Suitable midrange cone, for bandpass mid in Unity horn.

[Patrick Bateman]

Originally Posted by SunRa

I thought a lot about the unity in the last months, and a dillema keeps bugging me.

The Unity and Synergy horns have been designed to allow:
i) a single point source +
ii) an excellent power handling capabilities across the 300-18.000Hz while
iii) keeping the distortions at minimum in the 300-1000Hz, which is the most problematic for CD's to handle.

Next the design moved to hi-fi usage and I wonder if it really is the best set of compromises. My main concern with Unity, as I've pointed out earlier, is the interaction between the midrange slots/holes/ports or what do you want to call them and the 1" CD. In the light of the recent advancements in horn profile design, (LeCleach, Geddes), the terminations and discontinuities are playing a larger role than considered until now.

So what would be the alternative? How about the new coaxial drivers from BMS and B&C. Can you find any reason not to replace a unity design with those? Let's see:

+ similar system cost (one coaxial CD is about the same as 1" CD + 4 midranges and the additional headaches of mounting them).
+ lower crossover complexity than the unity
+ even better single point integration of the sources
+ no diffraction sources in the throat of the horn

CONS

- lower power handling in the 300Hz area (although is this really an issue in a home environment?)
- possible higher distortion figures in the 300Hz - 1000Hz domain. This is the greatest strength of the Unity in my opinion. Can this lack of distortion be however compensatend by the lower complexity, diffraction free design of the coaxial CD?

How would you comment the above?

I own Gedlee Summas, and I've built five Unity horns for my car. (If at first you don't succeed...)

I've posted some commentary on your question here:

Audio Psychosis • View topic - Unity VI: Crossover

The thread above will document my sixth Unity horn. Construction begins today.

[SunRa]

Thanks for reply. I'll really look-up to your new unity design, you should publish an article or something after this saga .

I guess it all comes down to experimenting. I am making all kind of theoretical models on what is better, but I really need to turn some waveguides and start experimenting...

[JLH]

Few notes about what I’ve found to work, and what doesn’t work too well in a Unity style horn.

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.

2.) The compression driver’s crossover point dictates where the mids should tap into the horn. Example -If the compression driver’s crossover is 1500Hz, then the mids need to tap into the horn where the cross-sectional area is 41.54 cm2 or LARGER. It’s 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 – any area larger than this becomes acoustically invisible to the compression driver. This is because the compression driver is cutoff at 1500Hz – 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 driver’s 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

[John Sheerin]

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.

[JLH]

Originally Posted by pk

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 let’s 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 – which is too low for it. This is one of the reasons why 1” compression drivers are used. The smaller the starting area, the easier it is to place the mid ranges at a practical location.

Rgs, JLH

[JLH]

Originally Posted by John Sheerin

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

[SunRa]

The points raised are very interesting, thanks for this info.

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.

[Patrick Bateman]

Originally Posted by JLH

Few notes about what I’ve found to work, and what doesn’t work too well in a Unity style horn.

<snip>

2.) The compression driver’s crossover point dictates where the mids should tap into the horn. Example -If the compression driver’s crossover is 1500Hz, then the mids need to tap into the horn where the cross-sectional area is 41.54 cm2 or LARGER. It’s 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 – any area larger than this becomes acoustically invisible to the compression driver. This is because the compression driver is cutoff at 1500Hz – 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 driver’s 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.

[Patrick Bateman]

Originally Posted by JLH

Few notes about what I’ve found to work, and what doesn’t 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!

[JLH]

Originally Posted by SunRa

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