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Old 17th February 2013, 03:14 AM   #11
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Haha, you are right. I am glad I made them. I had a lot of fun building/designing them, and yes I did learn a thing or two. Just too bad they didn't turn out as good as I had hoped. Lesson learned though. Next time I will do more homework.

I may try wiring up the configuration with the 5 passive radiators tomorrow and see how it sounds. I doubt it will work any miracles, but hey its worth a try, and pretty easy to do. Thanks for the suggestion.

Wow those plots are pretty cool, and look like they paint the picture as to why the sound is so "off" sounding. The combing effect is very profound, and I would agree based on my listening tests that I have done. Especially the plot of the vertical off axis response. This explains why it sounds decent when when at that one perfect position, but as soon as you stand up or move slightly the sound changes so much. Very cool. What software did you use to model that? I might need to invest in a copy. It looks pretty neat.

Thanks for the replies,

Charlie
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Old 17th February 2013, 11:44 AM   #12
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A wideband driver based array can work, but it needs to be very carefully implemented (including driver selection), and typically run with Eq since at higher frequencies the individual sources do not sum, the interference pattern / lobing / comb effect depending on the phase angles in question. For practical purposes, a basic ROT is that the top end output will have a similar SPL to that of a single example of the drive unit employed. The top end is never likely to match a good array of tweeters, but it should be adequate. Since your box is vented, active Eq is basically mandatory; passive is out. Other than that, the apparent comb effect seen in measurements / calcuations, providing it's not too severe (anything above 4in drivers is pushing your luck) is usually not much of an issue if at all, since the precedence effect kicks in.

The polar response of an array in the fresnel zone is largely cylindrical (bit of a fudge but it suffices) so as soon as you move vertically off-axis, the HF will fall off a cliff. That's why it's preferable for an array to be physically long, usually from floor to ceiling, or at least taller than the listener to ensure a reasonably uniform response if you're going to be moving about rather than remaining in roughly the same location / height.

As noted, the drivers in the boxes shown are spaced much too far apart (they need to be packed as tightly together as possible) which is one of the causes of the problems you mention in the mids & HF, particularly off-axis. This also depends on the off-axis response of the drive units employed; the 881 isn't too bad on this front, but it does drop off somewhat at the top end; using them in an array isn't going to improve this, and having them spaced that far apart will exacerbate the problem. You might be able to reduce this a little with some power-tapering, but it's not likely to help all that much with this particular box / configuration.

Jim Griffin & Tom Danley might have some more suggestions if they're around.

Last edited by Scottmoose; 17th February 2013 at 12:01 PM.
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Old 17th February 2013, 12:57 PM   #13
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Instead of bailing out of this project, I'd take a shot at removing the middle driver and replacing it with a 1 inch dome crossed around 4khz 2nd order. I've heard a few focused DIY arrays and they sound pretty darn good.
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Old 17th February 2013, 01:11 PM   #14
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Dissi,
Those are nice simulations. What software is this?
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Old 17th February 2013, 01:18 PM   #15
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OK. my 2 cents worth.

It would have been better to build the box with the drivers on the wide side. Dunno why everyone insists on thin narrow boxes, that creates more problems than you can throw a stick at. (silly idiomatic American expression)

To "fix" this box, move the port to the side or rear. Router out or saw cut out the old front baffle (oh, hey consider moving to the wide side! - ur response will be better in the mids and flatter), assuming you want the thin side out, and make a new front baffle with more drivers, go floor up, as little gap on the bottom as possible.

Floor bounce
cause a big NULL based on the height of the lowest driver and the distance to the floor and the reflection back vs. the ear position. Add drivers down to the floor - no floor bounce in the lower mids... it also does the array lengthening effect due to the reflection...

Now, depending on the drivers and the effect of the distance between centers you may need to A) do frequency tapering or B) put a center tweeter in.

(another idea is to add a 10-12- 15" woofer on the side and partition off the "full range drivers" inside the enclosure so that they are now mid/high drivers, eliminating the floor bounce problem that way. Move the array that you have so the drivers are as close as possible to each other. This would require a bafflectomy as well. Put the woofer as close to the floor as you can... it can be sealed or ported...)

Inside the box, with a port, you do NOT want "stuffing". What you need is absorption on the walls. What to use for that? The ideal material is wool felt. Synthetic felt is not as good but how it is deployed and what frequencies you want it to work at (thickness counts) will alter the performance. Keep in mind the absorptive material will change the volume of the box, and alter the tuning a bit. Foam is not very good usually.

Did you pick the volume of the box based on T/S parameter and a simulation? Or is this a guess? It needs to be based on a simulation, otherwise the result is random.

Can you post the mfrs response curves and T/S curves?

