Loudspeaker information sought

I have in my possesion an EMI 14" x 9" loudspeaker, which I've had for a good many years and fairly recently I've started using it as a sub-woofer in my workshop system (and it seems to perform well). At the moment it just sits on the bench, so its performance will be degraded by not being in a cabinet. I'm intending to build one, preferably I would like to make it a transmission line enclosure, but I need to find some more information on the unit itself first. The 14 x 9 speakers were manufactured by EMI sometime between the 1960s and 1980s and were superseded by 13 x 8 inch ones. They have a model number of 770 but this actually covers a range of speakers, some were customised for speaker manufacturers (I believe early B&W DM3s used them). I have seen several others speakers that I can't identify and that used them, They were also available as parts of speaker kits that EMI sold in this period. The speaker I have has the further marking AEP, which I guess defines the variant. It also has another number 3278 which I imagine is the serial number. The speaker has a cast aluminium chassis with a 5 inch ceramic magnet and a 2 inch voice coil. The voice coil former and inner cone is aluminium bonded to the outer cone, which is a multi-layer laminated paper with some sort fibre reinforcement and has a rolled plastic surround. The front face of the cone is coated with some sort of fur like material, which I've been advised is to reduce the effects of cone breakup. It has a DC resistance of 5 ohms.
I've tried to do some testing, but I'm not really equipped for doing this. I think I've identified the mechanical resonance as being 18Hz with a second harmonic at 36Hz, which was done by feeding it with a constant amplitude sine wave over the frequency range 10 to 150Hz and observing the cone displacement and I think I saw an increase in displacement at those frequencies, but I could be wrong.
If anyone has come across these speakers and can throw any more light on this, I would be most grateful.
Phil

Hello Phil,

I've tried to do some research concerning your EMI speaker. As you say there were many different versions made, all of which have a driver identity starting with 14A/770 (such as, say 14A/770N/NX, or 14A/770C etc.). The various versions differ from one another largely in the laminated make up of the elliptical cone, and this will no doubt affect the design of a suitable enclosure.

Regarding the latter, there is scant, almost non-existent information on the web. If you type "EMI 14 x 9 inch elliptical speaker", you will be directed to a strange site which inter alia has many photos showing commercial loudspeakers using EMI elliptical drive units: some are ported, and some are infinite baffle stuffed with loft-lagging fibreglass wool. The audio quality of these examples is not discussed. https://sfmkm.blogspot.com/p/blog-page.html
(Frankly I would take most of what is written on this site with 'a pinch of salt', as it is opinionated and some of it is factually incorrect!)

Lencoheaven.net discussed the use of these drive units in a ported enclosure back in May 2018, and one of the members there actually built a three way speaker using the EMI elliptical drivers for the bass. His forum name is the same as one of our one-time members here, who is now retired. I occasionally speak with him, and will do so again, but it is quite likely he has forgotten the details of his design. Unfortunately all the photos in the Lenco Heaven thread are now no longer viewable in the UK (most likely they are hosted by Imagur, who for reasons best known to themselves have imposed this restriction). The speakers are discussed here: https://lencoheaven.net/forum/index.php?topic=29536.0

Another interesting post can be found on the diyAudio forum: https://www.diyaudio.com/community/t...y-rare.402300/

If you want to design a transmission line enclosure, you will need to know the Thiele - Small parameters for the exact version of your EMI driver. Goodness knows where you will find them, even if they have been measured.

In the first instance, I would simply cut an elliptical hole of appropriate size into a piece of 1/2" thick plywood or chipboard, of say 2' x 3' in area. It will be better than no baffle at all.

Cheers
Barry

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Originally Posted by Barry

Unfortunately all the photos in the Lenco Heaven thread are now no longer viewable in the UK (most likely they are hosted by Imagur, who for reasons best known to themselves have imposed this restriction).
If you want to design a transmission line enclosure, you will need to know the Thiel - Small parameters for the exact version of your EMI driver. Goodness

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It's due to the idiotic Online Safety Act.

These drivers pre-date Thiele-Small!

From what I can gather from reading around, the bigger the cab the better. I'd go with a sealed box, as large as is practical for the deployment situation. Crossover in the 2KHz region, steep filters.

