BMS 4594 coax vs Radian 951BePB - AVS Forum
View Poll Results: BMS 4594 coax vs Radian951BePb
BMS 4594 Coaxial 0 0%
Radian951BePb 5 83.33%
Other 1 16.67%
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post #1 of 54 Old 02-11-2014, 12:52 AM - Thread Starter
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I have been asking a lot of questions here lately and I do appreciate everyone's help. But I still have one more I need some advice on. I am planning a build and need to finalize the parts list as I will have to buy pieces over time in order to afford them. The BMS 4594 seems to be getting some good reviews but I cannot fins much about the Radian's other than Beryllium diaphragms are supposed to be the best. I know the Radian costs a few hundred more but if it is worth it then I will spend it, on this build as I do not want to feel like I am missing anything from these speakers.

So which CD would you pick? If you pick a different CD please keep it under $1500 each.

Thanks
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post #2 of 54 Old 02-11-2014, 03:48 AM
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Like I said in the other thread.....I too was doing some research on these two different compression drivers, the BMS-4594 coax and the Radian 950BePB. I could not find anyone on the forums with direct experience with both, but I did find one guy who had some experience with both. According to him, they are extremely close when properly implemented. He said that he would give a slight edge to the Radians top end and upper mid-range. According to him the Radian 950BePB was more detailed, and had a clarity that the BMS-4594 just could not match. He also said that the Radian had a slightly more involving/lush mid-range, but, these differences were very slight. He said that his overall preference was for the Radian, and that his buddy's felt the same way.

With that being said, the Radian 950BePB cost approx $400 more per driver, assuming you pay the MSRP, that is $800 more per pair, or $1,200 for a trio! The guy that I spoke with said that although the Radian was his preference, he did not feel that it was better enough to warrant a $1,200 dollar difference in price for 3 in a typical theater setup.

It is my opinion that the ultimate setup would be three Seos-24's with a Radian 950BePB, (or a Radian 951BePB), mounted to each waveguide with perhaps duel AE TD15's covering the low end. Perhaps when my wife graduates Law School in May and starts working, which is when I would also not have to support two households, then and only then, perhaps I will be able to afford an ubber setup! The hard part will be designing the crossover! Make sure you have a buddy lined up for that!
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post #3 of 54 Old 02-11-2014, 09:46 AM
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As I said in the other thread, I am highly suspicious of coax CDs. With DSP you should be able to time align them appropriately, but I think they are inherently compromised to get a certain bandwidth in a certain package. For home use, I think a real Synergy or using the Radian might be better, but that is me.
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post #4 of 54 Old 02-11-2014, 07:41 PM
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I know I'm not directly contributing much to answer Ozzidogs question with another question but I'm hoping the discussion will help anyone with selecting a high-end compression driver.

Can anyone share their experiences with the Radian 951 vs the Radian 745neo ?

Both are 1.4" exits with different size voicecoils and diaphrams.

Does the 951 really offer extension to 20khz ?
The 745 has gained some recent followers on the incredible "Beyond the Ariel" thread but appears to need a true supertweeter.

There are some highly regarded speakers from Volti audio that are using the BMS 4592 2" cd with an additional horn loaded tweeter. The coaxes from BMS pop up on the various forums every couple of years but I have yet to see a documented build where the builder has been completely happy with them long term.


Regards,

Daniel
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post #5 of 54 Old 02-12-2014, 03:59 AM
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Quote:
Originally Posted by abby356 View Post

I know I'm not directly contributing much to answer Ozzidogs question with another question but I'm hoping the discussion will help anyone with selecting a high-end compression driver.

Can anyone share their experiences with the Radian 951 vs the Radian 745neo ?

Both are 1.4" exits with different size voicecoils and diaphrams.

Does the 951 really offer extension to 20khz ?
The 745 has gained some recent followers on the incredible "Beyond the Ariel" thread but appears to need a true supertweeter.

There are some highly regarded speakers from Volti audio that are using the BMS 4592 2" cd with an additional horn loaded tweeter. The coaxes from BMS pop up on the various forums every couple of years but I have yet to see a documented build where the builder has been completely happy with them long term.


