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Old 28th January 2013, 04:07 PM   #5161
GM is offline GM  United States
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Sure it can! When acoustically close to a more confining boundary the driver 'feels' a longer path-length, larger mouth horn same as a horn can be increasingly foreshortened, reduced in mouth area with increasing boundaries.

The only difference when the mouth is ‘gapped’ to another boundary is that due to the faster expansion it doesn’t begin to adhere to the simple +3 dB theoretically ideal gain with increasing boundaries until within a ¼ WL same as for summing multiple drivers.

GM
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Old 28th January 2013, 04:16 PM   #5162
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Quote:
Originally Posted by xrk971 View Post
How much stuffing is usually required and where do you put it?
Stuffing density up at the peak down to below the driver will have the most impact over the widest BW, so where the initial testing should be optimized, then lining or light stuffing may be required to damp any parallel wall, mouth eigenmodes below this point.

No clue about the huge peak since I'm guessing this is up around where the 3rd harmonic dip [not peak] should be.

GM
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Old 28th January 2013, 04:31 PM   #5163
xrk971 is offline xrk971  United States
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Default FIB Sim in HornResp

I did a quick simulation of my FIB geometry in HornResp and got something pretty ugly. Is this typical for a BIB (the characteristic sound of a BIB)? Of course the peaks will be smoothed over somewhat with stuffing but the main result is that the circa 190 to 200 Hz bump is really just one of the main horn peaks above the fundamental. I don't think any amount of stuffing will make this less than the desired fundamental (confirmed with more measurements with added stuffing which only broadened and shifted the 200 Hz bump to the left). Listening to it though, honestly, it sounds pretty good nonetheless.

Can anyone else comment on their sims of the BIB, perhaps one in MJK with proper stuffing applied?

This may be the perfect thing to test a Karlson slot to see if it can reduce the second and third peaks.
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File Type: png FIB-FR.png (68.7 KB, 308 views)

Last edited by xrk971; 28th January 2013 at 04:45 PM.
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Old 28th January 2013, 04:46 PM   #5164
GM is offline GM  United States
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Is this the horn only or combined response? Regardless, it looks nothing like the few calculator designed BIBs I've simmed in HR.

GM
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Old 28th January 2013, 05:12 PM   #5165
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Quote:
Originally Posted by xrk971 View Post
Flatter is Better Plan for Vifa TC9FD driver. What is not shown are numerous vertical braces every 2 to 3 inches, braces would be aligned parallel to direction of flow (diagonal in the corners). Probably 25 to 30 2 in wide x 4 in tall pieces of 3/16 in thick foam core braces glued with hot melt to back panel and then with PVA to front baffle. Use 90 deg square guide to ensure braces are vertical and square when fastening to back panel with hot melt glue. I would put stuffing in closed end and loosely up the 180 deg turn. Adjust to taste. I think that there may be extensive bass with this design and it may require more stuffing than usual.


For those wishing to build this out of wood. You can still use plywood (I would use 1/4 in thick to keep it light so it can be hung on wall). Use the foam core just for the internal diagonal as it is easy to curve by scoring lines on the concave side.

Hmm, I have one pair of Fostex FF85WK lying around. It's Qts is bit lower than Vifa TC9FD. I could try to build similar "FIB" from these.

Is BIB-calculator-sheet in any use of adjusting these measures?


Cheers,
hkk
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Old 28th January 2013, 05:32 PM   #5166
xrk971 is offline xrk971  United States
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GM,
My mistake, I had an incorrect setting (leftover driver-chamber from earlier sim with same driver) on the above sim. Here is the sim with what I think are the correct settings. Included are the dimensions and schematic. Does this look closer to a BIB? Note that I modeled the first part as a parabolic and the second part as an exponential to get the curves to behave the way the do on the as built unit. No attempt was made to deal with the split mouths. Horn output only.
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File Type: png FIB-FR-2.png (94.7 KB, 288 views)
File Type: png FIB-schematic.png (11.5 KB, 283 views)

Last edited by xrk971; 28th January 2013 at 05:36 PM.
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Old 28th January 2013, 05:36 PM   #5167
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by hkk View Post
Hmm, I have one pair of Fostex FF85WK lying around. It's Qts is bit lower than Vifa TC9FD. I could try to build similar "FIB" from these.

