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Multi-Way Conventional loudspeakers with crossovers

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Old 7th July 2012, 06:11 PM   #91
tvrgeek is offline tvrgeek  United States
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Flaring ports has several advantages. The best description to understand it were some drawings in David Vizzard's book on modifying the BMC-A engine. Basically, without at least a 270 degree flair and initial taper, the effective diameter is actually much smaller, but the mass in the port remains the same. This is a recipe for chuff-chuff noises and also requires differenced port length calculations. When feeding old British sports cars, the correctly designed "velocity stacks" meant as much ad 10% more power. This is fluid dynamics. The math is way the heck beyond me. I use a sim to get close and tune to measure. I would be concerned with the above picture that you will get wind noises by the relative small opening on the box end compared to the mass of air in the port. You have also built 4 Helmholtz resonators ( notch filters) in the cavities top and bottom unless you block the inlet to them. Only your ears will know for sure. You are using unconventional approaches, so we are just guessing until you listen to them. I'll take results over theory any day.
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Old 7th July 2012, 07:52 PM   #92
tvrgeek is offline tvrgeek  United States
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I am just not getting the low end response out of the FF125wk as the model suggests.
Even the 11L boxes, they roll off at 200. The 6800 resonance is really bad. It is interesting to compare ARTA to TrueRTA. As bad as the breakup is, I am wondering if 5K crossover is too high. The harmonic distortion of this guy is pretty high.

To confirm your box building, the big wad of stuffing does help measurably in the 600 t0 800 region.
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Old 7th July 2012, 08:00 PM   #93
ODougbo is offline ODougbo  United States
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No low end response....Well don't know now, maybe on to something with the flare ports. The bass is significantly stronger around 55hz.

The 1st attempt only took a few minutes, but with the results I can cut some filler blocks with more of a horn shape.

Okay, will fill the voids.
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Old 7th July 2012, 09:49 PM   #94
tvrgeek is offline tvrgeek  United States
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I just finished doing my own TS measurements on the Fostex. Qes came in at .56 and Qms at 7.35. Fs was 72 with VAS at 7.3L. Not as far off as I have seen. Usually it is VAS they lie like a dog about but this is only a couple of percent. The frequency response on the spec sheet, though very small, is closet to what I measure than the model. Of course, it does not show baffle step but the bad breakup at 6800 is there for all to see. I can't see how anyone could consider this driver a full range. A 200 to 2K is more like it. Even that, the harmonic distortion is about 3.5% This means the 11L boxes are tuned at 60 Hz. I think I would try them at 75 Hz. I am going to play with the electronic LR-4 crossover between 3 and 4K to see if it handles the resonance OK. Not as high as I want, but well into the easier range for a dome tweeter. Too low for a ribbon. I can try LR6, but that does force one to stay electronic.
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Old 7th July 2012, 10:02 PM   #95
tvrgeek is offline tvrgeek  United States
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I did not get the concepts across well enough, so let me try again. This is hard to explain without a picture. It has nothing to do with the length of the port being tapered. Remember, air is going both ways in the port. It should be symmetrical.

The sharp edge at each end causes turbulence that effectively narrows the size of the port. The radius reduces this turbulence. Each sharp edge adds about 10% to the "perfect" port length. To make it even more complicated, it varies with velocity. Flaired ports are both shorter and more consistent.
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Old 8th July 2012, 10:36 AM   #96
ODougbo is offline ODougbo  United States
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It's not that bad..have you ever heard a speaker image better?

2k? That sounds really low

It's a nice little speaker, lacking a little low - lacking a little high (it must be.........)

I did understand what you saying about the flare ports, yes all guess work at this point. Going to spend a little time on them and see if I can enhance the bass (yes yes, considered cheating in the HyFy world).


