Jump to content
The Klipsch Audio Community
PrestonTom

Half height Jubilee?

Recommended Posts

I was re-reading the AES article (Revised low freq horn of small dimensions, Delgado & Klipsch).

I noticed something that had passed me by before and it rasies some interesting possibilities. In section 3.2 they mention that the bass bin if it only used a single 12 in driver would only need .482 m (19 inches) in height. They then state the reason for a dual driver configuration was to double the height to .96 m so that the high fequency section would sit at a better height.

Obviously, there were certainly additional reasons for going to a dual driver configuration.

But let's spin this through the single driver configuration, and please correct my assumptions. This is interesting since a single driver bass bin opens up a number of possibilities: 1) compact design that can be used as center channel, 2) smaller pieces of lumber to run through my under-sized table saw, 3) smaller cabinet that is easier to experiement with (I am toying with comparing a tractrix flare to an exponential flare), 4) smaller cabinet that might more easily fit into additional rooms in my house, 5) perhaps fewer glaring scorns from my girlfriend re: the size of the cabinets, 6) certainly a smaller cabinet (but not footprint, however) would have other advantages also.

My assumptions are:

1. single 12 in driver (compared to dual) will produce approximately twice the distortion when measured with a signal producing the same SPL (not too extreme of a level, since distortion is not strictly proportinal). Would the level of distortion still be acceptable? This is judgement call but use the Klipschorn as a referent.

2. I assume the bandwidth (say the half power, -3 dB, points will be about the same. Am I missing something? I am not supposing the efficiency will be the same (although the amp would only see one woofer rather than two woofers in parallel - certainly an easier load)

3. The foot print (not the height) will be the same. Although does the required back air volume change? I believe it does, but is this taken care of however, since the height is reduced by two? Perhaps the footprint might need to change.

4. Does the smoothness of the frequency response remain?

Now going one step further....

5. Since the height is now reduced, would it be wise to widen the cabinet and use a single 15 in (rather than the 12in) driver. I realize a number of parameters change with this alteration in driver size. But what are the rule-of-thumb relations (12 in vs 15inch) regarding efficiency, distortion, and most importantly the the ability to produce energy at the higher frequecies. IOW regarding this last point, is the high frequency cutoff being driven (in general & practical terms) by the channel size/folding or by the driver itself (due to mass and magnet etc)?

This idea has been stuck in my head all day. It creates all sorts of possibilites and makes tinkering more feasible (I may again have access to an anechoic chamber in the future).

However at the end of the day I am starting to come to the conclusion that perhaps I simply borrowing from the article and suggesting a better version of a La Scala that happens to be pointing backwards.

Your thoughts please.......

Thanks,

-Tom

  • Like 1

Share this post


Link to post
Share on other sites
Guest " "

PrestonTom

This has been tossed around indiectly over the past few months, so starting a specific thread about it should be intresting.

When you consider this as an improved LaScala, another thought is to flip it 90 degrees to reduce the floor foot print. Sure it is not optimal...but would it be improved over a normal LaScala?

The driver size has implicaions on the upper bandwidht limit which is assumed to be higher using a 12 inch driver....where does a k-33 rolloff vs a k-31?

And if you are going to use a 15 inch, might as well convert a beater LaScala to a half height Jubilee.

I wonder if there is a market for LaScala cabs converted to half height jubilee's.

Share this post


Link to post
Share on other sites

The problem is mouth size, you're cutting it in half without changing Fc and that is a very bad thing for low frequency response.

You could look at the Jubilee as being two half Jubilee (as you're doing). But if so, each half "sees" the influence of the pressure from the mouth of the other. You could call the other mouth a substitute for a mirror like boundry. You'd have to operate the half size in 1/16th space rather than 1/8th space (a corner).

Gil

Share this post


Link to post
Share on other sites

You are right that some of the ideas have been kicked around, but it was usually in a tangental fashion. We'll see where things go.

Share this post


Link to post
Share on other sites

The problem is mouth size, you're cutting it in half without changing Fc and that is a very bad thing for low frequency response.

You could look at the Jubilee as being two half Jubilee (as you're doing). But if so, each half "sees" the influence of the pressure from the mouth of the other. You could call the other mouth a substitute for a mirror like boundry. You'd have to operate the half size in 1/16th space rather than 1/8th space (a corner).

Gil

Gil,

I see your point, but not clearly. Let me suggest a thought experiment and your response may make things clearer.

Starting with a regular sized, 2 driver Jubilee bass bin.

Imagine, that someone has put a taken a circular saw and sliced horizontally through the cabinet - clear through. Now in an effort to repair the damage, they glue a sheet of plywood through the horizontal slice (and mend the wiring). Now that cabinet is now composed of 2 adjacent compartments that are sealed from one another. I will also ignore certain boundary effects and that air volumes might be a bit "springy".

Now is this two compartment jubilee bass bin (with a driver in each compartment) similar to the original bass bin?. What is different? I think this will give you a clearer picture of my confusion.