Regards,

Daniel

Although I can't really answer your questions regarding the 951PB versus the 745neo, but, the 900 series is a step up from the 700 series. I am not really sure if the regular 951PB will go up to 20khz, but I know the 951BePB will definitely extend up that high. It has a Be diaphragm that will extend the top end over what the stock 951PB will do, and it also adds a very nice SQ to it as well. The 951BePB is very expensive, even compared to the stock 951PB. The other benefit to going with the 951BePB is that it does not need a tweeter above it.
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post #6 of 54 Old 02-12-2014, 07:01 AM
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That's not entirely true Marty.

The fundamental difference between these CDs is the size of the diaphragm. The 3" diaphragm has the potential for better HF response at the expense of lower frequency extension regardless of the diaphragm material. It is a function of physics. Yes, the phase plug is able to squeeze some HF response out of a 4" diaphragm but you can't defeat physics.

The flip side is that I wouldn't play a 3" diaphragm down to 500hz. Maybe 600-700hz.

Beryllium will extend the breakup modes further out and clean up the HF's but it doesn't fix all response issues with a 4" diaphragm.

As far as using a "supertweeter". That is a design choice with advantages and disadvantages. The traditional supertweeter route has been obsoleted IMO by materials like Beryllium, coax's like the BMS and wider range, high power ribbons like a TPL150.

In a nutshell, if you want "point source" behavior over a wide bandwidth do something like a BMS coax or 951BE on a SEOS-24. If you want cleaner HF response at the expense of this point souce behavior and possibly introducing some lobing and null issues, do something like a SEOS24 or other big horn with a BMS Mid CD (4594-Mid) from 400-1200hz and a TPL-150H or SEOS-15 above it. Don't do the supertweeter up around 5khz. That is old school.

I forgot to add that if you want something middle of the road, use the Radian 745Be with a midsize horn like the XT1464. It won't play as low as the bigger driver on the bigger horn, but it won't need as big of an enclosure and will have some HF benefits.

Oh and don't trust Radian provided frequency responses, they are the most smoothed I've seen from any manufacturer. They are completely useless.
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post #7 of 54 Old 02-12-2014, 10:00 AM
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A nifty quality when using Be phragms is that because the breakup modes occur at a higher frequencies EQing the high end becomes practical and you no longer need a supertweeter.
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post #8 of 54 Old 02-12-2014, 10:34 AM
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Quote:
Originally Posted by Carl_Huff View Post

A nifty quality when using Be phragms is that because the breakup modes occur at a higher frequencies EQing the high end becomes practical and you no longer need a supertweeter.
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Yep Carl. That is what I was referring to with the obsolescence of super tweeters. It still isn't cut and dry though. Maybe a large horn covering the midrange with a more complete "tweeter" covering from about 1300hz and above. It could be a 1" throat CD, an AMT, Or Raal. Those all have better response above 10khz than even the best mid or large format CDs with beryllium. Of course those solutions introduce their own set of compromises.
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post #9 of 54 Old 02-12-2014, 10:38 AM
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I agree that since the Be 'phragm controls the breakup you can use these much higher, but the larger throat means you will be beaming at a lower frequency. There is not getting around that. Some don't care, I happen to care about that.

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post #10 of 54 Old 02-12-2014, 10:38 AM
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Quote:
Originally Posted by coctostan View Post

Yep Carl. That is what I was referring to with the obsolescence of super tweeters. It still isn't cut and dry though. Maybe a large horn covering the midrange with a more complete "tweeter" covering from about 1300hz and above. It could be a 1" throat CD, an AMT, Or Raal. Those all have better response above 10khz than even the best mid or large format CDs with beryllium. Of course those solutions introduce their own set of compromises.

Yup. That's pretty much what I did.

Is it perfect? Of course not. Lol but what speaker really is?

One thing I like is the money I saved. A single Be diaphragm costs as much as all three of my mids. tongue.gif

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post #11 of 54 Old 02-12-2014, 01:45 PM
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Quote:
Originally Posted by coctostan View Post

Don't do the supertweeter up around 5khz. That is old school.

Why isn't it better to cover the more important midrange with a single driver and XO up high where issues are less audible?

Noah
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post #12 of 54 Old 02-12-2014, 04:10 PM
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Quote:
Originally Posted by noah katz View Post

Why isn't it better to cover the more important midrange with a single driver and XO up high where issues are less audible?
Because of nulls. Whatever is potentially gained is ultimately lost. There was a time when super tweeters crossed that high were the only choice because the only good CDs were large format 2" exit with aluminum diaphragms. They had not usable output above 8khz which was fine for old movies but when guys want do bring that into the home you had to add a super tweeter to play above that with similar sensitivity.

