Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 182 - diyAudio
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Old 23rd November 2006, 05:02 PM   #1811
mrbubbs is offline mrbubbs  United States
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Excellent. This may be the design path I'll take instead.

About the in-room response... yes, I have read your explanation on the corner loading smoothing out the response. Good to know about the +/- 4 db too.

Thanks, Scott!

Quote:
Originally posted by Scottmoose
If you increased enclosure height you'd extend the bass, probably by another 10Hz or so, and flatten the curve out somewhat as you've also got a fair bit extra box volume. However, the driver would be about 2ft over your head, unless you listen when sitting on a tall bar-stool. Not a terrible problem of a huge driver, but a trifle excessive for anything smaller... I chose the external dimensions for the monolith specifically to match the 1x4x9 ratio of the Monolith Kubrick & Clarke dreamed up, without needing to go to an excessive number of decimal places. You could do (external dims) 10in deep x 22.5in wide x 90in tall if you like. That would work. Very large of course, but Bigger Is Better after all.

Do you mean why does the response of the modelled cabinets look rough? The models are 1/2 space -they don't acount for the load the room imposes on the pipe when it's correctly corner loaded. You will get some ripple, but anything over about 250Hz is massively over-estimated by these models. In reality, it's usually contained + / 4db in my experience.
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Old 24th November 2006, 03:29 AM   #1812
mrbubbs is offline mrbubbs  United States
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Hmm.. now that I think about it.. if the "Z driver" cannot be adjusted so that the center of the speaker isn't my ear height... then I probably won't be happy. Guess I'll stick with the original 72" height plans. Unless the 10"D x 22.5"W x 90"H keeps the center of the driver around 43.25" as the original plan, then that'd be great!

Maybe I'm thinking about this too much and should just go make the originals now. I subscribe to the measure 43 times and cut 0 times methodology thus far.

Quote:
Originally posted by Scottmoose
If you increased enclosure height you'd extend the bass, probably by another 10Hz or so, and flatten the curve out somewhat as you've also got a fair bit extra box volume. However, the driver would be about 2ft over your head, unless you listen when sitting on a tall bar-stool. Not a terrible problem of a huge driver, but a trifle excessive for anything smaller... I chose the external dimensions for the monolith specifically to match the 1x4x9 ratio of the Monolith Kubrick & Clarke dreamed up, without needing to go to an excessive number of decimal places. You could do (external dims) 10in deep x 22.5in wide x 90in tall if you like. That would work. Very large of course, but Bigger Is Better after all.

Do you mean why does the response of the modelled cabinets look rough? The models are 1/2 space -they don't acount for the load the room imposes on the pipe when it's correctly corner loaded. You will get some ripple, but anything over about 250Hz is massively over-estimated by these models. In reality, it's usually contained + / 4db in my experience.
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Old 25th November 2006, 09:59 AM   #1813
stroop is offline stroop  Germany
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Hi Scott,

Thanks for that, I know you've said that before...sorry to make you repeat yourself. Sometimes seeing the graph and hearing it bears no relationship.... So, basically the lower frequencies are represented by the graph (kind of, discounting room gain) then from about 250Hz the sound is, again smoothed out due to the room and the lessening influence of the horn. The graph is very much an a guide not a rule as to the sound! I guess prolonged dips in the graph are reasonably important, like the one at about 100Hz, but again even that, is not that influential from what people say. Soooo the response of the driver itself becomes more important above 250Hz, is that correct?

I tell you, being an opera singer and working to produce overtones, there is so much to sound reproduction that cannot be comprehended, especially with regards to room gain! Ever heard a great Soprano do a pianissimo in a 2000 seat theatre?!! It is a tremendous experience! How is it, that a note that is barely audible when you are standing next to them, can be heard bouncing back to you from the rear wall, at what seems to be, almost the same sound level! It's like pouring concentrated raspberry cordial into a glass of water! Believe it or not learning more about horn shapes for different frequencies makes it more obvious to me, that it is really similar to what singers do naturally. That is...the core of the note...harmonics are a different story altogether....

Sorry about the dumb questions and the rant,

Cheers Stroop
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Old 25th November 2006, 10:25 AM   #1814
dmason is offline dmason  United States
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Good questions. My kind of rant.

0300, and I find this damn thread endlessly fascinating. Good going. Nice little machines, Chang...

ps: have both the FX120, and the El Cheapos. Both sound very nice. The Fostex is surprisingly refined, even in its raw state.
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Old 25th November 2006, 11:43 AM   #1815
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Quote:
Originally posted by stroop
Hi Scott,

Thanks for that, I know you've said that before...sorry to make you repeat yourself. Sometimes seeing the graph and hearing it bears no relationship.... So, basically the lower frequencies are represented by the graph (kind of, discounting room gain) then from about 250Hz the sound is, again smoothed out due to the room and the lessening influence of the horn. The graph is very much an a guide not a rule as to the sound! I guess prolonged dips in the graph are reasonably important, like the one at about 100Hz, but again even that, is not that influential from what people say. Soooo the response of the driver itself becomes more important above 250Hz, is that correct?

I tell you, being an opera singer and working to produce overtones, there is so much to sound reproduction that cannot be comprehended, especially with regards to room gain! Ever heard a great Soprano do a pianissimo in a 2000 seat theatre?!! It is a tremendous experience! How is it, that a note that is barely audible when you are standing next to them, can be heard bouncing back to you from the rear wall, at what seems to be, almost the same sound level! It's like pouring concentrated raspberry cordial into a glass of water! Believe it or not learning more about horn shapes for different frequencies makes it more obvious to me, that it is really similar to what singers do naturally. That is...the core of the note...harmonics are a different story altogether....