-Tom

Share this post


Link to post
Share on other sites

If someone could let us know how this La Scala worked compared to full size, the 1/2 Jubilee might be similar.

Bob

Runt

post-9312-1381931459197_thumb.jpg

Share this post


Link to post
Share on other sites

P.Tom,

Yes, I do understand the approach. Some MCM cabinets are split like that. The unsplit version is essentially two split units, stacked.

My understanding of the question is that you want to split the Jubilee and use only, say, the bottom half, alone. The issue is whether that will work - or at least work well.

The problem is that you've halved the mouth (the big end).

FYI, the full Jubilee has a mouth area of 5 square feet. You can convert the metric area given to square feet and it is very close to 5 square feet. The information in the article shows a K-Horn has a mouth area of 4 square feet (again, convert). The LaScala has a mouth area of 4 square feet too. I find this easier to remember than metric.

When you split there are three parameters to look at.

1) The throat area (small end), per driver, is the same. The total has halved, of course. The throat area is set by the driver parameters. We're still okay.

2) The flare rate Fc is the same. The area going down the length of the horn (if was a pure exponential) still doubles every X distance. PWK called this Lhamed (Hebrew L, my spelling may be bad; I didn't go to Hebrew school - Smile). But it relates to Fc. The cut off frequency of the horn. Another expression of this flare is the cut-off wavelenght.

3) The mouth area has halved. That is very bad for bass response.

= = = =

It is a hard fact that optimum mouth size (or workable mouth size) is based on the Fc of the horn (note that has not changed). We're talking finite length horns. The theoretic infinite length horns have infinite size mouths.

PWK has a table of workable mouth sizes in the MCM patent (IIRC). He shows it in terms of the square root of the cut off wavelength. There are other ways of expressing it. Don Keele's paper, "Optimum Mouth Size" (google to his website) gives the optimum in a much more complicated way.

= = =

You may ask: If we split the cabinet, and then put it back together by stacking, we have two half-size mouths which is supposedly bad. But, how does a given split unit "know" the other one (particularly the mouth) is there, or not? If it can't "know" we could take one (half one) away and get the same results, generally.

But it does "know."

When a pressure wave comes down the lenght of the horn, it pushes against open atmospheric pressure (if nothing else is around to affect pressure) when it reaches the open mouth. To a very great extent, this is like the throat condition (small end) where the driver likes something (confined air) to push against, and propel the air molecules. There is in each case an increase in pressure. This is the effect we want.

But in the combined split, there is the other twin. It, too is causing an increase in air pressure around itself, including the other twin. (Assuming same phase and frequency, which we have.) This is not exactly confined air but air pressure is already above atmospheric.

Now. The above may seem like voodoo book keeping. It is called "mutual coupling". Each half size mouth is causing a better impedance match for the other.

= = =

Actually, this mutual coupling is what happens with a direct driver. Generally, a bigger diaphragm makes for better coupling to the air. We can explain the same as considering the big diaphragm in a top and bottom half. Each half makes the other half work better.

To belabor the point. Suppose we have seven small round speakers. We arrange them as we can pennies to make a rough daisy shape, with one in the center. Sorry, no picture. We pass time in grade school doing this with coins.

When the center one moves forward, it is pushing against "atmospheric" pressure and increases local pressure slightly. But the six surrounding ones are doing the same, and increasing local pressure.

So the center penny speaker diaphragm is actually pressing against MORE than atmospheric. All the surrounding ones (six edges touch) simultaneously pushed air. So it is almost like the center one is mounted in a tube. The air from the center tries to run away to a low pressure area but the surrounding ones created a high pressure at the same time.

We know that WORK is force times distance. If there is increased pressure to work against, there is more work done.

The penny speakers out at the edge don't get quite the same effect. But the touching pennies (there are three for each) have increased pressure at the intersection, even if the air runs away toward the open edge.

So bigger diaphragms are a form of mutual coupling of its interior areas.

= = =

Does that help? Maybe not.

Gil

Share this post


Link to post
Share on other sites

Gil,

Thanks for taking the time. Yes, it does help.

Basically my confusion resulted from concentrating on certain internal volumes, flare rates, etc. I was worrying about the "throat". I should have kept the "mouth" in mind. When I was driving home tonight, I kept on thinking that the "box" could potentially be fairly small and yet still keep & maintain the benefits of "impedance matching / horn loading" at a low frequency. Ultimately that did not make sense to me. It was too good to be true.

I will keep working at it. Horn loaded designs really are an intriguing solution....

I can still try the tractrix flares for the bass bin. However, between burning up a great deal of plywood and lugging these beasts around, a smaller model would have been nice.

-Tom

Share this post


Link to post
Share on other sites

I find there is some gestalt to the issues. You have to look at it many different ways before the elusive issues clicks into focus.

In coupling to the atmosphere, bigger is better. The big mouth is just a way of making a bigger diaphragm.

Gil

Share this post


Link to post
Share on other sites

Hey, I understood that! Thanks Gil, and thanks Tom for bringing it up.

