Highest crossover point from woofer to midbass in tower speaker for best sound? And distance from floor

[mike7877]

I've been thinking of actively crossing one of my two way sets into three ways. The drivers are very high power and it'd be an inexpensive way to increase their power handling 3-4x, as well as get better low-end extension.

Their midbass driver is 5" with an underhung coil with linear excursion of +-6mm, acceptable excursion (Xmax) of +-10mm, and mech limit (Xlim) +-16 or 20mm (I forget)

I'm wondering, typically, for good performance in a wide range of rooms, how high can a woofer be crossed before its location starts to become problematic? My goal is to have a wide sweet spot. I think the largest potential problems of this design might be artificial vocal reproduction and altered (boosted/cut) frequency response at the top of the woofer's response (from boundary effect).

The woofer isn't planned to be placed like a subwoofer, I plan to have it below the midbass/tweeter some place between the floor and right below the midbass.
Anyone have experience with 3 ways crossed in the 100-300Hz range?
I've had a 3 way crossed at 900Hz and 4500Hz. The woofer was 10", and while it was located close enough to the midrange to blend with it well, directionality at its higher frequencies was a bit of a problem. When the towers were placed directly on the floor, the 100-300Hz range was smooth and present in a proper proportion, but also somewhat artificial sounding - I think from the floor reflection. Raising them a foot on stands lowered the artificial sound, but also level, which was problematic.

I'm also wondering - is there an optimal or minimal distance from the floor that a woofer should be for good sub-400Hz response (so the frequencies that are reflected are low enough in frequency that the small change in tone doesn't noticeably affect quality?

 

[DVDdoug]

Do you know the frequency ranges of the drivers? Usually that's the limiting factor. And the lower the tweeter is crossed-over the more power it has to handle.

You can calculate the wavelengths as a starting point. You'd want the wavelengths to be long relative to driver size and relative to the distance between the drivers (or the difference in distance to your ears). At 100Hz the wavelength is about 10 feet, at 1kHz it's about 1-foot. (The waves go out-of-phase a half-wavelength... if one speaker is a half-wavelength closer to your ears.)

I've been thinking of actively crossing one of my two way sets into three ways.

Are you adding a woofer or a tweeter?

it'd be an inexpensive way to increase their power handling 3-4x,

Probably not that much. A 100W tweeter is supposed to handle the high frequency part of program material hitting 100W on the peaks. An active crossover doesn't change that unless you reduce the frequency range covered by the tweeter.

Adding a woofer or subwoofer should allow a bit more power but probably not twice as much.

There is a small amount of loss in a passive crossover, but probably 1dB or less. That makes the speaker more efficient but each driver still has the same power limit. So theoretically the speaker might be rated for lower power since all of the power is going to the drivers.

 

[levimax]

I have DIY speakers with LR 4 analog active crossovers crossed at 300 and 3,000 Hz , drivers are 12", 4" and 1.25 ". This seems to work well. I do think you will pick up a lot of power handling because of the steeper slopes active crossovers allow and of course adding a woofer where most of the power will go. My only advice is learn REW and your DSP device as much as you can as integrating the drivers to work together is going to be harder than you would think but if you do your measurements and testing the results can be quite good. I don't know about woofer height beyond I read close to the floor is preferred but don't know the reason. Good luck and have fun.

 

[Thomas_A]

I've been thinking of actively crossing one of my two way sets into three ways. The drivers are very high power and it'd be an inexpensive way to increase their power handling 3-4x, as well as get better low-end extension.

Their midbass driver is 5" with an underhung coil with linear excursion of +-6mm, acceptable excursion (Xmax) of +-10mm, and mech limit (Xlim) +-16 or 20mm (I forget)

I'm wondering, typically, for good performance in a wide range of rooms, how high can a woofer be crossed before its location starts to become problematic? My goal is to have a wide sweet spot. I think the largest potential problems of this design might be artificial vocal reproduction and altered (boosted/cut) frequency response at the top of the woofer's response (from boundary effect).

The woofer isn't planned to be placed like a subwoofer, I plan to have it below the midbass/tweeter some place between the floor and right below the midbass.
Anyone have experience with 3 ways crossed in the 100-300Hz range?
I've had a 3 way crossed at 900Hz and 4500Hz. The woofer was 10", and while it was located close enough to the midrange to blend with it well, directionality at its higher frequencies was a bit of a problem. When the towers were placed directly on the floor, the 100-300Hz range was smooth and present in a proper proportion, but also somewhat artificial sounding - I think from the floor reflection. Raising them a foot on stands lowered the artificial sound, but also level, which was problematic.

