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Multi-Way Conventional loudspeakers with crossovers

Crossover frequency for transmission line
Crossover frequency for transmission line
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Old 15th April 2018, 01:23 AM   #11
planet10 is offline planet10  Canada
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Crossover frequency for transmission line
Quote:
Originally Posted by Cliveinuk View Post
what is the baffle step frequency...
Start here. Baffle Diffraction Step

and the next 4 articles.

dave
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Old 15th April 2018, 01:25 AM   #12
PeteMcK is offline PeteMcK
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Baffle step is the frequency where the sound starts radiating into a hemisphere rather than a flat plane, it depends on your baffle width (Fbsc =115/baffle width in metres). You don't have to crossover at this frequency, but it considerably simplifies the crossover design.

re:' you are saying make my midrange box to suit an Fs of the crossover frequency and not of the midrange speaker which is lower than the crossover" - yes (although I wouldn't put it quite like that, Fs pertains to a driver only, not a box or crossover)
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th April 2018, 01:37 PM   #13
Charles Darwin is offline Charles Darwin  United Kingdom
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It also depends on the eventual speaker placement. Baffle Step Correction is only useful if the speakers are a fair distance from any walls.

If the speakers end up close to a wall behind them BSC does more damage than good ie bloated ugly bass.

If they end up close to a corner you will need to do the opposite of BSC: reduce the relative bass level, not increase it.

Due to circumstances mine are in corners and I had to reduce the bass by nearly 8dB for a flat response at my listening position.
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Old 15th April 2018, 02:56 PM   #14
pkitt is offline pkitt  United States
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My speakers sit on a floor-level fireplace "hearth" with their backs 5 to 9 inches from the wall, depending on cabinets' depths (with almost all of the cabinets I build having the terminus or ML-port on the rear panel) and I've found that incorporating ~ 3 dB of BSC works just fine with well-defined and not bloated or ugly bass. See the attached photo of my setup.
Paul


Quote:
Originally Posted by Charles Darwin View Post
It also depends on the eventual speaker placement. Baffle Step Correction is only useful if the speakers are a fair distance from any walls.

If the speakers end up close to a wall behind them BSC does more damage than good ie bloated ugly bass.

If they end up close to a corner you will need to do the opposite of BSC: reduce the relative bass level, not increase it.

Due to circumstances mine are in corners and I had to reduce the bass by nearly 8dB for a flat response at my listening position.
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Old 15th April 2018, 04:36 PM   #15
pkitt is offline pkitt  United States
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When Qts is higher than 0.4, the optimum tuning frequency will be lower than fS, which is specified as 26 Hz. So I guessed at 20 Hz, did some quick modeling and found a little bit lower would be even better.
Paul

Quote:
Originally Posted by altie View Post
Thank you. That 18-20Hz tuning sounds plausible to me from the sims I've been doing lately, but for my own education, how'd you arrive at it?

@Cliveinuk, like pkitt is saying, yes those nulls would destroy midrange qualities, no you don't have to tolerate them. Look up some details on mass loading, tapering, driver offset, coupling chambers and stuffing, and try running sims so you can see how those approaches would help. The numbers and graph I posted are for the most basic possible box you could call something like a transmission line for the driver you posted - *not* one that's optimized like pkitt is talking about, or one you would actually want to use. It's a starting point.
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Old 15th April 2018, 04:53 PM   #16
Jerms is offline Jerms  United Kingdom
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10" sub and a 6" midrange per side.... Looking at the response and impedance plots, cross somewhere around 200Hz. The subwoofer impedance rises and the response gets a little bumpier higher up.

Baffle Step or Diffraction loss describes what happens around the frequency where the wavelength of sound waves approaches that of the baffle size. Freq below that tend to wrap around the speaker and radiate in all directions. Freq above it tend to project off the baffle forwards. The response is adjusted to attenuate the higher frequencies therefore apparently increasing the lower freqs.

"The Edge" program can be useful in identifying and correcting.
Tolvan Data.

J.
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Old 15th April 2018, 05:15 PM   #17
pkitt is offline pkitt  United States
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Default Modeling results

While there are likely other equally usable solutions, I modeled a line 80" long and tapered at 24:1 having a starting area of 180 in2 and an ending area (as well as the terminus) of 7.5 in2, with the the center of the UM1058 located 20" from the beginning of the line. The first 54" of the line is stuffed with polyester fiber at a density of 1 lb/ft3. Without the stuffing, the line is tuned to 21-22 Hz. After adding stuffing the tuning frequency becomes ~18 Hz. I've attached the modeling graph showing the predicted anechoic system bass response (red line) for an input of 150w/1m, which shows an f3 of ~21 Hz and an output SPL of 104 dB above 30 Hz with a very smooth response. At this input power, the woofer reaches Xmax at ~25 Hz, then exceeds it at ~17 Hz and all lower frequencies. Also with this input power, the peak air velocity in the end of the line and terminus is ~4.5% of the speed of sound, or ~15 m/s, and occurs at ~17 Hz.
Paul
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Old 15th April 2018, 10:46 PM   #18
pkitt is offline pkitt  United States
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I made a mistake in what I described in Post #17; the woofer's center is located 16" from the beginning of the line and how I modeled it, not 20".

Sorry,
Paul
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Old 16th April 2018, 07:58 PM   #19
Cliveinuk is offline Cliveinuk  United Kingdom
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Paul, when you say the woofer centre is 16 inches from the beiginning of the line do you mean there is a box that is 16 inches long and does not count as part of the line length

here is a question ? does the baffle step diffraction get influenced by the material used in the baffle
So for instance 12mm mdf vs 25 mm concrete as extreme examples Will the concrete exibit this to a much lower extent?

Speaker design is not as simple as ABC then

thanks again to everyone for the effort in replying

Clive
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Old 16th April 2018, 08:03 PM   #20
Cliveinuk is offline Cliveinuk  United Kingdom
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Paul what is a taper ratio of 24:1
Can you rather put it as a percentage of the Sd at the start of the line and a percentage of the Sd at the end of the line
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