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Old 4th January 2012, 09:45 PM   #391
winslow is offline winslow  United States
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Maybe something like JohnK's Transient Perfect 2nd order crossover is used. These filters have about an octave overlap past the XO point and then uses a notch filter to sum the response flat.
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Old 4th January 2012, 10:26 PM   #392
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by GM View Post
Hmm, I thought you wanted to make a SH95 concept. Using 8" for mids would make for a long three way horn. Anyway, here's what you posted:

GM
Thank you for posting that GM. One reason I'm interested in narrow vertical directivity is that I'm tired of high Q peaks and dips in the 200-600Hz region that cover small areas in space.
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Old 5th January 2012, 01:37 AM   #393
JoshK is offline JoshK  Canada
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Originally Posted by JLH View Post
They are $8.39 each for a half case (30 pieces). So, it was a little over $250 for them. If you buy a full case (60 pieces) the price drops to $6.44 each.
I am down for 12 if anyone is in with me. I'm not like to do much with them in the near term, but I've been itching to try out a Synergy design, so I'd love to have them. I consider this peanuts in the grand scheme.

Josh
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Old 5th January 2012, 04:15 AM   #394
JLH is offline JLH  United States
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Originally Posted by AllenB View Post
@JLH, about the discrepancies between hornresp and Akabak. I used your script from three years ago as a starting point. Apart from completeness of the model, would you still consider it useable? (BTW you had mentined problems with Akabak and Mmd. I have substituted Mms as it seems to work.)
It is usable, but as you noted it was totally complete. I've expanded it to included more variables. The problem I've ran into is I exceeded the maximum number of nodes that Akabak can process. I have to simulate it in two halves now. This is a pain in the butt, however it's still better than making senseless sawdust.
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Old 5th January 2012, 04:21 AM   #395
JLH is offline JLH  United States
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Originally Posted by kessito View Post
JLH,

Could you tell me where the number of 17m/s is based on?
Is this the number where air becomes non-linear?
If you have it, could you please point me to some information about this?

thanks,
Kees
Yes, this is were it becomes non-linear. Eminence used to have a technical white paper on their website about port velocity non-linearity. If I recall correctly, the exact number they gave was 17.12 m/s. I can't seem to find it on their website. Might try Google with key words like port velocity, air non-linearity, ect.
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Old 5th January 2012, 03:00 PM   #396
Sheldon is offline Sheldon  United States
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Originally Posted by JoshK View Post
I am down for 12 if anyone is in with me. I'm not like to do much with them in the near term, but I've been itching to try out a Synergy design, so I'd love to have them. I consider this peanuts in the grand scheme.

Josh

I'd take 8 or 10 (couple of spares). But maybe wait a bit until JLH finishes his investigations.

Sheldon
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Old 5th January 2012, 08:49 PM   #397
boris81 is offline boris81  United States
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Thank you, John (Patrick Bateman) for reviving the topic of the mysterious phase accuracy of the Synergy horn. Unfortunately your suggestions on the matter raise even more questions, for me at least.

I think that the folded pyramid shape of the horn helps to acoustically align the midranges to the tweeter better than conventional MTM designs. However I feel that the biggest phase distortion will be introduced by the crossover slopes and so the mechanical and electrical offset should be discussed together.

I might be wrong but I believe the phase delay at the low end of a driver is caused by the natural frequency response roll off and not the resonance. Phase should be linear in the usable bandwidth of the driver.

Regarding Paul's measurements of the Pyle driver I wonder if it's showing the effects of sealed box vs. bandpass enclosure. I've heard that bandpass ads phase distortion but I don't know what that looks like.

I'm sorry for throwing around so many guesses and no hard evidence. It would be great to hear from the experts on this topic.
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Old 6th January 2012, 12:22 AM   #398
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Originally Posted by Patrick Bateman View Post

The 2" will be trickier. Doug Kelley
You rang? (BTW - only one 'e')

Quote:
got me started on this Unity madness when he clued me in to one of his projects, which used the Dayton 2" at the throat of a Unity horn he built. Doug ended up buying Yorkvilles and has posted a few times in this thread.

But I've always thought the 2" would be a good candidate as a *midrange*, not a tweeter.

So I bought some of those on Friday too.

To use the Dayton will require some modding, as it specs aren't quite right. (Basically I intend to reduce it's back chamber, so it's FB and Q is much higher.) But it's combination of a powerful motor and a light cone may mean that it will be a better candidate than the W2-852SH from TB, which is still one of my favorite drivers for these projects.
.
Man, this was so long ago I don't remember whether we talked about this or not. It was always my intention to try the RS52 as the mid - the experiment using it as the 'tweeter' was one of those experiments that looked WAY easier than the 'real' project, and so seemed worth trying. Worked really well aside from dropping like a rock in the top octave.

