Which BIB Dimensions for this Pair of FE164-s? - Page 2 - diyAudio
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Old 21st December 2005, 02:58 AM   #11
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And i was wondering if you could just flip the cabinet over, raise it 5" to 10" and load the floor?

My basement ceilings are about 6" lower than normal and might not work right. Loading the floor might remove this variable.

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Old 21st December 2005, 09:30 AM   #12
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Good questions. Actually, it's not quite as significant as you might believe. Whilst you do drive the room's vertical resonant mode with these boxes, Martin says it isn't quite as simple as that. These things need to be pushed against a rear wall, or better, into corners to give of their best, right? But surely if they were driving the vertical mode alone, that shouldn't be as much of a factor.

The reason they work, as I understand it, is down to the position of what is effectively a horn-mouth on the top of the cabinet. I'll quote verbatim here as Martin can communicate ideas like this more lucidly that I could ever hope to. This was in response to a question I had asked about why these things have such terrible computer sim results, yet usually measure way better in-room.

First, with the open end backed up against the wall the effective mouth area is doubled, due to the reflection boundary condition at the wall, and this will allow lower frequencies to be more efficiently transferred into the room (the resistive portion of the acoustic impedance is doubled). At the same time, less energy is reflected back into the line reducing the magnitude of the standing waves. So more bass output and attenuated standing waves compared to the simulation results.

Second, by pointing the open end up you are listening over 90 degrees off axis. With the mouth output reflected off the wall, the depth dimension effectively doubles while the width remains the same. This shape is going to become very directional with increasing frequency so the ragged response predicted above say 300 Hz is probably grossly over estimated.


So, it's not so much the vertical mode as the position of the mouth in relation to a room-boundary in the form of a nice vertical wall that is the most significant factor at work here, bit like a corner horn. In my own experience, the height of the room and the cabinet in relation to it can make a difference, but it's more to do with the quantity, rather than the depth, of bass output. Lower rooms seem to make for more weight in the bass, though at slightly different points, but don't tend to affect the bass-depth very much. You also have to consider the drivers you are loading the cabinet with, the amplifier's damping or lack thereof, and the resitance of the wire you are using. I recall Terry telling me of a pair of these things he built using FE168Sigmas (pre ESigma model I believe) a few years back that now reside in alcoves in their new owners' living room. Apparantly, it would be too much bass except there is no boom at all, so it doesn't damage the rest of the frequency range.

Flipping the boxes might work -not sure on that, chances are you'd be reducing the bass-output a bit as there wouldn't be enough space to reflect the mouth properly. Also, a box this heavy on spacers that tall might not be overly stable. 'Zilla -what drivers were you thinking about using? Chances are, you'd probably be fine with a slightly shorter cabinet if you were still concerned about room-height.

Cheers
Scott
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Old 21st December 2005, 02:49 PM   #13
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Hi Scott!

I would use the older FE168Sigma i have now playing in ported boxes. 24 Liter... sounds nice.

(Server needs to be reboot so may be very slow to load today)

http://www.zillaspeak.com/zillaspeakfostex24L168.asp

My plan is to pull the drivers out and plop them into Straight Pipes i built... but my pipes are 8" wide inner dims (everything else the same - see Bob's sight below) to accomodate the driver.

http://www.geocities.com/rbrines1/Pa...ight_Pipe.html

I think these boxes would work well with the 168S but have to try it and see.

But i was wondering about the BIB.

Peace,
Godzilla
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Old 21st December 2005, 03:38 PM   #14
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Hey 'Zilla

You know, the BIB box, and Bob's straight pipes are the very first cabinets that got me interested in DIY hifi a couple of years back. I didn't build either, but they provided some inspiration to start looking further until I finally came back to Terry's big folded horn / TQWT a few months ago.

Non 'E' 168Sigma? Nice driver. The dims I suggested for the FE164/6/7 should work OK, but as the Sigmas' Sd is a little smaller you could reduce the cabinet a bit. Try this for a BIB box for them (assuming 3/4" build material is used, and should work for the ESigma too by my reckoning):

64" height (Increase to 66 1/2" for the Esigma)
15 3/4" depth (external)
7" width (external)
Driver 28 1/2" from cabinet top (29" from the top for ESigma)
End the internal baffle 6 3/4" from the cabinet base and 6 3/4" from the internal front and rear cabinet walls.

