low on cash, need advice on driver selection etc. please.

[Kram]

Hi everybody

Not so long ago the speaker cones on my dads speakers broke (old age i think) and ive been wanting to find some replacements.
what i require advice on is erm, everything basically.

I had origanally planed on just replacing the driver but upon inspection of the speaker i found that the cross over consisted of a 3uF capacitor only, and after reading on this site about speaker design i began to think that just one capacitor just didnt seem very good so now i want to build a cross over as well, then i thought that i may as well buy a new tweeter too.

Now the question is can anyone recomend a decent sounding mid/bass driver and a tweeter that will cost between 20-30 UK Pounds each and roughly the same for crossover components too.

By the way i am looking to keep the cases we allready have which has an 8in cut out for the mid/bass driver.

any help appreciated.
thanks.

[kelticwizard]

Can you give us the dimensions of the speaker? If you don't want to mess with inside dimensions, just give us the outside dimensions-minus any overhangs-and the thickness of the particle board.

Do you prefer a sealed or a ported design? Does it make a difference?

[bostarob]

That cap buffers low frequecies from entering the tweeter. The simplest crossover there is, but not the worst. If done well, it can sound quite good. Chances are, if you buy new drivers, you would need to design a crossover taylored for those drivers anyway. 8" cut out, eh? A typical 8" driver would not fit. The HiVi F8 ($60 US from partsexpress.com) is an 8" speaker with a huge mounting flange. It should fit.
Before one designs a xo, one chooses drivers.
We need cabinet dimentions, or volume if you can multiply.
-andy

[Thatch_Ear]

Before you do anththing are the speakers blown out ,or is it just the paper breaking uo around thr edges.If it just blown foam edging sets can buy sets with glue, surrounds and insructions, but if the paper is shot or threre are places where the coil(s) rub you wikk need a complete rebuilding
Is thre any chace that the drivers are painted a bright bleu and have a golf sticker with name Frazier. Those you rebuild.

[Kram]

speedy replies, thanks guys

Thatch_Ear
The drivers are well and trully dead but thanks for the idea any way.

bostarob
You seem to think I have mesaured the size of the driver wrong and you are probably right, so can some one tell me how to measure the driver eg from where to where do i measure?

Ok, the internal dimensions of the box are, height 16in, width accross the front 9in and frount to back are 8in which if im correct works out as 1152 cubic inches which = 0.666cubic feet.

The box is not ported and i really dont want to have to make them ported because i dont have a router but if you think it will make them sound much better then i could always see about buying/hiring one.

What do you think about Audax speakers?
There is a shop near me that sells them which would mean i wouldnt have to pay postage and packaging like i would if i orderd from the net.

Final question, how much on average do the parts for a crossover cost?

thank you.

[kelticwizard]

Unless you plan on using a subwoofer with these 8's, I suggest a ported design. The ported design allows the speaker cone to move less while producing bass, which gives a clearer sound throughout the midrange.

Danish-made Peerless is always a good place to start your search for a woofer. As a rule, I find that they usually incorporate design items that frequently are only found on more expensive speakers.

The Peerless 850136 is an 8" woofer that has relatively smooth response up to 5,000 Hz. They recommend that you cross over to a tweeter at 3000 Hz. Below is a frequency response chart for an unenclosed 850136. If put into your box, it will be 3 dB down from the midpoint at 55 Hz.

It has a magnetic structure that allows linear movement in a bass reflex enclosure-not every speaker does that. Very low distortion near resonance.

It costs $45 at Madisound in America-but I guarantee you, it is available in England. Probably at a similar price. I mean, they are made in Denmark. So that would be what-about 30 pds? That is within your guidelines.

To find an English dealer, Email the following address:
E-mail: post@d-s-t.com Peerless is owned by Dansih Sound Technology. Or perhaps one of the English members here will tell you where he gets his Peerless from.

[kelticwizard]

Just for the heck of it, I ran the simulation for this woofer in a box your size on WinISD. In a .66 cu ft box tuned to 47 Hz, (a 3 in diameter pipe of 10.5 inches length), the speaker is 3 dB down from midpoint at 51 Hz.

