[top]Speaker Design; Rules of Thumb
- Speaker design is FAR more complex than you think it is; in fact it's a lifestyle. If you're not thinking about designing them because you have a keen interest in subjects like mathematics, physics and biology then your interest in this subject is likely to be short lived. Consider browsing the many different designs on the web and constructing those instead as the designers will have already worked out the majority of the sonic issues already.
- Your listening space is just as important as your electronics and speakers; does it need room treatments?
- speaker design is about compromise; pick your compromises carefully because you can't build a perfect speaker
- audition lots of stuff to find out what you like;
- try to audition many amps with the same speakers in the same listening environment
- try to audition speakers with an amp that appeals to your style of music
- it's easier to get it wrong than right
- some seem to view the likes of Linkwitz, Burnett and Troels as deities to be worshiped
- your second design will be remarkably better than your first
- Simulate first and try lots of simulations to get a feel for how the response will change as you adjust the componets. This is especially important for passive designs as when you come to tuning you will be able to tune better if you know what components do what.
- Start small, maybe with a satellite project and a sub project
- Subs are generally easier to construct for first timers
- Do the following:
'What compromise best suits my specific needs'.
ie, Does footprint size matter to you?
Do you prefer BIG woofers?
Reflex, sealed or transmission line?
- A note on digital XOs:
You can always keep all music in the digital realm as much as possible. Rip it all to a lossless format, store it on a PC and play it back through digital outputs right into a DSP that accepts digital inputs.
- flat frequency response = good
- human ear is most sensitive between 2-4Khz; try to avoid crossovers in this critical range or take extra care to ensure that this frequency region remains flat through the XO (which appears to be nearly impossible)
- spend as much as you can on your mids; they generate the majority of the sound that your ear is most sensitive to
- crossovers are the hardest part to 'get right'
- active crossovers are easier for first timers to build
- passive XOs are very difficult to get right (took <name> 18 months, full time, to design his first commercially viable passive XO)
- active speakers offer less distortion because they don't need to go through passive electronics (amp has direct control)
- open spaces in the enclosure should never be square (standing waves)
- cylinder/spherical enclosures (for bass) are most efficient, but carry some drawbacks (I don't yet know *why
- but I'm reading as much as I can, in the spare time that I have)
- shape of enclosure is less emportant than the damping of the panel resonances and internal sound waves
- putting mid + tweeter closer together makes it easier to unify their images
- off axis performance is nearly as important as on-axis performance
- active XOs often offer less distortion than passive XOs; however, they're also generally more expensive
- Measure your drive units on and off axis to get some idea of the off axis response of your speakers. Consider at what frequency they will integrate best taking into account both the flatness of the response on and off axis.
- gfiandy - annecdotal info:
Here is a bit of my experience in tuning speakers although it is all only generalised and some drive units may respond differently.
Speakers with alot of energy arround 5KHz tend to sound very detailed but a bit harsh. Energy arround 8KHz tends to make the speaker sound detailed and tends to make the instruments highly defined in the image. This is not natural but some people like it. More energy through the 200 to 80Hz region will tend to make the speaker sound warm, too much and it will sound thick and boomy. The 2-4K region affects the vocal significantly and adjusting the phase of the crossove even if it doesn't have much affect on frequency response can adjust the presentation of the vocal.
- Active XO vs Passive:
low level circuits and active circuits create much lower levels of distortion than those that occur in passive crossovers and the distortion scales with the level.
It is not hard to create low level active circuits that have -100dB or greater THD. It is very diffcult to achive this for the large inductors that are used in a passive crossover. If you use large air cored inductors you can minimise it but the magnetic field escaping from them can easly couple into other inductors in the crossover creating a little transformer and causing crostalk from one part of the circuit to another. As the power level increases these inductors will get hot, something low level ciruits if properly designed should never do. When an inductor gets hot its charcteristics shift so its value will start to change.
But none of this is the main advantage of an active design. The main advantage is that the amplifer is directly coupled to the terminals of the speaker. This means that after a transient occurs and the speaker is returning to it resting position, it is a coil moving in a magnetic field so it will create a electrical signal. In a passive design this signal has to pass back through the crossover before it is damped by the amplifers voltage feedback. In an active design the electrical signal (back emf) is damped directly by the amplifier.
I could go on about this but much more is described on Rod Elliots site:-
His rational for using active crossovers is good but I think his design methodology is not. I don't agree with using restance in the output to adjust the roll off of the driver as this reduces the available damping of the back EMF. I would either design the box the right size for the response I wanted in the first place or use a electronic filter to adjust the response.
Designing good passive crossovers is very diffciult. There may only be a few components but just about every component intereacts with all the others in poorly predictable ways (this includes the speaker drive units). So none of the variables are independant, this make it difficult to tune. Due to the interaction of the speakers inductance with the crossover changing values somtimes has very different affects to what you are expecting if you think of it as a resistor.
- omnis and dipoles don't do well if close to a back wall; (wtf? omni, sure, but dipole?)
- At low frequencies (below about 500Hz, but particularly below 100Hz), the position of the woofer/subwoofer in the room dominates just about every other factor. Way beyond cabinet shape, cone material, box damping, ported or sealed
- For speakers that aren't total garbage, a cheap woofer in the right place will work a lot better than an expensive fancy one tossed in any old place. Two or more cheap subs in the right places will also usually work a lot better than one sub of high price. For heavens sake, don't restrict your low bass to have to come from the same place as your mids and highs! They have different acoustical placement requirements and the odds of the best place for subs being the same place as for tweeters is very nearly zero. Putting them in the same cabinet is a compromise right from the start. Get or build a couple of small active subs and experiment a little with room positions for them (use them as plant stands or hide them around the room to keep the SO happy). If done right, they will sound like nothing at all -- all sound will still seem to come from the mains but the mains will seem to have smooth tight bass instead of the usual lumpy mess.
- There's a lot of agreement (not universal, but almost) that off-axis radiation performance of the speakers is about as important as on-axis, in that the response off-axis should be similar to on-axis, but preferably dropping with off-axis angle. This is the failing of a large number of speakers, including many high priced ones. Floyd Toole's book would be well worth reading about this. Radiation pattern should be one of the highest design priorities.
- Crowhurst and Shorter - did work on correlating differences in amps to human sonics