Altec 604 cabinet design considerations

Hello,

In starting the process to chose a cabinet for my 604s, and then optimize the features of it, a private thread was started with some useful information. I am continuing to resolve some of the design issues, so I have started this thread to post that earlier information, and to allow others to contribute, access the information, and learn (depending on what you are looking for).

regards -- Roger


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Quote Originally Posted by GM
Greets!


Funny you should ask! I've gone from doing no design for quite awhile now to working on several different custom MLTLs [including 604s] for others ATM.


FWIW, Olson referred to his tall vented cab [MLTL] as just a reflex, though being fully aware of TL, horn design theory it seems reasonable to assume that he understood its additional 1/4 WL [TL] loading of the vent and like most designs is a compromise between height, size, driver/floor height, so while it will perform well, taller with an offset driver is better overall as it will allow much less internal damping, preserving more of its bass efficiency. The drawing is in a magazine article:

Gearslutz Pro Audio Community


WRT the Stonehenge V, my main complaints is driver offset, ditto vent location that ~defeats the point of a tall cab other than to get the driver near/at seated ear height and also adds a pretty big notch in its mid-bass response to get the traditional Altec/JBL 'West Coast Sound' [college party central's 'thumping' bass]. Great vintage vinyl playback/party speakers, but HIFI, not so much.

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Re: Olson's MLTL for 604

Thanks for the reply, GM. I appreciate the comment and the link to the original design. With regards to the Stonehenge, I had already decided to go with a vent like that of the Billfort design (split at the bottom of the cab). Don't know how much that will mitigate the vent concerns though.

I am certainly no speaker expert, or speaker designer - just like to listen to well presented music. Thumping bass is not high on my list - it should be appropriately presented like the rest of the spectrum. I will search for other posts of yours to find out what there is on MLTL. I know there is a quarter wave group on Yahoo, but imagine it is beyond where I want to go. Hopefully I can locate a design of interest. The design in the paper you sent is scaled about right, so I will spend some time trying to understand that.

best regards -- Roger

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Quote Originally Posted by GM
Greets!

You're welcome!


Huh! Wonder why part of it is in much smaller type as it's fine in the doc I copied it from? He asks rhetorically.


His vent doesn't allow any fine tuning.


Based on what you say, you'll theoretically want more of an offset driver and vent than Olson's and Billfort's, i.e. a ~56-61.5" o.d. height [depends on seated ear height] and at least a 30" wide baffle x 24" deep cab tuned to ~27 Hz or actual driver Fs if driven with a high output impedance.

Regardless, long sob story short, all my reference tech library is currently unavailable and with a bit of 'oldtimer's' disease I'm not remembering a lot anymore, so factor in only having a few hours/week to indulge in audio related stuff about all I can say is you can either wait till I get the others done [probably Christmas at my 'snail's pace'] or search 'gm' or 'gpm' or 'GregM' and 'altec' or 'mltl' and hopefully Google/whatever can find enough of what I've published over the last ~20 yrs to make it worth the effort.

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Thanks, but I think my wife might have something to say about a pair of substantially larger cabinets... the doghouse is way too small for all of my equipment.

I have been looking at the original 50's design, and actually like it a lot. Seems quite similar to Billfort's actually. I don't think I can get away with any larger a cab. You figure I will have issues with the 604 in there?? Any reference to designing in vent tuning, or am I pushing my luck.....

regards -- Roger


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Quote Originally Posted by GM
Greets!


Sorry, me and the folks I've known with large systems can't relate, none of the women in our lives seem to care how big they were once they got to enjoy their music through them and for some, we made a reasonable attempt to blend them into the decor, but it is what it is............


Anyway, as it turns out, Olson's cab just barely meets the MLTL performance criteria, i.e. its 1/4 WL action is just 'strong' enough to damp the vent a bit, so the vent will either be tuned a little higher or need to be a little larger for the same tuning, but pretty sure you don't want its ~58 Hz tuning [Fb]. Net volume [Vb] is ~7.5 ft^3 loaded with a 604.


Instead, an optimum vent [by the pioneer's standards] would be too long [deeper than the cab], so considering these will only be able to handle ~15 W max below ~90 Hz at low distortion, a single 4" i.d. tube/pipe x 2" long should be large enough for a low vent mach and get you to ~28 Hz once damped with 1" acoustic fiberglass insulation [AKA OC 703 ductboard] on the back, one side and top.