The last of the super tweeter users were the JBL Everest and K2 speakers. My opinion is that they employed them solely for specs. It is hard to charge $60k+ for speakers that are only flat to ~16k. The super tweeters push that spec up to 40khz.

I do think there is legitimacy to to AudioJosh and Scott's routes. Those aren't supeetweeters that are crossed so high as to cause response issues. Instead they are true horn midrange with a true horn tweeter on top.

If you look at JBLs latest top of the line studio monitor it no longer uses a super tweeter. Rumor has it that speaker is going to replace the Everest and K2 speakers or at least a very similar speaker will be used as the home totl speaker.
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post #13 of 54 Old 02-12-2014, 06:22 PM
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Quote:
Originally Posted by coctostan View Post

Because of nulls.

Ah, because the midrange horn's size will force a c-c distance of many wavelengths at 5 kHz.

Noah
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post #14 of 54 Old 02-13-2014, 04:32 AM
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Exactly Noah. Generally a horn that will cover from 500hz to 5khz will be fairly tall causing that problem. If it weren't for that fact it would be plausible solution.

If you look at unsmoothed measurements of JBL's Everest you can see the effect. Obviously it doesn't make a speaker sound "bad" but it also isn't the best choice. I've known some guys who actually disconnect the super tweeter and alter the crossover to boost the CD in the main horn.
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post #15 of 54 Old 02-13-2014, 06:34 AM
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So just out of curiosity, assuming that someone wanted to build a somewhat high efficiency 3-way utilizing a high quality woofer like the AE TD15 or JBL-2226, with a nice tweeter like the TPL-150 on its own waveguide/horn/thing-ie what would be a good driver to use as a dedicated mid-range? Perhaps the BMS-4592-mid, or a stock Radian 950PB, or perhaps even a JBL-2446? With that being said, what would then be a good horn or waveguide to use with this dedicated mid-range?

I do, of course, realize that you could potentially achieve similar or possibly even better results using something like the BMS-4594 or Radian 951BePB on a Seos-24 in a 2-way configuration.....

But let's have some fun here and discuss different designs just for the fun of it, sound good?
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post #16 of 54 Old 02-13-2014, 11:17 AM
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Quote:
Originally Posted by AudioJosh View Post

As I said in the other thread, I am highly suspicious of coax CDs. With DSP you should be able to time align them appropriately, but I think they are inherently compromised to get a certain bandwidth in a certain package. For home use, I think a real Synergy or using the Radian might be better, but that is me.

Hi Josh, I'm not sure if we have interacted here before, but want to make sure you know that I sell BMS. (disclaimer)

I don't get the time alignment comment. I have one customer who is using these drivers with DSP, (Most of my customers use the passive) for high end studio installations. Both 7.1 and stereo.
He is using about 1/4" of time alignment, at 6.3khz.
The length of a 6.3khz tone is about 2". So this is about 1/8 wavelength.
You compare the coaxial driver to synergy. Synergy does not time align (when used passively). It relies on being within 1/4 wavelength at the crossover point.

Why will you not grant a tighter tolerance to the coaxial compression driver than you will to the synergy?

Regards, Jack
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post #17 of 54 Old 02-13-2014, 12:01 PM
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Quote:
Originally Posted by Jack Arnott View Post

Hi Josh, I'm not sure if we have interacted here before, but want to make sure you know that I sell BMS. (disclaimer)

I don't get the time alignment comment. I have one customer who is using these drivers with DSP, (Most of my customers use the passive) for high end studio installations. Both 7.1 and stereo.
He is using about 1/4" of time alignment, at 6.3khz.
The length of a 6.3khz tone is about 2". So this is about 1/8 wavelength.
You compare the coaxial driver to synergy. Synergy does not time align (when used passively). It relies on being within 1/4 wavelength at the crossover point.

Why will you not grant a tighter tolerance to the coaxial compression driver than you will to the synergy?

