Econowave Speakers

[_Scotty_]

I believe it's called "we reserve the right to change specifications and designs without notice at anytime in order to improve performance or our bottom line",
or something very much like this.
Your inductance measurements can vary greatly depending upon the frequency at which it is measured, this may be a partial explanation. Have any drivers you measured met published specs?
I don't know if your design calls for a zobel network on the woofer and the tweeter, if you don't have the networks in place the crossover will not behave the way it is supposed to and the speaker won't sound right either.
Scotty

[richidoo]

That's a good point, inductance varies with frequency. I'll check with the mfgs at what freq they spec Le. Usually 1k, I think. WT3 just gives one number.

The original Econowave Delite design by Zilch  has no impedance correction, but they discussed it in the design thread, and it didn't appear in the final circuit. I assume Zilch tried it and thought it unnecessary. I can design correction if necessary. I have not gotten into that yet because correcting impedance will upset the compromises chosen to achieve flattish FR without zobels. I wanted to get the bass settled first. And the mid and crossover region does sound pretty good as it is. Shane and I assume there will be need for EQ in the final tuning, but impedance correction and slight filter adjustments might be all that's needed if the drivers are well behaved.

I'm attacking the worst problems first, which was the bass. I've learned a lot in the last month, things are starting to  move forward now, I think.

Designed crossover at 1500Hz:


Impedance for my woofer and horn attached below.

This is the impedance plot for the DE250 for which the crossover was designed. The new CD has flatter impedance and sounds better, without impedance correction.
http://www.parts-express.com/pdf/294-605.pdf

[richidoo]

Here's some measurements.

Crossover appears to be at 1.4kHz, that's acoustic not electrical.

Blue is whole speaker 15" from center height between horn and woofer. 

Light blue is mic buried deep inside tweeter horn (twss). Note the dip at 8kHz. Mic is surrounded on 5 sides with horn. Internal horn reflection? Woofer is also playing during this test.

Red is woofer with mic 1" from dustcap, and horn pot turned all the way down. I can still hear some horn though, but very low. Note the dip at 1kHz.

Green is a single port, mic centered in diameter and port length. Horn volume minimized.

SPL levels are not proportional, ignore relative SPL levels of lt blue, red and green.

Graphs Attached.

[richidoo]

Looks like the high voice coil inductance of the woofer is rolling off SPL before it rises to the crossover frequency.

Zilch's measurements show the woofer FR peaking at 550Hz. Mine peaks at 100. Premature peak. I hate when that happens.

Also looks like the Radian CD I am using now is crossing at a bit too low freq. This crossover is designed for B&C DE250, so this was expected. Of course the filter response is determined by its load, and these two CDs have very different impedance in this range, so impedance correction could help. But raising the filter freq would be better since Radian impedance is much better behaved than the DE250.

The predicted port resonance was 81Hz, but it peaks at 60Hz. Probably explained by my errant Vb estimates, and likely  incorrect Vas spec.

Nice to see all these problems on paper, even though the speaker sounds musically enjoyable now. More worms on the hook for me, hoping it can get even better.

[richidoo]

Attached is the free air frequency response of my #3 woofer compared to Eminence published FR.  The rolloff is obvious. I wrote back to Eminence to see what they say.

I can move the crossover lower, but it would need to be 500-600Hz lower, which puts CD too low and into its resonance band.

My next speaker will be a 3way with these used for bass, so it's not end of the world if Eminence gives me the bird, but I'd like to be able to use them in econowaves too.

In the future I'll purchase from Parts Express and measure immediately, so I can return them within 45 days if they are off.

[_Scotty_]

Rich, the droop in the response curve above about 800Hz is most likely primarily caused by the Mms being higher than the specified 49gr..
The less than 1mH of voice coil inductance contributes to the downward slope but it by itself will not give you a roll off of this magnitude but adding in the effect the moving mass will.
It's academic at this point but I am curious just what the Mms is on these drivers.
Scotty

[richidoo]

Thanks Scotty...
WT3 says Mms ranges from 44.1-45.5g, found while doing added mass Vas test. I think I used too much mass for the Vas test, I used 48g, because some website said use ~same weight as published Mms, but John K says use about 60% of Mms. I'll just build a Vas box to do them again. Learning to measure drivers takes some time and mistakes.

I've been trying to figure out how to derive inductance from  impedance and DCR, using info in this post:
http://www.pupman.com/listarchives/1996/may/msg00062.html
but I'm having a little trouble solving for L with the impedance formulas. Me and i have never hit it off. I'd like to make an Excel chart with impedance data exported from WT3 and calculated inductance plotted by freq, but I need to figure out the formula for L.

The quicker rolloff means that the Zilch crossover won't work perfectly with my woofers, so I have to make new crossovers from scratch. That's fun for me, and I took on this project knowing we would change things requiring crossover tweaks, and it is just a step toward learning crossover design. But some ewave builders might not appreciate the needed design skills if the drivers don't match the prototype. So buy from returnable supplier like Parts Express, and measure them immediately, or just do what Zilch wanted you to do, learn to use PCD to develop your own crossovers from scratch, AFTER you measure your drivers.

