I am developing an interest in 2.5 way designs. A couple of issues come to mind and I haven't seen much chatter in regard to them.
Number one is the issue of matching drivers. Most designs I have seen do use the same driver for the wide band woofer and the ".5" woofer. But is there any reason that completely different drivers could not be used such as an 8" and a 12"?
Secondly is it customary to use some sort of impedance levelling network to even out the resulting impedance variations in the low frequency range? what kind of sensitivity penalty would result from such a network?
Number one is the issue of matching drivers. Most designs I have seen do use the same driver for the wide band woofer and the ".5" woofer. But is there any reason that completely different drivers could not be used such as an 8" and a 12"?
Secondly is it customary to use some sort of impedance levelling network to even out the resulting impedance variations in the low frequency range? what kind of sensitivity penalty would result from such a network?
The whole beauty of the 2.5 way is getting better performance from cheaper woofers. At least that's how the industry thinks, more or less.
Also, two drivers from the same batch should match pretty closely with regards to efficiency and impedance. This greatly simplifies design.
But you could try using two different woofers. It will probably complicate the design.
Impedance matching woofers with resistors is folly. Are you going to use 25 watt resistors in your crossover? It has multitudes of drawbacks.
What you need to do is keep your eye open for higher impedance woofers. I've seen 12 ohm woofers and I should have bought them when they were available, because I'm thinking about a 2.5 way too. 16 ohm woofers aren't very common any more, except for maybe speakers intended for a line array.
Either that or you're stuck with 4 ohms; really closer to 3 ohms probably.
Not exactly, because the whole idea of a 2.5 way is for both woofers to work together below the baffle step. So if you achieve this, then you are still building a 2.5 way.
Of course, below a certain frequency, it will probably behave like a 3 way. So call it what you will- a "2.5 way down to 80 Hz" or whatever.
Absolutely.
indeed, but is often a faster/ cheaper way out than taking the time to get the overall design right.
I am going to have to chew on this. I have not heard what you are describing as a 2.5 way. Besides, why would you ever ask two different drivers to produce the same FR? Doesn't make sense in this guy's gray matter.
Come now Chris. Not like you to stir the pot like that my friend. If you have to add resistance to the bass, you have started out on and are continuing down, the wrong path, n'cest pas?
Wrong path? AR started this by including a 4 ohm resistor (optional) in the AR-1 to lower the mid-bass response of the grandaddy of sealed box woofers since at resonance 4 ohms in front of (say) 40 was imperceptible. And Bob Carver famously tricked people into thinking they were hearing a tube amp with the same trick. If it works, great. Use a 25 watt resistor. Or skinny wire. Air core coils. Try it you might like it. Conserving power is cool too.
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Compensation is usually imperfect so, what if you wanted to compensate 5dB, or 3?
At the same time you could use a larger unit to seek out some of the benefit of actual 3-way. Roll off your small woofer at the low end where your sub network comes in.
If your amp is a Voltage source (low Zo) then this won't become an issue. You can pursue it as an option.
I did a speaker a decade ago that was electrically a 2.5 way but acoustically a 3 way that used different size woofers. One woofer was a 18W8531 in an aperiodic enclosure and the lower woofer was a M22WR0908 in a vented enclosure. Acoustic crossover was around 125Hz and the drivers blended well but took a while to find drivers that had the required SPL, behaviour etc.
I still class it as a 2.5 way as that's how the power amp saw it as a load. Best performance was the lower woofer using it's own power amp. Some may call it a 2.2 system.
Yes it can be done if you choose the right drivers.
I still class it as a 2.5 way as that's how the power amp saw it as a load. Best performance was the lower woofer using it's own power amp. Some may call it a 2.2 system.
Yes it can be done if you choose the right drivers.
In general, I agree. But with regard to asking the drivers to produce the same FR, that's only correct below the baffle step.
It's all a matter or whether you can glean an advantage or not by using two different woofers. If you're going budget, say 4 woofers for $100, then the best and easiest thing to do would be to use the same woofers. But some nicer woofers might be chosen because maybe they have the midrange extension you need. A really nice 8" woofer for a two way is going to cost more than your budget woofer. Its midrange extension would be wasted on the lower woofer. You might be able to get a less expensive woofer to play nice with the other woofer below the baffle step, which is all that matters.
A definite disadvantage is that trying to use two different woofers will complicate the design. I've been thinking about a 2.5 way and if I can save $50 or $100 on my design and get essentially the same results, then that's the way I'm going to go. I haven't really committed to any design.
I can see using different woofers in a 2.5-way as an added tool. You can boost via different amounts just by varying the secondary driver sensitivity. This also rolls off the lower range woofer through the 2-way xover, so it can further attenuate problems in either unit for breakup etc. You could place the upper woofer in a different alignment than the lower, and make their outputs combine more to a goal.
It's doable, and just another tool to use,
Wolf
It's doable, and just another tool to use,
Wolf
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