Cabinets for Altec 515B woofers suggestions

Hello Lads,
Can some of you make suggestions for cabinets for the Altec 515B woofer? I have a pair of 256's with Jabo conical horns, and Behringer crossovers running right now, they sound great, but I do need a better Xover.

The point is, the tremendous size of the A5 boxes is eating into the room space.
If they were even a foot less in length and width, it would be a bit more manageable in my front room.

Are there any of the Altec or JBL bass reflex box designs for the 15" woofer that would help deliver an equivalent sound with a smaller footprint?

Thank you,
Donald Bowm

Sorry, I meant 828 or 826 cabinets, plus this photo has my 311-60 horns on.

Obviously, if you remove the horn, the reflex box can have a smaller footprint and of course it won't sound the same through the mids, but it will sound more tonally balanced over a wider BW once the HF horn is shelved down to match it. To narrow it up to the width of the 311-60 though and keep the same height requires and even deeper cab, so once we start shrinking its depth, its bass response starts leaning out also.

Bottom line, you can make the cab as small as ~3 ft^3, but it won't have any bass output.

GM

See my notes under "my Altec A10" - which uses 515b's
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The theater configurations get their low end from the huge cabinet surface area (AKA "wings") and the distance from the audience. 3 dB down at ~90 Hz isn't that bad. From what I remember from my acoustics classes is that the coupling (with air) roll-off (de-coupling) begins at the wavelength that matches the circumference of the radiator.
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A 15" radiator has a ~4' circumference, which puts the 3 dB down decoupling point in the 200 Hz .. ~250 Hz range. 4 such radiators will drop the de-coupling point an octave - which matches the Thiele-Small prediction quite closely.
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There are 5 ways to increase the radiator size - horns, ports, passive radiators, more, and wings (a form of horn for large diffraction situations - which require at least 1/2 wavelength to fully develop).
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The guiding rules of all engineering are: anything that works is a compromise and Mother Nature is a bitch.

I agree with GM. You could lose the horns in the 828 cabs and save a good bit of space.
Don't remember who much room they use up, but it's substantial.

The 828 box with the back of the horn flare open has a net volume of ~11 ft. You could probably get away with a net volume of about 8 feet with the 515B. That means a box of 40x19x22" (3/4" ply). That should save you a lot of room.

Don't recall if any of the 828 series had open horn cavities, but the closed off units are ~9.4 ft^3 net with driver installed. Altec listed the 825 with its open horn cavities at 12.66 ft^3 minus driver, so ~12.33 ft^3 net loaded with a 515B. From memory though, I recall calcing it at ~11.4 ft^3, so YMMV.

Regardless, when it comes to cab net volume (Vb), less is always less bass/tuning flexibility and if the signal's total impedance is high (source + any passive resistance), then at some point in the Vb reduction curve the system will become under-damped unless its tuning is made ~aperiodic in nature.

Also, in retrospect, the 311-60 with driver is ~as deep as the 825/828, so reducing the cab's outside width/depth dims to less than the HF horn's 'footprint' is as small as you can make it unless of course he wants them shorter also.

GM

Hello Lads, and thanks for the response.
I don't know if I made myself clear. The HF horns are not in the cabinet, I have them mounted on top of the box.

So now, I have just the 515B woofer loaded in the box, with a full open bottom port.
They sound very good now, with good clean Bass, and I was hoping to mount the LF 515B in a smaller footprint box and hopefully keep the same performance.

IS there a list somewhere of cabinets that Altec mounted the 515B only, or with a smaller HF horn?

Thank you,
Donald Bowman

We understand, we are referring to getting rid of the 515B's horn, i.e. put it in a simple ported box.

I don't recall 515s being spec'd in anything but horn cabs, though that doesn't mean they don't perform well in vented or sealed alignments if properly tuned and EQ'd for the app, i.e. the room and source impedance. Don't recall it being spec'd with any horn smaller than the 511 either, though it could be interchanged with any 803B/416 series cab design and EQ'd to suit.

GM

Yeah GM, about 11ft seems right to me.

I had done a quick sim on the 515B in an 11ft vs 8ft box and it looked pretty good. Group delay was better in the smaller box, if that matters. Tuning in the mid 30s for both boxes. Didn't look at damping.

So Mr. Monster you should be able to go with a smaller box and still sound nice. In a simple box you lose the A7 style bass flare which does take up some room. Would my 40x22x19 box fit your needs?

If you are running your cabs with wide open vents now, you really aren't getting much bass. What you may be getting is a nice hump circa 60Hz. A better tuned reflex box will give you lower, cleaner bass. I know, been there, done that! =)

The thing about GD isn't how much, as how low, it peaks, especially since it increases with decreasing Fb, so if you tune low enough that it decays away before our hearing acuity improves enough for it to be an issue........... and why I always recommend a low tuning for best overall vented alignment performance.