ARE YOU SURE YOU HAVE WIRED YOUR DRIVERs IN PHASE?
How do you know?

Fwiw, if you keep the drivers spaced where they are, you can roll them off lower, and put a high quality tweeter into the mix. Base the rolloff point on the frequency where the effect of the distance between drivers starts to become an issue with comb filtering.

A measurement or two using any random mic and some FFT freeware would tell you some useful information about what the speaker are doing. The Panasonic WM mic is a few bucks and flat enough out of the box for this sort of general investigation. Calibrated mics are not really needed for most things.

No matter what, any array is no better than one speaker alone. So have you listened to ONE speaker in a box alone to see how it sounds?? If it sounds essentially the same, then you know that this just isn't a good speaker to start with.
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Last edited by bear; 17th February 2013 at 01:24 PM.
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Old 17th February 2013, 01:44 PM   #16
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Follow up:

A quick look at Parts Express' site says VAS= 0.0670979cuft. Qts = 0.8 from the mfr and 0.58 by a Parts Express test. Fs is >100Hz.

Bottom line is that this driver does not appear to be particularly suitable for a ported design, wants a vanishingly small box volume, and looks like a candidate for a sealed enclosure. With stuffing for absorption of rear mid and HF energy...

It will run from above 100Hz up in an enclosure. You need a woofer, imo.

However it is very flat - good.
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File Type: pdf 299-113-factory-buyouts-w3-881si-specifications.pdf (20.0 KB, 22 views)
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Last edited by bear; 17th February 2013 at 02:05 PM.
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Old 17th February 2013, 02:30 PM   #17
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Thanks again for all the input. I really like the idea of replacing the center driver with a tweeter and crossing it over at the frequency where the comb effect starts kicking in. I could even add one additional hole further down in the box to keep the original 9 drivers. I like this options since it doesn't require ripping apart the whole enclosure.

Thats interesting that you say that the drivers would work best in a sealed box. When I modeled the response with WinISD it calculated an EBP of 148, which from my understanding is very much suited for a ported enclosure. The enclosure volume and port dimensions were all modeled using the T/S parameters of the drivers. Bass performance is not the problem that I am hearing with anyway. They have plenty of low range and kick. Its just the mids and highs that need work.

Thanks for the advice about the felt BTW. I will try that. I know that stuffing is not good for ported enclosures, but I had some lying around, so it was easy to test out.


I am positive everything is wired correctly, so I'm pretty sure that improper wiring is not causing the issue I am having.

Thanks for all the advice everyone.

Charlie
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Old 17th February 2013, 03:03 PM   #18
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I'd forget EBP. It's a 1st order approximation (i.e. it means very little). FWIW, these days I won't vent a driver < 4in, even in multiples. It's rarely worth the effort, & most of the time the tradeoffs are too severe.

Generally vented boxes are lined rather than stuffed, but it's not actually a hard and fast rule, and stuffing can be more useful in some cases, particularly of a high aspect ratio where you have standing waves (Helmholtz math, i.e. de rigure BR alignments assume a uniform air-particle density in the box & no standing waves). Since you don't appear to have any problems with the bottom end performance at present, I'd leave it alone.

I'm 99.9% that you've simply run into severe HF interference that is a direct result of the configuration (i.e. the drivers too far apart & no Eq). Unfortunately, there's nothing that can be done about this just with the current widebanders short of changing the box & adding Eq. Off the vertical axis, there's nothing that can be done, period, without a longer array. That's just the way they work. Shifting to a 2-way, with a central tweeter is probably going to be the best option.

I wouldn't rule arrays based on your current experience, but there are some things to keep in mind: if you're going to move about, you need more drivers for a longer array, you need to keep the drivers as close together as physically possible, and you need Eq for the top end. If you run the box sealed, this can be passive, at the expense of efficiency, so active is preferable since you'll preserve the dynamic range.

Last edited by Scottmoose; 17th February 2013 at 03:08 PM.
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Old 17th February 2013, 03:59 PM   #19
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This is what I would do.

1. Block the port with a sock to make it an aperiodic cabinet.
2. Turn it into a 2.5 way system so you have 8 of the drivers running bass and 1 as a midrange. You won't need BSC but you will have to isolate the single driver from the rest but that won't be too hard. You may be able to do this with a simple 1st order XO to start or maybe 2nd order if that doesn't work well.
3. Add a tweeter to the top of the cabinet. Get one that looks nice or build a little cabinet for it on top so it doesn't ruin the effect of your woodwork.

Easy fix, problems solved, and all that hard work is now rewarding instead of frustrating.
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Old 18th February 2013, 02:31 AM   #20
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Cal, the "one" driver has to be acoustically isolated too...
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