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Multi-Way Conventional loudspeakers with crossovers

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Old 6th March 2013, 02:57 PM   #21
wowo101 is offline wowo101  Germany
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Default TMT experiments, part III

Not really, at least not in the directivity department gain some, lose some, according to the Boxsim plots:

Endeavour TMT 2 x 4th order XO angles.png

On the other hand, a 4th order alignment for woofer and mids would of course reduce SPL and excursion requirements on the B80's low end.
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Old 6th March 2013, 03:47 PM   #22
6.283 is offline 6.283  Germany
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Those twp pictures are absolutely identical as if they were one and the same. Is that correct ?
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Old 6th March 2013, 04:18 PM   #23
wowo101 is offline wowo101  Germany
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Ha! You're right the two variants are similar, but not that similar. The correct plots are these:

Endeavour TMT 2 x 4th order XO angles.png
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Old 6th March 2013, 04:41 PM   #24
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I would go for LR4. It is only a switch in miniDSP. This way less bass is leaking out of the modal region into the transition region.
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Old 6th March 2013, 05:06 PM   #25
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How would having the woofer serve only the modal region be an advantage? As far as I understand, modal, transitional or statistical behaviour is a function of room and frequency, so the (nature and effect of the) behaviour in a certan frequency range should be independant of which driver is producing the sound…

After further studying the TMT responses and doing some math, it seems to me that the vertical directivity I'm gaining by this arrangement doesn't suffice to reduce floor bounce at the intended LP, although it may well attenuate other detrimental reflections, e.g. from the ceiling. Is there any published research on the audibility and effect on perceived sound quality of the floor bounce, apart from Bech's papers?
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Old 6th March 2013, 06:15 PM   #26
6.283 is offline 6.283  Germany
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Above the schroeder F, boundary effects come into play that do not exists in the modal region. As a result, the driver's relative position to surfaces start to play a role. The woofer would then start radiation into half space. On the floor that might not be an issue but the ceiling is further away and you might get a bounce from there, especially if crossed high with a flat filter, because the woofer is still omnipolar.
It is a purely theoretical consideration but a safe bet so to speak.

But since you can change miniDSP on the spot you might give it a try if you plan to perform measurements at the listening position.

Also, check 6.2.1 in Toole. After all, floor and ceiling bounces are not that
big of a deal especially if there is carpet on the floor.
In my design I take advantage of the real D'Appo because I can and I have a pretty reflective floor. The sound will show if that design measure is required for my place.
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Last edited by 6.283; 6th March 2013 at 06:17 PM.
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Old 6th March 2013, 07:36 PM   #27
wowo101 is offline wowo101  Germany
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As to the first point: If I understand you correctly, you are aiming at reducing the ceiling bounce by avoiding radiation from further away resp. down (i.e. from the woofer). But in my listing situation (3 m ceiling height, 3.1 m listening distance) the frequencies of the first ceiling bounce nulls will always be within the modal region of the room, regardless of W-M crossover point or alignment, and the first nulls above the transition region will always be caused by the midrange driver. So I guess the lower XO and/or steeper filter wouldn't help much there.

As to the second: Thanks for pointing me to the discussion in Toole! After rereading it, I'm asking myself if we aren't discussing two different but related phenomena:

On the one hand, there are first-order reflections, not qualified by reference to a certain frequency; this seems to be what Bech and Toole (and Toole and Olive) are discussing. These are easily treated with carpets et al. because they are mainly detrimental in the frequency range above 2 kHz.

On the other hand, when talking about (first) floor bounce nulls, we're looking at destructive interferences at the listening position that only occur at specific frequencies. Since the interferences result in clearly visible FR anomalies for the early sound, their influence on timbre should be equally clearly identifiable, I think (at least if you don't take into account psycho-acoustic arguments la Linkwitz). At the same time, they occur at frequencies where absorption isn't particularly effective.

At least that's my reasoning behind trying to avoid the nulls in the first place – but maybe I'm going wrong somewhere?
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Old 7th March 2013, 10:00 AM   #28
6.283 is offline 6.283  Germany
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Quote:
Originally Posted by wowo101 View Post
As to the first point: If I understand you correctly, you are aiming at reducing the ceiling bounce by avoiding radiation from further away resp. down (i.e. from the woofer).
Sorry, I did not want to confuse you with a theoretical consideration of high cross-over F and flat filters.

Quote:
Originally Posted by wowo101 View Post
But in my listing situation (3 m ceiling height, 3.1 m listening distance) the frequencies of the first ceiling bounce nulls will always be within the modal region of the room, regardless of W-M crossover point or alignment,
And so they become a don't care.

Quote:
Originally Posted by wowo101 View Post
and the first nulls above the transition region will always be caused by the midrange driver. So I guess the lower XO and/or steeper filter wouldn't help much there.
Correct. Again the theoretical point of view. On the other hand, as mentioned, LR2 vs. 4 is switch in miniDSP. And perosnally I would set it to LR4.

Quote:
Originally Posted by wowo101 View Post
As to the second: Thanks for pointing me to the discussion in Toole! After rereading it, I'm asking myself if we aren't discussing two different but related phenomena:
They are all related. It is just a matter of F or wave length what the results are.

Quote:
Originally Posted by wowo101 View Post
On the other hand, when talking about (first) floor bounce nulls, we're looking at destructive interferences at the listening position that only occur at specific frequencies. Since the interferences result in clearly visible FR anomalies for the early sound, their influence on timbre should be equally clearly identifiable, I think (at least if you don't take into account psycho-acoustic arguments la Linkwitz). At the same time, they occur at frequencies where absorption isn't particularly effective.
I guess we agree now that these have to occur above the modal region and the earliest within the transition zone, right ? So we are talking in the low hundrets of Hz but above say 200 Hz.
My peronal experience with these interferences is that I do not notice them or at least don't perceive them as disturbing.
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Old 7th March 2013, 10:26 AM   #29
wowo101 is offline wowo101  Germany
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You're absolutely right about LR4 – while maybe for different reasons, it's my default option, too. But it was interesting to see how the (simulated) drivers I chose are performing with a flatter filter.

And yes, the frequency range I'm concerned with in the handling of floor reflections is basically above the modal region and below where "room friendly" absorption becomes feasible, which means the low and middle hundreds of Hz. I guess some experiments with different configurations are in order for me before deciding on the importance of the bounces as a design constraint for me…
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Old 7th March 2013, 10:49 AM   #30
6.283 is offline 6.283  Germany
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Unfortunately, I have no scientific reference on hand that deals with the described interferences. Otherwise I would have pointed you to them, of course.
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