Full-range speakers in a bi-amped system?
I like the idea of full-range speakers. The simplicity and the potential for high performance appeal to me. I like the fact that there are no crossover components (in my speaker projects of the past, the crossover has been the most difficult part to get right, and as time has gone by, I am leaning more and more toward an approach that does not use capacitors or inductors in the amplifier/speaker circuit). I currently have a Tang Band W8-1808 project in motion, and I recently conceived of another idea on which I would appreciate the opinions and advice of other members.
I have wanted to try a bi-amped system for some time, and I had originally planned to build some sealed boxes with a 12-inch woofer powered by one amplifier for the bass frequencies and a first-order two-way combination powered by another amplifier for the mids and highs. I am now thinking of trying something else involving a more compact and efficient combination of drivers and cabinets. My current idea is to combine an efficient woofer of perhaps 8-inch size in a bass-reflex box with a small full-range driver in a separate box, with each speaker driven by its own amplifier. I may combine the two speakers into one enclosure with a separate tuned chamber for each driver.
My original thought on this was to use a sealed enclosure for the full-range speaker, with the crossover point in my preamplifier at 300 Hz 6dB per octave. For the most seamless transition to the woofer, this would require the full-range to be fairly flat to about 75 Hz. The small full-range speakers I have examined with software do not model that low---the common cut-off point seems to be about 100 Hz or higher in a sealed box.
I am now considering using the the full-range driver in its own ported chamber along with the woofer in its separate ported chamber. I have never heard of this being done before. Would the use of separate ported chambers producing differing frequencies in close proximity to each other present any odd phase relationship problems? I can not see why it would, but I am still a babe in the woods when it comes to DIY speaker design.
My motives for considering this project involve a desire to build a fairly efficient speaker combination that avoids the problems of both the multi-driver-with-crossover combination and the single-full-range-driver approach. It seems as though it should work fairly well.
I have found a number of efficient bass drivers that will work well in a ported box. The choice of full-rangers for the mids and highs is a bit more challenging, as I want something that is small enough to serve as a point source without too much beaming or too high a rising response while still having the low-end response to mate well with the bass driver. At present, the Tang Band W5-1611 looks pretty good, but I can't find out much information about its off-axis response.
If anyone could fill me in on the off-axis reponse of the W5-1611 (or any of its other characteristics), please let me know. If you have any suggestions for another small full-range that might work (given my requirements), please let me know that as well. Any and all comments and opinions will be appreciated.
Comments? Opinions? Helpful suggestions?
What you are describing is a FAST. There are a zillion possibilities and they can end up being VERY good.
Biamping gives you many more options than XOing passively. Using a (normally) ported box for the midTweeter is usually not a good idea, as the extended LF is accompanied by much more severe phase issues and a much harder (if possible) task of getting a seemless XO.
I started this thread (http://www.diyaudio.com/forums/full-...ions-fast.html) to promote the idea of FAST and to show some examples. It spawned a number of other threads plus there is and has been considerable coverage independent of this (Martin King's passive OB is a good example)
I second what Dave said.
I'd love to see, say for instance, an FE126En, perhaps touched up a tiny bit with some careful EQ'ing, seamlessly paired with a sensitive 10" or 12" woofer, electro-acoustic xo probably around 400Hz or so (1st order electrical, 2nd order acoustic on the full-ranger, and 1st or LR2 on the woofer).. vented or MLTL or some such, with solid in-room response down to 25-30Hz. How about a bunch of these for an 11 channel Audyssey DSX setup? :cool:
Just thinking, you know. :D
Forgot. In regards to the W5-1611 (there's a cheaper ferrite version now too), I have no personal experience with it. However, I've come across several positive comments from proud owners in the past. I'm sure it's a great driver. On the other hand, however, it's a poly cone. While polypropylene cones have some big advantages, I've come across far too many comments over the years about negative qualities of poly cones when used for mids and full-range. I can't say with certainty that I've had any real experience with using polypropylene cones for anything other than woofers, so take this with a grain of salt. All I know is that there are plenty of people out there who won't use them. So, that might be something to look into. As for off-axis response, it's probably pretty typical of most 5" full-range drivers. At a far enough listening distance, it shouldn't be too bad. At 30 degrees off-axis, response will probably drop somewhere around 5 KHz. At farther angles, such as 90 degrees, pretty much everything above a few inches in diameter will begin to fall off somewhere between 1 to 2 KHz.
