Cabinets for Altec 515B woofers suggestions

Hello again,
I am wondering if an Onken box would work for me?
I know they were designed for the 416, but I have been corresponding with a fellow in Japan, who reports that the 515B is all the rage in a large Onken cabinet, and I recently sold my other pair of 515B's to a Japanese buyer that wanted them for an Onken project. He was tickled ping to pay A whopping sum for them and the $360.00 shipping.

In my searching I have found some photos of Onken /515B combos, but the cabinets look a lot larger than the 33 inch tall quote I have read for the Onken cabinet.

Is there any plans I can download for the Onken? I have only found the Hiagra article, in French of course, and I can barely speak the King's English much less spend days running it through Babelfish.

Thank you,
Donald bowman

Quote:

---

Originally Posted by MrMonster

The Jabo horns gave me a better sound that 903, 805, or 311 horns.

hI have tried for days to load a photo.........

---

Hmm, I still don't have a clue what sort of bass performance you're wanting other than highly damped.

OK, how wide, deep are the Jabos since this determines the cab's minimum width x depth? Also, at what ear height from the floor do you want the Jabo? Once these are known we can determine a 'close enough' net cab volume (Vb) we have to work with.

This site doesn't allow hardly any file storage, so you must upload them to an on-line site such as Flickr, Picassa, Photobucket or similar, then post the links.

GM

Quote:

---

Originally Posted by MrMonster

I am wondering if an Onken box would work for me?

Is there any plans I can download for the Onken?

---

Yes, they will work great in an Onken and how big they will be will depend on what F3 you're wanting, what your driver's actual specs are and how much EQ you're willing to use to minimize cab size.

For instance my 515B's specs require a ~2x bigger cab tuned over a half octave lower for a T/S max flat alignment than the Altec published specs requires, ditto for an Onken, so designing without measurements means that the cab could range from way too large to way too small AFA getting a true Onken n= 6.34 alignment, though the larger the cab, the more tuning options available.

Frankly though, using one big vent works just as well and saves on woodworking and allows much more tuning flexibility, especially if a round tube is used, but the Onken's industrial chic 'look' can be enough for some folks to justify tolerating these 'shortcomings'.

FWIW, inputting Altec's 515B published specs in an Onken 360 sim using MJK's MathCad software requires a matching impedance to completely flatten it out to ~30 Hz/half space, i.e. Re = 12 ohms, so added 12 ohms of series resistance.

There's usually some room gain down low and especially if near/at a room boundary, so you probably won't need this much which in turn means you can use a smaller cab, but without a measured room gain curve from where the speakers will be plus driver measured specs combined with the system's total output impedance this can't be calculated with any degree of accuracy, so most folks build them as big as they can 'afford' and tune it as best they can and whatever bass response they get is 'what it is'.

Kind of a shame you sold a pair, dual 515Bs/channel are pretty impressive performers.

Anyway, if you want to 'run the numbers' you can with Cyr-Marc's Excel SS: http://www.mh-audio.nl/downloads/Onken_Calc.zip

Onken 360's critical dims for Altec 416-8B: http://nicolas.davidenko.perso.sfr.fr/plancaisse/onken360.html

GM

Dear GM,
Thank you for staying with me so far. This will be the first speakers I have built, so I am not up to your wisdom.
First, as to muffled bass, I didn't get a muffle when I packed the flares and added the insulation. I read in a lot of threads that users were andding layer upon layer of plywood to the outside, and extra bracing on the inside to gain a better bottom, I just worked from the inside. My thinking was if the cabinets are vibrating, that is lost bass. I did get a warmer and fuller bass this way and how should I say, more "projection of bass?
I did finally tune the port on the VOT cabinets with two vertical ports for the best sound in my room and to my ears

What I am trying to acieve is a a speaker that will give me the near live sound that I was getting from the VOT cabinet with the JAbo horns crossed at 700 HZ to the horn. To my ears I was getting the best sound from any speaker I have owned.
Plus, I was able to buy these VOT horn cabinet sets at less than $800 for two pair of them and the profits from the sale of the 515B and 288C drivers and the big horns paid for them and put a profit in my pocket to persue this project.
Since I have this set of 515B and the 288C drivers with the Jabo horn, Why not try to build them into a really nice speaker without spending $4 grand for better speakers.