I can run the same program with metric sizes, if you tell me what metric sizes are available.

The blue line is the midpoint, the green line the -3 dB line.

I am not saying that absolutely this is the speaker for you. By the way, it is 4 ohm-is that a problem? I am just giving you an idea of what is possible. I think this woofer is a good choice, but it need not be the ony one. I am sure that other members have other good choices for you to consider before you buy.

[bostarob]

you may not need a router, a hole saw would work fine, assuming you know someone with a drill press. PVC pipe works great for ports.

I don't think you measured wrong, but maybe you were not specific enough. Is that an 8" diameter hole in your box, or an 8" diameter driver? If the latter, I would second the peerless. A fine choice.

A crossover that i would design for this would cost 20 or 25 dollars a speaker. I don't know what that is in pounds, maybe 10-15? This crossover would be a 2nd order topology, (easier than other topologies to make and design, at least to my knowledge) slopes are of 12 dB per octave. It is likely you have no idea what I just said, but we'll talk you through it, be not afraid to ask.
For a simple xo, I would do a basic 2nd order centered at 2k to 3kHz.
Actually, the peerless rolls off nicely at 4.5kHz, so you could simply put a cap of correct value (youll have to experiment)in line with your tweet. As I said before, this can be very good (and cheap!). But your off axis performance will suck(sweet spot speakers).

If I wanted to get a little more complicated, I would consider the 3dB bump in the peerless's response around 1500 Hz. A first order (6dB per octave) low pass centered at 1500 would take care of that. The actual -3dB point would be closer to 2.25kHz. Then for the tweeter, a 2nd order high pass centered at 2.5 to 3kHz (again, you'll have to experiment). I think this would be the best solution.
-andy

[kelticwizard]

Yes, deciding what size hole goes to what size speaker can be deceiving, since the hole is often surrounded by an indented groove in which the speaker frame rests.

Complicating matters is the fact that the cutout can vary for different model speakers rated the same size-8 inchers, 10 inchers, or whatever.

For what it is worth, the Peerless 850136 requires a cutout of 184 mm or 7 3/8 inches, minimum. It can be a tad larger than that for ease of installation-the centers of the mounting holes are 206 mm, or 8 1/16 inches, apart. So the hole cutout should be okay if it is between 7 3/8" and 7 7/8" diameter.

One British pound is currently equal to $1.42 American. Mentally, I've always just rounded it off to "about $1.50".

[SteveG]

Kram,
I'm not trying to discourage you, but I have experience with what you are doing, and now I know better than to attempt it. It is a difficult way to go to get a good sounding speaker!
If I were in your place, I would consider starting over completely- especially if the speakers are older than 15 or 20 years. If you look at the cabinets, what are they made of? If they are made of plywood, or thin material (less than 3/4") they really aren't worth putting new drivers into- this is even more true if you have to go cutting on them make them fit anyway! It is very unlikely that you will find a direct drop-in replacement that will sound good. All I'm saying is that it is money better spent on something else. You would be amazed at the quality you can achieve if you have a design that uses drivers that really work together, which is much easier to do if you don't have other limitations imposed on you from the beginning.
If, on the other hand, you are interested in keeping the cabinets and you can do a little simple woodworking, I may have another route for you. Cut out the old baffleboard (board where the speakers were mounted) and replace it with a new one made of 3/4" medium Density Fiberboard. Cut braces and brace the cabinet up internally to stiffen it. This gives you more versatility in what drivers you can work with- all you have to contend with is a known cabinet volume. If you're going cheap on the crossover, I would consider finding a mid/woofer with a nice and smooth natural rolloff, and consider running it without a crossover. That way, you can just build a crossover for a tweeter to match it- very simple and has been used in tons of designs over the years (usually with just a cap, as your speakers were).
Also, If I am remembering right, the cabinet volume you have would fit a Vifa P17WJ pretty nicely, and it is a really easy woofer to work with. The only problem may be the price, which is about $35-40 US, but worth every bit. You will also find 10000 crossover designs for this woofer on the 'net.
Just a few thoughts.
Steve