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Old 12th October 2009, 02:38 AM   #21
dlr is offline dlr  United States
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Have I designed first order? Absolutely, a 3-way, one that I liked rather well actually. I had several crossovers for that system. Your assumption that I don't like first order is certainly wrong. At our annual gathering the first order was preferred by the others as well, somewhat to my surprise. It was a rather complicated crossover being a 3-way first order, something of the way Dunlavy did his I would guess, his were not simple. I think that I did a good job on that one given the group's response.

There wasn't much of fact in the statement "these combinations are rare". To what should I pay attention? It says absolute nothing with regard to the acoustic responses.

I am not setting myself up as some expert, I have some experience, certainly enough to ask what I believe to be pertinent questions. If something I've said is shown to be wrong, fine. I had to make a few assumptions at first because there wasn't much to go on. But with all said, I still see no relation to what Dunlavy did. He certainly never ran any drivers full range to my knowledge. Are you aware of any that he did?

So the tweeter Fc is set at 6000Hz. That may start as first order, but it will turn to third at the knee of the driver raw curve before the baffle diffraction influence is taken into account, that was my point. Diffraction will, of course, be much less of an issue with a modest horn loaded tweeter such as the MDT-37. A couple of measurements would be much easier to discuss, one would assume that they were made. It seems that the tweeter is the closer one in this case.

An Fc of 6K might also be an issue with regard to center-to-center spacing, having a wavelength of may 2.25". The spacing is easily going to be more than a full wavelength at Fc. That bears some attention as well. In that area, though, I've never been one that put as much emphasis on that as so many others do.

To me it would seem that the full range midwoofer is more problematic. If the driver examples that you used matched the Morel anechoic measurements (smoothing unknown if used as it was in some of the tweeter responses), the MW144 does not have a corresponding -3db point at 6k, it's more like 10K. Looks like a bit of overlap to me, but again, a set of measurements could put that to rest, at least on the design axis. The MW144 is still at 0db relative at 6K, so the interaction with the tweeter according to those numbers would not achieve a BW1 target. Maybe the MW144 drivers that you used did not match the Morel supplied curves that I've seen. I'm looking at a catalog from 2003 and the MLSSA anechoic response that they supplied. That one is in fact relatively flat to 8K, hence my suspicion that the integration would not be as desired.

If you could show the two measurements, that would be most helpful. We have not discussed the baffle step loss, of course, that's another issue that generally must be taken into account in a proper crossover. Some drivers have an inherent downward sloping passband response that coupled with the right baffle will provide a flat response when coupled with the step, but that MW144 shows flat down to 50Hz as seen in the Morel measurements, anechoic. Put that driver on a baffle with no crossover and there's no getting around a baffle step loss with a peak above the loss area. How have you handled that with no crossover?

How they interact (Marry as you call it) is immaterial when analyzing each driver. They ultimately combine, but they do nothing one to the other (except for tweeter diffraction due to the woofer in many cases). One has to cross each one to get a specific target summed acoustic response. Both have to be taken into account of course, but that's pretty much a given, wouldn't you say? It's all part and parcel of design.

It is not necessary for one to hear a system to discuss the technical aspects such as crossover slopes and targets. I certainly never even implied that it would sound poor. If one designs by ear, yeah, you've got to listen. But I don't design by trial-and-error listening. I set a goal, match it with measured driver highpass and lowpass, then listen and evaluate. If a change is required, I do that by setting and achieving a change to the target that I expect to result in the change I desire. But in the end it is all verified with measurements.

Dave
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Old 12th October 2009, 02:49 AM   #22
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Let me just take a moment to suppose that... Had you two been sitting in the same room together discussing these topics, I for one, would be willing to bet that there would have been no insults felt or implied - at least not to the point where anyone would feel one's "feathers ruffled"...

So, let me ask, do please continue your discussion about "first order" crossovers, just... pick up a little Zen attitude and even if "he started it first" be the bigger man, and graciously dismiss any insult that may have been meant, or not. Any questions or implications that may have implied insult - let's take them as if they hadn't, and simply respond sincerely.

I'm not saying anybody has been childish here - I just see an opportunity to further a discussion, rather than one person or the other maybe feeling that its headed down a negative path that will end up without much merit.

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I took the one less traveled by,..."
Sounds good to me! Perhaps you would like to put your views forward or ask questions. I have 'things I always do" when designing. Taking parts away from a designed xover is one of those things. Initially I had a 0.22 inductor on the MW144/142. When I took it off, the system measured better and sounded better. If I used an MW168 the inductor stayed. The MW144 has brilliant response out to 8K. It loves the DMS37. It should do, I had a hand in it's design. At the time I was the Aus distributor for Morel. When Morel was set to design the DMS 37 I sent them my research on time alignment which was based on the MDT30/32. They saw the light and lined up the acoustic centres to be spot on. It was when I was playing with the first development samples that I discovered the incrediable relationship that this combination has. Tis quite rare, but god it sounds incredible/

Terry
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Old 12th October 2009, 02:50 AM   #23
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Let me interject - have any of you not seen a speaker that measures superbly, yet sounds terrible?

