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Multi-Way Conventional loudspeakers with crossovers

Problems with Scanspeak Illuminator 12MU/8731
Problems with Scanspeak Illuminator 12MU/8731
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Old 15th September 2015, 09:59 PM   #11
ScottG is offline ScottG  United States
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Most spider designs are similar - it's almost certainly not the spider (at least when compared to almost any other driver).

What it might be however is a reflection off of the spider's support ring (driver frame) - which is a bit large. Consider applying a lossy ring of felt on it and see if that makes a difference.
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Old 16th September 2015, 12:02 AM   #12
5th element is offline 5th element  United Kingdom
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I would be very surprised if it was cabinet related or reflections from the driver's own basket. It's far more likely to bee the xover.

Designing active is no more trivial than designing passive. Both require good measurements for the end result to be excellent. And no textbook filters are going to give you good results.

A 3dB rise around the 1kHz mark can make things sound very forwards and fatiguing and is most certainly not something you should ignore. It would make my ears bleed.
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Old 16th September 2015, 11:11 AM   #13
rabbitz is offline rabbitz  Australia
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5th element makes a good point on the crossover and can make or break a speaker no matter how good the drivers are.

One thing you haven't mentioned is your mid enclosure size and shape etc as this is one of the hardest thing to get right in 3-way speaker box design. Usually builders end up with 1-2 litres for a single driver which creates terrible backwave issues. I tend to go way oversize on the mid enclosure with a Qtc <0.5 if sealed. An angled back wall as well as non parallel sides and felt wall lining helps. Since the mid is supposed to be operating well above it's piston range, oversize enclosures are not detrimental to the driver's performance (unless it's operating too low if the crossover point has been chosen poorly).

I remember working with Andy G on a mid issue (P13 which is one of the smoothest around) on one of his speakers and it turned out to be a backwave issue and when the back of the mid enclosure was removed, the issue was rectified. The driver ended up being used in a TL type arrangement instead of sealed.

You could check by operating the mid driver in an OB situation in a baffle about 450 x 728 and have damping material over the rear of the driver to provide some acoustic loading as well as reduce the rear energy. Run this with the crossover so it's operating in it's expected range and any breakup or lower end loading is reduced. Running full range without the filter will give an incorrect impression.

For mid box designs, Troels Gravesen has some good ones on his site.

Some drivers can be helped with a coating on the cone but I would not suggest that on the expensive driver you are using. I use the 18W8531G00 as a mid in one of my designs and prefer it coated with 1 coat of Visaton LTS50.
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Old 16th September 2015, 12:39 PM   #14
Mercury3 is offline Mercury3  United States
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Thanks again to everyone. I'll check into these additional suggestions when I get couple of days off work again. I got my work cut out for me but it sounds like I may eventually get to the bottom of this. Just take more tenacity on my part.

The midrange box is over sized at about 1.8 cubic feet. I noted earlier that I started out with the smallest Parts Express Cherry Curved box with only the 7 inch width front baffle. 7" by 11". I had this issue in that box which is why I went with the larger box initially thinking that was my problem. So basically I went from an undersized box to an over sized with no change in the issue I'm encountering. Regardless if it's the issue or not it does seem a good idea if I can make some modifications inside to eliminate parallel walls, line with felt etc. Currently it is rectangle shape so I need to work on that.

Again I appreciate all the feed back and will be looking into each of these suggestions as well as double checking some of my previous testing too.

Last edited by Mercury3; 16th September 2015 at 01:02 PM.
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Old 16th September 2015, 07:45 PM   #15
Mercury3 is offline Mercury3  United States
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This is probably a dumb question but something I've been thinking on. Would it make any difference at all if I tried wiring the drivers in Series (with required Zobal for series) for 16 ohm rather than in parallel at 4 ohm? I'm using a very expensive tube amp that does have 16 ohm taps. Is there anything detrimental to running two drivers in series vs parallel? If not it's another easy experiment I can try.