Regards, Jack

I don't think anyone is picking on the 4594 just because, and I agree that other designs have issues too. The 4594 isn't the easiest to get right and the stock passive with no mod doesn't even come close for these types of applications. I've talked to a lot of talented guys, including Ivan Beaver and other engineers and the comment is always the same....the 4594 isn't a magic bullet and it's really tough to get it perfect. Now I like the bms, I'm using it in my speakers and continuing to work to reach as close to perfection as possible, but want to be clear for those reading who may not be seasoned designers and are thinking of using it.....don't think you're going to buy it with a stock crossover from these guys and it's going to sound great. I don't agree that it can't be done, but it's tough....Josh may be right though, that in many cases it would be easier to get the Radian to sound best, that's an experiment that I'll be doing soon and the winner will stay in the seosr..loser walks. Really though, there shouldn't be a loser, I just think it will be preference.
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post #18 of 54 Old 02-13-2014, 12:05 PM
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I'm less concerned with the time alignment of the BMS coax as that can be handled via the crossover. My concerns are with the HF response due to the discontinuities inherent to the dimensions and shape of the space where the mid and HF sections meet. When I say concerns I'm not knocking it so much as pointing out there is a "price" to be paid with the technology. The frequency response of the HF portion is adversely affected. The problem is that the two sources are too close to each other.

The Synergy design is a bit of a "goldilocks". The HF section has to be within 1/4wl of the mids, but also far enough away that the HF's output doesn't "see" the discontinuities from the mid ports (based on the expansion of the horn). It is these discontinuities which are too close on the BMS coax that disturb the HF response.

Now I'm not ripping the BMS coax design. It is ingenious and revolutionary. It can be utilized to great effect and is a wonderful driver. It simply isn't the panacea that many tout it as. If it were that good, you would never see another type of CD used. It would have been "game over".
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post #19 of 54 Old 02-13-2014, 12:17 PM
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Quote:
Originally Posted by ChopShop1 View Post

I don't think anyone is picking on the 4594 just because, and I agree that other designs have issues too. The 4594 isn't the easiest to get right and the stock passive with no mod doesn't even come close for these types of applications. I've talked to a lot of talented guys, including Ivan Beaver and other engineers and the comment is always the same....the 4594 isn't a magic bullet and it's really tough to get it perfect. Now I like the bms, I'm using it in my speakers and continuing to work to reach as close to perfection as possible, but want to be clear for those reading who may not be seasoned designers and are thinking of using it.....don't think you're going to buy it with a stock crossover from these guys and it's going to sound great. I don't agree that it can't be done, but it's tough....Josh may be right though, that in many cases it would be easier to get the Radian to sound best, that's an experiment that I'll be doing soon and the winner will stay in the seosr..loser walks. Really though, there shouldn't be a loser, I just think it will be preference.

Absolutely, but I wouldn't assume it is "easier" to get a more conventional 4" diaphragm to sound better. Yes, you are eliminating one part of the design, but there are inevitable physical limitations with a diaphragm that big playing that high even with a theoretically perfect material used. Beryllium is an improvement over Ti or Al but it the dimensional issues stay the same. You can even see it in the response. The earlier peaks and valleys are in the same spots. Of course, the full on breakup modes are pushed much higher which is probably the most important benefit to Be.

Ultimately, it is a tradeoff and a hard one to decide on. I'd take a BMS coax over a titanium diaphragm any day and the BMS coax, until recently was a fraction of the price of a Be diaphragm driver from TAD or JBL. Now with TruExtent things get a bit murkier, but the Be is still a good chunk more expensive.
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post #20 of 54 Old 02-13-2014, 12:58 PM
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Quote:
Originally Posted by coctostan View Post

Absolutely, but I wouldn't assume it is "easier" to get a more conventional 4" diaphragm to sound better. Yes, you are eliminating one part of the design, but there are inevitable physical limitations with a diaphragm that big playing that high even with a theoretically perfect material used. Beryllium is an improvement over Ti or Al but it the dimensional issues stay the same. You can even see it in the response. The earlier peaks and valleys are in the same spots. Of course, the full on breakup modes are pushed much higher which is probably the most important benefit to Be.

Ultimately, it is a tradeoff and a hard one to decide on. I'd take a BMS coax over a titanium diaphragm any day and the BMS coax, until recently was a fraction of the price of a Be diaphragm driver from TAD or JBL. Now with TruExtent things get a bit murkier, but the Be is still a good chunk more expensive.

Agreed...I'm happy to have my 4594s, just gonna take some more work...which is fine, nothing good comes easy. The Radian would really have to impress me significantly over the BMS in order for me to sell the rest of my BMS and go all Radian. As you said, everything has it's tradeoffs.
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post #21 of 54 Old 02-13-2014, 02:18 PM
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Quote:
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Exactly Noah. Generally a horn that will cover from 500hz to 5khz will be fairly tall causing that problem. If it weren't for that fact it would be plausible solution.

