Tannoy Stratford rebuilding and/or retuning

[Jamesblond]

Hi, people.

I'm new to this forum. I've been reading a bit here, and, frankly, it's obvious that you guys have LOADS more knowledge and exsperience than I have. My question is this.

I've gotten my hands on a really cheap pair of Tannoy Stratford loudspeakers in reasonable condition. The dustcaps of the woofers were missing, so I've replaced them with new ones. I've also refurbished the filters with new, high quality components and leads. The soundquality has improved greatly - much better imaging and more depth. However, the cabinets are in not-so-good shape and made of 12mm chipboard. I'd like to rebuild them. Some people advised me to use 22mm MDF, others suggested I'd use as thick a sheet of "multiplex" (plywood?) I could get my hands on, because that would sound warmer and it's stiffer to boot, which wood decrease cabinet resonance.

The cabinets have some noticeable resonance between about 150Hz-200Hz - especially with some male vocals. A guy from a high-end audio store advised me to increase the volume of the cabinets to increase bass-extension. I'm not sure how the cabinets are tuned now, but I'm guessing they reach to about 40Hz without roll off. If I would make the cabinets a bit deeper (front to back) and taller and I wanted to tune them to 34Hz, how would that affect port-tuning?

Basically, I have no idea what I'll encounter if I'm going to alter the design. If it's adviseable to keep the design as it is (copy inner dimensions and port length/diameter/placement), please say so. If, on the other hand, it might pay off to increase the cabinet, what would I have to do and pay attention to?

Also, about the filter. There is a coil in there with no indicated value. I've included a schematic of the filter. The crossover is 3.5kHz, according to the manual of the speakers. I've gotten two different measurements, so no useable info: 2.2 and 0.22mH. Which would it be?

Thanks for any advise!

[sreten]

Hi,

If you make the cabinet larger keep the original port.

The speaker and port tuning will automatically lower in a bigger box.

As long as you don't change baffle width appreciably any new box should be fine.

I presume the coil is aircored, very little point in changing it.

/sreten.

[Jamesblond]

Hi.

Thanks for your reply. Indeed the coil is, or should be, air cored. However, the entire filter was attached to the input terminals, and all the wires wire wrapped through the coil, to keep them together. I cutted them away as close to the coil as I could manage, and replaced all cables with QED Silver 12. There are some remaining pieces of old cable glued into the core of the coil. I'm not sure if this is in any way comparable to a sort of ferrite or copper core in terms of saturation and distorition.

If I decide to enlarge the cabinet, and thus lower port and speaker tuning, will that affect linearity in one way or another? According to the specs the original cabinet was tuned to 50Hz, but it manages to output 45Hz easily, probably lower. I can't tell exactly how low, since I have no way of measuring. And my listening room is far from ideal. It outputs a tone which I know to be 33Hz, although not easily. If I want to tune to say, 38Hz, how much larger will the cabinet need to be?

I don't want to widen the baffle, just increase depth a little (front to back) and maybe make it taller. I have no idea how much, though... Also, is the location of the port important? Currently it's below and slightly to the right of the woofer. Can it be centered and placed more down? And what about internal bracing?

Darn... This sounds like designing a completely new cabinet... Well, as long as it turns out better than it is now, I don't mind!

Thanks for any input!

[Jamesblond]

No one?

I just need help some help here, since I'm an utter noob in loudspeaker and filter design.

My question is, what will I run into when I choose to design an new cabinet for the Tannoy speakers I have (Tannoy stratford). I'd like to sqeeuze a little more low end out of them without "hyping" the bass. It should be flat and solid down to the roll of point. And how do I calculate the correct port position and place?

WinISD has a "speakerpower" parameter. What does it mean/do?

Any help is greatly appreciated.

Thanks!

James.

[sreten]

Hi,

I suggest you try and obtain the Thiele Small parameters of the
Stratfords bass unit from Tannoy. I've heard they can be quite
helpful in this respect. Post the parameters here.

