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Is it correct to correct the dip at crossover?

amirm

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Is it correct to eliminate the dip by EQing?
Sure. What you indicate is one issue. There are others higher up. Use a parametric EQ and turn filters on/off and see which version you like better. Make sure you have at least half a dozen if not more, varied test tracks to test effectiveness.
 

MrPeabody

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I didn't say anything about not trying reversing the tweeter polarity, did I? :)
What I did say is that I don't believe this particular dip is associated with a possible wiring issue.....because it's not at the crossover frequency. The info I found on this speaker indicates a xover frequency of 4khz. (Which could be wrong I suppose.)
Dave.

The OP had indicated that the dip was in the vicinity of the crossover frequency. This may have led to confusion, but whether it did or didn't, the most likely explanation for the dip at about 1.8 kHz (judging from the Soundstage plot) remains phase mismatch between the two drivers at this frequency. At the vertical polar angle where the measurement is taken, it is most likely true that the two drivers are nearly 180 degrees out of phase at this frequency. This is unusual, but not impossible, and there is nothing else that comes to mind that could as easily explain the severe notch that is seen very clearly in the Soundstage plot and that is characteristic of phase cancellation between the two drivers. For this to occur, the phase difference between the two drivers would obviously have to be different for 1.8 kHz vs. 4 kHz. This could be simply a result of using different slopes for the two drivers, since the rate of phase change relative to frequency would then be different for the two drivers. Additional phase shift associated with the natural rolloff of the drivers could also be a strong contributing factor.

I don't understand why you would think it meaningful to point out that you hadn't said anything about not trying to reverse the tweeter polarity. We have a disconnect there, but what you did actually say in a previous reply, to popper, is this:

I understand EQ wouldn't be 'your' first move, but that's not what the OP asked about.
You seem to be having a discussion with yourself on how this particular speaker (B&W 603) could be 'fixed'. (Assuming it needs fixing.)
Or that maybe it emerged from the factory defective in some way and it needs to be troubleshot. You might be right in either or both cases.
But regardless, the OP's question was not primarily about this speaker, but rather a more general question. But since he hasn't returned to elaborate, the simplest answer to his question is Yes.
Dave.

I don't know why he would have been having a discussion with himself, especially since you had engaged with him all along. More to the point, while it is true as you point out that the OP had asked the question in a general way, the particular question he asked in a general way was this:

The amplitude-frequency response curves ... may have a dip around the crossover frequency.
Is it correct to eliminate the dip by EQing?

Given that the question he asked in a general way is concerned with dips found "around the crossover frequency", it was well within reason for popper to have responded with an assumption that the sort of dip to which the question pertains is a dip associated with the crossover, even if it isn't at the crossover frequency. You say that you didn't say anything about not trying reversing the tweeter polarity, but your criticism of his posts was undeniably based on his focus on the crossover and the suggestion that before applying EQ, it would be prudent to experiment with the tweeter polarity.
 
D

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You're still not convinced the tweeter is connected with the correct polarity in this particular B & W speaker?? :)

You're doing much more speculation than I'm willing to regarding this speaker. I would think that a noted manufacturer like B & W is capable of getting their tweeters connected correctly. But, that's just me. :)

Dave.
 

puppet

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Dave, seems we have a different opinion on how we'd approach a issue like this.

If I were to acquire something like this say, second hand, I'd look a little further before trying to EQ the problem away as the loudspeakers response didn't jive with B&W's published spec's. ... but then, since there are couple of independent sources that illustrate the same issue, I'd have to assume that there was an inherent issue with the network, mid driver or the wiring. From there, one can further evaluate the loudspeakers network and determine what's happening. The issue seems severe enough to warrant that at least.

That's where my thinking was when I posted. If the response was more in line with a couple 5db dips and peaks and tracked off axis as well, EQ would be the way to go. Heh, not my fault the OP picked a real beauty.

I agree with your suggestion of more thorough review measurements, especially in cases like these. They aren't exactly "white van" loudspeakers.

Regards,
Phil
 
D

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No, I don't think we really have a different opinion. I would stipulate that maybe some tweaking or further exploration of the crossover design of this speaker might yield a different/better response. (But that could be said of numerous speaker systems and their design.) :)
Crossover and speaker design is not one of those pursuits where you simulate/iterate and ultimately cross the finish line with a perfect result.

Just because independent testing doesn't jive with the manufacturers published isn't necessarily indicative of an "issue." Maybe they were perfectly aware of this irregularity but weighed the plusses and minusses of altering the design and decided this was the best trade-off???? I dunno.
The drivers and configuration 'bakes in' a certain amount of problems regardless.

