building tannoys...beginners help please

[cooky1257]

You don't want to make the job of damping internal resonances bigger than it need be-so before you start avoid multiples as the fundamental of one dimension can be reinforced by the harmonics of the second dimension. Golden ratios help as will angled sides.

Here's the voltage drive of the Tannoy MG15 crossover as used across all the Lancaster/York etc;

The 15" 75L Lancaster is sealed(leaky) and can sound lean when placed out from a wall as does the Devon/Mansfield etc ie they rely on boundary reinforcement to flesh out the early 'IB' roll off, the 12" Lancaster is ported @50hz and is AFAIR tuned maximally flat.

Heres some K-series plots;

 

[cooky1257]

Fine. 130 l sounds very well within the size range I was considering. That's about 33x24x12" internal so close to my plan.
Now what does 'tuned to 28hz mean'? Is this the function of the port's dimensions?

..and the box volume, yes.

 

[Rockmeister]

Excellent. I guess there's a formulae somewhere. No rush. Angled sides = joinery skills
Or asking a real joiner to do the angle cutting. It's a thought tho. I might manage the sides to be wider at the base than at the top, with the front baffle kept vertical.
Or Golden section...as an 'artist' I do know all about GS and it's maths.
Thinking hat on. 130 litres with driver at ear lever, no multiples, a few angles and some GS thrown in. Piece of cake.

What happened to the 'box'?

 

[Rockmeister]

Golden section solution:
Interior dimensions.32.5" H x 19.5" W x 12.5" D gives 129.88 litres. I'll probably need to enlarge this by 1 or 2% to allow for bracing and battening timber.
If I place the driver equidistant from the sides and top of the baffle (3.5" all round), I'll need an 8" plinth to raise the center of it to my required 30".

OK. Moving on

 

[h.g.]

Excellent. I guess there's a formulae somewhere. No rush. Angled sides = joinery skills
Or asking a real joiner to do the angle cutting. It's a thought tho. I might manage the sides to be wider at the base than at the top, with the front baffle kept vertical.
Or Golden section...as an 'artist' I do know all about GS and it's maths.
Thinking hat on. 130 litres with driver at ear lever, no multiples, a few angles and some GS thrown in. Piece of cake.

What happened to the 'box'?

To repeat what was said earlier. This is audiophile nonsense. If you add damping material to remove the internal cavity resonances, which you should for more reasons than just cavity resonances, then golden ratios and angled sides become irrelevant. Now you might want to create them for other reasons which is fine but you then run the risk of compromising dimensions/geometry that do matter like those for the baffle, driver height, location of ports, edge shape, driver to edge distances, bracing, minimising longest internal dimension, etc... You will have more than enough to juggle without introducing unnecessary constraints.

 

[Johnjo]

You don’t have to put the driver in the centre.

 

[h.g.]

Golden section solution:
Interior dimensions.32.5" H x 19.5" W x 12.5" D gives 129.88 litres. I'll probably need to enlarge this by 1 or 2% to allow for bracing and battening timber.
If I place the driver equidistant from the sides and top of the baffle (3.5" all round), I'll need an 8" plinth to raise the center of it to my required 30".

OK. Moving on

What does the baffle step look like with these dimensions? What does the edge diffraction look like given you will be reinforcing it with 3.5" on 3 edges? Where are the dips and valleys in the driver response which may guide the placement of the dips and valleys from edge diffraction? What are the dips and valleys from the crossover and how best to tweak them? What is the optimum off-axis angle to design for (coaxials typically have significant diffraction issues on axis which largely disappear 10-20 degrees off axis)? Etc... This is the type of thing speaker DIY hobbyists tend to consider when determining baffle size and driver placement.

You may not want to work at the level of knowledge but having some awareness of what has been skipped is likely to be helpful when you are assessing the results. I will drop banging on about this type of thing if it is missing the point of the project which may perhaps be to get the driver in a box as swiftly as possible with the minimum amount of upfront design required to avoid a bad design?

 

[Rockmeister]

h.g. This is in reply to you and a general note to other technical chaps who post here.

I won't be assessing the results except by ear, and if they need tweaking, then I can do that later. An added brace somewhere/ more or less damping or a change of damping density is easy to do.

What I asked for is help. Practical, simple advice to produce the best cabinet design for those drivers. It amazes me that after 60 odd years in production, a very close approximation to perfect isn't simply available as a set of plans.