I also have to disagree with Dave if he means to imply that the portion of drivers (mids/woofers + tweeters) which will function well as a system together with simple first order electrical crossovers (or, the "just a cap on the tweeter) is not an extremely small fraction of them?

I have seen VERY few designs like Zaph's Waveguide TMM in proportion to the vast majority of designs with higher order electrical crossovers (not counting bad sounding K-mart speakers and the like).

I have to admit to not have seen very many of the crossovers of older well respected commercial designs (by "older" I mean from the previous few decades of the last millenium).
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Old 12th October 2009, 03:21 AM   #24
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This is the completed response. I do not have a lot of design data. It was a long time ago, and two computer crashes ago.

Hope that worked!

Terry
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Old 12th October 2009, 03:35 AM   #25
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Originally Posted by critofur View Post
Let me interject - have any of you not seen a speaker that measures superbly, yet sounds terrible?

I also have to disagree with Dave if he means to imply that the portion of drivers (mids/woofers + tweeters) which will function well as a system together with simple first order electrical crossovers (or, the "just a cap on the tweeter) is not an extremely small fraction of them?

I have seen VERY few designs like Zaph's Waveguide TMM in proportion to the vast majority of designs with higher order electrical crossovers (not counting bad sounding K-mart speakers and the like).

I have to admit to not have seen very many of the crossovers of older well respected commercial designs (by "older" I mean from the previous few decades of the last millenium).
I remember the first xover I designed for the JV60. Measured like a dream come true. Then I took it out to the listening room and plugged it in, sat back, . It was woeful. I started from scratch again.

Terry
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Old 12th October 2009, 03:53 AM   #26
dlr is offline dlr  United States
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Originally Posted by pheonix358 View Post
This is the completed response. I do not have a lot of design data. It was a long time ago, and two computer crashes ago.

Hope that worked!

Terry
What was the design axis? Distance? Baffle dimensions? It's rather difficult to see what the situation is with a single point summed response and no other data as to conditions.

The 2k dip should I suppose be credited to baffle diffraction of the woofer and likewise the mile peaking at 1K.

There's a fairly broad dip centered at 4K, the source of which can't be discerned in seeing only a summed response. Given that the woofer is supposed to be flat in that area and that the tweeter is claimed to have had a true first order response in the crossover area, something is amiss to cause a significant dip such as that. It's sure not what I would expect from the two drivers' curves shown by Morel, but then manufacturers have a habit of showing optimistic curves. I would suspect phase issues.

The measurement stops at 500Hz. Baffle step is typically just at the relative 0db at this point. That output is trending down and will be dropping below that point by a full 6db, so the measurement is missing a significant part of the response. The indication would be a rather lean bass, but maybe that was considered desirable.

In the end it still does not appear to meet a first order summed target unless the woofer is somehow rolling off earlier than in Morel's curves. The phase influence of the tweeter rolloff may be part of the reason when such a high crossover is used.

It would be interesting to see the polar response given the rather wide CTC with a 6K crossover.

Dave

Last edited by dlr; 12th October 2009 at 03:57 AM.
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Old 12th October 2009, 03:55 AM   #27
dlr is offline dlr  United States
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I also have to disagree with Dave if he means to imply that the portion of drivers (mids/woofers + tweeters) which will function well as a system together with simple first order electrical crossovers (or, the "just a cap on the tweeter) is not an extremely small fraction of them?
I'm not sure what I said that left that impression, but it's not my position, far from it.

Dave
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Old 12th October 2009, 04:00 AM   #28
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What was the design axis? Distance? Baffle dimensions? It's rather difficult to see what the situation is with a single point summed response and no other data as to conditions.

The 2k dip should I suppose be credited to baffle diffraction of the woofer and likewise the mile peaking at 1K.

There's a fairly broad dip centered at 4K, the source of which can't be discerned in seeing only a summed response. Given that the woofer is supposed to be flat in that area and that the tweeter is claimed to have had a true first order response in the crossover area, something is amiss to cause a significant dip such as that. It's sure not what I would expect from the two drivers' curves shown by Morel, but then manufacturers have a habit of showing optimistic curves.

The measurement stops at 500Hz. Baffle step is typically just at the relative 0db at this point. That output is trending down and will be dropping below that point by a full 6db, so the measurement is missing a significant part of the response. The indication would be a rather lean bass, but maybe that was considered desirable.

