Bass horn ideas again. A possible build. Need criticism.

[jwc]

Actually...I just thought of one small problem with that. Let me draw this out on graph paper.

[jwc]

Nope

[DrWho]

I like that slot ported idea - would it be a difficult retrofit?

As far as bass response is concernced, I don't think the slot makes that big of a difference??? I'll have to go play with the models again later (gotta get to practice), but I seem to remember the slot size affecting more the high-frequency response than the low-end.

[Guest " "]

jwcullison

Since we are throwing Ideas out here....what about a tuned port (or 2) rather than a radiator. The tuned port might be an easy re-tro fit to your existing cabinet.

Placement could be in the center area between the two drivers at the center of the area between the lower ramp of the top driver and upper ramp of the bottom driver.

If there was enough space between the drivers to do so, all it would take is to drill thru the outer front cabinet shell, then continue thru the front of the inner dog house.

Perhaps the space to do so would be off center, maybe one on each side?

Basically determine the max port diameter, determine available tube diameters options, then based on the desired frequency and volume, determine your diameter and lenths.

Maybe Dr Who can recall some of his earlier numbers and graphs from the ports vs the radiator disccusions.

I just recalled one of your earlier CAD's. Depending on how far apart the drivers actually are, there may be some nice tuned port size options.

[Deang]

Thought by now you guys might be getting bored with this. I felt bad last night after all those plots I posted. I felt for a minute like I was a "hey look at me". I noticed for the first time that my name was in the "most users list". It felt a little weird.

You gotta be kidding -- this thread is great. You're in somewhat uncharted territory. I think your pretty gutsy -- it's not like you've been doing this stuff half your life. I look at this stuff and just shake my head -- way outta my league.

[jwc]

Dean. Yes I have been on this forum just less than 2 years. There is nothing special about me that gives me some advantage. Just takes patience and reading. I appreciate the continued interest because I couldn't do any of this w/o input.

Spk F.

I have many delemnas about porting. First of all...I can't resort to any paper or patent on how it was done in the Jubilee because it never was. We are really getting into experimentation compared to what weve done already. I am not afraid of that......would just need to hear many ideas and reasoning behind them.

Now porting the way you suggest is like how everyone wants to port the La Scala. Problem I have with porting directly from the inner sealed chamber to the outside is one of two. One: The sound from the port doesn't have to travel 140cm like the sound from the drivers. Two: The ported benifits will not have the SPL that it would if it were in the horn (because of restricted imedance?). That last comment could be incorrect but was my thinking.

Please fully try to understand my intentions on trying to place a port in the horn. I need input.

Now take a look at the image below. The right one has been posted on the forum many times as what most imagine what was in the real ported jubilee. Now I have a problem with this. To me...this greatly increases the total throat of the horn. Up to 135 sq in as opposed to the 90 sq in. I am assuming that the drone will have a throat of its own...correct? The horn will remain 140cm so changing the total throat will mess it up IMO. Every reference "point" A-D in the JAES paper won't be met with this mod. Now of course you could recalculate the horn to make it work for 140cm and you would probably get a lower Fc such as a 33 or 35Hz horn. But then it isn't a jubilee but a custom horn (fine if that is what you want to accomplish).

Now the only good thing that I can think of by doing it this way is that the throat of each active driver still remains 45 sq in and that is what the Jubilee paper calls for and that is about what these Pioneer drivers want. Also the other thing that could be considered appealing is that all three drivers have identical first flares and throat. Also the Vb of the sealed chamber stays about the same.

Now consider the option on the left. I have never seen this mentioned before. Each slot is not as tall....to 6 inches. The first flare depth is still 2.5 inches with the same splitter like used on mine. Now each throat is 30 sq in to a sum of 90 sq in. This keeps the horn right and all the calculations at each "point" in the paper.

BUT, now each throat is 30 sq in for each driver and the paper calls for 45. This is fine for the total horn but the active driver won't like it necessarily. The Pioneer's like a throat that size from a calculation standpoint. Most 12 inch drivers however, like closer to 30 sq in. Such as the Kappas I tried. The kappas may go lower with porting and there is more volume displacement in the back chamber wiht the drone in there.

Who. I can't retrofit.

Now one other thing to consider is place a port tube in there in the horn. This can be done in the Horizontal fashion like my previous image with the red and black. I got messed up in my thinking when I made that post. You could for instance place dual 3 " or dual 2" ports in there side by side in the middle and place a splitter between them. Then have the horizontal panel above and below only taking up a few inches in the total height of the baffle.

There are my initial thoughts.

By all means.....I'm not eager to do this because I'm not satisfied so far. The non ported version here sounds great....and I don't even have a network yet designed for it.

jc

[Guest " "]

jwcullison

You seem to have done 5hz better than the production model in terms of frequency bandwidth. Your graphs show a roll off at 40hz whereas the production model is cut-sheet at 45hz.

So best case, if you had a port (radiator, tuned port tube, etc), you migh pickup 6 db. But I think, if I recall DR Who's numbers that he did for a radiator and the volume of a Jub size cab, the enclosure volume of the Jub would tune the Radiator to 45hz. Since Radiators work over half an octabe, at an18db slope, it would be a stretch for the lower roll off slope of the Radiator to reach 30hz.