Sorry about the dumb questions and the rant,

Cheers Stroop
No question is dumb if you want to know the answer to it.

A friend of mine, Grace, is a soprano. Which reminds me -I must speak to her at some point; I haven't for ages. We've both too much going on. Speech is also difficult to get right. As well as being a historian and occasional teacher, I do some stage acting, so I know the feeling. I still love the old theatres best, with the horse-hair in the plaster. The acoustics are superb, rich, and warm, and you can hear every nuance of speach. Good for the performers too, as they can judge their level of projection to a fine degree.

You're pretty much on the right lines. The graph only gives a rough respresentation of the bass extension, sensitivity, and the rough shape of the response curve. Prolongned dips (nulls) in the response are important, but only tend to become so with increasing frequency. Below about 250Hz, they tend to be flattened by room-modes and psycho-acoustic masking also helps. Our hearing acuity drops with decreasing frequency as you will know from your profession, so we tend to 'key off the peaks', as GM would say, and mentally fill in the rest, just as we do subconsciously all the time in real life. Above about 250Hz, the curve will stay much closer to the driver's infinite baffle response (blue line) due to the room's effect upon the response -with these cabinets, the room actually forms a part of the speaker and completes the horn-mouth, the massive increase in (virtual) mouth size provided by the reflectional boundary conditions killing the harmonic distortion characteristic of a small mouth. Reduces pressure too. Baffle-step loss is not shown on the graphs either, but it's negated by room-gain, and running the horn chamberless, over the widest possible pass-band.

Nothing's ever completely straightforward is it?
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Old 25th November 2006, 11:47 AM   #1816
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Quote:
Originally posted by dmason
Good questions. My kind of rant.

0300, and I find this damn thread endlessly fascinating. Good going. Nice little machines, Chang...

ps: have both the FX120, and the El Cheapos. Both sound very nice. The Fostex is surprisingly refined, even in its raw state.

Nice unit isn't it. The detail will gradually improve over the next week or two. If they behave like the ones I heard, the bass will come very abruptly: one minute it's acceptable, the next you can hear it suddenly free, like a dammed stream being opened up.
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Old 25th November 2006, 12:53 PM   #1817
stroop is offline stroop  Germany
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It certainly isn't ever easy!!!!

The old theatres can be lovely until someone lines the set with carpet and curtains....then insist that you wear a felt wide brimmed hat and then wonders why you can't be heard.....now that is when my job gets frustrating. Of course this would make perfect sense to you all, as all that material soaks up the high frequencies that I would rely on to make my voice carry over and cut through the orchestra. Thankfully in my current job I'm very lucky. Nice theatre, good acoustically but has definately a couple of traps on stage....some places you can sound like john vickers (exaggeration!!) others you can sound like pee wee herman. It's nice to get reflections from a live space as we only hear a fraction of the sound we produce (I think 30% is a figure bandied about), as you would be well aware, there is a massive difference between volume and projection...

Reading this site should be mandatory for set designers!

Sorry...

Back on topic
So basically, the large size of the mouth (which includes the room) decreases distortion by not constricting the sounds favoured rate of expansion, allowing it all to mix together nicely and reduces pressure build up otherwise caused by a constriction of lower frequencies(ie. narrow horn mouth). The higher frequencies become infinitely baffled (like me) above a certain point because, due to the smaller wave length needs less space to be infintely baffled. Is that right?

All the frequencies that the driver poduces exist... but it is just a matter of hearing them at the listening position...at the right time and from the right direction (higher frequencies), and being somehow equalized. Which the BIB does very well...

Thanks for putting up with me today, a bit jumpy you see,

Stroop
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Old 25th November 2006, 01:53 PM   #1818
gychang is offline gychang  United States
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Quote:
Originally posted by dmason
Good questions. My kind of rant.
Good going. Nice little machines, Chang...

ps: have both the FX120, and the El Cheapos. Both sound very nice. The Fostex is surprisingly refined, even in its raw state.

Did u also make the BIB with El Cheapos?, Was I hallucinating about the excellence of sounds?.

I also just finished the FE107E BIB, only have less than 2 hours on it and also sounds excellent to my non-expert ear.

I wonder if anyone else have built the BIB with el cheapos...

gychang
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Old 25th November 2006, 02:53 PM   #1819
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Default Suprabaffles and FE127e BIB

I'm closing in on completing my BIB for the FE127e.

Though I have a supra baffle and everything is
cut, I want to do a dry fit without it. I prefer using
grilles on the completed project and eliminating the
supra baffle simplifies this greatly.

My question is on clearance for the driver: if the
driver touching or clearance is real minimal, how will that
effect performance?

Is there any fudge factor with the divider-- meaning
can a spacer be put at the apex so that the v is not
an absolute point at the closed end?

I have used all the measures stated for the 127e
as stated earlier in the thread at post #1469.
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Old 25th November 2006, 05:12 PM   #1820
dmason is offline dmason  United States
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Chang,

No you are not hallucinating. The little elCheapos are definitely music makers. I have heard some expensive drivers that were definitely not music makers, and as I said, I seldom equate expense with quality in this krazy realm. I will say that the FX120, with a good source and neutral sounding tube amp of 3+ watts will do a very nice job. Tuff little bastards they are, with healthy Xmax, and can take some current as well. I like. I think they are bullseye BIB candidates. That they remind me of my gone-but-not-forgotten FX200 is a source of comfort.
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