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Multi-Way Conventional loudspeakers with crossovers

Leaky supercardioid mids
Leaky supercardioid mids
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Old 31st October 2015, 08:13 PM   #11
keyser is offline keyser  Netherlands
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Quote:
Originally Posted by nc535 View Post
My friend, a relative of Occam, advises to put the absorber on the wall behind the speaker, instead of as resistance inside the speaker. Absorbing the rear wave is a lot easier than cancelling it, although not nearly so elegant.
Absorbers on the wall is not only a less elegant solution, it is also a lot less effective. A gradient has directivity all the way to its lower cut-off, while an absorber has high-pass characteristics. The most problematic frequency range of a front-wall reflection is the lower hundreds. You need in the order of half a meter of damping material for the absorber to be effective at 100 hertz. Not an attractive solution in my opinion.

Quote:
Originally Posted by onni View Post
2. What driver parameters should be suitable for this type of application? Any examples below 100 USD each for ~7" drivers?
Anton, are you looking to design a passive crossover?

By the way, if I were you I wouldn't use fiberglass or rockwool. Both are presumably carcinogenic.
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Last edited by keyser; 31st October 2015 at 08:16 PM.
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Old 31st October 2015, 09:08 PM   #12
nc535 is offline nc535
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If you only care about 300 Hz and up, which is where Nate achieved directivity, then 6" of fiberglass spaced 2" from the wall will do nicely. Considering the system solution, I would use more than that to help tame longitudinal room modes.

Not to say I don't appreciate Nate's good work; he may well have a room where the simple low tech approaches like absorber or baffle wall don't apply.
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Old 31st October 2015, 10:11 PM   #13
onni is offline onni  Sweden
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Quote:
Originally Posted by TBTL View Post
You need some kind of flow resistor to dampen the 'porting' AND to create (super)cardioid behaviour. Carpet without foam backing is said to work well.

Just curious, is that horn an 18Sound XT120?
I'll measure the fiberglass option first, then look at other materials.

It's indeed the XT120 in the photos (coupled to a Beyma CD10Fe), not in the measurement in the first post though. I liked the polars, but disliked the high sensitivity (noisy with my amplifiers) and crappy transient response.


Quote:
Originally Posted by bwaslo View Post
That's pretty impressive. I wonder if this could be done with a coaxial woofer/horn driver (like the Volts at diysg) to get it all to resemble a point source with directivity?
I agree, decent result from a very simple test. A nice coaxial together with a round (spherical) enclosure with holes could be really nice!

Quote:
Originally Posted by keyser View Post
I have extensive experience with the 'black art' and science of passive gradients. They are difficult to get right, but when you do you'll be treated to much improved transparency and less coloration in the midrange. With a well-optimized cardioid you can achieve rear rejection better than 20 dB. Combine the cardioid with a good waveguide and you can achieve constant directivity to a much lower frequency than would be possible with traditional loudspeakers.

What you need to remember is that you get the best possible rear-rejection the transfer function of the front-wave that wraps around to the back of the enclosure and the transfer function of the back-wave that exits the slots to the rear of the enclosure are identical, besides inversed polarity. The difficulty lies in the fact that you always measure a combination of the front-wave and back-wave. You know that when you get good rejection, both amplitude and phase are well-matched. Whenever the results are less than perfect, it is difficult to tell if the back-wave is damped too much or too little, or if it is delayed too much or too little.

The kind and amount of damping material in the enclosure, the dimensions of the enclosure and the size and locations of the holes all have an effect on the back-wave. You can't really generalize and say that a certain amount of damping material works best, or that a certain number of slots works best. It is the combination of all factors that determines the transfer function.

In my experience you need clean anechoic measurements with a significant frequency resolution to get a good grasp of what is going on. In-room measurements simply won't do. I usually perform my measurement on a large parking lot, where I can get a clean window of about 80 ms.
I'm glad to have you in this thread!

Does the length of the holes (thickness of the MDF) affect the response? Could something be gained from chamfering the holes (0.5 in setback, 19 mm MDF)?

I'm doing the measurements outdoors, closest object (wall) is about 4 m away. That's about as good as I can get.

/Anton
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Old 31st October 2015, 10:21 PM   #14
onni is offline onni  Sweden
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Quote:
Originally Posted by nc535 View Post
If you only care about 300 Hz and up, which is where Nate achieved directivity, then 6" of fiberglass spaced 2" from the wall will do nicely. Considering the system solution, I would use more than that to help tame longitudinal room modes.

Not to say I don't appreciate Nate's good work; he may well have a room where the simple low tech approaches like absorber or baffle wall don't apply.
I have to agree with keyser here. The supercardioid has constant directivity through a fairly large frequency spectrum, albeit not with a very narrow pattern. The side wall reflection is therefore reduced and the sweet spot should be wider.

I would not consider 8" to be thin, it would look quite weird in my living room. I tried to introduce a 4" thick absorber behind the speakers and got a no go from wifey some time ago. I'm guessing that a 0.5 sq.m slab is slightly too small to have desired effect and getting something larger than that on the wall would be difficult.

/Anton
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Old 31st October 2015, 10:24 PM   #15
onni is offline onni  Sweden
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Quote:
Originally Posted by keyser View Post
Absorbers on the wall is not only a less elegant solution, it is also a lot less effective. A gradient has directivity all the way to its lower cut-off, while an absorber has high-pass characteristics. The most problematic frequency range of a front-wall reflection is the lower hundreds. You need in the order of half a meter of damping material for the absorber to be effective at 100 hertz. Not an attractive solution in my opinion.



Anton, are you looking to design a passive crossover?

By the way, if I were you I wouldn't use fiberglass or rockwool. Both are presumably carcinogenic.
I'm going completely digital (nanoAVR, 8 channels)

What would you recommend to introduce resistivity?