[richidoo]

Sol came over yesterday, to verify the Le of a couple different drivers that seemed on the high side according to WT3. The Eminences are indeed on the high side as reported by WT3, the others are false alarm - WT3 is wrong on those. Shane's AE TD12X are very low impedance for a wide band - Awesome!! It will be very easy to make crossovers for these.

I finally figured out the box tuning for the Ewaves. 
In 121 liters of this box, two ports of 4"D x 5.25"L makes 38Hz as required by the driver and box volume as measured. The Woofer Box simulator says it should be 8" ports, go figure.

So I cut PVC pipe to extend the flared plastic 4"L ports I have and glued them together. Tomorrow I will install into the speakers. I may want to add more fluff, but otherwise the bass is done. I've listened to only one speaker, but it sounded good.

Next up is measuring the drivers in the box, and designing a crossover to better suit these woofers. I plan to lower the LR2 crossover a little bit if possible while staying away from tweeter resonance. Also experiment with impedance correction, baffle step correction, air core woofer coil.

The other possibility is 1st order with just a cap on the CD, since the woofer breakup is pretty tame due to the higher Le. With lemons make lemonade. But it will spoil the controlled directivity of the woofer to let it play up too high and beam, and the power handling of the horn with shallow high pass is a concern. But easy to try it out.

[richidoo]

With the ports installed the bass is quite nice, punchy but clean. But something in the midrange is off. I have not measured FR yet. I am going straight to the crossover work. 

I am trying to enter the data needed to simulate crossover in PassiveCrossoverDesigner. It requires impedance file (*.ZMA) and a Frequency Response Data (*.FRD.) I exported the ZMA right from WT3, but I'm having trouble with the FRD file.  How do I create this?

I have REW, but its exported SPL files don't have any phase data. How do I create a FRD file from my own driver?

Thanks

[richidoo]

I'm gonna give this free product a try:

http://www.holmacoustics.com/holmimpulse.php

It says it can include phase in the SPL measurement export.

[richidoo]

After a few hours listening I pulled out the ports. Still too much bass and it's making the mids sound dull or too soft. The speakers just went dead, no presence. I think I just hate the sound of ports. I have heard some speakers make good use of them, but they pointed away from me, and I think there is only so much I can get out of these Eminence drivers. Not sure what's up at this point.

I have the ports totally sealed up now. Qtc is ~.56. Bass is much more natural and realistic, less exaggerated punch. The midrange weirdness is gone.

I have always intended to build sealed box anyway. This ported detour is to make a portable speaker with good bass.

Eminence offers several designs for this woofer. The largest box is 78 liters vented. I'll try their exact recipe before moving on.

[BobM]

Sometime in the future you may want to try a slotted port rather than a circular one. There is a slight difference in what the port produces this way, but probably no difference in how the speaker itself responds to either port.

I tend to think of ports this way, they seem to help drivers 8" and smaller reach down deeper, but don't work so well for larger woofers. I think a 10"-12" or bigger driver benefits more from a sealed cabinet and the air-support-suspension it brings to the driver cone.

[richidoo]

You might be on to something Mr Bob!

[richidoo]

I wore out my WT3. The signal output strength just fades away while testing, and sometimes fades back in, sometimes not. Dayton Audio standard 5 year warranty should get me a replacement with the new version. Still looks the same, but hopefully the reliability will be better, along with the new features.

Here's some links about how to measure loudspeaker T/S parameters manually, with spreadsheet to do the calculations:
http://sound.westhost.com/tsp.htm
Measuring Le is not described. So...

Here's an article on what "effective" voice coil inductance (Le) really is and why it is difficult to measure on loudspeakers.
http://www.diy-audio.narod.ru/litr/Le.pdf

Update on the speakers:
Nothing new. I need a break from thinking about this. The box even when sealed vibrates with lower mid frequency tones, muddying that band. Not unexpected for a plywood box. The braces are not as effective as they need to be. So I am planning a new box construction to improve the low-mid resonances. I will be trying a foam sandwich construction which should be extremely stiff and light. Plus design in a lot more internal cross bracing than this last one. It will not be pretty, but hopefully it will work, or teach me something.

I was inspired by all the recent success with this project to look at a nice pair of Revel M22s on Agon today. I thought, "Why can't I be like all the other kids?"

Shane wisely suggested that the new port length and bass sound might actually be correct, but the rolled off inductance of the woofer is leaving a hole in the FR near the crossover, making the bass seem out of balance.

I am sending one driver to Eminence for measurement on their LMS system. Eminence measured a current production sample for me and got .48mH, almost perfect. LMS generates a inductance curve across frequency, but I don't know what frequency is chosen for their published Le. Just like a crossover coil, inductance varies with frequency. The WT3 sampled my drivers at 1kHz, we verified that on Saturday. But it's still based on WT3's impedance measurement which might be hosed since the unit it on the blink. But I don't think so. When it works it seems fine. 

[Inscrutable]

Rich
Just to take the box vibration out of play, have you thought about temporary external bracing? You could even go so far as to make an outside form and fill with grout.

Sorry this has turned into one of MY home improvement projects