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In Reply to: RE: latest open baffle project posted by sober1 on May 23, 2015 at 18:07:22
A design like that exhibits serious low freuqency cancellation. What do you do for bass?
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Buy Chinese. Bury freedom.
Follow Ups:
I am wondering if you are not aware of Martin King's work with high qts woofers such as the Goldwood 1858.
http://www.quarter-wave.com/Project08/Project08.html
I have a couple of these 1858's and use them in a JE Labs style open baffle. There is plenty of low bass. I tried the H frames but my wife hated them but she is tolerant of the JE Labs style.
ray
Try the articles in the URL mentioned below and also the link in my first reply.
It will probably also be helpful to read about the Manzanita open baffle speakers at
http://www.diyaudio.com/forums/multi-way/110583-fast-fun-inexpensive-ob-project-46.html#post2752617
ray
I don't have time to read every article posted on the Web. The majority are junk science. I did however take a few minutes to skim Mr. King's PDF, and it led me to the chart below. I can't vouch for the accuracy of his article, but this doesn't look too far out of line in terms of my expectations for a small, open baffle speaker. Is this what's being referred to in this thread as tight bass response?
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Buy Chinese. Bury freedom.
...as the old saw goes.
Really. Dipole bass excites the room in different ways than you're used to. It also inherently has a smoother rolloff than infinite baffle or ported speakers. These conspire to make the experience very different, and to me, very *good* in a way that I hadn't expected.
This is true even for zero-baffle loudspeakers, which take the front/back cancelation to the extreme; or, phrased differently, start rolloff at a higher frequency. Despite this, they can sound quite amazing.
If you're in the Boston area you're very welcome to stop by for a listen to my system (http://cabezal.com/pix/ob/).
If you like the sound, that's fine, but the response predicted for this system is appalling. Phase shift will also be extreme as the frequency moves between peaks and troughs, bouncing off surrounding structures from different directions. Sorry, but dozens of books have been written by competent loudspeaker engineers outlining valid reasons not to operate woofers in such a manner. This thread has barely scratched the surface.
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Buy Chinese. Bury freedom.
You don't run it that way, do you?
Without the back cover the diaphragm will be un-loaded and tear itself up.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Yes, I run it that way. It works fine (at normal home-listening moderate levels). The horn loads the front of the diaphragm as usual, despite the free-air rear.
Edits: 05/25/15
Normally, the rear cover is not there to load the diaphragm (if it
supposed to, it would have a gasket), which I have not seen on JBL
or Altec drivers. This was confirmed by a JBL engineer. There
are SOME Altec drivers that have a black bakelite cap very
close to the diaphragm that is there for loading.
"There are SOME Altec drivers that have a black bakelite cap very
close to the diaphragm that is there for loading."
Altec sold those bakelite caps to add to existing drivers.
The instructions were to remove the heavy felt damping pad from the inside of the back cover (to make room for the damping cap) and install the bakelite cap, which fit right on the diaphragm itself.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Okay, but in what circumstances do you use the loading cap?.
Not sure if for a 500 x-over but that seems familier.
"As I understand it, loading caps have been used to help control diaphragm excursions with high power inputs at lower frequencies. A diaphragm's suspension, especially if made from aluminum, can work harden then fail after many large excursions. The loading cap presents an acoustic load to the diaphragm that helps to limit these excursions and extend diaphragm life.To the best of my knowledge, the loading cap first appeared in 1945 in the high frequency section of the 604 Duplex, really an Altec 802. I'm not sure whether the standalone 802 driver of the time used the loading cap. This was the first appearance of the tangential compliance in Altec drivers, and it allowed for greater low frequency excursions. It is probably not coincidental that the loading cap appeared at the same time. Since then, Altec most often fitted the loading cap to drivers intended for high level use, and omitted it and substituted the felt in the rear cover in drivers intended for consumer use. The felt pad in the rear cover dates back to the original small format driver, the Lansing 801 field coil driver of 1937, and is present in most of these early drivers.
When using any of these drivers for typical hi fi use with adequate protection from the crossover, I feel that the loading cap is unnecessary and that the drivers sound better without it. I have also found that the drivers sound better still, with greater clarity and less confusion in the sound, with the back cover removed entirely. This is a subjective thing, and somewhat controversial, and measurements won't show any difference with the cover on or off. This can only be done when the driver is not located in a bass cabinet, and is in a situation where kids or cats won't have access to the naked diaphragm!