Don't have any program loaded [or otherwise for that matter] that will convert this to billfort's dual triangle vents, but if you want to experiment, then both vents combined must have at least as much cross sectional area [CSA] as the single 4" = 12.566"^2, so if round would be 4" x 0.707 = 2.828" dia./6.283"^2 each. Note that they will be >2" long since the combined internal pipe area will be greater, ergo will have more frictional 'drag' [stiction].


GM

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I actually feel pretty fortunate that the wife has bought into the Billfort size cabs (9+ cu ft) - hopefully with good construction and proper venting, they will allow the 604s to demonstrate their stuff. I am planning to inside mount the driver for aesthetic reasons, and assume that will not have any substantial impact.

I have been doing some port research, and found some useful starting information. The flared ports seem like a good solution compared to the straight, and with the variable pipe length, allows for tuning. Hopefully the affect will be fairly audible so I can tune by ear.

Have you an opinion on side vs front venting? I have heard that music/sound does come out of the vent, and should be directed into the room (recommending front venting). Also heard that various chuffing and breating sounds emanate from the vent, so the vents are better placed on the sides. I certainly don't want to punch punch a bunch of holes in the cabs to experiment......

regards -- Roger

Hello,

I have two questions that I am currently trying to resolve. Input would be appreciated.

1 ) Have you an opinion on side vs front venting? I have heard that music/sound does come out of the vent, and should be directed into the room (recommending front venting). Also heard that various chuffing and breating sounds emanate from the vent, so the vents are better placed on the sides. I certainly don't want to punch a bunch of holes in the cabs to experiment......


2) I have read about materials choices for the cabinets, and understand baltic birch plywood is highly favored (along with MDF). I also understand the issues with solid wood. However, I have spotted a local place that sells 'recycled' or 'reclaimed' wood. It would seen that this product, if in good condition (physical and appearance), would not have most of the concerns that have been raised about wood in general. It should have stabilized and dried out over the decades, and one might assume that the density of the vintage wood would be greater than the current product. If they have 3/4 or 1" thick product that could be used to build a cabinet, might that be a suitable choice, or would baltic birch ply still be the winner ??

regards -- Roger

as far as plywood goes I found a product called OSB 3/4" subflooring. I tried it on the last pair. it works great. it's very strong, water resistant, has a sound deadening quality, and cost less the 30$ a sheet 4x8. it's a lot like the environboard Altec used.

When I have the choice I prefer plywood over MDF. Plywood handles more abuse and still sounds good. I do have two pairs of Altec MDF cabs that sound nice. They are no where near as durable as plywood. A few of the corners are missing on my MDF 817a cabs.

Speakers can be built out of solid wood. Even if it is old it will still expand and contract though. And much worse so if you live in a climate where it gets cold and snows. My father has a pair of speakers he built in the late 60's or early 70's. They are made from regular boards. During the summer they look nice. During the winter the corner joints separate slightly

If you build a cabinet out of plywood, that was properly designed and braced for MDF, it will most likely ring(probably why the master engineer above is selling his brand new model 17/18). In fact it will likely have areas that ring at different frequencies. If you change the engineering of the materials, you need to appropriately change the engineering of the construction.

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as far as plywood goes I found a product called OSB 3/4" subflooring.

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In my neck of the woods we have a similar product called "Advantech". It's very heavy/dense and has somehow been plasticized. It looks like OSB, you can see the oriented strands. It is said to be waterproof, being aimed at roof decking and subflooring. One drawback is that the sheets are tongue and groove on the long sides so you lose that bit.

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Originally Posted by Phil-G

as far as plywood goes I found a product called OSB 3/4" subflooring.

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Originally Posted by bowtie427ss

In my neck of the woods we have a similar product called "Advantech". It's very heavy/dense and has somehow been plasticized. It looks like OSB, you can see the oriented strands. It is said to be waterproof, being aimed at roof decking and subflooring. One drawback is that the sheets are tongue and groove on the long sides so you lose that bit.

