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Dual 10" coupling

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Category: General
Forum Name: Advanced Discussion
Forum Description: Advanced discussion area for higher lifeforms
URL: https://forum.speakerplans.com/forum_posts.asp?TID=106498
Printed Date: 23 October 2021 at 7:33pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com


Topic: Dual 10" coupling
Posted By: Augusts
Subject: Dual 10" coupling
Date Posted: 24 August 2021 at 5:58pm
Hi!
 
A am about to make a compact project of PD 10".  As I understad the centers of cones should be as close as possibe,  I need to maximally awoyd phase issues, as I want them to be crossed at 4k

In the middle a CD, something like a line array but with 90x50 coverage

Something like this
https://www.dbaudio.com/global/en/products/series/v-series/vi10p/#tab-downloads" rel="nofollow - https://www.dbaudio.com/global/en/products/series/v-series/vi10p/#tab-downloads



Replies:
Posted By: toastyghost
Date Posted: 24 August 2021 at 8:35pm
You’d need the centre to centre spacing to be 21 millimetres to be within 1/4 lambda (0.25 milliseconds) at 4 kHz.

Perhaps you might want to rethink that choice.

The cabinet you’re comparing to crosses from the LF section to the cone midrange on the coaxial horn they’ve designed at a much, much lower frequency than that. Even that cone midrange can’t hit 4 kHz without beaming, and it uses the HF horn as a phase plug.


Posted By: Tinnitus Rex
Date Posted: 24 August 2021 at 8:44pm
 just use one 10"  or use a coax driver, problem solved. Using two drivers is only useful when you desire cancellation, like horizintal line array ellements do . If its a vertical box you would never locate the hf in  between two drivers as you create twice the problems above and below the vertical axis and practicality dictates that you need the hf as high as possible if ground stacked. Copy something good already available , These days, I  think you will be dissapointed if you to try to reinvent the wheel.


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"couldn't we just like... use headphones?"


Posted By: FOO
Date Posted: 24 August 2021 at 9:37pm
Originally posted by Tinnitus Rex Tinnitus Rex wrote:

If its a vertical box you would never locate the hf in  between two drivers as you create twice the problems above and below the vertical axis and practicality dictates that you need the hf as high as possible if ground stacked.


Eeeeh say what?

Outline Spektra
OHM TRS212 and MD-MH
DAS Audio ST215
Seeburg K20 and K24
Seeburg A2 and A3
Amate Audio X102FD and P212a

Just to name a few boxes with this allingment.
Most of them are really nice and loud sounding. OHM MD-MH is insanity!!



Posted By: Tinnitus Rex
Date Posted: 24 August 2021 at 9:50pm
Those are horn loaded.........................did I miss something


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"couldn't we just like... use headphones?"


Posted By: FOO
Date Posted: 25 August 2021 at 6:36am
Yes you did. Half of them are reflex. Outline Spektra is one of them. A real beast.


Posted By: Augusts
Date Posted: 25 August 2021 at 6:48am
Im thinking of crossing the bottom one 140-500 with passive high qual Low pass filter so 17,7cm cone to cone and the upper one just see how it does the high freq stuff, if I need to cross lower , I Have  BMS 1" 4550 :800-up to 20kHz and large faital tactrix horns..


like so. the black ones angled 10" PD and the green one the 60x50 horn.
Red line center to center


Posted By: Conanski
Date Posted: 25 August 2021 at 2:29pm
Just drop the crossover freq down to about 1khz or whatever the horn supports and experiment from there to get the best sound quality.


Posted By: Xoc1
Date Posted: 26 August 2021 at 10:29pm
MTM mid tops (with the tweeter in the middle) have a horizontally alligned dispersion characteristic which makes them useful for certain applications. I like their in your face when you stand up in front of the speakers, foccussed sound for small venue PA system.


Posted By: JonB67
Date Posted: 27 August 2021 at 1:29pm
There's some interesting discussions and info on mtm, if you google d'appolito array/arrangement/configuration you should be able to find some more thoughts on its pros and cons. 


Posted By: toastyghost
Date Posted: 27 August 2021 at 2:23pm
Originally posted by JonB67 JonB67 wrote:

There's some interesting discussions and info on mtm, if you google d'appolito array/arrangement/configuration you should be able to find some more thoughts on its pros and cons. 


