AR LST-2 Tweeter Replacements

[ukfan4sure!]

OK, so I've read a lot of Roy C, MichiganPat, and other's talking about the HiVi Q1R replacement, but I get the feeling some of what I've read may have been revised with new specs due to some more of Roy's tinkering.

Some of what I've read may only apply to the AR-3's, so I must admit I am looking for the correct procedure for replacing these tweeters in the LST-2 application.

I've read about the parallel 0.05mH coil on each one and that there needs to be a crossover mod, but I'm not sure about the cap value or placement. I'm also not sure whether it REPLACES the extra cap or is an addition TO the original cap value.

I have printed out the schematic, so if someone could describe the electrical changes, I'd really appreciate it.

Thanks in advance.

[RoyC]

The LST and LST-2 present unique problems when replacing tweeters. Since there are multiple tweeters connected together in each speaker, replacing one or more of them with something other than an original tweeter will affect the overall response due to differing electrical and mechanical characteristics of the new tweeter(s). Most any replacement will "worK" but the overall response will not be as it was. Adjustments to the crossovers for any replacement(s) will also affect the response of the remaining original tweeters, so the only way to achieve a uniform response is to replace all of the tweeters in each cabinet and adjust the crossover accordingly.

If you are contemplating the use of the HiVi Q1R tweeter in the LST-2, you should replace all of the original tweeters. You can add one parallel .05mh coil across any of the 3 tweeters (they are all connected in parallel) in each cabinet and replace the original 12uf cap with a 4.5uf +/- cap to get back into the original ballpark.

Roy

[ukfan4sure!]

Wow! Thanks, Roy. PE is out of the tweeters right now, but I've paid for 6 of them. I did go ahead and buy them all because I remembered you writing that they all should be changed at once (per speaker, of course). It looks like I ordered too many coils though, as i got one per speaker. I'll have to return the 12uf caps, too, I ordered 4.7uf's for the 4.5's you suggested. I purchased the Dayton poly caps at 250V.

Thanks again for replying to this thread.

[RoyC]

You're welcome, uk. Feel free to send me a PM if you have questions along the way, or just to let me know how your project works out. There isn't much feedback to go by in the LST world.

Roy

[teknofossil]

Roy, have you ever looked into the use of the Vifa D19 3/4" dome as a possible replacement for the original AR tweeter used in the AR LST2 or for the AR-5? While not quite as wide dispersion as the original AR driver one might assume its dispersion would close to the original that the HiVi unit (1-1/8 diameter).

http://www.parts-express.com/vifa-d19td-05-3-4-poly-dome-tweeter--264-500?utm_source=google&utm_medium=cpc&utm_campaign=pla

One last question, has there ever been the consideration of the use of an acoustic lens (such as what Electrovoice used on their Interface A and B systems) on the HiVi driver to enhance dispersion?

[RoyC]

Tecknofossil,

That Vifa tweeter has been around for a very long time, and is an excellent driver at a very reasonable cost, but like all other modern tweeters it is not a drop in replacement. As I have stated before, any number of modern tweeters could be used satisfactorily as a replacment for the early AR tweeters with the proper crossover modifications, and this one is probably no exception. The recessed dome, however, does not suggest any dispersion advantages regardless of dome size. (The tweeters I seem to prefer have at least partially exposed domes.)

Imo, dispersion is the very least of the issues. Wide dispersion is an attribute of the early AR tweeters, but it is not what primarily defines the "sound" of the old beasts in most listening spaces. Further, the old cabinet baffle moldings and grills greatly diminish this aspect of the overall sound.

Reasonable cost, original tonal balance, and ease of installation have been my primary goals when experimenting with replacement tweeters. This would therefore exclude drivers requiring cabinet modifications, adpater rings, irreversible crossover changes, and high cost. There are, of course, many modern tweeters to play with for the more adventurous hobbyists.

Roy

[ukfan4sure!]

Here are a couple of pictures of one of the speakers. I just refinished the cabinets on them. The drivers were actually Pyle Driver MH-1040's. Clearly the wrong application, but they brought enough money on that famous auction site to purchase the correct AR's. They were freshly refoamed. Whether that is the correct surround or not, I'm not sure. There has been discussions about that issue also.

[teknofossil]

Tecknofossil,

That Vifa tweeter has been around for a very long time, and is an excellent driver at a very reasonable cost, but like all other modern tweeters it is not a drop in replacement. As I have stated before, any number of modern tweeters could be used satisfactorily as a replacment for the early AR tweeters with the proper crossover modifications, and this one is probably no exception. The recessed dome, however, does not suggest any dispersion advantages regardless of dome size. (The tweeters I seem to prefer have at least partially exposed domes.)

Imo, dispersion is the very least of the issues. Wide dispersion is an attribute of the early AR tweeters, but it is not what primarily defines the "sound" of the old beasts in most listening spaces. Further, the old cabinet baffle moldings and grills greatly diminish this aspect of the overall sound.

Reasonable cost, original tonal balance, and ease of installation have been my primary goals when experimenting with replacement tweeters. This would therefore exclude drivers requiring cabinet modifications, adpater rings, irreversible crossover changes, and high cost. There are, of course, many modern tweeters to play with for the more adventurous hobbyists.

Roy

It has been my experience that besides frequency response, dispersion characteristics generally define the characteristic sound of a given design. That said at the highest frequencies the dispersion differences we are talking about here are likely pretty subtle. Thanks for your response.

[RoyC]

Teckno,

It is subtle...These tweeters are crossing over at 5000 hz (in some cases higher), which is very high by today's standards. AR approached this by mechanically limiting the original tweeter's response and enhancing the effect with a simple single cap crossover. It is the unusual design of the original tweeter that makes this issue challenging.

Achieving the original tonal balance is the hardest part of dealing with replacement tweeters for the old beasts. In this case dispersion issues are a distant second to a potential blaring upper midrange response, which is typical when dropping in modern tweeters. Simply disconnect the woofer and midrange of a 2ax, 5, 3a, etc, and listen to what is (not) coming out of the tweeter, and you will easily see/hear my point.

Roy

[fast_eddie_72]

Those look fantastic! You'll enjoy the heck out of them once you get the tweeters sorted. They're just fantastic speakers.