Building a BIB for a tricky room

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Hi guys! first off I want to say this is an amazing place and thank you all for the wisdom you have poured into this forum, I am learning so much. also sorry for the long post in advance.

So i have a very tricky room to get good sound: 12ft high ceilings, 40ft by 20 ft with hardwood floors, giant granite counter tops and the walls all windows with no drapes (Acoustic Armageddon!!). Due to WAF the speakers have to fit on a large mantle 5ft off the ground that extends over the fireplace and entertainment cabinet that has a recessed space. dimensions of the space are 40 in high 20 in deep and 10ft wide though the speakers can only be 15 in wide. they will be driven by a yamaha A3070 that sits below in the entertainment cabinet with the TV, passive soundbar and subwoofer which I can co-opt to fill in the bass for these speakers if I need to.

The goals for the build are casual but good quality stereo music listening at low/mid volumes with an emphasis on clarity (currently when I play through the sound bar and built in celiling/surround speakers it is muddy unless I am in the sweet spot on the couch). For these speakers the prime listening area will be in the kitchen and dining area which are on the other side of the room about 20-30ft from the speakers and standing (thus the driver sitting on the mantle would be at ear height). i listen to mostly jazz, blues, folk rock.

My thoughts are to use a Dayton sp-220-8(currently on sale for $100) or tang band 1772 (about double the $) in a (small) BIB style build that is basically set upside down. The driver near the bottom with the mouth of the horn pointed down into the corner of the recess with some feet 3-4 in high to lift the speaker and make an opening. My woodworking skills are up to snuff and I have a decent woodshop so cabinet complexity is not a problem. I would like to get the best sound given the bad acoustics and would like to keep the budget under $500 but have room to go up if justified by improved SQ.

So i throw my problem to the collective wisdom of this forum. Am I headed in the right direction? Are there better drivers for my application? would a different cabinet design be better? Should I abandon the single driver horn idea and use a 2/3way large bookshelf?
 
If the 15” wide restriction for the speakers is due to SWMBO wanting to use the mantle for decorations, why not build some Cornu Spiral Horns and mount them on the wall above the mantle? You could even find an attractive print or matching wall color in an open weave fabric to cover the horns and act as a grille. That way you score more points for WAF acceptance and it would leave the mantle completely free for knick-knacks.
 
A Cornu used for home theater as well will be huge.

A MLTL, mounted upside down on the mantle might do the trick.
Driver at the bottom, and vent near the top.

Then, you finish the speaker with a granite finish, and the columns look like they are part of the mantle.
 

GM

Member
Joined 2003
The goals for the build are casual but good quality stereo music listening at low/mid volumes with an emphasis on clarity

My thoughts are to use a Dayton sp-220-8(currently on sale for $100) or tang band 1772 (about double the $) in a (small) BIB style build that is basically set upside down.

This came to mind, though just in concept [ignore the title]: Hawaii 5.0

GM
 
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So how does a smaller driver improve the situation? Let’s say I put in a Dayton ps180-8 6.5 in driver instead of the 8 in would that be better? If so in what way?

Have you looked at the BIB calculator?

It's not a matter of "better" but rather a matter of what size enclosure you can fit in your space. As the name implies, BIBs are big! Generally, the bigger the driver, the bigger the enclosure. So I suggested a smaller driver as it will likely work in a shorter enclosure within your 40" height constraint.

I took the liberty of running the PS220-8 for you in the calculator I have, these are the exterior dimensions in inches:

Depth 27.43
Width 19.31
Height 75.98
 
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A Cornu used for home theater as well will be huge.

Why? Admittedly, it’s a large room (40’ x 20’ x 12’, 800 sq ft, 9600 cu ft) (12.2 m x 6.1 m x 3.66 m, 74 sq m, 272 cu m) but a very live one based on his description of hard surfaces and lack of surface treatments. Any speaker in that room is going to be a compromise without some form of surface treatment but, as you and others have noted, a BIB isn’t going to work in that space with the limitations he is imposing. I offered the Cornu as a way around those restrictions if they are amenable to wall mounting a speaker. A pair of standard Cornus (each one roughly 29” w x 29” h x 6” d, 74 cm x 74 cm x 15 cm) wouldn’t impose themselves on the space above the mantel and with the right finish they could practically disappear. Plus, he already has a subwoofer for low frequency reinforcement.

Ultimately, the decision lies with Etaoin314 and his wife as to what is acceptable but I’m more curious why you think the Cornus would have to be huge. Based on his description he isn’t planning to use these speakers for home theater anyway, just casual listening from across the room. If Etaoin314 would submit a drawing of the room it might help us offer him other possibilities. It sounds like the speakers will be on the the short (20’) wall and projecting across the entertainment area into the kitchen but a drawing would clear up these perceptions.

If he is indeed limited to them being mantel-mounted in the specified space then I completely agree that an MLTL is the way to go. Perhaps Planet10’s HalfTower MLTL (http://frugal-phile.com/boxlib/P10free/microTower-maps-020615.pdf) would be acceptable as it will easily occupy that space. Either flip the driver location so it’s at ear height or use the wall mount version but set it on the mantel.
 
