Re-designing speakers

[captrajesh]

I have a pair of two-way book-shelf speakers with the following specs, which are used to enhance the SQ of the TV.

Dimensions : Width 13.5cm (5.25") x Depth 17cm (6.25") x Height 25cm (9.75")

Drivers: 4" Kevlar cone woofer and 3/4" Polypropylene tweeters.

Construction: 1/2" MDF with no internal bracing. the speakers are mounted on a Plastic baffle which is inturn fixed to the speaker cabinet with 4 screws and has a rubber seal for air tight fit.

Problem: The woofer really goes down to 60 Hz or whereabouts. There is some jarring sound at louder volume.

I intend to make cabinets using 18mm MDF sheets like what Suri did. Something like in the picture (Magico Mini II cabinets) & make it front ported.

Points to ponder:

1. The TS Parameters of the drivers are not known.

2. I intend to change the tweeter to that of a fabric cone that I purchased from Richie street, which is sounding far better than the polypropylene one.

Any comments / suggestions / pointers are welcome.

 

[spirovious]

Gr8 work done captain,How did you you manage to cut round(spk mounting)?

 

[captrajesh]

Gr8 work done captain,How did you you manage to cut round(spk mounting)?

Hi Spirovious,

That cabinets are not mine. Downloaded from website and pertain to Magico Mini II. They cost 32k USD.

 

[lifewater]

Gee Captain,

That was what I was planning to do with the speakers. Junk the cabinet and tweeter and use the Kevlar cone woofer. Missed it !! All the best on your new assignment.

lifewater

 

[captrajesh]

That was what I was planning to do with the speakers. Junk the cabinet and tweeter and use the Kevlar cone woofer. Missed it !! All the best on your new assignment.

Thanks Pranjal for your encouraging words. My son didn't want to let go of the speakers so thought of improving the cabinets. Yes the woofers are very good.

 

[goldyrathore]

If I were you I would:-

1) Use Arta to measure the TS params. It only needs a cable, a resistor and PC with soundcard for TS measurement
2) Measure the Fs of tweeter and use twice that value as crossover frequency.
3) Use active crossover and power the drivers with 4 LM1875.

BTW, what make are these ?

Regards,
Goldy

 

[biyer]

Why dont you try modding the cabinet first??

I mean you can try out things like stuffing the cabinet to reduce resonance and jarring.
Or change the front baffle to wood.

 

[wishihadtubes]

Those look like spring clips on the current speakers. I hope you're planning to replace them with good binding posts. BTW, the design of the planned speakers is very nice. But to get close to that, you'll need a workshop with lots of fancy tools or a very good carpenter
All the best, Captain

 

[suri]

I have a pair of two-way book-shelf speakers with the following specs, which are used to enhance the SQ of the TV.

Dimensions : Width 13.5cm x Depth 17cm x Height 25cm

Drivers: 4" Kevlar cone woofer and 3/4" Polypropylene tweeters.

Construction: 1/2" MDF with no internal bracing. the speakers are mounted on a Plastic baffle which is inturn fixed to the speaker cabinet with 4 screws and has a rubber seal for air tight fit.

Problem: The woofer really goes down to 60 Hz or whereabouts. There is some jarring sound at louder volume.

I intend to make cabinets using 18mm MDF sheets like what Suri did. Something like in the picture (Magico Mini II cabinets) & make it front ported.

Any comments / suggestions / pointers are welcome.

hi captrajesh -

let us do this- with mdf and automotive lacquer -

i need the internal dimensions - if not available - give me the thickness of the 6 panels (4 sides and top and bottom)

keep your carpenter on standby (engine running and door open!)

should be an interesting thing to do - you know-

create a new (inert cabinet) with the same internal volume - and a slightly different (shapely and not box -like) exterior -

and see what happens to the character of sound reproduced -

yes, let us throw caution to the winds - and see what happens.

regds suri

actually - i assumed that your plan was to change the acoustic portraits!

 

[Ronnie]

What make are the old speakers? Have you checked whether the mid bass drivers are indeed kevlar cone? I am sorry, but I am used to seeing a lot of yellow painted Chinese paper-cone drivers these days...

I would suggest, start with disassembling the existing speaker and study the crossover in it(if any). if it is a no-brand speaker, chances are that, there could be just a bi-polar electrolytic cap or ( even worst case a normal polarized electrolytic cap) on the tweeter and mid bass driver wired full range. if indeed the speaker turns out that way, do you think there is any point building a new cabinet for it?

But if it is indeed a proper 2-way design, you can go full-scale. Then you can also see whether the existing cross-over can be tweaked for the new cabinet you are designing.

Ron

 

[anilva]

Rajesh,

I would go with Suri's idea of measuring the internal volume and sticking to that volume but in a new cabinet and shape, with better build, bracing etc.

Subsequently if you like the speakers too well, you can further upgrade the crossover. There will be a point of diminishing returns with your bass drivers. Do not go and do a complete new design and if you want to do, do it with new and more appropriate drivers and not the old unknow ones.....

Cheers.
Anil

 

[kaushik]

polycone tweeters are harsh sounding ...specially the ones i heard .all cheaper speakrs use them .
do think of replacing them ,with some silk dome

 

[quad]

You may be better off building a proven bookshelf design, perhaps
from one of the designs on parts-express, zaph or madisound forums.

Or, if you can find some way to get them from the US, there's a new
interesting set of speakers from Pioneer, designed by Andrew Jones.

