Tannoy DC 2528 box design

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Hi. I own a pair of Tannoy T165 chester with the dual concentric 2528 driver. Very nice sounding speaker, but I would like to make a better cab for them.

I've read this thread
http://www.diyaudio.com/forums/multi-way/205162-tannoy-2528-mjk-tl-help-please.html

some info on the driver here:
An externally hosted image should be here but it was not working when we last tested it.


I'm not really technically concerned but I can easily make the required woodwork

I think a bigger volume would be preferable for more bass and dynamics and to raisen the sensitivity..

All inputs are welcome :)
Best regards, Frolger
 
FYI, a Vb = Vas, Fb = Fs is a T/S max flat alignment when effective Qts' [Qts + any series resistance] = ~0.403, so adding some form of EQ such as driving it with a high output impedance amp or adding some series resistance to 'dial' them in in-room is what I normally do/recommend, ergo a 200 L tower bass reflex [aka MLTL] tuned to Fs simplifies the design process considerably and allows for some tuning flexibility that just 'running the numbers' in a T/S speaker program doesn't.

All that's left then is for you to tell us how tall, wide and/or deep you can tolerate the cab along with the desired seated ear height in relation to the driver's HF output, i.e. on or off axis below/above it.

Also, will they be in corners or just up against a wall or well away from any hard boundaries.

GM
 
More than enough info in the Above posts.
I've heard Tannoys fitted into sawn in half Barrels that sounded V good.
Once you give 'em enough Volume. Yer good to go.
Darned difficult to mess it up. The things are Hugely tolerant.
Nelson Pass has his fitted into Jensen Imperials.. where they work as his Reference speakers ;)
 
Hi GM
Thank you for the "ergo" part! very useful for a newbie like me :D I can't really make any technical installations in the amp etc, a little too difficult for me

So, to the "all thats left" part:
no limitations for the dimensions really, most important is the quality of the sound
I have the posibility for every mentioned speaker position.. currently they are playing approx. 30-40 cm from the side walls (will install DIY PRD diffusers on first reflection) and 40-50 cm from the backwall.. But nothing is determined

Seated ear height is 100-110 cm (unless I will get a better listening chair soon)
 
Hi Bare.
I'm quite sure there's plenty of info in the above posts, the problem is my missing understand of all those technically terms ;)

just googled the Jensen Imperials.. looks stunning!! Some research on them only led to designs for 15" drivers.. my 2528 is a 10". Well I have no idea if that's an important factor, otherwise it would be nice to make something a la Jensen Imperials

But glad to hear that the Tannoy's are quite tolerant. Makes me a bit more confident :D
 
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Been trying some WinISD - but can't seem to figure it out really

Don't know if possible, but since Bare mentioned Tannoys are really tolerant, would it be possible to just copy some Jensen Imperials and add a 10" driver hole instead of the 15"?

Found this on google:
[url=http://postimg.org/image/dfu4k3j4n/]
An externally hosted image should be here but it was not working when we last tested it.
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and then turn it 180 degree so I will have the driver in seated ear height?
 

GM

Member
Joined 2003
Yes, but........ if we compare a simple reflex [vented] alignment to a Model T Ford's beam axle with 'king pin' steering, then a BLH alignment would be more like a fully articulated independent front suspension system, so while they both are designed to traverse uneven terrain, the latter obviously requires a lot more design effort to get right for each type of application and the main reason why so few BLHs perform well 'full-range'.

Regardless, while the driver's effective piston area has no bearing on a speaker cab's design 'per se', I know that the 2528's specs aren't even close, so would require a ~ complete redesign, though you could probably get it to work 'after a fashion' with enough EQ and maybe some internal damping; but the bottom line is that its compression loaded ~8 ft path-length + room boundary loading is technically too much delay for the 2528's XO point, so you may be very disappointed with the mids reproduction without adding a separate mids system to isolate it above a few hundred Hz at most to keep it out of our acute hearing BW.

GM
 
Hi GM
Thank you for the "ergo" part!

So, to the "all thats left" part:

Seated ear height is 100-110 cm

Greets!

You're welcome!

OK, note that some other measurements list a much higher Vas [compliance], so bumped the cab's dims to ~300 L just in case.........

