Taking on the Slot loaded OB project... - Page 3 - diyAudio
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Old 29th January 2012, 03:13 PM   #21
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Default Interest...

Hi Charles

Just wanted you to know your not alone.

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Just received them the end of the week. Mine came packed well, double boxed...no problems with damage as far as visual inspection. Haven't hooked them up to anything to test function yet. And...

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Part of my hoard.

I tend to want to figure things out completely before I start to build as well. That has lead to about 4 years of lurking, trying to learn everything about speaker building and a couple of unfinished projects. It's not gonna happen for me without actually building and completing something.

My approach to this project will be different. I don't really have a lot of time to post up about my research because I'm in the middle of trying to finish a pine wood derby car with my son this weekend, but I have spent a lot of time re-reading MJK's paper on open baffle design and found several other sources with information that is helping clarify how to try a working approach with this project where something actually gets built and has the flexibility to have adjustments made to the design fairly easily. I think the OB format lends itself to that.

Some pages I found that have been helpful...

MJK's...http://www.quarter-wave.com/OBs/OB_Design.pdf

An Amateur Audio page...OB Design - amateur audio

Music and Design has a download link for the A, B, C, Dipole spreadsheet based application...it has a very in depth technical discussion about the approach to designing these open baffle dipole speakers. A lot is over my head, but there is useful info that is understandable. It is all in the included How To...file of the download. This didn't work on my Vista machine...I had to fire up my old desktop with XP to start reading it.
A, B, C, Dipole

I know there are a few other pages I came across, but I may have lost track of them. I also read the 37 page long original thread on here devoted to the subject of the slot loaded OB. As well as Mr. Pass' article at Enjoy the Music. Oh!...also some of the testing that was done on the design at.
Nelson Pass Slot loaded OB

I will try to maintain a design that will assemble the chambers for the woofers separately in pairs. I believe it was mentioned in the original thread on here that it appears the woofers were mounted in pairs in what looked liked three chambers that lead out to one larger slot joining them all. I'm not sure if that is correct. The info from Mr. Pass' original article states:

"The six woofers are mounted in a chamber formed by laminating five layers of 0.75 inch particle board, and are arranged to squeeze the air out a front slot 2.25 inches wide and having about one third of their combined piston area."

I think the important thing is that since Mr. Pass says that the design can be altered with some creativity...by either experimenting with the number of woofers, baffle size or etc...that the main point is to maintain a slot with an area approximately equal to 1/3rd of the combined Sd of the number of speakers that it is loaded with. Obviously there was no Sd parameter listed for the Peerless drivers at PE. Calculating it seems overkill for my attention span, as I looked into that. I found another thread on here discussing that topic...general guidelines were put forth by a member for about 200 CM squared for an 8" driver. My personal research through comparing currently available 8" drivers puts the number somewhere slightly over that figure in the range of 205 to 230 CM squared. I'll be working with a number in the middle of the range.

Besides that I have been thinking about what the total efficiency of the woofers will be when they are assembled with the open baffle as I was originally hoping to come up with a low frequency system that might be efficient enough to use with the 206e and a front loaded horn. Not sure if that can happen even if I do maintain a larger baffle size. This project may require experimentation with whatever active equalization I have around or maybe even the purchase of a MiniDSP to use with some multi channel amps I have for HT use. It is not ultimately how I want to drive the system. That I want to do with some push/pull horn tube amps I have hoarded. So some sort of testing and translation of any experiments into a passive crossover will eventually be required. Sorry...out of time...got to get to work on polishing axles. Sorry for the huge post...cheers.
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Old 8th February 2012, 08:58 PM   #22
chops is offline chops  United States
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Well this project has been at a standstill for a couple of weeks now, for a couple reasons. I've had other things going on that needed my attention and funds first and the fact that there's STILL no useful information and/or help offered for this design.

chromenuts, you're the only one that's offered any real kind of help and I appreciate that. It's a lot more than anyone else has done, including the "creator" of this design. With that said, it's still not enough information for me to move on and start with I think.

It's really quite upsetting that even Nelson Pass doesn't care to comment or help out at all on his own design (or answer emails for that matter). That alone makes me want to just scrap the entire project and sell the drivers, or at least go in a different route altogether. Why do I want to invest more time and money in a design from someone who could care less?... In the end, I don't think I'd be able to enjoy the finished product.


Sorry to be so harsh and negative, but that's how I feel.
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Old 8th February 2012, 09:59 PM   #23
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Why? Methinks you may be expecting too much. Nelson is a rather busy man: he's got Pass Labs & First Watt to run, plus, no doubt, a myriad of other things on the go. He put that project out in a generalised manner for people to experiment with, not as a finished deal with specific guidelines or design[s]. If that's what you want, then as far as I can tell you picked the wrong thing, which is hardly his fault. Since this has upset you so much, it would seem that your best option will be to sell the drivers, and build something comprehensively documented.

