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Discussion Starter #1
My L/C/R mains are 3-ways using an SEOS 8 horn for the tweeter section. I designed and built them myself, and am running them fully active with an Ashly ne24.24m processor doing the crossovers and EQ.

The current tweeters are Transducer Labs N26CFR-A carbon fiber dome tweeters. I 3D printed an adapter bracket that slides over the round face plate and bolts it to the SEOS 8, which works well. Overall, they sound and measure pretty good, but have a pretty steep roll-off above 10KHz. I realize that part of this is the horn, but the tweeters actually have a rising response on the top end, which should at least yield some minor compensation for the horn roll-off.

I EQ'd them up on the top end, which definitely helped, and I also added a homemade phase lens. The phase lens helped quite a bit, but you know how DIY goes. I am wondering how other drivers would sound, particularly compression drivers as this has not really been explored with the SEOS 8. There is a great thread on the PE forums that explored a few other dome tweeters with the SEOS 8, but I do not believe anyone has mated a compression driver to them yet.

The throat on the SEOS 8 is 38mm, or ~1.5". JBL makes a handful of 1.5" compression drivers, but I am limited to the physical size of the driver being able to fit my speakers. None of the JBLs will fit in my cabinet. Other 1.5" options are all similar in size or cannot be found anywhere for sale in the states, so I started looking at 1.4" drivers, which have A LOT more options available.

The max dimensions for the driver are 4.75" O.D. by ~2.15" overall depth. I might be able to squeeze a small amount more depth using a slightly thicker gasket around the edge of the horn, and if it came down to it, I could modify the inside of the speakers to allow a bit more depth, but the O.D is pretty much set by where the horn is located on the cabinet. The size restriction means a throat adapter cannot be used.

My question for the horn gurus is how much of a problem would using a 1.4" driver on a 1.5" horn pose? I know if one were to be jumping to a 2" throat horn you can expect a hole in the middle of the bandwidth and increased distortion due to throat reflections and the decrease in output through the range of the response 'hole'. The difference between a 1.4" driver and 1.5" horn is much smaller though. That, coupled with the fact that I will likely be running a negative gain on the order of ~15dB (110dB compression driver, while the mids and woofers sit at around 94-95dB sensitivity) should mean that the distortion numbers and droop in response from the mismatch shouldn't be an issue, correct?

I'll probably being using a combination of negative static gain with a shelf filter to keep the top end as flat as possible.

I'm definitely not as adept as I'd like when it comes to horns, so if this is a bigger issue than I think, please let me know.

Initially I wanted to try the new Eminence N314-X, but the physical dimensions do not allow it to fit. After narrowing down available options that do not require cabinet modification, I think I have settled on the FaitalPro HF142. I like that it uses their Ketone Polymer diaphragm, and it measured well on the AudioXpress Test Bench .

The plan is to purchase 3 more SEOS 8 horns and mate them to the HF142s. That way I can pull the other tweeters out and swap with ease. The HF142s are 4 bolts on 4" bolt hole CL diameter, so I'll have to drill new holes in the SEOS 8, but it should be easier than 3D printing a bracket. Even if I can only get 2 holes on the horn flange I think it will clamp down just fine. I have a drill press I will be using for this.

Does anyone see any major problems with this plan? (y)
 

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Discussion Starter #2
So I purchased the SEOS 8s yesterday afternoon. I am almost ready to pull the trigger on the FaitalPro drivers, unless anyone sees a problem with the 0.1" mismatch at the throat?

Just to reiterate, there really isn't a reason other than curiosity as to how a compression driver would do with the SEOS 8 and my cabinets. Sure, the efficiency of the compression driver will be nice, and given that the sensitivity requires A LOT of negative gain to get them to mate well with the midranges and woofers, I should be able to get to at least 18kHz perfectly flat with only cuts.

This is really just an experiment more than anything. Since I am replacing the horn and driver combo, if I don't like them I can always change back easily.
 

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I don't know the answer to your question, but why not ask Erich if you can buy SEOS-10 and use the B&C DE250 that has been measured and matches the 1" throat? You could even get SEOS-8 with the 1" throat but I've never seen the pair measured.
 

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Discussion Starter #4
Well my cabinets are routed for the SEOS 8, and the 10 wouldn't fit. I have about 3/8" either side of the horn, and they are countersunk into the cabinet.

Regarding the B&C DE250 and getting an SEOS 8 with a 1" throat: I would rather order from DIYSG since Erich, his team, and the members here were the ones who developed the SEOS profile. The option for the 1" throat is from Auto-Tech (AFAIK), and since my inside cabinet dimensions were developed from the DIYSG horn and the dome tweeter I used, I believe the extra path length to get the horn to terminate at 1" instead of 1.5" would reduce my allowable driver depth to such a small amount that I would be forced to modify the internals of the cabinet to use any compression driver. I think DIYSG and Auto-Tech have a sort of partnership, which is cool, so it is more the path length issue that would sway me from this path. And the fact that ordering from Auto-Tech would likely take quite a while for shipping and/or be pretty expensive. This isn't a cheap experiment for sure, and it isn't meant to be, but saving costs on shipping is always appreciated.

