and 'help' with the phase alignment, but that's only if it is necessary for your target crossover. One crossover implementation might require more or less tweeter displacement then another for example.

One thing you could do is measure the drivers in your test cabinet without any slant to the baffle. You could then simulate a crossover design, ie at your chosen frequency and chosen slope, then see how it sums etc. For a standard LW2/4 etc you want to see a nice symmetrical notch when the polarity of one driver is reversed from its normal connection. You could then simulate tilting the baffle backwards to see where you get the best driver integration then build the cabinet to fit.

[alexander91]

Thanks Jon for pm'ing me ;x( . I think I'm going to go with a slanted baffle, even if it is more for looks.

From my test enclosure and research I've found a few thing that I could do to make my final speaker design better, for one I need to move my drivers closer together. They have a 2 inch gap at the moment and from what I have read in the speaker cookbook this is bad. I'm also going to widen my front baffle while sticking to my set volume as this looks like it could help with the baffle step issue I have at 2kHz as it has shown up in all my measurements. I also need to look at round overs and facets as my test cabinet is sharp edge and Jon's measurements looked a lot better with the facets.

This project is actually for a University project so I have a deadline 2 weeks to get everything finished and then a month extra to do the write up, all while finishing all the other modules. So I think its going to get a rough crossover for now and then do it properly while I'm doing the write up. Shame the marker won't get to hear it at full ability but he's not an audiophile anyway so might get away with it. :T

[aldus]

Hi,

I'am looking for a good tutorial on using JustMLS and 5th Element wrote some posts back
"I wrote a guide on making loudspeaker measurements that can be found here.
http://www.mediafire.com/?i5fegsdgxwza5aj";
however, that file was deleted, could you upload it again?
Thanks