building tannoys...beginners help please

[Rockmeister]

ok, an hours fun later and, aiming in my ignorance to have a gently falling bass response with no humps, and the air velocity at the port at 17/18, I came up with a few that seem to work...

150Litre: tuned to 28Hz, Port D11, L16.
140 / 32 / D10/ L 12.
130 /28 / D10 / L17.

and the cleanest seems to be 120L
tuned to either 32 or 28Hz both work well. The 28 port is D10/L17 and the 32 measures D 10/ L 12

I'm guessing that D and L are dimensions but what (and where is the third dimension (H)? )?

or is this a round port? Diameter and length?

 

[Paul Burke]

Yep, not used that particular site before but it’s generally assumed round, diameter and length. Slots and other shapes can be done, but can have issues. Stuck with a round tube, preferably straight with no bends but if really required due to internal space a slow sweeping bend can be used without too much detriment

When working out volumes btw you need to work out the port volume (along with everything else internally) and add that on to your final figure for how much space you’ll actually require

 

[ToTo Man]

Hardest thing to estimate will be the internal volume occupied by the driver itself. Anyone have any ideas how much internal volume a MG12 or MG15 occupies when either front, flush or rear-mounted? Obviously front and flush-mounting will depend on baffle thickness but I suspect the volume differences will be pretty insignificant between these two methods. Rear-mounting will of course consume the most internal volume.

BTW - This is turning into a really great thread. Depending on the successes of @Rockmeister's endeavours, I may well copy your build for my own MGs!

 

[Fatmarley]

ok, an hours fun later and, aiming in my ignorance to have a gently falling bass response with no humps, and the air velocity at the port at 17/18, I came up with a few that seem to work...

150Litre: tuned to 28Hz, Port D11, L16.
140 / 32 / D10/ L 12.
130 /28 / D10 / L17.

and the cleanest seems to be 120L
tuned to either 32 or 28Hz both work well. The 28 port is D10/L17 and the 32 measures D 10/ L 12

I'm guessing that D and L are dimensions but what (and where is the third dimension (H)? )?

or is this a round port? Diameter and length?

For the 12" Rubber surround Monitor Gold - 122ltr with a 4 inch diameter by 7 inch long port gives me 28Hz tuning.

 

[Fatmarley]

Hardest thing to estimate will be the internal volume occupied by the driver itself. Anyone have any ideas how much internal volume a MG12 or MG15 occupies when either front, flush or rear-mounted? Obviously front and flush-mounting will depend on baffle thickness but I suspect the volume differences will be pretty insignificant between these two methods. Rear-mounting will of course consume the most internal volume.

BTW - This is turning into a really great thread. Depending on the successes of @Rockmeister's endeavours, I may well copy your build for my own MGs!

You can have a good guess by looking at datasheets for similar sized drivers.

 

[Johnjo]

Quick question about the internal volume of the rectangular Lancaster cabinet, isn’t it more like 100 rather than 75 litres?

 

[cooky1257]

Quick question about the internal volume of the rectangular Lancaster cabinet, isn’t it more like 100 rather than 75 litres?

More like 95L allowing for port/ driver and any internal bracing(!)but yeah you have a point.

 

[cooky1257]

The 120L/28 hz gives the lowest group delay- sweet spot really.
Old drivers( try to measure them) and normal tolerances would also suggest a bit of leeway of 5-10% so I personally wouldn't sweat getting the driver volume spot on, an educated guess is good enough.

 

[cooky1257]

I bet someone could take one of those B&C 12" co-ax prosound drivers, design a box and crossover for it, and have something pretty decent. You could even try to mimic the transfer function of a classic Tannoy.

There are few that do this, one that is as pricey as Tannoy DC allegedly sounds good But uses bargain basement Eminence drivers. Most pro coaxes do tend to have pretty bad hf responses though. A JBL 2435 bolted to a suitable LF driver could be really something.....

 

[Rockmeister]

For the 12" Rubber surround Monitor Gold - 122ltr with a 4 inch diameter by 7 inch long port gives me 28Hz tuning.

That is about where I am. However if we address the point about driver volume inside the cabinets, then surely those ports dimensions will be wrong, the bracing and that driver must take up at least 10 L so we will have to start again?

 

[ToTo Man]

The 120L/28 hz gives the lowest group delay- sweet spot really.

Noted!

Is 75L the sweet spot for the MG12R in a sealed enclosure?

What about the MG12HE in ported and sealed enclosures, what volume and tuning is the sweet spot for lowest group delay? (assuming Fs=49Hz which I realise is unlikely but for simplicity lets say it is!)

