improving speakers

sorry if this is rubbish for you, but in lack of a better place or forum to post i decided to write here(feel free to recommend me a better place to post). Unfortuntately i do not have the cash to buy hi-fi speakers or speaker boxes but i do try endlessly to improve the sound quality of my system. I live in Brazil, so you might not recognize the brand i'll talk about here, but hopefully it won't make a difference for me.
Sometime ago i bought a pair 3way speaker boxes in hope of enhancing the sound quality of my system(non-modular, sony fhw55av). The speakers on these boxes are one 10" subwoofer(QSL, 8ohms 100Wrms), one midrange(Overdrive) and one tweeter(QSL). Although the speakers by itself are good quality(not top, hi-fi, but good) it sounds a lot different than the sony's original ones(6"subwoofers, midrange and tweeter). They sound thinner and more concentrated on the mids, and due to this, i believe, it distorts a little bit. In december i decided to do something about it, and i dismantled the boxes in order to actually see what i had inside of it. Well, to my surprise, attached to the subwoofer was one component that i couldn't tell what it was exactly, but had the 15R 5W printed on it(i believe it is a resistor, but could not understand why it was there), to the midrange two capacitor and to the tweeter another capacitor(i could not read their values). Luckily, these boxes were not very expensive, R$350,00, both(about US$118,00).

To the box itself now. MDF, 55cm(height) x 33cm(width) x 30cm(length)(21,6in x 12,99in x 11,81in), 54,45l, vented, between 8kg and 10kg. Midrange and tweeter are side to side on top of the box and subwoofer on the bottom and centered. Looking from the outside you think there is a separation betweend these two parts, but guess what? there isn't, obviously. Does this configuration have any problems with phase delay?

What can i do in order to improve the sound of this? I was thinking about putting a lowpass filter on the subwoofer, bandpass filter for the midrange and highpass filter for the tweeter. All passive filters, 12db ones. Also, i am thinking about closing the space between the midrange/tweeter and sub, by putting some material(mdf probably) there. Then, midrange and tweeter would be in a sealed box and subwoofer in a vented one. I could also make the vents bigger to change the resonace frequency. Will this improve the sound of the box, or should i build an entirely new one from scratch and just keep the speakers?

I only found ways to build 2nd order filters with discrete components, i judge that by making the same association several times i will make higher order passive filters. Is this correct, or could anyone direct me to any tutorial of filter building?

As you could notice, the boxes are rectangular on the inside and outside. Does this form facilitates the creation of "walls" of sound? If i changed the inside to a trapezoidal form, would this make any difference?

Sorry for the extremely long post and thank you for your time for reading this. I hope you can help me with directions or lead me to a better suiting forum.

Thanks in advance for any replies.

 

Do the boxes have foam or fibre inside? If not, I would
get a sheet of soft foam, roll it up and put it inside before
you try anything else.

I do not know why there would be a resistor 15R 5W where
you said. You need to buy a multimeter [cheapest about 10US$]
Mail order if they are hard to find. This will tell you if it is a resistor. If it is between 1-3 ohms, it might be a choke [inductor] or an overload protector.
A crossover higher than a 1st order can damage your amp by
appearing to short out at certain frequencies, unless it is
the right values for the drivers. If you really want to try a
2nd order low pass on the 10" bass, you could use this URL:

http://www.eatel.net/~amptech/elecdisc/xoorder.htm

I wouldnt mess with the mid and treble capacitors. It's too easy
to damage parts

On the bass driver, I would measure the resistance with your meter
and design the 12dB crossover for double the DC resistance to be safe. This will give a slower cut-off, but is safer for your amp.
ie 5 ohms on a meter, choose 10 ohms for the x-over formula

 

graham, thank you for your effort on helping me. no foam or fiber inside of the box, plain wood. what kind of foam or fiber would be adequate to put there?

i looked at the capacitors connected to the midrange and tweeter. Two 22uF(parallel) to the mid and one 22uF to the tweeter. And i looked again at that part connected to the subwoofer to look at the scriptings: "15R 20W 10% 0,2 . 6"
i still didn't have the time to buy me a multimeter, but will do it very soon.

thank you.

 

There are a number of things you can do to enhance the sound of these boxes.

Stuffing is good !

look for dacron or long, haired wool or the stuff used to fill padded jackets. Do not used glass fibre as this has health implications. You need to fill the box so the volume of the box is full but the fill is not compressed,[as a rule of thumb].

Before that I would run a bead of silicon seal [stuff used in bathrooms to stop water getting down the back of the bath], around all the seams of each box....to make them air tight.

Next brace the cabinets by placing a 5cm by 2.5cm batten across the back and sides so that the batten crosses the mid of the boxes face and is glued to that face.