The 1" throat idea is definitely something to consider though., thanks for the comment! ;) (y)
 

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Discussion Starter #6
I am probably going to purchase the FaitalPro drivers today. Considering the mismatch is still probably less than I have with the dome tweeter, I do not think it will pose an issue. Even if it does have some internal reflections, I can always put my little makeshift phase lenses in to help cut down the reflected waves.

Speaking of phase lenses, I finally got around to measuring the dome tweeters with the phase lenses installed, and I have pretty dang flat response to 15kHz now. Like I stated above, they used to roll off pretty hard at 10KHz without the phase lenses, so the proof from the pudding says the phase lenses do work as they were intended.

If I don't end up liking the compression drivers, I'll put the dome tweeters back in and save the CDs for the basement speakers whenever I get around to building them. That's awhile out since the basement still needs finishing.

I'm thinking of doing a MEH (multiple entry horn) for the basement speakers.
 

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Discussion Starter #7
So I am going to have to purchase the CDs from 2 different places since PE only has 2 in stock and I need 3 total.

I loaded 2 of them into my PE cart, thought I'd check online for coupon codes, input the CJFIFTY code, and it tells me I have used this code before and cannot use it again? That's sort of whack considering the last time I used the code was almost 5 months ago. I was under the impression that as long as your total was greater than $500 that the coupon code would work every time. It's not a deal breaker per se, but I do always like to see discounts for bigger purchases. Anyone have any other codes that could be used? I like the 50 off 500 deal, that always feels significant enough that it takes a little edge off the purchase.

If not, Black Friday (can we say that anymore or has the term been cancelled?) is just around the corner, so I might wait and see what kind of deals they have available then. I'm not in any rush. The dome tweeters work fine for now.
 

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So I am going to have to purchase the CDs from 2 different places since PE only has 2 in stock and I need 3 total.

I loaded 2 of them into my PE cart, thought I'd check online for coupon codes, input the CJFIFTY code, and it tells me I have used this code before and cannot use it again? That's sort of whack considering the last time I used the code was almost 5 months ago. I was under the impression that as long as your total was greater than $500 that the coupon code would work every time. It's not a deal breaker per se, but I do always like to see discounts for bigger purchases. Anyone have any other codes that could be used? I like the 50 off 500 deal, that always feels significant enough that it takes a little edge off the purchase.

If not, Black Friday (can we say that anymore or has the term been cancelled?) is just around the corner, so I might wait and see what kind of deals they have available then. I'm not in any rush. The dome tweeters work fine for now.
Yeah, I’ve noticed that PE no longer lets you use coupon codes more than once. Started earlier this year I believe.

Black Friday was 15% sitewide last year, but no promise of a repeat.

Chris
 

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Discussion Starter #9
Cool, at least I'm not the only one that has experienced that.

I do think I'll wait and see what BF has in store since it is so close. It is a little sketchy since someone could buy them up before I get a chance, but it's still worth it if they have a decent discount.
 

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Discussion Starter #10
So, back to this...

Well I missed the PE BF 10% off since they decided to run it for 2 days (IIRC, might have been 3) only prior to ACTUAL Black Friday, and then proceed to have absolutely nothing for BF. Oh, a SALE on the items they want to clear out, which consists of nothing most people want to buy. Sorry, still a little peeved by that.

But I digress, I still wanted to purchase the FaitalPro HF142s. So I waited until after Christmas, watching and waiting to see if they threw a random Christmas discount in there, but they did not. I went searching and found 2 different $20 off $200 coupon codes, made 2 purchases, 1 for each CD, and at least got semi-close to the Pre-BF deal. I also purchased a single CD from speakersandamps.com, since PE only had 2 HF142s in stock. They go by a different name on eBay, tsgaudio, and have pretty good feedback. I bought through their website since I would rather not give the Bay their cut if at all possible. They are an authorized FaitalPro dealer - TRAX Audio in Utah, verified on the FP site, so should be safe for any warranty issues if needed.

So I now have 3 CDs on the way. I am hoping to have them early next week, but am not in a huge hurry. The first thing I will do is set one of them up with the SEOS 8 horn and take some measurements of just the CD/horn combo. I will attempt to EQ approximately flat, maybe a slight downward slope towards the top end, from around 1400Hz to 20kHz on axis. The raw response as measured on the AudioXpress test bench shows a pretty hard drop off at ~18kHz, but since I am going to have to reduce the output by around 15dB anyway, I think I can get 20KHz out of them without issue. The AX graph showed about 95dB at 20KHz, which is right about where I need them to be across the entire frequency range in order to mate well with the midrange drivers. I have ~160W available to drive them, and they definitely won't use all of that. They'll probably cruise along at 1-4W for their entire lifetime, if they end up sounding good.