That could be a really good combination. Only problem of course is that you would need to add a baffle like Terry's a) to assist with baffle-step, though with them rammed against a rear wall or in corners that shouldn't matter as much, and more particularly b) the driver is actually about 1/2" too wide to fit! If the additional baffle's a problem, then you could increase the external width to 8", reduce the external depth to 13 3/4", and terminate the internal baffle 5 3/4" from the floor and the internal front and rear baffle walls.

I like those vented boxes though BTW.

Cheers
Scott
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Old 22nd December 2005, 01:56 AM   #15
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Quote:
Originally posted by Scottmoose

The reason they work, as I understand it, is down to the position of what is effectively a horn-mouth on the top of the cabinet. I'll quote verbatim here as Martin....
Yes, that MJK stuff was beautiful, wasn't it?

Quote:
In my own experience, the height of the room and the cabinet in relation to it can make a difference, but it's more to do with the quantity, rather than the depth, of bass output. Lower rooms seem to make for more weight in the bass, though at slightly different points, but don't tend to affect the bass-depth very much.
I really can't thank you enough for your invaluable experiential input (not to mention everything else). I'm a zillion steps past where I would have been without it.

Quote:
I recall Terry telling me of a pair of these things he built using FE168Sigmas (pre ESigma model I believe) a few years back that now reside in alcoves in their new owners' living room. Apparantly, it would be too much bass except there is no boom at all, so it doesn't damage the rest of the frequency range.
I read that before and it made my hair stand on end.

Quote:
'Zilla -what drivers were you thinking about using? Chances are, you'd probably be fine with a slightly shorter cabinet if you were still concerned about room-height.[/B]
And from my own perspective, I think I'd be missing a good part of the fun if I flipped them over; for some reason I'm inordinately fond of the fact that these fire up.

Now regarding the issue of the spouse-pending-approval factor and "the donut," as she currently refers to the prospective round baffle:

Quote:
From GM
Make it big enough to blend into the room's boundary gain and no electronic BSC is required, ergo its size is room/location/desired f3 dependent.
From what I've gathered so far, the way to get a figure worth figuring for room gain is to measure it; I thought there might be a formula using room dimensions, but apparently there are too many other powerful influences to make that workable. (If I'm mistaken, of course, somebody please correct me). So I think that I'll plan on sizing and adding the donut at some later point when I have the means in hand to do it right.

Now I have just one more question for you, Scott: Do I understand correctly that you're using only a single run per channel of the 24/30 AWG magnet wire? (I'll be using an ASL SET/SEP for these, BTW).

Thank you again and all the best,
Don
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Old 22nd December 2005, 09:21 AM   #16
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You're welcome Don, glad to help if I can. You sound to me as if you're on the right lines re room-gain and baffle-step issues. In this respect, I think it will be a suck-it-and-see situation, so trying, then deciding on baffle-size (if you bother at all) upon investigation looks like being the best way forward to me. Quite right -I use a single run of 30AWG at the moment to each drive-unit (well, one piece of + and one for - obviously!), as I usually listen to solid-state amps. Though I have a PP valve amp, I find that I rarely get chance to use it, because I'm frequently listening to quite a few different cabinets and drivers, some of which are not overly efficient, but the higher damping factor of SS amplification tends to require more series resistance to prop the bass up. You could get the same effect by using a heavier gauge wire and placing a resistor of varying value in series with the driver if you like.

As you're running SET amps, you probably won't need to go to quite the ultimate 30AWG extremes -a single run of 24AWG, either magnet wire, or a twisted pair, extracted from inside a run of Cat5 or some such will probably be sufficient. That would be my initial choice anyway. However, both of these options are very cheap, so you'll have plenty of room for experimentation without breaking the bank, going both ways.

Best & good luck with the project, and for the coming year. Let us know how you get on, or if there's anything we can help with
Scott
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Old 23rd December 2005, 01:58 AM   #17
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Quote:
Originally posted by Scottmoose
[B] Quite right -I use a single run of 30AWG at the moment to each drive-unit (well, one piece of + and one for - obviously!)...