Last edited by Scottmoose; 8th February 2012 at 10:13 PM.
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Old 8th February 2012, 10:47 PM   #24
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+1

The site is diyaudio, and while there are some projects that are so well documented they almos build themselves, one of the things that will bring joy is struggling with implementing and tweaking a project.

The finsihed project, full of your blood sweat and tears, makes it all worthwhile vs. slapping down cash for a finished product.

The slot loaded project will remain where it is, perhaps you should complete another couple things then chew on this when you can do so without worrying about others input.

maybe one day it can be something you and Nelson discuss as a collaborative thing?
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Old 8th February 2012, 10:56 PM   #25
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To his great credit, Nelson does reply on diyaudio. Probably more often than he has time for. He also replies to emails. It takes time, but you'll get a reply. Just don't expect it to be a long one. He is not going to spoon-feed you.

And there is a reason for that. You will learn more and enjoy more if you find out things by yourself rather than somebody feeding it to you. If want to have a readymade design, pick something simpler. Or splash the cash.
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Old 8th February 2012, 11:25 PM   #26
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Quote:
Originally Posted by Etocynned View Post
+1

The site is diyaudio, and while there are some projects that are so well documented they almos build themselves, one of the things that will bring joy is struggling with implementing and tweaking a project.

The finsihed project, full of your blood sweat and tears, makes it all worthwhile vs. slapping down cash for a finished product.

The slot loaded project will remain where it is, perhaps you should complete another couple things then chew on this when you can do so without worrying about others input.

maybe one day it can be something you and Nelson discuss as a collaborative thing?
That might be what I end up doing. Just giving this a rest for a little bit, get some other projects sorted, then revisit this project at a later date. The biggest thing is needing someone else do the wood cutting for me. I don't have the tools or space anymore as I live in an apartment now. And trying to get my schedule and his to match up is next to impossible right now.


Quote:
Originally Posted by ra7 View Post
To his great credit, Nelson does reply on diyaudio. Probably more often than he has time for. He also replies to emails. It takes time, but you'll get a reply. Just don't expect it to be a long one. He is not going to spoon-feed you.

And there is a reason for that. You will learn more and enjoy more if you find out things by yourself rather than somebody feeding it to you. If want to have a readymade design, pick something simpler. Or splash the cash.
I don't want to be "spoon fed". I would however like to have a little bit more information to go on before starting any cutting. There's virtually no info on the innards of the slot itself.

If each pair of woofers are indeed in separate compartments, how tight are those compartments? Is it equivalent to having three ripoles stacked with their back sides totally open? Do those compartments terminate before the opening of the slot? And if so, how far from the opening?

The pics of the slot loaded open baffle are very vague. There's no well lit, close up shots of the slot. All you see is a black slot on a light bare baffle. No details to speak of.

All I really need are some details on the darn slot and I'd probably be willing to start on the building. But without knowing anything about the slot thus far, I refuse to go anywhere with this project.
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Old 8th February 2012, 11:31 PM   #27
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And trust me, I'm not trying to be some kind of jerk on here or give anyone a hard time. It just gets very frustrating when no one seems to want to answer a few very basic questions that would probably require a max of about 5 minutes, if that.
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Old 8th February 2012, 11:53 PM   #28
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You know, if you are finding that there are not enough details in Nelson's write up, it may be that he doesn't have anymore details. Maybe, there isn't any more to it than going with your best guess. This is by no means a finished project. Why don't you put some thought into it, come up with a design, specify the details, build it and see how it measures/sounds? Then tell us what you learnt. Share your experience. And maybe, someone can learn from your experience and build on it.

Edit: Try posting in the original slot loaded thread... there are people there who went ahead and built the thing.

Last edited by ra7; 8th February 2012 at 11:57 PM.
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Old 9th February 2012, 01:53 AM   #29
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Just thinking on your dilema i wanna start tooling around with TL's and horns but im in an apt too.

thinking of starting an audio club in my area, maybe find someone whose of the same mind with a lil shop space and see if we can work something out.

for now im gonna hammer throug some sims to get a real good hold on how the design side works so i can move quickly into prototyping and making a bloody good mess o sawdust.

hope you come back to the slot loaded obthing.

hell i might throw some sawdust at it just to see what nelsons so interested in.
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Old 10th February 2012, 01:30 PM   #30
chops is offline chops  United States
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From what I can tell, this slot loaded design is really nothing more than a modified ripole with an open back. I may consider going that route and build a stacked ripole. The only thing that concerns me there is the effects of the resonant frequency of the rear chamber which would be much larger than the slot. That's one of the reasons I like Nelson's design so much. There IS no resonance effect from the rear, and the slot would be so small that its resonance frequency would be up near 500Hz or higher, nowhere near the 125Hz crossover point I'd be running at. From what I gather, the woofer section should be down nearly -40dB at 400Hz.
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