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Old 27th May 2012, 05:25 PM   #1
bigdh31 is offline bigdh31  United States
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Smile TB W8-1808 mltl

I had the drivers on hand and MJ King's mathcad worksheets so I thought I would give a mltl box a try. I wanted to do an ob design for this driver but I just do not have the space right now. I was using the driver in a 89 liter rectangular bass reflex cabinet that was too large and heavy. I decided to try to design the smallest possible enclosure for this driver that still had reasonable bass.

After trying many different configurations in mathcad I ended up with 80 liters internal volume cabinet that is 48" tall, 11.25" wide and 12.75" deep. I have read recommendations as high as 100 liters for a mltl box for the 1808 driver but it modeled fairly well in mathcad. It suggested a compensation network with a 2.5 mh coil and a 10 ohm resister in parallel. The stuffing specified was .5 pounds.

I am pleased with the outcome. It is very easy to listen to all day type of sound. I hear small details that are not that obvious on my other speakers.

After listening for several hours I think the compensation network kills a little too much of the top end so I added a 2 mf capacitor in parallel to the coil. That worked out about right to my ears, maybe a tad too hot. I may order a 1 mf capacitor to try. The sound is a bit bass heavy. I think I will swap out the 10 ohm resister for an 8 ohm resister. I am thinking that would raise the mid-range and treble up a tad relative to the bass.
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Old 27th May 2012, 05:52 PM   #2
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Neat! Have you tried this without any circuit on the speaker at all?

Just curious.
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Old 27th May 2012, 11:18 PM   #3
bigdh31 is offline bigdh31  United States
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I think I will try them without the compensation network tomorrow. When I had them in a bass reflex box I did not use a BSC and it sounded good to me.
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Old 28th May 2012, 11:14 AM   #4
Scott L is offline Scott L  United States
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Default 1808's

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Originally Posted by bigdh31 View Post
I think I will try them without the compensation network tomorrow. When I had them in a bass reflex box I did not use a BSC and it sounded good to me.
Greetings Neighbor !

I'm currently using mine in crude open baffles with sub/bass support underneath.
I worked out the T/S for them and a B4 requires a four cubic footer, and i didn't feel like building boxes at the present monet as I have too much else going on.
The back burner project for them next, is to place them in some vintage Jensen horns i picked up.
Right now, my results vary from actually very good to **** poor, depending on the music source. I'd like to hear your boxed version some time.
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Old 29th May 2012, 12:35 AM   #5
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Red ... RED! I had to paint my speakers the same off-white color as our bedroom walls to get them into the house.

I purchased 4 TB W8-1808 when they were on sale. I will add my vote that the W8-1808 has a "natural timbre" and is very musical. 8" is the only speaker diameter I think makes sense for a whizzer cone. I know the whizzer high-freq measures poorly. I know the whizzer high-freq sounds nasty in critical listening. I STILL LIKE IT. I will also add my vote that a properly constructed MLTL has advantages over a generic BR cabinet.

I put one pair in a 120 liter MLTL (4 cu ft excluding speaker volume) for a bedroom speaker. The 52" MLTL height is ideal for in-bed listening. I found it necessary to sine-sweep the speaker and monitor the speaker_R to tune the port length, since after construction and stuffing a 0.5" port length change was very audible. FWIK, your port looks too close to the floor for an optimum MLTL. My speakers are pushed up close to the rear wall, and this compromises the sound stage, but removes the need for baffle step compensation.

I cut off the whizzers on the second W8-1808 pair and experimented with a dipole midbass. Mms ~ 9.3g. Again, a very "natural timbre", but JohnK's musicanddesign.com white papers on controlled directivity convinced me that I would need to build a dipole ribbon tweeter that could cross at 900Hz to satisfy the controlled directivity Fd naked baffle requirements. I built a 1" wide, 3" long dipole ribbon that is robust enough for a 900hz Xover, but it uses an untested mylar+Al construction, and just sounds "thin".

I put this 1808 in an aperiodic cabinet with excellent sound across the 80-1400 vocal range, but doppler type IMD was audible and measurable at high SPLs. This dopplier type IMD disapears at 100Hz for the W8-1808 midbass. Over this summer I plan to build a B&W style sphere+tapered tube out of sculpture concrete with my daughter for these non-whizzer W8-1808 plus a SB29NDC dome tweeter.
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Old 1st July 2012, 02:09 PM   #6
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That looks a nice speaker, bigdh31, and a very reasonable size for housing that driver! Would it be cheeky to ask whether you are prepared to share your plan? I might be tempted to give that a try with my W8-1808's if you are (as a complete amateur at this!).