Another thing is looking at my boxes they are rectangle. I don't "think" it's a box issue but if I determine it is I'm not opposed to building new boxes again to get it right. I'm not a very handy wood worker which is why I kept it simple. I'm going to try adding some type of angled baffling in the midrange chamber to possible break up any nodes and also line the whole thing with felt too. I sort of don't feel this is the issue though because it's an identical anomaly I had in the very small Dayton Parts Express boxes 7.5" by 12". If it was box related I would think the anomaly would have changed in frequency somewhat with the vastly larger box size but it sounds exactly the same.

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Old 16th September 2015, 11:56 PM   #16
rabbitz is offline rabbitz  Australia
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If the mid enclosure is 50 litres, then that's not the problem. A bit of felt lining could help with some reflections.

It seems to be coming back to a crossover issue. I'd leave them in parallel if the amp can handle it

You could try testing with a SS amp to see if it's different.
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Old 19th September 2015, 03:14 AM   #17
Mercury3 is offline Mercury3  United States
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Adding impedance curve (X-over frequencies: 290hz & 2500hz @ 24db)
Left Channel Sweep
Right Channel Sweep
Mono Sweep
Does anyone know why the Mono curve looks kind of mess up? (last one)
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File Type: png Capture.PNG (154.7 KB, 302 views)
File Type: jpg leftchannel.jpg (98.7 KB, 291 views)
File Type: jpg rightchannel.jpg (98.7 KB, 291 views)
File Type: jpg monosine.jpg (99.0 KB, 241 views)

Last edited by Mercury3; 19th September 2015 at 03:21 AM.
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Old 19th September 2015, 03:57 AM   #18
eriksquires is offline eriksquires  United States
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I wonder if this could be a weird ringing in the active filters themselves. Try listening to the outputs of your crossovers with a pair of headphones or another speaker altogether to eliminate that as the problem.
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Old 19th September 2015, 04:46 AM   #19
Mercury3 is offline Mercury3  United States
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Quote:
Originally Posted by eriksquires View Post
I wonder if this could be a weird ringing in the active filters themselves. Try listening to the outputs of your crossovers with a pair of headphones or another speaker altogether to eliminate that as the problem.
I don't think so. All the electronics is exactly the same used in my prior tri-amp setup in which I had a Focal 5k4411 & an Eton dome tweeter. (same 12 inch woofers) No hint of any issues in that setup.

I'm pretty sure I got bad drivers. Something is resonating/ringing it isn't a response peak I'm hearing. It's less detectable with 2 midranges and I can see how it could almost go unnoticed or chalked up as slight driver coloration. The fact I'm using four magnifies the issue.

The above curve is bad at the midrange/tweeter crossover but it doesn't matter because it does it only driving the midrange with or without crossover full range. (I tried it again today)

Earlier today when I had the drivers out and taped the terminals with a nine volt battery (phase check) I notice they ring. They ring to nine volt battery. I'm like what the hell.

I've tried 6, 12, 18 & 24 db crossovers at low or med Q's between 1800, 2200, 2500 & 2900 with zero difference in the anomaly. No crossovers full range they still do it.\

Also yesterday I lined the midrange section of the cabinet thick with sheepskin wool and installed some sloped baffles to help break up and internal nodes. No change either.

I'm about to throw in the towel. I've already found about four other driver choices within only a few mm size wise which will fit in my current cutouts. I'm willing to put money on my problem being gone with new drivers.

I'll play with it a little longer but I'm about to order four new drivers from another manufacture. I'm looking at these choices:

Tang Band W4-1879
Morel EM 428
Fostex FE108EZ
SEAS Prestige MCA12RC

Last edited by Mercury3; 19th September 2015 at 04:52 AM.
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Old 19th September 2015, 07:29 AM   #20
rabbitz is offline rabbitz  Australia
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I thought that 1.5V max batteries were normally used for phase check (it was decades ago).

Drivers don't like DC voltages as witnessed when amp rails voltages come through from an amp failure.

Since you are running active, just try a DC blocking capacitor about 100uF in series to the +ve terminal of the mid driver just in case some DC is coming through from the electronics.

I can understand you wanting to throw in the towel as it's very frustrating. Try returning the drivers as they are too expensive.

You could have a look around for other designs using these mids and even talk to the designers for some opinions.
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