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2-way Unity horn 250hz-20khz

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citizensc View Drop Down
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    Posted: 26 September 2020 at 8:57am
Hi All 

I am thinking about building a new sound system some time in the next 12-18 months. My goal is to build something that out performs my existing Xtro Punisher system in every measurable and subjective way. 

I will start with designing the HF/MF and work my way down. In the end I intend to have a 2-way unity horn on top of FLH Kicks and Subs. 

The design goals for the Unity Horn are:

- <25kg, pole mountable by one person
- 250-20khz frequency response
- 50x25 directivity, easily arrayable 2 per side
- clearer, smoother and louder than the de250 + 8pe21 on XR1064 + XT8 mk2 I use now
- cab will be bi-amped with DSP rather than a passive xover

I have run 100+ AKABAK 3 sims with different horn sizes, driver sizes, driver locations, number of drivers, tap sizes, tap locations, tap shapes etc. this is what I have come up with so far: 




The drawing of the internals only includes acoustic boundaries as it is intended for an AKABAK 3 simulation, I will add wall thickness etc. when I have finalised the design. 

Currently I have settled on:
-12mm birch ply, 24mm where the mid drivers attach to increase the external diameter of the horn, allowing the drivers to fit closer to the throat. 
-4 x 4NDF34 https://www.bcspeakers.com/en/products/lf-driver/4-0/8/4ndf34
-600x280mm mouth
-The centre of the taps are 53mm from the throat  
-The taps have 3.72cm^2 cross sectional area (2 per driver)
-Throat to suite one inch compression driver
-0.15L rear chamber volume for each driver

This gives good frequency response from ~210-2000hz, exceeding my expectations! It also only weights about 15kg on paper thanks to small size, 12mm material thickness and very light weight neo drivers. 

This also leaves me with some questions:

-Is there any better 4 inch driver I could use regardless of price? More BL, EBP, Power handling? 
-With all my simulations, have I optimised something that works great in sim land but has serious issues in the world? 
-What compression driver should I use? I have read that exit angle is important but the only maker I know to publish it is Faital. My current short list is: HF108/HF108R (whats the difference?), NSD1095N, 5530ND, CP/385/ND. Does anyone have experience with any of these drivers? Has anyone compared them? Has anyone got any other suggestions? 
-Is there anything I am missing? Do you have any ideas for how I could improve it?

I plan to order drivers soon and have a working MDF prototype by mid-late Nov.

Here are the sim results: 

2.83v @ 8 ohm - Red = On axis frequency response measure @ 10m and adjusted to 1m, Blue = power radiated from the horn irrespective of directivity. On axis response has a slope due to changes in directivity with frequency, at higher frequencies, energy is more focused on the measurement point. 

Group Delay

Horizontal directivity

Horizontal directivity normalised to the Y-axis (imagine EQing it perfectly flat)

Vertical Directivity

Vertical directivity normalised to the Y-Axis





Edited by citizensc - 26 September 2020 at 12:56pm
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Phil B View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil B Quote  Post ReplyReply Direct Link To This Post Posted: 26 September 2020 at 10:09am
Hiya

Just some first thoughts, as you prob' know we've built some 3 way Unities here in Aus.

12mm ply ... yes...we did the same to keep weight down.
Comp driver ... we settled on a 1.4" RCF ND2530TD .. overlapped the mids better than the original 1" Celestions.
We got some Celestion TF040MR 4" which are the same as in the Danley boxes. Not much info on the TS specs though.. might be worth looking if they are still available?

Pole mounting ....we built a cover for the rear of the horn only in our first version...the yokes attached to that. Saved a bit of weight and worked really well.



Things I would do different to ours if I could...

The throat piece for the Comp driver is critical and ours were done by hand with sandpaper and verniers ...measure, sand, measure... super slow and boring also getting the 4 flat sides of the horn to flow into the throat was very tricky ! I would get a 3D printer and make the whole throat piece which can glue direct to the square wood maybe even go so far as to make the mid taps as well ? Also you can print the flange for the comp to bolt to.

We had a few driver failures of our mids, the pressure on the opposite side of the tap to the mids seemed to be too much. We just shimmed out the mids but if we were building again I would route out enough for the driver to excurt into the horns themselves.

Good luck...and take lots of photos please !

.p.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 26 September 2020 at 12:54pm
Originally posted by Phil B Phil B wrote:


12mm ply ... yes...we did the same to keep weight down.
Does it resonate at all? How crazy did you go with the bracing? 

Originally posted by Phil B Phil B wrote:


Comp driver ... we settled on a 1.4" RCF ND2530TD .. overlapped the mids better than the original 1" Celestions.
How high did you manage to get the mids to play? 

Originally posted by Phil B Phil B wrote:

We got some Celestion TF040MR 4" which are the same as in the Danley boxes. Not much info on the TS specs though.. might be worth looking if they are still available?
I have been looking at these, they have less than 1/3 the power rating, and are a lot heavier. My thinking is that i will 3d print a back bowl/covers for the gaps in the basket and end up with a better result. I might try extract the T/S parameters for the Celestion from the impedance curve and sim it. 



