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Old 05-20-2014, 10:56 PM
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subwoofer = red, 21sw115 9 c.f. ported cab, tuned to 22hz, 2nd order high pass at 20, 2nd order low pass at 225hz. 6db of eq added to low end.
midwoofer = blue, 15" high sensivity, in sealed chamber. 2nd order high pass at 200hz and low pass at 900hz.
compression driver = green, ba750(?), seos horn, net 2nd order high pass at 900hz.
black line is net (if I've done this right; more or less)
sensitivity as seen by the avr would be 106db 1w1m. that's 126db 1w1m with 100 watts.
max spl would be dictated by the amp on the subwoofer.

taking a similar approach to what paul did, and I'm not sure if I've done it completely correctly, it would seem that the benefits of MTM for floor reflections may not be as significant as I was thinking.

for a listener sitting 9 feet from the speaker and with the midrange at 3 feet off the floor, the difference distance from direct sound (9 feet) and that of the floor bounce sound (10.81 feet) is 1.8 feet. that is half a wavelength that is 3.6 feet long and corresponds to a cancellation at ~311 hz.

in the picture at 311hz, the midrange is not the only source. it turns out that is about the point where both the subwoofer and the midwoofer are contributing equally to the sound. what is arriving at the listener's ear will be a combination of the midwoofer direct sound, midwoofer floor bounce, subwoofer direct sound and subwoofer floor bounce. this implies that a total cancellation will not occur. it may be simply a small dip in the response.

for many systems, a lot of the cancellations occur from reflections where there is only one source playing on the speaker. but in the case of the big overlapping 3 way, there is a large region of overlap from about 250hz to 750hz where several sources are contributing to the sound. of course, for most of the region above that point the horn controls directivity (more or less).

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Old 05-21-2014, 01:13 AM
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and if you want to go with a shallow cab and dual 18's...another rando concept. waveguide seems a little low in this one.

2x 18tbw100 woofers will outperform a 21sw115, but they would cost more too. of course, more modest woofers could also be used.


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Old 05-21-2014, 05:47 AM - Thread Starter
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Any 15's out there better for midrange than a 12" like this:

http://www.parts-express.com/bc-12pe32-12-midbass-speaker--294-660

B&C is slowly changing their line up and it worries me that they might be doing away with some of their current models like that one. But I guess there's really no way to know.

This might be the replacement model:

http://www.parts-express.com/bc-12mh32-12-professional-midbass-8-ohm--294-5953

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Old 05-21-2014, 05:51 AM
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;re'
for a listener sitting 9 feet from the speaker and with the midrange at 3 feet off the floor, the difference distance from direct sound (9 feet) and that of the floor bounce sound (10.81 feet) is 1.8 feet. that is half a wavelength that is 3.6 feet long and corresponds to a cancellation at ~311 hz

Did you model WMTMW like Paul W. did? With mids both above and below the waveguide, there will be a floor - reflection from the upper mid to fill in the null created by the floor reflection from the lower mid. Plus, as you say, contributions from the subs as well. I don't think you can make statements about the vertical response based simply on geometry - its too complicated with all those drivers. .

I like the WMTMW's vertical response and would deal with the height issue by stacking three modules - like Tux's 1099.

I'm hoping by the time I get around to it, the UM18-22s will finally be available (too bad that doesn't work for Eric). Its 22 mm Xmax outperforms the 21" pro subs. Two of them on each side sealed will be enough SPL and going sealed will lower the volume requirement significantly.

Jack
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Old 05-21-2014, 05:59 AM
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When it comes to which 15 mid outperforms the other I always seem to simulate that most of them are pretty close to each other. I personally like the 18 Sound products based on prices for me. So I like the 15" MB1000 for a midbass woofer in a 15" driver. There are other BC RCF BMS that would probably work also. When it comes to out performing I always come back to the AE products. Budget 18 Sound and all out performance I would go with AE. BUT you are on a time constraint so AE is out.
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Old 05-21-2014, 06:10 AM
 
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what about dual opposed 18's so you get better value than using a 21" and it won't make it too tall so the waveguide will be the right height?
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Old 05-21-2014, 06:34 AM - Thread Starter
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I don't think there are any dual 18's that will outperform the 21" for less money and the same sized enclosure.

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Old 05-21-2014, 07:24 AM
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Quote:
Originally Posted by LTD02 View Post

the graphic of the speakers combining is interesting because it suggests (?) that the c.d. sensitivity will run at about +6db or more over the midwoofer. does that mean with a subwoofer properly level matched that the mid/top unit can have something like 106db 1w1m sensitivity? i.e., high sensitivity 15" running at 100db 1w1m and c.d. running at 106db 1w1m matched to 106db worth of bass provides flat response across the whole spectrum (at least as a first order approximation)?

also, i think the ba750 compression driver can be crossed a little lower, such as whatever would produce a -6db point around 700hz or so, iirc. with a 15" driver and a 15" horn both should be losing directivity at about the same rate under 1khz, so the off axis should still be decent if going with a 5" midwoofer.