I'm also wondering - is there an optimal or minimal distance from the floor that a woofer should be for good sub-400Hz response (so the frequencies that are reflected are low enough in frequency that the small change in tone doesn't noticeably affect quality?

Depends on the response of your monitors. Are they ported or closed boxes? Can the port be plugged and how does the response change? A 80-100 Hz x-over point would leave most of the voice range untouched by x-over. I use 100 Hz as x-over point (plugged port, 12/24 dB filter)

 

[mike7877]

=

Depends on the response of your monitors. Are they ported or closed boxes? Can the port be plugged and how does the response change? A 80-100 Hz x-over point would leave most of the voice range untouched by x-over. I use 100 Hz as x-over point (plugged port, 12/24 dB filter)

They're sealed boxes, flat down to 75-80Hz. They have the nice, predictable, 12dB/oct roll-off you'd expect, and no peak in the octave above roll-off (present in suboptimal designs)

These are properly designed?
Yes, being the lowest frequency driver in a sealed box, frequency response needs to be as flat as possible to as low as possible, while taking into consideration the size of the box and other T/S parameters.
When a driver doesn't extend low enough and the only way to address the issue is in box design, there is a trick to get a 1-5dB boost in the octave above roll-off (which can give the illusion of lower frequency extension), but it comes at a cost (like everything in life lol...)

The higher the peak is made, the more the speaker will ring. The point that roll-off actually begins also increases a little bit, but this is much much much less detrimental overall to the overall subjective quality of the audio. Only ringing is noticed.

Optimal Q to integrate with another driver? 0.5

Good Q of the appropriately sized woofer in a speaker for the most
- amount of, and
- accurate bass
leading to the least artifacting ?

0.9 to 1.1.

This can vary, but overall, the number is probably just over 1.0
Which is what my speakers are. (fortunately! __)

I'm not afraid to use the first (lowest) octave of my speakers because their sound there is very far from unnatural. It's good lol. Q != 0.5 so it's not perfect, but as it is bass we're dealing with, and not a tweeter crossed in the 1.5-3.5kHz range, thing should be good.

Maybe I could double up the box's natural -12dB/oct with electronic -12dB (making 24dB/oct, obviously). I wonder how much that will add to power handling.
That might still be too low, because 100dB / 80Hz would get the driver moving +6.9mm and -6.9mm. To keep harmonic distortion as low as possible, I'd like to keep total excursion (both ways) to under 8mm, ideally 6.

The woofer has a gap of 20mm and the voice coil is 8mm, so technically there's 12mm travel. I've never noticed distortion under this amount, but it's good to keep it as low as possible anyway (doppler effect)

 

[mike7877]

I have DIY speakers with LR 4 analog active crossovers crossed at 300 and 3,000 Hz , drivers are 12", 4" and 1.25 ". This seems to work well. I do think you will pick up a lot of power handling because of the steeper slopes active crossovers allow and of course adding a woofer where most of the power will go. My only advice is learn REW and your DSP device as much as you can as integrating the drivers to work together is going to be harder than you would think but if you do your measurements and testing the results can be quite good. I don't know about woofer height beyond I read close to the floor is preferred but don't know the reason. Good luck and have fun.

So it's preferred to have a woofer near the floor - curveball!!!

I've seen examples of both, but now that you mention it, more of them are closer to the ground, especially if they're not doing anything above 200-300Hz


Since the frequencies being dealt with are low, are they unaffected by the material of the floor? Example: tiles are bad for reflections, killing detail in highs. <- known fact

Hypothetical: "tiles aren't any different than carpet on floors when it comes to the effect each has on perceived sound quality of music

 

[TimW]

Woofers suspended above the ground will create a floor bounce that can create a cancellation at the listening position. This depends on the dimensions of the room and how the speakers and listener are oriented in it of course. Best way to see if this is happening is to measure. Personally I have a big suck-out in the response of my stand mounted monitors between 150-200Hz. By placing a mid-bass woofer near the floor you can avoid the floor bounce cancellation but of course that creates a larger gap between the mid-bass woofer and midrange. In my system I have my monitors on 30" stands and my 8" mid-bass woofers on the ground with a 200Hz 48db crossover between them. I won't claim to know that is the upper limit for crossing over in this kind of setup but it is what works best for me so far. Crossing over the mid-bass woofers lower would reintroduce the floor bounce cancellation, which actually still exists to a small extent. Crossing over higher did not sound as good to me although I can't quite remember why.

