first baby ~ scan speak 25w8565-01

[fatboyphilp]

Hi,
I've never made loudspeakers before. All I know is that if I don't. I will die unfulfilled. I need to hear from those in the know (my friends and partner think I'm nuts).

Firstly, I am restricting myself to a particular amplifier set up. Rega Mira3 + 2x Maia3 power amps. I want to tri-amp my loudspeakers. The choices are many fold. At 8ohms the mira3 gives 60w per channel and each maia3 gives 85w per channel. However, at 4 ohms, the mira gives 91w, and if each maia3 only drives 1 channel at 8 ohms they provide 100w.

There are two questions; if I went for scan speak D3004 602000 treble, ss 12m 4631g00 - (combined nom power of 90w) through the Mira3. Then each maia3 powering a 25w 8565-01, would that work?

Question two; Fostex ribbon tweeter through mira3 at 8 ohms - amp 20w under nominal power, ss 13m 8640 through first maia3 at 8ohms - amp 15w under nominal power and 25w 8565-01 through second maia3 15w under nominal power, would the result be massive clipping even at 3/4 volume? (never listen to music too loud, seriously, never!)

[5th element]

I think you've missed the point.

Amplifiers have a maximum output they can provide, regardless of the loudspeakers watt rating.

If you've got a loudspeaker rated at 10 watts and you power it with your Mira3, it will all sound 'fine' up until the point where the loudspeaker fails. After this point it wont sound fine, the drive unit will be damaged and will need replacing.

On the flip side, if you've got a loudspeaker rated at 500 watts and you try the same thing with the Mira3, it will sound 'fine' up until the point where the amplifiers output stage can no longer keep up with the demands placed upon it and the signal clips. Now it will sound bad and if the amplifier is suitably designed, nothing will be damaged, not even in the long term. When you turn the volume down and the output of the amplifier is no longer clipped, the distortion will go away and it will sound good again.

In simple terms your Rega amps have more then enough power to produce decent listening levels with any loudspeaker that isn't either a)incredibly insensitive, or b) very difficult to drive.

If you're interested in building a three way loudspeaker, your best option is to build a design by a competent designer. This way you're practically guaranteed to get good results providing you follow the design exactly and that your carpentry skills are up to building the required boxes.

http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm

http://www.humblehomemadehifi.com/

http://www.rjbaudio.com/projects.html

http://www.zaphaudio.com/

Are websites with a whole variety of designs and are also filled with lots of useful information.

[fatboyphilp]

Cheers, as you can tell I know nada! Interested in what happens when two 4 ohms drivers are driven by a Mira 3? Does this mean the impedance is 2 Ohms, or does the cross over deal with the impedance , leaving the amp output relative to the 4 Ohms initial demand?

What about tri-amping, are active cross-overs better?

I am a novice, cheers John

[sonenelson]

WIKI HAS A GREAT PAGE TO GET YOU STARTED WITH UNDERSTANDING CROSSOVERS

http://en.wikipedia.org/wiki/Audio_crossover

[fatboyphilp]

I'm confused! A good read of links provided including wiki.

Having enough power in my amps to drive my chosen speakers; according to some sites and notable companies, a larger percentage of damaged loudspeakers is due to clipping from under powered amplifiers.

Crossovers managing loud speakers with impedance differences, drain more power than crossovers that manage drivers with the same impedance.

Keeping the volume down is the best bet, but are there monitors to show the point the power from the amplifier becomes to little/drained and starts to clip? Or is this just silly?

[5th element]

Originally posted by fatboyphilp
I'm confused! A good read of links provided including wiki.

Having enough power in my amps to drive my chosen speakers; according to some sites and notable companies, a larger percentage of damaged loudspeakers is due to clipping from under powered amplifiers.

This is true, however I think people who blow drive units are sort of asking for it. When clipping occurs, even quite mild clipping, it sounds pretty bad, so you're just asking for trouble if you want to turn it up higher.

Crossovers managing loud speakers with impedance differences, drain more power than crossovers that manage drivers with the same impedance.

Not quite. Loudspeakers with a lower average impedance will present a harder load to the amplifier, demanding that it delivers more current. The lower the impedance the harder the loudspeaker is to drive, and hence will most likely cause clipping earlier on as the output stage in the amplifier fails to provide the required current.

The crossover is used to 'knit' the drive units together. And although the crossover alters the impedance of the final loudspeaker, it's the impedance of the raw drive units that really set the overall impedance of a design, as long as the crossover isn't poorly designed.

Keeping the volume down is the best bet, but are there monitors to show the point the power from the amplifier becomes to little/drained and starts to clip? Or is this just silly?

You could create such a device. But keeping the volume down is the safest bet. If the sound is clean and dynamic you're probably not clipping the amplifier. If it starts to sound worse that's a good indication that you're starting to push things and should back off a bit.

Interested in what happens when two 4 ohms drivers are driven by a Mira 3? Does this mean the impedance is 2 Ohms, or does the cross over deal with the impedance , leaving the amp output relative to the 4 Ohms initial demand?