I can see that engineers argue, and I can see that partnering kit and my room will be important variables, but I have no means of factoring these things into the design. When I built Wharfedale's Unit 4 speakers in 1970 ish, they came with crossovers, some wadding and a simple accurate box plan. I made them in a weekend, plugged them in and happily listened for nearly 20 years. That's where I'm at.

I am doing my best to take on board anything vital that would make them sound, lets say less that 95% of their potential, and I asked for as much help as possible in guiding a beginner and non Scientist to a happy ending.
Happy for the academics to argue about the fine stuff, but if they wish to be helpful, a summary ('Rocky, make sure the front baffle is recessed by 13.7mm') etc would be useful. Knowing why is of academic interest if I understood it, which I don't.

All I know is that I have coming, at some point, some 12"R monitor golds and their crossovers. I have NIL technical understanding or the equipment and although I do appreciate the things that can matter, It's a waste of your time posting things like this 'What does the baffle step look like with these dimensions? What does the edge diffraction look like given you will be reinforcing it with 3.5" on 3 edges? Where are the dips and valleys in the driver response which may guide the placement of the dips and valleys from edge diffraction? What are the dips and valleys from the crossover and how best to tweak them? What is the optimum off-axis angle to design for (coaxials typically have significant diffraction issues on axis which largely disappear 10-20 degrees off axis)?', because I have no idea at all what any of it means.

As to speed, no, there's no hurry. As I say, I am doing my best to gather the info from people who contribute and summarise it as I go. I imagine that, at some point, people will stop arguing and I'll take that silence as a meassage that I'm close enough

Thanks for contributing. I'm just trying to explain that your talking to a non technical person. Not stupid, just an engineering black hole.

 

[cooky1257]

To repeat what was said earlier. This is audiophile nonsense. If you add damping material to remove the internal cavity resonances, which you should for more reasons than just cavity resonances, then golden ratios and angled sides become irrelevant. Now you might want to create them for other reasons which is fine but you then run the risk of compromising dimensions/geometry that do matter like those for the baffle, driver height, location of ports, edge shape, driver to edge distances, bracing, minimising longest internal dimension, etc... You will have more than enough to juggle without introducing unnecessary constraints.

It isn't audiophile nonsense rather it's established design practice.
How does paying attention to the ratios 'compromise' those other things? How does the stated dimensions 'compromise' the radiusing of cabinet edges, how does it 'compromise' the positioning of the ports, how does it 'compromise' driver placement? It does none of those things. Whatever your baffle size it will have baffle step, why not offer the builder some advice about asymmetric driver placement? Why not offer him advice on the size of enclosure edge radiusing to mitigate edge diffraction? Why not offer him advice on what you consider to be effective bracing? Why not inform him of the benefits of multiple porting and the use of new profiles as pioneered by JBL? No it's easier to carp from the sidelines without offering anything of substance. Please feel free to critique the published Tannoy enclosure plans that are forming the basis of the design and suggest how he can redesign the Tannoy Dual Concentric from the ground up.

 

[Tony L]

What I asked for is help. Practical, simple advice to produce the best cabinet design for those drivers. It amazes me that after 60 odd years in production, a very close approximation to perfect isn't simply available as a set of plans.

There is clearly a huge amount of knowledge and opinion gained over the 45 years since the Tannoys came to market. I guess if doing one’s own research and making a decision based on the opinion of more recent Tannoy users doesn’t appeal one wouldn’t go too far wrong with (ideally corner) Lancaster cabs, the plans for which are widely available. That was the best cab Tannoy themselves stuck the 12” Gold in.

 

[cooky1257]

There is clearly a huge amount of knowledge and opinion gained over the 45 years since the Tannoys came to market. I guess if doing one’s own research and making a decision based on the opinion of more recent Tannoy users doesn’t appeal one wouldn’t go too far wrong with (ideally corner) Lancaster cabs, the plans for which are widely available. That was the best cab Tannoy themselves stuck the 12” Gold in.

Funnily enough that was my first(well I passed my brother the tools) Tannoy project, 12" corner Lancasters using 12R's, the bass was a bit bloated tbh but they looked fabulous, Fiat 500 red with black tygan grills on a 1" chrome frame, they were absolutely solid/dead and that's when I became hooked on Tannoys...

