• Improved Art Array Crossover

A few thoughts:

The measurements that were made weren't close mic'ed, they were done at two meters, if I recall. I would have preferred a little more distance, but I was working in an area where I couldn't really throw the power at them so I wanted to be sure and be above the noise floor. I chose a power/distance that seemed to be the best compromise.

Also, perhaps more importantly, the measurements weren't done with the speakers on their sides. They were measured outdoors, standing upright with the microphone on axis with the tweeter. See the thread about ART Array measurements.

• ART Array Test Results

I think you might be thinking about the fact that I did lay them on their sides and measure them to get a comparison, to see the effects of ground reflecton mitigation from the array. I never published that dataset, but I am certain I commented about it, probably privately in an E-mail. I often comment on how vertical arrays smooth floor bounce, much in the same way that multi-subs smooth room modes.

The Vifa tweeter does benefit from a damping resistor, but I don't see a huge peak in acoustic output near its resonance. It works very well with a simple first-order filter and small amount of resistor damping. Of course, reducing excursion in turn reduces IMD. Then again, there are advantages offered by first-order filters too.I remember thinking it might be good to attenuate that hump with compensation in the woofer circuit. The trouble is, the hump is just below crossover so if you do it by overdamping the low-pass filter or simply shifting the crossover frequency down, then the Vifa tweeter would have to be used at lower frequency too. I don't think that's a good idea. You could use a notch filter, but that has never been an approach I particularly liked doing. In the end, I personally thought it was best to leave it simple. It sounds good.

Don't forget that unsmoothed LMS measurements are brutal. Lots of people are not used to seeing them. Most speakers measure far worse than your arrays did. Reducing the 700Hz hump would be possibly worth doing, but the rest of the curve is pretty good. Other than possibly smoothing the 700Hz hump, I would not expect to improve amplitude response by any significant amount with a crossover change.

One thing is for certain. Measurements will tell you if a crossover change is an improvement or if it is just different. I think it is worthwhile to try the notch filter to see if it helps, but I would not feel confident calling it an improvement until I had measured it to see. I would also want to do it under the same conditions, because just 1/3rd octave smoothing would make the response curve of your speakers look very smooth. So be careful to compare apples to apples as you proceed. Start with a new baseline for comparison on whatever measurement platform you choose. Measure the stock crossovers, then compare proposed changes with the same measurements system, environment and settings.

Good luck and keep us posted!

Sophisticated models would be required to get past where you are, or better yet, obtaining real data from measurements of actual samples. One suggestion is to use the Smith & Larson WTPro measurement system, which fuses Spice modeling and acoustic measurements into an extremely powerful development tool. That's what I use for development work, and I use LMS for measuring finished products.

Again, the main thing I would focus on is the hump at 700Hz. That may be reduced a little bit. But really, the response chart for the stock speaker is pretty good. At no point does the amplitude response vary more than +/-5dB in the passband. Average (3rd octave smoothed) response is within +/- 3dB from 40Hz to 25kHz. That's not bad at all, so I don't expect huge improvements from a crossover update. Only subtle improvements could be made, at best.

If the curve had been made for publication by a marketing department, they would have set the scale so it didn't show the peaks and valleys so well. It would have also been smoothed to 1/3 octave resolution. That's what people are used to seeing, and your speaker by comparison would have looked very good. I didn't post the chart that way, because I like seeing the detail. Trouble is, that makes it seem worse than it is I suppose.

If the chart had been "bad" I would have suggested some changes when you first presented the speakers to me for measurement. Not only was it "not bad" but I think it was pretty good, especially for an entry-level DIY speaker using relatively inexpensive parts.

The tweeter is fine with the first-order HP filter. I have literally thousands in the field in one π and two π speakers and I haven't had a single failure. That tweeter circuit is exactly the same as what you've used in the ART Array. Perhaps a different slope might be employed for phase/summing, but then again, measurements showed first/first summed better than second/first. From that, I'm guessing this speaker probably responds best to symmetrical or nearly symmetrical slopes.

The woofer circuit might be modified a smidge, maybe changing the LP filter, inserting a notch filter or modifying the Zobel. That might help reduce the 700Hz hump. On the other hand, the speaker with first-order LP filter measured better than the second-order, with less attenuation on the top end, not more. That tells me probably you want these particular midwoofers to run up just about as high as they can, just shaving any breakup modes from the top. In the end, you may find that this issue is specific to the woofer chosen, and that anything you do to correct its rise at 700Hz changes the response elsewhere, perhaps doing more harm than it does good.

Can your ART Array be improved, probably. Does it need to be? That's harder to say. Average response from 40Hz to 25kHz within +/- 3dB is pretty good, in my opinion. But if optimizations are found that bring it even flatter, say to within +/-1.5dB, that's even better. I'm interested to see, so please let us know how things progress. If there is a genuine improvement found, we'd like to post it in the Projects directory with the original plans and schematics.

• ART.com line array, at the Parts Express "Tech Talk" forum

ART Array Response, 1/3rd Octave

ART Array Response

ART Array Response

• Baffle step and collapsing directivity

I'm happy with the 1st order xover I have now, but if someone is willing to buy me parts I'll build one of Pete's designs and we'll just see what it sounds like

I don't care how many sims you run and on what software. Just because something sims out, or even measures great, doesn't mean it will sound good. Look at SET amps. They tend to measure crappy compared to SS or PP. But a great many of them sound very nice. If it doesn't sound good in the end then it's just junk to me.

• Baffle step and collapsing directivity