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Old 14th May 2011, 12:01 PM   #1
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Default Enclosure question - active 3way (passive radiator or not?)

Hi All!

it is really hard to get decent passive crossovers [around here] and I found opamps to be very easy to come by... even further... the high quality speakers I've seen around... don't feel very well made and most of the times cost very much!) so... I'm going active 3 way! its not all that more expensive, giving all the advantages of being able to control the speaker much more profoundly...

I'm handy with wood's. I've got tools and some time to spend (on things I like) plus... I'm in to electronics, I'm an electronics technician so I feel comfortable with most of the designs needed for this. I just don't know how to design an amplifier, so I'm buying ESP Elliott Sound Products - The Audio Pages (Main Index) design's

my goal is to have a self contained speaker (all needed electronics inside a back-compartment) receiving the audio (and power-on) signal from the preamp (balanced).

I'm trying to understand if I'll win something by using a passive radiator... in your opinion, will a passive radiator "cause" an interesting improvement in the speaker itself or a "simple" sealed box would do the 'same'?
since I intend to use a subwoofer, (hopefully lower than 80hz) I cant see much of a win on the passive radiator... but I haven't tested properly on any program/forum.

For some of the details I'm also thinking of having 2 compartments in the side of the woofers enclosure sand filled in order to make the speaker solid. what do you thing about that ?

one thing I'm yet to understand is the baffle step compensation... is there a way to measure/calculate/know the acoustic centers of the speaker drivers? (or is this just a very simple thing?)

is the baffle step compensation achievable by recessing the tweeter and mid (in a way similar to a horn loaded speaker) in order have a better correction?
I can make a blade to mill the wood into a horn-like recessed driver. I just need to have it calc. before

that makes my wondering about using coaxial speakers like the ones I've seen/listen in KEF speakers (and found similar selling at Europe audio) link:H1333-08/06 - Seas T18RE/XFCTV2 7 inch coaxial - Europe Audio

the cost of a (decent) coaxial driver will be more than a "good" mid and a tweeter... but if it helps to solve a problem I'll wonder about it!

Sorry for the long thread...
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Old 14th May 2011, 12:35 PM   #2
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OK, Baffle step correction is different to physical alignment.Difraction Loss / Baffle Step Compensation (BSC) Circuit Calculator

Also, whether a passive radiator is a better bet than a simple closed box, depends on which bass driver you had in mind. Generally a QTS greater than .4 = closed box, Low QTS drivers (0.2-0.3) will benefit from a passive radiator.

Mick.
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Old 14th May 2011, 01:15 PM   #3
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Quote:
Originally Posted by prickears View Post
OK, Baffle step correction is different to physical alignment.Difraction Loss / Baffle Step Compensation (BSC) Circuit Calculator

Also, whether a passive radiator is a better bet than a simple closed box, depends on which bass driver you had in mind. Generally a QTS greater than .4 = closed box, Low QTS drivers (0.2-0.3) will benefit from a passive radiator.

Mick.
Nice way to go. I'm starting to figure out some of the issues here. I already read the baffle step correction from ESP but I'll read-it again and cross-it with other articles that you just pointed out to me.

I'm yet to choose the drivers since I don't fully understand the "other" issues here. I've done "a bunch" of speakers with very cheap drivers so I know the problems physically I now want to correct them and build a "good" 3 way system with the correct values & drivers and therefor: sound

the driver I had tested had a "high" QTS so I got a misleading result... I'm going deeper in the drivers parameters to fully understand them... "the problem" is that I found "nice" priced passive radiators at Europe audio (easy for me to buy from there...) and now I'm evaluating the addiction of them.

plus all this, I'm considering making the main speakers sealed. I would only make reflex bass for surround/near-field monitors with active equalization to correct for the box size "not being perfect"

thanks Mick!
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Old 14th May 2011, 01:24 PM   #4
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UniBox - Unified Box Model for Loudspeaker Design - Kristian Ougaard

Unibox is a great tool for modelling/selecting potential drivers, you will be able to see what effects T/S parameters have on different box designs and vice-versa. Download is free, the rest is 'suck and see', but it is alot cheaper than burning wood. :-)
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Old 14th May 2011, 02:30 PM   #5
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Hi again!

