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A different imperial? (Read 9028 times)
stvcmty
Ex Member



A different imperial?
11/24/05 at 22:36:33
 
I was looking around for speaker plans, and I stumbled on this listing:

http://zmatek.jinak.cz/diy/

Then I clicked on a few links, and I found http://zmatek.jinak.cz/diy/elektro_archiv/900l.jpg and I thought it looked familiar.

Is that one of the imperial designs?

Stv
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gexter
Ex Member



Re: A different imperial?
Reply #1 - 11/25/05 at 02:52:15
 
did you check the measurements?
The likeness is uncanny.
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DirtDawg
Ex Member



Re: A different imperial?
Reply #2 - 11/25/05 at 12:54:41
 
I think it's an Imperial variant.
I've lost the DIY site link, but I've seen a very similar box, scaled up to use a 24" or 30" driver. He was using a full 4' x 8' sheet of plywood for the sides and several hundred pounds of sand in the voids.
I turned green. Cheesy
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« Last Edit: 11/25/05 at 12:55:25 by DirtDawg »  
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stvcmty
Ex Member



Re: A different imperial?
Reply #3 - 11/25/05 at 23:49:46
 
[quote author=DirtDawg  link=1132875393/0#2 date=1132923281]I think it's an Imperial variant.
I've lost the DIY site link, but I've seen a very similar box, scaled up to use a 24" or 30" driver. He was using a full 4' x 8' sheet of plywood for the sides and several hundred pounds of sand in the voids.
I turned green. Cheesy [/quote]


I remember that;

http://www.decware.com/cgi-bin/yabb/YaBB.cgi?board=Imperial;action=display;num=1...

Is that what you were thinking of?

Stv
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gexter
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Re: A different imperial?
Reply #4 - 11/25/05 at 23:51:49
 
Thats the one I was thinking of.
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stvcmty
Ex Member



Re: A different imperial?
Reply #5 - 11/25/05 at 23:57:05
 
From http://zmatek.jinak.cz/diy/elektro_archiv/900l.jpg

I just converted the outside dimensions of the box, and they are about 24 by 36 by 60 in.  That is dead on for the imperial cabinet.

So it looks like:  same size box, same size mouth, but different horn expansion and driver loading.

Stv

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gexter
Ex Member



Re: A different imperial?
Reply #6 - 11/26/05 at 04:07:24
 
the smaller compression chamber reflects a smaller driver and differant horn.
My guess ( guess) is it is tuned higher.
I have seen that one before but never looked at it that close before. I prefer Steves right off and simplier too.
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« Last Edit: 11/26/05 at 05:18:35 by gexter »  
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selmerdave
Ex Member



Re: A different imperial?
Reply #7 - 11/26/05 at 04:27:38
 
That is the original Jensen Imperial design that is the basis for the Decware version  (hence the striking similarity).  There were several versions of Imperials, but that is the one from the early 50's.  Doesn't seem as common as the '54 version, although Steve is probably contributing to a resurgence.

http://www.hifilit.com/hifilit/Jensen/bulletin1-1.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-2.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-3.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-4.jpg

Dave
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« Last Edit: 11/26/05 at 04:39:10 by selmerdave »  
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tubino
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Posts: 96
Re: A different imperial?
Reply #8 - 11/03/07 at 04:44:39
 
selmerdave wrote on 11/26/05 at 04:27:38:
That is the original Jensen Imperial design that is the basis for the Decware version  (hence the striking similarity).  There were several versions of Imperials, but that is the one from the early 50's.  Doesn't seem as common as the '54 version, although Steve is probably contributing to a resurgence.

http://www.hifilit.com/hifilit/Jensen/bulletin1-1.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-2.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-3.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-4.jpg

I know this is a two-year-old thread, but I'm hoping someone will explain the difference between the 1952 version in those bulletins, and the 1954 version!  I own two of the March 1952 version cabinets, and am very curious what was done in later Jensen designs.
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dank
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pair of dual 18
Imperials

Posts: 275
Re: A different imperial?
Reply #9 - 11/03/07 at 14:35:59
 
Looks to me like all the internal pieces in the compression chamber are removed in the 1954 version.  The angled pieces on the sides and the "U" shaped piece behind the speaker (probably built from 4 pieces of plywood) all seem to be gone.  Makes you wonder if this was done to make the build easier, or to sound better, or both.  

To go from the 1954 version to the Decware version it looks like the compression chamber volume was first doubled by removing the internal bottom piece that use to cut the compression chamber in half and create a "dead" space in the lower part.  Then the new, larger, compression chamber was divided in half by adding a vertical center piece - so now there are 2 chambers, each with the same volume as the single 1954 compression chamber.  Finally, add a second 15" driver, one for each of the 2 compression chambers which share a common "port" that is the throat of the horn.