 

[mike7877]

1 Do you know the frequency ranges of the drivers? Usually that's the limiting factor. And the lower the tweeter is crossed-over the more power it has to handle.

You can calculate the wavelengths as a starting point. You'd want the wavelengths to be long relative to driver size and relative to the distance between the drivers (or the difference in distance to your ears). At 100Hz the wavelength is about 10 feet, at 1kHz it's about 1-foot. (The waves go out-of-phase a half-wavelength... if one speaker is a half-wavelength closer to your ears.)

2 Are you adding a woofer or a tweeter?

Probably not that much. A 100W tweeter is supposed to handle the high frequency part of program material hitting 100W on the peaks. An active crossover doesn't change that unless you reduce the frequency range covered by the tweeter.

Adding a woofer or subwoofer should allow a bit more power but probably not twice as much.

There is a small amount of loss in a passive crossover, but probably 1dB or less. That makes the speaker more efficient but each driver still has the same power limit. So theoretically the speaker might be rated for lower power since all of the power is going to the drivers.

1.) Yes, the mid-bass driver (speaker are sealed design box) is good down to 75-80Hz before it starts rolling off.
I just measured the exact size of the driver (cone + 1/3 surround) and it's 5 3/8" or 13cm.

Piston Excursion calculator

www.baudline.com

Using the piston excursion calculator, a 5.375" driver producing 80Hz at 100dB would have its cone moving 5.97mm (11.94mm)
This is the absolute maximum linear excursion of the driver (20mm gap, 8mm coil - underhung design)

If, instead of 80Hz, I cross at 160, the new maximum SPL can become 112dB !

That is REALLY good, because most music power is in the bass, and kick drum? Those have most of their energy in the range 40-110Hz range

This project is mostly to increase power handling, so steepening the slope at 75-80Hz from 12 to 24dB at first look doesn't seem like it's going to be enough. Some genres yes, but others.. It'd depend. And on individual songs.
I'd
isn't going to be enough. It would for some genres but not others. I'd like to be able to turn things up and not worry about woofer excursion.
Actual power handling is not an issue, the voice coil is 3" and the magnet is like 200oz (yes, on a ~5.5" woofer!)

I'm not sure how much this matters but you asked about drivers and the tweeter is one:
The tweeter is crossed to the woofer at 2.1kHz. It's a Butterworth, 18dB/oct (my favourite kind!)
I measured the resonant frequency, and it's approx 800Hz (I think). Or 1200Hz. 200Hz from 1000 lol. Point is, it's low - low enough.
The tweeter's got a double suspension so it's impossible to rock. When new, when I was loosening the suspension (break in) I used 10Hz at a watt or two, and the dome was moving 1mm (2mm total). That was not its maximum though.
3x that amount is how far it could move. I chose not to break it in like that though, because in normal operation there's no way a 1" dome, crossed at 2.1kHz would ever move that far:
2100Hz at 112dB is a 1" dome moving +-1mm (2mm total),
Being ~94dB/w, 112dB is over 50W input. Since, in music, that 50W to the tweeter over 2.1kHz means total music power would have to be 250W and 250W RMS music listening in a 14x20 foot room... loud! ! !

2.) Woof!

 

[mike7877]

Woofers suspended above the ground will create a floor bounce that can create a cancellation at the listening position. This depends on the dimensions of the room and how the speakers and listener are oriented in it of course. Best way to see if this is happening is to measure. Personally I have a big suck-out in the response of my stand mounted monitors between 150-200Hz. By placing a mid-bass woofer near the floor you can avoid the floor bounce cancellation but of course that creates a larger gap between the mid-bass woofer and midrange. In my system I have my monitors on 30" stands and my 8" mid-bass woofers on the ground with a 200Hz 48db crossover between them. I won't claim to know that is the upper limit for crossing over in this kind of setup but it is what works best for me so far. Crossing over the mid-bass woofers lower would reintroduce the floor bounce cancellation, which actually still exists to a small extent. Crossing over higher did not sound as good to me although I can't quite remember why.