Originally posted by Phil B Phil B wrote:


The throat piece for the Comp driver is critical and ours were done by hand with sandpaper and verniers ...measure, sand, measure... super slow and boring also getting the 4 flat sides of the horn to flow into the throat was very tricky ! I would get a 3D printer and make the whole throat piece which can glue direct to the square wood maybe even go so far as to make the mid taps as well ? Also you can print the flange for the comp to bolt to.
I was thinking of just making the square hole at the throat slightly smaller than the diameter of the comp exit, then drilling a 1 inch hole. Would this not surface? 





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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 26 September 2020 at 2:00pm
My spidey-sense is tingling....

Danley haven’t used the Celestion for about 8 years or more, the variance between units was too much. It’s a totally custom OEM unit now, not from one of the normal manufacturers either. Minimum order quantity is 100 units, sadly, even if I could tell you. A pal upgraded a few of his older SH46 with them. He might still have the Celestion and be willing to do a deal, you’d have to ship from California though.

A sealed back is important for that section, so you’ll have to build one around the driver if going for that arrangement. Or you’ll need to tap it like a Synergy, with all the associated positioning and filter design associated with that.

You may find that your channels for the mids to enter the horn increase distortion quite significantly. That may be the cause for the rising response in your sims too. This is one of the areas that should remain consistent even at off-axis extremes if done correctly. Get GLLViewer from AFMG and have a look at some of the GLL files from Danley’s site for inspiration. Most of them are driven with no preset.

HF driver throat depth, and phase plug shape is more important than the exit angle. You need to account for that in your sims and/or filter network. That’s one of the places that trial and error still tends to reign supreme.

If you’re not going passive, make sure you have DSP for some “odd” filter choices including out of band IIR EQ. Charlie Hughes’ paper on using allpass to optimise directivity through the crossover region is worth a sniff at too.

The boxes end up pretty front heavy, so make sure you consider a yoke rather than top hat mount. Mr Phil B can advise on that front I’m sure 😉



Ta-ta for now!

Edited by toastyghost - 26 September 2020 at 2:03pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 26 September 2020 at 3:11pm
my unity build is documented on the forum. I used HF146 and the 6" celestion drivers which are a standard driver. I don't know if I just fluked it but they seem to work pretty well. I did a lot of akabak modelling, three prototypes, and I didn't get the passive crossover right until I got some better measurements using REW. the mid section is -3dB at about 210Hz but I'm not sure what the excursion is like. I've stuck my finger in the port while they've been going full wack and it doesn't feel like they are getting near the 1mm xmax.

my boxes have pretty good constant directivity but a small amount of midrange lobbing. I've had the chance to hear some Danley SH50s and they seemed to have pretty much the same issues - miles better than most speakers though.

it seems a pity not to use the rear volume for something - which means sticking some woofers in and making it a three-way box. but I can see the advantage of being able to make it very lightweight if it's not having to support the weight of heavy woofers. thinner wood will be stiff enough, just stick some damping material on to reduce midrange resonances.

If I was doing it again I would design something like the SH96 and possibly use the same 15" drivers in some FLH or ported horn subs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil B Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 2:28am
Originally posted by citizensc citizensc wrote:

Does it resonate at all? How crazy did you go with the bracing? 


Our first versions had no bracing as such, the flare added strength and the cover over the back provided the support for the yoke..




Originally posted by citizensc citizensc wrote:

How high did you manage to get the mids to play? 


We have very small taps but managed up to 1.5k



Originally posted by citizensc citizensc wrote:

I was thinking of just making the square hole at the throat slightly smaller than the diameter of the comp exit, then drilling a 1 inch hole. Would this not surface? 


As Toasty alluded to the whole throat assembly is the key part including the depth of the phase plug in the comp driver. And the initial flare into the horn needs to be as close to oblate spheriod as you can make it...

Check out here for loads of info...

DIyaudio - 3d Printing

We added a flat piece to the end of our horn drilled out the centre and then cut & sanded that to get our initial flare..





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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 3:12am
Thanks for your replys, they are all very helpful! 

A lot of the potential issues you guys have posed suggest the next step is to build a prototype. A prototype would answer questions about distortion relating to the taps, issues relating to the throat for HF, actual weight, weight distribution etc. 

With regards to the rising response, I think this is related to my sim, I had the same issue regardless of driver configuration, driver size, tap size, tap location, tap shape etc. I have tried 2 x 8nsm64, 2 6nsm51, 4 x 5nsm38, the current 4 x 4ndf34 and a few other options. One other thing I have been thinking about is the fact that I am using a simple inductance model, maybe this has some impact? although the Le on these drivers is quite low. 

Here is a hornresp sim of the same design. I think hornresp is a little too simple to sim a mid horn like this, especially with how much tap placement, size, shape etc. matter. It will be interesting to see the real measurements. 





