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Actualsizeaudio 27th November 2012 09:36 PM

Soffit mounted 15" Tannoy Dual concentric project
Hello DIY community.

I am undertaking my first speaker building project, and it's a doozy. My grandfather passed away in the spring and he was an avid audiophile. He was also a hoarder, and it took us many months to comb through his belongings and pick out what was worth saving. One item that did not need thinking about was his 15" Tannoy silver from 1959. It was his prized possession, and he requested that I have it. Well, I got that thing out of there as soon as I could (wasn't easy), and after many months, and after consulting with my brother I have decided to sell it in order to build a set of mains for my recording studio. He wanted my brother and I to make a record together, and I can't think of a better way to honor him than to build a stereo Tannoy Dual Concentric system.

I am selling his driver currently, and I already purchased a new set of drivers. I have 2 Lockwood re-coned, and re-coiled hard edge 15" HPD drivers sans dust caps. I'm looking to build 2 300L cabinets and have them soffit mounted (yes I have the room). The soffit mounting will be tricky considering how large a 300L cabinet is, but it affords not just sonic benefits, but cabinet design flexibility.

As of now I am planning on using a MiniHD4x10 as an active digital crossover. This will allow me much flexibility in the setup of the system. I know many of you are gasping in horror, but since my Pro Tools audio interface and monitor controller is digital to begin with, going into that unit via AES makes a lot of sense.

The system will be bi-amped with a Bryston 4B, and a Bryston 3B amp. They are from the same era, approx 1985.

I will probably use a sub woofer with a HP filter to relieve the low driver the stress of frequencies below approx 50hz. This will also make the system a little safer to run loud (which is not my thing, I listen at 85, or at the most 90db on a daily basis).

The advice I'm looking for: general cabinet building advice. I'm planning on using Baltic Birch with a veneer on the front baffle. I need advice on the ports, damping, bracing, box size ratio, etc.

I also need advice on the interface between the amps and the speakers. Do I need to worry about using a zobel, or do I need anything pre driver to protect them since I will not have passive crossovers?

Thanks in advance, and I'm hoping this project will get updated regularly, and with some great pictures.


JRKO 28th November 2012 12:23 AM

Nice drivers. I had both 10" & the 15" HPD's.

I'm not 100% on what you mean by soffits. Over here is means the underside of the roof overhang so I'm guessing its lost in translation :D

As for the box, this thread is about a 360l box for another 15" fullrange. Although its a standard box, it covers most of the bases like bracing etc -

Actualsizeaudio 28th November 2012 12:30 AM

Thanks for that link. That looks like good reading.

Soffit mounting refers to having the speakers built into the wall of your listening environment so the front plane is flush with, but not actually touching the wall. Many, many studio control rooms have soffit mounted monitors, and many of those have large dual concentric designs as well. Here is a great thread that gets into it.

John Sayers' Recording Studio Design Forum • View topic - Soffit mounting?

JRKO 28th November 2012 08:59 AM

1 Attachment(s)
Ah ok!

It was lost in translation. We get so much spam about double glazing companies about windows, facias, soffits & guttering the other meanings have been washed away.

I was hoping you were going for in wall. Just seemed plain weird to put your nice Tannoys under here :D

planet10 28th November 2012 09:06 AM

Do you have a set of (reasonable) T/S data for these drivers?


Charles Darwin 28th November 2012 09:30 AM

With regards to speakers soffit mounting means the same in the UK as in the US btw.

Personally I would use two woofers and make the Tannoys into 3ways like FSM or DMT215s. (tannoy & tannoydmt)
I did something similar with my 12" Tannoys which I cross in at about 175Hz.
This improved midrange clarity quite a bit and also dramatically decreases the cabinet size need for them. Usually the 12"s need 200L cabs but relieved of their bass duty they are quite happy in sealed 46L cabs.
As woofers I use 12" Volt radials. These are truly excellent drivers and on that basis I would recommend 15" Volt RV3863. They reach 29Hz in a 200L cab so you'd still get away with 300L for both Tannoy and Volts.

