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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd July 2016, 03:46 AM   #71
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by mrk7 View Post
Hi bwaslo,
Can you please provide more information about how the slotted-woofers extend the horizontal directivity? Also, what would be the low frequency directivity limit using the slotted-woofer technique?
Hi Mark,

It's not so much the woofers being slotted, it's the woofers being spaced apart, basically the array effect (that normally gives comb-notching). They're spaced so that they start to cancel when you get way off-axis, the far one approaches being a half-wavelength further from you than the closer one. The dip is narrow in frequency range, though, while the drop in directivity from the midrange (in the waveguide) is less narrow, so the crossover has to be finessed to balance between mid and woofer to keep the directivity as even as possible with the woofer spacing effect working as low as it can. At least that's the intention. Below that it just goes omnidirectional, as usual. You can move the woofers further apart to make the effect happen as low in frequency as you want, but then the midrange has to provide directivity to a lower frequency (i.e., needs a bigger waveguide) to control it until the woofer spacing can help. So, it's only good for extending the waveguide directivity by a little bit (though the simulation imply something near an octave extension..... we'll see).

The point of the woofers feeding through slots (rather than just baffle mounting them below the waveguide) is for the vertical polar behavior. In the vertical, the waveguide directivity is gone already at a relatively high frequency, but if the woofer is too far away from the waveguide center vertically, it will start to cancel with the midrange and cause nulls. Sitting the woofers partially behind the waveguide and feeding their output through narrow slots at the edge of the waveguide keeps the effective centers of the woofers closer to the waveguide center, enough to still let the system perform like a point source. It's not a lot different from what happens with bass drivers in a Danley Synergy horn, where the woofers feed through slots in the waveguide near the mouth of the horn The horn doesn't really help the woofers' output any, but having them located there keeps them closer to the center of the other drivers so that the whole arrangement can still act like a point source; it's a good trick, and I think its aural benefits make it very worthwhile.

My arrangement differs in that I use a rectangular waveguide and put the woofer ports on the baffle instead of in the waveguide. And only put them on one side. in this version at least. Danley always seems to keep things balanced, for maximum SPL capability, I assume. This design is more focused on trying to get the best polar performance with a small size, and in something that doesn't require scary skills with a table or radial-arm saw.
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Old 3rd July 2016, 12:31 AM   #72
mrk7 is online now mrk7  Australia
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bwaslo, thank you for the detailed explanation of the woofer slot concept and other design variables influencing your build. Hopefully the sims hold true so you get that last bit of directivity. Out of interest, if you could, how low would you control directivity to?

Re: Danley's preference for symmetry, I suspect design for manufacture and assembly (DFMA) principles play a big role in his final designs.
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Old 3rd July 2016, 02:09 AM   #73
bwaslo is offline bwaslo  United States
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Quote:
Originally Posted by mrk7 View Post
Out of interest, if you could, how low would you control directivity to
Probably not much below 200Hz, if that low. Room modal effects rule down there.

Though it would be neat if directivity was all the way down into the 40Hz range, to make the wall behind vanish. Like the cardiods some here have played with. I'd hate to lose the bass dynamic range eaten up by all the cancellation cardioid uses, though.
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Old 4th July 2016, 09:17 PM   #74
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by bwaslo View Post
Here's where I'd like to be doing measurements - sadly, the crossover being measured in the picture was a miserable failure from about a month ago, horrible vertical pattern. I live right between two elementary schools, so I can't do outdoor measurements during weekdays till summer break. I'm pretty sure the scary alien noises made during speaker testing would have them sending a SWAT team out on me.... I got a couple of troubled visits from the neighbors the Saturday I took this pic. It's near 100F here this weekend, so I'm not up to dragging out all this stuff until the weather cools again.
Click the image to open in full size.

The jist of saying all this is that the measurements shown earlier were made in a somewhat cramped basement, so they don't go very low in frequency and have some unavoidable reflection interference....
Click the image to open in full size.
Looks like there's an anechoic chamber in Portland, might be worth a look : Research on hearing loss ramps up on multiple fronts press | OregonLive.com

Vance Dickason lives south of Portland, I wonder if this is where he does his measurements for Voice Coil magazine?
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Old 4th July 2016, 09:26 PM   #75
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by bolserst View Post
Yeah, the wax and varnish used is low viscosity so it will wick up in between the laminations.
Vacuum is used if you need absolutely all air pockets removed; a must for HV applications.

Hmmmm....I wonder if some thin CA glue would work for bonding the laminations together thru wicking action?
This would be a fair amount of work, but you could do the following:

1) stick the inductor in one of those bags for sealing food
2) Vacuum out the air with a FoodSaver*
3) Put epoxy into the bag using a syringe. If you're careful, no are will get into the bag

It's a lot of rigmarole, but I think it would be airtight.


* everyone should have a foodsaver, greatest kitchen item ever
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Old 4th July 2016, 09:36 PM   #76
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by Beau View Post
Id love to do one with a seos24 loaded with a Aurasound whisper driver.
Click the image to open in full size.

Here's a frequency response and distortion plot for an Aurasound Whisper mounted on a waveguide that I 3D printed for my car. The blue line is the Whisper's response in "free air", with the back sealed off. The red curve is on the waveguide I made.