MDF is cheap but drivers are expensive, I think the first step is choosing and ordering the correct drivers then I will start prototyping (when I get back to my home city in Nov). 

For me, the current winner for mids is the 4NDF34.
-It has high power handling for a 4 inch driver
-It has 5.7mm of xvar, meaning BL should stay quite static even at high power levels. I don't expect to use more than 2.5mm of xmax 
-its very light weight
-It sims better than any other 4 inch I know of that has full published T/S parameters 

I intend to measure the dimensions of the cone and basket when I get it and calculate the volume between them then draw up and 3d print a back bowl/covers for the holes in the basket to make it a closed back driver with a specific rear volume. It will likely be ~150ml. 

If anyone has a better idea than this, i'm all ears.

Choosing a compression driver isn't as clear cut to me. I want the best driver I can get (with in reason, not going to use some exotic $4000 driver). As much as I would love to, I cant afford to buy 4 drivers and compare them. Obviously people cant just tell me X is the best driver but some indication of what I should be looking for or some anecdotal experiences with them are better than nothing and would be greatly apricated. 

Edit: 

Only read Phil's post after writing this.

Thanks a bunch for the info, it is good to know that 12mm seems to work fine. I think I am just going to build a trapezoidal cab around the horn, this way I can easily array them provided I got the splay angle right before deciding on the trap angle. 

Based on what you guys are saying about compression driver suitability, I think I am going to buy a compression driver with a phase plug that is very close to the exit as I can then add length if I need it.  Right now I am leaning towards the 5530nd, I just hope that its compact size doesn't compromise its sound. 


Edited by citizensc - 27 September 2020 at 3:52am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 11:39pm
Exit angle doesn't matter if the comp is very short and the phase plug is at the throat as there is no horn built into the comp.  Its also important in a unity horn to get the reflection point from the comp as close to the mid taps as possible as this causes a cancellation notch.  Its also a good idea to have the comp capable as going as low as won't compromise other aspects as the design as possible as there are a lot of factors that cause the mids to not hit high frequencies.  In my unity horn using 3.5" drivers I cross at 1.27kHz but getting this high needed me to design a crossover around the natural rolloff of the mids.  Taking all this into account I would use a 1.4" driver of pancake design like the faital pro HF1440.

Over here:
we have been discussing an alternative way of doing a multiple entry horn that horn loads the mids as well as the tweeter potentially allowing a higher crossover frequency and increased efficiency so it might be worth simulating....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 27 September 2020 at 11:41pm
heres my unity horn if you want some data on the 3FE25:
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 28 September 2020 at 5:38am
I think the 4NDF34 is a very different driver to the 3FE25, it has almost 3 x the BL and EBP, hopefully this helps me with the wide bandwidth I am aiming for. 

I think the 5530nd is a good choice for all the reasons you mention, it is very shallow meaning there isnt much room for long flared exit. It also plays quite low for a 1 inch comp, so if I do have issues getting the mids to play higher than 1.5khz I am not doomed to failure. 

Interestingly I have read that there is a HE version of the driver. Apparently it has a shorting ring which to my understanding reduces Le which would in theory improve HF response. 

With regards to variations on the unity horn design, I want to keep it cookie cutter, I know it works if designed properly and so far at least, it hasn't been very difficult to design... lets see if I stand by this after building a prototype. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 28 September 2020 at 1:10pm
Hopefully but also the 4NDF34 has a mms of 6.1g Vs 2.2g so perhaps the mas break frequency will not be much higher.  Also your simulation is assuming pistonic behavior which looks to be OK to 1.5kHz.

Yep 5530nd is a good choice.  The only weaknesses I know of is that it uses reflectors so the top octave decay is not the very best and potentially if you used a larger throat driver the THD at high level would be lower as the distortion due to air non linearity would be less,  depends on SPL target, upto 110dB/1m should be fine above that I would consider larger throat drivers:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 29 September 2020 at 4:12am
That is an very interesting paper, 'Contrary to what many people believe, the smaller drivers do not necessarily have more extended high frequency response than the larger models.' and 'Obviously, the mass of the larger diaphragm assemblies is greater than that of the smaller devices, as is its voice coil resistance. However, the larger magnet structure and the increased length of wire in the voice coil provide more driving force, and this enables the larger driver to maintain its mass break-point substantially in the same frequency range as the smaller driver.' are big eye openers for me. 

I have read a lot of reviews on audio xpress/voice coil and noticed that the THD of 1.4 inch drivers seems to almost always be lower than 1 inch drivers. 


Compression drivers are not something I know a lot about, but I'm starting to think that if the size/weight/cost isn't an issue, a 1.4 inch driver is always better than a 1 inch for PA use. Correct me if this is wrong. 

The HF1440 you mentioned in your other post appears on the surface to be the perfect driver for this. It plays low so I would have a lot of flexibility with xover, the phase plug ends at the exit of the driver, its a ring radiator so its HF is good. It appears the only issue is actually getting one, there seems to be on going supply issues, that and cost although I think it will be worth it as it will make a fraction of the cost of the complete system. 
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