Pioneer's new budget speaker designed by Andrew Jones - Blu-ray Forum

http://www.avsforum.com/avs-vb/showthread.php?t=1278774

 

[captrajesh]

1) Use Arta to measure the TS params. It only needs a cable, a resistor and PC with soundcard for TS measurement
2) Measure the Fs of tweeter and use twice that value as crossover frequency.
3) Use active crossover and power the drivers with 4 LM1875.

@goldyrathore

Thank you for the input. Actually, AFA technicalities are concerned, I'm a noob. Could you explain the concept a little more.

@biyer the tweeters are not so great but the woofer is very good. I tested with better tweeter and the integration sounded very nice to me.

In,fact, I did make the front baffle with 18mm ply but the work involved pasting the baffle permanently to the box and the existing system of baffle being fixed using screws would become redundant and I can't revert to the original design if required. Hence the plan is to make new cabinets altogether.

Thank you @wishihadtubes, yes I intend to do the speakers with proper binding posts. If I'm not mistaken, the curvy cabinets are made of identical slices of MDF pieces cut into the exact shape. Yes, it would involve lot of labour.

let us do this- with mdf and automotive lacquer

Yes, that is what is precisely in my mind. Jet black piano gloss finish.:licklips:

i need the internal dimensions

Here they are: Width - 11 cms, Depth - 12.5 cms, Height - 23 cms.

create a new (inert cabinet) with the same internal volume - and a slightly different (shapely and not box -like) exterior

What is your opinion of changing the volume slightly? Also, what about the shape that I have posted (Magico mini)

actually - i assumed that your plan was to change the acoustic portraits!

They are playing ok now after running the mid-woofer full range and not through the crossover. My next step would be to change the caps in the crossover to better ones but the manufacturer says he cannot divulge the values citing proprietary nature of the design.

@goldyrathore & @Ronnie, The make is "Top Audio" I picked them up from a sale organised at some foreign diplomat's place at Delhi when he was moving out. I picked them up sometime in 2002 for 2K.

@Ronnie, they are made of cone made of woven Kevlar fibre. Pics of Cross-over and the woofer are enclosed.

@anilva, yes, that is what I plan to do. Keep the volume near about the same but change the cabinet thickness, shape & bracing for better.

It appears that the existing crossover is fairly decent but I'm open to the idea of tweaking.

polycone tweeters are harsh sounding ...specially the ones i heard .all cheaper speakrs use them .
do think of replacing them ,with some silk dome

Yes Kaushik, that's what I planned. I've already bought fabric dome tweeters & plan to use them.

@quad, the point of the whole exercise is to learn the intricacies not to build new speakers. If it doesn't work, then I simply junk the mod jobs & revert to the original.

 

[GeorgeO]

I agree with Anil's suggestion.

 

[grubyhalo]

Cap'n, looks like you're on a DIY roll! Good luck with the project(s)!

capt..........i know the only guy who can make cabinets like that,,,he can make them to near perfection..............

he is too busy guy,, but will do the job and he is pricey tooo

thinks about it......

reddy

Hello,
Please could you share the contact details of this person with me? I am assuming that this person is in Chennai. Thanks much!

 

[captrajesh]

Cap'n, looks like you're on a DIY roll! Good luck with the project(s)

Thank you Ritchie. What about your projects? Hope you have not given em up post marriage.

 

[grubyhalo]

Thank you Ritchie. What about your projects? Hope you have not given em up post marriage.

No way! I've decided exactly what I need and right now am in the process of planning and checking out various options to source parts and to have them built. As usual, I'm waiting for the moolah to kick off the whole saga...

 

[suri]

hi captrajesh-

the magico mini shape and jet black piano lacquer (including about 6 coats of clear lacquer would be - A THING THAT IS BEAUTIFUL!

not sure how the curved shape would change the mid-range - BUT, I RECKON, IT CAN ONLY GET BETTER -

no point, i think, changing the crossover/values for this exercise - let the initial hearing session be a (pleasant) surprise.

individual MDF (three-fourth inch thick) cut similarly and stacked (with fevicol in between) will give you the required shape and internal volume. the volume calculation will have to be done as for an elongated pyramid and slight excess added for the curve.

one point to note is - do not make a separate front baffle - when the mdf is cut let the front baffle and the sidewalls be a single piece- better to make a removable top for access to internals. -and the thickness of the front baffle and sidewalls is to be decided by the DIY'er - possibly two and a half inches -if so, no bracing is required - the cabinet will be massively heavy and strong.

the magico mini uses multiple stacked layers of birch plywood - not MDF.

best of luck

regds suri

 

[captrajesh]

Thank you very much for detailed suggestions Suri. I appreciate em very much. A few points to ponder.

individual MDF (three-fourth inch thick) cut similarly and stacked (with fevicol in between)

Yes. I intend to cut the pieces and affix them stacked one over the other with fevicol. Is it ok to tighten them in place using screws to ensure tight bond or should I apply fevicol, stack all together and tighten the entire box with 'U' bracket till they dry up?

one point to note is - do not make a separate front baffle - when the mdf is cut let the front baffle and the sidewalls be a single piece.

Yes that is what is my plan. I'll make a small recess (3-4mm) on the baffle to affix a plywood piece wrapped with leather (to absorb baffle reflections) which will be slid into the recess (over the speakers) for a snug fit.

better to make a removable top for access to internals.

Is this required? Can't we access the internals through woofer hole?

possibly two and a half inches -if so, no bracing is required - the cabinet will be massively heavy and strong.

Won't it be an overkill. Size of the speaker would become huge. What is your opinion of providing internal bracing as in this pic below? May not be so many braces but may be one or two in the middle of the speaker which would also be held in place by vertical braces? I'm thinking of 1" thick walls.

BTW, Suri, you are the right person to ask; how much do you think this project would cost approximately?