The front of the speaker is a little mor difficult. Find a point between the drive unit holes and place another length of your wooden batten so that the end touches the back of the cabinet and the other end the point on the front face, it should be tight and yuo may needa small hammer to knock into place if you are acsessing from the driver cutouts. When in possition glue in place.


Beg, borrow, buy some decent speaker cable about 1/3more than you need. THe extra thrid can be used to rewire the internals of the seakers. The rest is used to connect to the amp.

When you replace the drive units use a gasket to seal the drive units to the cabinets and prevent air leaks.

Place the speakers on stands so that the tweeter is at ear height when your sat in your listening possition. You don't need expensive stands just sturdy and stable.....I've seen garden stone plinths used or homemade types there are many on the web.

Hope this gives you some ideas.

 

To much stuffing can kill the sound, so be prepared to play around with the amounts. Large egg cartons can also help with standing waves.

You could also try adding soft foam to the outside (driver side), with holes for the drive units, a la Spica speakers, sometimes works very well, sometimes not - obviously the speakers loose their looks

 

i sure am getting some ideas. i decided that i will first fill the cabinet with the reccomended acoustic treatment and later on i will change the crossovers and midrange and tweeter.

by what i've been reading i am guessing that once i glue acoustic foam to the inside of the cabinet i won't be able to pull it out. so, this gives me no room for mistakes, right?

 

Nah Zullo, you can always remove the profiled accoustic foam.
Look, all this talk can help you learn about loudspeakers, and eventually you could design your own. But there is more to it than that: A good technical design does not make a good sounding loudspeaker. You may in the end spend a considerable amount of time and money on modifying what you have, only to find that a well reviewed diy kit will blow it away for much less money and effort. There are other ways to learn.
Yes for the money, kit's usually blow away the ready made product. It's an opinion, think about it: in order for Mr. Mass Hifi Company to put his product on the shelf at your local shop he has to make or buy loudspeaker transducers at about $1.75 each, and you have to pay perhaps $30.00 each. - And what do you think such a transducer is really going to sound like? Then there's the labour in making the box and crossover. At this level of expenditure brother, you should seriously consider cutting your losses & building from scratch from a respected and well reviewed design. You'll also learn some wood working skills.

 

thank you for clearing that stuffing business up for me.
unfortunately, here in brazil anything that comes from abroad has extremely high taxes(60% avg), not counting the currency conversion(US$1,00 ~ R$3,00). This takes me away from imported stuff. I am going to work only with brazilian material, less expensive. Also, i won't do everything at once. i will do things sparsely and very probably will be doing the improvement on my speaker boxes throughout the year. i am first going to stuff the box, believing that it is the least expensive of all my plans. Later on, i intend to buy a midranger and a tweeter(probably with 2 to 3 months between the purchases). Then i will play with crossovers. Right now i got a QS10P30 working as a sub and midranger(no low pass filter, here), one midranger from an unknown manufacturer(atlanta, that is) and a tweeter from the same brand. The high pass filter on the midranger is first order at ~ 850hz and the high pass on the tweeter is at ~ 1400Hz.

 

Zullo..

Oi..!! Tudo bem??

Where in Brasil are you from?

Ok.. speakers..

The suggestions so far are good.. bracing and stuff the cabinet are good ways to alter the overall sound of speakers.. stuffing will affect both the bass and midrange.. other things you can do are:

a) Enclose the mid range unit in it's own internal volume.. there are plastic "cup" shaped enclosure that you can buy.. you'll need to stuff it.. take out the mid range unit.. fit the enclosure in to the existing hole .. then fit the midrange unit back over the end of it..

b) Change the Capacitors for better quality ones.. if they are electrolytics..(very likely.. look for + and - signs on the metal case) .. change them for same value Polypropalene ones.
Note : Capacitors in parallel are equal to one capacitor of the sum of their capacitance. ie two 22uF caps in parallel can be replaced with one 44uF capacitor.

c) Change the internal wiring from the very thin stuff to thicker decent copper cable.

b) and c) are easy.. relatively cheap and should make a noticable difference... (especially the capacitors)

That "15R 20W 10% 0,2 . 6" marked thing attached to your 10" unit is a 15Ohm resistor..rated at 20W and 10% (of value) tolerance . It's probably there to change the resistance of the 10" unit as seen by the amplifier.. so it matches the impedance of the mid and tweeter units. Removing it.. will either overload the 10" unit or reduce it's output.. (depending on if it's in parallel or series with the unit).

Espero que isto te ajude

GTM

 

Cheap and easy stuffing? Try an old cushion or pillow

 

gtm, thank you for your broad answer. I live in campinas, sao paulo. i imagined that what i had connected to the woofer was a resistor, but have never seen one like that. I will follow those suggestions for now. Placing an inductor at the woofer will change the sound signifcantly? I am trying to have the three speaker play three different sound ranges, in hope that it will improve how it sounds.