The peak in response between 4 and 7 kHz (mentioned in a previous post) was largely 'solved' by adding another layer of damping material (Dynamat Xtreme) on the 511B's, between the driver and where the horn rapidly expands horizontally. Damping this part of the horn was suggested by Troy Swan of Iconic Manufacturing, (makers of the Iconic Model 102-16 drivers I am using). Things like cymbals, sibilance and applause no longer jump out at you. Interestingly, a change to zip cord for the tweeter wiring also 'solved' this problem. It also took away much of the resolution and extended HF this combination is capable of.

Some (Sam!?) had suggested that 500 Hz was a lower than optimal crossover frequency, because its too close to the horns cutoff. I made an impedance run on the 511B/102 and found a strong impedance peak centered on 400 Hz. I also measured the response (Stereophile test CD with warble tone sequence, and tripod mounted Radio Shack SLM) and found that the response was pretty level from 1.2 to 6.5 kHz. At the low end there was a gradual drop to -2.5 db at 800 Hz (Looks like Sam was right!), then a trough centered on 600 Hz, followed by a 400 Hz peak. So...I am redesigning the crossover for 800 Hz. Above 6.5 kHz there was a drop of a few db, then a shelf with a gentle downward slope of about 3 db/octave. EQ in the crossover nearly levels this out. Note that the SLM is only accurate out to 10 - 12 kHz.

A few posters have suggested that the 515B did not have a very extended response, even suggesting that it took a nose-dive above 800 to 1 kHz. That would be good to know if one were designing an 800 Hz crossover! I made a response run in one of my 515B's: other than a few boundary (?) related dips, it had a very even response up to around 1.6 kHz, followed by a rapid rise to a broad peak of about 6 db between 1.8 and 2.2 kHz, then by a rapid drop off. This is very similar to a response graph from the Altec 515B spec sheet.

I have found these response measurements useful in identifying some fairly audible problems. For example the 400 hz peak in the tweeter is rather obvious on music having sustained notes in that area, (male singers, piano and string quartets for example). Moving the crossover from 500 to 800 Hz should help, but may not be enough. Any suggestions on dealing with this would be appreciated. The peak in woofer response has shown up consistently through numerous crossover alterations, as a suckout in system response. Any ideas on how to deal with this? Please note, before any flame wars begin, that I do not think that these response measurements are anything other than a useful, semi-quantitative tool. They have been useful for identifying some fairly obvious audible colorations to the sound.

Regards,

AstroSonic

If it isn't designed into the drivers/horns you can adjust other ways. An equalizer could take care of a 6 db spike quite nicely. They've got nice little 30 band models now that should let you play with "spots" to your hearts content. Just make sure the bands you want to adjust are covered by the equalizer before buying.

It sounds like you're not completely sold on the "zip cord" (whatever that is). High resolution and extended HF is a good thing.

It sounds like you've put a lot of work into your speakers. I hope they're great other than the little bit of tweaking they need.

Grant.

I may get an equalizer, if only to use as a design tool. I have listened to a few in the past, but found them to bring other problems with them - like veiling, grain or harshness. I certainly haven't listened to all of them though. Perhaps someone could recommend a good one.

Zip cord is another name for lamp cord, commonly used on appliances. By making a small cut between the two insulated wires and pulling the ends apart, the cord can be unzipped (the two wires can be separated). For a relatively low power, in-home system, zip cord would have adequate power handling. Some people feel that it works very well for speaker cable.

A lot of work has gone into them, but it is a hobby that I really enjoy. At this point, most visitors (including a few 'philes') find the sound to be amongst the best they have heard. I enjoy listening to music through them, but can hear a few defects. So the quest will continue...

Regards,

AstroSonic

Thanks,
Russellc

All my experience with these horns confirms Wayne's contention that the best way to damp these horns is to de-stress them by parting the sectoral webs (cut the welds). I really don't know how to do that neatly with hand tools, but if I couldn't buy a pair of late production horns, I'd take welded horns to a local machine shop and pay them a few dollars to part the webs for me.

While you and he may be artists with a sawzall, I certainly am not. I know I could part the webs with a hacksaw blade in one of those "jab saw" holders too, but neat it wouldn't be.

OTOH, A couple of years ago I needed to trim down a brass kickplate to fit the narrow bottom rail of my front door. I didn't think I could cut it very well, so I took it to a local shop asking them to take a couple inches off of it. I figured they'd put it in a shear and lop it off. They cut it freehand in a band saw - I could have done as well with a chainsaw. I spent an hour squaring the ragged edge with a flat mill file, the plate clamped bewteen pieces of angle iron as a reference.

Upon reflection, maybe a sawzall is the way to go....

AstroSonic

I'd stick to the sawzall, MUCH safer tool.