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-   -   Cabinet for Tannoy 3149 DC driver, vented port or passive radiator? (http://www.diyaudio.com/forums/multi-way/220760-cabinet-tannoy-3149-dc-driver-vented-port-passive-radiator.html)

Ro11 1st October 2012 12:07 AM

Cabinet for Tannoy 3149 DC driver, vented port or passive radiator?
 
Last month I purchased a set of Tannoy SRM 12X loudspeakers, I run them on my Quad 303.
The sound is superb, except for the lower frequencies. It's exactly like I read in many topics on the web, I can confirm Tannoys SRM 12X lacks both low-mid and bass.
After reading lots (lots!) of stuff about DIY speaker building I have a basic idea on how to build new cabinets for my Tannoy drivers (no. 3149 if I'm correct, I still have to open the SRM 12X cabinets).
Please note I´m not a physicist, I just hope my brain and senses are in the right place, I do know those come with no guarantee!

My plan is to stick to the golden ratio, it's more or less where Tannoy put their drivers in (outside cabinet measures). So I build a rectangle shaped box, the driver will be placed in one of the short sides, this makes the cabinet become a column (high, narrow, deep cabinet made of thick birch plywood).

So far so good....

I plan on keep using the original cross-overs, I am confident the clear mid and high tones will come out smooth in the larger cabinet, but now for the low frequencies..... With the new cabinet I increase its volume to roughly 177 liters.... shall I use a vented port or passive radiator design?
A passive radiator design attracts me, but what radiator to choose? What size should it have? Which brand produces good passive radiators? Are there even good and bad passive radiators? Where in the cabinet is the best place to put it (I prefer in the back panel of the cabinet)? What else are important things to look at?

As you see I can use some fresh inspiration for this project. Any twist of mind is welcome here.

Thanks.

Bare 1st October 2012 05:37 PM

Interesting question. Wrong arena to ask IMO. Although DC's are effectively Full rangers. Arguably amongst the best Ever built.
Although it's.. Very Odd.. that Bass is a concern. IF there is criticism of the later DC's (yours) it's that there is too much mid level content.
I'd be examining Every part of your supply chain..as well as the Driver innards/crossovers / wiring.. First!
Although these drivers Do need a 20A current capable Amp to deliver their full dynamics . [Not all amps are adequately designed. and price is not necessarily the determinant either.. Read Amp specs carefully before buying ].
Again: Bass should still be substantial.. as is.
Appropriate info sources are:
tannoy
Tannoy Monitor Gold

Plus the Tannoy Groups on Yahoo.

Lots to read /digest before chopping up wood.. armed only with a hope and a prayer.
One can assemble genuinely proven Enclosures: GRF's or Royals are the Ultimate.. Huge things though

sreten 1st October 2012 06:21 PM

Hi,

Passive radiators only make sense in very compact cabinets where a decent
sized port simply can't fit in the cabinets. In big cabinets port design is easy
and using PR's is pointless, unless you want the "look" of extra drivers.

Parameter wise the cheapest PE 12" suits big boxes the best :
Dayton Audio SD315-PR 12" Passive Radiator 295-496
But you'll only get up to low twenties tuning in a big box, 5cuft to 6cuft,
unless you use two per box, then it goes up to the low thirties, and then
you can tune down by adding mass to the PR's.

rgds, sreten.

Parameters for the 3149 would help .....

Ro11 5th October 2012 11:48 AM

Thanks for the replies Bare & sreten,

Seems like I DO have to do some more math first.... I have to find some local help with checking the electrical components. Unfortunately I do not have the driver parameters, so more research on the web might be needed as well.

Thanks again! I have a new direction now.

GM 5th October 2012 02:26 PM

Greets!

Have you searched the Tannoy Forum for answers? You’ll need the driver’s published T/S specs to be able to get an approximation of what’s required and measured specs of your drivers to get an optimum solution: tannoy : Tannoy Dual-Concentric loudspeakers

Don’t have the 3149’s specs other than these, which may, may not be similar enough to yours to calculate an optimum alignment : http://www.diyaudio.com/forums/multi...tml#post997888

k3148/k3149

Qts=.4
FS=32Hz
VAS=9.54ft3
Re=5.6R
BL=22
SPL=92dB
12 inch driver

Then there’s these: http://www.diy-audio-guide.com/image...urgh_specs.jpg

Qts = 0.41
Fs = 38 Hz

Both imply the existing 68 L net cab is way too small if you have a rolled off [mid] bass response: tannoy

A ‘worst’ case combination of these specs calculate up to a ~280 L net/32 Hz alignment, which short of your drivers being way off these specs should be large enough to allow a decent amount of in room tuning flexibility.

