TIA,

AstroSonic

Thomas

• crossover doc

In a nutshell, I try to reduce nulls in the crossover region within the desired dispersion angle. The ways to limit the crossover region involve using high slope filters. The ways to limit acoustic interaction between subsystems are to use narrow dispersion, at least in the axis where adjacent subsystems combine. Measurement tools available today are pretty inexpensive and can help in this regard, making your job much easier. As you've said, you will look for response anomalies, with flat response through the crossover region being your goal.

Some call this "time alignment" but it is not. It is done to reduce response anomalies in the crossover region at the target listening position. Alignment on-axis at the crossover frequency centers the coverage window so that any anomalous artifacts occur off-axis and away from the crossover frequency, towards the stop-band of one of the two adjacent subsystems. A well-formed system is one that has fairly wide windows of operation where nulls are avoided or suppressed. If dispersion is controlled to limit overlap and the crossover also limits overlap, then the anomalous regions can be minimized.

I have not seen or been able to locate Altec (tech note?) AN-9. I did find a suggestion, in an un-numbered tech booklet on the Lansing Heritage site, to try reversing the leads on the drivers (i.e., wire the tweeters in phase with the woofers). I tried this tonight and knew at once that that was not the solution in my case! Sam emailed a picture of a sliding horn assembly using common drawer slides. This will have to be tried!

The sound quality with the horns projecting just off the front edge is really quite good. Just a little thin in the mids and thrown in contrast by the metallic ringing from the 511b horns. I am currently researching solutions to that problem. Good possibilities include destressing by cutting through the fins, surrounding the horns with sand, and damping with adhesive backed damping material like Black Hole 5 or VE-1. Also, the low pass crossover values are those of Hiraga (I am using 515b's) which were developed for the front loaded horn commonly used with these components. I may revert to classic 2nd order values with a Zobel. Any suggestions greatly appreciated. Again, thanks for your help.
Regards,
AstroSonic

a search for "gutting a lexus" will probably turn up the original posting in the archives, written when the banshee scream of the sawsall was still fresh in my mind:) ear plugs AND ear muffs.

You won't believe this stuff until you see it with your own eyes. You'll think I'm exaggerating. But the facts are that you can watch your headers glow red-hot and not damage the finish with this treatment. It's a silver finish that looks very much like polished aluminum and feels like plastic or vinyl. It lasts several years and keeps your tube headers from rusting or heat fatigue. Not only that, but 15 minutes after running - and seeing the tubes glowing red-hot - you can touch the headers and not get burned. It directs heat away so well that most heat passes out the pipes rather than being conducted through the metal. That also keeps your starter and other nearby peripheral assemblies cool. The coating is some form of ceramic that can expand and shrink with the change of metal at temperature. You can get it in a variety of finishes, with black and silver being the most popular. Really cool stuff!

Thanks for the info. I was able to locate Altec AN-9 at the Sound Practices website as you had suggested. The method of achieving acoustic alignment by changing the relative position of the drivers while wired in phase to produce a maximum null at the crossover, then reversing the driver phase (for 2nd order xover) is ingenious.

Now about destressing the 511b's... Just how much sawing/weld removal are we talking about? Just the fins, fins and flare, or the entire horn?

Regards,

AstroSonic