!!! about 10 years ago, 150-200Hz was where my suck-out was when I had my Infinity SM-112 speakers (3 way towers with 10" woofers) mounted on stands that held them 10-12" above where they'd be naturally. This was with the bottom of the 10" woofer about 15-16" from the ground, or the centre of the woofer at 20-21"
How far above ground are the centres of your woofers?

48dB/oct seems mighty steep. Does it still sound natural?
Which software do you use?

Obviously electronic is the way to go. I have an RME Babyface Pro - which has 4 channels out. THD/SNR/dynamic range are all good enough and I'll be using the Power Amp input of my Denon x3700H receiver (I'm being funny - it doesn't have one, but if you treat the preamp outputs like they're power inputs, and the channels you're feeding are defined active in settings (eg. 5.1 amplified mode, you can do inputs to front, centre, and surround). The amplifier's THD is tested to be just under 90dB (5W / 4 ohms), meaning 93 dB / 8 ohms. This is obviously through the preamplifier section. The increase in clarity I noticed from pumping directly to the amplifier though, DANG! It sounds classy! And there are 9 channels. I have to figure out how to measure THD of amplifiers using my audio interface... Denon receivers may be the best amps around for multi way active setups!

 

[Thomas_A]

=


They're sealed boxes, flat down to 75-80Hz. They have the nice, predictable, 12dB/oct roll-off you'd expect, and no peak in the octave above roll-off (present in suboptimal designs)

These are properly designed?
Yes, being the lowest frequency driver in a sealed box, frequency response needs to be as flat as possible to as low as possible, while taking into consideration the size of the box and other T/S parameters.
When a driver doesn't extend low enough and the only way to address the issue is in box design, there is a trick to get a 1-5dB boost in the octave above roll-off (which can give the illusion of lower frequency extension), but it comes at a cost (like everything in life lol...)

The higher the peak is made, the more the speaker will ring. The point that roll-off actually begins also increases a little bit, but this is much much much less detrimental overall to the overall subjective quality of the audio. Only ringing is noticed.

Optimal Q to integrate with another driver? 0.5

Good Q of the appropriately sized woofer in a speaker for the most
- amount of, and
- accurate bass
leading to the least artifacting ?

0.9 to 1.1.

This can vary, but overall, the number is probably just over 1.0
Which is what my speakers are. (fortunately! __)

I'm not afraid to use the first (lowest) octave of my speakers because their sound there is very far from unnatural. It's good lol. Q != 0.5 so it's not perfect, but as it is bass we're dealing with, and not a tweeter crossed in the 1.5-3.5kHz range, thing should be good.

Maybe I could double up the box's natural -12dB/oct with electronic -12dB (making 24dB/oct, obviously). I wonder how much that will add to power handling.
That might still be too low, because 100dB / 80Hz would get the driver moving +6.9mm and -6.9mm. To keep harmonic distortion as low as possible, I'd like to keep total excursion (both ways) to under 8mm, ideally 6.

The woofer has a gap of 20mm and the voice coil is 8mm, so technically there's 12mm travel. I've never noticed distortion under this amount, but it's good to keep it as low as possible anyway (doppler effect)

There is no way to defy physic limits but in practice you can get a bit more SPL in-room (gains). A 12 dB xover at 80-100 Hz wins a few dB and near-wall placement against a suitable damping panel give you a few more. Add using two speakers and you may well end up with 110 dB max. Need more? Then its time to step up speaker.

 

[TimW]

How far above ground are the centres of your woofers?

48dB/oct seems mighty steep. Does it still sound natural?
Which software do you use?

If you're talking about the 8" mid-bass woofers they are in a 13" square enclosure with 3/4" rubber feet so roughly 7 1/4" to center. If you're talking about the monitors, they are MTM speakers with 6" woofers on 30" stands so roughly 40 1/2" to center of tweeter between woofers.

I tried shallower slopes but they sounded worse to me, definitely less natural because the frequency response was less flat.

I use a miniDSP SHD connected to a Behringer DCX2496 for the bass woofers.

