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I want to thank Coner, Kloss and Mr. David Yost for ther very useful assistance.
David. I used Coner's tip of insulating with 2" thick Water Heater Blankes. However, it has been Sooooooo very long since I have insulated a reflex cabinet so I am asumming that I way over did it. I insulated every surface accept the roofs of the modified 620 cabinets. Absolutely DEAD! DEAD! DEAD!. Almost no life coming from these cabinets at all.
So, I guess that I must get back inside (will need to entirely remove the baffles, yikes) and remove some insulation. But, if the old theory of insulating only one of each apposing serfaces, then I shoulf only need to de-insulate the one long side of the cabinets? However, that is a lot of insulation.
Lance A.
Follow Ups:
The earliest 620 cabinet I ever saw had nothing on the walls, only a rigid piece of mineral board installed at an angle.
See the angled thing from top to bottom at at http://www.dayton-wright.com/ZZZ-altec620.jpg
That is stiff mineral wool board as is used to insulate fireplaces.
here's a pic of my 618 cab insulated that way
http://www.audioasylum.com/forums/critics/messages/6/64018.html
Slightly later versions had a little bit of mineral wool or cotton batting stapled to the sides.
See http://soundup.ru/images/stories/archive/Classic/Columns/altec-620-speaker-cabinet-original-condition/altec-620-speaker-cabinet-original-condition-7.jpg
I'd say less is better with Altecs. you can either start with a lot and remove a bit at a time until you get there or start witn none and add until you get there.
Hi Joe, what about when using altec 605B coaxes in a 620 box? Do your comments still apply?
Thanks
Paul
Paul,
Can't address that specifically because I have never tried 605s...funny I was just talking to Jeffrey Jackson on the phone about those today. He just boxed up a pair.
I'd like to check out early 605s someday. I could never get 604s toned down enough for long term happiness for short-range listening. I think the 416-based 605 might be a little easier to manage.
With regard to the OB/620 hybrid under discussion in this thread, I was thinking that the livelier and more open the woofs sounded the better the overall consistency would be. My theory here is that less internal damping might be worth investigating.
Similarly, with the 605s, the challenge will be to keep the woofer sounding as fast and detailed as possible. Last thing I think you would want is a super-damped out LF to marry to that HF horn.
With respect to Altec LF drivers, what I like about them is that they sound rich yet alive. I have wound up pulling out fiberglass (or cotton batting, which I prefer to work with) a few times while dialing them in by ear. It is possible to overdo the damping. The modern tendency seems to overdo it, perhaps.
A samll box monitor might be a different thing. there path lengths are short and internal reflections possibly more damaging. In old school big box speakers there is more room to breathe.
To me, it makes sense to start out lean on damping and work my way up. I'm picking up a pair of 2.5 cu.ft slant front cabs this week for 756Bs and that's what I'm going to do. I think I will try recycled denim insulation this time around, having heard it works (and measures) better than fiberglass. Cheaper and easier to get than cotton acoustical batting.
I'm thinking I should do most of the back wall and part of the side panels then listen for a while. The slant front no doubt assists in confusing reflections.
Obviously I'm dealing out speculative subjective hypotheses here, but I think the notion of letting your ears be the ultimate guide applies universally. If it sounds over or under damped, then it probably is.
Thanks, Joe. I'll need to get busy trying different amounts.
And thanks for sharing your thoughts and experiences! It's always interesting to read your posts.
Paul
Joe,
I greatly appreciate the advice and examples in your reply. I will get to toning down the insulation in these boxes right away. Thanks.
I think the old Altec boxes "look" under-damped inside, but they do sound good--maybe even better than they should.
Altecs can sound very lively and that is what you do not want to lose. These speakers and boxes come from a somewhat different world view and sonic menu. Maybe it is best not to shoehorn them into modern overkill concepts of speaker construction, although it can be done that way.
I'd be careful to do the back panel behind the speaker with a good layer, to catch the rear wave off the driver, then here and there around the sides. If it sounded boomy, I'd add more...but that's just my mental picture of what is going on.
There is no precise formula. Let your ears be your guide...
Be sure to listen to what you have now and learn what it sounds like as a baseline. Don't automatically assume that there is too much. Maybe it has something going on right now that you like.
Maybe only one image at a time, sorry.
NT
Have a beer and fire em up!
hit preview after selecting the first one - then hit browse again - hit preview again - on ad infinitum
"Man is the only animal that blushes - or needs to" Mark Twain
So sorry about the sideways thing.
From the back/side.
This is the last photo. Thanks for your help and patience. Now that you can see the insulation amount, any further suggestions are welcome. To remove some, use thinner (2 1/2" inside as is), what ever. Thaks guys.
Use 1 or 2 deflex sheets on back lose fill with wool or acusta stuff. Fiberglass isn't near as good. To much of anything will kill the life or transients etc. This will keep a standing wave from forming and the lose fill will attenuate upper range a bit so its not coming out of weak slot port used on 602, hope you used a full flared port.
The newer flavor is minus the itch factor as well. Much cheaper and readily available to boot.
4 u maybe 4 me and my test equipment no.
Fibreglass sheets have long been classed as carcinogenic in the speaker manufacturing industry, very poor advice from Kloss
ataraxia
Poor advice to not use fiberglass? Think you misread my post I was suggesting wool deflex or acusta stuff. Another was suggesting fiberglass. Why not read the thread before reacting.
Yes, my apologies to Kloss, I misread the thread and attributed the comment to the wrong poster. I see red when see fibreglass and speakers in the same sentence, must be memories of all the gale 401's I have unstuffed , I will pull my head in and zip the tongue
ataraxia
Looked at my stock 612's....all sides have 2 layers of 1" pink
fiberglass, unfaced, for total of 2" thickness. All sides have a diagonal
brace...the braces are not covered, insulation was cut to fit inside
of the braces. Very solid cabinet, but not pretty. I don't know what you
did wrong if anything.
Edits: 08/09/12 08/09/12
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