Time coherence - how important and what speakers?

Royj, the link you provided is for ads about surfing the web. I believe this is the link.

http://svt.se/hogafflahage/hogafflaHage_site/Kor/hestekor.swf

http://svt.se/hogafflahage/hogafflaHage_site/Kor/hestekor.swf
He used one too may http's.....
Nice link!!!!!!!

Cdc, if you can listen to a Jordan-driver based system- do so. It is a real treat- I probably should have made it more clear that I greatly respect their level of performance. I worked with them a lot in the 1970's when the 2" modules became available. All of Twl's advice is sound, and I am sure that the $1500 is more than a fair price- so you should listen.

As far as the NSM drivers being too close together? That just means you get quite loud "tweeter low-end" reflections off the mid/woofer cone. It is those and also the reflections off the cabinet surface which force NSM's hand in "voicing" their crossovers- which then changes the phase response and leads to recommending the tweeter be at ear level- which is then not time coherent with the midrange.

NSM would have a hard time measuring their changed phase-response and may still think "it's close enough" to claim time-coherency, because of the clutter that those close-order reflections off the cabinet impose on their measurements. They are really hard to separate distinctly from the direct sound with a microphone and computer.

Also, even if they had put heavy felt around that tweeter, ala Vandersteen and Dunlavy, and then re-voiced the crossover (which would really help), then the tweeter's direct sound would no longer be flat, but would exhibit a rising response, from that particular tweeter's low-frequency tuning- its raw Qts being too low for any artificial "free field" mounting. I hope that makes sense the way I wrote that- it's been a long day.

Let me try this another way: Basically, the tweeter- most tweeters, are overdamped by their large magnets to roll-off what would normally be a rising low-end response caused by all the reflections off the cabinet face, and indeed off just the usual 3.5"-4"dia tweeter mounting flange.

This low-end rise is exactly the same as seen when comparing a woofer flush in a wall to the woofer outdoors, relative to the woofer's upper range at 300Hz. But unlike the low bass where we hear the nearby reflections blend, we hear this reflection in the tweeter as a "splash", so the reflections are worth removing. But it takes a tweeter with a higher Qts to do so, and those are rare, especially with enough stroke and thermal capacity to stand up to a first-order crossover.

Twl- the main reason I "require" more dynamic headroom is that our speakers are sold into many different environments, including really large rooms and for large home theaters. Plus, after years of pro-sound work and recording, from classical to reggae, I knew what it really meant to hear something at live levels- it is a different experience than you expect when you can hear it the way the musicians "felt" it. And so I wanted to be able to rock the house in any size room, and on any type of music.

Sorry I screwed up that link address- there was a sale on extra http's that day. Thanks Albert, thanks Gsselling. It is a nice one- send it to all your women and children. I have not looked back into that site yet- wonder what they do there??

We did go ahead and post a simple home page today at greenmountainaudio.com, if the moderators will permit me to mention that.

Best to all,
Roy

Roy,
I have read the entire thread again (whew), and I have a few questions:

1) the detractors of time coherent designs almost always mention: dispersion characteristics, smoothness of power response, distortion,wave interference, off-axis lobing, and compression. I think you touched on wave interference and off axis lobing, how about the rest? Can a 1st order crossover based speaker be good in these areas or are they mutually exclusive? Can a 1st order crossover based speaker compete with the best 4th order based speakers in these parameters?

2) someone in this thread mentioned that crossovers, 1st order and others, can be implemented in series or parallel. Can you talk a bit about the pro's and con's of either implementation in a 1st order crossover?

Thanks. This is one of the best threads on the Gon! My audio wish, lol, would involve getting other knowledgeable people like yourself involved in this thread. Here is my dream team, in no particular order:

1) Roger Sanders
2) Richard Vandersteen and/or Pat McGinty
3) Alvert Von Schweikert
4) Joe D'Appolito or Floyd Toole

Now THAT would be a discussion. Who can make this happen? Maybe we can collectively e-mail these individuals to encourage a dialog to help eductate the supporters of this wonderful hobby???? I would pay to see/read it :)

Dolphin ... add John Bau (Spica) to that list.