D’Appolito does not apply to any old MTM configuration. It requires specific fourth order slopes to broaden the vertical coverage and maintain phase coherency. That dictates spacing and loading somewhat.

The real benefit of MTM is the vertical polar response. Especially if you’re able to design the system based on the use of all-pass or FIR filtering (based off anechoic listening window data) to adapt the off-axis response.


Posted By: JonB67
Date Posted: 27 August 2021 at 6:43pm
Im aware its a specific thing, but it was in discussions and info on the d'appolito arrangement that I found out about the pros and cons of mtm

I didn't suggest he used the d'appolito arrangement, just that googling it was a source of some info.


Posted By: John Boom
Date Posted: 28 August 2021 at 12:52pm
Your mid spacing will lead to lobes in the vertical coverage pattern. The main lobe will get smaller as you go up in frequency. The size of that lobe at your crossover freq is a limit on the vertical coverage angle of the system. So, the narrower your design vertical coverage, the higher the crossover frequency can be. Using this method you can space the drivers more than a quarter-wave.

What you have to trade against this is, can your compression driver/horn combo really go that low and not start to distort at power? Manufacturer's specs can be misleading - you often have to double the specified usable lower limit. And compression drivers have a harder time driving smaller horns. Generally, beefy comps and carefully chosen horns with the lowest possible horn cutoff freq are the way to go.



Posted By: moyano
Date Posted: 11 October 2021 at 4:47pm
I’m also interested to know exactly what happens once you’ve been forced outside of the 1/2 wave coupling distance even though the drivers are still touching / very close together ? 

What are the negative effects after this point ? 

Xx 


Posted By: Augusts
Date Posted: 11 October 2021 at 5:25pm
Phase issues and therefore distortion in the range over the point of 1/2 wavelength. Is that corrrect?


Posted By: moyano
Date Posted: 11 October 2021 at 5:27pm
I was hoping that you were the genius here ! Lol 


Posted By: fatfreddiescat
Date Posted: 11 October 2021 at 6:18pm
Here's something for you to play with:

http://www.tolvan.com/index.php?page=/xdir/xdir.php" rel="nofollow - http://www.tolvan.com/index.php?page=/xdir/xdir.php








Posted By: toastyghost
Date Posted: 12 October 2021 at 10:17am
Originally posted by moyano moyano wrote:

I’m also interested to know exactly what happens once you’ve been forced outside of the 1/2 wave coupling distance even though the drivers are still touching / very close together ? 

What are the negative effects after this point ? 

Xx 


It’s not 1/2 lambda for coupling. At 1/2 lambda you’re in full cancellation.


Posted By: moyano
Date Posted: 12 October 2021 at 11:05am
Yes, destructive interference can start at 1/2 lambda. The idea is to keep all drivers between 1/4 and 1/2 lambda. 

I was wondering what else happens between 1/2 and 1 for example. But if interference starts at 1/2 then surely nothing good can come of it. 

Xx 





Posted By: fatfreddiescat
Date Posted: 12 October 2021 at 2:10pm
One method to get a better picture of what happens is to measure the response at various degrees off axis and import it into a program such as Vituixcad. You can then add copies of the measured response, adjust spacings and angles and then scroll through the frequencies whilst viewing the 'Polars' etc graphs.


Posted By: toastyghost
Date Posted: 12 October 2021 at 2:19pm
Not quite right. Summation occurs in the ‘coupling zone’ of the 'phase wheel'. Where that can get confusing is that the cycle isn't really in a 2D plane, but along a cylinder that represents 'laps' behind or ahead of the current frame of reference to relative phase.

This a good place to start:



Posted By: Augusts
Date Posted: 12 October 2021 at 3:16pm
There is so much to learn in the field of acoustics, it gets easier if you read heavy books I guess but I learn by doing, so there are some conclusions I have came about but they also change over time as they where wrong. So I'm no genius, merely a student. But an enthusiastic one :)


Posted By: moyano
Date Posted: 14 October 2021 at 12:11pm
I’d love to know how the new nexo ID 84 works. 

I thought that multiple dome tweeters would cause issues. 







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