Building nineteens

[tinears]

I have a pair of 19s which my son has become quite attached to so I'm toying with the idea of building new enclosures. Drivers and horns are not common in this part of the world (Australia) but they appear every now and then.

This will be my first speaker project in about 30 years, materials and techniques have changed raising a few questions.

Reading the forum I gather MDF is preferred over ply or particle board. Not a fan of MDF for DIY home projects but if it's superior in this application I'll go with it.

My approach would be simple mitred corners using PVA wood glue but fully cleat (batten) all joints using an epoxy glue and a few screws. Had a few problems removing leaked epoxy glue from veener in the past, that's the reason for PVA on the visible parts, easy to get off.

I have the Altec drawings and have been planning cuts to the pre veneered sheets. It does appear there is an element of economy in the design, 48 inch (1220mm) wide sheets can be cut with very little waste. Sheets here are metric sized, 1200mm wide and I end up wasting heaps of board because the panels just won't fit into the slightly smaller width board.

If I make the cabinet dimensions 1.6% smaller I can do it economically, but the volume is then 4% less, would you?

Crossovers will be built using air wound chokes and decent caps, just have to source the big 8 and 35 ohm pots. Anything to be gained by going to 800Hz xover? Does the 802/511 combination work down to 800?

Any suggestions for improvements, thicker material perhaps, flush mount woofer, damping for horns?

All input appreciated, Ken

[Tom Brennan]

I wouldn't change the crossover, one reason 1200 hz was chosen was to match the directivity of the woofer and horn at the crossover point and this probably is a factor in the 19's outstanding imaging.

However an 802-511 combo will work fine down to 800hz.

[dc270]

Speaking to the horn damping aspect when I rebuilt my 19's a short while back I did encase the horn bodies in 1.5" cut to fit block foam from the fabric store. These horn are very dead sounding with no hint of ring thru. I sprayed the foam with a 3M adhesive spray and it stuck very well!

I also rebuilt my networks to the schematic suggested by Zilch with very good results! Finally I pulled all the fiverglass out of the cabs ( except the horn box) and put 1.5" bumpy foam on 3 wall sides. This too worked out sounding pretty good! I have not rebuilt any drivers- a plan for another day- but I am enjoying a well improved sound as they are now!

Best of skill with your project.
DC

[Earl K]

If I make the cabinet dimensions 1.6% smaller I can do it economically, but the volume is then 4% less, would you?

Yes.
- Changing a boxes stuffing density can easily create a box volume differential of +/- 5% . Therefore you can easily make up the lost volume .


- The original construction used partical board. Why not start with that ?

- The top horn section seals were loosey-goosey/ & "leakey" according to all accounts / therefore I don't see how the wood type matters terribly in this design. It is seemingly, all "part of the charm" .

- Personally, I use Baltic Birch plywood for boxes & prefer slimmer profiles in the looks department . But that's just me .

>< cheers :)

[Val]

Reading the forum I gather MDF is preferred over ply or particle board. Not a fan of MDF for DIY home projects but if it's superior in this application I'll go with it.


I use 1" MDF for my large cabinets.
Pros:
- Very dense and "still" in a enclosure
- Easy to work with

Cons:
- Brittle...not good for cabinets that will be moved a lot
- Dust is nasty. I wear breathing protection when routing.
- Glue joints firmly but not deeply. Under stress the surface layer pops off. Using real wood to corner block and brace is required.

[Mr. Widget]

My approach would be simple mitred corners using PVA wood glue but fully cleat (batten) all joints using an epoxy glue and a few screws. Had a few problems removing leaked epoxy glue from veener in the past, that's the reason for PVA on the visible parts, easy to get off.Just use a modified PVA glue... one of the yellow glues that are meant for wood. They will very likely give you a superior joint since they will be more easily absorbed into the wood. Most epoxies tend to sit on the surface with very little absorption... while the epoxy itself is much stronger, the joint may not be and moreover, if your joints are sound they will not fail regardless of the glue used.
I use 1" MDF for my large cabinets.
Pros:
- Very dense and "still" in a enclosure
- Easy to work withEasy to work with? I can't safely work with a full sheet of 1" by myself... it is just too heavy.