Many folks prefer higher tunings though, so from this we can infer that either GD isn't the 'bad thing' that the ported 'bashers' maintain and/or many folk's LF hearing acuity is nowhere near as good as they believe it is and judging by the overwhelming commercial success of a certain consumer brand combined with the perceived high SQ of highly resonant tapped horns, I'm going with the latter.

Again, the horn's rather large dims sets the smallest practical footprint, so your width/depth appears to be a little small based on its published drawings.

Hmm, IIRC the cab's Fb is up around 80 Hz with no baffle boards, making it a crude BLH which yields enough of a broadband tuning peak to extend the LF horn's gain BW down to around its 110 Hz flare frequency, so for deep, bass shy, music it's an acceptable tuning choice, though I imagine it ideally needs a bit more damping around the driver to quell excessive mids emanating from its mouth. A good tuning if XO'd to a suitably 'fast'/efficient sub system also now that digital EQ/delay down into the single digits is available at a reasonable price.

GM

Thanks Lads,
I think the general consensus here is that there is no easy answer to mounting the LW in another box. It seems Altec designed the woofer to fit a flared box.

I have had great luck in increasing bass response by stuffing the inside of the flars with foam padding, and increasing the thickness of insulation of rest of the box to 3 inches, and adding insulation to the top of the back panel and to the underside of the LF horn.

I am going to experiment with the port size, in front, any suggestions for port size? as they are now, it is the full length horizontal port, and I see most of the boxes with two vertical ports of about 6 to 8 inches in width.

I may just have to do a bit of room rearranging to accommodate their size or find a different LF driver to go with my HF horns.

Thank you,
Donald Bowman

Donald,
As was discussed before in other threads, there are many variables to be considered for port size. The main thing is what sounds best to your ears considering all the variables.

The easiest way to do this is with removable baffle boards to vary the port size. You can do all the math and measurements you want, but in the end it is what sounds best to you.

I called GPA and told them what I was using. 826 cabinet, 416 woofer, 800Hz XO and they gave me the dimensions for the port size for these components. Still, I may vary this slightly considering room size in a new location.

This may not be the way some people do it, but I still think it's the easiest and best.
Good luck...

Quote:

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Originally Posted by Panomaniac

If you are running your cabs with wide open vents now, you really aren't getting much bass. What you may be getting is a nice hump circa 60Hz. A better tuned reflex box will give you lower, cleaner bass. I know, been there, done that!
=)

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The A7 cab is not like a standard BR box, and its results are also very different from that of a standard BR box. The hump that you have mentioned about, will only be audible in the case of a standard BR box. But for the A7 it is actually needed, in order to mate properly with the higher output coming out of the LF horn. Thus the overall sound sounds more natural. And probabely that is the reason why Altec never supplied any of the different versions of the A7 with a very small-ish port that we often talk/discuss about. Anything less than 150/160 inch^2 makes the LF horn sound stand out like a protrusion, and the overall flatness is gone...!

The sound of the A7 setup is very much like that of a very (very) good quality FR/MR speaker, with its slightly limited top/bottom end response. Probabely the A7 is the best simulated FR/MI-like speaker of the world...!

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Originally Posted by GM

Many folks prefer higher tunings though........
GM

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I think the room is a very very important factor here for somebody to opt for the high-ish tunning in the case of the A7 with its biggy size.....

I personally prefer flat-ish sound.....but for the past 2 months I have been playing around with a pair of A7 cabs (original design with 2 vertical slots), and finally I have settled for the full-open-port tunning, after a nightmare-like phase in my life. Everything else sounded muddy. And to be frank here, it was actually an accidental revealation, bcoz I was so much bent upon and biased with the idea of tunning them perfectly in order to get the best possible bass, that I had straight gone ahead and had closed off half of the port area with a contraption capable of varying the tunning. And talk of bass ?....when I sweep from 20-200Hz, it growls around 27/28Hz, then at 35/36Hz, then at 42/43Hz, and then it just goes up without any bumpy-ness....... the overall bass is extremely good...... It just speaks the truth. Hip/hop stuffs sound just great with butt kicking bass......and it is such a relief as the nightmare of the past 2 months have come to end finally.

I think my room suits better to this full-open port tunning. It is 42'x23', and the A7s stand 10' from the rear wall. I seat at 22' away approx....

Aditya

Hey Aditya - I have to say I agree with some, disagree with some and am confused by the rest! :)

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The A7 cab is not like a standard BR box, and its results are also very different from that of a standard BR box.

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Disagree here. Sure it's different because of the horn flare, but it is not very different. I responds to port tuning just like any normal BR box. The horn does add some SPL to the upper end, that's all.