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3/4" Oriented Strand Board (OSB) has lots of voids.. It is not the best material for cabinet construction IMHO... I agree with Bowtie it also does have a tongue and groove edge.. I Just put some down not long ago.. If someone is going to go through all the trouble of building their own cabinets they shouls use Baltic Birch plywood.. It is the best material to use IMO ! It comes in 5' sheets in 3/4" or 4x8 sheets in 1" thicknesses in my area.The 1" stuff is extremely heavy,so bring a friend... Lol

Thanks very much for all of the feedback and perspective. My plan is to go and look to see if they have any reclaimed wood that is even interesting. My guess is that they will not, and so it is to baltic birch. If they do have some reclaimed wood that is compelling, I will have to think long and hard about which way I want to go. Clearly there are real risks associated with the reclaimed wood route.

thanks again -- Roger

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Originally Posted by Phil-G

as far as plywood goes I found a product called OSB 3/4" subflooring. I tried it on the last pair. it works great. it's very strong, water resistant, has a sound deadening quality, and cost less the 30$ a sheet 4x8. it's a lot like the environboard Altec used.

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I've thought for some time, that if I build a cabinet it will be made of OSB....... and yes, I too see the Altec Enviroboard as being very OSB like, although maybe not as coarse.

FYI, you can by 3/4 OSB without the T&G and it is substantially cheaper-$18 at Menards not on sale.

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Originally Posted by Altec Best

3/4" Oriented Strand Board (OSB) has lots of voids.. It is not the best material for cabinet construction IMHO

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after cutting through several sheets I have yet to find a void.

that's more than I can say for some of the BB I have come across.

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Originally Posted by rogerh113

I am planning to inside mount the driver for aesthetic reasons, and assume that will not have any substantial impact.

The flared ports seem like a good solution compared to the straight..........

Have you an opinion on side vs front venting? I have heard that music/sound does come out of the vent, and should be directed into the room (recommending front venting). Also heard that various chuffing and breating sounds emanate from the vent, so the vents are better placed on the sides.

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Well, at ~7.5 ft^3, it can start demonstrating a bit better than Altec's ~same net Vb cab and of course the room will help, so just a matter of finding the best overall tuning, which may not be the same for both speakers.


While in theory all driver cutouts should be chamfered when rear mounted and many on the backside when front mounted, it's obvious that most manufacturers, DIYers don't bother, but when it's a wide BW one, and especially if there's a coaxial tweeter, then it really should be; and not just a simple cosmetic roundover, but one that knocks it back at least 60 deg. relative to the baffle, then do the cosmetic blending of this waveguide [WG] 'mouth' [terminus] to the baffle and this radius should be at whatever the WG's flare frequency is.


In the scheme of things though, making a 30 deg cut relative to the baffle beginning at .707x the 60 deg's axial length is sufficient. Since even this only gets one a subjective improvement over just making it look smoothed over, virtually no one does it unless the baffle's quite thick.


In kind of short, doing just the 3/4" router bit round over to the cutout serves no useful purpose acoustically, just cosmetically as it still has a theoretically infinite number of the same eigenmodes back where this round 'wall' is still parallel, so at the least, knock it back 90 degs and smooth the outer edge for the cosmetics.


Note that these are included angles, so divide by 2 for bit angle.


How audible this is depends a lot on the person's hearing acuity, SPL, sound source, but me and some others liken it to 'lifting a [diaphanous] veil' from in front of the speaker, which in a way it actually is.


For max effect though, it requires seriously rounding over the cab's corners or at least sufficient foam/whatever to damp its much larger [stronger] eigenmodes and no doubt why Olson horizontally canted the baffle [vertically is less important due to our ears being on the sides of our head].


Note that my vent length suggestions are too short [will tune higher] for flared vents, so will need to take that into consideration.


Contrary to popular opinion, 'music' per se doesn't come out a vent, just its own pipe harmonics and a narrow gain bandwidth [BW] centered at its tuning [Fb] that falls in and out of phase, ergo when tuned down low, we want the vent to have a <0.05 vent mach [< ~17 m/s, though some claim <0.035% = ~12 m/s] to ensure a high acoustic impedance and no vent 'chuffing' from being overloaded. Done this way, the vent can be put anywhere on a typical BR, though with a MLTL it's a bit more critical for best overall performance.