At 177 – up L cab net volume [Vb], vented is the preferred way and a tower [MLTL] floor-stander to both get some extra vent damping along with getting the HF up to at least ear height is normally the way to go with large cabs. With these, only using the golden ratio for the width x depth is desirable.

GM

Ro11 5th October 2012 10:41 PM

Thanks GM,

That Tannoy archive is very useful, I checked it before (also the photo section gives a lot of inspiration on cabinet building methods).

Your explanation supports my approach on increasing the cabinet size, nice to hear that!

So you say vented port design is the preferred way... About tuning then: the ability to tune the low freqs with a PR (by adding/removing weight to it) sounds appealing to me. Can you say something about that compared to vented port design? Is it just like @sreten says: PR design is pointless in large cabinets? Maybe I also have to dive into in-room tuning then ;-)
About placement: the cabinets are supposed to have some air around them, each like 50 cm from the walls in a 30 square meter room, I like to place them on some sort of feet, not that much from the floor (+/- 10 cm).

Looking forward to your reply!

Cheers

GM 7th October 2012 03:22 AM

You’re welcome!

Well, really, it’s the only practical way unless you morph the cab and vent into a TL or at least a MLTL.

The PR[s] required to get the proper amount of moving mass [Mms] to tune them to 32 Hz would be either so tiny with such a short stroke that its acoustic efficiency would be inaudible or so large to get up to a realistic Mms that all things considered it would seem ‘pointless’ to consider either option.

The 280 L/32 Hz alignment in a golden ratio cab for instance. A 13.52 cm diameter x 4.91 cm long vent is plenty large enough for a very low vent mach at 100 W.

Its air mass plug [Mms] should only weigh around 0.8-0.9 grams. This is tweeter weight needing a tweeter’s piston area [Sd] if a PR, so its excursion would obviously be much too long to be linear.

Going in the other direction using the Dayton PR’s 200 gr. as an example, it will need [4] of them plus whatever may need to be added to offset their much less compliant suspension [compared to the air vent] to fine tune them.

This much vent acoustic efficiency might sound a bit ‘one note’ or at least a bit ‘bloated’ in room, so would probably have to be tuned lower still. I guess if cost isn’t a concern, then having a pair of 12” PRs on each side of the cab to ~ cancel out their vibrations would make for a bit of uniqueness.

“The cabinets are supposed to have some air around them……”

This depends and the larger the cab, usually better to build the cab wide and place it near/at the wall or corner. If space dictates a narrow cab, then for a tonally flat response down low requires either backing it up into a corner or using baffle step compensation [BSC], which lowers system efficiency.

WRT spacing it up, this too depends on room acoustics and how much vent loading from a near boundary is desired. FWIW, I only space up cabs with a bottom firing vent, but then they are all tall TL or MLTL cabs.

GM

triodes4ever 22nd January 2013 01:35 PM

Did you start on your cabinets?
 
Curious to what is your design outcome..I have SRM12X here and lucky enough I have no bass complaints (small attic room, they are under a tilted roof). I have some filter upgrade plans though (nice AmpOhm polyprops instead of the el-cheapo yellow Philips MKT's..

Cheers Leonard

Ro11 1st November 2013 05:45 PM

Still/again working on this.... :-)

Testing the 3149's now in a 180 L BR cabinet, new xo's attached and playing around with stuffing/damping materials....

Cabinet tuned all the way down to +- 32 hz using a bottom firing vent.

This setup already sounds very, very good. And there's a lot of room for improvements, using plywood instead of MDF and better bracing for example...

@Triodes4ever: My experience with the SRM 12X is that there was almost no bass, really. My test cabs take their place now, literally, and the sound is so much bigger now. Also, the new crossovers do a great job here.

Cheers

Ro11 1st November 2013 06:36 PM

Quote:

Originally Posted by GM (Post 3190926)
Greets!


At 177 – up L cab net volume [Vb], vented is the preferred way and a tower [MLTL] floor-stander to both get some extra vent damping along with getting the HF up to at least ear height is normally the way to go with large cabs. With these, only using the golden ratio for the width x depth is desirable.

GM



@GM: I basically followed this design in the test setup, with good results :-)


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