Without these it would not be wise to attempt a large change
in bass tuning, and it may well be you can simply detune the
port, i.e. making the box bigger would not help significantly.

In this case you could refurbish the cabinets and add internal
bracing, relatively painless compared to building new cabinets.

it may also be the case you could use significantly larger
cabinets with lower tuning, but the parameters are needed.


/sreten.

[Jamesblond]

Hi, Sreten.

Thanks for your reply. I sent an email to Tannoy (hopefully to the right address) and asked them if it was possible to get the needed parameters, or otherwise, if they knew where to find them.

Internal bracing alone probably won't be enough for these speakers. The cabinets look hideous, chips on corners missing, veneer badly damaged, etc. So I'll have to remake them anyhow. The question is whether or not it's worth it to try to improve on the original design. They sound excellent. Especially knowing that, including new filter components, I paid less than 100 Euro's for them. These components are high-quality. Not top-notch, but waaayyyy better than what was originally fitted into the speakers. And they really came to life with these new capacitors, resistors and cables.

With this increased performance in mind, I'd like to see how far I can stretch them.

The included picture was made after when I fitted new dustcaps.

[sreten]

Originally posted by Jamesblond
Hi.
There are some remaining pieces of old cable glued into the core of the coil. I'm not sure if this is in any way comparable to a sort of ferrite or copper core in terms of saturation and distorition.
Thanks for any input!

Hi,

if its steel wire it could theorectically cause some distortion.

If you use a craft knife you should be able to slit the end of the
insulation and pull out the remaining wire in the core of the cable.

/sreten.

[Jamesblond]

Originally posted by sreten
Hi,

I suggest you try and obtain the Thiele Small parameters of the
Stratfords bass unit from Tannoy. I've heard they can be quite
helpful in this respect. Post the parameters here.

Without these it would not be wise to attempt a large change
in bass tuning, and it may well be you can simply detune the
port, i.e. making the box bigger would not help significantly.

/sreten.

I've recieved a reply from Tannoy, saying they no longer have the T/S parameters for the 2048 Tannoy bassdriver in their file:

"I am sorry to inform you we no longer have the T/S for the driver(2048) used on the Tannoy Stratford. I have check our archive store and the T/S perameter no longer exist for this model it must have been deleted or distroyed. ".

So I'll have to do without them. I guess I'll leave the internal volume the same, copying heigth and width. I'll make it a tiny bit deeper to compensate for the volume internal bracing takes up. I'll also experiment with two tube lengths, to see whether the change is worth it. WinISD is useless, since I have no T/S parameters.

The next thing I need to worry about is damping. I'll do some reading on this forum to look for a thing or two.

Note to anyone reading this: I you ever come across the T/S parameters of the Tannoy 2048 mid/bass driver used in the Stratford model, please send me an email, and/or post them here.

Thanks!

[sreten]

Hi,

I'd say you could increase internal volume by 25% to 33%,
especially if you are prepared to experiment with port tuning.

Plug your box size and port size into winISD,
what frequency do you get ?
(use any driver it doesn't matter)

/sreten.

[Jamesblond]

Hi.

I've input the current dimensions of box and port into WinISD, based on a Visaton W200 mid/bass driver, which has roughly the same dimensions as my current Tannoy 2048 driver. The gain plot I get looks true to the real-life situation. With a 51mm port diameter and 102.7mm port length, I get a tuning of 40.5Hz. Seems pretty probable to me. Inner box dimensions are:
W: 240mm, H: 455mm, D: 240mm. Volume = 26,2 litres. In my listening room, I notice roll-off at around 36Hz.

I also made a model of a 65.6 litre cabinet, tuned around 32Hz, based on the same W200 driver. I posted the plot below.
W: 240mm, H: 855mm; D:320mm. Keeping in mind that in my listening conditions a small boost below 40Hz occurs, this might not be such a good idea, right? The peaks gets boosted even more. When I model with two W200 drivers, the roll off gets very smooth, but the -3dB point moves from 29 to 36Hz.

Any suggestions?