In all cases though, one has to consider any local vertical boundary impact, so in most cases where there's a corner nearby [like < 3x the vent's effective diameter] and the cab/corner's toe'd in included angle is < ~9.5 deg, put them on the front; or if up against a wall, then lower rear corners of the cab to get some free vent corner loading.


GM

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Originally Posted by Phil-G

after cutting through several sheets I have yet to find a void.

that's more than I can say for some of the BB I have come across.

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Well I don't know what kind of BB ply you are getting in your neck of the woods, but up here it is super heavy and solid as a rock (Void-Free)..The 5 sheets I bought for my project were all void free where all the cuts where made...MDF has to be glued 100% as mechanical fasteners are all but useless in MDF..And MDF doesn't like moisture at all, even high humidity will make it swell if not properly sealed..Personally I don't feel that a product that can swell like MDF would make a good choice for cabinet construction...Has to be sealed or painted completely.

But the biggest and most important aspect of the MDF vs.Baltic Birch Plywood is how they sound IMO&E.... Baltic Birch cabs sound a lot better to my ears.. But that is my personal preference.But as usual YMMV.

at 50$ a sheet you can have all the BB you want. :D
aside from the wood grain and the exotic name, I don't see any great benefits over OSB.
I have no use for mdf especially here in florida where it starts expanding as soon as it leaves the air conditioned store.

It's a lot stiffer [higher MOE], so the cab will have a higher Fs for a given panel thickness even before bracing is added, though one can increase their thickness to get up to the BB's:

Modulus of elasticity:


MDF = ~527,000 psi


BB. etc., no void plywood = ~1,800,000 psi


Grade O-2 [OSB plywood equiv.] = 800,000 psi


Grade O-1 [general purpose] = 650,000 psi


Grade R-1 [waferboard] = 450,000 psi

GM

Hello GM,

Thanks for the info. Just to clarify my understanding of your terminology - you are suggesting running a 30 degree chamfer bit around the outside face of the speaker cut out, and then easing the edges. The start of the chamfer would be at .707 of the depth, so for example on a 1" thick baffle, the chamfer would start at approximately .3" in from the inside face of the front baffle, and extend outward at 30 degrees to the outer face.

regards -- Roger

OSB/2 is not what I use

OK, what's the one you use? O-2 is the stiffest I could find?

GM

#3 is the the least I see here. #2 is not rated for flooring or humid conditions. the flooring material sold in florida is guaranteed not to go to crap when it gets rained on. it's not unheard of for a rainstorm or storms to come thru before the roof get finished. im not finding PSI specs but I will say the material I've played with is very stiff.

At that angle, you will never be able to install inserts without blowing out the chamfered hole. You will have to mount it like GM earlier mentioned by front mounting the speaker in a dadoed panel and then mount that onto a chamfered hole baffle.

I will upload a new diagram as soon as I can log into stupid Photobucket. :(
(I had to directly upload the picture into Altec User's Board so it is a little LARGE.)
(Also, the drawing is of a 15" speaker that I stretched out to 16", so some dimensions might not be accurate.)

Attachment 3190

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Originally Posted by rogerh113

Hello GM,

Thanks for the info.

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Greets!

You're welcome!

Not quite, I posted the theoretical best overall flair [AFAIK], but then I basically said it's not worth the effort unless the baffle's quite thick. Guess I should have added > 2".

At the end, I basically said to just angle it at 90 deg/2 = 45 deg its whole depth, then just sand/smooth the sharp edge on the baffle face, but if you want to router another little flair in lieu of sanding, then it's ideally at 22.5 deg..

But back to the ideal if you want to do it.......... [wish I had at least a scanner set up to post a sketch]

The 30 deg [60 deg total] initial flare is full depth, then measured axially out to 0.7 - 0.71" [0.3 - 0.31" measured from the baffle face] begin the 15 deg [30 deg total] 'flip out' flare end correction out to the baffle face.

GM

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Originally Posted by Phil-G

#2 is not rated for flooring or humid conditions.

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Must be a Fla.code as all that I listed is subfloor rated nationally unless it's changed since I last had a need to know a few years ago.

Regardless, no OSB is going to be anywhere near as stiff as BB, apple or marine no void plywood unless it's anywhere from relatively a little to a lot thicker or braced a lot more.

