Jump to content

Jub-Like Drone Build (Jubilee)


Recommended Posts

A) There are writings saying that the passive should be larger (or equal) in size compared to the active. Something to noodle / read about. In the Forte they are equal and in the Forte II the passive is larger. But in the project, the passive is half the size of the two actives (combined). So I'm wondering if we need two passives and one active.

The passive should be able to displace more volume - that can be accomplished with a larger radiating area and/or more excursion.

B) I'm still thinking that a good starting point for design is to assume we are just making a box type direct radiator(s) and passive(s) system. We can look at designs on software simulators. But in the project we can't vary box size and the choice of drivers is fairly well fixed, and the only thing we can vary in the passive is the mass. That is the good news and the bad news.

Unlike ports, passive radiators give you two degrees of freedom: the moving mass, and the suspension compliance. However, the limitation you'll run into is the natural Fs of the passive radiator itself...it is easy to move the passive at its natural frequency which will counter the normal resistance to motion needed to set the resonant frequency - so at this point, it's just like a big hole in the box and that's why you see the dip (rear wave cancels the front wave).

As far as the design approach - a passive should be approached just like a port. The difference in behavior is related to the "high" frequency performance of the devices. A passive radiator doesn't suffer from the pipe resonances of a port, which makes it a better option for a broadband device. The passive radiator also takes up less volume.

Anyways, the only way we can adjust the second degree of freedom with a passive is to buy a totally different device.

Although, if we really wanted to increase the rear volume, there's no reason the hatch lid couldn't be removed and a larger extension put over the same hole...

Link to comment
Share on other sites

  • 1 month later...
  • Replies 313
  • Created
  • Last Reply

Top Posters In This Topic

  • 2 weeks later...
  • Moderators

I just finished going through all 19 pages of your build thread and I am thoroughly impressed. Your ambition, zeal and craftsmanship are to be commended. Love the pics and the details you have provided. What an incredible journey you have been on. Looking forward to following this thread till completion.

Link to comment
Share on other sites

Time for a little story:

This past Sunday, I took a Carry Concealed Handgun Class (CCH) which is a requirement to obtain a Carry Permit in NC and most other states. The class was nine and a half hours of very intense training and well worth the cost, time and effort to take it. (I would certainly recommend this class to ANYONE that is involved with handguns…!) Since I am retired, I figured that I will be spending just about all of my free time at home/shop, which is in an Industrial neighborhood, that I should at least be “Legal” to carry a weapon. I have been around guns all of my life, have had formal training (Military) and was an avid hunter up until I went to Viet Nam (Whole “nother story”). Anyway, to make a long story short, I learned a whole lot about the safe use of firearms, handling them, the use of “Deadly Force” and self protection. While I thought I knew everything there was to know about guns, I was sorely mistaken and found this class to be some of the best time that I have spent in recent history. The instructor was a professional, a championship shooter and generally made the class interesting as hell. Nine hours is a very long time to hold peoples attention and he did it with ease. This whole experience taught me a very valuable lesson; In general, if you want to know something in depth, find a professional and learn from them, very simple formula. I have, for the most part, been self taught and while I will acquire most of the information that I need on a subject, I am not all that familiar with, learning from a true professional, is the best course of action.

That leads (I guess segway would have been a cuter phrase) me into my next statement, in reference to the Jub-Like Drone Project: This project has been on hold for a while, due solely to my lack of understanding about the proper way to test these new speakers. While I have acquired all of the test equipment known to man, have studied the proper procedures until I am blue in the face, I have absolutely zero comfort level in the fact of whether I will be able to do the test right and be able to present any kind of proof to my peers (here and elsewhere) that the test were done properly and that I had any idea of what I was doing. I know that if I do the test, I will have to provide documentation to the public and be able to explain exactly what I did with some sense of intelligence. Here in lies the problem,; while I THINK I know what to do with them, and what I should do, I have NO confidence in myself at all, in this area. I want to be able to provide solid information, that can not be questioned and I am pretty sure that I am at a point of needing that EXPERT level of person to HELP me get through these test. It will be a learning experience for me, help me to be able to provide very accurate information and will be the milestone, by which this new speaker design will fly in the future. This is the main reason that I have been putting the testing off, as I am not that sure of myself, to do the process, it is THAT simple.