Quote:

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Originally Posted by Barry

Hello Phil,

I've tried to do some research concerning your EMI speaker. As you say there were many different versions made, all of which have a driver identity starting with 14A/770 (such as, say 14A/770N/NX, or 14A/770C etc.). The various versions differ from one another largely in the laminated make up of the elliptical cone, and this will no doubt affect the design of a suitable enclosure.

Regarding the latter, there is scant, almost non-existent information on the web. If you type "EMI 14 x 9 inch elliptical speaker", you will be directed to a strange site which inter alia has many photos showing commercial loudspeakers using EMI elliptical drive units: some are ported, and some are infinite baffle stuffed with loft-lagging fibreglass wool. The audio quality of these examples is not discussed. https://uk.search.yahoo.com/yhs/sear...fr2=sb-top&vm=
(Frankly I would take most of what is written on this site with 'a pinch of salt', as it is opinionated and some of it is factually incorrect!)

Lencoheaven.net discussed the use of these drive units in a ported enclosure back in May 2018, and one of the members there actually built a three way speaker using the EMI elliptical drivers for the bass. His forum name is the same as one of our one-time members here, who is now retired. I occasionally speak with him, and will do so again, but it is quite likely he has forgotten the details of his design. Unfortunately all the photos in the Lenco Heaven thread are now no longer viewable in the UK (most likely they are hosted by Imagur, who for reasons best known to themselves have imposed this restriction). The speakers are discussed here: https://uk.search.yahoo.com/yhs/sear...fr2=sb-top&vm=

Another interesting post can be found on the diyAudio forum: https://uk.search.yahoo.com/yhs/sear...fr2=sb-top&vm=

If you want to design a transmission line enclosure, you will need to know the Thiel - Small parameters for the exact version of your EMI driver. Goodness knows where you will find them, even if they have been measured.

In the first instance, I would simply cut an elliptical hole of appropriate size into a piece of 1/2" thick plywood or chipboard, of say 2' x 3' in area. It will be better than no baffle at all.

Cheers
Barry

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Don't know if it's just Tapatalk but all those links go to the same place for me.

Ah! - I see what you mean.

Sorry about that. I have now provided the correct urls for the individual websites cited.

Thanks for getting back to me Barry. I have been searching for information for a while and I have seen those sites before. I managed to access the pictures on the lencoheaven site. The speakers are the later pressed steel 13 x 8 units (also available in many variants). The pictures that you can see in the UK are it except that mine has a furry cone, but there you go and it doesn't have an EMI label on the back. I am starting to wonder if it was some sort of prototype and prior to me getting my hands on it, didn't look to have had much use.

There is already a plan in place for the outer cabinet, which will be a sealed enclosure, to begin with anyway. I'm thinking that knowing the enclosure design, if it's performance can be measured, it may be possible to work backwards to determine the speaker characteristics, and who knows it may sound OK like that.
Things like the free air resonance can be measured without a cabinet, but I'm not equipped to do other than a very rudimentary estimate and I don't have the facilities to do the other stuff, including the woodwork. So I am a bit reliant on others, most of whom are very busy.
The cabinet design is constrained by where it's going to be located. The idea is, that it will fit in the dead space underneath the workbench at the top and the back, so the cabinet will be 36.5" wide (I'm leaving 1/4 inch each side so I can fit flooring felt between the cabinet and the cupboard sides), 15" front to back at the top, 10" at the bottom and 12" high with the baffle at 30 deg from the vertical. The sloping front is so I don't kneecap myself when I sit at the work bench. I've got no latitude on the width but I may have a bit of wiggle room on the others. Material is going to be 18mm chipboard, or possibly 2 layers of 15mm chipboard laminated together, if 18mm turns out to be too flexible and which would make some of the corner joints more robust. I would like to make a go of this, it looks and feels (and sounds) like a good speaker and the evidence that I've been able to find, such as it is, seems to support this and I also really dislike throwing things away, if there's nothing wrong with them.
Well we'll see how goes, I suppose.
@ Macca, I'm using it as a subwoofer, the max frequency it's ever going to see is 200Hz and it's a 4 pole active filter with a switchable cutoff at 120, 150 and 200 Hz. 150Hz seems to be the optimum.

