Tannoy HPD315 Build
- Thread starter Raoul Duke
- Start date
Raoul Duke
pfm Member
Thanks Chas B!
I think this has been a really worthwhile exercise.. These drivers just seem to need breathing space to do their thing. I do need some assistance from the wise re this port calculating.. I am now trying a much longer (20cm) port tube which according to this
http://www.linearteam.dk/default.aspx?pageid=ventcalculator
is giving me a tuning of around 28Hz. I have to say I am enjoying the lower tuning vs the approx 40Hz tuning I had before with a 6cm port tube. Bass seems drier and tighter and midrange more forward. What is "correct" here I am not sure but most seem to suggest that 35 - 40Hz is where you want the tuning..
I think this has been a really worthwhile exercise.. These drivers just seem to need breathing space to do their thing. I do need some assistance from the wise re this port calculating.. I am now trying a much longer (20cm) port tube which according to this
http://www.linearteam.dk/default.aspx?pageid=ventcalculator
is giving me a tuning of around 28Hz. I have to say I am enjoying the lower tuning vs the approx 40Hz tuning I had before with a 6cm port tube. Bass seems drier and tighter and midrange more forward. What is "correct" here I am not sure but most seem to suggest that 35 - 40Hz is where you want the tuning..
calorgas
Generic middle-aged man
They look fantastic 
I went through a similar journey with my old pair of 12" Golds and finished with new heavy duty ply cabinets pretty much the same volume as yours - it really does seem to free them up and gives them a much greater sense of scale.
I've now downsized to a little pair of Eatons, but looking at these pictures does rekindle that familiar desire to revisit the cabinets to allow these lovely drivers to really sing.
I went through a similar journey with my old pair of 12" Golds and finished with new heavy duty ply cabinets pretty much the same volume as yours - it really does seem to free them up and gives them a much greater sense of scale.
I've now downsized to a little pair of Eatons, but looking at these pictures does rekindle that familiar desire to revisit the cabinets to allow these lovely drivers to really sing.
fraserking
Trade: custom speaker cabinets
Hey Raoul
I had the same thing with my 315 HPDs ( HE) - the port length was supposed to be like yours in my 95L cabs ( think it was around 9cm for 35hz) but i found it too bloated and am nearer your 20cm length with my 10cm diameter ports. Still a bit honky on certain material but that could be the room. If you can bare to spend the money on Clarity MR caps for the main tweeter cap( 1 @ 4.7uf i think) you`ll be rewarded. I certainly was - having tried a couple of other brands and Clarity ESA (which were all pretty close) the MR was perfect.This was on the advice of Paul Mills who was the head guy at Tannoy r & d .
Regards
Fraser
I had the same thing with my 315 HPDs ( HE) - the port length was supposed to be like yours in my 95L cabs ( think it was around 9cm for 35hz) but i found it too bloated and am nearer your 20cm length with my 10cm diameter ports. Still a bit honky on certain material but that could be the room. If you can bare to spend the money on Clarity MR caps for the main tweeter cap( 1 @ 4.7uf i think) you`ll be rewarded. I certainly was - having tried a couple of other brands and Clarity ESA (which were all pretty close) the MR was perfect.This was on the advice of Paul Mills who was the head guy at Tannoy r & d .
Regards
Fraser
Just seen this
Nice build Raoul. My own advice is that bracing should NEVER be de-coupled as the whole purpose (for measurists it is proven using finite element analysis which I use on my own Tannoy builds) is to coulple the panels, and distribute resonance to improve the efficiency in reduction of frequency resonance amplitude. There is a school of design to de-couple, but it is by specific design, including laminate panels which are designed to efficiently damp the vibration and resudual resonance to be idssipated at specially designed joints.