...As you're running SET amps, you probably won't need to go to quite the ultimate 30AWG extremes -a single run of 24AWG, either magnet wire, or a twisted pair, extracted from inside a run of Cat5 or some such will probably be sufficient. That would be my initial choice anyway. However, both of these options are very cheap, so you'll have plenty of room for experimentation without breaking the bank, going both ways.
(Yes, excuse me, I meant to say terminal, not channel.)

I'm so accustomed to the garden-hose sized speaker cables that grace my livingroom landscape, the thought of these wispy little filaments tethering the massive BIBs to their amp was taking a while to click, and I sort of had to verify it with you even though I was sure that that had to be what you meant.

Thinking about it today brought up a related question I'd almost forgotten I had about speaker wire. I'll go ahead and raise it even though it follows the 'just one more' question I asked last time:

Is there perhaps a school of thought that favors lighter-gauge speaker wire generally over the 'garden' variety (independantly of the application we've got going here with the BIBs)? I thought I remembered reading something to that effect two or three years ago, perhaps at the single driver website (and for that matter perhaps specifically in connection with full range, high-efficiency drivers and speaker systems, which is what I was researching at the time), and more recently I thought I noticed some people recommending untwisted strands of CAT5 here on the DIY forum in applications that didn't seem especially in need of the resistance (though I could be wrong on that, of course). IOW if you feel like saying anything about the general qualities of light gauge magnet or CAT5 wire as a speaker cable in your experience, I'd love to hear.

And I really don't expect there to be another just one more..but who does? ;-)

Regards,
Don
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Old 23rd December 2005, 09:22 AM   #18
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I'm probably not the best person to ask this, as I try to stay out of the voodoo associated with cables, 99.99% of which is sheer nonsense in my view. Now, I always qualify any remarks I make on cables with the statement that this is my view, albeit one shared with plenty of other people, and under no circumstances do I suggest that anyone else has to agree with me.

Right. Thin wires. There is indeed a school of thought that suggests that all speaker cables should be as thin as possible, whatever the circumstances. This is as big a fallacy as the complete and total drivel propounded on topics like 'dielectric absorption', 'strand jumping', 'burn-in' and innumerable other matters (none of which have the slightest effect at audio frequencies or audio lengths of cable, and several of which do not exist, period). It has some technical basis, but it's frequently taken completely out of context, or simply incorrectly applied. As with everything in this life, it depends on the application.

With full-range units, the majority of which are high-efficiency types with very powerful motors and light cones, a high-damping factor amplifier (i.e. solid-state as a rule) will over-damp the driver, and bass will slump as a result. For more on this, have a look at Nelson Pass' First Watt article on current-source amplifiers and full-range drivers. Adding series resistance, either by placing a resistor in series with the amplifier and driver, or simply by using a high-resistance wire (i.e. a thin wire most of the time) between them will artificially raise the Qes of the driver (and also incidentally lower the Qms -a trade-off), and prop the bass up, bringing it into line with the rest of the frequency range. Valve amps, especially SETs on the other hand, have a much lower damping factor, and tend not to need as much, if any, resistance between them and the driver, because they are not over-damping the driver in the first place. On the other hand, as they do not put out much power, and you'll never need much anyway in a high-efficiency system to go very loud indeed, you don't particularly need a thick, low resistance, high-power-handling cable anyway.

In a lower efficiency system, a multi-way or perhaps a full-range unit with heavy, passive BSC applied, you have to be a little more careful about using very thin wires however. They need more current and power than a thin wire can deliver, either properly or safely; the thought of a length of 24AWG lying on your carpet whilst glowing red hot as it attempts to deliver high currents... you get the picture. A thinner than average wire can certainly deliver a touch of the benefits they bring to high-efficiency systems, allowing better bass performance (so many commercial speakers have a very bright balance nowadays, and this can help mitigate it, at least to a degree in my own experience) so long as you don't go too far -20AWG is about the limit I would suggest. None of this, of course, has anything to do with the black-magic waffle perpetrated by the cable industry: it's just the most basic electrical principles imaginable.