That said, you posited that the tweeter polarity might be wired incorrectly. Some sort of assembly line problem, or similar? I don't see any indication of that in the measured results......based on what's published in manufacturer specifications. Generally, a sorted design with a driver hooked up incorrectly would exhibit a response anomaly much more severe than what we're seeing here. Especially if it's an even-order crossover.

Dave.
 

pma

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Simple reversing polarity usually helps only in case of fatal design mistake. The phase mismatch at crossover frequency normally is influenced by distance of drivers, crossover frequency and filter type. A competent designer would not produce a speaker with phase inversion between drivers at crossover frequency.
 
D

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Simple reversing polarity usually helps only in case of fatal design mistake. The phase mismatch at crossover frequency normally is influenced by distance of drivers, crossover frequency and filter type. A competent designer would not produce a speaker with phase inversion between drivers at crossover frequency.
Uh, quite a few speakers are designed with polarity inversion of adjacent drivers. But that's to facilitate phase-matching through the crossover region.....with certain crossover alignments....like maybe LR2.
I suspect/guess you understand this, but your statement is nebulous.

Dave.
 

pma

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It must be a misunderstanding. I am suggesting that simple attempt to swap wires of tweeter would work only in case it was a totally wrong design. I will write no more comments on this as I believed it was obvious.
 

puppet

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Generally, a sorted design with a driver hooked up incorrectly would exhibit a response anomaly much more severe than what we're seeing here. Especially if it's an even-order crossover.

Dave.
That's the assumption.
 

rdenney

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Toole tells us that dips at specific frequencies that appear in response curves of difference directions show the effects of room nulls, and can be corrected by EQ. But when the dip only appears off-axis and not on-axis (or vice versa), it's not a room null but rather phase cancellation between the drivers, where, for example, a mid is pushing out while a woofer is pulling in. Changing polarity can address that if the cancellation is near total (180 degrees out of phase), but might not help if the phase error between the drivers is 90 degrees or less. But Toole tells us that those phase-caused dips in only some directions can't be fixed by EQ.

There might also be some early reflection resonances where the early reflection is out of phase with the direct path, and EQ probably won't help there, either.

Rick "simplifying for his own sake" Denney
 
D

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That's the assumption.
No, it's not an assumption. It's a recognized fact.
Reverse the polarity of an adjacent driver in properly designed speaker system and you will measure a noticeable response aberration owing to the altered phase response in the crossover region.

Dave.
 

preload

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As others have pointed out, the dip is likely to be intentional (or known/understood) as part of the design. It may be that the loudspeaker sounds terrible/harsh at the dip frequency. B&W's doesn't use the same design philosophy as Harman (I.e. Smooth directivity and adherence to the Harman curve). Sure you could invert the tweeter polarity jff and remeasure/relisten and it may or may not make things worse (likely worse). Also keep in mind that not all B&W crossovers are symmetric, so polarity inversion won't have as clean of an effect as one might predict.

Personally I'm a bit curious as to why the B&W 800-series floorstanders sound so good, even when they don't follow the Harman design "rules." In fact EQ'ing my Gen 8351b to match my B&w 802D including that BBC dip surprisingly results in a much better sounding system.

The fact is, there are hoardes of ppl who like the B&W house sound. Those that do, tend not to congregate on ASR.
 

Thomas_A

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A dip at 1,8 kHz on and off axis just enhances the stereo system errors. One way this can be dealt with is to have a slight peak at 1,8 kHz, especially a wider angles. This is one way to let reflections do the work to fill in the dip that is always present. Subjectively I prefer to have 1-2 dB more energy 1-2 kHz and 1-2 dB less energy 2-5 kHz and 7-8 kHz.
 

puppet

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Dave ... I know that. I'm referring to your assumption that this particular design is "well sorted" . In other words, one would assume to see a null at the xo frequency when one driver is out of phase if the xo is properly done. Still waiting for an explanation that holds water on this particular anomaly. Care to give one?
 
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D

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I never said this particular design is "well sorted." Are you actually reading my posts?
I said, "generally, a sorted design.............." That means, generally,.......as in not this one specifically.
My goodness.

I've commented, (numerous times now,) that I'm not totally sure what the issue/anomaly is with this particular speaker.........or even if there is an issue, from B&W's standpoint.

Dave.
 

Andysu

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The dip would indicate to me that the tweeter's polarity isn't correct. Try reversing the tweeters polarity and observe the dip.
that is correct . use pink noise RTA real time and mic placed near to speaker and reverse wiring until the dipped frequency raises upwards .
 
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