It is much more difficult to make isolation damping work on a ply build like this and more efficient in terms of reducing amplitude of resonance well below program to brace the cabinet as Raoul has done. By the way, there is an optimal number of (specific thickness) braces which added to a cabinet of a given size have the exact same effect as simply doubling the panel wall thickness. This implies a similar value for the Young's Modulus of the braces to panel materials. For a cabinet like this, using 18mm thick ply braces, the optimum number of braces would be 5 and no more. You also have to take into account the volume occupied by the braces when calculating cabinet tuning, their effects on internal reflections and standing waves also.
Great build Raoul, and look forward to seeing the end result once you're happy with the results. I can help you with port tuning via PM if you supply me with the NET internal volume as there is really only one efficient tuning point for a given net volume and these drivers. Get it wrong and in theory, it can cause driver, or amplifier issues and lead to loss of system efficiency.
A tip on crossovers. As this is a clean sheet build, you may be better externalising the crossovers (just make them sit in their own boxes). One trick is the height of the centreline of the drive unit doesn't correspond with your ear height from the listening position (best with DC drivers) is to raise the speakers to the necessary height by building them into a plinth which in turn houses the crossovers. You take the crossovers away from the EM field of that big drive unit magnet and way from internal resonances of the speaker enclosure, which IME is the best way to do it. Otherwise, some shoe-boxe sized enclosures with a connector on the back of the speaker works well. However, as you have already built them in, I'm sure they'll sound fine as-is. You've done a really neat job there and should be proud of your achievement.
Nice build Raoul. My own advice is that bracing should NEVER be de-coupled as the whole purpose (for measurists it is proven using finite element analysis which I use on my own Tannoy builds) is to coulple the panels, and distribute resonance to improve the efficiency in reduction of frequency resonance amplitude. There is a school of design to de-couple, but it is by specific design, including laminate panels which are designed to efficiently damp the vibration and resudual resonance to be idssipated at specially designed joints.
It is much more difficult to make isolation damping work on a ply build like this and more efficient in terms of reducing amplitude of resonance well below program to brace the cabinet as Raoul has done. By the way, there is an optimal number of (specific thickness) braces which added to a cabinet of a given size have the exact same effect as simply doubling the panel wall thickness. This implies a similar value for the Young's Modulus of the braces to panel materials. For a cabinet like this, using 18mm thick ply braces, the optimum number of braces would be 5 and no more. You also have to take into account the volume occupied by the braces when calculating cabinet tuning, their effects on internal reflections and standing waves also.
Great build Raoul, and look forward to seeing the end result once you're happy with the results. I can help you with port tuning via PM if you supply me with the NET internal volume as there is really only one efficient tuning point for a given net volume and these drivers. Get it wrong and in theory, it can cause driver, or amplifier issues and lead to loss of system efficiency.
A tip on crossovers. As this is a clean sheet build, you may be better externalising the crossovers (just make them sit in their own boxes). One trick is the height of the centreline of the drive unit doesn't correspond with your ear height from the listening position (best with DC drivers) is to raise the speakers to the necessary height by building them into a plinth which in turn houses the crossovers. You take the crossovers away from the EM field of that big drive unit magnet and way from internal resonances of the speaker enclosure, which IME is the best way to do it. Otherwise, some shoe-boxe sized enclosures with a connector on the back of the speaker works well. However, as you have already built them in, I'm sure they'll sound fine as-is. You've done a really neat job there and should be proud of your achievement.
Rallye_punk
pfm Member
Wow excellent work these look fantastic. Did you apply a veneer to the cabinets or is that just a varnished finish?
Raoul Duke
pfm Member
Hi gents, thanks so much for the positive comments Rallye_punk no the baltic birch just has several layers of stained Woodoc polyurethane sealer over it.. finish worked out ok but could have been better.
I did a lot of reading and research before starting out, but decided to go for the simple bass reflex birch ply design.. (to suit my limited skills) I am glad I chose that route as even this has been enough work, and not over yet.. all the CLD theory and the BBC extensional damping theory is fascinating though. I am still interested in trying to decouple the rear panel from the rest of the structure to see if this is beneficial vs attaching it rigidly.
I also have a pair of Monitor Gold 15s waiting for cabinets so this started out as a bit of a test run to see how things worked out.. The Devons were my first taste of Tannoy and it looks like I am going to travel further down this road yet. I appreciate I could improve things by externalizing the crossovers, upgrading the caps.. and I definitely will be raising the cabinets up so the drivers are at ear level.
Pac1 I will definitely take you up on some additional assistance with the tuning.. thanks for the offer! I must first check all my measurements again to calculate the net volume accurately. Good night for now, been a long and very hot day here
Rallye_punk no the baltic birch just has several layers of stained Woodoc polyurethane sealer over it.. finish worked out ok but could have been better.I did a lot of reading and research before starting out, but decided to go for the simple bass reflex birch ply design.. (to suit my limited skills) I am glad I chose that route as even this has been enough work, and not over yet.. all the CLD theory and the BBC extensional damping theory is fascinating though. I am still interested in trying to decouple the rear panel from the rest of the structure to see if this is beneficial vs attaching it rigidly.
I also have a pair of Monitor Gold 15s waiting for cabinets so this started out as a bit of a test run to see how things worked out.. The Devons were my first taste of Tannoy and it looks like I am going to travel further down this road yet. I appreciate I could improve things by externalizing the crossovers, upgrading the caps.. and I definitely will be raising the cabinets up so the drivers are at ear level.
Pac1 I will definitely take you up on some additional assistance with the tuning.. thanks for the offer! I must first check all my measurements again to calculate the net volume accurately. Good night for now, been a long and very hot day here
Raoul Duke
pfm Member
Things have come a long a bit with these after some very helpful correspondence with member pac1 I now have the cabinets tuned to around 38Hz and they are sounding wonderful. After calculating more carefully my net volume at close to 100 liters this seems to be the right place to be. I have been listening to everything from Bill Evans "Live at the Village Vanguard" to Aphex Twin and back.. these cabinets are definitely making the Devons sound small and boxy in comparison!
I must now decide how to attach the backboards. At present I have them firmly screwed down and am detecting no ill effects from this.
20170204_112008[1] by Bregtje Cals, on Flickr
I must now decide how to attach the backboards. At present I have them firmly screwed down and am detecting no ill effects from this.
20170204_112008[1] by Bregtje Cals, on Flickr
Tony L
Administrator
Experiment very carefully with how you attach the backs, for me tight is never right! I'm of the BBC mentality that the key advantage of a srewed and/or thin-wall cabinet is that you can keep resonance very low-Q and damped. I tend to look at it like a drum or guitar string; they only make noise when under tension, and the more tension they are under the higher up they will ring. I am very careful when torquing the back doors of my lovely Lockwood cabs and do the bolts up so there is no prospect of rattles or coming lose, but also no prospect of a note or resonance. This comes out as spinning them in until they stop, then maybe a quarter turn. The backs of mine have a strip of foam draft excluder that I think is an original fitting and I suspect this helps get such an inert and dead thump when rapped with a knuckle. These cabs just don't have a 'note', and I'm sure that is what is wanted and a screwed back panel is a massive asset in achieving this IME.
PS I'd certainly not glue the backs on, that will likely move them closer to a conga drum in behaviour!
PS I'd certainly not glue the backs on, that will likely move them closer to a conga drum in behaviour!
cooky1257
pfm Member
FWIW, this is taken from the Tannoy 215 DMT manual explaining the cabinet construction.
The bracing frame is rigid but where it joins the cabinet panels lossy adhesives are used, the same stuff is also used between the panels themselves, the slug of damping putty connects the rear of the driver to the brace frame. The layer of draught excluder could well be functioning in the same way as the lossy adhesive....
The bracing frame is rigid but where it joins the cabinet panels lossy adhesives are used, the same stuff is also used between the panels themselves, the slug of damping putty connects the rear of the driver to the brace frame. The layer of draught excluder could well be functioning in the same way as the lossy adhesive....