My listening room will be 17' long 14' wide with 9' ceiling. the HF horn will sit on top of cabinet. The height now, from floor to center of the Jabo horn is 56 inches. After standing squatting and sitting, I think a height to the center of the horn from floor would be approx. 46 inches, give or take.

These Jabo horns are round and are 21 inches in diameter, and are 22 inches long from the face of horn to the back of the 288C driver. They are said by maker, that are tuned at 500 HZ

You can get a good idea of the horns and their use at this thread on the Lansing site..
Altec 828 project - Lansing Heritage Forums

I would like to use the Onken cabinet, as it is the easiest for me to build with my tools, and if width and depth of cabinet is at least 18 inches less than the VOT cabs, they will be able to fit in my house.
I do like the side vents on a cosmetic level, and if I ever need to sell them it would be a better choice for buyers.

Thank you for your time,
Donald Bowman

Quote:

---

Originally Posted by MrMonster

Dear GM,
Thank you for staying with me so far.

This will be the first speakers I have built, so I am not up to your wisdom.


First, as to muffled bass.........

What I am trying to acieve is a a speaker that will give me the near live sound that I was getting from the VOT cabinet...........

I would like to use the Onken cabinet, as it is the easiest for me to build with my tools...........

---

Greets!

You're welcome!

Understood!

'Muffled bass'?! Not sure what you're referring to.

That said, adding insulation raises the cab's F3 (where it's 3 dB lower than in its ~flat BW), rolling off deep bass by lowering the speaker sytem's Qtb (reflex box quality factor) which up to a point increases both the perceived and real world accuracy of the reproduction. Once its roll off slope decreases to a Qtb <0.5 ('critcally' damped, i.e. transient perfect (no 'ringing' after the signal stops)), then it becomes over-damped, ergo the driver stops before the signal does.

This results in a harmonics emphasized, tonally unbalanced presentation similar to what a musical instrument (MI) speaker is designed to do, so while it will sound 'musical' (and then some), it's adding a second layer of it to what's on the recording. While technically 'bad', many folks prefer it when listening to SS Vs tubes and/or CD Vs vinyl since both SS, CDs tend to sound overly 'dry', i.e. lacking the tube's, vinyl's perceived 'rich' harmonic distortions. Not surprising considering we tend to prefer the velvety texture of 'rich' foods, highly saturated colors, etc., but technically it's not the accurate reproduction some folks prefer.

Anyway, this description indicates you've over-damped the system somewhat versus the 'highly' (~critically) damped tuning that your earlier comments implied, though without a properly measured response plot, no way to know for sure.

Note that an A7's horn cab presentation is considerably different than a speaker using the same driver with no horn attached to it, so while the latter will sound more natural/life-like due to not having any horn induced distortion, it won't sound nearly as 'focused', i.e. 'project'.

Hmm, don't see how a simple six sided box with some bracing and a round cardboard tube vent is somehow harder to make than an Onken, especially since the same tools would be used, but if the Onken poses no building issues and don't mind the limited tuning of a bunch of fixed vents, then certainly no reason to not use it.

"......width and depth of cabinet is at least 18 inches less than the VOT cabs......." This makes no sense to me considering both the A7's and horn's dims, so from where I sit, height = 46" - 21"/2 = 35.5"H with the minimum WxD = 21" x 22" based on the horn's dims.

