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Multi-Way Conventional loudspeakers with crossovers

Suitable midrange cone, for bandpass mid in Unity horn.
Suitable midrange cone, for bandpass mid in Unity horn.
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Old 19th December 2010, 03:18 PM   #141
JLH is offline JLH  United States
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Few notes about what Iíve found to work, and what doesnít work too well in a Unity style horn.

1.) You can greatly reduce the effects of the mid range entry ports on the compression driverís frequency response by making careful engineering choices. When Iím designing the crossover points between the mids and compression driver, I leave them very flexible. What you should shoot for is a situation where the following is true : The expansion rate (flare frequency) that the compression driver ďseesĒ must be lower in frequency than the actual crossover frequency. i.e. Ė If the flare rate is 900Hz, then your crossover frequency must be above 900Hz.

2.) The compression driverís crossover point dictates where the mids should tap into the horn. Example -If the compression driverís crossover is 1500Hz, then the mids need to tap into the horn where the cross-sectional area is 41.54 cm2 or LARGER. Itís not about just trying to get the mids as close to the compression driver as possible. Because the compression driver is low passed at 1500Hz, the cross-sectional area where the circumference is equal to 1 wave length Ė any area larger than this becomes acoustically invisible to the compression driver. This is because the compression driver is cutoff at 1500Hz Ė thus its output cannot create acoustical pressure against the horn walls when the cross-sectional area is larger than 41.54 cm2. This pretty much removes the effects of the mid entry ports on the compression driverís frequency response.

3.) The nice thing about Akabak is you can look at the air velocity of the mid ports while adjusting the applied power. I keep the air velocity below 17 meters/sec for good sound quality. Big mid ranges with small entry ports is generally not a good idea. You can run into air non-linearity with surprisingly low powers. If you want to go small on the mid entry ports, then use small mid ranges.

4.) You must juggle the angle of your horn (flare rates) with the crossover frequencies, mid range entry port location, and mid entry port size. I work all four at the same time. It is very difficult to just pick one and then make all the rest fit into your design.

Rgs, JLH
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Old 19th December 2010, 03:26 PM   #142
John Sheerin is offline John Sheerin  United States
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On air velocity, this also directly relates to the LF crossover point of the mids. If you run big mids but don't run them low or loud, then you don't need big holes because the volume velocity through the holes is low. If you run small mids low and loud, well, it's probably not a good idea to begin with because the drivers will have to move farther and produce more distortion, but the holes will still have to be larger to get the same volume velocity and limit distortion from turbulence due to the air velocity in the holes.
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Old 19th December 2010, 03:34 PM   #143
JLH is offline JLH  United States
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Quote:
Originally Posted by pk View Post
Hi,

I can't help wondering: Why not use the Beyma TPL-150 as tweeter in an all-out unity speaker?

Best regards
Peter
The opening is about 2.6cm X 12.65cm. So, our starting area is almost 33cm2. Since it is impossible to place the mid range entry ports right at the opening of the TPL-150 letís say we can get within 5cm. With a 60 degree conical horn the area would have expanded to 118 cm2. This means the crossover for the TPL-150 would have to be 890Hz or lower Ė which is too low for it. This is one of the reasons why 1Ē compression drivers are used. The smaller the starting area, the easier it is to place the mid ranges at a practical location.

Rgs, JLH
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Old 19th December 2010, 03:35 PM   #144
JLH is offline JLH  United States
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Quote:
Originally Posted by John Sheerin View Post
On air velocity, this also directly relates to the LF crossover point of the mids. If you run big mids but don't run them low or loud, then you don't need big holes because the volume velocity through the holes is low. If you run small mids low and loud, well, it's probably not a good idea to begin with because the drivers will have to move farther and produce more distortion, but the holes will still have to be larger to get the same volume velocity and limit distortion from turbulence due to the air velocity in the holes.
Yes, exactly. Its always a balancing act. You spelled out some points that I keep in my head, but just failed to mention.

Rgs, JLH
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Old 19th December 2010, 03:45 PM   #145
SunRa is offline SunRa  Romania
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The points raised are very interesting, thanks for this info.

Quote:
1.) You can greatly reduce the effects of the mid range entry ports on the compression driver’s frequency response by making careful engineering choices. When I’m designing the crossover points between the mids and compression driver, I leave them very flexible. What you should shoot for is a situation where the following is true : The expansion rate (flare frequency) that the compression driver “sees” must be lower in frequency than the actual crossover frequency. i.e. – If the flare rate is 900Hz, then your crossover frequency must be above 900Hz.
I would have a question, I am not sure what "flare frequency" means. Is it referring to the frequency at which the horn loads the CD? For example a 15" oblate spheroid waveguide (or conical horn probably) will have a knee frequency of about 700Hz. The advice would be then to make sure the crossover frequency is above that point? I am not sure I got it.
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Old 19th December 2010, 06:58 PM   #146
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by JLH View Post
Few notes about what Iíve found to work, and what doesnít work too well in a Unity style horn.