What you are thinking about doing is a great idea. Go for it!
My W3-1364 passive 2-way biamped with the VIFA NE265W. The W3-1364, when used alone, was simply too dull and muddy for me. Sounds much better with a Vifa XT25.
Thank you all for your replies so far. They present exactly the kind of information I am seeking. A few more questions:
Dave, can you elaborate on the potential phase problems from using a ported box for the mid/high driver? How would this approach make a good crossover transition to the woofer more difficult?
My hope is to use a simple first-order 6dB/octave active crossover at 300Hz in my preamplifier to feed the two power amps. Are there any reasons not to use this approach?
My current thought is to employ a Peerless 830869 8 inch driver (good sensitivity, flat response, plays very low in a ported box) for the woofer while using the full-ranger (I am leaning toward the TB W5-1611) in a separate ported chamber (again, they may share one speaker structure). The Peerless driver has a truncated frame that would allow it to be mounted close to the upper edge of its enclosure , and I would mount the TB close to the bottom edge of its enclosure, to avoid problems of lobing between the drivers (with the dimensions of these drivers it works out well in theory). The TB baffle would most likely be recessed from the plane of the Peerless baffle in an effort to achieve time alignment between the drivers. So, the orientation of the drivers and ports on the face of the speaker from bottom to top would be: the port for the Peerless, the Peerless itself, the TB, the port for the TB. Are there any reasons that this should not work well?
Again, my goal here is to build a good-sounding bi-amped system without any resistive, capacitative, or inductive elements between the amplifiers and the drivers in an effort to avoid some of the problems of both the multi-driver and the single-driver approach. It seems like it should be possible.
Thanks again for the replies. I will definitely check out the FAST concept.
Edit: I assume that FAST is an acronym for the words in the name of the concept. To help me in my search, can someone tell me what those words are? Thanks.
FAST = fullrange assisted.
FWIW any 5" FR driver is going to have some serious off axis treble issues,
which will render the in room power resonse very dull, even if you have
acceptable on axis treble, not so much an issue nearfield.
A 3" is your best bet IMO and you will need to consider baffle step issues,
though a low order c/o at 300Hz should moreorless automatically give you
the baffle step when you equalise apparent bass and mid levels.
With the same amplifier for both drivers the 90dB peerless (which due to
baffle step loss will be 84 to 86dB in the low bass) can be matched to
a 86 - 88dB FR quite easily.
Fountek make some nice higher senstivity 3"ers, and not expensive.
Also note that with 6dB/octave roll off, mid excursion will continue
to increase below the cutoff, 2nd order L/R has a lot going for it here,
excursion levels off to constant the lower you go, until you hit
the mid drivers bass roll-off, and then it falls with the roll-off.
Thank you for the information and suggestions. I am hoping to find a full-range driver for the mids and highs that has a smooth roll-off off axis (no large peaks or valleys). Unfortunately, Tang Band does not publish off-axis graphs with their spec sheets, so I am not sure about the W5-1611, for example.
My plan is to build baffle step equalization circuitry into my preamplifier. I have not yet settled upon the speakers' baffle width (driver dependent), so I have not yet settled on the BSC frequency.
If I keep the simple first-order active crossover, would it be likely that I would have better results from my first idea of using a sealed box for the mid/high driver?
After reading some of the FAST thread to which Dave provided the link, I believe I should correct and clarify some of my terminology. The crossover I would build into my preamplifier would be of the passive line-level variety (simple, few parts). The baffle step equalization would be built as shelving tone circuitry into the feedback loop of an opamp (again, frequency to be determined).
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