I have used PB, MDF, Baltic Birch, and other substrates... they all have pluses and minuses. Use whichever you prefer to work with and brace the hell out of the cabinet.

As an aside, I prefer the sound of the Altec 511 horn over the 811... you may as well.


Widget

[Goodwill_HiFi]

MDF is cheap, has a nice smooth surface, and a very even density, that is all it has going for it. I'd sooner use a higher grade plywood. The plywood will be more rigid, requiring less bracing. It'll also be lighter and more durable.

[tinears]

Thanks for all the good info.

Crossovers stay at 1200 then, I'd like to try 800 at some later date.

Horn damping, what is "block foam from the fabric store"? Don't think I've seen anything suitable on those absolutely thrilling trips with my wife to such places. I was considering using automotive sound deadening spray, thick black tarry stuff.

Dimpled acoustic foam for lining, wouldn't have thought of that, good example of how techniques have changed. Was thinking of using several layers of bonded acetate fibre, white wooly material from fabric shops

I'm leaning towards original size, not my 1.6% cheapskate approach, yellow glue on real wood cleats and particle board. I would hate if the characteristics of the boxes was altered (negatively) by using a different material, other planned changes can be easily undone if they don't work.

Resale value is only important if they are to be sold ;)

Thanks again for the suggestions, more welcome.

Ken

[Tom Brennan]

As for cabinet lining, keep in mind that Altec used the fibreglass to absorb upper bass and midrange from the back of the woofer cone, not to effect cabinet tuning. So make sure whatever you use can absorb sound as well as the original fibreglass. Best thing to do would probably be to use-----fibreglass.

IMO&E there's no need to get heroic with horn damping. Simply bolting the horn to the baffle eliminates ringing and if you want you can apply ropes of non hardening modeling clay to the inside of the "lips"; that eliminates ringing even with freestanding horns. The clay on the back of the pictured horn wasn't doing a damned bit of good but the clay in the lips was useful.

http://i254.photobucket.com/albums/hh92/Irishtom29/1972.jpg

[rgwalker]

I have a pair of 19s which my son has become quite attached to so I'm toying with the idea of building new enclosures. Drivers and horns are not common in this part of the world (Australia) but they appear every now and then.

All input appreciated, Ken

I was going to drastically alter my Model 19s but got a good offer to sell them and ended up building a modified version using a pair of Altec Model 17 (620A) cabinets. I was absolutely amazed with the bass response using a 416-8B and even though the crossover has been upgraded the coil for the woofer wasn't touched and other than the cabinet and the capacitors it's the bottom end of a Model 19. That's where my system stops imitating a Model 19 but there's no reason why you can't use the stock horn and driver and mount them on top or build a cabinet to suit.

The main reason that I suggest this is because the Model 19 wants space to open up and the 416-8B in the 620A cabinet is an excellent near field monitor.

Bob W

[tinears]

A quick question, I was reading the "1974 Enclosure manual" in the library. On pages 13 and 14 it covers polarity, phasing and physical planes of drivers. The middle diagram of the three on page 14 shows what I believe to be the nineteen relationship, is that correct?

On the fibreglass damping, you might be right, stick with how it was... but is fibreglass today the same as it was?

Correction - I mentioned 511 horns, I meant the smaller 811.

Ken

[WWaudio]

Just use a modified PVA glue... one of the yellow glues that are meant for wood. They will very likely give you a superior joint since they will be more easily absorbed into the wood. Most epoxies tend to sit on the surface with very little absorption... while the epoxy itself is much stronger, the joint may not be and moreover, if your joints are sound they will not fail regardless of the glue used.Easy to work with? I can't safely work with a full sheet of 1" by myself... it is just too heavy.

I have used PB, MDF, Baltic Birch, and other substrates... they all have pluses and minuses. Use whichever you prefer to work with and brace the hell out of the cabinet.

As an aside, I prefer the sound of the Altec 511 horn over the 811... you may as well.


Widget

511 agreed but even better....a 311-90 style horn. Words cannot describe!