Quote:

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The hump that you have mentioned about, will only be audible in the case of a standard BR box.

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Well it was certainly both audible and measurable on my A7s. And it sounded awful in my room.

Quote:

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But for the A7 it is actually needed, in order to mate properly with the higher output coming out of the LF horn.

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Agreed. But only in a very large space or outdoors. And that's what the box was designed for. You're right that the low end hump helps balance out the bass horn section. And gives more efficiency as a bonus. But not in a space the size of a typical domestic listening room. There all you get is lower mid bloom and no real deep end. For example my listening room is about 4100 cubic feet. (116 meter cubed). That's much smaller than the A7 was designed for, but typical for domestic use. Your room is much larger. 42'x23' is not the typical living room! You're lucky to have that much space. And to be able to pull them out 10' from the wall.

I don't understand the second part of your post. You seem to be saying that you halved the port area and the bass was "extremely good...... It just speaks the truth." But then you say that full open port tuning fits your room better. So I'm not sure what you are using.

Needless to say, the box tuning is going to depend on a lot of things. The room is a big factor, speaker placement, the drivers, the amp (as GM as pointed out many times). With the box tuned to extend the lower end you will get more bass extension. But you will also be in an EBS (Extended Bass Shelf) alignment. So the response will gently rise with frequency. Room gain will flatten that out to some extent - more in my room than yours - and a little EQ does the rest.

The nice thing is that as we are capable of doing it ourselves, we can tune it to the room and amplifier we have. Just buying off the shelf speakers and hoping for the best isn't going to get the poor punter anywhere near what we can achieve.

Hmm, FWIW, unless you have very high ceilings, your room has ~25% more floor area than mine and it's considerably larger than most folk's listening rooms that I've either been in or seen posted on forums. Even my first home's ~26 x 46 ft 'great' room that covered almost one floor of a tri-level and able to house three 210s laid end to end on their sides along the short wall for a derived three channel stereo system doesn't measure up to Aditya's acoustic space.

So Aditya, IMNSHO you're cheating yourself by 'making do' with a couple of 'puny' A7s. :D

GM

GM...i gotta agree. my listening room is 28 x 40 and im running 210's, plus a couple of healthy subs

Hi Panomaniac :),

I meant to say that the A7 is really not like a standard BR box. This thing has already been pointed out by GM in your earlier A7 thread. Yes, there is a port, but its behavior is not so uniform like the standard ones. The bottom portion also to some extent behaves like a crude horn.

About the second part....I meant to say that I was so much biased by this port tunning thing that I never gave myself an oppurtunity to hear it as it is without any modifications.
I actually went straight for the tunning thing.....

Regards
Aditya

Quote:

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Originally Posted by GM

..........So Aditya, IMNSHO you're cheating yourself by 'making do' with a couple of 'puny' A7s. :D

GM

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:D:D:D

Yes...yes....you are absolutely correct here.
And you also can afford to be NSH here...:D

Yes..I actally had planned to build a pair of 210s as it is easier compared to the A7. But I somehow have shelved the whole idea for the time being.

Yes, I am aware of your 210s, bcoz during my past 5/6 months of research on 210/A7, I came across many of your posts, here & elsewhere...

I cherish your writings for their depth and insight.....

Regards
Aditya

I happen to have an Altec Voice of the Theater with a 515 and a pair of Klipsch La Scalas.

I hear you on your desire for something smaller, but that would give you more bass.

Most here know vastly more than I about cubic feet and tuning, crossovers and such....

But I can inform you that my La Scalas have terrific bass and are much smaller than the A7. They do have a unique cabinet design that looks like it is copied from a very old 1940's design by Western Electric....or a very old Altec design called the "805".

The La Scala speakers are by no means "small" they are large speaker cabinets....BUT they are smaller than the A5 or A7 Altec design.

They are folded horn cabs....and not the open flared horn design.

If I ever get around to it.....My dream was to design and fabricate a La Scala style cab for dual 15" woofers....and then go ahead and put my Altec horns on top. (not that you would need 2 515 to get the bass you want). I thought to put 2 in the design to make the cabinet bigger/taller.

Perhaps you could look at some La Scala speakers and see what you think. I guarentee you will be happy with the bass they produce.

There are also various "folded horn" designs on the web.....for cabinets.

Here is a link to show you what I'm talking about.

HISTORY FOUND

and some pics.

http://dl.dropbox.com/u/142937/Speaker%20%233.jpg

http://dl.dropbox.com/u/142937/Speaker%20%232.jpg

http://dl.dropbox.com/u/142937/Speaker%231.jpg

There is this guy on ebay that has a low frequency Altec cabinet.....Perhaps to get the ideas flowing.