<snip>

2.) The compression driverís crossover point dictates where the mids should tap into the horn. Example -If the compression driverís crossover is 1500Hz, then the mids need to tap into the horn where the cross-sectional area is 41.54 cm2 or LARGER. Itís not about just trying to get the mids as close to the compression driver as possible. Because the compression driver is low passed at 1500Hz, the cross-sectional area where the circumference is equal to 1 wave length Ė any area larger than this becomes acoustically invisible to the compression driver. This is because the compression driver is cutoff at 1500Hz Ė thus its output cannot create acoustical pressure against the horn walls when the cross-sectional area is larger than 41.54 cm2. This pretty much removes the effects of the mid entry ports on the compression driverís frequency response.
I wonder if this is why the original Unity horn was sixty degrees, but the first synergy horn was fifty degrees? In other words, a horn with a narrower angle would allow one to locate the midrange holes further from the throat.
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Old 19th December 2010, 07:02 PM   #147
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by JLH View Post
Few notes about what Iíve found to work, and what doesnít work too well in a Unity style horn.
Also - I've built five Unity horns now, John's built at least three, and Cowan has built at least two. It's time for you to make some sawdust!
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Old 20th December 2010, 02:07 AM   #148
JLH is offline JLH  United States
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Quote:
Originally Posted by SunRa View Post
The points raised are very interesting, thanks for this info.



I would have a question, I am not sure what "flare frequency" means. Is it referring to the frequency at which the horn loads the CD? For example a 15" oblate spheroid waveguide (or conical horn probably) will have a knee frequency of about 700Hz. The advice would be then to make sure the crossover frequency is above that point? I am not sure I got it.
Start by reading Tom Danley's white paper on tapped horns.

http://www.danleysoundlabs.com/pdf/danley_tapped.pdf

On page 4, it explains why conical horns have a variable flare rate. At the throat the flare rate is high, as you move to the mouth the flare rate lowers. The local expansion rate determines the flare rate. To find the local flare rate you can use Horn Response. Input the values for your conical horn and then change the horn type from Conical to Exponential and Horn Response will calculate the flare rate for you. What the compression driver "sees" is the throat and the distance required to double in area.

Read the Synergy Horn patent to get a better understanding of what I'm talking about.

http://www.goodsoundclub.com/PDF/Synergy_Patent.pdf

I'm not Tom, but if I were a betting man, I'd say Yes to Patrick's assumption as to why the Unity was 60 degrees and the Synergy horns tend to run more narrow angles.

I've made enough sawdust. You just need to use a bigger stick to get it out of me.

Before I release my verison, I want to make sure everything is available and people can build their own. No sense in designing an off the wall one of a kind that will never see the light of day. That really doesn't help anyone here.

Rgs, JLH
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Old 20th December 2010, 03:58 AM   #149
dwk123 is offline dwk123
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Thought I'd throw out an interest check.......

I think I'm getting close to admitting that my Yorkville U15s are unlikely to make it back into a functioning system as long as we're in our current house. I had them sounding spectacular with a PC based system, but then the PC died and I lost the EQ filters, and the room they were in got overrun with other requirements. I haven't played them in ~2 years, and it's not looking like I'll get back to it in the foreseeable future.

I know most here are diyers, but is anyone interested in either the U15's or else just the Unity horn assembly and xover? I have a number that I think I'd have to get for the full speakers if I sold them, but since I'm not sure of the market value of the 18Sound 15's I'm not entirely sure what I'd need to get for the horn assembly by itself.

I'm not committed to selling at this point, but if the price is right they'd be better put to use by someone rather than sitting collecting dust.
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Old 20th December 2010, 07:19 AM   #150
pk is offline pk  Denmark
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Quote:
Originally Posted by JLH View Post
The opening is about 2.6cm X 12.65cm. So, our starting area is almost 33cm2. Since it is impossible to place the mid range entry ports right at the opening of the TPL-150 letís say we can get within 5cm. With a 60 degree conical horn the area would have expanded to 118 cm2. This means the crossover for the TPL-150 would have to be 890Hz or lower Ė which is too low for it. This is one of the reasons why 1Ē compression drivers are used. The smaller the starting area, the easier it is to place the mid ranges at a practical location.

Rgs, JLH
Hi JLH,

Thanks a lot for the explanation!

Best regards
Peter
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