I had a quick play about with modelling my MG12HE in my 200L Edinburgh based on a guesstimated Fb=35Hz (I've still to do the 5mm mic measurement trick that fatmarley suggested) and the bass shelf starts really high, losing output from 400Hz downwards but peaking up at Fb.

Depending on what I find when I measure the Edinburgh's port tuning, my easiest solutions are either to:
1) Stick with MG12HE and fill the Edinburgh enclosure with suitable displacers (bricks?) to reduce the internal volume to optimum size;
2) Same as 1) but with MG12R;
3) Put the MG12HE or MG12R into either genuine stock Lancaster cabs or the DIY Lancaster cabs (made from 3/4" oak-veneered chipboard) I've got lying around and either keep them ported or close off the port.

The first two options seem a bit of a waste of floorspace given that I'll have 200L monoliths in my room when they'll only have an effective internal volume of 80L-120L. The Lancaster enclosures are a more practical and manageable size, but they don't have the Edinburgh's grandiose appearance. Aesthetics comes second to sonics of course so it will ultimately depend on whether either of the Lancaster cabs are inert enough with the MG12HE/MG12R not to colour the sound too much.

PS - I suspect my Edinburgh cabs are near enough ideal for the MG15 or HPD385, I just don't know if I could commit to irreversibly enlarging the baffle hole without being certain that I'd prefer the sound of the 15" driver over the 12".

 

[Johnjo]

Have you tried sealing up the port of the Edinburgh cabs and trying them like that?

I’m enjoying my larger cabs sealed, different driver of course but bass still goes low but tuneful.

 

[Fatmarley]

That is about where I am. However if we address the point about driver volume inside the cabinets, then surely those ports dimensions will be wrong, the bracing and that driver must take up at least 10 L so we will have to start again?

Now we've reached our golden figure (120ltr), you need to work out everything that is going to take up internal volume, so driver, port, crossover, bracing, etc? And then increase the enclosure volume by that amount. It's probably best to keep the baffle dimensions as Tannoy intended, so I would just increase the depth of the cabinet.

As Cooky says above, a few litres here and there isn't going to make much difference, so don't worry too much.

https://www.diyaudioandvideo.com/Calculator/SpeakerBoxVolume/

 

[Fatmarley]

There are few that do this, one that is as pricey as Tannoy DC allegedly sounds good But uses bargain basement Eminence drivers.

WLM Diva? They used an Eminence Beta 10CX.

 

[Fatmarley]

(I've still to do the 5mm mic measurement trick that fatmarley suggested) and the bass shelf starts really high, losing output from 400Hz downwards but peaking up at Fb.

May be worth taking the measurements with and without the crossover connected to get an idea of what it's doing to the frequency response (keep the mic position fixed and the volume the same).

 

[Rockmeister]

Now we've reached our golden figure (120ltr), you need to work out everything that is going to take up internal volume, so driver, port, crossover, bracing, etc? And then increase the enclosure volume by that amount. It's probably best to keep the baffle dimensions as Tannoy intended, so I would just increase the depth of the cabinet.

As Cooky says above, a few litres here and there isn't going to make much difference, so don't worry too much.

https://www.diyaudioandvideo.com/Calculator/SpeakerBoxVolume/

Brilliant! Ta

 

[ToTo Man]

May be worth taking the measurements with and without the crossover connected to get an idea of what it's doing to the frequency response (keep the mic position fixed and the volume the same).

Will be difficult as the only way I can swap cables is to remove the driver from the cabinet. I wish my Edinburghs had screw-on backs, would make life a lot easier!

 

[Rockmeister]

RIGHT!!!
Cabinet design now complete I think.

I was interested in the golden section idea (being aesthetically pleasing as well as helping build a good basis for resonance control).
I was keen to end up on the 120 litre sweet spot.
I wanted to tune the port to 32Hz since the plots made this look smoothest, and,
I wanted the driver at ear level, which for me was 30" up at its center whilst placing it symmetrically at the top of the baffle with even timber all round of enough width to provide rigidity, room for battening and strength for bolts and washers.

The one flexibility is that driver height, since Tannoy commonly build a plinth under the cabs, so I allowed 3" for that.