For expediency (this was a 90 minute exercise) I used active filters so driver sensitivity didn't matter. The smaller mids should enable a little higher crossover to reduce excursion related IMD in the CD, reduce the likelyhood of WG pattern flip, and improve articulation in the upper midrange.

I haven't optimized the WMTMW at all...just picked some reasonable possibilities and ran the sim. Driver size, location, crossover frequencies and slopes, etc are all subject to improvement. For example the 6x5" midrange I used is "interesting" but it remains to be seen if if is actually better than four...or just two larger drivers. Lots of possibilities in optimization.

My main purpose was to ensure the baby didn't get tossed with the bathwater! I also favor the modular approach since it can provide an easy upgrade path for those who start small and get the itch later on.

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Old 05-21-2014, 08:04 AM
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I really liked the dual mid MTM in its own cabinet and the dual woofers above and below idea. I have heard four 6" mids playing before and that was LOUD. So I curious what everyone comes up with or Erich settles on.
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Old 05-21-2014, 09:26 AM - Thread Starter
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Small dual 6" woofers between a SEOS-18 and 21" woofer will look a bit strange.

I drew up a design using 3-4 of the buyout 5" Celestions on the top and bottom of the waveguide, but Tux didn't think they would be efficient enough for this design. I know there are other 5" mids, but at $100 each, that's $600 on mids, which isn't going to happen. smile.gif

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Old 05-21-2014, 09:39 AM
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Wayne Parham's midhorn system is pretty efficient and affordable.
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Old 05-21-2014, 09:44 AM
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I don't think Wayne and Erich are on very good terms for that to happen wink.gif
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Old 05-21-2014, 09:55 AM
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Old 05-21-2014, 09:56 AM
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ryanC on the DIY Sound Group forum has built a pair of SEOS18/BA750 as a Malcolm array. He uses (4) 6" woofers mounted horizontally beneath the SEOS 18.
Here's the thread.http://www.diysoundgroup.com/forum/index.php?topic=31.30


He has also built a SEOS24 Malcolm array.
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Old 05-21-2014, 11:50 AM
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"Any 15's out there better for midrange than a 12" like this:

http://www.parts-express.com/bc-12pe32-12-midbass-speaker--294-660"

that looks good.

interesting thing about that driver is that it has so much motor on it, in a small sealed cab, it may have about the right rolloff point for this project even without any crossover parts.

nice find.

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Old 05-21-2014, 12:01 PM
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Quote:
Originally Posted by LTD02 View Post

"Any 15's out there better for midrange than a 12" like this:

http://www.parts-express.com/bc-12pe32-12-midbass-speaker--294-660"

that looks good.

interesting thing about that driver is that it has so much motor on it, in a small sealed cab, it may have about the right rolloff point for this project even without any crossover parts.

nice find.

Excellent specifications all around. Nice smooth impedance graph worth checking out.
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Old 05-21-2014, 12:02 PM
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here is that midrange in the model. 0.25 sealed cab. nice high rolloff point with no crossover parts.



[just in case some folks don't see how that could sum to flat response, take a look at 450hz. at that point, the subwoofer and the compression driver are producing about 93db each. those two sources together combine +6db. which would put the spl right on the blue line at 450hz. so then combined with the blue line, they will add another +6db bringing the level up to 106db. I'm not sure if my lines are in exactly the right place for perfect linear summation from all sources, but that is roughly the idea.]

I'm not sure what the sensitivity of the ba750 on waveguide is, so I've just been plugging in 106db 1w1m, which is probably in the right ballpark.

one thing that I'm kind of wondering about this whole build is how likely folks are to have "noise" problems.

with a mid/top cruising at 106db 1w1m, noise is definitely a concern. that could be up to 20db more "noise" than folks get out of their typical "hi-fi" speakers. since the idea is to run the mid/top passively, one can't just plop an isolator inbetween the source and the amp. there are all the potential ground loops that are shared into the avr. just something to keep in mind.

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Old 05-21-2014, 12:51 PM
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Quote:
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it may have about the right rolloff point for this project even without any crossover parts
Here we go with that stupid idea again.
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Old 05-21-2014, 01:33 PM
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I can find anything on that midhorn or a flatpack?
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Old 05-21-2014, 01:35 PM
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Here we go with that stupid idea again.

When joking use some emoji faces. If your not , well...
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Old 05-21-2014, 01:51 PM
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"Here we go with that stupid idea again."