Some people think [that would have been me] that the volume of air trapped by the back cover is a designed part of the driver, like the sealed rear chamber used for reactance annulling in a bass horn. I don't think this is the case in most drivers though. Early examples of the Western Electric 555W vented the rear of the diaphragm through a mesh screen, and Wente's patent on the original compression driver with circumferential phasing plug, as used in the Fletcher System, indicated screened vents in the rear cover. Lansing's first compression drivers for the Shearer Horn System were based on Wente's experimental driver, and his rear covers had a series of vent holes around the perimeter. My guess is that the pioneers eventually found that sealing the rear covers eliminated a source of contamination to the driver and made no difference in the response curves. Still, I have found many times that removing the cover eliminates a subtle layer of sonic hash from the driver's sound. YMMV of course. "
Steve Schell
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 05/26/15
I'd heard somewhere that old WE systems didn't use a rear chamber, but not seen that amount of detail nor the Altec pictures. Perceptually with my JBLs I feel they provide some "air" that's not present with the loading cap on.
As far as unloaded excursion-limit danger to the drivers, that's much more of a problem in the bass :)
This would also seem to indicate that these horns can't be installed inside the same cabinet with a woofer, even if the back is in place. Good info!
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Buy Chinese. Bury freedom.
I'm not familiar with Martin King. What does he say about front-rear cancellation of a small open baffle?
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Buy Chinese. Bury freedom.
"I'm not familiar with Martin King."
I am not familiar with Triode Kingdom.
"What does he say about front-rear cancellation of a small open baffle?"
It happens at a frequencies determined by the baffle dimensions. It is very predictable and can be incorporated easily into design calculations. Designing dipole speakers, including appropriate crossovers, using simulations and measurements is relatively easy if you understand the physics.
"Designing dipole speakers ... is relatively easy..."
Easy to construct , perhaps, but "design" implies the ability to meet objectives founded on a reasonable minimum level of performance. I don't see that happening here.
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Buy Chinese. Bury freedom.
Clearly I disagree. To each his own.
could you point me towards any literature in particular that will allow me to get at least a rudimentary understanding of the physics?
"the only thing necessary for evil to succeed is for good men to do nothing"
Google Linkwitz's website, he presents a very good/detailed overview of dipole speakers in a reasonably clear presentation. His design methods and products represent one set of trade-offs that can be made, my method and DIY designs are just another set of trade-offs. There are pro's and con's for each method.
Edits: 05/26/15
'
"the only thing necessary for evil to succeed is for good men to do nothing"
In my experience, bass performance from open baffles is truly extraordinary. It doesn't boom and thud, the way monopole bass does. It goes down -- deep down -- smooth. You should try it some time. Try it on your favorite acoustic bass tracks. Or on something with wobbly subsonics like James Blake.
There's a physical 1/f rolloff that needs compensation and produces high excursion at the lowest frequencies, but it's gentle and sounds very unlike the 24db/oct rolloff below resonance in a vented box.
What kind of speakers have you built?
Edits: 05/25/15
If the bass is canceling in my living room, then it's a good thing. It is fast and tight. When the volume is cranked it stays tight but also presses on my body. It literally shakes the room.
Now don't get me wrong, I didn't like the Alpha with the GW-1858 as it got way to boomy when cranked. That's why I dropped from 15" to 10". I was thinking that was not going to work either.The Eminence T/S parameters are very close with the GW, not so much with the Faital and I'm relying on the drivers roll offs. Using the LT Sound ECU-2, to my ears on my turf with my gear, seems to be able to sort it all out.
The future son-in-law was in disbelief had how spooky good stand up bass notes felt. Literally, tingles the forearm hairs at mid volumes.
I'm no design genius, I just got lucky after weeks of voicing my build with lots of driver swapping , solder slinging , cooking a few drivers , redesigning the wings and ranting and raving that this shit was making me even more freaking crazy. I trust my ears to tell me what I like bottom line. I'm not saying I stumbled on to a formula or design that can work for anyone else. I just know it works for me in my system, and as the late, great B.B. KING would say" I'm paying the cause to be the Boss". Just wanted to share my joy at finally get one right after so many bombs.
