Help designing an LF cabinet.

**chopsrr** · August 27th, 2006, 10:15 PM

Originally posted by Old Guy:
Just a note- I saw mention of 15" drivers going up to 1.5 k. While they certainly may, it is with seriuos polar problems.

I don't use 12" above 1.2k, even with phase plugs. I would not recommend 15"s higher than 800.

If you are able to place your listening position at the "sweet spot" the polar problems become less.

Otherwise beware. Not a great idea. As always YMMV.

Yep, that was me that mentioned that 15" driver @ 1.5kHz.

I guess I don't think about how things sound off-axis since I always sit in the sweet spot. And if I'm not in the sweet spot, I'm in the other room, which the off-axis response wouldn't matter anyway. forums

**Old Guy** · August 27th, 2006, 10:43 PM

Dat be true.

I'm used to, for instance studio monitoring. I an in the room with the group mixing down. Need a pretty big sweet spot.

Had a load of overweight fellows come in- we had a problem. It was an issue of band width... forums

**bfish** · August 27th, 2006, 10:55 PM

That would have been Canned Heat.

You're killing me today, man!

**chopsrr** · August 27th, 2006, 11:34 PM

Originally posted by Old Guy:
Dat be true.

I'm used to, for instance studio monitoring. I an in the room with the group mixing down. Need a pretty big sweet spot.

Is that why a lot of those large in-wall monitors have 2 large drivers mounted side-by-side? For a wider sweet spot?

**Panomaniac** · August 28th, 2006, 12:29 AM

Dudes! Where's the love? Where IS the love? forums

Originally posted by bfish:
incorrect statement about 3dB being the smallest change you could hear.



I saw it, but chose not to comment, since this isn't an amp design thread, nor an amp design forum. And I am not here discuss amp design. OT, AFAIK. 3dB should be audible just about anywhere, but is that the point of this thread? Do I have to pass a test to post here? Did I miss the secret handshake?

Evan Schultz does (or did) your testing for you.

He was nice enough to run a few amps thru the AP testing equipment for me, yes. He asked if I would like to have the amps indepenantly tested and post the results - I said yes. But I do most of my own testing. I have to.

Further, in this thread, you claim to be able to design and build amps, but also say "I do not have the design knowledge to build a good and tune 3 way passive crossover".

At least I'm honest enough to to admit that I don't have passive crossover experience. Yeah, I could plug the numbers into a x-over calculator and come up with a circuit. But I doubt that is the same thing as building a really GOOD crossover that is adapted to the drivers, box, room, etc. Perhaps you think it is. And it may be, but I just don't know. At least the designs I've seen and heard rarely seem to be "textbook." How to go about optimizing those values for a particular application is what I don't know much about.

Methinks you are full of doo-doo-hockey.

Of course you do. And you seem not to be alone. forums

But in my own defense, all I did was start this thread asking if something like one of the stock mid size Altec LF cabinet designs would work well with my 811/806s and in my room. I've been told over and over here that it won't - so I've tried to understand why. Lately I've been treated like an idiot and gotten grief for my posts and questions.

You may find it hard to believe, but that has NEVER happened to me in my 12+ years of posting everyday to user groups and forums. Guess I stumbled into the wrong "sanctum" here.

On another thread in this forum, "9849-A studio monitor need help please'''??" - you guys have jumped all over those 9849s like it's party time. Wonder what would have happened if I had proposed those? Hmmm....

Oh well, I have at least learned a few things here and I thank you for the knowledge, really, I do.
But since the most knowledgeable among you now seem to think I'm a **** and a fool, more useful knowledge isn't likely to be forthcoming. Too bad.

forums

Not sorry to have shaken your tree, I think you guys needed it. forums

**Old Guy** · August 28th, 2006, 12:30 AM

If you are referencing the Altecs with 2-12"s and the 90 degree horn, yes you are right. Many a mix down room for vocal groups had those.

GM · August 28th, 2006, 01:26 AM

Originally posted by Old Guy:
Just a note- I saw mention of 15" drivers going up to 1.5 k. While they certainly may, it is with seriuos polar problems.

Otherwise beware. Not a great idea. As always YMMV.

Greets!

Yeah, Altec really screwed up with their 15" duplex series.

GM

**Old Guy** · August 28th, 2006, 02:17 AM

Originally posted by GM:
[
Yeah, Altec really screwed up with their 15" duplex series.

GM[/QB]

Well- not really the same and you know that- the Duplex does a couple things.

One- it is a point source. By the time the woofer starts to roll off the horn has begun producing appreciable energy an octave below, emanating from the same point.

Second the horn is a narrow 60 degree instead of 90, likely to compensate for just what I'm talking about.

Yes I was assuming that someone would be using standard Altec horns. Most of which are wider than the 60 degree unit in the Duplex.

Of course there are guys using 203's. My argument dies there.

I have tried 604's with 24 and higher db/octave slopes and found it screwed with the sound IMHO- best left to Altec specs on that issue.

Running 15's up to 1.5 k with most common horns will result in jagged response off axis was my point. It can be ignored or dealt with, but should be noted.

Note Altec also built a 15" duplex crossed at 3000. I don't care for those at all.

**chopsrr** · August 28th, 2006, 02:38 AM

Originally posted by Panomaniac:
You may find it hard to believe, but that has NEVER happened to me in my 12+ years of posting everyday to user groups and forums. Guess I stumbled into the wrong "sanctum" here.

On another thread in this forum, "9849-A studio monitor need help please'''??" - you guys have jumped all over those 9849s like it's party time. Wonder what would have happened if I had proposed those? Hmmm....

Oh well, I have at least learned a few things here and I thank you for the knowledge, really, I do.
But since the most knowledgeable among you now seem to think I'm a **** and a fool, more useful knowledge isn't likely to be forthcoming. Too bad.

Not sorry to have shaken your tree, I think you guys needed it.

Well if it makes any difference, I'm still here for you. If I can only offer suggestions above anything else.

Speaking of suggestions, would you or could you possibly move up to 511B horns? I only ask because you could at least get down to a lower crossover point and probably have a little wider range of drivers to choose from.

Just a friendly thought. forums

GM · August 28th, 2006, 02:32 PM

Originally posted by Old Guy:
Well- not really the same and you know that- the Duplex does a couple things.

Greets!

Gees, I was only agreeing with you by way of a prime example that I have stated on several similar threads, though I don't agree with you that being a point source ~negates it enough to matter. The original 'large' horn/1 kHz XO is the only one that has an OK off axis power response IMO and then only because its HF response is rolled off more than later models since it wasn't needed. All the others, including the Mantarays, have narrow 'sweet spots', though not as bad as the small 'multicell' waveguide (WG) models.

Bottom line, it's going to take a large horn/relatively low XO point to properly mate to a single flat baffle loaded 15" driver whether it's a duplex or separates, so adding a WG or horn to it is the 'hot ticket' for XO points in its beaming BW, and if it's a duplex, then HF horn extenders are required to control its directivity to a lower frequency so that you wind up with a shorter depth/simpler expansion version of a 9894.

GM

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