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Old 6th February 2012, 07:41 PM   #481
soho54 is offline soho54  United States
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Quote:
Originally Posted by MSeddon View Post
Hi,
A couple of questions for any Synergy Akabak guru's out there:
1. I have noticed in many of the Synergy scripts out there that people have added a small rear chamber to the script to cater for the closed back drivers. e.g.:
Code:
Enclosure 'Mid Rear Chamber A' Node=60 Vb=1.8L Lb=5cm
I am wondering if these should be included in the scripts given that the drivers' T/S parameters have already been measured with the effects of the rear chamber present.

Do you think this needs to be in the script? I assume not.
It is a place holder. Mainly, for the use of open back drivers.
With a factory closed back driver you can remove it, or make it infinity large.

Quote:
Originally Posted by MSeddon View Post
2. Regarding the wiring of multiple drivers (parallel/series). In HornResp this is easy as you can specify the number of Parallel and Series drivers (for example the wiring of the 4 midrange is 2 groups connected in parallel both containing two drivers in series).

How do you do this in Akabak as it is important to be able to determine power handling?

Thanks,
Mike
In Akabak you do this by adding the correct number of drivers into the script, and then connecting their nodes together into whatever configuration you need.
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Old 6th February 2012, 07:43 PM   #482
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Quote:
Originally Posted by MSeddon View Post
Hi,
A couple of questions for any Synergy Akabak guru's out there:
1. I have noticed in many of the Synergy scripts out there that people have added a small rear chamber to the script to cater for the closed back drivers. e.g.:
Code:
Enclosure 'Mid Rear Chamber A' Node=60 Vb=1.8L Lb=5cm
I am wondering if these should be included in the scripts given that the drivers' T/S parameters have already been measured with the effects of the rear chamber present.

Do you think this needs to be in the script? I assume not.

2. Regarding the wiring of multiple drivers (parallel/series). In HornResp this is easy as you can specify the number of Parallel and Series drivers (for example the wiring of the 4 midrange is 2 groups connected in parallel both containing two drivers in series).

How do you do this in Akabak as it is important to be able to determine power handling?

Thanks,
Mike
The easiest way for me to figure out how to do series-parallel in Akabak was by doing a series-parallel wiring scheme in hornresp, then exporting it to Akabak
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Old 6th February 2012, 08:17 PM   #483
JLH is offline JLH  United States
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If you have the T/S parameters to a closed back driver, then you should NOT include a back chamber.

To wire drivers in series/parallel you just use node numbers arranged in series/parallel. In the below example the "+" terminal is node number 2 and the "-" terminal is 0. Mid drivers 2 and 3 are put in series by node number 48. Mid drivers 4 and 5 are put into series by node 49. The whole thing is in parallel because of applying drive voltage between nodes 2 and 0.

Driver 'D2' Def='MidDriver' Node=2=48=100=120
Driver 'D3' Def='MidDriver' Node=48=0=101=121
Driver 'D4' Def='MidDriver' Node=2=49=102=122
Driver 'D5' Def='MidDriver' Node=49=0=103=123
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File Type: jpg Akabak mids.JPG (22.6 KB, 439 views)
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Old 7th February 2012, 06:42 AM   #484
MSeddon is offline MSeddon  Australia
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Thanks all Akabak gurus.

Once again with Akabak, once you see an example it makes perfect sense but to think through it is a lot trickier. It would be nice if you could name the nodes more intuitive names (like PositiveTerminal instead of just 0)

I am glad that the rear chamber is not needed as this means that I am actually learning something.

I have simulated my 60x60 horn again with the Celestion TF0410MR 4" closed back midrange drivers that Paul Spencer is organising a group buy for. You can see that the -3db point is just under 300Hz which is backed up by Paul's measurements. This has been modelled for maximum output at 120db which is basically just my target for dynamic range and to keep distortion extremely low. This does come at the expense of HF linearity due to larger input ports.

To achieve 120db I have had to use 2x 2cm ports per driver which achieves just over 17m/s port velocity. You can also see that the drivers are only moving a maximum of 0.6mm which should result in very low distortion at realistic levels. To achieve 120db in a 2 Parallel x 2 Series driver configuration only 54W is needed. Who is going to listen at 120db anyway?

Interestingly you can see the same 'twin peak' predicted response that keto has measured on the previous page of this thread. I guess that DSP is the DIY easy solution to the problem.

