Mirage's Latest Crazy Idea - Baffle-Less 2-Way No Xo - diyAudio
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Old 9th August 2014, 05:19 PM   #1
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Default Mirage's Latest Crazy Idea - Baffle-Less 2-Way No Xo

Build goals:
Minimise all possible cabinet and driver resonances.
Phase and polarity coherence.
Simplicity of signal chain.
No components between drivers and amplifier.
No electronic crossover. Capacitors have phase changes over FR.
Soundstage, midrange, tonal accuracy and no boxiness.
Vocal realism.
Smaller size than a large OB.
More bass than a single driver, my preferred setup is a single driver.

I hunted down some old distressed window frames - not faux weathered as you see in some retail establishments, but really weathered, set outside in sun and rain. The glass is gone and in the corners are going eye bolts.

Hanging from a combination of small link chain, elastic bungee bands, and cantilevered 50mm long by 4mm dia bolts will be 2 drivers.

One 2 inch wide range-ish
One 15 inch woofer

The two inch is chosen for diaphragm size and baffle interaction. The baffle being the rectangular face plate of the driver. With free-hanging NOB the driver response will ring and fluctuate above a certain point to beyond audible range. This will cause large dips in FR of -/+6dB or more. With a 2 inch driver the first dip is elevated to ~14kZ. I have no hearing beyond 13.5kZ. There will be a +7dB hump centred on 4500hz, dropping to 0dB at 1750 and 12000.

If the 12kHz notch proves to be too much, then a very small circular baffle will be attached to even out the FR from 7k-14k.

If a 3 inch or 4 inch driver is used the ringing drops well into the upper mid-range. This can be reduced by placing the driver in a circular baffle and positioning the driver off centre on the baffle.
If an actual tweeter is used the FR is insufficient to roll off properly and provide upper mid-range support.

The 15 inch is chosen for its upper roll off FR. Various drivers with upper limits of 800-5500 are available.

The 2inch will roll off with no baffle at 1750 to mechanically and acoustically crossover to the woofer.

There will be no Xo, no high or low pass filter, not even a capacitor.

Drivers will be in parallel, presenting a ~4 ohm load.

The 15 inch rolls off on the higher frequencies first dip at 1750 hZ with a 381mm driver in a 430mm circular baffle, the baffle being its own mounting ring. Selecting a driver that rolls off at 1000-2000 will take advantage of the natural response of the driver and get it out of the way just when baffle ringing begins at 2k and above at 4k,5.5k, 7k and so on. This will be based upon driver size and a round mounting plate.

Lower end roll off is at 0dB @ 75 and is -3dB @48. This includes room placement, boundary reinforcement and ideal distance from side and back walls.

This technique can work with smaller drivers, but they have extended FR and would become shouty without a crossover. 10 inch drivers roll off ~2750 which is ideal but they mostly have FR to 5kHz in most cases and are unsuitable.

Angling of the drivers to the listening seat will be done by the support bands to alter the FR to reduce shoutiness which will be a problem if the 1k-4k range is not properly matched.

As with most of my builds there will be little bass below ~250hZ and this is desired, wanted and intentional. This is a feature, not a bug.

Measurements? No.

Room boundary reinforcement will give the bass driver some lift as it will be near to the floor. Modeling suggests usable bass to ~48hZ, more than ample for my tastes.

Future tweaks include:

-Two frames, bass on floor, mid/tweeter in its own frame supported separately.
-Sound proofing on the spider and frame of the drivers, placing the damping facing OUT to absorb reflections.
-Possible addition of baffles around the tweeter and woofer to smooth response and reduce ringing.

I look forward to the comments.
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Old 10th August 2014, 02:20 PM   #2
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The response varies little, what happens is that it moves down the FR curve as the size of the driver increases.
Without eq, DSP, a crossover, or any baffle this makes the design impractical
unless a small circular driver or rectangular diaphragm (no back wave cancellation) is used for the highs.

Room boundary affects smooth out the FR, graphs from Edge.

Widerange small 2in-2.5in drivers used as tweeters, "crossover" point is due to lack of baffle and the drop
in FR as a result.

63 mm piston on 78 mm square faceplate, no baffle.

Click the image to open in full size.

43 mm piston on 53 mm square faceplate, no baffle.

Click the image to open in full size.


15inch woofer:
381 mm piston on 430 mm round faceplate, no baffle.
This driver chosen to roll off beyond 1500-3000 so that it has no FR remaining when the ringing resumes.

Click the image to open in full size.

Last edited by miragem3i; 10th August 2014 at 02:27 PM.
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Old 10th August 2014, 03:54 PM   #3
Dissi is offline Dissi  Switzerland
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Hi Mirage,

Trying an unconventional approach always is fine. But you inevitably get confronted with some physical facts. Even a 15" woofer does not play below 100 Hz at sufficient level without EQ, the frequency response is very ragged due to circular edge diffraction and the 2" fullrange driver is hopelessly overdriven by low frequencies without a high-pass filter. I unfortunately have no idea how to overcome these problems.
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Old 10th August 2014, 04:30 PM   #4
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Could be amazing if you get it to work. ;P
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Old 10th August 2014, 10:57 PM   #5
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Quote:
Originally Posted by Dissi View Post
Hi Mirage,

Trying an unconventional approach always is fine. But you inevitably get confronted with some physical facts. Even a 15" woofer does not play below 100 Hz at sufficient level without EQ, the frequency response is very ragged due to circular edge diffraction and the 2" fullrange driver is hopelessly overdriven by low frequencies without a high-pass filter.
I see that I shall have to repeat my stance on bass response for every post I make.

