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Tannoy HPD315 Build

Raoul Duke

Raoul Duke

pfm Member
Not wanting to reinvent the wheel but wondering what life my 12" HPD's could have beyond the Devon's they are in at present.. I set about knocking up some 125litre BR boxes. These are golden ratio and should be tuned to about 40Hz.

Must get the camera out for some better shots but this is where I'm at now.

HPD315 Box Build by Bregtje Cals, on Flickr

A friend did the mitres for me and everything is going together quite well so far despite my limited woodworking skills. All 18mm baltic birch ply and the front baffle is mostly a double layer as can be seen.

I am still trying to decide if I should add more bracing.. I am tempted to leave them as is and add bitumen sheets and foam felt and see where I'm at. I know the Tannoy cabs from this era were not huge on bracing and used a lot of chipboard in construction so feel like I'll come out ahead of those with a bit of luck! Still any tips would be great at this stage :D
 
They look really nice and solid. I greatly admire people who can make more than blood, splinters and swearing out of wood/tools.
 
Nice. so long as you allow room either side of the brace to get at the crossover through the driver cut out you will be able to glue the back panel in place.
 
Thanks for the compliments gents! Wish I could take all the credit but am really enjoying the project. I am hoping to glue the backs on in the end but they will be screwed at first in case any changes are needed with damping/lining.

Will add some better pictures later, but for now would you folks say I am ok with this bracing? Cabinet is 81cm tall x 50cm x 31cm deep. Sorry we're metric down here in South Africa :)
 
I'd not necessarily assume glueing the back panel on was better than screwing. There is a very well (BBC researched) school of thought that some decoupling here is a very good move. The time to glue it is if you have a lot of internal bracing, i.e. multiple levels/shelves etc, if the panel is still large enough to resonate at all I suspect you will find it lower Q and better damped if screwed, and not done up too tight. As an example I very much wish my La Scalas were screwed not glued as I bet I could tune the cabs to be a lot more dead than they are.
 
Tony L said:
They look really nice and solid. I greatly admire people who can make more than blood, splinters and swearing out of wood/tools.
Click to expand...

I feel the same way, I can certainly visualize how I want something to be, but getting there, nothing but pain and agony!

These cabinets look great Raoul, look forward to the rest as it comes along!
 
Tony L said:
I'd not necessarily assume glueing the back panel on was better than screwing. There is a very well (BBC researched) school of thought that some decoupling here is a very good move. The time to glue it is if you have a lot of internal bracing, i.e. multiple levels/shelves etc, if the panel is still large enough to resonate at all I suspect you will find it lower Q and better damped if screwed, and not done up too tight. As an example I very much wish my La Scalas were screwed not glued as I bet I could tune the cabs to be a lot more dead than they are.
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The BBC research is on thin wall/damped construction a la BBC research paper here http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf

Note the BBC did not adopt the loose fillet construction method/accident, though were very specific in the type of wood used for the fillets(eg pirahnna pine was a disaster compared to beech, a hard wood). In the research they refer to the close coupling of the enclosure panels being evident in the measurements/graphs.

I can't find where the BBC say back panels aren't done up tight-I'd assume the enclosure be it IB or Reflex would need to behave as intended and not have any air leaks for example though Harbeth mention 'precise tensioning' of the screws so you could be on to something. If the op does decide to glue I'd go for a mastic type 'lossy' adhesive in any case-something I'd've recommended for the bracing too but we're down a path of not thin/damped, and not DMT.
 
Thanks for the interesting discussion gents. cooky1257 I had always assumed that bracing should be under compression (ie a tight fit) and bonded as rigidly as possible to panels.. still I am fresh to speaker building! It does seem that there are always at least several valid approached to every problem with acoustics. I suppose I can also experiment with the back panel, first screwing it down, adjusting tension etc. If I do decide to glue I will use something flexible. Meanwhile have decided to install 2 vertical "beams" the length of the cab and then be done with bracing.
 
Raoul Duke said:
Thanks for the interesting discussion gents. cooky1257 I had always assumed that bracing should be under compression (ie a tight fit) and bonded as rigidly as possible to panels.. still I am fresh to speaker building! It does seem that there are always at least several valid approached to every problem with acoustics. I suppose I can also experiment with the back panel, first screwing it down, adjusting tension etc. If I do decide to glue I will use something flexible. Meanwhile have decided to install 2 vertical "beams" the length of the cab and then be done with bracing.
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Don't sweat it Raoul mate, they look good cabs to me, make at least one of the vertical braces butt up against the back panel, that way you are tying base, back, shelf brace and top together.The lossy thing comes from the DMT construction that modern Tannoys employ that effectively doesnt just stiffen and shift panel resonances upwards but damps them at the same time. I think KEF also do something similar.
 
