PT Waveguides vs. Exponential Horn

[Uncle Paul]

PT-F95HF vs 2307 w/ 2308 lens for example.

I'm mulling over a 434x inspired DIY and wondering if the waveguide would be a better choice than the horn. Would that be a sacrilege?

Anybody had a chance to compare a waveguide to an exponential yet? Zilch, perhaps?

[Zilch]

Hi, Paul.

To the best of my knowledge, JBL has only made protypes of the PT-F in the 90° X 50° pattern. I've got some on order, but they show no inventory, ever. :( It's certainly the main one I want to compare with the PT-F1010's (100° X 100°) I've been using....

The PT-H95HF square version is available, tho. You might want to spring for the $100 for one of those and a throat adapter (if you're not gonna use 2431H or 2435H as your driver) and try it. That's the advice I'm giving everyone right now. I like the PT's personally, and as you have seen, have committed to using them in some of my "upgrades" here.

But, I'm about the only member who's actually used them extensively and reported on them here. Thus, there's no consensus about anything relating to them, and I'd like folks not to take my word alone, rather, that they try them for themselves. They're cheap, and if you don't like them, it's very likely another member will buy yours to try out.

PT waveguides are constant directivity like biradials, both decidedly different animals from exponentials. They require equalization, usually built into the crossover, to compensate for the power response characteristics of compression drivers they're typically used with. (JBL is also using PT's with cone drivers, but that's not the subject here.)

Exponentials do that compensation "automatically" by progressively narrowing the beamwidth at higher frequencies. Constant directivity horns and waveguides, on the other hand, put out a controlled-width sound field of essentially constant amplitude at all frequencies within the operating range.

The lenses on the front of exponential horns function to spread or disperse the conical beam they produce. I recall from the literature that the pattern is typically something like 140° X 60°, but don't hold me to that until we find the reference. However, it still narrows with increasing frequency, since no additional high-frequency energy is provided in the first place.

I've seen many members use biradials successfully in their DIY projects in lieu of exponentials. JBL's best systems like K2-S9800 (and Project May, of course) use constant directivity horns. PT waveguides should work nicely too, but with either, be aware that constant directivity is an entirely different approach than JBL employed in the 434X monitors. Try it out first and see if you like it. You're venturing into uncharted territory, a FUN place! :thmbsup:


It'd be good if some of you members that have PT wavegudes would report your findings and feelings about them. I KNOW you're out there.... :p

[aust-ted]

[QUOTE=Uncle Paul]in part "Anybody had a chance to compare a waveguide to an exponential yet? Zilch, perhaps?"

There has been some interesting discussions on waveguides on the Audio Asylum High Efficiency Speaker Asylum over the last 6 months. I suggest you read the thread started by Mark Seaton on December 31, 2004 entitled Revisiting Horn Soundstaging & Imaging. It can be found at http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=81938&highlight=Revisiting+Horn+Soundstaging&r=&session=

Earl Geddes and Tom Danley have been substantial contributors to the discussion

In a nutshell the discussion ended up discussing all types of horns/waveguides including tractrix and CD horns and included an interesting part involving 'sweet spot' or not listening. I gather waveguides are essentially conical horns with a specially designed throat which allows them to exhibit excellent HF response with the right driver. They do require equalization.


Regards
Ted

[Ian Mackenzie]

Ted,

That was a very interesting discussion, however the focus is more on the effect dispersion and of room interaction.

While I have not heard the PT horns yet, I imagine the thing to compare would be a exponential horn like the 2307 & lense with 80 x 45 dispersion and a similar recangle PT horn over a similar bandwidth. At least this is what I propose to do as soon as I can arrange it.

As far a sound stage goes, I find the angle of toe in sensitive and even more so the distance between the speakers for what I term true imaging and sound stage. I find there is a sweet spot or distance b/n the speakers where the overall sound comes equally from between the speakers and from the speakers themselves. The toe in seems to effect the depth of the image while the space between the speakers controls locatisation and imaging.

When the blend is correct there is an image but also precise stereo localisation as opposed to a halo or holographic representation which is bigger than the space between the speakers.....franky I find that effect crap.

I found the bi radial 2344 gave a great halo effect in a normal living room but the size of the image was un realistic, hence I find the exponential horn and lense despite its less even dispersion vs frequency more realistic on the proviso you are prepared to play around and tweak the placement of the speakers. Within a dead studio I am sure the 2344 would work much better.

Unfortunately with the waf factor, not everyone has the luxury of positioning large cabinets to suit the best results and for this reason they are often less than satisfied and blame the horns or what ever and move onto something else or employ multiband equaliser to improve the alling stereo performance.

To this day I have never employed an equaliser to improve imaging or flatten the amplitide response. No doubt they are useful but not to correct gross problems that are the result of room placement.

Just my 2 cents worth

Ian

I also think its interesting that the best vinyl recordings of contemporary Jazz in the USA in the 70's were all done before the advent of the bi radial horn and application in a studio monitor. Today these recordings are highly sort after by audiophiles because of the life like qualities. It no surprise that when these albums are played back on the same vintage of equipment that you can get excellent results. Of course not everyone owns a good vinyl collection so maybe this is all bye the bye.

Just my 3 cents worth

[Robh3606]

Is that the set-up he used for his listenning evaluations??? You should read it I found it interesting. I very much would like to hear a pair of them. From his site he seems to have found a way to reduce distortion caused by reflections back down the horn. Uses a foam phase plug and an specific flare with less reflections. His design is very much an improved 4430. Zilch he beat you to it!!

http://www.gedlee.com/downloads/Subjective%20Study%20Results.pdf

Rob:)

[Robh3606]

Giskard

Did you get a chance to hear them??

Rob:)

[Ian Mackenzie]

Well they sold well and heck that was 20 years ago after all.