~63.43"/161.11 cm high

~28.5"/72.39 cm wide

~10.16"/25.8 cm deep

driver down ~22.14"/56.24 cm

vent down ~54.37"/138.1 cm

All dims inside [i.d.]

Ideally the 5"/12.7 cm diameter tube vent is tuned to Fs, especially if driven with a high output impedance amp, but without knowing.......... experiment with a baffle thickness - 6"/15.24 cm long one to find the ~best overall blend to the room at whatever location you choose; with the closer to a wall, corner the longer the vent normally. Anyway plenty of tuning flexibility and if your room has lots of corner gain, then maybe even damping the vent to near sealed may be required.

Lining the walls works best overall in high aspect ratio vented cabs with typically the top, one side and back plus wrapping any horizontal, motor braces, vent tubes with 1"- 2" [2.54 - 5.08 cm] acoustic fiberglass insulation is all that's required.

Recommend 0.75"/18-19 mm Baltic Birch, Apple or marine no void plywood.

Panel bracing is normally vertical boards on edge [1x3, 1x4 or similar size scrap] with one riser board behind the driver and notched for the motor to brace/support/mass load* it and some side/side, front/back boards on edge to tie all braces on the six sides and the riser together to keep the cab from 'breathing', losing acoustic efficiency on any low organ, etc., fundamentals.

* By 'mass load' I mean put the driver into minor compression [pre-load it] between the motor support/brace and baffle once tightened down to further reduce any driver induced resonances, i.e. doing basically the same to the driver like one ideally needs to do with many speakers, even some heavy ones if not well braced: High Efficiency Speaker Asylum

GM
 
Wauw, GM - thank you very much.
But with you recommending 300 ltr and Charles recommending 75-100 ltr, I must admit that I'm a little confused.
well your shot on a cabinet seems really reasonable anyways, though (maybe) a little too big? Or maybe the difference from 200-300 ltr isnt that big??

I don't know if my amp is high output impedance or not.. it's an integrated amplifier with 8x EL84 tubes :)
Is there any way or formula to "tune" the vent to Fs? saw some formulas on the ideal vent length, yet I can't seem to remember how they did

Can you please elaborate what it means by "one riser board behind the driver and notched for the motor" and maybe the following.. can't really understand it, nor by the link, unless it just means adding some mass (like illustrated on the pictures in the link)?

By the way, i really appreciate your well explained and detailed help (yet im to noobish to understand it)
Regards, Daniel
 
If you choose a ported design there is a problem when you make the cab too big ie close to Vas.

What happens is that the response drops a few dB below around 100Hz but then it rises again at Fb (which should be equal to Fs) to the level upwards of 100Hz or even higher.

If you get the size right you get the drop below 100Hz but the response remains flat down to Fs. This can easily be fixed with practically any bas tone control.
You can't do that if the box is too big because at Fs you would have a hump of about 3-6dB above average ie the dreaded 'one-note' bass.

The published data I linked to for this driver indicate that anything above 125L will cause problems that are not easily fixed without a parametric equalizer.
 
Hi Charles.
I will go read the low Qts speaker link u posted before.. as i understood, it wasn't really a problem with a "little" peak in some lower frequencies.. Had alot of speakers with a peak at 50-60 Hz (interfering with the first axial room resonance).. i kinda liked the "boom" in the lower frequence there, but it caused some problems when interfering with the room resonance, making it wayyy too "boomy"

maybe 75-125 ltr is the way to go, though it's not a big difference from the 49 ltr the original cabs are? I feel like the drivers wont come to their best in the 49 ltr cabs, sounding "locked up" with missing dynamics

Best of luck on the hospital, hope it isn't anything serious. Looking forward to more guidance :)
regards, Daniel
 
Wauw, GM - thank you very much.
But with you recommending 300 ltr and Charles recommending 75-100 ltr, I must admit that I'm a little confused.
well your shot on a cabinet seems really reasonable anyways, though (maybe) a little too big? Or maybe the difference from 200-300 ltr isnt that big??

I don't know if my amp is high output impedance or not.. it's an integrated amplifier with 8x EL84 tubes :)
Is there any way or formula to "tune" the vent to Fs? saw some formulas on the ideal vent length, yet I can't seem to remember how they did

Can you please elaborate what it means by "one riser board behind the driver and notched for the motor" and maybe the following.. can't really understand it, nor by the link, unless it just means adding some mass (like illustrated on the pictures in the link)?

