Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 461 - diyAudio
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Old 1st October 2009, 05:36 PM   #4601
GM is offline GM  United States
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Works for me. The few pipe horns I did were triangle shaped to fit the corner and went all the way up, so obviously, its top was sloped to allow tipping it into place. Mine were all limited BW though with XOs in the 300-500 Hz BW.

In the same vein, one of the more interesting DIY speakers I auditioned back in '66 was a long cardboard tube with some cheap, small, car audio 'FR' drivers loaded at each end near the floor/ceiling and a horn (super) tweeter at its midpoint. This got me to rethinking TL apps in general and an easy way to have a ~Klipschhorn's LF performance without so much time consuming/tedious woodworking. Most folks back then weren't interested enough to pay extra even if they had the corners, so never fully developed it.

To my way of thinking then, the BIB concept comes up a bit short in most 'FR' apps, so when (if?) I build some they will be a true ceiling loader (and maybe floor too with a different folding) to potentially not need a corner or 'rumble' filter to protect the driver in a typical music app.

GM
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Old 1st October 2009, 08:46 PM   #4602
sedge1 is offline sedge1  New Zealand
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Quote:
Originally Posted by Pit Hinder View Post
sedge - wavelengths. Good idea, but the wavelengths involved won´t even notice that size of deflector.
Having the perfect room would mean having a perfect bank account...
Ah, OK, are you saying the shock waves are formed by the interface of the terminus to the room air ? (IE the mouth of the bottle)

And the corner placement helps reduce ripple anyway by having less interface area than a free space mouth exit ?

In order for a deflector to work at 40Hz it would need to be >10m away from the top of the speaker !

I'm still learning, only just coming to terms with the woodwork part of building speakers, the theory is even harder.

Thanks for the reply I'll go back to sniffing wood glue now.

Sedge.
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Old 10th December 2009, 05:45 AM   #4603
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Just finished reading this entire thread. So much info here that I'm not sure what all I've forgotten! Over 4600 replies. Wow.
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Old 10th December 2009, 07:35 AM   #4604
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sedge - in German we call it the mirror soundsource principle - no idea if there is such an English word.

Hang your boxes into free space - the sound energy will radiate into a sphere.
Put them on the floor - half sphere.
Floor and a wall in the back - 1/4 sphere.
Corner - 1/8 sphere.

It only works in bass, a mids or highs waveguide is much smaller - but it can get you the few more dB at 40Hz.
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Old 11th December 2009, 12:11 AM   #4605
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I know this has been touched on before in this thread, I haven't been able to find anything conclusive, so here goes.

I have a set of 126's that I want to put in a BIB, but looking at the recommended caps I'm a bit confused.

The speaker placement in the upwards firing BIB is way to low, so I was planning on making the cab that much taller and filling the bottom with small sandbags. That would make for easy tuning, improved stability and acoustic deadness, while at the same time allowing the driver to be higher.

But, and here is my problem, I have 275cm to the ceiling. If I extent the speaker to say 160cm, that still leaves 115cm to the ceiling. Isn't that too much to really use the room coupling too full effect? Would I be better off doing a floor firing version, even though the path of the sound is less ideal because it is obfuscated by furniture on the floor?

I guess in short my question is: Considering the hight of my room, should I try to stretch the top firing design to about 160cm, or should I just do an inverted BIB?
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Old 11th December 2009, 02:46 AM   #4606
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Invert it...

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Old 11th December 2009, 02:50 AM   #4607
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Not sure about your measurements but you do not have to 'fold' the BIB... you can straighten it out and leave the opening at the top if it will fit. Just a thought.

Godzilla
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Old 11th December 2009, 10:07 AM   #4608
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Quote:
Originally Posted by sedge1 View Post
RE Ripple...

If ripple is caused by the roof reflecting back into the horn has anyone tried fitting a corner wedge to combat this ?
Quote:
Originally Posted by Pit Hinder View Post
sedge - wavelengths. Good idea, but the wavelengths involved won´t even notice that size of deflector.


G'day Sedge and Pit,

Have a read of my EnABL room corner treatment, then try it for yourself when you stop laughing. If your results are similar to mine, then it will change the way you think about how big things have to be to have an effect on low frequencies.
I copied the following posts from the EnABL - Listening Impressions and Techniques thread here to make it easier to read.

Quote:
Originally Posted by Alex from Oz View Post
G'day,

Last night I made up some EnABL strips to treat the room corners directly behind my speakers.

Block size: 4 cm x 2 cm
Block Material: Norton 'All Weather Tape' (clear)

I stuck the blocks onto sheets of clear contact (the stuff you use to cover books).
The contact sheets have a 2 cm x 2 cm grid printed on the backing paper, so I took the lazy approach and defaulted to the 4 cm x 2 cm block size.
I only wanted to go up 60 cm because that is the height of the vintage speakers I'm currently playing with (see attached pic).

Results?
- Another level of clarity and depth in the soundstage.
- Bass is noticeably tighter and more detailed, but subjectively sounds a bit thin - however, the vintage speakers don't do really low powerful bass to begin with, so YMMV.
- diffraction off furniture that is in between the speakers has become audible.

There is a low cupboard in between the speakers that holds up the TV, amp etc. (not my choice).
I EnABLed the external edges of the cupboard using blocks made from the clear contact (2 cm x 1 cm) and stuck on individually.
This does seem to address the audible edge diffraction in the same way that it does on speaker cabinets.

Cheers,

Alex
Quote:
Originally Posted by Alex from Oz View Post
UPDATE - EnABL Room Treatment

YOU'VE GOT TO TRY THIS!!!