Here is the DEAL: I will pay ALL expenses, to anyone that is willing to come and spend some time with me and do the proper testing of the Jub-Like Drone Project. This can be during the week, over the weekend and can cover several trips, whatever it takes to get it done. I have everything here and have the set of Goldens to use as a reference set of speakers. There are several of you out there that have the credentials and qualifications to do this and I am seeking your help, to get this project back on track. This is a serious offer so please give it some serious thought, if you are interested. Everyone has been GREAT in their support of my/our efforts on these speakers and now is the time to get them finished, as I know there is a lot of interest out there. They will either be a winner or will fade away as an unsuccessful venture.

Please PM or email me if you are interested.

W. C.

Charlotte, NC

P.S.: Also….All the Bud you can possibly drink…..! (That should get some takers

Link to comment
Share on other sites

I've been focused on work too.

In looking back at my posts what I've written might be vague or wrong. I've been dong some reading.

I've found my old impedance plot for the Quartet (this is at the input to the crossover), which of course has a passive radiator.

This is consistent with what I've read. That is, that the passive does indeed work somewhat like a port except that it has its own suspension spring.

At the risk of repeating myself: If this was a sealled box, we'd see a hump in impedance at the resonance of the system. There is a Dope from Hope about amplifier distortion which shows the input impedance of a Heresy. Compare to my plot.

A port or passive is tuned so that the box/port resonate close to the driver resonance. Therefore the box/port system causes a dip in the middle of the hump. Some people misread the results as two peaks but it is really the hump with a dip in the middle.

Therefore I think the Passive Jubilee should be tuned to have an input impedance like what I've shown here.

WMcD

.

post-2552-13819692909208_thumb.jpg

Link to comment
Share on other sites

VERY generous offer W.C. Hopefully someone will take you up on it. Your time involved in this project merits it. Hell, I'd take you up on it but it wouldn't take you long to realize I was relatively clueless as to what you want to have done.

I'll stay tuned as well. (No pun intended)

Carl

Link to comment
Share on other sites

Carl,

Thanks....I'm sure that the "required" testing is probably very simple and I have no doubt that I could do it. My biggest concern is the pundits and naysayers on here and in the general public of interest, that will attempt to rip apart anything that I do on my own and I will not have a comeback for them. The idea of two, relatively competent people doing the testing will take any bias out of it, which I may have. I want someone else with expertise and a neutral attitude to verify everything about these speakers, at the time of testing. That way, NO one can say....[bs]

You are right, with the amount of time and cost that are involved, this will be a very small issue and have a huge payback, in the long run. Anyway, whomever comes, it will be a grand time for all.....!

Link to comment
Share on other sites

Gil,

Thanks for taking the time to reply. The information that you are providing is very valuable to this project and the kind of stuff that I need to know. For testing I have two different passives that can be adjusted and THAT is the area that I need help in. The fine tuning of the passive is the key to this whole project and I need badly, for someone to hold my hand through the process. Again, I am looking for verification of what I am attempting, so there is NO doubtin aanyone's mind, as to the reliability of the testing. I hope that made some semblance of sense.

You wanna come to Charlotte for a few days, my schedule is certainly wide open....? I would be honored if you could find the time to help me out with this.

Link to comment
Share on other sites

A port or passive is tuned so that the box/port resonate close to the driver resonance. Therefore the box/port system causes a dip in the middle of the hump. Some people misread the results as two peaks but it is really the hump with a dip in the middle.


