Difference of front vs rear loaded horns?

[Coytee]

I get what a front loaded horn is... I'm just confused a bit on... could the rear loaded horn be considered (ever) a compression driver?

Is the logic of the rear loaded that most of the sound comes directly at you and the rear wave does what?

Or.... does most of the sound go to the rear and if so, then the front does what?

Wouldn't you get some kind of cancellations when the rear signal comes out and meets up with the front signal? (if not, what am I missing here)

I do not think I've ever heard some of these single driver, rear loaded horns. Even though they are evidently horns, might one presume that their real strength is one of articulation rather than dymanics? Or... do our Khorn type horns have more dynamics simply because they're far far larger than these smaller units? Would these smaller units have similar dynamics if they were the size of a Khorn?

Just being curious.

[WMcD]

Long story which probably could benefit from diagrams. Lacking those, we'll have to use our imagination.

In the "classic" front loaded bass horn and most other horns, we have the horn in front of the driver and a chamber behind the driver. The compressed air, say in a sine wave, moves down the lenght of the horn.

At some low freq, the horn stops working. That is F cut off. What happens is the mass of air in the horn effectively moves as a single mass rather than a transmission line. Ths leads to the diaphragm "seeing" that big mass of air. This is the so-called "mass reaction" near Fc. Now the electrical motor is bogged down because it is trying to move a big mass of air.

What to do? One thing we can do is put that chamber behind the diaphragm. It acts as an air spring. Now we have a resonance with reaction mass in the horn resonating the spring. Therefore, in a somewhat narrow band, the diaphragm can move. It is sort of like a kid on a swing. (Or consider a tuning fork. You can't bend that steel easily. But when the mass reaction and the spring reaction are the same at some freq, it will ring for a long time all on its own with no additional force applied.)

There is another problem though. At high frequencies we have the effect of the mass of the diaphragm. Increased frequency means faster acceleration. And as we know from F=MA that if you want more acceleration, we need more force. Unfortunately our electrical motor is only so strong and so high freq response drops off. It is sort of like in a car. There is finite available torque.

- - - -

What to do about this problem at the high end? One thing is to do away with the back chamber and let the back of the diaphragm radiates high freqs. Of course that explanation of what is front and what is back has to be flipped around. The folded horn is at the back of the driver, and the front of the driver is open to the listening area. The back of the driver is horn loaded and the front is not. So we call that back loaded.

This is what we see in back loaded horns.

- - - -

So what is a compression driver and do we have them in familiar bass horns?

In my view, there is the compression effect in all horns. Professor Leach has an example in his book. The horn is basically a tube in front of the driver. So we have to compare that acousic effect to the driver just in a flat surface. His calculation is that if we have a tube (throat of the horn) the same size as the driver, the acoustic resistance of the tube is 60 times (IIRC) higher than the driver in a flat surface.

PWK describes this as the difference between a piston sloshing in a tub of water versus a piston is a tube. The latter makes a good pump but without the tube (my words) we have more like a paddle.

- - - -

One thing that goes on in some schemes is that the throat or tube in front of the diaphragm is smaller than the diaphragm. In this way there is more compression. Note we have much more compression if there is a full size tube (same as the diaphragm) over the "just mounted in a flat surface) But with a smaller throat, there is even more compression. In the Klipsch speakers, the throat is about half the area of the diaphragm. We'll ignore the whole issue of the 3 x 6 slot.

I'd say that a back loaded horn still has this compression factor even assuming the throat is the same size as the driver.

And, yes, I'd expect there are cancellation and reinforcement effects in the back loaded horn as you suspect.

Wm McD

[DrWho]

could the rear loaded horn be considered (ever) a compression driver?

If the surface area of the driver is larger than the cross-sectional area of the throat of the rear loaded horn, then there is a compression ratio happening. I think what defines a compression driver though is the fact that the driver creates its own compression and then has its own fixed throat size. I could be wrong though. I'm curious why you ask []

Wouldn't you get some kind of cancellations when the rear signal comes out and meets up with the front signal?

