9844A cabinets

[bowtie427ss]

Why are the 9844A cabinets so ineffectively braced, or should i generalize and say "underbuilt"?

Since i have a couple cabinets with a lot of blemishes and scars, my intent was to do a complete restoration of them. Upon opening the cabinets and looking them over more closely, i'm inclined to trash them and start from scratch. My excitement soon turned to disappointment, very low quality plywood, the backs are MDF, and not a single brace or stiffening member anywhere!

This did however explain why the bass response goes away as the listening level increases.

Did the cost of the components force the company to skimp this much in order to still be able to get this model to the marketplace competitively?

I find it difficult to swallow that these were made in the same factory by the same people that built cabinets as dead and sturdy as the 620A and model 19.

[GM]

Greets!

Search Todd's name for Altec history and its raping. Anyway, to keep shipping costs down, no manufacturer built anything stronger/heavier than it needed to be for the app and at least back when 9844s were ~commonplace I don't recall the SPL being very loud (especially bass) in a studio control room, and in church, etc., apps, not much bass came from the monitors.

What I find interesting though is that I use to have some 'A's and they were all decent quality plywood construction with a cross and front/rear bracing like on many of their other cabs, but then here's one that doesn't seem to even have any damping material!: http://img61.imageshack.us/my.php?image=altecva2.jpg

GM

[bowtie427ss]

Thanks GM, very understandable, they are certainly more than capable of both quality and quantity in a near field environment such as a studio/booth, and considering both the intended purpose and location for these certainly makes the weight a factor.

I was probably too quick to berate the plywood quality of these, the issues are really limited to two cabinets, and upon closer inspection i think it's from moisture and poor handling.

I'm definitely going to try a front/back brace and at least 1 diagonal stiffening rib across the back. I'm tempted to do side to side braces and ribs as well, but i don't want to muck things up by causing unwanted reflections near the port, or altering the internal volume too much. Opinions and suggestions welcome here.

Interesting side note, the 1975 pro catalog prices list the 9844A at $495, the 620A empty cabinet is $255, and the 604-8G with network is $270. I quickly added up the components for the 9844A........... approximately $380.

[bowtie427ss]

Thanks for the input Grasshopper, you've greatly helped cofirm my thoughts and ideas here. Since i have 4 of these to play with, and have been trying to nail down a fun winter build this is what i think i'm going to do:

With the nicest 2 cabinets, i'm going to add internal bracing, dynamat or bedcoat the horns, and recap the x-overs. Cosmetically they'll get all their blemishes fixed and then go across the street for a few coats of theater grey lacquer. To satisfy the purist in me i will try to keep this pair as close to original Altec as possible.

The 2nd pair will become organ donors for my own DIY cabinets. As you did, i will observe the original box volume, porting, and 1,2,3 ratio of dimension. I think there are 2 secrets to the magic of these boxes, the first being that 1:2:3 ratio of depth to width to heigth (the best sounding bass reflex boxes i've heard adhere to this concept), and the 2nd being the symmetrical and equidistant relationship between the bass drivers and horn. Again as you did, i'm envisioning front mounting the bass drivers. But, i'm thinking of extending the baffle enough to incorporate the horn outside of the woofer box, or partitioning off the correct volume for the woofers in a yet larger box, either way effectively isolating the horn from the woofer box.

As for driver orientation, i'm hesitant to arrange the woofers vertically, as i stated before, i think the symmetry and proximity to the horn is part of what makes these special. So, i think i'm going to try to keep the woofers side by side, as close as possible/practical with the largest box dimension becoming verticle. Maybe locating the port horizontally, centered on the bottom portion of the baffle will be ideal in regard to avoiding internal bracing, or should it be kept closer to the woofers?

I'm not a big fan of speaker stands, i'd sooner cut 6 or 8 inches off my furniture! Altho i'm not beyond the use of a riser to gain up to an additional 3 or 4 inches if necessary.

What am i forgetting or overlooking with this 2nd venture?

Comments, observations, and suggestions are welcomed.