I will follow your progress with interest, I have a pair of 315s waiting for a home.
Is there any reason that you chose 125 litres? My reading so far suggests 150 litres. Please don't take my comment as any sort of criticism, from my reading I also conclude that there is more talk about such things than actual building!

Good luck.

Chas.
 
Hey Chas B I was initially going for 150litres as well but my reading suggested that the larger you went the "slower"the bass could become and that the sweet spot might be closer to 120litres. I think it was member pac1 here on pfm that had played a lot with this driver and found this to be true.. At any rate when compared to the Devons 46 litres, hope I'll come out ahead in bass response and "effortlessness" I do rather like my Devons though... listening to them now hooked up to a Sansui AU999. I just have an extra pair of drivers and like most always strive for the next best thing :)
 
cooky1257 said:
I can't find where the BBC say back panels aren't done up tight-I'd assume the enclosure be it IB or Reflex would need to behave as intended and not have any air leaks for example though Harbeth mention 'precise tensioning' of the screws so you could be on to something. If the op does decide to glue I'd go for a mastic type 'lossy' adhesive in any case-something I'd've recommended for the bracing too but we're down a path of not thin/damped, and not DMT.
Click to expand...

Where similar BBC designs exist with both screwed back panels and glued the screwed always seem to sound best, e.g. the few Harbeths with glued cabs have a reputation of being pretty naff. I agree you need to retain the sealing, but the loosely screwing up of a panel just deadens it/takes the resonance right out. Think of a intact bell vs. a broken bell, the former rings, the latter doesn't. The lossy adhesive you mention may achieve similar, I don't know, but getting rid of any pitched note is the key IMO.
 
Progress looks like this so far on my boxes.. I missed cooky's note about making one of the verticals run along the back panel :( Cabs are definitely very solid now however and next step will be adding bitumen sheeting. Also found some perfect fitting cardboard tube so I can experiment later with different port lengths.

Bracing by Bregtje Cals, on Flickr

front view

Front Baffle by Bregtje Cals, on Flickr
 
They look really good. One thing that puzzles me is the front view looks mitred panels top and bottom, yet the rear view bottom looks like a flat joint to the base? I can't figure that one out! Are they going to have grilles?
 
Thanks for compliments Tony L :) But all this stuff I've been reading is messing with my head... and has me worried that the bracing might have shifted my box resonances higher into more audible range.. Oh and I can see the confusion, the bottoms are indeed but joined but the edging added front side after is "mitred" :) Havnt actually thought as far as grilles yet.. !
 
Great, I just wanted to suggest 1 sided glue bitumen mat
for the surrouding of the backplate if you like to screw but ensure you get an airtight and non -resonating solution.

Your build looks great. :)
 
Thanks for ecouragement torstoi :)
Yes I am planning to attach the backboard onto either 3mm neoprene or butyl tape. Screws will then be tightened just enough to hold everything together. I am also undersizing the backboard so there is approx 2mm gap all the way round, the gap will be filled up with a butyl sealant. This way hopefully the backboard will be somewhat isolated while still sealing well.
 
Well... some months fell off the calendar while I was moving house etc.. good news is the living room is larger and can accommodate more speaker! :)

Happy 2017 everybody!

I have aimed to tune the enclosure to approx 40Hz as was recommended to me. I am not entirely sure how to go about this other than by using some web based calculators. So far I have the rear panels screwed on not too tightly and am using a temporary cardboard tube port of calculated length and they do sound right.. no boom and well articulated in the low end. The sense of scale and effortlessness I am now experiencing over the tiny Devon cabinets is undeniable. A promising start I think!

More photos of assembly:

recapped crossover:

Tannoy HPD315A Reflex Cab 120liters by Bregtje Cals, on Flickr

Doubled up 4mm bitumen sheets on large panels:

Tannoy HPD315A Reflex Cab 120liters by Bregtje Cals, on Flickr

Lining and driver test fitting:

20161224_114102 by Bregtje Cals, on Flickr

20161225_082020 by Bregtje Cals, on Flickr

experimenting with port lengths:

20161226_131020[1] by Bregtje Cals, on Flickr
 
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