Econowave Speakers

[richidoo]

I'll get started on that. Thanks

While measuring to set the tweeter level, I was seeing that 8.2kHz null in the FR. I saw it outside too, even facing up. I suspected it is the horn reflections, and this measurement confirms that. Taken with mic at the throat of the horn, 1/8" from the CD screen.

Radian says the 475 biding posts are marked correctly, red is positive. So ignore previous rant.

[Face]

Radian says the 475 biding posts are marked correctly, red is positive. So ignore previous rant.

I believe JBL marks them incorrectly for those who have no idea what they're doing. 

[mgalusha]

I believe JBL marks them incorrectly for those who have no idea what they're doing. 

Yes indeed, at least on the JBL woofers I have, thankfully they note it in the data sheets.

[richidoo]

I installed a removable floor panel just below the woofer, reducing internal volume by almost half. This makes net volume (Vb) of 65 liters, which makes Qtc = .52. Perfect!   The chesty sound is improved. Bass is much punchier and tighter now, no loss in bass extension, actually sounds like a little more extension. Speaker sounds a little bass heavy now, so back to the crossover.

The FR bump at 600Hz is still there. I think the 2mH woofer coil might be still too big. I will reduce it to 1.5 to see if the hole just above the bump fills in to meet the tweeter more smoothly. Then I can turn up the tweeter to balance out the bass.

The resistors arrived from Mouser today, so after I choose the woofer coil, I will start work to replace the adjustable LPad with a single fixed pad. I plan to tilt the tweeter down a bit at the top, which the LPad did not allow but discreet resistors will. When I turn up the tweeter to match the woofer, then the highs are too loud. When I turn down the tweeter for music listening, then the midrange hole returns.

[richidoo]

I reduced the woofer coil, but that did not fix the bump and dip at 600-800. The smaller inductance sounds too midrangy.

I looked at the measurements I made outside last week. Red is woofer only, no filter, with driver axis pointing vertical with speaker lying flat on the ground, outside, mic 1meter. Blue is speaker standing up as normal, outside, mic 1m. Box was sealed 120l, lined with 2" pink FG.  Test signal MSSLA

What are those bumps? Do I need more stuffing to damp the woofer? 

[Face]

What's going on at 600 looks similar to this one(TD-15x): http://5e8772ee-a-62cb3a1a-s-sites.googlegroups.com/site/drivervault/driver-measurements/15/ae-speakers-td15x/frequency-response/SPL_nearfield.PNG?attachauth=ANoY7cpjuk9H7xJw5IqYu_giIuhtyRe-eDXoJoSMgje8FqfW1mT-S82uB2alWcJlljj-Osi2vTsWcoKogoHH4quHg3T7t2OQ8VutHyh-y0cXNtpwIUYsv63KiUym0aWZTF2qRGewAu0NN6AiMMmbUuAnFsiVSREnso0s8IOX2ud65O27aeK01xVPe79U7KMSJTSCEMq-SoL0Xw6MXz4vzMI1TWmzVj79s9uWK0NkTIN3z-a6OLKSXubbgKJvmzOuu5YKzNxy0k8Wia1s6GzikfDckjHM8NskX23LGCosIgeXnfz-2Iv-DLI%3D&attredirects=0
Source: http://sites.google.com/site/drivervault/driver-measurements/15/ae-speakers-td15x/frequency-response

There's a chance it's a surround resonance...  FYI, when measuring nearfield, measure a couple inches from the phase plug, too close and you'll get wonky results too.

But judging by this post: http://www.audionervosa.com/index.php?topic=3697.msg52556#msg52556  I'd say it's probably a combination of diffraction and your room. 

Have you modeled your cabinet/woofer with The Edge: http://www.tolvan.com/edge/ 

Without going through all 16 pages again, any distortion plots with and without an x-over in place? 

[richidoo]

Thanks Mike! The dip at 700 is always there, inside or outside, at any mic distance, so it is likely a driver thing. Fortunately a null and somewhat narrow.  But I agree with you that the ~600 peak is probably acoustic because it changes. I'll get around to improving the placement after I get closer on the crossover tweaks.

Edge is cool, thanks. Attached is the sim. Not related to the woofer anomalies.

I also tried stuffing the boxes with acoustistuff. It just killed transient speed, chesty was still there, worse maybe. How could it be worse - maybe it was phase, so I wondered if chestiness could be related to tweeter?
 
So I changed the 20ga tweeter coil to 14ga, very nice improvement, much more detail and dynamics! Seems like the chestiness is also gone. Could that <500 mud have been coming from the horn?  

I haven't done any distortions yet. Holmimpulse is supposed to do it but I haven't figured out why it's not appearing.

[richidoo]

Spent the morning replacing the Zilch adjustable tweeter pad with fixed. After about a dozen changes on each speaker it is getting very close now. 17dB attenuation on the CD at Fxo, then a little more rolloff as it goes higher. Pad is 12ohms series, 2ohms parallel.

The QSC horn does beam a little bit. So I had to bring down that beam. The best imaging is when horns are toed in a little, so the sweet spot is a little less treble than I would like. But it is easy to get used to less treble, and better than having too much.

The plastic horn needs damping.  

I also put the driver polarities to the way they should be, reversed and it worked fine. When I was using the 3mH coil there was an issue with that. With 2mH woofer coil I don't have a nice clean null at Fxo like it should when they are not reversed. I don't know how to tune xo to get that null. I think changing the original woofer coil screwed up the phasing at crossover. I have some ideas to work on that. Still need to try LCR on the tweeter.

Now I will work on room placement for the speakers to flatten the bumps in the bass. I'd like to pull 3dB out of 400-600Hz bump. Might have to notch that we'll see what the room does.

