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As I have posted before I bought my Model 19 cabinets that I have been wanting. I am building two crossovers and should have those done in a little bit. I am now saving money up for the GPA drivers and am almost there. In the meantime a quick question. Do most people using these replace the insulation with some higher grade material or some such or just leave the old insulation? I replaced the insulation in my 846A's but what was in there was pretty poor.
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I would just experiment, see what sounds best, to YOU.
After all, your soon to be Altec Clones will never sound exactly like a factory model 19 because you have changed the cabinet.
I found this out the hard way when a speaker I owned fell and cracked the cabinet. I duplicated the construction almost exactly, it still sounded different.
I'm not the expert on speakers that many here are but I actually own a pair of 19s (and 604-8g's). If you bought them because you like the sound or always wanted 19s then why not try to make the stuffing similar to original model 19s? 1" fibreglas with a black scrim cloth over the insulation on the port side and the inner back wall to hide the yellow or orange glass. I've tried felt, lambs wool and pillow stuffing and went back to something close to the original because of how it sounds.
Also, don't screw with the xovers. Do the ground mod and replace the caps because the originals are usually out of spec but once again, I've tried many of the so called magic bullet xovers and while at first they OK they didn't stay in mine for long.
As for sealing the cabinet, the top part is held on with 2 or 4 screws that are easily accessible from the horn opening when you remove the 811. You may find that there is a considerable gap between the top, bottom and middle joining sections due to age and being bounced around for 30+ years. You may want to do something about that.
Edits: 08/01/12
I decided to take your advice and leave what is there as it is in pretty good shape. Not screwing with the crossovers isn't an option as I don't have the originals, I just bought the cabinets. So I am building Zilch M19s.
Before you put the 811's in, take a flashlight and point it towards the inside joints on the recessed middle section. Look for any light coming through the joints between the upper and lower sections, there's almost always a gap.
Will definitely do that, thanks for the tip!
If it has a vent on the back of the magnet, cut a small hole in the Deflex, then listen.If you are going to remove the existing stuffing (take precautions) and IF you can easily tune the port lower, consider a brace each between front and rear and side to side. find the noisiest spots with a stethoscope and brace there. 2" by 3" minimum. You need to calculate their volume - with any bracing* to know how much you have lost.
You may be able to do the above with a glued-in front baffle, given there's a 24" hole in the front baffle. Deflex wall damping is also doable, listen after each change so you don't kill the sound.
The following ideas require a removable front baffle.
One idea is long hard-wood strips * - two per wall, glued and screwed. This was written up in a spkr bldg magazine IIRC.
Another - cheaper than Deflex rectangles and IMO more effective - is a layer of 3mm ply or MDF *, pressure-glued with PVA contact-cement and screwed to each inner wall. Use sandbags or bricks to weigh it down, or lots of screws! Constrained layer damping. Takes days to do with weights. PVA? because it uses water and not a volatile solvent. Most of the HFN & RR mag's DIY boxes by Dave Berriman uses this idea.
Long-fibre wool or acousta-stuff for fibre damping, on each inner wall, including the baffle. Stapled in place or glued.
Note that a post in response is preferred.
Warmest
Timothy Bailey
The Skyptical Mensurer and Audio Scrounger
And gladly would he learn and gladly teach - Chaucer. ;-)!
'Still not saluting.'
Edits: 08/01/12 08/01/12
Lots of ideas. I wouldn't want to do anything that would be too permanent like gluing MDF in. I like the stethoscope idea. Having read other posts, the stuffing that is in there is in pretty good shape, stapled down and mostly covered with a black cloth material. I think having read the other posts that the best thing at this point is to go ahead and use what is there and then see what kind of vibrations I am getting with a stethoscope. If I think the vibrations are a bit much then go ahead an stiffen the cabinets. If that isn't enough go ahead and replace the stuffing with some better modern damping material such as you list.
I just bought a pair of one-owner Model 19s that had been well cared for. They were lined with what looked like industrial felt material ca. 1/2" thick.
I wonder what others have seen in unmolested models?
George
Mine are definitely unchanged from 1977 and have about 3/4" fiberglass covering all sides, bottom, and even the upper horn chamber. A light weight black fabric is stapled over portions of the fiberglass where it is visible through the vent opening for cosmetic reasons. Most vintage Altec I've owned only has fiberglass on adjacent sides but here all the inside surfaces were covered except the baffle.
Mine too, decided to leave them like that.
Since your not restoring you can replace with Wool, Acusta Stuff and Deflex. I would also re-glue any seams. Or if its still intact leave it. Still It takes a bit of knowledge to improve on whats in there. I have heard many loudspeakers where owners stuffed the heck out of them pretty much filling cabinet volume with costly materials and killing sound quality.
I don't know what the factory standard stuff is/was. If it is a fiberglass type product, I would replace it because I just don't like breathing 40 year old dust and fiberglass bits. Wear a dust mask, disposable gloves and a shirt you don't mind tossing away.
Maybe it is just me?
John
As sealed up as the enclosure is, even with porting, that hadn't really been my line of thinking. Maybe it should be but I was just thinking in terms of damping resonances. I doubt putting in modern eggshell type material would make it worse though, right?
imao wool and cotton is best less hard sounding but I think stuffing increases your theoretical cab sis so under stuffing will raise your tuning.Could be wrong. I read that 15 years ago. The more stuffing the less bass impact. For me a larger sealed cab with just 1/2" of wool on walls is best. But smaller cabs compromises have to be made.I got yammy comp drivers this week:) you know which ones. sorry had to boast now go get stuffed:)
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