[URL="http://cgi.ebay.com/ALTEC-LANSING-817A-Horn-Loaded-LF-Speaker-Cabinet-Empty_W0QQitemZ220543427424QQcmdZViewItemQQptZLH_D efaultDomain_0?hash=item335969a360[/URL]

I don't know what the Altec group here thinks of the "folded horn" design. But I believe Altec did use it for some speakers.

The La Scalas are by anyone's idea large speakers....but they are substantialy smaller than the Voice of the Theater....which is what you were talking about in your OP. And mine have great clean punch-y bass.

mentioned sooner, and I'd have pointed out the 4 peavey FH-2's that were up near Allentown the other week with a full project 2 compliment for $650!. Worth the van rental and drive to save the carpentry! May still be there... Per the OT, may have trouble cramming 515's in them though, dims would need to be checked.

I have a couple of corner horns I am considering as a DIY project The Altec version is beautiful, but I am really leaning tward the Jensen version. I bet the 515 would fit nicely.
I would prefer the 416 though.
Jensen Technical Bulletin No. 3

Here is the Altec version...
Altec Lansing - Page 31 - diyAudio

Hmm, maybe with enough EQ, but every Jensen driver I've measured or seen measured specs of indicates that none of the VOTT woofers is even close to being suitable. Only one way to know for sure though.........

GM

Hello Lads, and thanks for all of the input.
From reading these posts, most of you are well versed in speaker design and I appreciate learning from the posts.

So, am I correct in my idea of a front loaded cabinet of 11 cubic feet with a tuned port below the driver, I think I have seen some photos of a current Hiagra design that uses a tall front loaded cabinet with the 515B and a rectangular port.
but can't find that photo.

After thinking this through, I might not be married to the 515B's, but do want the 288C horn. is there a LF driver in cabinet that would marry well with the 288c?

Thanks,

Quote:

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Originally Posted by Leland

But I can inform you that my La Scalas have terrific bass and are much smaller than the A7.

Perhaps you could look at some La Scala speakers and see what you think. I guarentee you will be happy with the bass they produce.

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Hmm, not to disparage the LS's performance or your opinion of it, but the physics of the situation dictates it's more like mid-bass unless corner loaded in a relatively small room and why djk came up with converting the mid horn's cavity into a reflex to extend its response. Even this apparently falls somewhat short since I've helped folks who've done this mod and still dissatisfied.

For sure, its mid-bass is considerably better/more extended than the A7's but falls short by the same amount (and maybe then some) when compared to its 'sweet' BW, so comparing these two are an apples n' oranges one overall since each is optimized for different BWs.

All that said, I'm still not clear on how extended a bass response Donald wants since he claims that with a "full open bottom port" (which unloads around 80 Hz IIRC, i.e. the beginning of the mid-bass BW) "They sound very good now, with good clean Bass." If this is the goal, then the LS is a good option if his horns go low enough to XO to it, which so far my assumption has been that they probably don't.

If by "full open bottom port" he means the stock port as shown in his picture, then tuning is around 55 Hz, so the LS with djk's modification may suffice.

Plus he mentions having "256's with Jabo conical horns" which I'm not familiar with, though conic implies they won't load anywhere near low enough to mate to the LS unless they have a much larger 'footprint' than the A7 and his picture shows what seems to be 311-60s, so until we know what all the particulars are we're just 'shooting the breeze'.

GM

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Originally Posted by MrMonster

Hello Lads, and thanks for all of the input.

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Greets!

You're welcome!

Oops! I didn't see your response before responding to Leland's. I list some needed clarifications plus I forgot to include what amp you're using as it affects box size, tuning choices.

If you want real bass and the amp's output impedance isn't too high, then ~11 ft^3 loaded with an original or GPA 416-8C is big enough to have solid output all the way down to Fs if desired. The 515B in theory will have a bit more high SQ mids at the expense of a more rolled off LF response, though some EQ to trade a bit of its extra HF efficiency for LF gain BW can balance it out, so being a four+ decades long 515B user this would be my choice. ;)

GM

Hello Lads
I did forget to say that I got a better bass response by stuffing the flares full of foam sheets, and lined the reflex box below and inside the back with 3 inch thick fiberglass insulation. I also experimented with the vents by using a sheet of 1/2 inch thick foam board and trying different vent. The best was the two vertical vents as seen on the A7 cabinet.

The Jabo horns gave me a better sound that 903, 805, or 311 horns.
hI have tried for days to load a photo, but I keep getting a message of exceeding my limit, but when I try to delete old attachments I get a internal server error when I try to edit on any of my details.

Thanks

mr monster... if its worth anything, i have a devil of a time loading photos as well, the old hostboard was very easy to use. now it seems very difficult to me as well..even tho ive alot of pics to post

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

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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.........

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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:

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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?

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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

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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...........

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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

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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

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

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

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'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