Phil

If I understand it, you want to put the drive unit into a prism-shaped enclosure: of width 36.5", with right angle triangular end faces, having dimensions of 10" and 12" about the square corner. That will make the angle about 40°, and the hypotenuse, i.e. the breadth of the driver mounting baffle, 15.6".

The total volume will be 2,190 cu in, or 1.27cu ft.

Is that correct?

Almost, It will actually be a 5 sided enclosure, the baffle is planned to be 10 inches rising up at a 30 degree angle from the 10 inch base. The baffle will meet up with a vertical panel 3.34 inches dropping down from the 15 inch top panel. So it will have a little bit larger volume, but not much, so yes, that will be pretty much the size of it, less of course what the material takes out of it, and the larger panels may well need battens to control the vibration, again taking up volume. The speaker is going to be front mounted, and probably rebated in, so that will also take a bit more of the available volume.
I've crawled under the work bench and had a bit of a re-measure, I think I can probably get 3 more inches front to back so consequently that would make the top panel 18 inches instead of 15 and the bottom panel 13 inches instead of 10. Not ideal, but it's the space I've got. I only chose 30 degrees for ease of calculation, sine 30 being 0.5 and cosine 30 being 0.8660, though to be honest, if I'm going to fit my knees under the bench, it can't be very different. I did have a sort of scribble sketch, but that's with the person, who is going to make the initial cabinet.
It sounds to me like you might be trying to work out what I'm likely to end up with, at least in the beginning. I am, or rather I was an electronics engineer, so whilst allied to what I did, this is just a tad outside my skill set and any help or guidance I can get would be appreciated.

Sorry just re-read your post, The side faces will be pentagonal, not triangular. The back face will be vertical and 12 inches high, at a right angle sticking forwards from the bottom, will be the bottom panel 10 (or possibly 13 ) inches, front to back. From the top of the back panel, at a right angle will be the top panel, which will be 15 (or possibly 18) inches front to back. From the front edge of the top panel sticking vertically down at a right angle, will be the front top panel which will be 3.34 inches top to bottom. Joining the front edge of the bottom panel to the bottom edge of the front top panel will be the baffle at an angle of 30 degrees forward from the vertical i.e. the top is forward of the bottom, and which should be 10 inches high. If it isn't obvious the speaker will be mounted with its long axis horizontal. All dimensions are external.

I hope this has made things clearer rather than confusing them more.

Phil

I make that roughly a 45 litre cab without the diagonal deducted. So maybe 35 litres without it. I think you're in the ballpark if so.

Given the dimensions of the pentagonal prism, I calculate the overall external volume to be 7,092 cu in,, or 4.1 cu.ft; quite a bit larger than I had previously thought.

Assuming the volume is reduced by 20% to allow for the material thickness and possible strengthening battens, that makes the internal volume about 3.28 cu ft., or 93 litre.

If you agree with my calculation and estimate of the internal volume, I will pass on this updated information to our Member 'Walpurgis' for his thoughts on the matter.

93 litres is very large, are you sure?

If you ignore the slanted part of the enclosure, and just consider it as a simple cuboid of external dimensions of 1' high by 1.5' deep by 3' wide, that is a volume of 4.5cu ft. There are 28.32 litres in a cubic ft, so 4.5cu ft equates to 127 litre.

(1 cu.ft is 1728 cu.in. An inch is 2.54cm, and a litre is 1,000cm³. So 1 cu.ft = 1728 x (2.54)³/1000 = 28.3168 litre.)

Taking the pentagon prism shape into account, the external volume is 4.1cu ft, or 116.1litre. Again, assuming the internal volume is 20% smaller than the external volume, that reduces the internal volume to 116.1 x 4/5 = 92.88 litre.

The actual internal volume is yet to be determined, but it will be something like 92 to 100 litre. The real unknown is how to dampen and load the elliptical drive unit, with say 1" thick felt, or by stuffing the internal volume with loft insulation. Total fidelity is not required as the sub woofer is located away from direct earshot. A lot of room for experimentation.

Here's an image with a bloke for scale of a 100 lite cab - that's a big subwoofer!

https://i.ibb.co/s9Ktpx24/PSC5-Y-3-web.jpg


Not sure that Phil's thinking of something that big if it's going under a desk/bench. But maybe he is...

The internal volume looks as though it could house 4.5cu ft. We will have wait for Phil to post a photo of his 'infinite baffle' enclosure.

