Tannoy Enclosure

Dedicated to those large boxes at one end of the room
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Ray P
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#46 Re: Tannoy Enclosure

Post by Ray P »

izzy wizzy wrote: Mon Mar 09, 2020 9:53 pm Ray's thread got me excited about fancy shapes and all kinds of good ideas, but ultimately I have to realise and accept, I want this to happen and going that route will mean it's too complicated for me to build so this has to be a simple box I can get CNC cut so I can stick it together.
I appreciate you need to get something built but the curved shape I've been working on is really not that difficult to build, especially with some careful planing up-front in CAD. I've got an internal structure (work in progress) that is like the keel and ribs of boat (but a consistent cross-section - no pointy bits at either end) that just gets wrapped in flexible plywood. The planning is to build off the front baffle and to interlock the internal structure so it aligns properly and is self-supporting - all to be CNC-routed of course.
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izzy wizzy
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#47 Re: Tannoy Enclosure

Post by izzy wizzy »

Ray P wrote: Tue Mar 10, 2020 5:42 am
izzy wizzy wrote: Mon Mar 09, 2020 9:53 pm Ray's thread got me excited about fancy shapes and all kinds of good ideas, but ultimately I have to realise and accept, I want this to happen and going that route will mean it's too complicated for me to build so this has to be a simple box I can get CNC cut so I can stick it together.
I appreciate you need to get something built but the curved shape I've been working on is really not that difficult to build, especially with some careful planing up-front in CAD. I've got an internal structure (work in progress) that is like the keel and ribs of boat (but a consistent cross-section - no pointy bits at either end) that just gets wrapped in flexible plywood. The planning is to build off the front baffle and to interlock the internal structure so it aligns properly and is self-supporting - all to be CNC-routed of course.
Thanks Ray. You might be right that it is an option. I was encouraged by Colin's build like that and also his translam build up method however I don't want to use MDF and there's a huge amount of waste. I have no experience of bendy ply. Sounds like a dip into YouTube tutorials. I can do it all in Sketchup and SWMBO is a wizz with Autocad and imports from Sketchup to produce the CNC files.
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#48 Re: Tannoy Enclosure

Post by IslandPink »

The only thing that worries me about the bendy ply in layers option, is how do you get all the layers tight to each other with no voids ?
My experience from building the first midrange horn like this, with layered bendy MDF, was a disaster, and James D warned me away from that independently by warning how bad a violin or guitar sounds if there are voids or delaminated layers.
"Once you find out ... the Circumstances ; then you can go out"
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Ray P
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#49 Re: Tannoy Enclosure

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IslandPink wrote: Tue Mar 10, 2020 8:10 pm The only thing that worries me about the bendy ply in layers option, is how do you get all the layers tight to each other with no voids ?
My experience from building the first midrange horn like this, with layered bendy MDF, was a disaster, and James D warned me away from that independently by warning how bad a violin or guitar sounds if there are voids or delaminated layers.
To eliminate voids the simple answer, as I've said several times, is to vacuum bag it.

But it might be desirable to leave voids and fill them with something else, such as a damping layer.
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#50 Re: Tannoy Enclosure

Post by izzy wizzy »

I've had a bit more time to think and come to terms with my limitations. Also, I have to consider for the first time, where these things will live and how they will fit in. And I think a rectangular box will do it best as it's all part of a "look" the whole system is meant to be a part of with the rest of it in a kind of stereogram sideboard kinda thing. So that's where I'm headed all things considered. I've only veneered a box once before so there's another limitation. Don't think I want to try curvy things. I accept I could do the curved, laminated thing in time but that's not now. If at some time in the future I fancy reinventing these things, then who knows.
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#51 Re: Tannoy Enclosure

Post by pre65 »

Probably your best option. :)
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#52 Re: Tannoy Enclosure

Post by izzy wizzy »

Does anyone know if there's a guide as to where you should site the ports if I have 3 of them?
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#53 Re: Tannoy Enclosure

Post by izzy wizzy »

I got worn down by this and gave up and went back to finalising plans for the R-GRF. But then more resesarch/reading led me to thinking I wouldn't like the rear horn reproduction so here we are again.

The answer to my last question about where the port should go would seem to be not near the floor coz reinforcement although if dealt with, then placement not so critical. Not on the back or sides coz boundary reinforcement becomes an issue. So on front, not near floor and unobstructed WRT driver. That seems doable. I reckon rectangular and then I have more control over it rather than a bought tube.

I did some more sims and EBS alignment should work well in about 200l cabinet. If I divide the rectangular port into three sections, I can have some adjustment for room gain. Also there is adjustment to its area by placing slips inside.

Lynn Olson had some interesting design information about some resistive port loading that could adjust a ported box to be somewhere between pure reflex and closed due to some zero in the filter theory applied to ported boxes and T&S parameters. Does this make sense? Anyone done it?

