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'Altec' 816 Upgrade

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Klang View Drop Down
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    Posted: 26 November 2020 at 9:36pm

Hello forum, 

Longtime lurker, first time poster here. 

I have a cabinet design dilemma and I wish to seek guidance. 

Apologies upfront, this is a lengthy post.

May I first state that I have indeed searched and read an extensive amount of related threads on this forum as well as Lansing Heritage, DIY Audio, Klipsch Audio Community and others. I have learned a great deal, especially from the posts of the prolific DJK, he truly possessed a wealth of knowledge. 

For reference, here are the details of my system, which is primarily used for the reproduction of pre-recorded music (vinyl DJs) at parties with up to 200 people: 

4-Way Stereo, 2 Stacks.

Each Stack:

x1 JBL 2405 Slot - 8Khz 

x1 JBL 2441 on 2390 Horn/Lens - 800Hz

x1 JBL K140 loaded 816 - 120Hz

x2 JBL 2206 loaded Tuba 30

I am currently using a pair of 'Altec' 816 cabinets for low-mids in my system (4-way, run in stereo), loaded with JBL K140s. I say 'Altec' as they are not the genuine article. I believe they were produced by a British company (not Fane) in the 80s, perhaps a veteran member may know more? They are constructed to the same specification as the 816 MKV, particle board wrapped in vinyl, the horn flares are ply however, not plastic. Build quality wise, they are very sturdy. 

After living with these boxes for a few years and learning more about their design foibles, I have a reached a point where I wish to assess my options. 

It has come up quite a lot that 816s have a tendency to sound muddy (at least above 250), and I very much hear this in mine. I use a K.T DN410 parametric EQ, and can make some improvements, but ultimately cannot completely cut the mud. 

I must say, I have never heard a genuine pair of 816s loaded with factory spec drivers, 421s or 515s, this could be a very different experience. I know the K140 is a pretty good match for these boxes, but an Altec it aint. A JBL 2220 would be my ultimate choice, but they are hard to come by. 

I have also read that the B&C 15NDL76 works very well in 816s as a modern driver choice, T/S parameters seem to confirm this. I would like to hear this for myself, but I fear the tone of the cabinet may be inescapable, so I've not been able to justify buying one to test. 

Another known issue with the 816 design is that the parallel top and bottom panels in the horn section cause nulls in it's passband. The solution to this is to build a modified 816 with a sloping bottom horn panel, the same as the A5 horn section. This is something I have considered if it turns out sticking with the 816 is my best bet. 

The Altec data sheet for the 816 states it is useable from 50Hz-1K. Horn loading operates down to around 200Hz, and below this the box acts as a ported bass reflex. I run mine from 120-800, and I have found that below 140 output starts to drop and output below 100 really isn't great at all. Again, this has been written about, the reflex loading can't 'match' the horn loading in level. Higher up, my boxes do okay, seemingly happily crossing at 800, but I have read that pushing this box past 600 isn't really recommended. 

In light of all this, I am left wondering what the best course of action is. It feels like it is a bit hasty to condemn the boxes without first trying out a different set of drivers in them, but the evidence (and my ears) suggests it is ultimately the design at fault. 

If this is the case, I am in the position of looking for a new mid-bass cabinet design that can do 120(ideally 100) to 800HZ that is ideally horn loaded (easier said than done), as I am a horn kinda guy.

As I understand it, horn loading down to 100 would require a very deep cabinet, perhaps unfeasibly so, and folding the horn isn't an option as it would then not get up high enough.

This reality led me to 1/4 space and 1/8 space horns, and Klipsch design territory.

My research suggests that the bass section of a Klipsch La-Scala, with the right driver, can in fact do 100-800Hz (just) and will sound pretty good doing it, even better if built out of thicker ply + more bracing.

Q.1 - Does anybody have experience using a La-Scala bin for mid-bass? 

Further questing in Klipsch forums led me to a design by a well respected member of the Klipsch Audio Community Forum, which has me intrigued:

https://community.klipsch.com/index.php?/topic/147849-jc-minipunch-bass-horn-plans/ 

https://community.klipsch.com/index.php?/topic/165983-jwc-bass-horn/

This is a dual 12" tractrix bass horn, measuring 31 1/8" W x 25" H x 20" D. It can be run down to 50Hz (comfortably) ported, and to 70Hz if sealed. The few plots floating around show response starts to drop off around 500/600Hz.

Q.2 - In theory, if this cabinet were to be loaded with a highly efficient driver, with a high EBP, such as a B&C 12PE32, perhaps it would extend more happily to 800Hz? Or maybe a 12PLB76? 

Q.3 - Can someone with more speaker design knowledge than myself offer any immediate thoughts just from looking at this MiniPunch design? Apologies if this is a silly question. 

I guess I am looking to find a definitive reason to discount this fringe DIY design as a possible option.I understand that with such a shallow horn, there won't be much directivity, but perhaps not a problem given my system is used in small rooms. 

The definite pros for me are that its horn loaded, the dimensions are about right for my stack and it's a straightforward build. The same applies for a La Scala bin. 

I now invite the forum to offer comment on all of this, and to propose alternative designs and options. I am open to any suggestions. 

I have much to learn regarding speaker design and acoustic theory, so when reading this please forgive me if the application of my knowledge is misplaced. 

Many thanks, 

Klang.



Edited by Klang - 26 November 2020 at 10:10pm
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Robbo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 26 November 2020 at 10:25pm
Have you thought about replacing the Altec 816 cabinets with a pair of JBL 4560 cabinets and load them with your JBL K140 drivers which sound superb in that box.
You should be able to pick up a pair of empty 4560s from Ebay very cheaply as they not exactly in fashion these days but I still rate them for bass/mid bass performance.
The Altec 816 boxes have never really been a good design and Altec 15" drivers are not very good either so putting the two together is not a good idea.
You could also run the K140s a lot higher than 800hz that you are currently using as this would definitely let the 2441 drivers sound a lot sweeter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Klang Quote  Post ReplyReply Direct Link To This Post Posted: 27 November 2020 at 12:58am
Hi Robbo, 

Thanks for your reply. 

I can't say I have considered 4560 cabs. I was always under the impression that their response wasn't much better than that of an 816, and they were even bigger and heavier. 

To be fair, I have never had the chance to critically listen to a pair of 4560s. I have only ever heard a fairly knackered pair used for band PA in a local practice space. I doubt they had JBL drivers in them. 

Interesting you say that about Altec drivers. It seems they are quite coveted by some, so much so, certain models are being remade to original spec (at great cost) by Great Plains Audio over in Oklahoma! 

Regarding x-over point, prior to the 2441s I had 1" 2420s crossed at 1200 and I wasn't so sure I liked the sound of the 816 going up that high. I have put aquaplas coated diaphragms in 2441s, which sound very smooth indeed. 

K. 
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