Having had your Tannoys reconed means that the power capacity will have gone up dramatically to something like 300W as opposed to the 60W they could safely cope with originally. The power limiting factor with the originals was the combination of former and glue rather than the voice coil itself. Contact Lockwood Audio for more details on this.

You will of course need an extra amp and here I suggest MC2 Audio which are very, very good indeed. Personally I very much prefer them to Brystons in every respect.

Charles Darwin 28th November 2012 12:18 PM

Here are the T/S parameters for HPDs:


From what I hear the Lockwood hard-edge conversion is not supposed to change them.
Although I suspect in the case of the measured ones in the link the suspension may have softened over a few decades of use. After the recone they are probably closer to the ones provided by Tannoy. Again I'd contact Lockwood to clear this up.

Oh and a zobel should not be necessary but the tweeter will need some eq to get it flat.
It'll need a notch filter somewhere between 2.5 and 3.5kHz and a 6db/oct boost from around 5 to 6kHz.
Here is a link to the xover schematic so you can work out at which frequency to notch:
No need to bother working out how deep the notch is as it provides two functions in the passive xover. On the one hand it does the notch on the other it modifies the 6dB slope created by that tiny cap in the hi pass to provide a shelf-like response below 5k down to the xover point.
A few dB is all that is needed. Without the notch you'll get that dreaded horn honk.

I run my 12" analogue active and I get away with a -3dB notch or so. I use a parametric eq to achieve this.

Charles Darwin 28th November 2012 12:45 PM


Originally Posted by Actualsizeaudio (

I hope that guy in the link did NOT soffit mount his Mackies!
If they are the ones I'm thinking about (HR824) they have a large oval passive radiator mounted in the back.

Actualsizeaudio 28th November 2012 11:58 PM


Originally Posted by planet10 (
Do you have a set of (reasonable) T/S data for these drivers?


They exist for these drivers on the Tannoy site; I can get them. I've read however that I need to make those measurements of my particular ones. Do you have an opinion on that? Sounds like I should probably start breaking them in since they have new cones/coils. I would imagine that Thiele/Small measurements change once a speaker is broken in? These drivers were in one of the Charisma records studios, so I imagine they saw some use!

Actualsizeaudio 29th November 2012 12:17 AM


Thanks for the great info. I really appreciate your input. I've thought exactly about doing what you are suggesting with the bass driver. I do own a sub woofer, and know people who run 2 sub woofers, but a bass driver is an interesting concept. 175 is much higher than I had contemplated, but I'm open to suggestions. The beauty of the digital crossover is that I can change my mind at a later date.

I'll send an email to the people at Lockwood on your suggestion. I guess it would be good to let them know where those things ended up.

After reading through the soffit mount threads again over at the Sayers site, I realized that these speakers will have to be up high, and pointed down. Since they are permanent installs this should not be a problem, but it does point to the possibility of building these things in place. It also brings up the possibility of having the box be a non rectangular shape. I'll see if I can post a pic of the wall they would be going into tonight. I was thinking, what's the difference between soffit mounting a speaker to simulate a late baffle, and a speaker mounted to the wall that has a very large baffle. For instance, with the standard 300L cabinet you see posted on the web that people have put these things into, whats the reason the instead of having a 4 ft tall cabinet, why can't you have a 4ft wide cabinet. Just a thought.

One thing is clear, I need to rebuild the front wall of my studio. Better stock up on sawz-all blades.


Originally Posted by Charles Darwin (
I hope that guy in the link did NOT soffit mount his Mackies!
If they are the ones I'm thinking about (HR824) they have a large oval passive radiator mounted in the back.

Man I agree. About 15 years ago I used to use those dreaded speakers. They were awful because they just had too much low end that wasn't accurate. Soffit mounting them would be terrible for that reason alone. I don't remember them having a passive radiator. I still have the sub they made for that speaker sitting here idle. It's actually a good piece, and it has a passive radiator in the front, and the 15" bas driver firing into the floor (which I don't love).

I've contemplated using it as the sub for these, or finding a second one and going with a dual sub system.

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