By the way, i really appreciate your well explained and detailed help (yet im to noobish to understand it)
Regards, Daniel

You're welcome!

You said you wanted more LF efficiency; well, the only way to get it is with a larger cab, it's as simple as that, so used the highest Vas spec I found + a bit more for the space that the driver, bracing will reduce it by. Charles apparently just plugged in the specs he posted with no consideration for increasing its bass response or the impact of either any added series resistance or the room's acoustics, consequently it will have a higher power handling, but guessing its bass response will be little/no improvement over your existing cab unless it's tiny; whereas by going bigger we're trading some power handling for bass extension and since the driver has a low Fs and potentially a very high compliance [Vas] it must be huge by today's standards, severely limiting power handling, but its efficiency will be greater, so overall a lot more bass at a lower distortion level.

With such a large baffle, 200-300 L just means a bit deeper cab, which frankly, this driver with its shrouded basket needs to keep from obviously obstructing the cab's 1/4 WL pipe action that damps the vent.

OK, need all the amp's info then.

Calculating the vent length for a MLTL alignment such as this one requires the higher math of wave equations, so well beyond my math skills and why I did it empirically. There's horn design programs available now to do it, so what I posted will get it down to the average of several measured drivers, which will probably be good enough unless you have a SET amp.

The 'bricks' thread was just to enlighten you on the benefits of mass loading vibrating devices, whether a driver, speaker cab, etc., be it from adding mass or simply clamping it under a bit of pressure such as a [notched to fit] full height vertical [riser] board [brace] behind the driver, 'pushing' it against the baffle [lightened riser board]: http://www.frugal-phile.com/boxlib/GM-A10-MLTL.pdf

Normally, DIYers leave a little gap between the notch, driver and use wadding to cushion, fill the gap + a little extra to pre-load the driver when attaching it to the baffle.

GM
 
Going that big gains you nothing but a frequency response problem.

It is kinda explained in the Living with low Qts speakers link I posted earlier.
If you got anymore questions I'll try and help but at the moment I'm on my way to hospital so it might be a day or two before I look in again.

Mr. Briggs got it right, so it's only a 'problem' when you don't have clue what to do with it. It does cover the basics of the 'extended response' alignment I submitted though, which I'd already explained in my initial post minus the impact of a 1/4 WL tuned pipe [TL] alignment on vent damping

Regardless, hope all goes well, been spending way too much time in such places in recent years myself. Really sucks when 'life' keeps getting in the way of our hobbies.

GM
 
I will go read the low Qts speaker link u posted before.. as i understood, it wasn't really a problem with a "little" peak in some lower frequencies..

FWIW, the sims shown in the article assume an infinitely rigid, empty, box, so once damped will be much more rolled off and the MLTL I submitted will require less added damping to get even better sonic results due to its TL damping.

GM
 
Hi GM. Think I will go for the cab you suggest - sounds like you have the "cure" or clue for what to do about the bad lower frequency response.

the "lightened riser board" will be no problem to make; does size of the holes an amount of them have an impact??
By the way can you give an illustration of "the little gap between the notch, driver and use wadding to cushion, fill the gap + a little extra to pre-load the driver".. can't seem to get it :D

I'm not so technically concerned about the amp, only thing i know is that there's 8x EL84 tubes as output tubes, delivering 2x40 watt class A?? Will a picture of the inside of it be for anything useful :)

best regards, Daniel
 
All went as normal: Postponed! :-(

Anyways I'm just not sure what there is to be gained with a 300L ML-TL over a 90L ported box. It doesn't need to go deeper than 26Hz (Fs) and it doesn't go louder for 1W (at least I hope not as that would need some serious reworking of the xover), it's just bigger.
With a 90L ported I'd just make them wide&shallow and place them with their backs on a wall and probably wouldn't need any eq at all. Possibly a reduction in bass if anything, my Tannoy 3ways are in corners and I had to reduce bass by about 8dB to get a level output.

Besides that IMO a single 10" driver looks ridiculous in a 300L cab so I might be a bit prejudiced. ;-)

The Chester by the way is a 50L box with a 55Hz lower cut off.
 
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