 

[Rockmeister]

There is clearly a huge amount of knowledge and opinion gained over the 45 years since the Tannoys came to market. I guess if doing one’s own research and making a decision based on the opinion of more recent Tannoy users doesn’t appeal one wouldn’t go too far wrong with (ideally corner) Lancaster cabs, the plans for which are widely available. That was the best cab Tannoy themselves stuck the 12” Gold in.

Gathering other peoples opinions on what is current best practice, this is exactly what I am trying to do so that the final product is the best that can be made now. But that information has to come to me in a form that I understand!

 

[cooky1257]

Golden section solution:
Interior dimensions.32.5" H x 19.5" W x 12.5" D gives 129.88 litres. I'll probably need to enlarge this by 1 or 2% to allow for bracing and battening timber.
If I place the driver equidistant from the sides and top of the baffle (3.5" all round), I'll need an 8" plinth to raise the center of it to my required 30".

OK. Moving on

Looking through some old enclose brochures, you could simply copy the Balmoral from the time compensated series, 125L, 930x416x455 inc 50mm plinth

 

[h.g.]

It isn't audiophile nonsense rather it's established design practice.

It may be used to help market to audiophiles but no designer of speakers with a competent technical performance will include audible levels of cavity resonance in their designs.

How does paying attention to the ratios 'compromise' those other things?

As stated above it introduces extra (unnecessary) constraints to be met when working out speaker dimensions.

Why not...

It is not my design and nor am I sure what kind of advice is or is not welcome by the OP hence I have asked.

There is nothing wrong with building a speaker based on audiophile nonsense and there are plenty of examples out there. Many builders are happy with the results and had fun building the speakers. No problem but it is not something I can make a positive contribution to when faith and technical knowledge are in conflict hence the question.

 

[h.g.]

Gathering other peoples opinions on what is current best practice, this is exactly what I am trying to do so that the final product is the best that can be made now. But that information has to come to me in a form that I understand!

Not sure opinions are wise. Facts are more reliable and you can often get a clue to what is a fact and what is not when a "do this" statement is qualified with a "because" which is straightforward to understand. But it is going to be tricky if you are unfamiliar with the basic engineering knowledge on which engineers will base engineering reasoning. If too much is not understood then following a recipe provided by someone you trust might be a reasonable way forward. I am not going to be the source of such a recipe because I am currently just chatting on the internet.

 

[cooky1257]

no designer of speakers with a competent technical performance will include audible levels of cavity resonance in their designs.

Exactly. You do that by avoiding their creation/stacking those resonances in the first place-that's competent design.

As stated above it introduces extra (unnecessary) constraints to be met when working out speaker dimensions.

No it does not, why is avoiding dimensional multiples a constraint-it's very easily avoided?

It is not my design and nor am I sure what kind of advice is or is not welcome by the OP hence I have asked.

There is nothing wrong with building a speaker based on audiophile nonsense and there are plenty of examples out there. Many builders are happy with the results and had fun building the speakers. No problem but it is not something I can make a positive contribution to when faith and technical knowledge are in conflict hence the question.

That's just unnecessarily insulting to everyone who has contributed. I gave you very specific areas where you could contribute and you seem unable/reluctant to do so.
So far we've discussed enclose types, bracing, adhesives, wall thickness, the use of sub baffles, rebating drivers, distributed ports...-to suggest this is audiophile nonsense is well, nonsense.

 

[Rockmeister]

You won’t no. Chat away, I’m afraid your total lack of empathy has you in the ignored corner. Not you cooky, we posted together

 

[cooky1257]

Nice;

 

[Fatmarley]

So that = bigger is ok?

Forgot about this one.

Sealed is a lot more forgiving than ported. The main thing to worry about is xmax as the box gets bigger, but that's less of a worry with a large driver like a Tannoy (Depending on the xmax (anyone know 15" MG xmax?) - I'd be very surprised if your ears didn't give up well before the driver hits the end stops).

This is the Tannoy Monitor Gold 15 modelled in a 75ltr (grey line) and 200ltr (black line) sealed enclosure. The red line is just a rough guess at what I think the crossover does to the frequency response.

 

[Fatmarley]

Here's a model of the 12" Rubber surround Monitor Gold in ported enclosures. 128ltr grey line, 200ltr black line - Both tuned to 28hz. Add room gain and that 30hz peak could be even worse.