Dan
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tubino
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Posts: 96
Re: A different imperial?
Reply #10 - 11/03/07 at 15:59:29
 
Thanks, Dan!  I would love to compare the same driver in different cabs... but am very happy with the Tannoy Monitor Gold 15s in mine.
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selmerdave
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When words fail,
music speaks - HC
Anderson

Posts: 461
Re: A different imperial?
Reply #11 - 11/03/07 at 23:04:18
 
Dan,

It seems to me that the 1954 version is significantly different from the 1952 one, and the Decware design only bears resemblance to the earlier one.  Perhaps we are looking at different things but this is what I know as the 1954 version:

http://www.hifilit.com/hifilit/Jensen/cabinart-1.jpg

It seems to be folded differently and fire differently and have a completely different mouth area than the earlier one, and is also significantly smaller albeit still a rather respectably-sized speaker Smiley.

Is that the one you were talking about?

Dave
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Altec 604E's in MLTL cabs biamped w/Rane AC-22
Zen Select on HF
Radio Craftsmen RC-2's on LF
Eico HF-85
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tubino
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Posts: 96
Re: A different imperial?
Reply #12 - 11/04/07 at 02:19:47
 
It would have been a lot less confusing if they had used distinguishing names consistently.  "Imperial" is not in the 1952 brochure.  That 50"h corner version is clearly labeled an Imperial, but if they are counting the legs in the height, the cabinet is more like 44" in height...

If someone has a link to a ~ 60 x 36 x 24 rectangular BLH cabinet that differs from the 1952 drawing, I'd sure like to see it.
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dank
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pair of dual 18
Imperials

Posts: 275
Re: A different imperial?
Reply #13 - 11/05/07 at 00:14:15
 
dank wrote on 11/03/07 at 14:35:59:
Looks to me like all the internal pieces in the compression chamber are removed in the 1954 version.  The angled pieces on the sides and the "U" shaped piece behind the speaker (probably built from 4 pieces of plywood) all seem to be gone.  Makes you wonder if this was done to make the build easier, or to sound better, or both.  

To go from the 1954 version to the Decware version it looks like the compression chamber volume was first doubled by removing the internal bottom piece that use to cut the compression chamber in half and create a "dead" space in the lower part.  Then the new, larger, compression chamber was divided in half by adding a vertical center piece - so now there are 2 chambers, each with the same volume as the single 1954 compression chamber.  Finally, add a second 15" driver, one for each of the 2 compression chambers which share a common "port" that is the throat of the horn.

Dan


This article:

http://dcaudiodiy.com/jensen_imperial/jensen_imperial.html

that came out in 1956 shows what I think is the 1954 Imperial.  It matches selmerdave's picture:
http://www.hifilit.com/hifilit/Jensen/cabinart-1.jpg

but the article goes on to show another Imperial, the built in, that I was talking about as the 54 version.  That one is quite close to the Decware version.

I'm assuming these are the 52 version:
http://www.hifilit.com/hifilit/Jensen/bulletin1-1.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-2.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-3.jpg
http://www.hifilit.com/hifilit/Jensen/bulletin1-4.jpg

Dan
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tubino
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Posts: 96
Re: A different imperial?
Reply #14 - 11/05/07 at 19:03:04
 
Thanks again, Dan!  For the first time, I think I'm beginning to glimpse the many Imperial designs and how they got that way.  While actual cabinets built on any of these designs are not commonly found, I'm beginning to think that particularly few of the 1952 design were actually built.  You ask a good question, though: was the elimination of many chamber pieces in the 1952 design primarily for ease of construction by DIY guys, or were there good sonic reasons?

I once tried a 12" EV coax in my cabinets. Mounting was easy because the driver was already mounted to a large panel, so I just bolted it to my existing baffle board.  BIG FLOP.  Not much good was happening. Immediately after mounting one and trying it, my buddy and I rear-mounted one of his Tannoy 3808's on the existing baffleboard, and it was really REALLY good right off the bat. So we put in the other one, using the monitor crossovers, and were astounded at how good it was.  But the point I want to make is that the 12" in a cabinet designed for a 15" was a total mismatch, with the chamber behind. I could have improved it greatly, I guess, by filling it to occupy some volume, but I thought -- why bother? just go with 15"s.

So ... I wonder about using a single 15" driver in the Decware Imperial designed for 2 15"s.  Wouldn't the increased chamber volume make that sub-optimal?  To put it another way, if I'm trying to make the most out of a single vintage dual concentric per side, isn't it possible that the 1952 design I've already got may work as well (with adequate bracing) as the Decware Imperial, and maybe even better?  Not that the old design is better, in any absolute sense, just a better match for a single 15".

The 190 lb. Tannoy DMT 215 speaker (http://www.primalgear.com/tannoymon007.html) uses a 15" woofer along with a 15" dual concentric (3833GG as in the DMT 15, I think), so there's a sort of design parallel with the mismatched 15"s people use in the Decware Imperial.  But those particular drivers are kinda high on the Qts, and are probably better off in the box they come in.  Still, I suppose one could build a sort of "vintage-style DMT 215" by using a Monitor Gold along with an appropriate woofer in a backloaded horn ...
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