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Multi-Way Conventional loudspeakers with crossovers

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Old 20th February 2019, 02:46 PM   #791
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Juhazi View Post
^Try this. Still, that is estimation. A tube will always have standing waves too.
Volume Calculator For Closed Loudspeaker

Port tuning should be tested in the final box with all bracing and drivers conencted. If length allow, it would be easy to change the straight part after the 90¤ bend.


We already know the port tuning. My question was "how can we fit a bent tube port (or two) into the Monkey Coffin?" The way I see it is that the geometricak constaints will be a problem. Either the bent ports are too shorting bend around the woofer and upwards, or their diameter gets too big. If someone finde a solution, please show us a drawing that is to scale.

Apart from that I dont think it will be possible to implement KaffiManns rule of a woofer/port distance larger than 1/2 of the longest enclosure dimension using bent tubes below the port.
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Old 20th February 2019, 06:26 PM   #792
Juhazi is offline Juhazi  Finland
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Subwoofer Vent Length Calculators - Diameter of Vent, Number of Ports, Volume of Box, Tuning Frequency, End Correction Factor

This calculator gives around 25cm length for double ¤7cm vents. The angled tube in front wall and straight pipe 15cm up - means next to driver's midline. I wonder if that would be doable. It just has to be tested in a proto. How about 45deg angle?

I am happy that I don't even try to design BR speakers for myself!
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Old 20th February 2019, 09:05 PM   #793
Qts is offline Qts
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5cm tube for 12" woofer? Eight of them could be good.
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Old 21st February 2019, 06:55 AM   #794
KaffiMann is offline KaffiMann  Norway
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Originally Posted by mbrennwa View Post
That would mean.that a port below the woofer is too close. I guess the only solution within the limits of the current Monkey Coffin design would be to put the port in the upper half of the box then. Front baffle is out, so: rear, top, or side of enclosure?
Correct.
I have done some experiments with ports on all possible sides of enclosures, front ports are just better.
I had an idea that ports on the sides and top would be brilliant, they are not.
Same with rear ports. It seems impressive until you start listening for minor details in phase and the way the sound behaves between reflective surfaces.

Front ports are just better, particularly if they are a bit away from the floor/ceiling = lesson learned after a lot of time and wasted building material.

No directivity in bass?
Allright, maybe you can say that based on SPL alone looking at a SPL meter, but if you start looking at what the signals (original vs reflections) actually are, how they relate to each other, and how you perceive them.
Then there most definitely is directivity in bass.

You're more than welcome to either verify or disapprove this. But it really is quite simple, no magic involved.
Cheapest and easiest way would be to just make a box with a woofer, port on front, for a "subwoofer" or what you want to call it.
Xo at let's say between 120- 200hz if it behaves nicely a bit further than that, then move the box in various locations in your room. Try aiming the woofer+port into corners, at the ceiling, behind a couch etc.
Then try putting it on a shelf next to the speakers firing back at the wall, firing up at the ceiling, then directly at you in listening position.
Between each and every placement, be sure to walk around in the room, listen to music extensively, try to hear the difference in sound quality, if it's "muddy" or "thin" or "tight" in the various locations/directions all around the room.
See which you prefer.

I did it the hard way, it was more expensive, and involved more sawdust and time.

My conclusion: What some may call "tight" bass, might relate to less phase variations, and is usually the most direct sound from the speaker.

*Flamesuit on*

Last edited by KaffiMann; 21st February 2019 at 06:57 AM.
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Old 21st February 2019, 04:58 PM   #795
Brett is offline Brett
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^^ It's your claim, and I don't believe it, so show some empirical evidence to back it up. It's not for others to disprove your assertions, but for you to prove them.
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Old 22nd February 2019, 06:47 AM   #796
Boden is offline Boden  Netherlands
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Kaffiman,


I think you are mixing up a) directivity in bass and b) the fact that the port forms a second source. Bass below say 100 Hz is certainly omni.

The problem with ported enclosures, as I see it, is twofold: firstly there are 2 physically separated sources, that are partially out of phase, and then there are the pipe/port resonances, which often in level are several dB above the speaker passband level at anywhere between 300 and 1000 Hz.

I do not think one can generalize about port placement, although my personal preference is to have them at the back, attenuating the port resonance peaks. YMMV.
Actually, a ported enclosure that reaches into the realm of the 20-30 Hz band is somewhat of contradiction, because optimal in-room placement of the entire system is often at odds with proper in-room placement of the bass driver. See the attempts of AR with the AR9 or the Roy Allison designs.
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Old 22nd February 2019, 08:29 PM   #797
KaffiMann is offline KaffiMann  Norway
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Brett, it is my claim, and it is the way I see it. I do not have the measuring equipment and/or time to back it up. Might be possible to get something tiny but useful out of the umik though, but I my surrounding environment is not suited for this kind of testing. Small kids, no time at all.
In fact, I just decided to kick hundreds of $ away in DIY parts because I just do not have the time, went and ordered new amps and signal processing off the shelf, feels like a lost battle...

Boden, I understand your view, and it is indeed the established opinion that the sound of bass under 80hz is omnidirectional, and I do agree it is hard (impossible) to localize if you put the sub in a location away from the main speakers. But it doesn't sound good, it sounds like those young peoples cars with no concept of tuning their new and expensive aftermarket car stereo. It's not in sync with the rest of the sound.

Last time I went to the parents of my wife's sisters husband, I asked the man of the house if there was some kids next door with a big sub tuned to death. He proudly proclaimed it was the small 10" closed sub in the corner making all the ruckus. I could not tell if it was random noise from a neighbouring house or a badly tuned sub behind a couch in the same room connected to the tv!

My first clue was when I built the 320liter TH, I just could not for the life of me, make it sound like it was part of the system, it was impressive, gave a lot of "wow" moments. But I just had this feeling something was "off", comparing it to something like a live drum kit after I went to a concert with no extra sound reinforcement I started hunting for the same "feel".

Like I said, I've had ports on all sides of enclosures. And after eventually getting the port to the front, and off the floor, for me, there is no going back.
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Old 23rd February 2019, 07:19 AM   #798
mbrennwa is offline mbrennwa  Switzerland
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KaffiMann, I have no doubts about your observations. However I dont think your interpretation in terms of bass directivity is correct. It is well established physics that (low) bass from a point source is omnidirectional. Maybe your observations are related to group delay (as discussed much earlier in this thread)?
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Old 23rd February 2019, 07:46 AM   #799
Guerilla is offline Guerilla  Denmark
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A bookshelf speaker does not mean that its suitible for placing in a bookshelf. This should be avoided, and you should not design your speaker for such a placement. If you really want to place a speaker in a bookshelf you should make something completlely different
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Old 23rd February 2019, 08:23 AM   #800
KaffiMann is offline KaffiMann  Norway
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Quote:
Originally Posted by mbrennwa View Post
[LIST=1]Maybe your observations are related to group delay (as discussed much earlier in this thread)?
It's all related, one way or the other. And increasingly so when the frequency goes down.
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