3" Audio Nirvana 2-way project
For starters I would like to thank member StevenZ for completing my "mini monitors" using the AN 3" driver. From 80 Hz and up they are perhaps the best sounding and most balanced speaker I've heard to date at low levels. I am reluctant to really drive this speaker to higher levels as it really not meant to be a massive bass producer.
Its imaging characteristics in the midrange and wonderfully smooth highs is what I like most about it. Its midbass is also surprisingly good. Unlike most other full rangers, its on-axis response is very controlled and non-fatiguing.
I would now like to tackle building a 2-way speaker using this driver and an appropriate woofer. My preliminary search has led me to the Seas Prestige ER18NRX 7" woofer priced at $92 from Madisound as used in the Zaph ZR71 speakers. The efficiency and impedance's are very closely matched.
Speaker Building Supplies from Madisound
Audion Nirvana Super 3
Almost all the competent 2-way designs that I have come across use a woofer and a tweeter crossed in the 1,500 Hz-3,500 Hz region. My outside the box thinking is wondering what a 2-way speaker will sound like crossed much lower, perhaps as low as 400 Hz.
I first thought of the concept "Double Driver Dynamic Loading for Low Q Drivers" from this website. From my memory all they did was run the drivers in parallel to "bump up" the bass output.
I cannot seem to find this article any longer, and if anyone has saved this information or know of a different source to locate it, I would greatly appreciate it!
Most of the woofers I have looked at do not roll off sharply enough below 400 Hz to allow the woofer to roll off naturally, so a choke circuit of some kind will need to be used. I'd like the crossover to be as minimalistic as possible with a single inductor and capacitor network. If this proves to be the wrong method I will of course consider other alternatives.
Anyone with any suggestions or comments would be most appreciated.
Search on FAST's. Ideally you want a bass unit 3 or 4 dB more sensitive
than the FR and cross it over 1st order series at around the baffle step
mid point to give around 3 or 4 dBs worth of baffle step compensation.
What sreten said.
Some examples that we did;
There are more than a few others, particularily with OBs which almost force this approach.
Here is a 1st pass of our current FAST project.
Where would I reference the FAST principle. I can't seem to find the threads with a simple search
Here's one I recently did. Unusual goal in this one though.
Simple networks are very easy for a fast, except you do have to consider the Fs hump of your mid tweet. With only one cap, you'll likely still get a big output at Fs (or what ever the impedance peak is in the box). At higher levels this will sound really grunty. Also on the woofer is the natural inductance impedance rise. A single choke will only give 6db/oct at best. Often less if the woofer impedance rises quickly. Consider a zobel, or a second order filter.
Also consider that woofer breakup needs to be wayyy down on that woofer if you don't want to hear it. If you crossed at 300hz 1st order on that woofer, the break up would be down 24db. But consider that it's about 12db above the output at 300hz, it will actually only be down 12db. And it'll sound nasty.
I used second order on the speaker I linked to combat these issues.
Here is an example of the Fostex FE83. Blue is the box plot (just a simulation, not the real thing) and Red is the driver output with a single 30uF cap in series with the driver. At the impedance peak, the cap is very ineffective at the driver is almost outputting its full sound right there. Also has hardly any power handling as a result. May as well be running full range.
It's a similar, but better result with a series cross over.
Thanks for those plots. Would a second order Linkwitz-Riley network be the best bet for this situation and proposed drivers? Think this combo could "work" without noticeable differences in response with the correct crossovers?
Either a second order or an impedance compensation circuit. Dave might know a handy way to knock down the impedance with clever box design, but I can't help you there. Cap and coil would definetely solve the issue. For the Fostex FE83 I ended up with 30uF and 2.2mH. That gave a smooth roll off at 12db/oct.
And trust me, that woofer breakup either needs a notch, second order, or both. Again, maybe Dave knows how to treat the thing to make the break up benign. My silver flute woofers were treated and when I listened to them full range the break up was extinguished. There was still a measurable peak in the response, but the nasty sound was gone. I used 3mH and a sorta zobel. 72uF and 2ohms. Gave a little peak in the 150hz area, but it had to be done to achieve my other goals.
All of the above pretty well demonstrates why FAST has to be active crossed. Then you do not care about the efficiency of the two drivers. All is handled in the DSP or by adjusting the volume of the separate amps.
I've had to use an active crossover on most of my other speakers for similar reasons, but was hoping a passive network could serve the same purpose.
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