Do you need 4x 4-inch midrange drivers, horn loaded? If maximum SPL in PA use is the target, then you might. But I suspect you could get away with just two of them.
In my latest Synergy-ish speakers (for home use) I use just one midrange (on a 90x50 horn), and it is more than enough for that, haven't ever heard the midrange sound strained in use.
David is describing how to use the multiple entry horn wizard to simulate the path length of the compression driver. The Nd record is the one that describes the compression driver and the entry is simulated with the same parameters as the midrange port. Before that feature was available the best way to approximate it was to add the length to the con12 value so that the reflection notch was more accurate. The help function in hornresp describes how to use the multiple entry horn wizard, reading that might help to clear things up for you.
Because BMS uses an annular diaphragm there is a longer acoustic path inside the driver. The reflection notch happens due to the cancellation from the midrange sound reflecting off the back of the tweeter. This is why you need to add in the path length of 6.47cm for the 4555, no need to ask BMS for the value I did already. If you use the 4550 then it is 6.7cm.
You may find that by using a DE250, RCF350 or something similar you can cross higher and not need to push the compression driver lower. The path length is more like 3 to 3.5cm for those style of drivers. If you choose to use a BMS compression driver you will have to cross over lower.
Hulkss did a series of posts on simulating a synergy design in this thread
http://www.diyaudio.com/forums/multi-way/88237-suitable-midrange-cone-bandpass-mid-unity-horn-86.html#post3476980
If you haven't seen it already this was helpful to me to understand the mechanics. The information is pre multiple entry horn wizard but I think it is valid anyway.
@fluid thanks for the explanation about horn wizard. I looked at the wizard a little and decided I better learn a little bit more about the parameters and what they do before I start messing with it.
Some not so good news, I have to go out of town. And probably won't be back until Sunday evening. Which means no speaker fun for the rest of the week.
I'll do some more research on the compression drivers when I get back. I guess at the end of the day, I just want it to sound good. Or better than good. Super good. Hifi even. In the beginning of the project, because I like Eminence so much, I thought I could use the 6-inch Eminence drivers and even an Eminence Neo compression driver. But you just can't throw anything into the horn and expect it to work. I wish! So I thank McBean for Hornresp. I may just test out an all Eminence horn.
So I finished a redraw of the Celestion drivers and had to rethink the horn dimensions. Luckily I didn't have to change the box much. It's now a 90x50 horn. Very happy with that. Also did a Horn Response model of the Celestion TF0410MR (4 drivers). Let me know if you see anything wrong.
Some not so good news, I have to go out of town. And probably won't be back until Sunday evening. Which means no speaker fun for the rest of the week.
I'll do some more research on the compression drivers when I get back. I guess at the end of the day, I just want it to sound good. Or better than good. Super good. Hifi even. In the beginning of the project, because I like Eminence so much, I thought I could use the 6-inch Eminence drivers and even an Eminence Neo compression driver. But you just can't throw anything into the horn and expect it to work. I wish! So I thank McBean for Hornresp. I may just test out an all Eminence horn.
So I finished a redraw of the Celestion drivers and had to rethink the horn dimensions. Luckily I didn't have to change the box much. It's now a 90x50 horn. Very happy with that. Also did a Horn Response model of the Celestion TF0410MR (4 drivers). Let me know if you see anything wrong.
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You have an Atc of zero. I would estimate this as 4 x 71cm squared i.e Atc should be around 284. As you still have to account for the path length the reflection notch will move down quite a long way from where it is now.
I would seriously consider using a celestion cdx-1747 as this is the same combination that Paul Spencer uses in his PSE-144 point source horn. Looking at the frequency response and impedance graphs with a 24db/oct crossover you could cross anywhere between 1k and 1.5K quite easily. I would imagine the path length on these to be about 3 to 3.5cm. Just as a quick test until you get to grips with the multiple entry wizard add 6.7cm to the con12 value and see what happens to the reflection notch.
As you are planning on a 90 degree horizontal I would lay the drivers out like Bill did in his cosyne. Two on the top and two on the bottom. That way the sides can be extended and the drivers placed more centrally over the port holes. It also looks like you could move them further back towards the compression driver. As the drivers are already sealed they can be mounted almost on top of the CD. That leaves the shorter sides open to allow the CD mounting bolts to be accessed. A single 15 to 19mm hole per driver should be OK.
I would seriously consider using a celestion cdx-1747 as this is the same combination that Paul Spencer uses in his PSE-144 point source horn. Looking at the frequency response and impedance graphs with a 24db/oct crossover you could cross anywhere between 1k and 1.5K quite easily. I would imagine the path length on these to be about 3 to 3.5cm. Just as a quick test until you get to grips with the multiple entry wizard add 6.7cm to the con12 value and see what happens to the reflection notch.
As you are planning on a 90 degree horizontal I would lay the drivers out like Bill did in his cosyne. Two on the top and two on the bottom. That way the sides can be extended and the drivers placed more centrally over the port holes. It also looks like you could move them further back towards the compression driver. As the drivers are already sealed they can be mounted almost on top of the CD. That leaves the shorter sides open to allow the CD mounting bolts to be accessed. A single 15 to 19mm hole per driver should be OK.
The attached screenprint shows a compression driver specified in the Nd record using Sd, Vrc, Lrc, Ap1, Lpt, Vtc and Atc. For the throat chamber, set Atc = Sd and choose a value for Vtc that keeps the chamber length quite short, as shown.
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The CDX-1747 isn't bad at all. It's cheaper too. I like the idea of keeping all the drivers in the same brand. And thanks David for your example. I'm gonna start working the wizard as soon as I get back home. I'm hoping to find a tutorial somewhere and if I don't I'll probably have a crap ton of questions.
I'm in St. Louis, Missouri. And it's been raining all day.
I'm in St. Louis, Missouri. And it's been raining all day.
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