Ian

[Robh3606]

"I'm mulling over a 434x inspired DIY and wondering if the waveguide would be a better choice than the horn. Would that be a sacrilege?"

Hello Uncle Paul

Of course not. It's DIY you can try anything. Only problem I see is trying to integrate something like a 2405 into the mix with a CD horn. With an exponetial it's a simple crossover point. With a CD you need compensation. To build a crossover with compensation and one that sucessfully integrates another driver is no easy task. Take a look at the Project May crossovers as an example. If you go the CD/Wave Guide route I would try to make it so you don't have to drop a 2405 on top.

Rob:)

[aust-ted]

Ted,

That was a very interesting discussion, however the focus is more on the effect dispersion and of room interaction.

While I have not heard the PT horns yet, I imagine the thing to compare would be a exponential horn like the 2307 & lense with 80 x 45 dispersion and a similar recangle PT horn over a similar bandwidth. At least this is what I propose to do as soon as I can arrange it.

As far a sound stage goes, I find the angle of toe in sensitive and even more so the distance between the speakers for what I term true imaging and sound stage. I find there is a sweet spot or distance b/n the speakers where the overall sound comes equally from between the speakers and from the speakers themselves. The toe in seems to effect the depth of the image while the space between the speakers controls locatisation and imaging.

When the blend is correct there is an image but also precise stereo localisation as opposed to a halo or holographic representation which is bigger than the space between the speakers.....franky I find that effect crap.

I found the bi radial 2344 gave a great halo effect in a normal living room but the size of the image was un realistic, hence I find the exponential horn and lense despite its less even dispersion vs frequency more realistic on the proviso you are prepared to play around and tweak the placement of the speakers. Within a dead studio I am sure the 2344 would work much better.

Unfortunately with the waf factor, not everyone has the luxury of positioning large cabinets to suit the best results and for this reason they are often less than satisfied and blame the horns or what ever and move onto something else or employ multiband equaliser to improve the alling stereo performance.

To this day I have never employed an equaliser to improve imaging or flatten the amplitide response. No doubt they are useful but not to correct gross problems that are the result of room placement.

Just my 2 cents worth

Ian

I also think its interesting that the best vinyl recordings of contemporary Jazz in the USA in the 70's were all done before the advent of the bi radial horn and application in a studio monitor. Today these recordings are highly sort after by audiophiles because of the life like qualities. It no surprise that when these albums are played back on the same vintage of equipment that you can get excellent results. Of course not everyone owns a good vinyl collection so maybe this is all bye the bye.

Just my 3 cents worth

Ian

There were some other threads in the High Efficiency Speaker Asylum around the same time that also touched on waveguides including the Peavey Hughes design and how it compared to Earl Geddes design.

Would be very interested in your proposed experiments with PT horns. I am planning, time permitting, to make some home made 500Hz waveguides along the lines of the Peavey Hughes design to use with 2451 drivers. One of the benefits of these is that they look fairly easy to construct. However I gather one of the disadvantages of waveguides is that you need a larger horn for the same frequency cut-off than for example tractrix horns.

Your point about vinyl recordings is interesting. Without getting sidetracked too much, I would tend to agree but think you might be a decade out. I have always thought that some of the best recordings, both classical & jazz are from the 1960s in the early days of stereo. I am not sure if this is related to speaker technology but it could have played a part. Other factors could be related to recording techniques (eg simple tubed recording equipment, the lack of cut & paste with the whole piece rerecorded until it was got right and simple miking techniques to name a few). I particularly like the Mercury Living Presence classical recordings which still shine in reprocessed CD format as well as some of the Verve, Prestige and Blue Note Jazz recordings (to name a few) of the period.

Regards
Ted

[aust-ted]

Is that the set-up he used for his listenning evaluations??? You should read it I found it interesting. I very much would like to hear a pair of them. From his site he seems to have found a way to reduce distortion caused by reflections back down the horn. Uses a foam phase plug and an specific flare with less reflections. His design is very much an improved 4430. Zilch he beat you to it!!

http://www.gedlee.com/downloads/Subjective%20Study%20Results.pdf

Rob:)

Rob

You can get more hints of Earls comments on other posts he has made to the Asylum forum and from his book which he sells from his webpage. I gather the shape of the throat from his patent is an oblate spheroid (which is formed by rotating an ellipse).

Regards
Ted

[Titanium Dome]

And where does JBL's EOS (Elliptical Oblate Spheroidal) Waveguide fit in all this? I've often thought of it as a tiny horn. Sort of.

[Zilch]

Zilch he beat you to it!!
Naw, me LIKE reflections!

[Gotta read that stuff yet, tho....]


I found the bi radial 2344 gave a great halo effect in a normal living room but the size of the image was un realistic....That's certainly an issue. Not every presentation is as "expansive" as 4430's make them. I look forward to your experience with the PT waveguides.

On the other hand, "Three Wishes" on Waters' Amused to Death was killer in QSound here last night. That genie MUST be bigger than life. ;)


If you go the CD/Wave Guide route I would try to make it so you don't have to drop a 2405 on top.'Zactly....

[aust-ted]

And where does JBL's EOS (Elliptical Oblate Spheroidal) Waveguide fit in all this? I've often thought of it as a tiny horn. Sort of.

Titanium Dome, I am not sure what the connection between JBLs waveguides and Earl's is but they certainly appear to be based on similar principles.

Earl discusses the concept here http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=80335&highlight=good+directivity+control&r=&session=

My understanding is that the term waveguide is used because the underlying theory is different from the Webster theory which horns are based on but essentially they are conical horns with a specially designed throat (eg oblate spheriod).

Regards
Ted

[Titanium Dome]

Thanks for the link. I'm digesting it now. :biting: