Suitable midrange cone, for bandpass mid in Unity horn. - Page 43 - diyAudio
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Old 11th January 2012, 02:38 AM   #421
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[QUOTE=Patrick Bateman;2855348]
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G'day John



I need to state up front that my grasp of phase isn't intuitive. IE, there are a lot of things in audio that I 'get' off the top of my head, but phase is one of those things that's quite bewildering.

But I was thinking about it this morning, and it occurred to me that the phase of the sound coming off of the midrange drivers won't change in any appreciable way as long as the dimensions of the chamber in front of the driver is smaller than one quarter wavelength.

I still think the diameter of the cone poses a problem; at one half wavelength we should see a dip around 1500hz. (Assuming a 4.5" cone.)

But tweaking the ports so that the pathlengths are reduced seems like it would buy us a few hundred hertz.

Phase is tough for many, and you do need to get your head around the physical interactions that are taking place. Be aware that phase and frequency response are linked in linear devices. A change in the frequency domain will give a change in the phase behavior. If the phase behavior is good, the frequency response will also be good.

You are right that if the area under the cone is small, any resulting phase changes will be insignificant. That trapped air will start to look like a stiff spring, and combined with the slug of air in the port will create a low pass filter. If the spring is very stiff (small amount of trapped air) and / or the slug of air in the port is very light the the frequency of this filter will be pushed higher, further reducing the phase shift at a given frequency too. It is favorable not to push this too high, and to actually utilize this physical LPF to clean up some of the out of band distortion components coming off the cone and also to provide some of your crossover slope.

I successfully use 8" drivers crossed to a BMS 4550 at around 900Hz. The Unity horns I use in my main system are crossed only a little higher, I'm not sure why you want to cross at 1500Hz? The mid drivers have to be impractically close to the compression driver if the X/O is so high, or the notch from the reflection out of the apex of the horn will be in your passband. That little BMS (or the B&C DE25 in the main system) can handle everything an Australian Monitor 1K2 can throw at it, so surely driver protection is not your issue here? If your compression driver is too fragile, then perhaps you should buy the B&C or BMS to relax the constraints on your mids and simplify your design.

Speaking of crossovers, you will find that a well implemented unity type system will have a fairly simple crossover. I have found even a simple 1st order design with notch filters to correct response irregularities often works best. The nature of the CD horn means the compression driver has maximum attenuation at the bottom end of its response, reducing the load considerably. It's actually the top end of the compression drivers response that sets the sensitivity for the whole system. You will probably have to pad back the mid section a lot to allow the the compression driver to keep up. A decent driver will have no problems with a 900-1KHz crossover.

I should stop rambling.

William Cowan
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Old 11th January 2012, 02:52 AM   #422
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Getting the crossover up higher than 1k is more of a preference than a necessity. I have used as low as about 850 Hz.
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Old 11th January 2012, 02:56 AM   #423
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Hi William,

In my S2 I was able to get 90 x 40 and extension to 220 Hz by using 6 drivers. S1 was 60 x 60 with only 4 drivers and simpler construction, extension was more like 250 Hz.
Wide dispersion removes the biggest advantage of using a unity type horn in a domestic environment. With a 90 degree horn in a rectangular room, you have no way of controlling where the sound goes. You are simply "lighting up" the walls. If I could control the beamwidth of my system full band, I would aim for a 30-40 degree pattern. That would fill the listening position without filling the room with sound. As it is my main system gradually broadens its pattern below 500Hz to 90 degrees in the horizontal plane. This is not such a problem because the imaging cues don't go down that low and the absorption of the walls is starting to increase too.

Look up Critical Distance and think about the ramifications of going for a wider pattern. A narrower pattern increases the critical distance in a reverberant room.

My workshop speakers are 90 degrees wide because there is no defined listening area. I needed to flood the whole area with high quality sound, not just one seat. In that environment they work great, but I would not use them in my main system.

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Old 11th January 2012, 03:03 AM   #424
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Getting the crossover up higher than 1k is more of a preference than a necessity. I have used as low as about 850 Hz.
Why would you prefer to go higher? The only reason I can think of is so a cheaper compression driver can be used. It causes many problems along the way.

Cheers

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Old 11th January 2012, 05:23 AM   #425
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With a 90 degree horn in a rectangular room, you have no way of controlling where the sound goes. You are simply "lighting up" the walls.
This could open up a different discussion that I don't want to get into here. Suffice it to say, I'm conversant with the issues involved. My particular room, system, philosophies, preferences and goals are also factors.

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Why would you prefer to go higher? The only reason I can think of is so a cheaper compression driver can be used. It causes many problems along the way.
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Old 11th January 2012, 02:03 PM   #426
MSeddon is offline MSeddon  Australia
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Hi William,
Can you tell us more about your 8" driver based Unity/Synergy horn?

Specifically:
1. Beam Width (i.e. 50x50 degree, 60x60 degree)
2. 8" Drivers Used
3. Horn Dimensions

It sounds like with the work that you, Paul and Mr Bateman have done it will be possible to reproduce a lot of the characteristics found in the Danley Synergy horns. Good work.

Cheers,
Mike
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Old 11th January 2012, 03:24 PM   #427
JoshK is offline JoshK  Canada
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I do think this is probably the coolest thread on diyAudio. At least in my view. I get only a tip of the idea, but I want to play as well.
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Old 11th January 2012, 06:35 PM   #428
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Hi William,
Can you tell us more about your 8" driver based Unity/Synergy horn?
Here's a link

It's an old project (on an older webpage) that I haven't written up yet. I'll do some polars first. Similar dimensions to the SPL Runt. The 90 degree horizontal beamwidth makes it less applicable for most domestic indoor use. See the banter between Paul and myself above.

Cheers

William Cowan
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Old 11th January 2012, 08:00 PM   #429
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Here's a link

It's an old project (on an older webpage) that I haven't written up yet. I'll do some polars first. Similar dimensions to the SPL Runt. The 90 degree horizontal beamwidth makes it less applicable for most domestic indoor use. See the banter between Paul and myself above.

Cheers

William Cowan
I don't know - if you take the 'build it into the corners' route, 90 degree dispersion seems to make sense. In fact, near the top of my 'projects I hope I get to someday' list is a Unity style setup designed to be an in-wall right in the upper corners of a room - i.e. a 3-sided "90x90" arrangement. The idea being that it would take up zero floor space but offer wonderfully uniform coverage and avoid near-wall reflections entirely. Not necessarily the ultimate placement for imaging/soundstaging, but great in some difficult circumstances.
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Old 11th January 2012, 08:19 PM   #430
Flaesh is offline Flaesh  Russian Federation
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in theory i like this placement
practically i quickly (2-3 min ) experimeted with 90x40 2380a at 2+ m height and go back to "normal" height..
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