The path length to the screen is 67mm. This does not take into acount the gasket, which is about 2mm thick, which I guessed is also about the offset to the element inside the WM 61 capsule in the end of my measurement mic. These two distances therefore cancel themselves out.
BTW, you will probably add 6mm or so in your mounting plate to mate this driver with the back of a unity horn.
Cheers
William Cowan
BTW, you will probably add 6mm or so in your mounting plate to mate this driver with the back of a unity horn.
Cheers
William Cowan
Thanks William! That is some great information. Thank you for taking this measurement for us. In your opinion, would it be reasonable to then state that the acoustical length of the 4552ND should be 51mm? (I subtracted the overall depth of the 4552ND (36mm) from the 4550 (52mm) and came up with a pauseable acoustical length of 51mm for the 4552ND)
Rgs, JLH
Rgs, JLH
What's the deal with reactance annulling in a unity horn?
I read the Klipsch paper, and it indicates that the cutoff of the horn should be lower than the resonance of driver. For instance, one might use a 400hz cutoff with a woofer that has a resonance of 500hz.
A few questions about that:
I read the Klipsch paper, and it indicates that the cutoff of the horn should be lower than the resonance of driver. For instance, one might use a 400hz cutoff with a woofer that has a resonance of 500hz.
A few questions about that:
- In hornresp, I seem to get flatter response if I tune horn cutoff, horn length, and the resonance identically. For instance, when using a Misco JC5RTF-B I get good results with a 500hz mouth, a 500hz resonance, and a horn length of about 17cm. (1/4 wavelength)
- When calculating the length of a unity horn for reactance annulling, do you start at the throat? Or the entry point of the midrange holes? Or even the compression driver diaphragm?
It really depends on what you are trying to do. What really controls the Fo of the mids in a Unity is the local expansion area - i.e. the local flare rate. What I've found is if your mid driver Fs is above the local flare rate, then it is the local flare rate that controls Fo. Whenever I tried using a form of reactance annulling its made it much harder to get a good looking frequency response. So far, I've been more successful with the RDC3T-A than any other mid.
Rgs, JLH
Rgs, JLH
Here's some updates on all this.
- I take back all the terrible things I said about the Misco JCRTF5-B and KCN5FD
While I've complained about their distortion performance in the past, I've found that many of my past designs were using throat holes which were too small. I am running Unity horns under my dash for the past few weeks, and based on what Sheerin said, I really went crazy with the hole size. I am running dual 1.5" holes and it improved the sound dramatically.
That's not to say that the distortion isn't a problem - it's still quite a screamer when you run it full range.
I think the reason that my old attempts at this sounded poor with the Misco woofers was that the small hole size was reducing my efficiency, so I compensated by cranking up the volume, which then increases distortion. Big holes give you big efficiency, and that makes all the difference in the world.
In fact the efficiency is so high now that I almost need to pad down the midranges! - I still like the Faital 3FE20, but now I'm a bit nervous that the Misco will work better. If you go with the Faital the front chamber (the little pocket of air in front of the cone) will be smaller, and that means you'll need even LARGER holes than the Misco to achieve the same tuning frequency. Well, theoretically at least.
- I am starting to consider suitable woofer choices for a Unity horn. Parts Express just started selling a TC Sounds woofer which looks like a good choice. It's called the "Epic 8" and it's under $150 each. One of my concerns is weight; four of these are almost a hundred pounds. Madisound sells an 8" woofer from Aurasound, and four of these would weigh less than 15lbs. Also, a case of nine woofers is about as much as ONE of the TC sounds woofers.
An externally hosted image should be here but it was not working when we last tested it.
John,
If making the holes that big for a 5" (?) midrange improved the sensitivity a lot, it probably means the drivers aren't well suited for a unity. I have the same thing - my mids need really big holes to have flat response and high sensitivity. But that destroys the smoothness of the tweeter's response.
If the mids are 'screamers' when run full range, that subjective description would suggest that they have cone breakup at high frequencies. That means you're using them too high in frequency. Alternatively, they might have a large rise in the response at high frequencies, in which case the problem is that you need to eq them to have a flat response. I suppose you could argue that that's linear distortion, but it's fixable. In either case, a frequency response measurement would show you either of these problems before you ever listened to it and you could plan how to avoid it.
If making the holes that big for a 5" (?) midrange improved the sensitivity a lot, it probably means the drivers aren't well suited for a unity. I have the same thing - my mids need really big holes to have flat response and high sensitivity. But that destroys the smoothness of the tweeter's response.
If the mids are 'screamers' when run full range, that subjective description would suggest that they have cone breakup at high frequencies. That means you're using them too high in frequency. Alternatively, they might have a large rise in the response at high frequencies, in which case the problem is that you need to eq them to have a flat response. I suppose you could argue that that's linear distortion, but it's fixable. In either case, a frequency response measurement would show you either of these problems before you ever listened to it and you could plan how to avoid it.
Ordered a half case (30) of the Misco RDC3T-A 3" sealed mids. That's the smallest amount that can be ordered. Also decided on the BMS 4552ND instead of 4550 due to its shorter acoustical pathlength. New laptop is being configured. New measurement software and hardware comes in another 2 to 3 weeks. Progress will be slow, but when the time is right, I'll start a new thread. Planned crossover points will be in the ball park of 500Hz and 1300Hz for a 3-way Synergy style horn. Should be interesting. It most certainly will be frustrating.
Bwaslo, you're one step ahead of me
JLH, I'm keen to build a synergy horn, more so than a unity horn. Looking forward to your new thread
Good luck with it all!
If the RDC3T-A is a success, then I will sell any remaining stock. After I'm out of stock, a group buy would be in order. Misco is building my RDC3T-A's right now - March 16th ship date as of now. I'll be ordering the Smith & Larson Audio speaker tester in a couple weeks. It has all the tools needed to get the driver spacing and crossover correct. There will be a learning curve with all this, so don't get overly excited. This will take some time.
Consider this a stupid question, but for home use, is there really any advantage to adding the midbass drivers to this horn (ala Synergy)? I mean if the lower xo point is 500hz, that is low enough to get a good lobe crossing over to a direct radiator, isn't it?
I am just trying to see the advantage.
I am just trying to see the advantage.
It depends on how you load the midbass. If you put the exits from the midbass front chamber right by the mouth of the horn, the primary advantage would probably be the bandpass configuration reducing harmonic distortion via the acoustic filter plus the smaller source size of the midbass and getting that source closer to the horn than would be possible with an MTM arrangement. So say you did dual 15's in an MTM with a 15" mouth unity in between. You'd have polar narrowing from the 15's in the 150hz range. If you put the exits of a bandpass in the horn where the horn is less than ~7" across for JLH's stated goal of 500hz, then that effect does not exist. The pattern should be smooth and symmetric (assuming the horn is symmetric) as you go down in frequency and the pattern widens based on the size of the horn mouth. But if you made the horn mouth bigger, you could get some loading for the drivers, match the sensitivity of the mids and lower power compression from the midbass drivers.
Putting all that aside, when I made a 3-way unity about 10 years ago even though I didn't know what I was doing and had a crappy alignment for the midbass drivers, it was awesome and very coherent sounding.
Putting all that aside, when I made a 3-way unity about 10 years ago even though I didn't know what I was doing and had a crappy alignment for the midbass drivers, it was awesome and very coherent sounding.