Oh well.

From the OP at the beginning of this thread I wrote...

Quote:
As with most of my builds there will be little bass below ~250hZ and this is desired, wanted and intentional. This is a feature, not a bug.
I also prefer quiet listening volumes and other things that most here do not prefer. Thus over driving the 2 inch shall not be an issue.

With small baffles and an off centre placement for the 2/3/4 inch driver, smoothing of the FR occurs nicely and the XO point can be manipulated by mechanical means alone. I have been spending several hours running various driver piston sizes on various circular baffles, and working with a proper baffle size for a given driver, and placing the driver off centre, the FR can be smoothed to +/- 1dB in some cases from 2000-20000. There is always a hump of 2-4dB immediately before the rolloff below the "cutoff frequency" but if done correctly and mated with a driver that has FR of 50-1200 to 3000, the dropping tweeter response due to baffle loss will cross with the dropping woofer response due to driver limits and make a fairly every FR SQ.

I have no fewer than 8 different pairs of drivers arriving this week, so I shall have some results to post soon.
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Old 13th August 2014, 02:57 PM   #6
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Received the 2 different 2 inch drivers today, mocked up with a 3 inch.

The 2 inch will make a fine tweeter. Woofers should be here soon.

One of the 3 inch drivers (orange cloth surround, DQ30TZF-03, 118.2 Fo, AIRS, 4 Ohm) is in the door sized baffle and sounds very good. It would make a fine tweeter in a box or baffle with a larger driver and a crossover. An Xo point of 300hz would free it up and dump the congesting frequencies into a woofer. Nice high FR, but a bit elevated as the graphs reveal).

Click the image to open in full size.

One thing that occurred right away is that the higher quality drivers with more FR cannot be played even at the modest levels I listen as the bass response, previously lacking on cheaper wide range units, causes the driver to max out and become congested very easily with lots of midrange in a piece. Let it Bleed being a surprise as I had to reach for the volume and turn it down.

Rock that is pre-1990 sounds fine, but put anything complex or modern in the mix and the 3inch wideranges cloud up very quickly and at low volumes.

Yet another reason I prefer no bass and quiet volumes. With drivers that do not attempt bass they are naturally clear of the stresses and strains of trying to do it all.

But the phase, polarity, time alignment and soundstage issues arise as always whenever I have a build that is not one driver.

The drivers are all Chinese made, G-Audio. Coste, AIRS, HiVi and their variants. Huge selection in the 3 inch space for small bookshelf DIY.

I am thinking that once I get done playing with various setups that a 2-way with a Mark Audio Alpair 7 as the tweeter crossed to the 10 as a woofer may make a nice system. OB or boxed.

But, again, that means a crossover and those have so many audible artifacts...
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On my builds there will be little bass below ~250hZ and speakers/amps are intended for quiet listening volumes - these two qualities are desired, wanted and intentional. They are features, not bugs.

Last edited by miragem3i; 13th August 2014 at 03:04 PM.
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Old 13th August 2014, 06:13 PM   #7
OllBoll is offline OllBoll  Sweden
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Caps doesn't cause phase changes, the impact of the caps on the frequency response causes phase changes.

What of the phase changes due to the low frequency roll offs? Or phase changes due to the falling off axis response of the woofer? If you really want a linear phase speaker then why not just buy a FIR capable DSP and do it that way?
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Old 13th August 2014, 07:31 PM   #8
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Quote:
Originally Posted by OllBoll View Post
Caps doesn't cause phase changes, the impact of the caps on the frequency response causes phase changes.

What of the phase changes due to the low frequency roll offs? Or phase changes due to the falling off axis response of the woofer? If you really want a linear phase speaker then why not just buy a FIR capable DSP and do it that way?
I prefer simple signal chains and eschew DSP.

One of my design mottos is "Simpler is better".

I am listening to Miles on one of the wide range 2 inches and a 3 inch that rolls off ~5500, have the M-Cap 4.7uF measures 5.32 in as a high pass filter and this sounds very good considering it is in a cardboard baffle at my PC desk.

Total price: 26.75 Euro.

I like this implementation of widerange as tweeter and larger widerange or woofer as bottom FR.

I enjoy listening to my boxed 2-ways that are on stands in the living room, but not seated in front more as something to play music around the house. Once I sit down in front of them, the soundstage and phase issues distract from the enjoyment of the music. So, I use that system for its strengths and do not attempt to have it do all things. Similarly the OB and NOB have limited slam and bass but excel at soundstage and I use that system for its strengths as well and do not have it do all things.
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On my builds there will be little bass below ~250hZ and speakers/amps are intended for quiet listening volumes - these two qualities are desired, wanted and intentional. They are features, not bugs.
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Old 13th August 2014, 08:17 PM   #9
badman is offline badman  United States
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Awful idea IMO. Why on earth would someone build a speaker with a 15" that can't play loud or low and is likely to burn up the 2" every time someone sneezes? Your misgivings about the crossover are driving you to accept a much bigger set of problems than even a poor crossover would introduce, and there's no reason the crossover has to be badly done.
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Old 13th August 2014, 09:49 PM   #10
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Why not go with something like a Markaudio Alpair 10.3? Or even the Alpair 7 for even more magic?

If you don't need to play super loud and if you don't want bass under 250hz and your hearing only goes up to 13.5kHz I don't see how a Markaudio driver can't be perfect for your needs.
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