In the end it still does not appear to meet a first order summed target unless the woofer is somehow rolling off earlier than in Morel's curves. The phase influence of the tweeter rolloff may be part of the reason when such a high crossover is used.

It would be interesting to see the polar response given the rather wide CTC with a 6K crossover.

Dave
I thought that +/- 2dB was quite good. It was +/-2.5dB with raw data and +/-2dB with 0.1 Octave smoothing. That response is taken at 1 metre. with less than 1 watt of power. Speaker was 92dB at 2.83V. It was a point source using 2 MW144 and the DMS37 tweeter. Sorry but that's the only graph I have of that system.

Terry
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Old 12th October 2009, 12:22 PM   #29
dlr is offline dlr  United States
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I thought that +/- 2dB was quite good. It was +/-2.5dB with raw data and +/-2dB with 0.1 Octave smoothing. That response is taken at 1 metre. with less than 1 watt of power. Speaker was 92dB at 2.83V. It was a point source using 2 MW144 and the DMS37 tweeter. Sorry but that's the only graph I have of that system.

Terry
Maybe the sensitivity was different back then, but that would be a surprise. The Morel info I have shows a sensitivity of 1W/1m as 88db. The MLSSA curve would be about 87db and I suspect is 2.83v. Neither one gets to 92db. If at 1m on the tweeter axis, a full range midwoofer will likely have some off-axis droop, these aren't truly point source drivers. That would help explain the 4K dip as well as relative phase in that area.

The DMS-37 would be in the 92db range with just a cap, but I don't see how the combination does 92db given the data that Morel provides. In any case, a full range MW144 on a baffle is going to act as all dynamic drivers do on a baffle, it's going to operate into 4-pi below baffle step so the area below 500Hz is going to lose 6db. That was one key point I've been trying to make. The measurement supports that this in fact occurring, even though we only see the area above 500Hz that will be peaking due to baffle diffraction. Maybe lean bass wasn't an issue, that falls into the area of preference. It will be the case, however.

There does still seem to be some destructive interference in the overlap region. If the woofer is flat to 8K (0db relative) and the tweeter is crossed to be -3db at 6K, there is not going to be proper summation as a BW1, especially with two drivers with different sensitivity ratings. It may be relatively flat due to phase issues, the 4K dip indicates something is still a bit amiss, but then we're also still limited to a single point. I actually would have expected the area above 6K to show some interference (call it non-optimal summation), but it may be that the off-axis droop (assuming that the measurement is on the tweeter's axis) is responsible for preventing peaking that would have to occur at 6K up if the responses were as shown by Morel. The gradual rolloff of the MW144 is certainly better than most to 10K, though there will likely be a much quicker rolloff at relatively low off-axis angles. I can't say if it's like the Dynaudios I used to use.

In the end it is a relatively smooth on-axis response, but the baffle step loss and the expected uneven power response would give me pause. I'd need to see individual responses to include off-axis (or sims) to get a better feel for the actual integration. I would have an issue with a driver that is becoming directional well below the crossover point. Morel's curves show only one off-axis response, I suspect it's 30 degrees, they don't even say. It starts to drop at 4K. Personally I wouldn't take that driver so high, especially given the ability of the MDT-37 to go as low as it can. I would consider as high as 4K and that doesn't address the CTC spacing issue. Very small changes vertically are guaranteed to see quickly varying destructive inteference due to path length difference where the spacing is at least 2x the wavelength at Fc (6K).

But again, to each his own.

Dave

Last edited by dlr; 12th October 2009 at 12:24 PM.
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Old 13th October 2009, 12:26 AM   #30
dlr is offline dlr  United States
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I thought that +/- 2dB was quite good. It was +/-2.5dB with raw data and +/-2dB with 0.1 Octave smoothing. That response is taken at 1 metre. with less than 1 watt of power. Speaker was 92dB at 2.83V. It was a point source using 2 MW144 and the DMS37 tweeter. Sorry but that's the only graph I have of that system.

Terry
Seems I missed the point of there being 2 midwoofers, certainly explains the sensitivity question I had. I guess I wasn't fully awake this morning. Two drivers that are spec'ed at 87db will easily get to 92db, but that's only 2-pi. I'm still looking for feedback on the baffle step since two drivers full-range that are flat anechoically as measured by Morel are going to lose 6db starting somewhat around the 500Hz point that is not shown in the measurement. It doesn't matter whether there's one or two, there will be a 6db step loss.

The issue that concerns the 4K broad dip still remains unanswered as well, since the claims were that this is a true first order crossover. Were that the case, there should be a peak at the stated Fc of 6K given that the MW144 is flat (not down 3db) at 6K.

Dave
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