Any comment on without the BSC?
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Old 1st July 2012, 11:04 PM   #7
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I don't think the whizzer is nasty at all. Designing an 8" with whizzer is its own thing, not an augmented full range. Actually the total design is quite good (cast frame, underhung, bamboo cone, 5mm xmax). If you read stereophile's voxativ loudspeaker of the year, that 8" full range was +5db all the way out from 1.5khz up. That gave a flatter response far field (in room). The 1808 is very similar. If it seems a bit tipper up, sit a squeek off axis. And at that time I wanted wider dispersion that 2 people at 12'. But I'm sure a 6db crossed ribbon would be better than a whizzer, but a whizzer on an 8" also improves dispersion from 2-4khz and lowers the response. If it was flat before, then you remove the whizzer on an 8", you probably have a response climbing to 4khz before rolling off.

I didn't like it when I had it, but now it would work for me (apartment, highly reflective setup needing high intelligibility for low volume movies, paper thin ceiling so neighbor hears even my tv). At the time (and even now) I'm used to big setup, but I've been thinking about a large folded open baffle, full range 8" setup. If you use lighter bass music, or cross it over, I think you have a winner.

I think an interesting shootout would be the 1808 vs the fa22rcz. I think the 1808 would edge it out due to a smaller peak near 3khz (that is in the fa22 and the betsy). And the 1808 has a phase plug. But we are talking a $200 driver versus a $130 and $50. But notch the 3.2khz peak in the betsy and the fa22 and it would be interesting. I was told to not remove the dustcap on the betsy, I'd imagine the response past 10khz goes away if that mod is done on that driver.

That open baffle is WAY to small, and again, I wouldn't expect too much bass from an 8" full range.

I don't think you are hearing Doppler distortion. You are hearing simple frequency modulation (lows modulating the voice stuff and higher).

Norman

Last edited by norman bates; 1st July 2012 at 11:10 PM.
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Old 2nd July 2012, 12:18 AM   #8
bigdh31 is offline bigdh31  United States
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The enclosure is 48" h x 11.25" w x 12.75" d. It is 3/4" material. I put a window brace 10" down from the top outside of the enclosure. I put a second window brace 23" down. I probably should of added a third window brace but I was concerned about reducing the internal volume too much. It should be about 89.9 liters internal volume with two braces. The driver is centered 14" down from the top. I used parts-express part 260-403 for the port tube. It is centered 4" from the bottom.

I put .25 pounds of polyfill on top of the two window braces for .5 pounds total. I also put 1 inch foam, part 260-525 from parts-express, on the sides adjacent to and behind the driver. This might be overkill but I wanted to reduce the possibly of reflections back through the driver.

After some long listening sessions I ended up using an 8 ohm resister and 2.5 mh coil in parallel for the baffle step circuit. I also used a type of zobel made up of a 2 mfd capacitor and a 10 ohm resistor in series across the speaker terminal to kill a little of the top end sizzle.

Overall I am very pleased with the results. The bass is very solid. The midrange and treble present a nice amount of detail and texture. I downloaded a high resolution copy of Rumors from HDtracks and was amazed how good it sounded through these speakers.
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Old 2nd July 2012, 08:16 PM   #9
Scott L is offline Scott L  United States
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Default 1808's now horn loaded

As I mentioned several weeks ago, I intended on horn loading my 1808's.
All the glare I heard before, when they were open baffled, has now vanished.
They are really quite superb. I operate them in this system from 250 Hz up.
I left a spot for a tweeter near the bottom of the stand, but at this point I don't think it's needed at all. In some ways this is the best sounding system I have put together. It's a 3 way, sub to 50, ppsl's 50-250.
active x-overs. sub/ mid-bass 24 db/oct ; mid-bass to horn 18 db/oct
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Old 2nd July 2012, 09:11 PM   #10
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Thanks for the detail bigdh31. I'll post back if I make them. Alternatively I might get up an hour or two earlier tomorrow morning and knock up a pair like Scott's before breakfast (awe-inspiring work there Scott!).
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