 

[mike7877]

If you're talking about the 8" mid-bass woofers they are in a 13" square enclosure with 3/4" rubber feet so roughly 7 1/4" to center. If you're talking about the monitors, they are MTM speakers with 6" woofers on 30" stands so roughly 40 1/2" to center of tweeter between woofers.

I tried shallower slopes but they sounded worse to me, definitely less natural because the frequency response was less flat.

I use a miniDSP SHD connected to a Behringer DCX2496 for the bass woofers.

Ah, so you're using the natural rolloff of the monitors? They're ported and have a pretty steep (~24dB/oct) rolloff?

Woofer very close to ground at up to 200Hz is good. May I ask what your floor is made of and covered with? Eg. Concrete + subfloor + carpet, joists, plywood, hardwood.

Aside: I love MTM speakers. I've got my HT centre channel placed vertically, and, though integration isn't great at over +-8 deg, it's superior to MT in the sweet spot. Some of that is definitely from reduced reflections. Superb!
My HT speakers are Monitor Audio Silver series, 5.1 pack - sans sub (those are 2x KEF Kube 10b)

 

[Tangband]

I've been thinking of actively crossing one of my two way sets into three ways. The drivers are very high power and it'd be an inexpensive way to increase their power handling 3-4x, as well as get better low-end extension.

Their midbass driver is 5" with an underhung coil with linear excursion of +-6mm, acceptable excursion (Xmax) of +-10mm, and mech limit (Xlim) +-16 or 20mm (I forget)

I'm wondering, typically, for good performance in a wide range of rooms, how high can a woofer be crossed before its location starts to become problematic? My goal is to have a wide sweet spot. I think the largest potential problems of this design might be artificial vocal reproduction and altered (boosted/cut) frequency response at the top of the woofer's response (from boundary effect).

The woofer isn't planned to be placed like a subwoofer, I plan to have it below the midbass/tweeter some place between the floor and right below the midbass.
Anyone have experience with 3 ways crossed in the 100-300Hz range?
I've had a 3 way crossed at 900Hz and 4500Hz. The woofer was 10", and while it was located close enough to the midrange to blend with it well, directionality at its higher frequencies was a bit of a problem. When the towers were placed directly on the floor, the 100-300Hz range was smooth and present in a proper proportion, but also somewhat artificial sounding - I think from the floor reflection. Raising them a foot on stands lowered the artificial sound, but also level, which was problematic.

I'm also wondering - is there an optimal or minimal distance from the floor that a woofer should be for good sub-400Hz response (so the frequencies that are reflected are low enough in frequency that the small change in tone doesn't noticeably affect quality?

A 5 inch midbass will have some trouble playing loud If its crossed at 75 Hz . But a 3 way is a compromise anyway ( a 4 way isnt ) with limited spl in the midbass , so this is my advice :

Do the crossover somewhere between 70 - 250 Hz ( both HP and LP ) and put each stereo coupled subwoofer away from the floor, as near as you can to each L&R midbass . You can DIY two subwoofer towers with the same hight as your main speakers. Stereo subwoofers with drivers placed near the floor cant play any higher than about 100 Hz before you gonna notice theres something wrong with the music. A single subwoofer must be crossed much lower.

A good compromise in loudspeaker building is to build a real threeway speaker, such as an ATC 100 . This is much better soundwise that having a threeway with the subwoofers placed on the floor, with the compromise of a low 80 Hz crossover.

You can also get some inspiration with the help of Revel 208 .

With a real threeway speaker such as ATC100, you can often cross the subwoofer to the midbass as high as 250 Hz without sound issues.

Using an odd order crossover at 250 Hz, ( as example 18/18 dB oct ) you might also get a better power response in the room ( the perceived impact of percussion sound will be better than using an even order crossover in this frequency range ).

Read more here :

Power

 

[gene_stl]

Although it is true that passive crossovers eat a lot of power going active (which I am a great proponent of) will not really increase your power handling by your mentioned 3x to 4x. The voice coils insulation will still melt at the same temperature and the surrounds will tear at the same point they did before. Only you will reach them earlier , and with a smaller amp because you won't be heating passive crossover components.

Tangband's advice above is good. It is hard to imagine getting "big" and great sound from a two way with a six inch wooofer.