[jwc]

I'm hoping that is accurate. After I realized that my so called listening position....about 12 feet back had some issues. Anyway.....full corner placement fixed most of that.

I then just placed the mic about 2 meters directly in front of the jub about mid height.

Yes I was quite surprised with that curve. That wasn't a "cleensweep" of tones. It was a tone played one at a time hoping to eliminate some reflections. As you can see I skipped some tones...this is the software doing that. I could have done each Hz but it would have taken forever.

After that...I just started to listen. It sounded good so I think I'm hearing what the curve shows. I know I'm getting at least the -3 dB at 45 HZ. This plays at least as low or better than the Cornscalas and dbb's tuned at about - 3dB at 45Hz. I also recognized the sound.

I have put the mic away for now as my basement is cluttered and I had to clean.

Now remember...the RTA is in my room in a corner. My room may be doing the curve a favor. So I'm not gonna tout this project as being as low and flat as those curves show. I will remain cautious.......but still enjoy.

jc

[DrWho]

Problem I have with porting directly from the inner sealed chamber to the outside is one of two. One: The sound from the port doesn't have to travel 140cm like the sound from the drivers. Two: The ported benifits will not have the SPL that it would if it were in the horn (because of restricted imedance?). That last comment could be incorrect but was my thinking.

1) If you're creative with the port and front-wave pathlength differences, you can actually enter into a "tapped horn" situation. Apparently that's how Danley is getting so low in that DTS-20 (note how the efficiency suffers with it too...). I'm not sure what the actual distances are for the Jubilee, but you'd want it to be a 1/4 wavelength...about 6 feet.

2) I absolutely agree with you on this point. One of the main things people tout about horns is the reduction in cone-excursion...well this cone-excursion is what causes more air to displace inside the rear cabinet - making more air move through the port. Reduce the cone-excursion required for the front-wave SPL, then you end up reducing the output from the port. The port doesn't magically become more efficient. At least that's my take on the issue.

Who. I can't retrofit.

Does that mean any porting experiments will be done on a new build? Or would your idea work with your existing situation? I'm a bit confused because you're talking huge changes in the motorboard.

One of the advantages to using ports over PR's is that they're easier and cheaper to modify. For an experimentation stage where the math is already fuzzy, I think dropping in some ports would be more practical - problem is they take up more space and have more losses associated with them.

[D-MAN]

I would go for finding better drivers than attempting to making mediocre drivers sound "better" by hacking up the cabinet.

There are many examples of ports in horn throats. However, these won't work in the Jub design because the throats are too short. That means porting to the corner channels is an alternative.

Building an extra throat as posted above would have to be done at build-time, of course.

There are inherent problems associated with that particular approach. First, phasing, second, the single-throat back-wave portion is too small for the horn channels, so you are gaining a little, but its not going to be that efficient, anyway. IME, it seems like a lot of work for little return, and I would go as far as guessing that it probably hurts more than it helps. Doing it right would be a pain, as you would need (best case) 4 throat sections, not three.

However, you could retrofit ports into the side channels, and if you don't like it, cover with panels, and you are stock again. This would let you experiment and decide whether a redesign is worth the bother or not.

I would port to the side channels in the non-expanding part, and forget a drone-cone or front-port which would alter the throat configuration and is non-reversable.

See the attached patent drawing for porting into the channels.

DM

[jwc]

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Driver S_T V_B Reactance Annulling

Jub Cabinet 45 sq in 37L/driver

Jub Driver 39 39.3 40Hz

E.KappaPro 31.6 36.87 37.9

Pioneer51F 48.9 48.18 48

Pioneer51D 41.9 38.5 39.39

E.OmegaPro 31.15 25

E.Kappa12 40 52.7

E.LabGen12 30.6 35.76 37

You knowI stated it was lazy that I didnt calculate some of these things out before hand and was relying on input from others.

Now the two woofers I tried are the Kappa pro and the Pioneer 51F. I still have the 51Fs in there and the sound is getting more and more appealing.

The first woofer I ever heard mention to try in here was the Pioneer 51D. This was mentioned in BigFDs thread on his build. Is this the woofer he used? I really would like to know as this would be very helpful. Anyone know this fella? I had said previously that I had two different sets of Pioneer woofers here and I sent one type back. The ones I sent back were the 51Ds. Now I wish I had kept them for testing purposes as thse are the ones that are the closest to the real jub driver by looking at the parameters above. The Qms for the 51D is much less than the real jub drivers but that particular figure isnt included in the above calculations. Maybe someone here will tell me what compromise that Qms difference will compromise.

These Pioneers are cheap which makes me happy in one way and bummed in another. I would never know I have a $60 woofer in there. Heck, the 51D is even cheaper.

Mike B. I put the LabGen in there for giggles. The above looks pretty good except for the throat. Would the oversized throat be more of a compromise of the higher frequencies? The Vb and Anull look good. Worth trying if you wanted to crossover the bass bin low say 300-350. Could be a real chest kicker.