The Mira 3 has two channels of amplification and most like one transformer in the power supply.

If you were to connect one 4 ohm driver directly to one amplifier channel, this would present a 'nominal' 4 ohm load and the amplifier would respond accordingly.

If you were to connect another 4 ohm driver to the other channel of the amplifier, both channels would now see a 4 ohm load as they are entirely independent of one another. However there is also the possibility that the transformer in the power supply is underrated. This could result in a single channel being able to deliver say 100 watts into 4 ohms. But if both channels are used they each only manage say 80 watts.

If you connect two 4 ohm drive units in series to the output of the power amplifier the amp will now see an 8 ohm load. If you connect them in parallel the amplifier will now see a 2 ohm load.

Say you've got a two way loudspeaker with a 6" mid/bass and a 1" dome tweeter. The crossover point is set at 2000hz. In an ideal situation the crossover on the mid/bass will increase the impedance of the mid/bass section, with rising frequency, as we approach and pass the 2000hz mark. The tweeters crossover will do the same but in reverse, increasing the impedance with decreasing frequency as we approach 2000hz.

This means that at say 100hz the tweeters impedance can be considered infinite.

The formula for two resistors (or drive units) in parallel =

1/R1 + 1/R2 = 1/Rtotal.

So at 100hz

R1 = the mid/bass = 4 ohms
R2 = the tweeter = 1 million ohms

We end up with Rtotal, the combined resistance = 3.999984 ohms, or 4 ohms.

The same happens the other way around at high frequencies, where the tweeter = 4 ohms and mid/bass = lots.

As you can see the crossover, if properly designed, marries the drive units together, so that a nominal 4 ohms is seen from 20hz-20khz.

What about tri-amping, are active cross-overs better?

Tri-amping can refer to two things.

1) The loudspeaker is three way and has a passive crossover and you connect a separate channel of amplification to each drive unit. This has benefits. If one section of the loudspeaker is VERY difficult to drive, say the bass drivers. The loudspeaker could wire two bass units in parallel for an average impedance of 4 ohms, whereas the midrange and tweeters are 8 ohm. If wired to a single amp this could cause heavy bass to clip the amplifier, sending a highly distorted signal to all three drive units. However if tri amped the bass drivers amplifier would now clip, but the midrange and the tweeters wouldn't, keeping the sound cleaner.

2) The loudspeaker is a three way and has an active crossover.

In a passive crossover a flow diagram of the signal would look like this.

CDplayer => Amplifier => Crossover => Drive unit.

Here the amplifier amplifies the entire audio signal, then the crossover filters it out at a 'high' level before the signal reaches the drive unit.

In an active crossover a flow diagram would look like this

CDplayer => Crossover => Amplifier => Drive unit.

In this instance the signal is filtered at a 'low' level, BEFORE the signal is amplified. Now the amplifier only has to amplify a small portion of the signal, rather then all of it. Not only this, but because the filtering has been done already, the amplifier can now connect directly to the drive unit, without a crossover in the way. This increases the control the amplifier has over the drive unit and for a number of reasons results in active crossovers being superior to passive ones.

By definition a three way active loudspeaker requires 6 channels of amplification to work (stereo). Whereas a three way passive loudspeaker gives you the option to use a single amp, to bi-amp or tri-amp.

Active gives you way more flexibility when it comes to design and also produces the best results sonically. However they are somewhat harder to implement then a passive crossover for beginners of DIY and require a different set of skills to effectively construct. Not only this but there are very few designs based around active crossovers.

One website that has designs is

www.linkwitzlab.com

If you were to build an active loudspeaker I strongly recommend you choose a design which provides you with the crossovers already built. If you're feeling adventurous you could perhaps buy the active xovers in kit form and solder them yourself.

But as this would be your first attempt at DIY loudspeakers, I'd recommend you build a passive loudspeaker of proven design, as per the links above.

[fatboyphilp]

Cheers! I am going to get a firm to build passive cross-overs for me. With the stereo amplifier and two stereo power amps, I can deliver the exact amount of nominal working power at the corresponding impedance - when the volume is turned up full. Now I can be sure there will be no clipping.

Thank you very much! All very useful.

[5th element]

I hope the ones you're getting built are to a proven design, or the firm building them is going to measure the drive units of your choice in a completed box, then design the crossover from that. Otherwise the results could be less then stellar.

I'm only saying this because building a passive crossover is not hard in the least. In other words, you'd be far better building one of your own, then getting some firm to make a random crossover that's 'supposed' to work with XYZ drivers.

I cannot stress enough the importance of a good crossover, this is what can make $100 worth of drivers sound like an 'audiophile' grade loudspeaker. Or can make $2000 worth sound so unpleasant that you'd rather turn it off.

Folk here will be more then happy to answer simple questions regarding the assembly of a crossover, or about what parts to use, if you choose you build them your own.

Note when I say building a passive crossover, I mean just that, putting the parts together. Designing one is a totally different game.