"the only thing necessary for evil to succeed is for good men to do nothing"
"If the bass is canceling in my living room, then it's a good thing. It is fast and tight."I'm not referring to your livingroom. Estimating the front-to-rear distance at the woofer cone, based on the photos you posted, the system should be down about 2.5dB at 100 Hz due to cancellation, and more than 7.5dB down at 50Hz. IOW, low bass is practically non-existent. You need a very large baffle (or an enclosure) to prevent this effect. That's why I asked what you're doing for bass. I just assumed you'd be using a sub in order to reproduce the lower frequencies.
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Buy Chinese. Bury freedom.
Edits: 05/25/15
the brains behind it all
Temporarily unemployed Velodyne in music setup.
First and foremost let me state unequivocally I know just enough to be dangerous, but I keep trying to learn.
Now I understand your query me thinks. The baffles are 35.5"s wide with wings as seen in the second pix. With passive crossovers, the bass sounded very good at low levels but lacking authority at my listening position. More volume just exasperated the problems,e.g. boom, muddy and the likes. After switching out the 15"s for the 10"s and extending the wings 6"s deeper is when I noticed the potential. I dumped the passive xos and notch filters for the active xo. Having absolutely NO experience with an active and unable to locate any documentation on this particular unit, it's been adjust, listen, readjust, scratch head hard, repeat as required.
Sunday was the first day I was able to have a couple fresh set of ears give them a listen. They (one being a musician) seemed to really enjoy them.
I've been attempting to find the optimum xo points via the active crossover for best output at approximately 9' to my listening position. The room measures 13' w x 18' long. The baffles are 3' wide and are 3' from rear wall and 6' V.C. to V.C. and I honestly don't have a clue as to what my settings "should be" but the current settings seems to keep the high end from beaming and glaring but still have excellent cymbal and brush reproduction with the bottom being authoritative and tight.
"the only thing necessary for evil to succeed is for good men to do nothing"
Semper Fi my fellow Marines!
and something else just occurred to me;
I demand my systems be able to perform at rock concert sound levels without breaking up and distorting all too shit. I demand it of my system in my Tundra as well. I don't listen at those levels but it's like how my scooters are; when I twist the wick I want to feel the Gs and do triple digits on the speed gun. Do I ride like that every day, HELL NO, I want live. I maybe nuts but I'm not crazy! When the urge strikes to choke the living shit out the throttle and the open road obliges, we go!
"the only thing necessary for evil to succeed is for good men to do nothing"
I understand what you're trying to do, but you can't achieve rock concert levels without a huge baffle (more than 20 ft in all directions), an enclosure or a compression chamber and horn. Without acoustic separation, the front and rear of the woofer cone are working against each other. You can create movement (and breakup) at low frequencies, but not significant SPL.
As for the asphalt, this is triple digits! :)
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Buy Chinese. Bury freedom.
I understand what you're trying to do, but you can't achieve rock concert levels without a huge baffle (more than 20 ft in all directions), an enclosure or a compression chamber and horn. Without acoustic separation, the front and rear of the woofer cone are working against each other. You can create movement (and breakup) at low frequencies, but not significant SPL.
As for the asphalt, this is triple digits! :)
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Buy Chinese. Bury freedom.
350 ci ? i see the 4 barrel, auto or stick? rear gear? looks like a tricked out front suspension. like the old Fuel Altereds' that has to be quite a handful off the line! I'll post my scooter when I get on my imac - have no pix on the iPad
Life is not a journey to the grave with the intention of arriving safely in one pretty and well-preserved piece, but to slide across the finish line broadside, thoroughly used up, worn out, leaking oil, and shouting GERONIMO!
OB's defy science in the bass department ........
Not literally.
Everything follows the laws of science/physics.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
> Everything follows the laws of science/physics.
Then, as in other aspects of audio, the model used
by science does not conform to perception.
Perception and preference rule the day.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
There are those who build and proudly share
and those who don't, and without a care
throw bombs at those who do.He hasn't heard them, it's just his thing
we must all bow down to the Triode King.
Edits: 05/25/15
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