Honest opinion (peer review) about this 4Way before I build it - diyAudio
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Old 13th December 2010, 04:53 AM   #1
Yoshy is offline Yoshy  Canada
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Default Honest opinion (peer review) about this 4Way before I build it

Hello,

Before I go and buy MDF and drill in it, I'd like some honest objective/subjective criticism on this design just to make sure. Might even try glass for this; while the monster passed the WAF test it didn't exactly excel in it.

It's a 4 way with in the shape of a uniform hexagonal prism (I think that's what they're called). Attached are the plans in full details. This monster will be fully active (amps are working; yay. Crossover not so much). If I remember grade school the formula for calculating a hexagonal prism is V = 3ash. Bracing is not included in the plans but if glass is used then the less the better.

In my design, 'a' and 's' are constants at a = 231, s = 230.

Subwoofer
=====
Volume = 1.71115664 cubic feet
(There are 2 subs; this is more to balance the design)
Both subs are Scan-speak Discovery 30W/4558T low-pass at about 80Hz

Lower Woofer
=======
Volume = 1.26648106 cubic feet
Is a Hi-Vi M8a. I just happen to have one.
From 80Hz to ~850Hz

Upper Woofer
======
Volume = 0.872464733 cubic feet
Is a SEAS Excel W15CY-001.
850Hz to about 5kHz

Tweeter
=======
Volume = 0.675456567 cubic feet
5kHz to infinity, and beyond !

Many thanks in advance. Construction is not expected to start very soon as the budget is a bit tight for hobbies this time of year. If this does not turn out nice at least I'll learn from it.
Attached Images
File Type: png Full Perspective View.png (65.0 KB, 529 views)
File Type: png Full Views.png (78.1 KB, 503 views)
File Type: png Lower Woofer.png (109.3 KB, 494 views)
File Type: png Subwoofer.png (124.2 KB, 491 views)
File Type: png Tweeter.png (101.7 KB, 482 views)
File Type: png Upper Woofer.png (86.5 KB, 128 views)
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Old 13th December 2010, 05:29 AM   #2
djn is offline djn  United States
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Are those all seperate boxes? I like the looks of it. Is there president for all those drivers working together or are you going to work out the xover? Seems like it could be a very good looking speaker, but a lot of bits involved.
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Old 13th December 2010, 07:25 AM   #3
Calvin is offline Calvin  Germany
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Hi,

itll be most definitely a hellot of work.
I wonder though about the choice of drivers and crossover-freqs.
Sorry to say, but I get the impression that You think, that buying a bunch of terribly pricey drivers will do the job. No, it aint so. If ones a experienced or talented designer, one may really get the extras from out of those expensive stuff, but Im afraid in more cases this simply does not happen and the end result remains just a bunch of overprized and overhyped stuff. Well, Yes it will certainly look expensive no doubt about that, but will it sound? As with any system the role of the crossover should not be underestimated. A well designed Xover driving into mediocre drivers certainly will sound superior to a mediocre X-over driving fine drivers.
If You dont want to use digital filters Id suggest to build a dedicated analog filter (with dedicated I mean filters that they are designed like passive filters, with the special drivers characteristics in mind and not as standard cookbook filters), preferrably using discrete devices and no OP-amps. You might rethink about the Xover frequencies. Especially the mid-high transistion at 5kHz seems a bit too high for my taste. I assume that the distribution character will show a break here. Id rather opt for a bit lower frequency. Anyway this needs to be evaluated in praxis.

jauu
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Old 13th December 2010, 07:31 AM   #4
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Sounds like fun! 5 Khz for a Excel 5" magnesium might be a bit too high not only because the evil resonance peaks up in that area. Good luck!
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Old 13th December 2010, 10:07 AM   #5
keyser is offline keyser  Netherlands
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If this is your first design, start off with something simpler, maybe a 2-way.
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Old 13th December 2010, 11:08 AM   #6
keyser is offline keyser  Netherlands
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But then again, designing something big and powerful is a lot more gratifying, isn't it?

Just don't underestimate the complexity of a speaker like this. What kind of crossover are you planning to use? Digital crossovers like a Behringer DCX can make your job a lot easier, but you still have to be able to do measurements and know how to interpret them.

If I were designing the system, I'd ditch the Hi-Vi and couple the Scanspeak (drool drool) to the Seas (still drooling) directly.
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Old 13th December 2010, 01:05 PM   #7
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I see some problems here indeed. The internal shape of your boxes is almost circular - its close to the worst possible shape when regarding internal standing waves. Should be avoided! Only a sphere would be worse than this.

Also as others have noted, 5 kHz is way too high for the 5" Excel magnesium. I suggest crossing it over well below 2 kHz for optimum results, or choose a (paper) midrange better suited for a high XO point.

And then - why a 5" and then an 8"? Why not simplify a bit, and run two 5" instead? Two 5" has the same cone area and output capacity as one 8". Running the midwoofers down to 80 Hz also seems a bit too low, I suggest 150-200 Hz.

Even with XO at 150-200 Hz, a passive XO network is going to be difficult to design, so either way an active XO is recommended.
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Old 13th December 2010, 07:04 PM   #8
Yoshy is offline Yoshy  Canada
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Being at work I can't reply in deep details. For the drivers I already have them from other projects so I'd like to reuse them as the other attempts are now, let's just say full of holes.

As for crossing the Excel 5" magnesium so high, I did test it first and I can't say that it sounds bad; I'll give it another listen to night with some other music and try a movie. The XO is active and will either run on a FPGA or ARM7; having a bit of problems with the FPGA right now.

5" and then 8" is more for looks then anything else; maybe a SEAS Excel W22EX to keep the same look as with the 5". That would leave my M8a unused but the last thing I want to some other project that is not allowed in the living room without a divorce; listening to them in the workshop is nice but it's not where I'm most comfortable. And besides, I'd like to make something useful.
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Old 13th December 2010, 07:43 PM   #9
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I would be hesitant to mount drivers horizontaly as the cones do sag under gravity over time (years). I would recomend the FPGA as it should be able to impliment much higher order filters than the ARM7.
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Old 13th December 2010, 07:59 PM   #10
sreten is offline sreten  United Kingdom
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Hi,

If you want an honest opinion start from scratch again, and try and
understand what every engineering detail is trying to achieve. Active
is no shortcut whatsoever to getting it right, and usually unfortunately
an expedient that guarantees it will be wrong, its simply not that simple.

(e.g. hexagonal cabinets are a very bad idea, over e.g. six
sided but different face lengths, e.g. like the old Tannoys :

Click the image to open in full size.

Dreadful speaker placement BTW, not the intended point of the shape.

rgds, sreten.

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