I already have "all" FRD Consortium tools (including unibox) but thanks any input its worth!

I messed up! got confused between baffle step and phase/time alignment...

link:Phase, Time and Distortion in Loudspeakers

so... : is this compensation achievable by recessing the tweeter and mid (in a way similar to a horn loaded speaker) in order have a better correction?

I can make a blade to mill the wood into a horn-like recessed driver. I just need to have it calc. before.

so... any input appreciated
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Old 14th May 2011, 04:02 PM   #6
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The target is to have the sound coming from the drivers in perfect timing to your ears . this can be reached in many ways 1) by using a single driver ,preferably with limited BW 2) by using 2 or more drivers with the necessary dividing network (crossover) ... 3)by splitting the signal at line level ,preferably in the digital domain so the time costant (delay) may be managed much better than in the analogue world .
Each modality has its pros and cons . Perfect phase alignement then must be measured with sophisticated instrumentation ,after the whole work is done ,because the ear cannot discern phase ---under milliseconds---
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Old 14th May 2011, 04:18 PM   #7
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Originally Posted by picowallspeaker View Post
The target is to have the sound coming from the drivers in perfect timing to your ears . this can be reached in many ways 1) by using a single driver ,preferably with limited BW 2) by using 2 or more drivers with the necessary dividing network (crossover) ... 3)by splitting the signal at line level ,preferably in the digital domain so the time costant (delay) may be managed much better than in the analogue world .
Each modality has its pros and cons . Perfect phase alignement then must be measured with sophisticated instrumentation ,after the whole work is done ,because the ear cannot discern phase ---under milliseconds---
hi, the goal is active 3 way (tri-amp) with analogue crossovers (not "smart" digital one...)

thanks for you post
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Old 14th May 2011, 04:22 PM   #8
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and all comes to:

from this forum I already got 2 answers I needed. passive radiator will 'only' be useful with drivers with low QMS (didn't know this...) plus I was messing up with 2 different concepts: baffle step (easy to calc and fix) and time/phase alignment...

one of the "old" techniques to fix the time alignment was to recess the tweeter and mid in the baffle (in steps) but this causes to much diffraction and its worse than a slight out of phase driver.

so I'm wondering, making something like a waveguide/horn to the tweeter and mid will help to get the drivers phase (near) good ?

I've read this article Practical DIY Waveguides - Part 1 but it is not fully clear to me yet...

I rather waste much time in software's and on the box itself than in cutting it down for burning wood because it is not right...

other detail its the fact that I want the amp to be in the speaker itself. so it will have a separate compartment for this purpose.

what about the sand filed compartments ? (on the sides. maybe the back either) this technique has been used before... but "in real life" will it help much? its not that hard to make so I'm looking at it as an extra.
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Old 14th May 2011, 06:06 PM   #9
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One thing you might think on, if going active with the all the amplifying electronics in the speakers or close to them, is using true balanced interconnects.

And by "true" I mean using real balance/unbalance chips.
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Old 14th May 2011, 06:12 PM   #10
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Quote:
Originally Posted by carlmart View Post
One thing you might think on, if going active with the all the amplifying electronics in the speakers or close to them, is using true balanced interconnects.

And by "true" I mean using real balance/unbalance chips.
good thinking! I was going for balanced... but that is the least of my problems :P its actually the 'module' that would be very cheap to improve/change so... that's a pretty good Idea!

Thanks

edit:

actually... I was looking at Project 125 from ESP (http://www.sound.westhost.com/project125.htm) since its quicker to use and has, for sure, less problems to solve. this unit would enable me to have an subwoofer output (4th way) in the speakers so, If i need I can throw a party with this speakers and a sub. (its possible that I will include a compression/protection circuit... bypass-able just in case.)
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Last edited by firefart_1st; 14th May 2011 at 06:38 PM.
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