?

seemed like in the right size cab the mid could rolloff second order and mated with a second order from the woofer, might work well.



"I can find anything on that midhorn or a flatpack?"

http://audioroundtable.com/PiSpeakers/messages/14407.html

and

http://audioroundtable.com/forum/index.php?t=msg&th=16581

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Old 05-21-2014, 02:28 PM
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Although I disagree with how his statement was made. I think Bill would be inclined to high pass the mid woofer to keep the sound clean. Not to mention getting everything else about the XO right would likely require some XO influence. Possibly adding two poles to make it 4th order would be wise. Although the overlap band pass gain you show is useful and second order helps in that respect. Unfortunately it never works that easily. I used band pass gain on the 1099 design. But not that much. That requires everything to be phase aligned across two octaves. And there's likely a hole in the power response like that also.
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Old 05-21-2014, 04:41 PM
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Old 05-21-2014, 07:32 PM
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Quote:
Originally Posted by LTD02 View Post

"Here we go with that stupid idea again."

?

seemed like in the right size cab the mid could rolloff second order and mated with a second order from the woofer, might work well.


I've already explained before why it's a stupid idea, and John, you normally come up with much better than this. Even though the cab may acoustically roll off second order, it will still be getting full voltage applied below bandwidth and it will still try to reproduce that, causing much more excursion and distortion than necessary and more than there would be with even a matching second order electrical filter before the driver. This could give you a nice LR4 final acoustic swap which would match well to the proposed active filter to the LF driver(s). Seems a waste to build a potentially very nice design, then intentionally hobble it for the cost of a couple of passives in the filter. Like putting cheap re-treads on a high performance car.
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Old 05-21-2014, 07:43 PM - Thread Starter
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I think we're getting pretty close to narrowing things down to 3 design ideas. All 3 use the SEOS-18 with the BA-750 for now. I can't really find justification not to use the monster 21" B&C woofer. It gets the waveguide up to the correct height, the price beats any dual B&C 18's that could go that low. Plus the one woofer could use the 8cuft space by itself versus having two 18's only getting 4cuft each. If someone has a reason to sway back to the dual 18's, please let me know.


The midrange section seems to be the decision area.

These dual 8" B&C midranges crossed around 700hz would act as a point source:

http://www.parts-express.com/bc-8pe21-8-midrange-speaker--294-652

I don't know if wiring them to a 4 ohm load is an issue or not.



This 12" B&C could be used instead and take up less internal volume than a 15" midrange:

http://www.parts-express.com/bc-12pe32-12-midbass-speaker--294-660?AID=1457483&PID=6155355&SID=1nq6y0i5wi3gw

I have a feeling that one might be getting discontinued because B&C is slowly changing their line up. This might be the replacement:

http://www.parts-express.com/bc-12mh32-12-professional-midbass-8-ohm--294-5953



If a 15" model is used, Bill thought this one looked good:

http://www.parts-express.com/bc-15ndl76-15-neodymium-woofer--294-683




15" Pluses: More power handling, less power needed. Matching directivity better to the waveguide?

12" pluses: I think it could be used over an 18" later without any complete crossover changes from being in the Maximus-21. Probably plenty for midrange use.

Dual 8" pluses: Interesting new design, possibly point source. Should have plenty of midrange.



Possible issues: The 15" model will probably need a bigger internal enclosure and take volume away from the subwoofer. It has to go over a 21" subwoofer because it would look kind of dumb over an 18". Some people not following this thread will likely not understand why a 15" was chosen for a midrange. "That's too big".

Would anyone ever max out a 12" midrange or dual 8's? Dual 10's has already been shot down.
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Old 05-21-2014, 07:50 PM
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You know à9 I generally don't like the tone of you responses often. Many times you make statement's like were lucky to even be able to be blessed by your presence. Your treatment of John, who has helped hundreds here is to me.... Ridiculous. You talk like you have the credentials of jeff bagby or Dennis Murphy. Even if you were accomplished treating people poorly is cowardice. No place for it.
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Old 05-21-2014, 08:15 PM
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Old 05-21-2014, 08:20 PM
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Maybe another benefit for the 12" : space to have front firing ports/vents on the sides of the 12 for the porting area of either the 18 or 21 since the 12 would likely be in its own sealed cabinet.
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Old 05-21-2014, 08:22 PM - Thread Starter
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I did think about using the internal walls of the 12" enclosure as sides for the subwoofer ports, they fit next to the 15 as well, just shaped a little different. I drew it up both ways, but making the elbow on the back wall might be harder to line up properly for such a large panel. I redrew it with a slot port on the bottom, but still not dead set on that either.

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Old 05-21-2014, 08:49 PM
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Quote:
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21sw115?
Yes
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