Yes it is voodoo, isn't it?

M

Share this post


Link to post
Share on other sites
Guest " "

ben.

Those are very good low frequency performers....certainly a better low end bass bin than either the jubilee or khorn. But since they roll of rapidly above 200hz....a k-horn or jubilee or even a lascala would still be needed.

The tuba 36 seems to pack the most puch.

Share this post


Link to post
Share on other sites

ben. Those are very good low frequency performers....certainly a better low end bass bin than either the jubilee or khorn. But since they roll of rapidly above 200hz....a k-horn or jubilee or even a lascala would still be needed. The tuba 36 seems to pack the most puch.

Although I am happy with my Klipschorns, the reason I have bringing these things up is because I would like to pursue a 2-way system. In doing so I would like to add some steepish crossovers and time alignment (probably a Behringer unit). Very importantly, price considerations and the tweaker/DIYer in me, preclude purchasing a new Jubilee.

A bass bin that only goes up to 200-300 Hz is going in the wrong direction.

-Tom

Share this post


Link to post
Share on other sites

Tom. I have thought through with what you are trying to accomplish.

Having a Horn with an Fc of 40Hz or lower brings about a large footprint. The Jubilee was able to maintain about the same footprint as the Khorn as it moved to smaller drivers.

I feel the same thing can be done with a dual 10' woofers loaded 1/8 th space. You could have an Fc of around 48-50Hz. It would have the same shape as the Jubilee but scaled down some in H x W x D. It would easily be able to do two way and hit much lower than a La Scala.

Now this is total DIY. I sketched this up on paper and it works. It isn't a scaled down Jubilee. It is a complete new calculation from the throat to the mouth. Would be beautiful as a center or surrounds for the real Jubilee or stand alone.

I'm glad I'm not the only one bouncing this around in my head.

Share this post


Link to post
Share on other sites

Yeah, that Fitz stuff isn't the answer - I don't think there's a way to get it all. They trade bandwidth and ruler flat response for size and cost of drivers. Interesting stuff, though and I thought you'd find it worth looking at on an academic level.

I use a Tuba 24 with a Beta 10 and DR250 w/ a PS Audio (IIRC) Neodymium 10 and a piezo tweeter array in my bass guitar rig. It kills 300W SVT and 1200W modern rigs just using a Bassman 135.

Share this post


Link to post
Share on other sites

Too small of a horn mouth is called "foreshortening", meaning that you have a flare rate for Fc (low frequency cutoff) "n" and an available mouth size for "y" which is a higher frequency.

The low frequency response will therefore suffer peaks and troughs due to reflections from the mouth.

Now, whether you can live with that is up to you.

Will you get bass out of it? Yes.

Will it be consistently flat across the bandwidth? No.

DM

Share this post


Link to post
Share on other sites

Beenie, you never fail to surprise...

BassMan 135 .....

not a Blackface, but sooooo Retro ....

the truth is, most early Silverface amps, differed from the Holy Grail ...only by the faceplate

I have tinkered with some of Fitz's designs, like the 250

Share this post


Link to post
Share on other sites

Tuba 24 shows exactly what happens when you don't have enough mouth area, note the huge dip just above 60hz. Tuba24_28v.gif

Share this post


Link to post
Share on other sites

Yeah, I think Bill would be the first to say it's not for use in a hifi with no eq. He's very upfront about the tradeoffs and compromises. The T24 is such a great pro sound box for a lot of folks. I refuse help carrying mine as it's easier to carry by meslf than with someone else on the other side.. Weighs about 65 lbs or so.

The measurement shown doesn't really line up with what I'm hearing in rooms. I'm not saying it's much flatter - there's peaks happening which don't trouble me for bass (or for PA which would be corrected with processing), but the LF extension seems weak to me. The low B on my StingRay is extremely strong - this with flat on the instrument & cut a little on the amp. To be that far down in a real room at 30Hz doesn't jive with my ears - maybe I'm just used to bass rigs that are nowhere at 30Hz - I don't know. What I'm hearing from these is just plain impressive from a single cheap 10" driver.

Bill does say that best performance from a single Tuba is achieved by aiming the mouth into a corner from about 6-8" (IIRC). Sound familiar?

The guys that post on his forum that use these things for PA tend to use multiple boxes per side to increase the mouth area to overcome what you guys are so accurately pointing out. I 'd like to hear his top boxes set up as line arrays to hear if they really hang with the KF760 or Vertec.

Duke - did you build a 250? PM me if you see this with what you played around with. As far as the Fender goes - they're a steal. People hate em, so I got one as a trade for a Music Man HD 130 (ss pre with 4x EL34 that sounded like crap) that I got for under $200. With the Fitzhorns I get the vintage sound with all the output and extension at both ends I'd ever need. I've been toying with trying an Alembic pre and biamping with a small QSC PLX, but I'm not dieing to change anything. It's interesting to mic up , too... Still the B15 when it matters to record...

Share this post


Link to post
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...