[grasshopper]

Hi Chevy guy,

I'm playing around with some 9844A's myself. I agree with most everything you said- the components are top notch but the cabinet is nothing short of garbage for today's music material and SPL's. I used them for test beds for a while before getting out the router, and here is some of what I discovered-

Heathkit made cabinets for the 9844A and marketed them for home use. I hear the quality was greatly increased due to the higher quality enclosure build. That was enough for me. I cut a few pieces of plywood and glued/screwed them to all panels (it wasn't pretty!) just to see if it would make a difference and WHOA! A very understated "yes". I then stapled some acoustic foam on all sides of the interior and THAT made another HUGE leap in quality of sound. I then experimented with porting and eventually found that the factory 30Hz was simply the way to go and I should just leave well enough alone. The drivers have a Fs of 25Hz, so it was by no accident (30Hz tuning) on behalf of the engineers at Altec. Despite that, I still didn't like the WAY it was ported though- that stupid looking slot hole put smack in the middle of the most critical part of the baffle (the part between the drivers) and I just KNEW this was a weak spot structurally. Taking a radical approach, I glued and screwed an entirely fresh piece of 3/4" plywood to the existing front baffle and made the following accomodations: front baffle mounting of the drivers, a port hole located near the bottom of the baffle (two smaller ones- one under each driver), and (as a result of the new porting location) NO HORN (more on this later). Did this make a difference? OH YEAH! Let's just say they were entirely different speakers (that's a good thing) yet the Altec soul was still there. I was proud, but it wasn't enough....the cowbell (AKA the 811B horn) was in the crosshairs.

I mounted the 811B horn on top of the enclosure. Why? Three reasons:

1. The drivers were beating the **** out of them and a lot of the mechanical distortion was being caused by activity in the enclosure itself. It's a double edged sword- on the one hand, baffle mouting the 811B helps reduce the ringing, yet on the other hand- sharing the enclosure with two 12" workhorses were CAUSING most of the ringing. I took the horns out, mounted them on top ala VOTT and have not found the ringing to be a factor anymore.

2. Taking the horn out allows the two piece baffle (weak) to become a solid single piece (stronger by far). This was a key element in the performance increase. Night and day. It also allowed me to put the port holes in a more ideal location- further adding to the strength of the baffle.

3. Orientation. The 9844a is designed to be mounted horn side down. This is not practical for home use and so you just flip it upside down, right? Problem is, you have to get it high off the floor to get the horn to reach ear height. Mounting the horn on top (with the drivers also on the top) gives you a combination in which you only need about 10" of speaker stand height to get the center of the horn at seated ear level (+/- 36"). So, you can just use whatever you prefer for a speaker stand- it's only a few inches worth of height you need. I used a pair of Lovan JAZZ stands for each monitor and that's working beautifully right now.

Having done all this- I built new cabinets using the same exact specs for internal dimensions. I used a sandwich of MDF to make approx 1.5". Since I didn't have a horn in there anymore- it alloted enough volume justify putting in some proper braces, but the walls were thick enough to stand alone. I put two 2X4 braces in an "X" with ends touching the center of the front and rear baffle and left and right walls. I used a notched glue/screw join where the two 2X4's intersect. That's it. Pretty simple. I'm not quite done with the cosmetic aspects of this build (when I do- I'll post them).

Also, your crossovers are probably garbage by this point, too. The 70's models used crossover components that lost all of their ability to capacitate over the course of time and the specs are probably WAY off from the original schematic. I have mine biamped at the moment (another performance increase) but I'm working on rebuilding the passive crossover with high quality caps. I'll let you know how that works out, too.

I'd love to put these toe to toe with factory model 19's. I don't wish to start a war or anything, but I bet these (albeit heavily modifed) 9844A's will blow the snot out of them.

In short, these speakers are total sleepers and if you want something worth putting the effort into- these are it.

[grasshopper]

Hey Bowtie,

I don't think you're overlooking much, if anything. You've got a nice scenario in that you can save a pair in original form; I wished I could have done that. My original plan was to have four and use them for home theater but I've fallen in love with them and use them in my main listening system. Funny how that worked out...
You can also A/B any changes you made to your project speakers and compare them with a stock pair. That's advantageous for sure!

I think that the driver array is paramount in keeping it "right". I considered a vertical array, but that puts part of the LF proximity too far from the horn and I think the sound would be too "out of the pocket"...know what I mean? Fooling around with location- I quickly learned that keeping ALL the drivers up close and tight was very important to success. I think the original stepped or broken (two piece) front baffle served two purposes:

1.) It somewhat decoupled the vibrations of the horn/transducer relationship and,

2.) It allowed the engineers to tighten up the driver array and get the horn in as close to the transducers as possible; The edges of the horn/drivers almost overlap.

You mentioned the front baffle being more forward in your idea. I like that. I sorta did that, too. It was initially going to be flush with the sides so that deflection would be minimized- but the nostalgic side of me favored the look of the "picture frame" enclosure. I did put the baffle almost flush, though. I veneered the (slightly recessed) front baffles and shot the rest with color. I'm working on getting the clear coats right as we speak; turning out pretty nice.