I have a question about baffle step correction. Traditionally it would seem that these drivers ended up on what today would be a wide baffle. By narrowing it to some point, I know not where, there would need to be some BSC in the crossover. Clearly I want to avoid that so my choice is just stick it on a wide baffle and be done with it, circa 600mm OR understand the issue a bit and design with some knowledge. Anyone have a good resource I can look at to gain some understanding or maybe even a simple explanation?

Cheers,
Stephen
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#54 Re: Tannoy Enclosure

Post by chris661 »

If in doubt, see what Rod Elliott has to say on the subject: https://sound-au.com/bafflestep.htm

The approach to baffle-step is a little complex. For instance, my current speakers have some BSC. Probably. The crossover frequency is 900Hz-ish, and the baffle is 23cm wide, so the baffle-step should be occurring in the 500Hz range.
By using a too-large inductor (ie, the inductor is cutting at 500Hz instead of 900Hz), I can roll BSC into part of the low-pass filter. No need for a separate resistor and inductor in series.

Doesn't always apply, of course, but sometimes it does.

In your case, I'd keep the current crossover etc, and see what you think. If the new system is a bit thin in the 100s of Hz range, BSC is probably what's needed. Rod Elliott suggests a line-level solution to that, which is certainly preferred, but you can look at doing it at speaker-level, too. Would recommend putting a big Zobel in there to linearise the impedance seen by the BSC circuit.


Your plan for 3x ports is a good one. I've done similar with my PA speakers, allowing the tuning to be dropped from 80 to 60 to 44Hz, with changes in LF extension and output. I EQ the difference, but that means the lower bass directly requires more amplifier power and driver excursion - only suitable for smaller venues.
In my case, I used 3" circular ports and some large rubber bungs to block them. It's not particularly elegant, but it does work.

I'd suggest, once you've decided on the porting (0, 1, 2 or 3 open) that you block them from the inside so that the speakers still look clean from the outside, even if some of the ports end up merely decorative.

Resistive porting can be done in a couple of ways:
- Make the ports so narrow that the air doesn't flow too well
- Add something to reduce air flow. Pair of socks, for instance, or a T-shirt.

IMO, it would be better to play with the port tuning frequency first. Resistance simply drops the port output, while changing the tuning frequency would re-purpose the port output to elsewhere. So, a 40Hz resistive box would have less output at 40Hz and still drop away pretty quickly below that. A 30Hz box (down from 40Hz) would have less output at 40Hz, but more at 30Hz. Probably more useful.

Hope that's useful.

Chris
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#55 Re: Tannoy Enclosure

Post by izzy wizzy »

Very useful link thanks Chris. It works out about 57 to 69 hz so that's not in an area I need worry about as there's a lot of other things going on that will probably mask it if I understand right.
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#56 Re: Tannoy Enclosure

Post by chris661 »

Not sure you've done the maths right there - 115/(baffle width in metres).

So a 0.5m wide baffle would give a 330Hz baffle step, for example.

Chris
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#57 Re: Tannoy Enclosure

Post by izzy wizzy »

chris661 wrote: Mon Apr 27, 2020 6:15 pm Not sure you've done the maths right there - 115/(baffle width in metres).

So a 0.5m wide baffle would give a 330Hz baffle step, for example.

Chris
You're right, thanks. I multiplied. Wondered why the numbers didn't look like an example on a Tannoy build I was looking at.

Most of these older cabs are about 600mm wide so 191Hz. My current cabs are 480mm wide and are a Tannoy design. I'd never heard of BSC applied to this before I read about it on that build thread so maybe it's taken care of in the crossover anyway? Knowledge is a dangerouns thing sometimes as it leads to prevarication over some things, that maybe, have been considered by others anyway in the design.
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#58 Re: Tannoy Enclosure

Post by chris661 »

You'll probably be fine.
As I think you've said before - room effects are kicking in down there anyway.

Still, nice to know that a couple of resistors and a cap at the amp input will do the job if needbe.

Chris
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#59 Re: Tannoy Enclosure

Post by izzy wizzy »

chris661 wrote: Wed Apr 29, 2020 9:26 am You'll probably be fine.
As I think you've said before - room effects are kicking in down there anyway.
Still, nice to know that a couple of resistors and a cap at the amp input will do the job if needbe.
Chris
Yes it is thank you.

Think I've finally got a way forward. Now to fire up Sketchup and get plans for CNCing.
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#60 Re: Tannoy Enclosure

Post by izzy wizzy »

Looking at the crossover for now. Has anyone got experience on coils? I'm looking at Jantzen copper foil inductors; wax coils or cross coil or wax litz coil. I went looking at these as Troels Gravesen used them and I liked his capacitor recommendations. Anyone got any experience with these? Or recommendations for any others?

In each range, they have wider and wider foils for lower DCR. For the woof, is lower DCR such a big deal? I ask as my amp is not low Z out so unlike a SS amp with low o/p Z, the coil DCR won't impact as much. Is that right?

thanks,
Stephen
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