Yes.

The rear wave is technically opposite polarity from the front wave, so most of these single driver type horns are really long so that the acoustic phase rotates an extra 180 degrees before coming out the front. This will only happen at one frequency though. As you go lower, you get less phase rotation for the same length (the wavelengths are longer as you go lower) so you start becoming more and more out of phase, which causes it to roll off at ~24dB/octave if I'm remembering right. The same problem happens as you go higher in frequency (relative to the special in phase one), where basically you see more phase rotation for the same length (the wavelengths are shorter as you go higher). To help alleviate this issue, the rear horn path tries to attenuate the highs so that there is less energy to do the canceling with. Another thing they try to use to their advantage is that the rear horn will tend to be more directional as you go higher in frequency if the mouth area is large enough...this can force the high frequencies to go backwards, whereas the low frequencies are free to wrap around. If you pull the speaker out away from the wall (like 10ft or so), then the reflections coming back from the front of the room can take enough time so as to be outside the Haas window and can add to the perceived "reverb" of the room. If the reflections happen too early, then it just muddies up the sound by causing comb-filtering (comb-filtering technically happens both ways, but if the comb-filtering arrives after the Haas window, then it's not perceived the same way).

Btw, it takes time for the 180 degrees of phase rotation to happen (the time it takes to travel that distance)...so those frequencies aren't arriving at the listening position at the same time as the frequencies coming from the front of the driver. This causes a shift in the group delay, which arguably has its own audible effects...

Even though they are evidently horns, might one presume that their real strength is one of articulation rather than dymanics? Or... do our Khorn type horns have more dynamics simply because they're far far larger than these smaller units? Would these smaller units have similar dynamics if they were the size of a Khorn?

I dunno if one can really claim better articulation from the single driver rear loaded horn speakers....the sound coming from the front of the driver behaves like any normal direct radiator. Excursion really isn't more limited at lower frequencies as compared to a sealed box or even a bass reflex. I believe you get extra articulation you get from front loaded horns (like the Khorn or Jubilee) because it lowers the excursion for the same SPL.

I have heard some very very large single driver rear loaded horns and they don't come anywhere close to the Khorn in terms of dynamics.

[LarryC]

I don't know the science of rear-loaded horns, but have fond memories of my Shorthorns. What I remember being told and feeling they sounded that way, is that below some acoustical crossover point, the output from the back of the speaker was more efficiently propagated by the back-loaded horn. As I understood it, the DR output became relatively insignificant below that point.

The disadvantage would be if the back-horn length isn't very long and/or not designed to propagate from a corner. Cases in point:

• The Model "S" Shorthorn had a very short back horn length (front to corner, 22"), with little bass below 60 Hz
• The Model "T" Shorthorn had a much longer back horn length (front to corner, 35"), with "substantial" output down to 45 Hz

In contrast, I doubt that the JBL C435 or C550 back-loaded horns would go as low, because their horns weren't designed for corners or even to sit on the floor! See http://www.hifilit.com/hifilit/JBL/1956-4.jpg.

[ZAKO]

You can get both in one system,,,Its the TANNOY WESTMINSTER ROYAL,,,, Plus its two way,,and you dont need a electronic xover,,,And looks 10 times better than the Jubilee

[Speakmeister]

You forgot one little detail Horonzak. The Tannoy is 4 times the price.

[ZAKO]

You pay more than that for gas for your truck,,,Oh I fogot,,this is the poorboy speaker Forum.

[DrWho]

When did lack of xover and good aesthetics become criteria for good sound? []

Sounds a lot like Bose actually []

[Coytee]

Ya know... I just now did a look up on them to see if I was thinking they were the speaker I was remembering (they are)

I then clicked somewhere else and found some intersting comments. I guess even they aren't perfect. I'll bet though that the Warthog fits in the room better []

Also....are these considered REAR loaded horns?

http://gadgets.softpedia.com/gadgetsViewOpinions/The-Tannoy-Westminster-Royal-SE-Loudspeakers-6058.html

(by the way, this "Richard" is not ME)

Richard: ....I have had these babes for a couple of months now, having owned GRF memorys for 20 years or so. I love them and hate them. Why do the cones hit the cabinet when you turn the volume up?.