I also think your 'horizontal slot' porting is a good idea. I toyed with that until I read an article on port turbulence and it's affect on amplifier performance. Frightened, I opted for flared ports (I know..kinda trendy..but it works very nicely). I'm a sucker for stuff like that, I guess. I can't say that it made an audible improvement because I've nothing to compare it to. With regard to your port location- I may be wrong here but from what I've read, it doesn't matter too much where you put the port so long as the mechanics of the flow of air and driver movement are not affected. For example, you don?t want to put the port aiming at a nearby wall or blocking the movement of the driver itself with a tube. Common sense, really. Also, as in the case of our tandem drivers, the port must be SYMMETRIC. Favoring one side means that one driver will perform differently from the other and that can't be good. Again, common sense and it sounds like you have plenty of that. Put that port right in there like you described. I think it's a perfect way to do it. Obviously, if you make it exactly like the original- you'll have the exact same tuning. That's what you want. The performance gained from a proper enclosure and wave damping will give you the clear bass you want- not a lower tuning. You know this already, though.

I'm looking forward to this continued discussion; I'm quite passionate about this speaker and all of its wonderful potential! Mind you, these are my first Altec speakers and I think I got a winner from the start. Wait till you hear the difference your improvements will make. They are world class.

'hopper

[bowtie427ss]

Thanks for the encouraging words 'hopper, I'm sure i'll need them down the road. I'm gonna try to post my first pics.

[THUMB][/THUMB][THUMB][/THUMB]

[grasshopper]

That's exactly what mine looked like- we must have approx the same manufacturing year. I've seen other 9844's that had bracing (early green drivers) but the ones you (and I) have are NAKED inside! I say it again- just wait until you put them in a proper enclosure with better damping materials....stand back.

I'm really wanting to complete a pair of replacement (passive) crossovers but there were no values marked on the caps inside the tar filled N800's. I measured the capacitance but I figure its a moot point considering how old they are. The inductors would be swapped out for air cores, btw. The original crossover point is 800Hz, yet I wonder what advantage crossing over slightly higher (say 1000Hz or even 1200Hz) will have. I'd also like to incorporate a steeper slope (say a 24db/oct Linkwitz-Riley). I'm also wondering if I should just leave the high frequency L-pad out of it. I figure the lobing errors might be a bit extreme since there's the loading of the horn to consider, but I could always experiment with delay on the LF until the rig becomes somewhat time-aligned. I'm thinking these are good ideas but since I know SQUAT about designing crossovers, I was hoping to have a little light from the experts shine down...

Anyone see anything wrong with that crossover scenario? Oh, one more thing- shouldn't I build the crossover around the actual readounts of all drivers (a consistant 11.5 Ohm DCR) instead of the published (16 Ohm)?

help is appreciated- all kinds.

[bowtie427ss]

I too have wondered about the crossovers, but i can tell you from what i've been told in other threads, stick with iron core inductors or you risk undesireable HF performance. Hopefully others will weigh in their opinion and experience.

I like Solen metalized propylene caps, i think they're a premium cap at a reasonable price, but my experience has been that when tested, most of the factory altec caps are usually within acceptable tolerance. I'm not by any means saying "don't recap", but tested against budget new caps, IMO, the 30 plus year old original caps sound better.

I have also wondered about moving the crossover point. As the colder weather moves in i plan to biamp my project just to "toy" with a different xover point. However, i'm reluctant to change the slope. Firstly because i am not by anymeans qualified to design my own scratch networks beyond simple 1st and 2nd order types, and secondly, i feel the factory altec inductors are an important part of the recipe.

As for designing around the DCR of your drivers, i have to leave that to the experts beyond simply saying that that measurement only shows you the resistance of the driver at DC, something the driver will hopefully never see in use.

[grasshopper]

Hi Bowtie,

..kinda makes a guy think twice about changing anything.

I can say that crossing them over with an active crossover @ 800Hz/24db L-R makes them sound "better". I'm using one amp (single ended triode) for low frequencies and a matching amp for high frequencies. I think I have what you'd call a horizontal biamp set up. I don't have to worry about the imbalance of different amps- yet the high frequencies are heavily attenuated (backed off). All this aside, I'd rather use the same two amps as channel monoblocks and just go with a pair of quality passive crossovers.

Perhaps the original iron core inductors are best left as they are, but I'd need to know what values the caps are in order to replace them. I'm sure the old caps are better than average- isn't everything Altec? Still, I'd like to experiment with different brands of caps to get the sound I'm looking for.

I've taken the N800 apart (not a fun job!) and sketched out a schematic. Unfortunately, I do not know the values of anything; Can anyone help me? Is there an N800 schematic posted anywhere??