FM's latest calculator asked for the volume of the tannoy driver which I estimated. I found a depth dimension (7") and guessed the rough area at 6"x6"x7" = 4.2L. The calculator allows for 1" battening all round. There's probably a bit more needed for some bracing but only maybe 1 L so no need to be that fussy (tho I was)
Final result then is:

Exterior of cabinet using 1" Birch ply. 36" H x 22" W x 13.5" D. = 128.5 litres interior volume. 120 after the battening and driver are allowed for.

Port 4" D x 4.8" L. If this should be rectangular, I'll just have to work out the equivalent slot size. It's exactly 1 Litre so it won't be big.

Just about to get the saws out, so if anyone want's to comment, do it soon please

 

[cooky1257]

Noted!

Is 75L the sweet spot for the MG12R in a sealed enclosure?

What about the MG12HE in ported and sealed enclosures, what volume and tuning is the sweet spot for lowest group delay? (assuming Fs=49Hz which I realise is unlikely but for simplicity lets say it is!)

I had a quick play about with modelling my MG12HE in my 200L Edinburgh based on a guesstimated Fb=35Hz (I've still to do the 5mm mic measurement trick that fatmarley suggested) and the bass shelf starts really high, losing output from 400Hz downwards but peaking up at Fb.

Depending on what I find when I measure the Edinburgh's port tuning, my easiest solutions are either to:
1) Stick with MG12HE and fill the Edinburgh enclosure with suitable displacers (bricks?) to reduce the internal volume to optimum size;
2) Same as 1) but with MG12R;
3) Put the MG12HE or MG12R into either genuine stock Lancaster cabs or the DIY Lancaster cabs (made from 3/4" oak-veneered chipboard) I've got lying around and either keep them ported or close off the port.

The first two options seem a bit of a waste of floorspace given that I'll have 200L monoliths in my room when they'll only have an effective internal volume of 80L-120L. The Lancaster enclosures are a more practical and manageable size, but they don't have the Edinburgh's grandiose appearance. Aesthetics comes second to sonics of course so it will ultimately depend on whether either of the Lancaster cabs are inert enough with the MG12HE/MG12R not to colour the sound too much.

PS - I suspect my Edinburgh cabs are near enough ideal for the MG15 or HPD385, I just don't know if I could commit to irreversibly enlarging the baffle hole without being certain that I'd prefer the sound of the 15" driver over the 12".

Sealed will always have lower group delay than ported.
Given the tunable slot ports in the Edinburgh I'd use the 12R and enjoy the extra bandwidth and good looks.
The 12HE will work well in the Lancaster ported and tuned to 50hz-a la Tannoy 12" Lanc or sealed as in the 15"Lancaster for a leaner but tighter bottom end.
There seems little other than more bass extension as shown upthread to be gained going larger than the 95L when sealed imho.

 

[cooky1257]

RIGHT!!!
Cabinet design now complete I think.

I was interested in the golden section idea (being aesthetically pleasing as well as helping build a good basis for resonance control).
I was keen to end up on the 120 litre sweet spot.
I wanted to tune the port to 32Hz since the plots made this look smoothest, and,
I wanted the driver at ear level, which for me was 30" up at its center whilst placing it symmetrically at the top of the baffle with even timber all round of enough width to provide rigidity, room for battening and strength for bolts and washers.

The one flexibility is that driver height, since Tannoy commonly build a plinth under the cabs, so I allowed 3" for that.

FM's latest calculator asked for the volume of the tannoy driver which I estimated. I found a depth dimension (7") and guessed the rough area at 6"x6"x7" = 4.2L. The calculator allows for 1" battening all round. There's probably a bit more needed for some bracing but only maybe 1 L so no need to be that fussy (tho I was)
Final result then is:

Exterior of cabinet using 1" Birch ply. 36" H x 22" W x 13.5" D. = 128.5 litres interior volume. 120 after the battening and driver are allowed for.

Port 4" D x 4.8" L. If this should be rectangular, I'll just have to work out the equivalent slot size. It's exactly 1 Litre so it won't be big.

Just about to get the saws out, so if anyone want's to comment, do it soon please

If you tune to 32hz you achieve a slightly lower group delay than for 28hz but if you look at the excursion and port air velocity the 28hz is to be preferred(D100, L177). Some fine tuning of port length may be required, see FM's calc to see the variation the modelling software(s) sometimes throws up.
I'd be inclined to increase the enclosure depth by an inch or so to allow for more cross bracing and the port vol.
Use flared ports.
Do you plan to rebate the driver cut out or just bolt to the baffle as in the Balmoral pic?
See how they brace the Legacy range; http://www.audiocostruzioni.com/a_d...rden-replica/tannoy-legacy-arden-replica.html