I really dig the Aurasound Whisper, but I don't think it's possible to get it to play to 20khz on a horn or waveguide. The problem is that you get a dip and a peak in the octave of 10-20khz. I don't think this is a problem related to the geometry of the horn; I think what's happening is that the Whisper on a flat baffle will "beam", and when it beams, the energy is focused *forward* into a narrow lobe. When you put the Whisper on a waveguide you get a dip around 12,000hz, and then the output comes back up.

I think the rise above 12,000hz is caused by a resonance in the driver.

When they design compression drivers, they design them so that the resonance in the diaphragm adds constructive output in the top ocatve. You can see this in a CSD plot.

In a nutshell, if it wasn't for that high frequency resonance, the response of the compression driver and the Whisper would look closer to a bandpass filter.

It's easier to see this behavior if you look at some 'raw' measurements of compression drivers, particularly at the CSD. Augerpro has published some good ones here. My measurement above is from one of my threads at diyma.
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Old 30th July 2016, 02:19 AM   #77
bwaslo is offline bwaslo  United States
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At long last I got outside to do some measurement on the final crossover. Been delayed by lack of a space (needed to wait till shared driveway was clear), illness (again, but not serious.... germs seem to like me), and a visit by daughter and toddler grandson (a week here, preceded by a week toddler-proofing the house). I don't know how I ever had time to have regular employment.

Anyway, here is the outdoor setup:
Click the image to open in full size.
I wanted to make measurements as fair as I could, with a real wall behind the speaker as it was designed to be used. I did put the speaker up about 65 inches above the hard concrete to try to avoid reflection effects from that.

Here is a plot of the horizontal response curves, every 5 degrees from 0 to 90
Click the image to open in full size.
That's an unsmoothed plot, full disclosure worst case, and you can see it gets pretty ripply on the way-off-axis curves because of reflections off the garage wall behind it when the mic gets over there, and from diffraction off the cabinet edges.
You can also see the deep quarterwave reflection notch due to the space between the baffle and the back wall.

Here it is again with only the 0 to 45 degree curves, also unsmoothed:
Click the image to open in full size.
Here are the same two graphs but done with "ERB" smoothing (which is supposed to mimic the smoothing done by human hearing's Equivalent Rectangular Bandwidth, to better resemble the audble effects:
Click the image to open in full size.
Click the image to open in full size.
Looking pretty good, if I do say so myself.
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Old 30th July 2016, 02:35 AM   #78
bwaslo is offline bwaslo  United States
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Default Vertical curves

Next up, some vertical response curves. First the "going upwards" curves, 5 degrees per step again to 90 degrees off axis, in unsmoothed and ERB smoothed versions:
Click the image to open in full size.Click the image to open in full size.
No lobes worth mentioning (at least not until getting toward 80 degrees of axis), so that's good.

Here are the same curves for "going downwards":
Click the image to open in full size.Click the image to open in full size.
That one is downright pretty. There's no vertical directivity to speak of below about 2.5kHz, of course, but the trend is a nice rolloff.

Here are some of the color plots of the patterns, unsmoothed and ERB (these are un-normalized).
Horizontal:
Click the image to open in full size.Click the image to open in full size.
The horn is nominally 90 degrees (+/-45). The apparent narrowing at higher frequencies is actually just because of the response curve used (rolling off toward HF rather than flat, which seemed a bit too bright to me). Directivity below about 800Hz comes from the spaced slot-fed woofers.

Vertical (nominal 40 degrees down to 2500Hz):
Click the image to open in full size.Click the image to open in full size.
Not as pretty, but about what can be expected with a horn of this dimension. Still, rather well behaved (look at polars from "normal" speakers sometime!) and they play beautifully in a room, without looking like audio nut speakers!
Click the image to open in full size.
(that'a s 32" video screen shown)
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Last edited by bwaslo; 30th July 2016 at 02:42 AM. Reason: formatting
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Old 30th July 2016, 02:54 AM   #79
bwaslo is offline bwaslo  United States
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Last measurement of the day, a distortion sweep. The level is between about 97dBSPL (at bass frequencies) and 90dBSPL (treble frequencies). It gets to about -40dB (1% 2nd harmonic) around 450Hz, but stays around -50dB elsewhere when above 150Hz. Gets to about 3% at 100Hz as the low end starts to roll off. 3rd Harmonic is very nice and low through most of the band.
Click the image to open in full size.
(sorry for the long/skinny plot, forgot to reformat it)
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Old 30th July 2016, 03:06 AM   #80
bwaslo is offline bwaslo  United States
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I'll probably give the design details (crossover and how to attach the midrange to the horn) in blog form so it doesn't get easily lost. I did a minimum/linear phase FIR EQ (with a Linkwitz transform type LF boost since it's being used without a subwoofer), will post the miniDSP files for that in the blog, too. Will try to do a video of a square-wave sweep using that when I work out how I did that before.

I'm starting in on a shelf-ported version next. I just got a new (to me, actually very old) table saw for that project. I made the mistake of leaving the fence from my old saw outside and it seems to have been stolen (ah, city life!). But the new saw has a MAGNIFICENT fence on it, is belt-drive, and is wide enough for up to 42 inch panels, so I think it all worked out well and didn't cost much. (A table saw isn't really needed at all to make the SmallSyns, but will certainly make it easier.... and who doesn't like power tools??)
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