Anyway you may already have this but in this thread at htguide someone actually pulled the rear chamber off and measured the RS52 t/s specs. May not be 100% accurate, but should be close enough to start plugging in to a model. I do think there may be some construction challenges with the front chamber given how much the dome protrudes, but it should be easy enough to experiment with a flat cylindrical chamber and some modeling clay to reduce the volume. I'm guessing you won't get down much below 5-600 Hz, but getting up to 2k would be worth the trade.

HTGuide Forum - RS52 tests and tweaks

I'm still in limbo on projects - trying to decide whether we're going to try to move or not. If we do move to somewhere with more space, I'm really torn between working on the U15s and joining the seeming stampede of folks trying diy versions. Tougher decision since Jdubs is selling some spare U15 horns and mids which would make it easy to get a center and still have a spare for modding/experimenting.
OTOH, the idea of a DIY version with a Neo 3 or a ribbon and the RS52s is oddly appealing.
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Old 6th January 2012, 12:43 AM   #399
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I made an Akabak model with the Synergy horn-style ports. This is where the port is a frustrum instead of a hole. (Note the big end is on the inside.)

Click the image to open in full size.

Here's Paul Spencer's measured and simulated Unity horn. This is from his blog. I am using this as an example as we have enough pictures to figure out the dimensions. The simulation was done with hornresp.

Click the image to open in full size.
Here's an Akabak sim with a frustrum instead of a hole. I don't know if Paul's measurements used a hole or a frustrum. In the sims, I found that it doesn't make much difference until the frustrum's depth is at least 2cm or greater. This is interesting to me, as all of my Unity horns have used extraordinarily thin material. One of them even used aluminum for the mounting plate. If the sims are to be believed, there may be some advantages to using a deeper frustrum.

Click the image to open in full size.
For instance, this sim has three changes to Paul's 60x60 Unity horn:

#1 - The frustrum is nearly 4cm deep (1.5")(!)
#2 - The midranges are slightly closer to the throat. Based on my guesstimates of the area from Paul's pics, it looks like they're a little bit further away than you would want for a 1500hz xover. For instance, to get them up that high you'd want to tap in where the throat is about 40 square cm, and in Paul's pics, I'd estimate it's about 140cm^2. As noted earlier in this thread, I think this is one of the reasons the synergy horns use a narrower coverage angle than the Unity horn. As the angle of the horn walls grows, you have move the midranges closer and closer to the compression driver, and you reach a point where you can't get them close enough.

Here's the Akabak script. Note the addition of an "api" and "apo" variable, for the frustrum. "apo" is the outer area.

When you mess around with this in Akabak, you might notice a few things:
  • If the midranges are very close to the throat, you need small and shallow frustrums. Conversely, as you move further away, you need wider and deeper frustrums. If this observation is true, then moving the midranges too close to the compression driver may limit the SPL of the system. (IE, there seems to be a 'sweet' spot, not too close and not too far from the throat.)
  • I think there's a correlation between the size of the frustrums and the diameter of the throat where it taps in. IE, if the throat is relatively large the frustrums need to be large too. I'm guessing the continuity between the frustrum and the horn is important.
  • To a great extent, we are modelling a compression driver here. To *really* do this justice, we should probably break up the midranges into a 'real' compression driver model. I took a stab at doing just this, based on a PDF file named 'winderm.pdf' that's freely available.

System 'S1'

|DATA EXPORTED FROM HORNRESP - RESONANCES NOT MASKED

|COMMENT: redspade Unity horn

|================================================= ================================================== =====

|REQUIRED AKABAK SETTINGS:

|File > Preferences > Physical system constants:

|Sound velocity c = 344m/s
|Medium density rho = 1.205kg/m3

|Sum > Acoustic power:

|Frequency range = 10Hz to 20kHz
|Points = 533
|Input voltage = 2.83V rms
|Integration = 2Pi-sr
|Integration steps = 1 degree ... 1 degree
|Integration method = Cross

|================================================= ================================================== =====

Def_Const |Hornresp Input Parameter Values
{
|Length, area and volume values converted to metres, square metres and cubic metres:

S1 = 5.07e-4; |Horn segment 1 throat area (sq m)
S2 = 100.00e-4; |Horn segment 1 mouth area and horn segment 2 throat area (sq m)
S3 = 1000.00e-4; |Horn segment 2 mouth area and horn segment 3 throat area (sq m)
S4 = 2116.00e-4; |Horn segment 3 mouth area and horn segment 4 throat area (sq m)
S5 = 3716.00e-4; |Horn segment 4 mouth area (sq m)

L12 = 6.20e-2; |Horn segment 1 axial length (m)
L23 = 20.00e-2; |Horn segment 2 axial length (m)
L34 = 11.00e-2; |Horn segment 3 axial length (m)
L45 = 13.00e-2; |Horn segment 4 axial length (m)

Vrc = 1.00e-3; |Rear chamber volume (cubic m)
Lrc = 1.27e-2; |Rear chamber average length (m)

Apo = 20.35e-4; |Throat chamber port cross-sectional area - outside(sq m)
Api = 160.00e-4; |Throat chamber port cross-sectional area - inside (sq m)
Lpt = 3.81e-2; |Throat chamber port tube length (m)

Vtc = 180.00e-6; |Throat chamber volume (cubic m)
Atc = 296.00e-4; |Throat chamber cross-sectional area (sq m)

|Parameter Conversions:

Sd = 296.00e-4; |Total diaphragm area for 2 series x 2 parallel drivers (sq m)

Arc = Vrc / Lrc;

Ltc = Vtc / Atc;
}
|================================================= ================================================== =====

|Network node numbers for this offset driver horn system:

| 0-Voltage-1
| |
|4-Chamber-5-Driver-6-Chamber-7-Port-
| |
| 8-Segment-9-Segment-10-Segment-11-Segment-12-Radiator

|================================================= ================================================== =====

Def_Driver 'Driver'

Sd=74.00cm2
Bl=3.60Tm
Cms=8.96E-04m/N
Rms=0.20Ns/m
fs=107.9395Hz |Mmd = 2.06g not recognised by AkAbak, fs calculated and used instead
Le=1.00mH
Re=6.70ohm
ExpoLe=1

System 'System'

Driver Def='Driver''Driver 11'
Node=1=13=5=6
Driver Def='Driver''Driver 12'
Node=13=0=5=6
Driver Def='Driver''Driver 21'
Node=1=23=5=6
Driver Def='Driver''Driver 22'
Node=23=0=5=6

Duct 'Rear chamber'
Node=4=5
SD={Arc}
Len={Lrc}
Visc=0

Duct 'Throat chamber'
Node=6=7
SD={Atc}
Len={Ltc}
Visc=0

Waveguide 'Throat adaptor'
Node=9=7
STh={Apo}
SMo={Api}
Len={Lpt}
Conical

Waveguide 'Horn segment 1'
Node=8=9
STh={S1}
SMo={S2}
Len={L12}
Conical

Waveguide 'Horn segment 2'
Node=9=10
STh={S2}
SMo={S3}
Len={L23}
Conical

Waveguide 'Horn segment 3'
Node=10=11
STh={S3}
SMo={S4}
Len={L34}
Conical

Waveguide 'Horn segment 4'
Node=11=12
STh={S4}
SMo={S5}
Len={L45}
Conical

Radiator 'Horn mouth'
Node=12
SD={S5}

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Old 7th January 2012, 11:55 AM   #400
JLH is offline JLH  United States
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Quote:
Originally Posted by Patrick Bateman View Post
As noted earlier in this thread, I think this is one of the reasons the synergy horns use a narrower coverage angle than the Unity horn. As the angle of the horn walls grows, you have move the midranges closer and closer to the compression driver, and you reach a point where you can't get them close enough.

I think you got that backwards. The local area of expansion (i.e. the flare rate) of a conical horn is higher near the throat. As you move closer to the mouth, the flare rate lowers. If you move the midranges close to the throat, then you'll never get them to play low enough in frequency to meet up with the woofers. It is more like a three way tug-of-war with the factors being:

1.)Cross sectional area the midranges tap into
2.)Distance from the throat the midranges tap into
3.)The local area of expansion the midranges tap into

If the cross sectional area the midranges tap into is has a circumference equal to, or less than the lowest frequency played by the compression driver the ports will cause interference and frequency response abnormally.

If the distance from the throat that the midranges tap into is too far away you get a half wave cancellation notch before the midrange's high frequency output can meet up with the compression driver's lowest frequency output.

If the local area of expansion (i.e. flare rate) is too high, then you will never get the midranges to play low enough in frequency. The flare rate controls where the midranges will cutoff in the low end.
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