Assuming a ~3/4" (19 mm) material thickness, this equates to ~7.86545 ft^3 (~222.72474 L), so not a lot of cab volume (Vb) for a 515B, especially once the driver and vent system is subtracted out, so at this point I'm thinking you'd be better off with a sealed alignment and EQ to shape its LF response. That, or use a much smaller vent system more in line with a typical ducted port alignment to keep net Vb losses to a minimum. You can always use molding to create the Onken's 'look'.

If you really do want a cab with a WxD smaller than the horn, then sealed is definitely the way to go.

GM

Thanks for the Reply and math lesson.

So for the moment let's throw out the fact that I even have the A7 cabinets, and only have the 515B woofers, and the 288C driver with the round/conical Jabo horn.
What is the best cabinet other that an A7 to use, and what kind of dimensions should the box be and what kind of vent? again, not going back to the washer/dryer size of the A7 box?
Thanks,
Donald Bowman

Quote:

---

Originally Posted by MrMonster

Thanks for the Reply and math lesson.

So for the moment let's throw out the fact that I even have the A7 cabinets, and only have the 515B woofers, and the 288C driver with the round/conical Jabo horn.
What is the best cabinet other that an A7 to use, and what kind of dimensions should the box be and what kind of vent? again, not going back to the washer/dryer size of the A7 box?
Thanks,
Donald Bowman

---

Stephane Rame cabinet with GPA components seems like what your looking for.

http://www.hostboard.com/forums/alte...ml#post1769131

................

'Best' is dependent on the needs of the app. FWIW ~10 ft^3/driver works best for me, but mine are both MLTL and corner loaded, so can be a bit on the small side.

Based solely on what you've posted it would seem an A7 size minus the space its woofer horn takes up or ~12.66 ft^3 gross, so not all that much smaller, trading a lower height and width for a greater depth: 35.5"H x 21"W x 34.5"D or some combination of width x depth that = ~724.5"^2.

Based on room size alone, a ~30-35 Hz tuning using whatever size vent yields a low vent mach seems a good place to start experimenting.

GM

Thanks GM,

Would I need a baffle below the woofer or a tube vent to the port, or just an open box to the vent?
Thanks,
Donald Bowman

Well, the cab will need some bracing, but otherwise will be just a big, open box with a tube vent if you want to keep it as simple, efficient as practical. WRT vent location, this cab is tall enough to have some 1/4 WL action on the vent, so placing the driver at the extreme top and the vent at the extreme bottom will have the most damping effect on the port, reducing its length for a given tuning referenced to what a typical box calculator programs specs.

AFA vent size goes, a 10" dia. cardboard tube such as used for pouring concrete pilings is big enough to get Onken-like performance in a much smaller vent system.

WRT tuning, a ~17" long vent should tune it to near/at the published 24.9 Hz Fs with a simple 10 dia. hole in a 3/4" thick baffle pushing it up to ~42 Hz, so plenty of basic tuning flexibility and of course EQ can be used to further shape its in-room response. During testing, the vent doesn't need to be flush with the baffle, so it can protrude as much as required to easily handle it, just use some type of putty to temporarily make a good seal around it as any leaks will completely ruin the tuning.

Note that the above is based on the most recent suggested box size.

Altec's default cab damping of lining the top, back and one side with 1" acoustic fiberglass insulation plus covering any braces and the vent tube if it winds up being more than a few inches long should suffice, though some folks have found that 'less is more' with the 515, so probably a good idea to just line the top and top half of the back, side and only add more as required if it sounds 'hollow'. To get that last little bit of Onken-like tuning due to all those vent's slightly resistive loading, tightly stretch grill cloth or similar density material over the inside end of the vent tube.

For easy access, best to make the front baffle a two piece affair with at least the top driver baffle removable like on the later Valencia/Santiago cabs and if you make the driver baffle square, then it makes periodically rotating the drivers somewhat easier.

Also, if a separate, rigidly mounted horn 'sled' isn't used, then I recommend a double layer cab top plate. That, or add a decorative marble, slate or similarly massive material top.

GM