How about suspending a teardrop shaped tweeter asy in the center of the WG, perhaps with a ring of foam around the forward edge around the tweeter?

Noah
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post #22 of 54 Old 02-13-2014, 04:12 PM
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I've seen some stuff like that, but I'm not sure how you would get decent directivity.

It also begs the question of why. Something like a SEOS-24 with BMS 4594-MID or a cone midhorn like the Pi midhorn crossed to some smaller horn around 1200-1500hz is a much better solution IMO. Is it better than a coax or Be 4" diaphragm, I can't really say. It would have smoother HF response, but you would have a null to deal with and you'd lose the benefits of the wide bandwidth point source.
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post #23 of 54 Old 02-13-2014, 04:24 PM
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So it becomes a balancing act of compromises, just like any speaker. wink.gif

Either have the extended/smoother response at the expense of negatively affecting polars or give up extended response for a simple single point source 2" system.


This was a decision I was battling with the final year of design for my new system. Obviously you all know which direction I picked but I did hang on to my JBL 2445's and 2380's just in case I ever want to compare or use them in some other project. Honestly, I think I'm going to save them to build some old-school 2-way with Be diaphragms loaded and .....something for bass. tongue.gif

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post #24 of 54 Old 02-13-2014, 04:33 PM
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I've seen some stuff like that, but I'm not sure how you would get decent directivity.

Out of the mid or tweeter?

If the former, it becomes an annular waveguide.

The tweeter module would be small and near the central rays so shouldn't disturb the wavefront too much.
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It also begs the question of why.

To make c-c zero and eliminate the null issue.

Noah
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post #25 of 54 Old 02-13-2014, 04:58 PM
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I guess I'm not sure I understand what you are saying. Would this hanging HF tweeter be near the throat of the horn?

The issue is that a very small tweeter will radiate >180deg and back into the horn creating cancellations. It is like using a dipole tweeter very close to a boundary.

I understand it would address the null issue, but why do that over just using a lower cross and more low frequency capable tweeter?
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post #26 of 54 Old 02-13-2014, 05:08 PM
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The tweeter would be nearer the mouth to minimize occlusion of the mid-horn radiation.

It would also have a horn, which would only need to be a few inches in diameter.

I guess an issue might be what it does to the midhorn radiation at the top of its range.

Maybe it would just be like Geddes' WG's, where you just don't listen directly on-axis.

Noah
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post #27 of 54 Old 02-13-2014, 06:01 PM
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Yeah, it would need to be about 4" in each direction so that most of the energy would be contained in front. I'm not so sure it would work very well to be honest. That is a large chunk of diffraction sitting right on axis and probably within 10-15deg of axis too. I'd be surprised if it would be a net positive over the alternatives. You could do some boundary sims or just mock something up and measure. I would initially test the mid performance with a big chunk sitting in the mouth of the horn.

Now there is one other possibility. Are familiar with conical mid horn phase plugs? Maybe you could mold a small HF horn into the front of a phase plug.
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post #28 of 54 Old 02-13-2014, 08:10 PM
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Quote:
Originally Posted by coctostan View Post

Yeah, it would need to be about 4" in each direction so that most of the energy would be contained in front.

Not sure which direction you mean, but if a 13" wide WG can maintain directivity down to 1000 Hz, then a 2.6" wide WG should work for 5000 Hz.

The teardrop shape at the back can smoothly blend around to the WG radius on the front, perhaps with a low density foam ring around the O.D. at the widest point for good measure.

Noah
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post #29 of 54 Old 02-13-2014, 08:23 PM
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The problem I'm seeing with this homebrew coax plan is sure, you eliminate CTC differences in the X and Y axes, but you still have an offset in the Z axis. You can allow for that in the crossover or DSP for on-axis but the offset will change off axis in any direction including off to the side.

Or am I thinking about this wrong?
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post #30 of 54 Old 02-13-2014, 09:06 PM
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I guess it depends on which horn or waveguide we're measuring, but if we measure on tweeter axis zero degrees vertical and look for the best horizontal fr (provided all constants remain unchanged), the z axis should not change at all on or off axis. Is that what you mean?

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