/Anton
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Old 31st October 2015, 11:22 PM   #16
onni is offline onni  Sweden
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Default Drivers

Here are some drivers I've found that look decent.

The only specific parameter that I can think of that is important (when compared to a closed box, and used as mid) is that I want a large Xmax, correct? I would like to be able to rear mount so that a speaker grill (cloth) could be attached directly to the baffle. Intended crossover around 1.5 kHz.

Faital Pro 6FE100
Cheap
5.25 mm Xmax
Rear mounted
Discrete looks
Flat to above 3 kHz
Click the image to open in full size.

Click the image to open in full size.

Seas CA18RLY
Not expensive
5 mm Xmax
Discrete looks
Flat to above 2.5 kHz
Seems popular in the diy community
Click the image to open in full size.

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Seas ER18RNX
Slightly expensive
6 mm Xmax
Discrete looks
Flat to above 3.5 kHz
Click the image to open in full size.

Click the image to open in full size.

Wavecor WF168WA02
Not expensive
? mm Xmax
Discrete looks
Flat to above 2.5 kHz
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Leaky supercardioid mids


Dayton RS180P
Slightly expensive
6 mm Xmax
Slightly aggressive looks
Flat to above 3 kHz
Click the image to open in full size.

Click the image to open in full size.

Monacor SPH-170
Not expensive
3 mm Xmax
Discrete looks
Flat to above 3 kHz
Inverted surround should work well for rear mounting
Very positive review in Klang+Ton
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Monacor SPH-175HQ
Not expensive
5.5 mm Xmax
Discrete looks
Flat to above 3 kHz
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Any one of those that look good for my application?

/Anton
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Old 1st November 2015, 09:25 AM   #17
keyser is offline keyser  Netherlands
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You lose up to 6 dB per octave due to gradient cancellation. Therefore you'll have to boost lower frequencies. Most hifi drivers require a lot of power to drive them to reasonable excursion in the lower hundreds. Look for pro drivers with a resonance frequency close to the lower end of the bandwidth. Then the driver doesn't draw as much current because of the rising impedance at resonance. Suitable drivers generally have low Mms and low Cms. You don't necessarily require very large xmax, because the volume displacement isn't very large at those frequencies.
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Old 1st November 2015, 11:11 AM   #18
onni is offline onni  Sweden
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Quote:
Originally Posted by keyser View Post
You lose up to 6 dB per octave due to gradient cancellation. Therefore you'll have to boost lower frequencies. Most hifi drivers require a lot of power to drive them to reasonable excursion in the lower hundreds. Look for pro drivers with a resonance frequency close to the lower end of the bandwidth. Then the driver doesn't draw as much current because of the rising impedance at resonance. Suitable drivers generally have low Mms and low Cms. You don't necessarily require very large xmax, because the volume displacement isn't very large at those frequencies.
Doesn't the excursion increase heavily if I'm boosting the lower frequencies?

Of the 7 drivers in the last post I'm guessing the Faital Pro 6FE100 was best suited (91 dB sensitivity). How about these:

Faital Pro 6FE200
Fs: 120 Hz
Sensitivity: 95 dB (1 W/1 m)
Xmax: 4.67 mm
Rear mountable
Cheap
Click the image to open in full size.

Click the image to open in full size.
Slightly jagged response.

Faital Pro W6N8-120
Fs: 100 Hz
Sensitivity: 95 dB (1 W/1 m)
Xmax: 5 mm
Rear mountable
Sligthly expensive
Click the image to open in full size.

Click the image to open in full size.
Not extremely flat, but should be fairly simple to fix with PEQ.

Faital Pro 6PR110
Fs: 100 Hz
Sensitivity: 96 dB (1 W/1 m)
Xmax: 2.75 mm
Rear mountable
Sligthly expensive
Click the image to open in full size.

Click the image to open in full size.
No sharp dips.

Beyma 6G40Fe
Fs: 102 Hz
Sensitivity: 94 dB (1 W/1 m)
Xmax: 3.1 mm
Rear mountable
Sligthly expensive
Click the image to open in full size.

Click the image to open in full size.
100 dB scale and few datapoints -> I can't really comment on flatness... Slightly troubling dip at 1 kHz.

Beyma 6P200Fe
Fs: 65 Hz
Sensitivity: 93 dB (1 W/1 m)
Xmax: 5.5 mm
Rear mountable
Sligthly expensive
Click the image to open in full size.

Leaky supercardioid mids

Seems fairly flat.

/Anton
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Old 1st November 2015, 11:32 AM   #19
keyser is offline keyser  Netherlands
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Quote:
Originally Posted by onni View Post
Doesn't the excursion increase heavily if I'm boosting the lower frequencies?
Yes it does. However, unlike at bass frequencies, you are more likely to run into thermal issues before you run in to problems with respect to excursion. Remember that for the same acoustic output excursion doubles for every halving of frequency. At low frequencies you need very little power to get a driver to its xmax. If you want to drive a typical hifi 7" driver to xmax at 100 hertz you might need 150 watts or more.

If your design requires large excursions (think more than about 8 mm p-p), I would advise using 8" drivers instead. You not only get more volume displacement, you also get a greater distance between front and back, for less cancellation.
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Old 1st November 2015, 11:46 AM   #20
Max Headroom is offline Max Headroom  Australia
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Quote:
Originally Posted by Face View Post
Try filling the enclosure with different amounts of denim(or fiberglass) insulation for better separation down low.
Never use fiberglass in a vented enclosure.
Open the curtains so the sun shines across your speakers and you will see little sparkles on every drum beat .

Dan.

Last edited by Max Headroom; 1st November 2015 at 11:48 AM.
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