The price differential though makes O-2 with plenty of bracing from scrap a good substitute if a fine finish isn't required.

GM

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Originally Posted by VolvoHeretic

Attachment 3190

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Cool! Got us a draftsman! Join Flickr, it's a lot more user friendly or at least has been for me, but haven't loaded anything new in years, so YMMV. I hate Photobucket, what with all the pop-ups, slow to load.

Yeah, cosmetic baffles look good, though normally only used to 'flush' mount the driver, which negates the need for a flare.

For rear mounting, I long ago switched to clamps, [2] locating pins for big, heavy drivers, beveled cutouts mounted on baffles just tall enough to do it.

GM

Thanks GM, I don't know what's wrong with photobucket, the login window is totally missing.

Is this what you are talking about with the 30 and 60 degree flares? I like the ideal of dowel pins and clamps. :)

Attachment 3191

Thank you! :Thumbs up::Big smile:

GM

So basically you are using the dowels as alignment pins, and the clamps secure the speaker to the back of the baffle. Willing to reveal your preferred clamp??

regards -- Roger

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Willing to reveal your preferred clamp??

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Modified JBL MA-15.

For clamping the rear of the rim you need to grind off that little lip that is intended to "catch" the rim edge from the front.


http://www.hostboard.com/forums/hbmc..._id=880000500f

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Originally Posted by VolvoHeretic

Thanks GM, I don't know what's wrong with photobucket, the login window is totally missing.

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Its your browser... Google Chrome ? I use Opera 36 and photobucket works fine for me..

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Originally Posted by Phil-G

at 50$ a sheet you can have all the BB you want. :D
aside from the wood grain and the exotic name, I don't see any great benefits over OSB.
I have no use for mdf especially here in florida where it starts expanding as soon as it leaves the air conditioned store.

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OK yeah don't know why I thought you were using MDF... But even still OSB is a compressed wood chip Ply.. By its nature will have voids in it..Even at $50 sheet why wouldnt you use the best thing available... Most folks will only ever build cabs once twice,three times in their lifetime so...

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Originally Posted by Phil-G

the flooring material sold in florida is guaranteed not to go to crap when it gets rained on.

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It has a thin wax coating that allows it to get wet once ! After that the wax wears off and disappears..

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Originally Posted by rogerh113

Willing to reveal your preferred clamp??

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That's what BB, etc., ply and hardwood scraps are for if one has a modest woodworking shop. ;)

Large 'Curb Queen', etc., used or God forbid :Trauma:; new retail, conduit clamps works too. They use to sell fancy milled alum. block ones at the local MI Emporium like JBL championed, but can't find them in a quick search. You can also make heavy duty versions of simple speaker grill retainers: Penn-Elcom G0780KIT Large Speaker Grill Clamp Kit

GM

So what are the benefits of using clamps versus screws and t-nuts? I notice that many of the big JBL's use clamps. All the Altecs I have seen use t-nuts and screws.

For me it was cosmetics with my bartering builds and after I got 'deep' into helping garage, frat house, roving dinner bands, wanted a 'lazy' man's way to swap out drivers as well as keeping folks from over tightening them.

In short, all one needs to justify it is to have a screw or two drop down in an A7 with close mesh screen over the vent to limit retrieval while the frat's off campus party is in 'full tilt boogy'/'God's own drunk' mode. :Afraid:

GM

I would still use screw-in epoxied inserts to secure the clamps. There's a BIG chance of blowing out the edge of the chamfered speaker opening with the insert's corner only 1/8" away using them at the speaker bolt pattern location. I would also find or make out of bolts, a 1/4" steel dowel and screw them into epoxy filled holes to locate the speaker. I will draw another picture tonight when I get home. :)

Huh?! I agree that an insert is a good plan or even a T-nut, but the clamp's hinge point is well away from the driver, so baffle thickness at this point. My dowels are threaded rod just screwed in the wood with a bit of PL400 on the threads.

GM

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Originally Posted by Altec Best

Its your browser... Google Chrome ? I use Opera 36 and photobucket works fine for me..

But even still OSB is a compressed wood chip Ply.. By its nature will have voids in it..


It has a thin wax coating that allows it to get wet once ! After that the wax wears off and disappears..