Is BIB-calculator-sheet in any use of adjusting these measures?


Cheers,
hkk
I got my dimensions from the BIB calculator spreadsheet - based on driver Fs, Vas, Qts. The Fostex FF85WK should work very well in this and you will probably get a smaller cabinet than the Vifa as the volume scales with Qts to the 1.2 power, IIRC.
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Old 28th January 2013, 07:18 PM   #5168
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Default Update FIB Freq Response

Here are the latest results with more stuffing added. There are some differences between the two in the higher frequencies, may just be contamination from driver direct source, or it could be due to differences in the bracing and variability in stuffing. The 190 to 205 Hz peak has now broadened and shifted to the left. I am not sure what to do about it at this point - at least the two channels are somewhat balanced. I am open to suggestions as to how to fix.

Measurements were made 2 in away from mouth of large horn with speaker flat on floor (red and blue lines). Green line is 12 in away between large and small horn. 1/7th octave smoothing.
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File Type: png FIB-FR-Both-FR.png (27.3 KB, 237 views)
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Old 28th January 2013, 09:01 PM   #5169
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Hi Greg,

Thank you again,
I have now gone through all 500 plus pages.
Wow there is a lot of information here.
It's a nice problem to have.

I wish I had read this earlier.
Didn't have access to internet on the weekend and went and bought plywood and had it cut to spec. (Have a table saw but it's not easy manhandling a 4*8 sheet all by myself)
I was a little impatient to get started.

In an earlier post you said with regards to the FE206E that one should raise the qts in the spreadsheet to 3.5-4 and alter the dimensions. Or at least that is what I interpreted. From what I gather here, you are saying the same thing about the FE206EN.

Qts at .4 it gives me 18*25*76 (as opposed to 12*16*76)
Now that I have my wood cut, will it still sound okay?
I'm planning on building a wing for it and extend the front baffle.
Can I do anything to mitigate the lack of bass with the current dimensions.

The Bottlehead S.E.X. amps is well reviewed.
It is a stereo integrated single ended triode (SET) amplifier of 2 watts per channel output.
Terry Cain had ordered several units to go with his Abbys.

Single Ended eXperimenter's Kit

My current amp is a Cambridge Audio Integrated amp the Azur a540.
Cambridge Azur 540A integrated amplifier
Power output: 60Wpc into 8 ohms; 90W
into 4 ohms

I'm also playing with a sonic impact T-amp (the original)

A few pics of progress so far.
Click the image to open in full size.
Chamfered out with a rasp that belonged to my great grandfather... Feels good to use his tools.

Sawtooth marks on barn lumber (not going to sand these out as they add to the character.)
Click the image to open in full size.

Front baffle right side up.
Click the image to open in full size.

-andré-

Quote:
Originally Posted by GM View Post
Greets!

You’re welcome!

Hmm, best overall to tailor the speaker to the amp, i.e. build them too large acoustically, so that it won’t cause the flea power amp to ‘lay down’ trying to drive a smaller than optimum net Vb due to the amp’s high output impedance effectively weakening the driver’s motor [raising Qes/Qts].

lacking any SEX amp specs, I can only assume it’s a ~matching impedance, so using a ~0.4 Qts to calculate the BIB should be plenty high enough and if it should sound too ‘boomy’/’loose’ and/or has too much mid-range coming out the terminus with the higher DF amps, then you can either add some series resistance and/or more stuffing initially.


GM

Last edited by B00B00; 28th January 2013 at 09:05 PM. Reason: image link fixed
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Old 28th January 2013, 09:15 PM   #5170
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This project using warn lumber is going to be interesting. The wood will be recycled into a fantastic pair of speakers!

Zilla
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