Loudspeaker Electronics

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#62
Sorry if my post was misleading. You only need one of the two inductors either the 2.8A or the 4.5 A part.

I would go with the 2.8A amp part as I don't belive inductor saturation will be the limiting factor in sound quality.

They are listed at £3.22 each and you will have to pay postage as well so it would be worth working out all the stuff you want and ordering it all in one go.

Regards,
Andrew
 
#63
Hi gfiandy. Re the x-over. I've got no problems with the low pass section but I am not 100% sure about the feed to the tweeter. If it is still the piezo horn that was originally metioned it might be worth checking it. Bost (I think that's how you spell it) did the original development of these tweeters back in the '70s while working for Motorola. (CTS subsequently took over their production but I understand they have stopped now.) In his papers (2) published in the JAES he attenuates the unit with series capacitance. (Due to the nature of the piezo, which is capacitive, this lowers the whole range uniformerly.) Values from 0.1uF up to 1uf were typical. A series resistor is used to reduce the high frequency component. Something in the range 10-50 ohms from memory causes a gentle roll off and was used as safety measure to protect against supersonic frequencies. So I'm not exactly sure the potential divider as suggested will achieve the desired results.
 
#64
Hi,

I belive the impedance of these parts varies from approx 50R to approx 250R accros there working range.

Hence a very approx crossover can be made by bypassing it by 47R and using a series resistor.

Doubtless a better response can be had with better crossover but this was just to get something that doesn't sound broken and is easy to adjust.

Regards,
Andrew
 
#67
I have now received the skytronic speakers.

The woofer has a foam ring around its face with six screw holes. Is this for the purpose of producing an airtight seal, and therefore means that the woofer is to be mounted on the inner side of the MDF as opposed to the outer side?

Also, where the metal screw holes are, they are slightly obstructed by what looks like the edge of something rubbery (probably parts of the cone) - is it normal for there to be a slight overlap and is it ok for me to simply drill through this?

Is there a particular type of screw/bolt that I should use to mount the speaker, and will this create enough force on the foam to make it airtight or do I also need to glue it?

Here is a picture of my design which I need to show you in reference to the final questions.

http://img167.imageshack.us/img167/5079/perfectedfinalmodelyn7.png

The tweeter box is mounted above the woofer box on a hollow metal cylinder. The wiring from the tweeter will be run down this cylinder and go into the woofer box. How should I go about routing the wire through the MDF top face without losing the airtightness of the enclosure - would a simple drilled hole filled with high strength glue around the wires do the job ok?

As recommended, I am using wooden battens in each corner to improve structural integrity. Is the cube batten structure strong enough, or will I need some extra bracing?

Thank you for any answers, your help is appreciated 🙂
 
#68
The inductor high current torroid from maplins is not designed for audio and its value is less than half what you need. You could try two in series, but I don't really know how well it will perform at low frequencies. Maybe someone else can comment on this.

The ones labled RF chokes are not at all suitable as they won't be able to take the current.

You can normally just push through the rubber in the mounting holes with the mounting screw. Don't use the drive unit as a drill guide you will fill it up with MDF dust mark with a pencil then drill the holes. The drive unit can be mounted from the inside or outside but will look neater inside. To mount outside you will need something to make a gasket to go on the back so I wouldn't do this.

Normally speakers are held in with cap head screws, but any wood screw that fits will be OK. Its best to use a small pilot hole in MDF so it dosn't split near the edge of the drive unit hole. No need to glue the screws will give you a good enough seal.

A small hole for the wires can be sealed with mastic like bathroom sealant or glue.

Regards,
Andrew
 
#70
Hi,

It may be possible to remove the gasket and transfer it to the rear
of the chassis if you are front mounting the driver. It is somewhat
normal in cheaper drivers for the surround to obstruct the mounting
holes. I'd use a sharp edge rather than a drill.

FWIW I expect the 70p tweeter to sound dreadful. It may look like
a Motorola piezo but I believe at this point any similarity ends.

🙂/sreten.
 
#72
Yes the inductor limits the high frequency to the woofer.

If you are thinking of leaving it out you need to leave out the cap on the woofer as well; as a pure capacitance accross the amplifer will could cause damage and without the inductor it won't work to limit the HF.

Regards,
Andrew
 
#78
I don't understand why they have any reason to charge a total of £17 for a small component that costs around £5 and should cost no more than a few quid to post.

They seem to add loads of extra sub charges to try and rip you off as much as possible as I see it. Take a look at this screenshot:

An externally hosted image should be here but it was not working when we last tested it.


Perhaps I may not be able to get the actual component cheaper elsewhere, but surely, I can get the total price including delivery for a much more reasonable price somewhere else.
 
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