Barry, it might be a while, before I have anything to photograph, apart from the speaker. The guy who is making it for me is very busy. I did some rough calcs this morning and I came up with a volume of approximately 107 litres, but that was based on the external dimensions, so the 93 for the internal volume sounds entirely plausible.
Don't forget the eventual aspiration is to turn this into a transmission line speaker, so internal baffles are going to soak up some more of the volume. I was going to line the the inside faces of the panels with 6mm flooring felt, to minimise internal reflections and then strategically place other material in there to adjust how it sounds. I also theorised that having the speaker mounted at an angle, whilst it wont reduce reflections, from the panels behind will provide a variable path length so should remove, or more accurately, smear out the reflected wave over a range of frequencies, so (hopefully) preventing a standing wave between the back of the speaker and the back panel causing colouration at a specific frequency.
@ Macca, there is a big space under the desk which I can't really use for anything else. I suppose if I were younger and more agile, I probably could. Getting into the space isn't so bad, getting out can take a while. I have a 100 litre LPG tank in the back of one of the cars and it would just fit in there so that looks to be about right, and I'm sure I've heard somewhere, the more volume you've got for your speaker the better.
Phil

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Originally Posted by Phil M-W

@ Macca, there is a big space under the desk which I can't really use for anything else. I suppose if I were younger and more agile, I probably could. Getting into the space isn't so bad, getting out can take a while. I have a 100 litre LPG tank in the back of one of the cars and it would just fit in there so that looks to be about right, and I'm sure I've heard somewhere, the more volume you've got for your speaker the better.
Phil

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Indeed, make the cab as large as is practical.

A box measuring 18" x 18" x "24" has a volume of 4.5 cubic feet, or 127 litres. Probably have an internal volume of about 100 litres, when allowing for cabinet wall thickness. So plenty of room to 'go big' under the table :)

Any update on the speaker enclosure being made for you Phil?

Funnily enough Barry, I wasn't expecting anything this soon, but it appears the cabinet has already been started. I contacted him last week to mention another minor issue we had, and mentioned the increase in size of the cabinet at the same time. He came back saying he had already started but the change wouldn't be a problem. I haven't got an eta yet though, and as the other issue is trivial, and probably caused by the excessive heat we've had recently, it won't be high on his list of priorities.
It would be nice, once it's built, to find someone who could test and analyse both the speaker (driver) and the assembly - and has the time to do it. Just to get an idea of what I'm starting with and where improvements could be made.
You mentioned Walpurgis (flashbacks of Procol Harum there!) in an earlier post. Is this the sort of thing he (presumably not she) could do? I did approach Matt at Haycross Audio, but he is trying to focus on building speakers and wasn't very keen.

A quick p.s. Have there been issues with the forum recently. This is the first time I've been able to get on for a couple of days.

Phil

I've had problems for about 4 days now, and yesterday couldn't get on at all. Dunno why.

I have sent Geoff (Walpurgis) a message describing your woofer enclosure project using an EMI elliptical drive unit. Geoff is the only one I know of who has some experience with these units.

He won't be able to test or measure the finished speaker, but he may be able to offer some advice. When the enclosure is finished, post some photos of it here, and try if possible to evaluate the internal dimensions, and hence volume.

Quote:

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Originally Posted by Pigmy Pony

I've had problems for about 4 days now, and yesterday couldn't get on at all. Dunno why.

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I also had no access for a while yesterday.

Quote:

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Originally Posted by Barry

I have sent Geoff (Walpurgis) a message describing your woofer enclosure project using an EMI elliptical drive unit. Geoff is the only one I know of who has some experience with these units.

He won't be able to test or measure the finished speaker, but he may be able to offer some advice. When the enclosure is finished, post some photos of it here, and try if possible to evaluate the internal dimensions, and hence volume.

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Probably over forty years since I built my EMI based speakers. I don't recall that much, but they were around 70 litre reflex boxes.

Hello Geoff, I've had this speaker at least that long. Can't remember where I got it from now, it was just something I intercepted on the way to the skip and which I thought I would be able to find a use for at some point in the future.
When I have something more concrete, or rather wooden, I'll post it.
Phil

Well, let me know. I'll definitely have opinions :).