To give a commercial example: the Audience Au24. Very thin for a commercial wire indeed. I remember a nominally blind multi-wire test where all cables were used in two systems: a high-power one, and a high efficiency one, both of which played at the same sound pressure levels. In both tests, the bass on the Au24 was praised, but in the first, high-power, low efficiency system, there were also comments about it sounding 'muddled', 'confused', 'lacking in detail' etc. Now, I don't know what any of these comments really mean, and I'm pretty sure the reviewers in question don't either, but I can certainly explain why the Au24 didn't work overly well in the first system, and so can you: being a very thin gauge wire, it simply couldn't deliver the power and current it was being asked to, and the fact that this affected the sound-quality in some way is hardly surprising. In the second, high efficiency system, all such comments vanished. I note that several reviewers who use big horn systems use this cable, and love it to bits.

That is not an advert for the Au24 however, just an example. You asked about Cat5, and its popularity. I used the Au24 as an example, because it reminds me of Cat5 or magnet wire in many respects because of the basic electrical properties it shares with these wires.

Cat5. My view is that it's versatile, looks OK, and is also very cheap. You can do quite a bit with Cat5. You can extract a single twisted pair from it, or use one whole run, or two, or six (!). It has other advantages too. The fact that it is twisted together helps it to reject RFI. However, by introducing twisting, we're also moving away from the purely resistive properties we've been discussing, and moving on to capacitance and inductance, a whole new minefield. However, again this tends to be of less importance for the high-efficiency brigade than for high-power applications. So long as both are kept to a reasonable level, it shouldn't matter a whole lot for us. (It shouldn't matter that much much anyway, but there are those who persist in stating that one or the other of these factors is the devil's work, and desperately work to lower it at the expense of raising the other. Fair enough. I'll let them get on with it whilst I sip a glass of port and get on with enjoying the music, whether it be a touch of June Tabour's acoustic folk, or a full-on blast of P.J. Harvey).

Also, because each wire is individually jacketed in a nice plastic sheath means it's a little more flexible than the ceramic-coated magnet wire, whose coating can crack if you don't watch what you're doing. Twisting this stuff together is not a good move unless you want a short-circuit. Untwisted Cat5? 'haven't seen that, but then, I haven't been looking. Fair enough I suppose. I don't think it'd make much difference though, at least not in high-efficiency applications. There will be a different measured performance between a twisted and untwisted pair -whether that would be audible? I don't know, I haven't tried it, but you could always try extracting two pairs, leave one twisted and untwist the other and see if it makes a difference. I doubt it though, again, in this sort of application at any rate.

So, general conclusions. Well, for horns, like the BIB box (which is what it really is), without a correction circuit and a high-efficiency driver, very thin-gauge wire is a useful little trick to pull, especially if you're running solid-state amplification. It is not such a good idea in multi-way speakers which need more current, or high-efficiency drivers with a passive BSC circuit, which tends to lower efficiency somewhat. You can realise some of the benefits with these other types by using a thinner than average wire, but not quite so thin. 20AWG would be about the limit in my view. Tube amps, especially SETs powering high-efficiency drivers, do not need as much as they have a much lower damping factor, so you can use a slightly thicker wire if you wish. Experiment if you wish however -Cat5 and magnet wire are cheap!

Cheers
Scott
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Old 23rd December 2005, 02:21 PM   #19
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Thanks Scott for your measurement ideas for a modified BIB. I think i will try plopping my 168S into my current pipes so i have an excuse to build another powered sub.

This way i will have another future project in the back of my mind for the 168S... I've already build a small 11L ported box, 24L box, 48L box and a Bk161 for them. They are a great value driver for someone looking to experiment with different types of cabinet designs.

Pipe and BIB are next. So far the 48L box sounded best to me... fullest, bounciest and overall the most fun to listen to.

Peace,
Godzilla

http://melhuish.org/audio/DIYBX19.html

http://www.zillaspeak.com/zillaspeakfostex24L168.asp
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Old 23rd December 2005, 04:41 PM   #20
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Most appreciated, Scott. I hope a beautiful holiday launches a fulfilling and productive year for you and yours.

Be well,
Don
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