I think your height constraint of 40" limits you to smaller drivers if you want to go with a BIB.

So how does a smaller driver improve the situation? Let’s say I put in a Dayton ps180-8 6.5 in driver instead of the 8 in would that be better? If so in what way?

Here's the spreadsheet's math: Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 59 - diyAudio

As you can see, driver size is irrelevant beyond its physical size and even then a supra-baffle has been tacked on to mount overly deep and/or so bulky [massive motor] it needs to be spaced away from the pipe to keep from audibly restricting its airflow.

Neither does any height limits per se, only how low it will load, so with a max ~77" i'd. path-length = ~13560"/2/77" = ~88 Hz it will need to be vented to go low, hence the vented mini BIB alignment I suggested earlier [aka ML-TQWT, ML-Voigt, ML-horn depending on when and who you ask], though of course an [inverted] MLTL or TQWT or ML-TQWT works also.

To the first approximation then, driver choice is dominated by how much bass can be had from a ~5.5 ft^3 net volume [Vb] assuming nominally 3/4" thick material, preferably a no-void plywood such as BB, apple, marine grade.

GM
 
Wow thanks guys this gives me a a lot to think about.

Just to give a bit more detail wrt the room: It is an open concept design With mantle on the short wall in the living room at the end and the kitchen and dining areas parallel to each other with a large island on the kitchen side that goes almost the entire length of the kitchen area and a large dining room table in the dining area. It is reflective enough that you get just a bit of echo if you clap your hands. I also forgot to mention that I have another setup on the other side of the room that currently has a couple o f klipsch bookshelf speakers on top of built in cabinets that are all integrated together with chrome cast. Eventually I will get another Yamaha receiver for that side and use music cast and build another pair of matching speakers there. But that is for a later time.
 
thanks for all the good advice so far!! So looking around I saw the Singularities (Speaker Design Works) They are very close to my requirements, I am just 2 inches shy on the height (i reameasured carefully and have 41 in of clearance) and could even get a little closer if I use 1/2 inch wood for the top and bottom (I could use solid oak and brace it well and hopefully not lose much stiffness). So my questions are:1. how much does 2-2.5 inches of height matter in this case, and in what way (lower SPL, higher tune, steeper rolloff, distortion, etc) 2. does moving the port from back to front matter (it will be near the ceiling so a little HF sound should not be too problematic.) 3. can I compensate for the shorter height by moving the driver or port. Other ideas are to put a small angled reflector behind the driver to increase the path length a little bit to compensate. Would these adjustments even correct the problem or just introduce problems of their own. finally am I just barking up the wrong tree and I would get better results from a smaller driver/speaker.
 
So full disclosure I am pretty new to DIY audio in general this is my first real build so please excuse my ignorance... but my understanding was that in a ported cabinet the volume was the critical variable and the dimensions that acheive a specified volume are less important but I thought that in a MLTL the length was critical. Is that a mistake on my part, if so what is the difference between a portend enclosure and a MLTL design?
 
While I'd built a few speakers over the past 20yrs, I was always eager to let others do the math and just wait for the drawings, and never got around to learning the modeling part. From what I have gleaned over this period - and am happy to be be clarified on this - there are 4 main factors in the physical dimensions of a proper MLTL design:
- CSA (cross sectional area), with which I think you're free to juggle the WxD - but I personally try to avoid exactly square ;
- Line Length;
- Driver offset from closed end;
- Location / area of terminus / vent. There may be some who'd opine that its offset from the "bottom" of enclosure / line is less critical, or that placing it at the end of line should qualify it for a different name. I'm still living with a couple of designs that place the vent at the very end of the line, and am quite happy with the results.

FWIW, the only BIB I've I heard were Terry Cain's originals, and a somewhat compromised DIY build about 15? yrs ago, and for a variety of reasons just never got around to building any myself. They don't look to be a particularly difficult build compared to many I've accomplished, I guess there was just something about the aesthetics / size required for larger drivers that didn't appeal to the WAF submissive in me. If they're the right design for your particular application - great.
 
I have no reason to doubt Chrisb’s observations as he’s hung out here far longer than I have. On that basis the internal cross-sectional (CSA) dimensions could change from 9”x14.5” to 8.28”x15.25”. That might require using a supra-baffle for the driver depending on the cutout hole for the driver. I calculate a 28.75” vertical distance from the center of the driver to the center of the vent. Keeping in mind the new 40” cabinet height that would require moving the vent down to the bottom edge of the cabinet and converting it to a slot vent to maintain the appropriate distance. A slot vent the width of the new internal dimension of 8.28” would need to be 1.52” tall to equal the area of a 4” circle (but still 3” deep). The vent could be moved to the front of the cabinet.
 
Dims are normally i.d. [inside].

High aspect ratio cabs ideally should have the driver, vent at an odd pipe harmonic, i.e. from top [i.d.]*0.21, 0.349, 0.424, 0.698, 0.848 on down to the bottom for the vent being the most common, so with a short floor- stander, 0.21 is most common, though 0.349, 0.424 yielding the smoothest response with the least amount of stuffing.

At a glance it appears Curt followed these guidelines, but if you do your own i.d measurements Vs Curt's o.d. dims that will be fine too.

GM
 
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