Releasing my inner Tannoy (Eaton Clones )

[montesquieu]

That is true of the IIILZ, but the HPD 295A is capable of some proper bass output in the right box. I know what they can do as I've owned many pairs. The bass performance is superior to early 12" Monitor Golds, which I've also possessed.

Totally agree on this, the 12in HPD (**in the right box** as you say) can match the 15in MG for bass depth and weight, albeit at the expense of some efficiency (which is why HPDs need a lot more welly than MGs). Likewise the 10in HPD is potentially a great performer in many areas where both the 12in MG (which is sweet but bass light) and IIILZ - that is the '10in MG' - fall behind.

I was actually astonished when I replaced my 12in MGs with HPDs in the RFC Canterburys, with the approriate crossover mods. I gained an extra octave in the bass with no compromise at all. I had previously resisted all Paul's entreaties to give away my beloved MGs in favour of HPDs. I was so wrong! (I actually still have the 12in MGs here, in a cupboard).

Part of the ongoing confusion over what speaker dimensions to use for the various Tannoy drivers is that Tannoy made a lot of sub-optimal boxes over many years, both in terms of cabinet volume and in terms of physical construction. As Guy R Fountain, Tannoy's founder, famously said: 'We aren't furniture makers'. This attitude certainly shows right through to the early 80s at least.

[Reffc]

Totally agree on this, the 12in HPD (**in the right box** as you say) can match the 15in MG for bass depth and weight, albeit at the expense of some efficiency (which is why HPDs need a lot more welly than MGs). Likewise the 10in HPD is potentially a great performer in many areas where both the 12in MG (which is sweet but bass light) and IIILZ - that is the '10in MG' - fall behind.

I was actually astonished when I replaced my 12in MGs with HPDs in the RFC Canterburys, with the approriate crossover mods. I gained an extra octave in the bass with no compromise at all. I had previously resisted all Paul's entreaties to give away my beloved MGs in favour of HPDs. I was so wrong! (I actually still have the 12in MGs here, in a cupboard).

Part of the ongoing confusion over what speaker dimensions to use for the various Tannoy drivers is that Tannoy made a lot of sub-optimal boxes over many years, both in terms of cabinet volume and in terms of physical construction. As Guy R Fountain, Tannoy's founder, famously said: 'We aren't furniture makers'. This attitude certainly shows right through to the early 80s at least.

Totally agree Tom.

The box is a vital component for the SQ of ANY Tannoy DC drive unit. The more rigid and acoustically dead the front baffle, the better. When you consider that the front baffle acts like a speaker driver in itself, due to the larg-ish size of many DC cabinets, you're essentially creating an out of phase driver, randomly damped wrt frequency, and this adds a significant amount to direct sound colouration. It's what gives many older cabinets their "vintage" sound which can be indistinct, warm and woolly.

The cabinets for DCs do NOT follow thin walled theory, or at least should not. The more rigid and better damped they are, the better. Often, a combination of Birch ply for stiffness, and a layer of high density MDF (750KG/m3) brought together form the ideal laminate for a DC cabinet.

As the cab grows in size, MDF becomes less desirable as a structural element because of its tendency for damage, especially joint damage, if dropped or knocked, so using the correct grade of slow grown Birch Ply tends to be the most practical solution, although you can still line the structure with MDF. Personally, when building large cabs, I prefer to work in very slow grown Latvian Birch of furniture grade quality with a higher than normal resin (ie bonding glue) percentage. This provides a well damped and very stiff structural timber. Assessing thickness and bracing requirements takes a little science, but get it right and people would be astonished at just how neutral and revealing vintage DCs actually are.

[smangus]

Thanks for the comments all , tried to get back to bodging today and measured up some more ply but couldn't cut as the rain started, a bit frustrating . I have to cut outside as there is no room anywhere else so it's all dependent on the weather!

[danilo]

So much urban lore on pore old DC's.
Much more than when they were current TBH Likely just as much as on MGB's
DMT's were the epitomy of Dual wall constructions. Well excecuted actually.
Typically these provided the sounds for a Myriad of Stipper bars across North America. A few even ended up in residences.. decent speakers.. Butt ugly tho.
Nelson Pass uses 15" HPDs in Jensen Imperial cabinets of 3/4' Plywood with a crossover variant developed in his shops.
These are His reference Speakers..not because they are the best speakers in the world (he doesn't think so) but because they reveal even the tiniest Typology differences in his continuing explorations with Amp circuits.
This from a man who built klienhorns ( https://www.passdiy.com/project/spea...einhorn-part-1 and the required Subs.. Decades ago.

[smangus]

Well, just to prove I had not forgotten about these, a brief update, although progress has been slow due to time constraints. I also had a distraction with my Karcher adventure http://theartofsound.net/forum/showt...Kleaning-Kaper

I managed to cut a load of ply which consists of the components of the tops bottoms and sides of the cabinets. I've decided to glue and screw the tops and bottoms together and then mock up the cabs so that I could work out where to places the braces (2 per cabinet) in relation to the drivers. The aim is to recess the braces into the front , sides and back by about 3 or 4 mm all around so that they tie the structure together neatly. (me being optimistic here. )

I'll have to crack on with the baffles at some stage, double thickness with a sub baffle added so 3 layers of ply.

Due to the protrusion of the driver and bass port internally I had the bright *cough, cough* idea of incorporating the bottom of the port into the area of the top brace so that less area internally is lost , this is going to take a bit of thinking about but hey all in the name of adventure . No pain no gain etc, as they say.

Warning , what follows are some gratuitous wood shots...

Boring shed pic of bits of wood and other "useful" stuff.

[smangus]

Marking up the screw positions in the top of a cabinet, thought about 9 but went for 15 in the end , I've got 200 of the buggers so what the hell , let's live a little.

[smangus]

I love a good countersink....

[smangus]

Glued and screws added, I added some more clamps after this photo for better pressure all round. The glue was Titebond 2 yellow stuff. It seemed to weep out of the sides forever but this should be a good sign I guess.

Next update in about 6 months....

[struth]

double thickness. My speaker walls are double thick too. makes em quite heavy

[smangus]

double thickness. My speaker walls are double thick too. makes em quite heavy

Yeah I can feel that already , means SWMBO won't be able to throw them out ,