88 replies to this topic

[Zilch]

In preparation for which most auspicious of events, I have measured 6 ea. AR4x tweeters:

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[Carlspeak]

What's the difference between the two charts posted test-wise?

#1-#6 and no grille seems consistent between the two.

[Zilch]

What's the difference between the two charts posted test-wise?

#1-#6 and no grille seems consistent between the two.

The horizontal and vertical scales. Harder to tell what's what on the 10 dB plot, but it puts them in a full-range context.

[There's a 20 uF protection cap in series with all of the measurements.... ]

[Zilch]

First ever look at AR4x HF directivity, Tweeter #6, with grille:

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[Zilch]

No Grille:

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[Zilch]

Normalized, i.e., if it were flat on-axis; compare AR3a, first image:

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[Zilch]

Discussion:

1) Tweeter uniformity - there is considerable variability among samples, but the general response trend is similar and a single crossover design could work well with all, provided that level adjustability is included. Matching pairs in detail would yield optimum results.

2) Grille - benign, but a bit better with that in place; it seems that most are used this way, as they're not particularly handsome without. Design accordingly.

3) Directivity - Uniformly narrow (~45° beamwidth) above 10 kHz. The on-axis VHF peak is somewhat mitigated off-axis, but there are other issues apparent inboard between 10° and 20° at 2.4 kHz and 3.8 kHz, and HF directivity collapses at 25°. Thus, not suitable for orthagonal 90° deployment; design for on-axis, toed-in. If they were mirror-imaged, there'd be more options, but alas, they're not. Could be better horizontal, but that determination can only be made in combination with the woofer response and resultant driver interaction about the crossover region.

[Zilch]

Tweeter impedances - damping, "variable":

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[Zilch]

Tweeter #6 with Speaker Dave's AR4x crossover; Lt. Gry is system minimum phase:

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[Zilch]

For attenuation, I'm using a standard 8-Ohm L-pad. Response above was with it set at 3:00. Here's the top 180° adjustable range:

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[Zilch]

SO, how do the rest of the sample tweeters work with this setup?

[Don't be BS'n us now, Zilchster.... ]

With grille installed:

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[Zilch]

After seeing that most all of the tweeters could benefit, I knocked down the top-octave peak with a parallel notch filter, 4.3uf, 0.025mH, and 3.3 Ohms:

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[Zilch]

I'm playing in freespace, so I bumped the LF L up to 1.5 mH for a bit of BSC. That bought me a little more headroom, as well.

Also, a peek behind the curtain....

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[Zilch]

O.K., last blast with these, here's the full Monty to 90°; next installment on another forum:

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[Zilch]

[With shootout.... ]

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[genek]

[With shootout.... ]

So is the objective to mod the crossovers to try to get the speaker with the OEM tweeter closer to the E-wave version, or the other way around...?

[Zilch]

So is the objective to mod the crossovers to try to get the speaker with the OEM tweeter closer to the E-wave version, or the other way around...?

Neither.

The objective is to see if us Westies can better Dave's design using the stock tweeter(s) (we have a baseline, now), and then see how an eWave variant performs in comparision....

[speaker dave]

Neither.

The objective is to see if us Westies can better Dave's design using the stock tweeter(s).

Bring it on guys!

Nice group of curves. Any idea about the asymmetry around 1500Hz? I can't tell if it is a cabinet effect or crossover effect. Do you have any phase curves of woofer and tweeter individually?

Variation in the impedance curves and also of the tweeter LF response seems to indicate that the silicon grease is pretty hit and miss. The 8 ohm L-pad seems to work well for compensating tweeter sensitivity.

David

[genek]

Neither.

The objective is to see if us Westies can better Dave's design using the stock tweeter(s) (we have a baseline, now), and then see how an eWave variant performs in comparision....

And what is the criteria for "better" in this exercise...?

[Zilch]

Any idea about the asymmetry around 1500Hz? I can't tell if it is a cabinet effect or crossover effect.

The first two sets of curves were done with just a 20 uF cap in series, and it's there in those. The pattern stays throughout the progression; I'd say it's the cab edge and the tweeter location on the baffle.

Do you have any phase curves of woofer and tweeter individually?

I'm showing normal phase at normal polarity in the inverse polarity plot. That -40 dB notch clearly defines the location of the forward axis, by my view. The vertical polars in Post #12 led me to look there:

http://www.classicsp...-1277516236.jpg

Color code for those is:

On axis midway between drivers = Red,
Up toward tweeter = Yel, Org, Brn, Gry,
Down toward woofer = Grn, Blu, Vio, Cyn.

The upper null is prominent at +20°, whereas the lower one hasn't yet begun to form at -20°, indicating that the forward axis is down below center somewhere.

I'll be generating FRDs for PCD, which will include minimum phase for both. I'll post those plots here, as well.

Variation in the impedance curves and also of the tweeter LF response seems to indicate that the silicone grease is pretty hit and miss.

That's certainly consistent with what Ken found when he dissected some, as shown in his pictorial report. I hope readers are getting that there's correlation between and among these measurements.

The 8 ohm L-pad seems to work well for compensating tweeter sensitivity.

I have never seen the anomalous behavior others allege occurs when applying mismatched L-pads like this. At "Max," it's essentially out of the circuit.

[There was a time when I'd have made a huge deal of how wrong it was.... ]