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Forgot about you telling me about Opera......gotta try it if I can ever get the time to screw around with computers.

Hmm, the OSB sheathing they used to fix my roof decking didn't have any visible voids, just what looked like a baked glue/sawdust filler where a void would otherwise be.

WRT waterproofing though, I laid some long strips of scrap to make a temporary walkway across my rotted deck and after a few rains it had mostly turned to mush, so long gone to the landfill now.

GM

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I would also find or make out of bolts, a 1/4" steel dowel and screw them into epoxy filled holes to locate the speaker.

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Hey thats a good idea. It sucks holding a 30 lbs driver with one hand while threading in screws with the other hand. Having the studs there and then just using nuts is a good idea

Really compelling suggestion on the dowels and clamps. It really eliminates the tolerance stack-up that was building up close to the speaker cutout. Plenty of space and meat with the clamps (plenty far away from the edge). I went ahead and got the JBL MA-15 clamps. Pretty nice deal on eBay, and they look like an excellent choice. No need to keep fussing on that one.

Sounds like you recommend steel dowels rather than wood?? Is the concern not getting the speaker against the rear face of the baffle and snapping off the dowel?? Better safe than sorry, I guess...

regards -- Roger

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Originally Posted by Elitopus1

........then just using nuts........

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.......then just using wingnuts...... :wink2: and to make it easier still, make a wrench from plastic pipe. The one I use most is 3/4" dia. x 6" long with 3/16" x 1/2" notches. I started painting them dayglo orange when they began growing 'legs' and disappearing.

GM

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Originally Posted by rogerh113

I went ahead and got the JBL MA-15 clamps. Sounds like you recommend steel dowels rather than wood??

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Right, those or similar was what I was looking for. Surprised Google didn't find them for me.

Well, threaded rod in my case after finding out how hard it is to cut the drill blanks used for 1/24th scale slot car drive axles; but yeah, something I can drop heavy drivers on without worry.

GM

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Originally Posted by rogerh113

Hello GM,

Thanks for the info. Just to clarify my understanding of your terminology - you are suggesting running a 30 degree chamfer bit around the outside face of the speaker cut out, and then easing the edges. The start of the chamfer would be at .707 of the depth, so for example on a 1" thick baffle, the chamfer would start at approximately .3" in from the inside face of the front baffle, and extend outward at 30 degrees to the outer face.

regards -- Roger

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My Altec 612C's came with that chamfered edge from the factory...

http://www.hostboard.com/forums/hbmc...1.jpg~original

http://www.hostboard.com/forums/hbmc...2.jpg~original

Well, drawing #4. :)

Attachment 3193

Hello,

Thanks for all of the input so far, things are very much coming together on the design. There are 2 more aspects that are not eminent, but useful for me to understand, and input would be helpful.

1) Speaker cloth / grills ?? I would guess that no matter how 'good' it will have an impact on the sound. I am in a situation where the speakers will be exposed to fairly bright, indirect light, so speaker cloth stretched across the face of the speaker would take the brunt of that rather than the cones. I have also heard (perhaps urban myth), that the grills will keep bugs and such out of the horn portion of the speaker. Insight appreciated.

2) Cabinet stuffing. Is there a clear winner in this category?? It seems that there are several popular ones. I assume they are all a bit different, so it probably matters. Perhaps application specific?


thanks again -- Roger

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Originally Posted by Altec Best

My Altec 612C's came with that chamfered edge from the factory...

http://www.hostboard.com/forums/hbmc...1.jpg~original

http://www.hostboard.com/forums/hbmc...2.jpg~original

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Someone is selling a 612c cab loaded with a 15" 515b woofer local to me. They have the woofer front loaded. The way the opening is cut allows this without the woofer or cabinet being modified right? Usually I see either the ribs are ground off the woofer or little slots are cut into the cabinet

I'm curious too since I've never seen any factory flared cabs. Personally, I don't like the idea of mounting it on what is in effect a very thin 'baffle', so just used a file or grinder to rebate for the ribs. A bit of Silly Putty or similar in these grooves combined with a notched gasket seals well.

GM

This is drawing #5. :)

Attachment 3203

Yeah, trim rings are real popular with the 'full-range' crowd.

GM