And in a perfect world, you would want that impedance dip to be associated with an SPL peak 1/4 to 1/2 octave below the FS of the driver. Passives only contribute a half octave max. In real world application, we really don't give a hoot about impedance that has no correlation to SPL output. For the sake of clearer explanation with some familiar spec's, take the LaScala.......impedance peak is at 90hz, the LaScala horn is a 50 to 70hz hi pass horn, tuning a port to be in the middle of the lascala impedance peak is inconsistent with successful tune port results for the LaScala. Tune port efforts for the LaScala targets the 40hz range. A 3db to 7db gain is realized using the volume expansion and/or port method. So in this instance, real world application of a tune port puts the target tune frequency 1/4 to 1/2 octave below the FS or usable FS of the driver in the given horn. Horn is 50 to n70 hz....tune goal was 40hz. Jubilee is simular to the lascala in internals. One needs to thinnk what the goal of the port in a jubilee really is. Is it to add low end spl of 3db to 7db, if so, tune frequency should be below FS. Or is it to clean up the low end with out necessarily adding SPL, then tune frequency would be higher. In terms of clean up...we are talking about reducing distortion and harmonics. Basically, I would not spend a hole lot of time playing with impedance until the goals of using a port is established.....why are we porting?


Link to comment
Share on other sites

The initial taper rate for the Jubilee is 97hz, the final taper rate is 40hz (as per JAES).

I would start out trying to tune the PR between 1/3~1/2 octave below the Fc of the last taper rate, IE: between 32hz~28hz.

It is difficult to tune a PR if you can't see it adequately, and the broad impedance minima is also difficult to interpret. The best method here is to measure the frequency of the two impedance peaks, take the product of the two, and then take the square-root of that product, the answer is the tuning frequency of the box-volume and PR combo. Example: 10hz and 70hz peaks = 700, the square-root being 26.46hz.

Link to comment
Share on other sites

The initial taper rate for the Jubilee is 97hz, the final taper rate is 40hz (as per JAES).

I would start out trying to tune the PR between 1/3~1/2 octave below the Fc of the last taper rate, IE: between 32hz~28hz.

It is difficult to tune a PR if you can't see it adequately, and the broad impedance minima is also difficult to interpret. The best method here is to measure the frequency of the two impedance peaks, take the product of the two, and then take the square-root of that product, the answer is the tuning frequency of the box-volume and PR combo. Example: 10hz and 70hz peaks = 700, the square-root being 26.46hz.

a 5 Star answer

Link to comment
Share on other sites

Conceptually.....with out playing on words.... fig 4-8 and the narrative to support it in the PDF is consistent with our discussion. True the the impedance dip is in the middle of two spikes....but look at where the tune is targeted....to the left or below the low end output...not at the low end of the response range. the figure and write up indicate at tune targeting 30hz which dropped the impedeance about 4 ohms abd resulted in about a 3db gain in low end spl (or down 2db at 35hz). Also notice in the write up that this particular configuration needs EQ cut below 25hz which is consistent with earlier discussions concerning the trade offs between SPL gains vs increase in distortion or harmonics. So as you tweak to boost low end SPL....you may need EQ to reduce distortion or harmonics like wise the inverse...you can tune to reduce distortion or hramonic's but that would get you less SPL gain. So depending what you are after...if it's SPL gain, you need to tune below the targeted frequency. One of the things I wonder about is if the horn is 40hz hipass.....tuning at the throat at less than 40hz would not make any sense....it would make more sense to block the passive hole and just put a nice sized port on one of the access panels outside of the cabinet like in the earlier LaScala model. Any way, the charts and PDF are helpful and consistent with my understanding of DJK's planning concepts.

post-22082-13819692981896_thumb.png

Link to comment
Share on other sites

I dislike when some pedant says "back to fundamentals." But we have a few issues going around here.

1) SF is pointing out an important issue about the potental need for an electrical filter which removes music frequencies down at 25 Hertz.in the described ported speaker system. This is to prevent the music from driving the diaphragm and motor beyond its linear region. This is not a problem when the driver is in a sealed box because the acoustic spring of the box prevents the diaphragm from moving too much.

Very generally, this was not a problem in the days of FM radio as a source which was limited to 50 Hz transmitted. Some LPs would get to 32 Hz or so on organ music. Sometimes turntable rumble could get that low. Rumble was mostly motor noise or something related to it.

Also, consider rock music. The unfretted string on a bass guitar is about 42 Hz. That is (I think) the same as the bass fiddle. But a timpany can go lower.

