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Old 7th December 2003, 09:10 AM   #1
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Default 6th order box - what's your experience?

I'm humm-ing and haa-ing about building a 6th order sub box but I'm worried it might be a flop because I have heard people say that they are difficult to get going properly. If you have ever built one, would you like to tell of your experience with it? Did it live up to expectations? Was it difficult to tune properly? Did the software do an accurate job of predicting the box and port stuff? What does it sound like? Is there any truth in the saying that they have poor transient response? Did it really shake the place? I'm all ears.
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Old 7th December 2003, 09:54 AM   #2
FACTOR is offline FACTOR  India
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Default Some Facts

The So called 6th order enclosure is some what very easy to build but not with softwares but with ears
I have build this one 2 yrs ago to ramshack the windows of my drawing room which was powered by 1KW amp
The response was 10Hz to 100Hz
The Port tuning was 20Hz & 80Hz
If u wanna build this than contact me for greates details
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Old 7th December 2003, 10:02 AM   #3
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normally a ported box 4th order will do,

i dont see why tuning would be a problem

To me it seems,the more gradual the roll off,the better the transient response

Dipoles sound good,sealed almost, ported worse, increasing order=worse still....pick ur poison

extension vs quality


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Old 7th December 2003, 12:30 PM   #4
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Assuming that you mean 6th order reflex rather than bandpass box.

I built a 6th order sub from plans in Aug '83 Audio mag using a JBL 2245H in '84. I love it, replaced the surround 5 years ago, still haven't heard anything I like enough to consider replacing it. If I can get hold of another driver, I'll build another one. It is 8.5ft^3, tuned to 24 Hz, Q=2 HP @ 24 Hz, 60 Hz 12db/octave Low pass. I modeled it with Boxplot, and that seems to match actual response. In a 15' x 22' room it seems flat down to 20 hz or so, applying published corrections to my Radio Shack SPL meter.

Caveat: high power handling, high Xmax and tons of power are are required. With 250 watts, it runs out of steam at slightly louder than normal levels. A bridged Leach amp (60 Volt rails) is acceptable, but it really prefers my bridged Hafler DH-500 for home theater. I replaced the worn out original fan, but need to find a quieter one for the Hafler to live in the living room. Works great in my bass rig, though
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Old 7th December 2003, 01:30 PM   #5
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BobEllis do you mind giving me more info on the enclosure you designed, i have 2 of those woofers and have been deliberating on what to do with them. I've only ever heard of a 6th order bandpass.
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Old 7th December 2003, 04:25 PM   #6
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Amoeba86, You are a lucky stiff - I really wish I had another driver, just to go stereo sub. There is plenty of output for reasonably large rooms. When I first built it, my living room had a cathedral ceiling and an open loft on the second floor, and a full width opening to the dining room. Gave me a room roughly 25x 40x 17, and I didn't run out of bass.

I didn't design the enclosure, I just built it per the article I mentioned. I pulled it out and I mis-spoke - they call the alignment quasi-fifth order. Think of cascading filter sections. A vented box is a fourth order filter, add EQ in the form of a high Q first order high pass filter and you have a 5th order filter/ alignment.

Internal dimensions from the article: 23.5 x 32 x 19, port is 12" long, 5.25" square or 5.675 diameter. This should tune the 8 cubic foot enclosure to 26 hz. Adjust proportions to suit, and brace well .

The crossover should provide 6 db of boost at 24 Hz. I bought the JBL BX63 crossover, because I didn't have the knowledge to build a crossover myself back in 1984. Grey has provided some very useful information in the Zenover thread. Fred D. also has started an active crossover thread with good info. All this talk got me going - I prototyped a LR crossover with baffle step compensation and tweeter phase correction for my focal TL's. My initial impression was very positive, But that's another thread once I have made some measurements and tweaked.

Don Lancaster's Active Filter Cookbook is also a good reference. Simply make a second order high pass filter with an Fc of 24 hz and a Q of 2 for your EQ.

An alternative that the article mentioned is to increase the volume to 12 cubic feet (44 x 29 x 21") Tune it to 25 Hz with a 9" x 20" port and you've got a 25 Hz sub with no EQ. Or increase the port length to 30: to tune it to 20 Hz, add 6 db of boost with a Q=2 HP filter and you have an F3 of 20 Hz. I suppose a bandpass filter with Q=2 and 6db of boost would work, too.

I also remember an article somewhere describing a system using 8 2245Hs in an IB array, it got down to somewhere around 10 Hz with several kilowatts and EQ . (Funny, as I write this I am listening to Jimmy Buffett's "Overkill")

Observations: The BX63 crossover has an adjustable cutoff frequency, from 63 to 125 Hz at 12 db/octave. With the croossover frequency set at anything over 70, I find that the bass comes from the sub if it is not centered. If the crossover is set below 70 hz I cannot locate the sub. My Yamaha DSP-A1 has a 24 db/octave crossover fixed at 90 hz. With that I can barely locate the sub if I try. I'd recommend a 24 db/ octave cutoff as low as possible consistent with your mains' low end if you use a single sub. Two 8 or 12 cubic foot subs has a SAF approaching 0. Even one is pretty tough to sell.
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Old 7th December 2003, 07:58 PM   #7
sreten is offline sreten  United Kingdom
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6th order bass alignments have a bad name because the early
adopters used maximally flat alignments that didn't take room
gain into account and basically did not suit most rooms.

B&W's website has some good information.

basically the 4th order response has to be overdamped, they
use a Bessell alignment which is a good choice - in smaller
rooms its often fine on its own.

I seriously reccommended making the Q of the final 2nd order
high pass adjustable - you can then tune it to your room.

Good results are almost guaranteed.

/sreten.
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Old 7th December 2003, 08:56 PM   #8
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The fixed Q (boost) explains why I liked the sound best in the biggest rooms - in smaller rooms it can be boomy. Variable Q crossover is in the works. And it won't be based on a TL084, like the BX63.
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Old 8th December 2003, 09:45 AM   #9
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Quote:
Originally posted by BobEllis
Assuming that you mean 6th order reflex rather than bandpass box.
No, sorry. I mean a badass bandpass as per the picture.
I didn't know there was such a thing as a 6th order reflex.
I am shooting for -1dB at 20Hz and 60Hz. Power ~50W. Efficiency - reasonably high, with the emphasis on wood being cheaper than a fancy driver.
Attached Images
File Type: png bandpass.png (388 Bytes, 922 views)
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Old 8th December 2003, 10:12 AM   #10
sreten is offline sreten  United Kingdom
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If you got a 6th order bandpass right it would have very
high SPL capability given the drivers excursion capability.
Pretty useful in PA applications.

A maximally flat alignment for 20Hz and 60Hz will have
utterly hideous transient response. With the two points
so close together lower Q alignments will be difficult.

Personally for hi-fi use I wouldn't go near a bandpass of
any sort - very difficult to integrate with the main speakers.

If an adjustable electrical low pass is also used to allow
integration with the main speakers then the low pass
section of the bandpass becomes fairly pointless.

Much better to use the total volume for the high pass
section, i.e. a standard relflex arrangement.

/sreten.
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