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Originally Posted by tvrgeek View Post
I can't see how anyone could consider this driver a full range. A 200 to 2K is more like it. Even that, the harmonic distortion is about 3.5% This means the 11L boxes are tuned at 60 Hz. I think I would try them at 75 Hz. I am going to play with the electronic LR-4 crossover between 3 and 4K to see if it handles the resonance OK. Not as high as I want, but well into the easier range for a dome tweeter. Too low for a ribbon. I can try LR6, but that does force one to stay electronic.
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Old 8th July 2012, 11:33 AM   #97
tvrgeek is offline tvrgeek  United States
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Heard a speaker image better? Yes. But it is not just the speaker that is the magic. It is the room and room treatments. I can bring my little Dayton RS/Vifa's out and you will probably not like them. Crossover is not as good as it can be and the tweeter is,well a $25 tweeter. But, where they are sitting with my panels and room arrangement, the imaging can cause one to do a Tex-Avery. That is the eyeballs pop out and jaw extend to the floor Wil E. Cyotee stuff when sounds come from outside the speaker widths and from behind the wall. The edginess and lack of top octave of the Fostex stops them cold. I think they have great potential. For me, full range is not it.

On the other hand I was checking out the current market and listened to some of the current $3 to $6K speakers out there. In the room where they had them, all of the imaging was point-source from the box or a narrow line between them. No depth, no height.

I was thinking last night about modifications to the driver. One could dope it with a very rigid material, raise the breakup frequency, only slightly increases mass, lowering Fs and increasing VAS. Or, dope them with a very low modulus to try and control the breakup, probably increasing the mass even more and moving their roll off even lower. I may play with this on some much cheaper parts first. Fostex is not a fool, so making it worse is probably much easier than making it better.

Why a low crossover? To get far enough away from the breakup modes. The steeper the crossover, the higher. I don't do 4th order passive. Just too complicated and expensive. So I would prefer to be two octaves away. Hooking up my DCX today to see what dialing in some BSC, 6th LR crossover and the XT25's will sound like. These 11L boxes may be a candidate for a small side firing woofer. 50 to 200. They behave so large as the tuning does very little. Almost IB. I added my blocks to bring them down to 7.5L and played with smaller ports. Nothing helped much.

More java and time to get busy. All out of primer for the SEAS boxes.
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Old 8th July 2012, 02:38 PM   #98
ODougbo is offline ODougbo  United States
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I worked on this a bit today, I cut some wider boards and cut them horn shape. They lowered the tuning quite a bit; so just kept trimming them as needed to bring it back up.

With the lower tuning (low 50s) the bass rolled off more smoothly, so as I trimmed the boards I stopped at 60hz.

This is where I starter to hear the "loud" uneven sound I heard yesterday around 55hz.

The roll off is somewhat even now (tuned at 60hz).

(Fostex does recommend 57hz in a 9 liter box)
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Old 8th July 2012, 03:46 PM   #99
tvrgeek is offline tvrgeek  United States
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Did a bunch of impedance sweeps and then crunched the numbers. ( I need to build a spreadsheet for this before I wear out my D'Appolito book)

The 11L box is in fact tuned at 67Hz. By blocking some of the port, I could reduce the tuning to 44Hz. Reducing the box to 7.5L I could tune between 64 and 532 Hz. Of course, lowering the tuning is the opposite direction we need as we are looking for a broad hump before rolloff 100 to 200Hz If I were to pick an alignment from comparing the models with the measurements, I would go 7.5L at 75Hz.

I still don't know where you are going with that horn shaped port. Other than looks, what is it you are trying to achieve?
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Old 8th July 2012, 05:05 PM   #100
ODougbo is offline ODougbo  United States
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In a few words... trying to warm the speakers up a bit, a little more umpf in the low end.

I made 4 pairs of boxes, I think this pair might be heading in the right direction.

Will be gluing sides and trimming later today.

One thing nice about this, I can add damping material in the top and bottom of box, no worries about it getting into the slot.

*The square boxes you have...could cut an angle on back(s) making them smaller.
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