I am still not sure how well they will mate to the SEOS 8. It is entirely possible that I will set up, measure, and be disgusted with the result. No big deal really, this is all an experiment anyway. At least I don't have to modify the cabinets to get these to fit!

If the results of this experiment are unsatisfactory, I might break out the 3D modeling skills and design my own horn that matches the HF142 1.4" throat, 29 degree exit angle, and the major dimensions of the SEOS 8, mainly the cabinet mounting flange. Then I'll 3D print it.
 

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Discussion Starter #12
just make a small adapter plate, should be trivial.
Are you saying make an adapter plate to reduce the SEOS 8 throat diameter from 1.5" to 1.4", or just to mount the CD to the horn flange? For mounting it, the holes actually all fit on the flange. I just have to drill new holes, which shouldn't be an issue. For the reduction of throat diameter, a thin piece of plastic 3D printed at the right diameter with the hole slightly beveled to transition to the 1.5" horn throat might work pretty well. Right now I don't know how much room I'll have between the back of the CD and the back of the internal midrange box that also houses the tweeter/horn. The design dims say I'm pushing the allowable room as it is, so a spacer may not be possible without modifying the cabinet a touch. I'd like to avoid that, but would be willing to as a last resort.

My main concern now, after having done a lot more research, is that the horn throat angle is not really matched to the CDs exit angle. The HF142 has a 29 degree inclusive conical exit angle. I am not sure what the SEOS 8 is exactly. The SEOS horns that are made for the DE250 have a 14 degree inclusive throat angle, which may be what the SEOS 8 is, but maybe not. There isn't a whole lot of info in the SEOS thread about the 8 since it was made for a dome tweeter. Since I am not really a horn expert, it makes me wonder if they will play well together. Depending on who you listen to, the slightest mismatch in things will wreak havoc on your frequency response, or it may not be a big deal.

I'm getting more and more interested in printing a waveguide the more I research. Patrick Bateman (obv a pseudonym, lol) on DIYAudio has some really interesting horn threads, and he favors small horns, so adapting one of his designs is intriguing.

Hopefully I get these installed and they sound great, but as I said before, it is really just an experiment. To my knowledge, I do not think anyone has mated a CD to an SEOS 8 yet.
 

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Discussion Starter #13
I received the CDs the middle of last week, and finally got around to getting them into the speakers this weekend! Holes drilled out on the 4" hole centerline just fine, narrowly missing the stock holes. Even if it had created a slot instead of a single hole, they still would have been usable. I barely got the towers done last night before bedtime, with a quick reduction in output in the DSP and gave them a short lower volume listen with non-demanding material. Subjectively, they sound really good so far. I would have had a lot more time, but had a little whoopsie that took about an hour of cleanup. The chalkboard paint I used on my front baffles does not like to adhere to sharp edges, so everytime I remove a driver or the horn in this case, it chips off a little on the edge of the cutout. So I usually just apply a little black paint and it is back to looking good. Well, I was using some flat black model paint, in the living room, with the speaker on its back. I was super careful to not tip the bottle of paint when I set it down... on the carpet (mistake!). I brushed a little paint on a small chip, got up to go grab a paper towel and give it a little swipe, came back, and the bottle was tipped over! EEEEEEEEEEEEGADS! After I stopped freaking out, I grabbed some mineral spirits and went about cleaning the carpet as best I could. I almost got it all out, in fact, I was really surprised at just how faint it was when I was done.

I am going to try to get some measurements tonight after work. The first thing I noticed however, was the sensitivity of the CDs. They hiss a bit more than the domes for sure.Lowering the output gain in the DSP made it quieter, but still louder than the domes. I am thinking since they don't need very much power to get super loud, instead of reducing the output in the DSP, I am just going to lower the gain on the tweeter channels, and then tweak the DSP slightly to get things matched with the midrange/woofer sections. Will lowering the gain at the amplifier reduce the hiss more than lowering the output gain in the DSP, or is it basically the same thing? The level of hiss is not super loud - I can hear it during quiet scenes when seated on the couch about 8 feet away. If I can reduce the level a bit that would be nice. If not, I do not currently think it will be much of a bother when source material is playing.
 

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The hiss is from the noise floor of whatever's getting sent to your amp. It depends if its from the dsp itself or from the source. If reducing the gain in the DSP doesn't do it, then you can reduce the gain in the amp.

Using very sensitive CDs, I use a 3636 autoformer to knock down the levels 12db since I didn't feel like modifying my amps to adjust the gain (26db).
 
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