I added the EnABL wall strips to the back corners of my listening room tonight.
Also put a strip on the wall on each side of the two archways.
I'm blown away by this!

Results
I should have learned from last time, but I was so amazed I couldn't wait.
- more clarity in the soundstage
- more dynamic range across all frequencies
- bass is noticeably tighter, fuller, more open and more detailed

Even my 11 y.o son (who thinks I'm nuts BTW - yeah I know, smart lad) commented on the difference.
Usually he is completely disinterested in anything audio

Application Details
Block size: 4 cm x 2 cm
Block Material: Norton 'All Weather Tape' (clear)
Strip Material: Clear Contact self-adhesive book covering
Strip Height: 60cm

Click the image to open in full size.

Here is the picture I posted earlier.

Click the image to open in full size.

I had to hold a very bright lamp directly over to show the blocks in this photo.
It is pretty much invisible normally.

- - - - - - - - - - - - - - - - - - - - -

My Listening Room
I feel obliged to provide some details about my listening room.
It's nothing special and there is no acoustic treatment at all.

Click the image to open in full size.

Size:
3.3m x 4.7m x 2.4m (W x L x H)

Floor:
Concrete slab on ground with carpet.

Walls:
Timber stud frame, gyprock (drywall)

Furnishings:
- there is an archway at both ends (both are the same size)
- the other archway (not pictured) leads into a hallway with tiled floor
- curtain on one side wall over a window
- leather lounge on the other side wall
- two leather recliners side by side ay the listening end of the room
- you can see the speakers and the cupboard I referred to in earlier posts.

That's it for now.
I'm far too distracted by all this to say much more now.
I'll wait a day and see what happens when the tape settles in.
Quote:
Originally Posted by Alex from Oz View Post

[snip]

You could lay the blocks on strips of static cling whiteboard sheets
This would allow easy application and removal without risk of damage to the paint on the walls.
Also would be a really easy way to apply EnABL to speaker baffles.

If I was given permission, I would apply the EnABL pattern:
1) vertically from floor to ceiling in all four (4) room corners
2) horizontally along the skirting boards around the entire room
3) horizontally along the top edges on all four (4) walls just below the cornice.

If I was to do all the above, I would:
a) re-paint the entire room
b) mark up the pattern with masking tape
c) paint the blocks with clear matt finish paint.

This would give you the benefits of the EnABL pattern without the aesthetic issues.
A good compromise!

[snip]
Quote:
Originally Posted by Alex from Oz View Post
UPDATE - EnABL Room Treatment - Part 3

Well, I have now added horizontal EnABL strips into all four (4) corners (marked in red).
The yellow and red area represent the clear contact paper that I stuck the blocks onto.
The grid is a 2 cm x 2 cm to make it easier for you to see the layout.


Unlike the verticle strips which I applied in stages, I applied the horizontal strips (marked red) all at once.
The impact was both dramatic and awful.
Thankfully, I know that the tape takes 24-48 hours to settle in.
So I've had them in place for 1 week.

Results
The change that struck me most is in the bass.
There is a new level of deep bass.
At low volumes the bass is still there and very clearly defined.

I'm so pleased with the results that I don't plan to do any further room treatment for now.

Application Details (repeated)
Block size: 4 cm x 2 cm
Block Material: Norton 'All Weather Tape' (clear)*
Strip Material: Clear Contact paper (self-adhesive book covering)

(*I've been made aware that this is only available in Oz.
So alternative block material thickness
- 3 layers of contact paper OR
- 2 layers of PVC duct tape).

A good alternative to contact paper may be those static cling whiteboard sheets cut into strips.
You can peel these on and off at will without damaging the paint.

If you can to try this in your room, then do it!
And if you do, please post your listening impressions.

Cheers,

Alex
Quote:
Originally Posted by Alex from Oz View Post

64cm x 54cm (h x w)

Click the image to open in full size.
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Old 11th December 2009, 10:08 AM   #4609
Squeak is offline Squeak  Denmark
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So what is the max, or recommended distance you'd advise from mouth to ceiling, if I go with the option?
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Old 22nd December 2009, 05:26 PM   #4610
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Question Optimum distance between horn mouth and ceiling/floor

Quote:
Originally Posted by GM View Post
Greets!

It's dependent on the room and the amount of gain BW required to make it ~flat in-room, so all of this would ideally need to be calc'd on an individual basis using pressure wave math. As a general rule though, the pioneers of audio considered mouth sizes in the 110 - 120 Hz range sufficient for corner loading, so Ron's ~36" would be my point of flopping it over for floor loading if corner loaded and the longer of ~18" or the (3*mouth radius) for mid wall mounting.

GM
Hi GM

Could you please clarify what you are saying above for me. I am planning for a pair of BIBs, using fostex fe164's. Actual measured: fs=58Hz, Qts=0.35 and Vas=28.8Ltrs. Tuning to fs(ie.58Hz) gives me line length of 295cm and height of 147cm. Tuning to fs*0.707(ie. 41Hz) gives me line length of 417cm and height of 208cm(!)-and then there is everything in between the abovementioned line lengths. My ceiling height is 270cm. BIBs wil be up against wall but not in corners. So, from the above, the horn mouth can/will/should/could be between ~60 and 120 cm from the ceiling.

What should I consider in order to, hopefully, get good/optimum results without having to rebuild, thereby saving time and money.

Any advice from the BIB gods(won't mention names-you/we know you are!) will be highly appreciated by this speaker-building/full-range rookie.

Happy holidays and a happy new year to all.

Thanks
Peter
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