Edit: Oh, I forgot to mention, it sounds good! I've heard commercial speakers that cost more and sound worse, so I am going inthe right direction, slowly.

[BobM]

Rich - when do you work to support your family? I keep reading daily exploits of cabinet tweaking during the day. I have to assume you work at home or are independently wealthy (can you please adopt my youngest daughter?).

It's good to read about your discoveries and progress. Keep up the good work.

[richidoo]

Thanks Bob!  Independent, yes, wealthy, not yet...  

Edited:  Too much personal info posted in a rare, paranoia-free moment . 

[Tytte71]

Hi Rich! I haven't got the chance to read all the posts in your thread yet, but will do when I get the time. I love your project and look very much forward to follow its progress.
Now I have looked at the 700Hz null a bit and wonder if it's caused by cabinet reflections and not driver edge resonance. Please have a look at the impulse response. As you can see, there are some reflections identified at 60-80cm (corresponding to a distance of 30-40cm). When gating to eliminate the reflections, the nulls are gone. Just a thought

[richidoo]

Welcome O!! Good to have you here. 

Thanks for looking at my measurements. I understand the concept of impulse measurement, but I don't know how to intepret it, or how to properly use gating. There is so much to learn...

Now with a new fake floor installed in the box to reduce the Vb the interior vertical dimension is about 60cm, but when those measurements were taken, there was no reflective dimension between 60-80cm. I have enough acoustic damping installed to kill off an internal reflection that high.

If it is a surround resonance, would it show up in nearfield free air measurement?
Thanks!

[Tytte71]

Thanks Rich, it's my pleasure!

Since the woofer otherwise looks so fine it would be so incredibly nice to get rid of that midrange inconsistency. But that would off course depend on some further investigations.

I received two measurement files from you - one with the speaker standing and the other with the speaker laying with its back to the ground. Both measurements done outdoor and with both frequency response curves showing the same tendency of the null at ~750Hz. The two independent measurements should eliminate the ground as the sinner since the heigth from the driver's acoustic centre to the ground would be different in the two cases. Second, the measurements were done with the cabinets sealed, which eliminates any strong quarter wave pipe resonance from the port(s). And third, the measurements were taken without any filter which eliminates any misaligned or faulty filter.

The impulse starts with a high and sudden signal and quickly rings out with some minor ripple. This is perfectly normal.  But then... a strong signal suddenly occurs again after a "long delay". We read two successive and relatively strong pulses, starting at 64cm (~57 +~7cm) corresponding to a delay of 1.87ms. This late arrival is an indication of some kind of surrounding reflection and could not be caused by the driver itself (like i.e. the diaphragm can't suddenly break up after a while when the cone motion have stopped).

To see the impact of these late arrival pulses I gated the measurements to exclude their contribution to the summed frequency response. What happens is that the problem area around 750Hz flattens out. When gating the signal this way the accuracy in the lower frequencies is lowered and ripple in the mid/tweeter band is filtered (eliminating any sorrounding reflections creating the summed frequency response).
My preliminary conclusion is that we have two potential sources for the error ;
1.Something on/in the cabinet reflecting out the diaphragm and
2. Reflecting surroundings in the area where the measurements were taken.

Let's assume it is from the cabinet itself. Then it is reason to believe that the reflection comes from the inside. Length of first delay is approximately 64cm and divided by two should give a distance of 32cm to the reflective surface (180 degree phase shift occurs when a soundwave is reflected). What we also can see from the impulse response is that the late arriving pulses is attenuated compared to the first pulse. This could very well be due to the internal wall damping. Pulse No.2 arrives after some 76cm giving a distance to a reflective surface of 38cm. After pulse No.2 there is a period of repetitive smaller pulses like somehing rings out.
I am thinking these reflections could very well be caused by first reflections from the back wall and then internal standing wave modes within the cabinet.

If you have the possibility, then I will propose to take a uncut sheet of plywood (inifinite baffle) and mount the woofer to it. Remeasure and see if you still have the problem. If that's impossible then do a new measurement of the raw woofer at some 2m above ground.

I hope it could be worth it

[richidoo]

Thanks Oystein for your explanations and ideas. 

I can't do infinite baffle test, but I can test the driver free air outside.

I can also measure with the cabinet stuffed solid with acoustic damping.

I don't notice the 750Hz null much, except on trumpet recordings that I've listened to for 35 years, then only if I concentrate and look for it. I do notice the warm midrange glow of the bump just below at 400-600. I'm hoping that's room related.

If interfering waves cancel with floor bounce, can they not also combine to make a peak at adjacent frequencies to the null?

One thing I am noticing is that the speakers sound really good out of the sweet spot, especially far away, owing to the good power response, and the pro-audio origins of the design (horn + woofer.)

The speakers seem to reveal flaws in recordings very well. I think some of the flaws are still in the speakers, but some stuff is obviously recording related. There are a lot of bad recordings out there! Maybe a good reason why tubes go well with horns.

[Carlman]

There are a lot of bad recordings out there! Maybe a good reason why tubes go well with horns.

Maybe a good reason ANY setup likes a little glossing over/pleasing distortion/rosey-ness/etc... If your system is too revealing, you'll only be able to listen to well-recorded music.  There is a balance of what we think "natural" is.  It comes with some flaws with the details... something has to trick us into believing it is real.  When you can hear all the tricks in the studio, it's obvious we're trying to be tricked.   Our brain refuses to allow us to love the music at that point.

Glad to know the speakers are getting to the point where you can discern this.. NOW is when the real art of voicing can happen. Cool!