Pipedream

[johnny5jz]

This is kind of a weird project, that I am not 100% sure they will work the way I hope. That is part of the reason for the name, because it may be a pipedream that they actually sound good. I have always been intrigued by the LXminis, but not a big fan of active crossovers. I also don't have any duplicate amps to run them properly. I also really like the idea of an omni speaker, and an open baffle speaker.
The other downside to the LXminis is the bass output. If a speaker doesn't play low, I generally don't like it. Bass is important to me and I like to integrate my subs as low as possible when I run them. This speaker uses 6" PVC instead of 4" and I have them ported and tuned to an F3 in the lower 40s. I used the RS180S-08 driver since I had them on hand, and used the FaitalPRO 4FE35 full range driver. I chose the FaitalPRO for a couple of reasons. It was reasonably priced, has high sensitivity(not really needed for this project, but good for future projeccts), and I would like to use it in a 3-way speaker this fall. It has a nasty peek at 8k, that needed a substancial not filter. For a 3-way, I hope to cross around 3-4k and hopefully won't need to worry about it. I also needed to add a notch filter at 2.3khz due to the dipole peak created with the open baffle use of the full range. The rest of the crossover is pretty simple. Due to the two notch filters, and the high sensitivity of the full range driver, the impedance curve is pretty ugly. Hopefully it won't pose any issues. I have redone this crossover about 5 times, and remeasured the drivers a couple of times trying to make sure they are ok due to the fact I have never worked with open baffle. One thing you will see in the frequency response graph is a big dip at 211hz. This is due to standing waves within the cabinet. I did not do anything to the cabinet (PVC tube) prior to measurements. I have since fixed this with stuffing and batting, but may need a bit more tuning. It looks like the woofer will do abbout 103db in this box before xmax, but I am not sure in an omni setup like this, if it will get that loud. So far testing with bass tones, it sounds pretty good. It may be a little bit before I order all oof the crossover components, but I am excited to listen to it.

[johnny5jz]

Here are the measurements and box data.

[johnny5jz]

Just to get an idea what kind of a mess I started with, below if the measured data.

[johnny5jz]

I wanted to cross a little lower, but because there is no baffle on the 4" driver, it starts it's 6db per octave drop around 1600-1800hz. The drivers worked together really well around 1500hz. The LXminis cross at around 700hz, but that wasn't going to work here. I tried it, but it looked terrible. I got the best phase integration where it is now. I even tried a first order on the full range since there is already a natural 6db per octave slope due to the nature of open baffle, but the impedance curve was even worse.

[DeZZar]

Cool. Good to see someone try something a little different. Curious what you think of the sound once you get them into a listening session.

[Wolf]

I must say, you really achieved a lot there... A LOT of attenuation.

Are you really sure you have to kill that much output? 25 ohms in series is a lot. The other thing I see is the 2.7uF cap paired with a 4mH coil? The 25 ohm resistor will dictate more copper and less cap usage and make it more costly than a lesser load impedance. The 33 ohm resistor for the lower peak in addition to the 25 ohm attenuator seems excessive too. Maybe broaden the cap and coil to a bit wider and less of a resistor?

I'm only seeing about 10dB of loss required from FR to woofer, so it should not take such drastic attenuation to get there. What you have achieved LOOKS good on paper, but that's about all I can say other than be a bit cautious of how much cut is practical.

Best regards, keep us posted, and let us know how it sounds,
Wolf

[johnny5jz]

Wolf, I totally agree with you. I have played with a few layouts, and this one looks better than others I have tried. I am not ready to order components for the exact reasons you have listed. I am going to keep playing with it and see where I end up. Sent from my SM-G973U using Tapatalk

[johnny5jz]

I decided to scrap the crossover I had and start completely over. I kept doing a save as and modifying the crossover, and I am not sure where I was headed. I think I came up with something much more reasonable this time.

[djg]

LXmidis? Visually very similar to the Linkwitz design. I built a pair of LXminis so I have the advantage of the design instructions which are proprietary. Is your main tube heavily stuffed? Is your mid/tweet tube stuffed?

Have you looked at the response of the LXminis? It is anything but flat.

I know next to nothing about speaker design but I love building them. I ended up with a used Adcom 4 channel amp and a single Dayton 8" dsp sub. I also built DIYaudio passive crossover for the LXminis by Nelson Pass.

It all wasn't that expensive but it was spread out over a couple of years.

Good luck. I have seen a few designs with this arrangement.

[Wolf]

That looks a lot better from an average components perspective. If you wanted it flatter in the xover region, 3rd order electrical on both might help you out.

Later,
Wolf

[johnny5jz]

LXmidis? Visually very similar to the Linkwitz design. I built a pair of LXminis so I have the advantage of the design instructions which are proprietary. Is your main tube heavily stuffed? Is your mid/tweet tube stuffed?

Have you looked at the response of the LXminis? It is anything but flat.

I know next to nothing about speaker design but I love building them. I ended up with a used Adcom 4 channel amp and a single Dayton 8" dsp sub. I also built DIYaudio passive crossover for the LXminis by Nelson Pass.

It all wasn't that expensive but it was spread out over a couple of years.

Good luck. I have seen a few designs with this arrangement.

My main tube is actually ported, but will need to be heavily stuffed. I am working on that also. I did stuff the tube behind the full range like the LXminis. I am not really trying to copy them exactly, since there are a few changes that I wanted to make. I did want to hear what an omni speaker and open baffle sound like.

Wolf,
I may try third order, but my component count is getting quite high. I may just give it a try and tweak from there. Either way, it should be fun.

[johnny5jz]

I gave it one more refinement, and I am finally comfortable enough to order parts and see what it sounds like. I should have it put together in a week or so. I am going to work more on tuning the cabinets now to get rid of the standing waves. It doesn't show up in the overall impedance plot, but it does when I measure the woofer alone. It matches the dip at 211hz, and the next 2 dips as you move up.

[4thtry]

Looking at the dip at 211Hz and the next two dips up, my initial reaction would be that these are listening room resonant modes and not standing waves within the cabinet (internal). Where did you place the microphone when you made these measurements?

Bill

[johnny5jz]

Looking at the dip at 211Hz and the next two dips up, my initial reaction would be that these are listening room resonant modes and not standing waves within the cabinet (internal). Where did you place the microphone when you made these measurements? Bill

I measured these outside about 4 feet off the ground. I just ran an impedance sweep tonight on an empty box. There are large spikes that match those dips. I stuffed the bottom of one and lined it, and the impedance sweep is pretty good. I still have a bit of work to do to get them to go away completely. Sent from my SM-G973U using Tapatalk

[johnny5jz]

Here is two impedance sweeps. One is an empty box (tube) and one is stuffed at the bottom and lined. When I did the measurements, I had a bit of stuffing in the bottom of the box, but I had not lined it yet. The measurements I did first were with an empty box and it had much larger dips.