Tang Band W8-1808 in a bi-amped FAST - diyAudio
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Old 28th November 2011, 06:57 PM   #1
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Default Tang Band W8-1808 in a bi-amped FAST

I have owned a pair of TB W8-1808 full-range drivers for several months now. I have meant to install them into cabinets for some time as part of a revamping of my entire sound system. My original thought was to use them full range in a bass reflex cabinet, driven by their own amplifier, with a custom DIY preamp that could also feed a separate bi-amped sealed speaker system, so that I could choose the speaker system that sounded best for a particular recording. I found that the multiple cabinets necessary would take up rather too much space in my listening room. In an effort to reduce the size of some of the cabinets, I thought I might try a bass reflex FAST system as an alternative, but I was having difficulty finding the right full-range driver to mate with the woofer in a bi-amped arrangement with a first-order 6dB/octave crossover in my preamp. The small drivers will not play low enough to allow a gentle-sloped acoustic rolloff to maintain the first-order characteristics of the electrical crossover.

Today an idea struck me: Why not abandon the two-speaker-system idea and use the W8-1808 in a sealed cabinet with the chosen woofer (a Peerless #830869 8" which has good efficiency, plays low in a BR cabinet, and has flat, extended response well into the midrange) in a FAST bi-amped arrangement? All the parameters I have examined suggest that this would be a match made in heaven. Here are the particulars:

First, the Peerless 830869: It is one of the HDS Nomex woofers about which I have read many good things. It has a low fs of 30Hz, an efficiency of 90dB, and has an extened frequency response that is quite flat both on and off axis to almost 2500Hz. The software model suggests that it should have an f3 of about 30Hz in a BR cabinet.

Next, the TB W8-1808: Again, I have read many good things about this driver and the similar TB W8-1772. The 1808 seems to be more versatile, in that it seems to have been used in a variety of cabinets and baffles and produced good results each time. I have not read of anyone using them in a sealed cabinet, however, so I plugged the TB specifications into a software model and found that they should play very well indeed sealed. The acoustic roll-off on the low end has an f3 of about 70Hz, and beyond that is quite gentle, about 9dB/octave. If I use a first-order crossover in my preamp centered at 300Hz, this would give me a two-octave transition to the f3 point, after which I would not expect the 9dB/octave roll-off to disturb the phase or amplitude response too much.

Additional benefits: I would probably build the cabinets as two single enclosures, each one containing two chambers (one BR and one sealed). They would be fair-sized floor standers, but they would take up much less space than the four or possibly six boxes that I would have built otherwise. One baffle can accommodate both drivers well (they are the same diameter), so the baffle step correction circuitry I would build into my preamp would need only one center frequency. The two drivers can be mounted close enough together so that lobing would be minimized. Because they are the same diameter, I expect that the acoustic centers will be close enough together on the vertical plane that time alignment should not be too much of a problem (if necessary, I should be able to time align the drivers with minimal positional adjustment). I can use a higher-wattage amplifier for the bass driver so that I get good damping and control, and a lower-wattage amplifier (perhaps a class A or a T-amp) for the critical midrange and high frequencies.

My goal is to build a speaker system that combines some of the best characteristics of both the multi-driver-with-crossover approach and the single-driver full-range approach. I want no resistors, capacitors, or inductors between the amplifiers and the drivers. I understand that the off-axis response of an eight-inch-diameter full-range driver may leave something to be desired, but I also understand that speaker design is the art of acceptable compromises.

I would appreciate comments and opinions from members who are experienced in DIY speaker design and building. Is my reasoning sound? Am I relying too much on manufacturer specifications and the software models? Have I overlooked anything? Are there any reasons this should not work well?

Last edited by majerjack; 28th November 2011 at 07:23 PM.
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Old 28th November 2011, 10:43 PM   #2
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>>> I have not read of anyone using them in a sealed cabinet, however, so I plugged the TB specifications into a software model and found that they should play very well indeed sealed.

I searched my hard drive for the pic i took of the 1808 in a small sealed box but could not find it. Probably .5 to .75 cubic feet. It sounded excellent with deeper bass than expected and was satisfying on its own. Using this driver in a small sealed box with a helper woofer of some kind will produce excellent results.

Zilla
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Old 28th November 2011, 10:48 PM   #3
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Godzilla, thanks. You have given me helpful information on all my full-range inquiries. I truly appreciate your comments.

Anyone else?
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Old 28th November 2011, 11:02 PM   #4
Bigun is offline Bigun  Canada
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I like this proposal, the x-over frequency is just where I would have chosen for an ideal FAST. I'm thinking of something like this myself, I can't offer any advice since I'm actually further behind you on this but from the research and reading I've done this approach is solid. My concerns would be the high freq. dispersion of the 8 incher, which you've noted already.
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Old 28th November 2011, 11:08 PM   #5
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Bigun, thanks for your input. My research indicates that the 1808 and 1772 (which apparently share the same cone, whizzer, and phase plug) are pretty good off-axis for an 8-inch driver. Bob Brines has reported on this forum that the 1772 has decent off-axis response, and I have read good reports on both drivers from other sources.
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Old 28th November 2011, 11:21 PM   #6
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The 1808 has a nice soft treble that's non fatiguing and a bouncy bass. It's midrange is colored and where i think folks love them or hate them. They do have a very extended range for an 8"... They have a lot of flexibility and have been used sucessrully in OB, sealed and ported designs. They are among the best drivers i've heard but they do have a personality. I think they are very good drivers.
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Old 28th November 2011, 11:39 PM   #7
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Godzilla, can you describe how the 1808 midrange is colored? The reviews I have read indicate that it does not have the midrange "shout" of many full-range drivers.
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Old 29th November 2011, 10:12 PM   #8
Ginge is offline Ginge  Australia
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Majer I have also been thinking of the 1808, but for OB. How do you do the crossover at the preamp stage , build it into the preamp or after. Is there a proprietary unit you can use. The other question is what computer program do you use for your calculations. Off topic I know.

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Old 30th November 2011, 04:28 AM   #9
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Ginge,

I plan to build simple 6dB/octave RC filters into the outputs of the preamp, with the R of the high pass (low cut) filter being the input impedance of the mid/high frequency amplifier.

I use the online calculators at www.lautsprechershop.de and www.mh-audio.nl.
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Old 30th November 2011, 10:37 PM   #10
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I found an old thread about the TB and a few other fun full range drivers where I describe how they sound to me.

Tangband W8-1808 and PE Buyout

The pic of the 1808 in the small sealed box is there too.

Zilla
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