David:......They do not fit well into a normal domestic living space. Size is a real issue however. They are a four man lift because they are of truly architectural proportions .

[LarryC]

Also....are these considered REAR loaded horns?

http://gadgets.softpedia.com/gadgetsViewOpinions/The-Tannoy-Westminster-Royal-SE-Loudspeakers-6058.html

Rear loaded something...

[Speakmeister]

You pay more than that for gas for your truck,,,Oh I fogot,,this is the poorboy speaker Forum.

Well, with your deep pockets maybe you should buy all us poor folks Tannoys Horonzak. That way we can throw our poorboy speakers in the trash and not look back.

[Speakmeister]

You pay more than that for gas for your truck,,,Oh I fogot,,this is the poorboy speaker Forum.

No truck here either, FedEx had to bring the Jubes to my door.

[garyrc]

All I know is that the several rear loaded horns by JBL sounded precise but bass-shy.

I had a JBL C34 rear loaded horn. Almost no bass below 80 Hz. With the bass control turned way up it worked well enough, but taxed the amplifier with about a 12 dB boost. Still, though, with the bass turned way up, it sounded much better than my ADC acoustic suspension speaker.

JBL made a rear loaded horn twice the size of the C34 .... I think it may have been called the C55. It had two 15" woofers that were rear horn loaded, still with very little bass. My favorite record store of the 1950s, Stairway to Music, had one. It used a JBL 375 midrange (same one as in the Paragon, and many of the better theaters, including the 70 mm Todd-AO theaters Ampex got the contract to equip) for both midrange and treble, attached to a magnificent gold horn lens. It started to roll off at 11k, so JBL added the 075 super tweeter. The universal, inevitable comment of my friends was ..."So clear!" and then "No bass" ,

I also had a Karlson enclosure that was both front and back loaded, It had more bass, but it was peaky.

None of them could hold a candle to a Khorn or a Jube.

The big theater systems could, though ... one of the JBL/Ampex/Todd-AO versions had 4 woofers in one enclosure that was front and rear loaded, and a large baffle area that reinforced bass.

[ZAKO]

Well like my sweet ol grandma used to say ,,,You want to play,,You gotta pay... The Westminster Royals not only sound great...But look great.. Plus you can use the shipping crates to make a tree house. Or a hunting blind for Deer shooting.

[Johnlw7]

How bout we use the boxes to ship you to overseas or make a casket. I doubt your big head would fit in.

[ZAKO]

Now now john... I,d still pick you up from the gutter and give you a buck for another drink.

[Johnlw7]

Now you talking.Reckon what kind of booze you got.I was thinking you could send more than a buck.

[ZAKO]

John,,, The Tannoy Royal have a special place in my heart,,, a large two way horn system that sounds good and looks good,,,Its been around for a long time,,It has had several tweeks over the years,,,Came in two versions,, The Westminster Royal,,and Westminster TW.. Horn structure almost the same,,But drivers differ,, Both sound great,,But will drive you to drink as to wich one to pick... I,m sorry for not being to offer you more than a buck,,Thats my allowence,,Wifey keeps a padlock on the purse.

[Johnlw7]

Just pulling your leg man.If Seti says you ok that's good enough for me.I have some old Philips and Stephens fullrange drivers.Any ideas about enclosures.12 and 15 inch woofers.I'm also looking for a JBl D130 16ohm to put in my C-37.I have heard the Tannoy Gold's in monitor speakers they were very good.I heard the Churchill also very good.The Royals are spectacular as well i assume.

[ZAKO]

The Karlson enclosure always intrieged me on how it works...Audio Asylum is full of info on that design... I have two JBL 130B,,,Re 14ohm,, Both came out of a scoop enclosure if interested... PM me or Email.