Dana, how is it that I got a different calculation than you regarding Vb for the Kappa Pro. You had stated earlier that you think it is about 25 liters vs what I calculated at 36.87 liters/driver. You are rightthe annul for the Pioneer 51F is too highsomehow it sounds good. The 51D is closer to the right value as is the kappa pro.

The more expensive Eminence drivers such as the Omega and Magnum are a bad fit as their Vas is way low. Infact, looking around on the web, it is very hard to find 12 woofers with a Vas above 10 cu ft like the driver in the real Jub.

I think I will back off the porting idea right now. This thing is hitting some real low notes to my surprise. If I wanted a few dB extra in the 30s and 40sI could just EQ as these frequencies on my RTA arent that much behind the 80s-100s HZ. Right nowI dont feel I need too. This seems typical of most exponential horns that I have seen with an M=1.0. Dana..when I see these flat curves on bass horns that are spread around the web now and then, are they using a M=0.6 or 0.7 to achieve this or is there a better explanation of how to get that curve. I believe I was reading one of the Edgar articles stating he would use say .6 or .7 to keep the bass horn from being peaky.

jc

[DrWho]

Ya, I'm pretty sure that the larger mouth reduces the HF extension. Oversized also reduces the efficiency all around, but the horn will be more linear at larger signal levels (kinda the same effect of air velocity in a port). You planning on dropping in the Lab12 just for kicks to see how they do? They have gotta be one of the most versatile horn drivers out there.

One idea for messing around with ports - you could cut out a circle from plywood and drill holes that line up with your current driver holes and then mount a port to the middle of this circle. You can make the port as small as you want to get it to fit inside - just keep in mind to measure the output at low SPL's to avoid overloading the port. I know you mentioned not going this route for now, but I thought I'd throw it out there in case you ever change your mind []

[djk]

"You planning on dropping in the Lab12 just for kicks to see how they do? They have gotta be one of the most versatile horn drivers out there."

Approximate mass corner of various drivers (not adjusted for throat size), don't count on getting much more than an octave higher than this without EQ.

Pioneer 51D 287 hz

Pioneer 51F 152 hz

Eminence Lab 12 II 117 hz

Eminence Kappa Pro 12A 308 hz

Klipsch Jubilee (AES specs) 205 hz

Response from fig.8 (AES)

200hz 104dB

400hz 98dB

800hz 92dB

(note that the response falls 6dB/oct above the mass corner, as predicted)

[jwc]

I have a couple of things to post as I would like to hear some comments.

The below image is the bass bin only with the two Pioneer woofers. This does have the network in front of it. Again, 2.5 mH inductors on each woofer in series.

Unlike with the Kappas, they start to roll of at 1000Hz as opposed to the two kappas rolling off at 600Hz.

I want to point out some things. The mic is about 1 meter in front of the bass bin on a pillow for this particular image. Regardles of where I put the mic, the red arrow and the green arrow point to areas that are reproduceable at most all locations of the mic. I always get a strong output in the 35-40Hz area which is definately noteable on music. My dbb's don't do that. There are also some small dips always in the 350-400Hz. I can't notice this in the music I play but it is there.

Now the yellow arrow points to something that is always there but changes with different areas of the room. Meaning the "dip" isn't this bad in some areas and worse in others.

jc

[jwc]

Here is something else that I can't figure out. The same hookup as above. Tweeter and midrange disconnected.

When playing a 100Hz sine signal.....I'm picking up other Hz further down the spectrum. Can't hear them as they aren't as loud. I walk up to the speaker as it is playing and don't hear anything out of the ordinary. No reasonance as well.

ideas?

jc

[jwc]

Here is the same thing again but with additional frequencies. Always the signals just before and after 100Hz do this.

[jwc]

I guess it could be my room.

I RTA'ed my 902-8b wide open. Did the same kinda thing around 800Hz.

I bought these Altec drivers off Ebay in mint condition. Looks like the diaphragms may be in good condition. Lower than 600Hz wasn't as strong as I would have liked. However, easily went out to 20,000Hz. I can't hear anything after 14000Hz.

So two way with these drivers at least temporarily may work well crossed at 600Hz.

[jwc]

Here is the 902 in series with a 40uF cap and a 0.2mHy inductor.

Followed by and autoformer with a swamping resistor in parallel.

[Al Klappenberger]

JC,

Those plots that show 100, 300, 500 and 700 Hz. are typical of clipping. This is the harmonic spectrum of a square wave! Look carefully at the source of that 100 Hz. I think it is a high distortion source. What is generating the 100 Hz signal? When I get the HP function generator you won on eBay I'll do distortion measurements on it. I suspect it will be clean and you can do that test again.

Al K.

[jwc]

I didn't think of that. The source is from my PC.

I guess that proves I am in need of real test equipment.

Al, do you agree that a 600Hz crossover point is the way to go for 2-way here. The Altec 902 with the 511 will be my start up HF driver/horn combo. May move to 2" compression driver in the future. That is still up in the air.

The 902 with 511 horn seems to be strong from 600Hz out. Look at image 902-8b-wideopen.JPG