Now with CD's and movie effects on DVD and Blu-Ray, there are these infrasonics down to 30 Hz or lower. Subwoofers are designed to go down to 25 Hertz or lower. But they also usually have sophisticated filters to prevent over excursion. .

It is a problem with ported boxes because the box/port system loads the diaphragm down to a freq (preventing movement just below the system resonance. Then the box/port stops loading the diaphragm and it is free to move as far as it can, often more than it is designed to do. This is X max as far as excursion in some distance..

2) It may have not been descibed as such, but amplifier clipping and driving a speaker beyond its linear limits are pretty much the same thing. The respective systems can not respond to the peaks of the music. What should be a round peak of the sine wave gets flat topped. While diffucut to describe, the sudden or even slow flat topping is the equivalent of a a new frequency of sound. That is distortion.

3) Why are we looking at the elecrical impedance versus frequency measured at the input terminals of a bass driver system on a graph? There are descriptions of peaks and dips at frequencies and voodoo mumbo jumbo. Would it not be better if we had sensors to show exactly what is going on?

The answer to this is that instrumenting all the data is difficult. However, the elecrical impedance as reported at the input to the driver supplies a lot of data.

While this is getting a bit whacky -- it may be a sticking point of understanding why elecrical impedance as measured at the woofer input terminal tells us something about the box to which the driver is mounted in.

This is somethat like Sonar and the fact that the driver is actually also a microphone at the same time. It does "see" and report back on what it is attached to.

So an amplifier and sweep generaor sends a signal to the box system and then the microphone of the speaker also responds to what the box sends back to the speaker voice coil, particularly about when the system is resonating. It is complicated but the measured electrical impedance is actually showing that return signal in a way.

This may be something which is not well described in books on speaker design, but is of vital importance to an understanding. It is about "information." which is transmitted back though the speaker driver terminals in the form of impedance, which can be measured. It is telling us what is attached to the driver and how it is working acoustically or mechanically.

For example. We have discussed that acoustic port tuning is at a given freq. We are infering it from from a dip in electrical impedance. To a large extent we are using our woofer driver to as a sensor for he box and port to which it is attached to.

3. As far as alighnents and freqs. Much of this is like having a graphinc equalizer with one slide pot, and the ability to shift its peak in freq. Just where is the system falling off, and where do we put the boost.

My rant for tonight.

WMcD

WMcD

.

Link to comment
Share on other sites

Gil,

SO, if I understand correctly; The woofer impedence sweeps that I did a few pages back are providing us "most" of the information that we need to get started? Please remember, these were taken with and UN stuffed chamber, where the Golden Jubilee is completely filled with soft foam.

Gil, thanks to you, Mike and djk, for taking the time to really get into this, in depth, as I had got to a point of not knowing, in what direction I should travel.

As a reminder, the test subjects are:

Golden Jubilee - Reference

Cabinet A has the K-12 Stock Passive

Cabinet B has the Passive from Hell (TC Sounds VMP 12), which has about four pounds of washers that can be installed. It is loaded, at present, with 400 grams.

I will go back and check, but I do not believe that we did a sweep on the B cabinet, as of yet. Just the Golden and the A Cabinet. The nice thing about the Dayton woofer tester is, it is very simple to hook up and test with. I also have a Kenwood CS6040 ocilliscope, if needed.

I also looked into purchasing "The Loudspeaker Handbook" Man, they are pretty proud of that Puppy....at $150.00 plus dollars.....Probably will be leaving that one out of my Library, for a while.....

W. C.

Link to comment
Share on other sites

This is to prevent the music from driving the diaphragm and motor beyond its linear region. This is not a problem when the driver is in a sealed box because the acoustic spring of the box prevents the diaphragm from moving too much.

Just as a sanity check, I'd like to point out the sheer number of ported speakers on the market, including all those made by Klipsch too. They're not all blowing up....even the pro sound stuff.

Below tuning, you still have the mechanical damping of the driver.

In all reality, a typical home listening session should not be pushing the system anywhere near its limits anyway.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...