Tang Band W8-1808 in a bi-amped FAST

[majerjack]

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?

 

[Godzilla]

>>> 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

 

[majerjack]

Godzilla, thanks. You have given me helpful information on all my full-range inquiries. I truly appreciate your comments.

Anyone else?

 

[Bigun]

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.

 

[majerjack]

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.

 

[Godzilla]

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.

 

[majerjack]

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.

 

[Ginge]

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.

 

[majerjack]

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.

 

[Godzilla]

I found an old thread about the TB and a few other fun full range drivers where I describe how they sound to me.

http://www.diyaudio.com/forums/full-range/160068-tangband-w8-1808-pe-buyout.html

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

Zilla

 

[majerjack]

Zilla,

Thank you so much for the link. That was most thoughtful. Thanks also for posting your listening impressions of the 1808 originally. Your comments describe exactly the kind of sound I am hoping for. I am looking forward even more to hearing this speaker.

 

[LineSource]

Hi majerjack,

I own a couple pairs or Tang Band W8-1808 speakers. Because of the 9.5 gram Mms super thin paper cone my ears can hear rear cone reflections if the box is not properly shaped, sized large, and heavily stuffed behind the speaker. With this speaker I think you can only obtain the full sonic potential in a sealed box if the box is large, cleverly shaped to minimize resonances, and uses a large amount of fiberglass stuffing beind the driver. Personally, I would not use a small sealed box because of concerns for reflected cone distortion. I suspect using a small sealed box is why some reviews report poor midrange clarity.

I ended up with a wider than average MLTL cabinet with more stuffing behind the speaker than average. I am very happy with these bedroom speakers.

 

[Godzilla]

LineSource may very well be correct! I noticed the small sealed boxes sounded best when heavily stuffed and in those boxes is where i noticed the not so perfect (but still quite fine) midrange. If i ever get around to putting them into larger boxes i will report back.

Thanks for your comments LineSource.
Zilla

 

[majerjack]

Thanks, guys. The model I use suggests a sealed box of 56 liters (2 cubic feet). I would most likely go with a golden ratio box of that size lined with damping material and then add stuffing if I feel it is necessary.

 

[cervelorider]

reflections

I can attest to the reflections inside the cabinet beting transmitted back into the thin cone. As I tuned my MLTL with stuffing, I could hear this midrange resonance without fiber fill behind the driver. Once I applied the acoustic stuffing to the sides, back and top of my cabinet, the midrange resonance/coloration completely dissapeared. I can't say enough good things about this driver and I'll be buying more. It is truly the most balanced "full range" (bass to treble) driver I've heard.

 

[cervelorider]

1808 Video

Tang Band 1808 video. For what it's worth.

Fleawatt DIY Tang Bang 1808 Speakers - YouTube

 

[LineSource]

Tang Band 1808 video. For what it's worth.
[/url]

Yet another generic MLTL cabinet.

Do all MLTL cabinets look alike? Must they? Should they?
Building a better MLTL cabinet ... any ideas?


I built my MLTL with double thick walls plus internal corner braces to support a 1.5" round-over on all exterior edges to reduce diffraction effects. I used fiberglass 703 boards for absorption, plus an (itchy) batt of insulation fiberglass directly behind the speaker and in the TL. I rolled on the same latex paint as our bedroom walls. LAZY.
http://www.bobgolds.com/AbsorptionCoefficients.htm

I wonder if a different MLTL cabinet shape similar to the lumen white design (pic) would improve diffraction, and upper frequency details by moving the absorption material further back toward the rear tapered cabinet section. Lumen White web site.

Lumen White

"instrument grade cabinets
the superlative performance of our driver arrays is complemented by highly advanced cabinet acoustics .

as traditional damping technologies cause a clearly audible loss of musical information, we have developed new, signal-preserving alternatives. the same applies to the majority of fiber boards, industrial composites and bonding technologies which dominate today's speaker manufacturing, even at the high end. acting as absorbers, they cause transient time smear and a loss of musical information or feature a psycho acoustically unbenign spectral signature, leading to perceptional stress, listening fatigue and ownership dismay."

 

[Scottmoose]

Yet another generic MLTL cabinet.

Do all MLTL cabinets look alike? Must they? Should they?

No, no, and depends, respectively. There are certain laws of physics which have to be adhered to of course.

Building a better MLTL cabinet ... any ideas?

How do you define 'better?' If a relatively simple box meets the performance goals, then logically we need to ask, what's wrong with it? Granted, aesthetically, there is much to be said for something that isn't a rectangular box / is a little more interesting, and there can be acoustic benefits too (that doesn't mean there necessarily are but there can be), unfortunately, it is not always practical for many people, who lack the fabrication facilities / tools / skill set to create complex shapes.

I wonder if a different MLTL cabinet shape similar to the lumen white design (pic) would improve diffraction, and upper frequency details by moving the absorption material further back toward the rear tapered cabinet section. Lumen White web site.

Depends on the driver in question to a large extent. Generally speaking, when it comes to large wideband drive units their power response narrows to such an extent as frequency increases (i.e. they are beaming) that diffraction becomes less of an issue. As for the internals -again, depends. 'Detail' is essentially another way of saying 'low distortion [of xyz varieties].' In some cases, you may prefer to have damping further away from the cone. You may (may) get more of a load on the cone if the damping is very close, which again may (may) cause diaphram deformation at high SPLs, affecting the midband / HF behavior of a wideband drive unit. Again -depends on the design. If this is taken into consideration in the design stages, then it should not be a problem.

Lumen White

"instrument grade cabinets... the superlative performance of our driver arrays is complemented by highly advanced cabinet acoustics.

Can't comment on the designs, as I haven't taken a close look, but this reads like the usual advertising speak.

as traditional damping technologies cause a clearly audible loss of musical information

More advertising speak. No specific statement of what they are refering to, by 'traditional damping technologies' or 'musical information', or evidence to support it.

we have developed new, signal-preserving alternatives.

Hooray! Salvation is at hand!

the same applies to the majority of fiber boards, industrial composites and bonding technologies which dominate today's speaker manufacturing, even at the high end. acting as absorbers, they cause transient time smear and a loss of musical information or feature a psycho acoustically unbenign spectral signature, leading to perceptional stress, listening fatigue and ownership dismay."

In other words, they appear to be implying that they don't care for MDF, particleboard, or similar due to their relatively poor MOE specs. / low stiffness - weight ratio which often puts panel resonant modes slap bang where you don't want them (viz. within the cabinet's operating BW), and a time-delayed, low-level energy release that combs with the direct radiation & tends to 'suck the life' out of the sound. Not exactly news, and nothing new here that I can see, just the usual carefully presented advertising.