Thanks for your help everyone.

Cheers,
Mike
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Old 7th February 2012, 07:38 AM   #485
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Mike,

In my room I listen at about 3m away and SPL doesn't drop a great deal from 1m. I estimate at around 5db. So I need about 110 db @1m to reach THX reference. Anything more is headroom, nice to have. So with a Synergy horn you can easily have 10 db headroom, or only slightly less in a bigger room. With S2 each driver only requires 0.1w to reach THX levels.
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Old 7th February 2012, 10:26 AM   #486
JLH is offline JLH  United States
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Mike,

I noticed that you are using Node 1 to drive your speakers. Do understand that Node 1 in Akabak is a perfect voltage source that has zero source impedance. It would be to your advantage to include your amplifier's output impedance, and any associated speaker wire resistances in your model. Without this, the low end response of each driver type (i.e. comp driver / mid / woofer) will model as being much more damped than it really is. Once you account for this series resistance you'll see the bottom end is a bit under damped. I've always been in favor of modeling things as close as real life as I can get them.

You'll need to define the output impedance by placing the below Rg term between your midrange entry port definitions and the S areas and L lengths that define the expansion of your horn. This should be near the top of your Akabak code. The value for Rg should be whatever you output impedance plus wiring resistance. For a tube amp this would be closer to 2 ohms.

Rg=0.35; |Amplifier output impedance (ohms)




You'll also need to place the below Resistor terms just before the waveguide "wg1" construct orders near the end of your Akabak code.

Resistor 'Amplifier Rg' |Amplifier output impedance
Node=1=2
R={Rg}
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Old 7th February 2012, 01:04 PM   #487
keto is offline keto  Mexico
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Mike,

"Interestingly you can see the same 'twin peak' predicted response that keto has measured on the previous page of this thread. I guess that DSP is the DIY easy solution to the problem."

Click the image to open in full size.

The twin peaks are less at a distance (5 meters). I'm still very new at measuring, but I've been going for the magnitude graphs that correspond to the lowest harmonic distortion. Yesterday I measured outdoors but didn't realize that the little 2W amp was distorting until I'd brought all the gear inside, so all my plots are still in-room. Also, the measurements are made with the 2-ohm load (of 4 paralleled mids) on the amp's 4-ohm tap, which may be increasing the LF hump.

I don't have a good measurement of it here, but by placing a 1st-order line-level HP @ 300hz, that lower hump pretty much disappears. I'm going for minimal filtering (done inside each pass-band's tube amp, or at line level before the amp, or at the speaker-level) and no DSP.

I find all the Akabak info you guys are talking about really interesting. I've got to figure out how to run that on my MacBook.

Is it still possible to get in on the Celestion group buy? If so, I'd take a dozen.

Thanks.

--keto
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Old 8th February 2012, 06:18 AM   #488
MSeddon is offline MSeddon  Australia
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Hi everyone,
Thanks for your suggestion JLH I have incorporated that into the Synergy scripts.

The next problem that arises is the lack of T/S parameters on the BMS compression drivers' data sheets. The Synergy script has measurements for the BMS 4552ND compression driver but I have not been able to find anything for the BMS 4555. If anyone has these details (hopefully measured) are they able to post them?

For fun I had a play in LspCAD using the Behringer 2496 digital crossover filters. I have attached an image showing the output. These are only the simulated Akabak power response values and don't have any measurements so are just a theoretical approach to a Synergy horn. The transfer functions are at 300Hz and 1000Hz at 48db/octave. Potentially you could push the midrange a little bit higher (~1100-1200Hz) to help the compression driver but this is just measurement required speculation.

Cheers,
Mike
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File Type: png Synergy.png (36.4 KB, 394 views)
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Old 9th February 2012, 12:29 AM   #489
jdubs is offline jdubs  United States
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Guys, has anyone directly compared the Misco JC5RTF-B (supplied with the original Unity) with the Pyle PDMR5 for sound quality?

The Pyle is really cheap, but just wondering if you're "paying for it" with lesser sound quality.

Thanks,
Jim
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Old 9th February 2012, 03:02 AM   #490
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Jim I've heard both, admittedly at different times in different horns. The original Unity kit about 3 or 4 times and my simplified version of it (S1) with the Pyle driver. The Pyle drivers are obviously cheap when you see them, but in my less than ideal comparison I didn't notice a sonic penalty in using them.
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