 

[mike7877]

A 5 inch midbass will have some trouble playing loud If its crossed at 75 Hz . But a 3 way is a compromise anyway ( a 4 way isnt ) with limited spl in the midbass , so this is my advice :

Do the crossover somewhere between 70 - 250 Hz ( both HP and LP ) and put each stereo coupled subwoofer away from the floor, as near as you can to each L&R midbass . You can DIY two subwoofer towers with the same hight as your main speakers. Stereo subwoofers with drivers placed near the floor cant play any higher than about 100 Hz before you gonna notice theres something wrong with the music. A single subwoofer must be crossed much lower.

A good compromise in loudspeaker building is to build a real threeway speaker, such as an ATC 100 . This is much better soundwise that having a threeway with the subwoofers placed on the floor, with the compromise of a low 80 Hz crossover.

You can also get some inspiration with the help of Revel 208 .

With a real threeway speaker such as ATC100, you can often cross the subwoofer to the midbass as high as 250 Hz without sound issues.

Using an odd order crossover at 250 Hz, ( as example 18/18 dB oct ) you might also get a better power response in the room ( the perceived impact of percussion sound will be better than using an even order crossover in this frequency range ).

Read more here :

Power

View attachment 288813

Coincidentally, the speakers I have are the ATC SCM20 Pro PSL Mk2. The tweeter is the S-Spec, (same as the one used in the most recent 50/100/110), and the midbass is underhung with 12mm travel and a 3" voice coil which uses the dome of the midrange of those 100s in the centre as a dustcap/radiator. The crossover between it and the tweeter is third order (2.1kHz) as well (which purely coincidentally is my favourite slope for mid to tweeter, but not something I ever considered before for mid to bass (esp at such low frequencies), mostly because of component size

I'll be going active with this though, so third order between the two will be easy.

You say up at ear level... I can definitely try that.

To start I have two (active) KEF Kube 10b subs I can cross as high as 140Hz with a 24dB slope. I think if I do that and feed them with 3rd order at 90Hz integration would be decent.

About KEF Kube 10b:
- sealed
- 10"
- 24Hz -3dB
- linear movement (estimate) +-12-15mm (24-30)
- max excursion (estimate) +-20-25mm (40-50mm)
- 300W RMS class D

I reinforced them like I do all my speakers. Even my SCM20s benefitted nicely from some high-force cross bracing (much higher fs and much less reactive at it)

My only significant concern with the Kubes is, because their drivers' moving mass isn't 1.3kg and their amps aren't 5000W, the 24Hz -3dB point comes from DSP. This DSP... I don''t know the effect it will have on phase at the top end of frequency response. Hopefully it's minimal. I know that the amplifier's DSP completely ignores the mechanical limits of the driver (lol), so I think it's unlikely I'll run into compression from any cause other than power limit.

Room correction software - do you think it would adjust the signal well enough to compensate for any unwanted effects from DSP?

Just had a brainwave: to separate room from signal, instead of using a microphone for correction, I could use the audio outs for each, combined to one channel digitally, and use that channel instead of the microphone as the source for the correction software.
Worst or best idea ever?
My first thought was to take the speaker outputs with, say, ~0.1 ohm output impedance) from both channels (sub, satellite) each making the same SPL in the room (90dB or whatever), put each output through 100 ohm resistors, then attach the outputs of those resistors together and into a (~10k) line input.

 

[Thomas_A]

If you already have a 12 dB slope (sealed), x-over at 80-100 Hz would be a start. Combine 18/30 dB with subs and you get 30 dB odd-order filter.

I am hesitant to x-over higher due to the voice region and introducing phase shifts in the more audible/sensitive region.

 

[mike7877]

Although it is true that passive crossovers eat a lot of power going active (which I am a great proponent of) will not really increase your power handling by your mentioned 3x to 4x. The voice coils insulation will still melt at the same temperature and the surrounds will tear at the same point they did before. Only you will reach them earlier , and with a smaller amp because you won't be heating passive crossover components.

Tangband's advice above is good. It is hard to imagine getting "big" and great sound from a two way with a six inch wooofer.

But the woofer has a cast basket, 3" 8mm underhung voice coil and ~200oz magnet (with 20mm gap), and its cone is well damped!

And the tweeter is used in speakers rated for 300W RMS! Although... those speakers cross the domes at 3.5 instead of 2.1kHz. Still, the domes have a dual suspension so it's impossible for them to rock.
When I was running them in with 10Hz (yes, 10 Hz), although most of the 40 hours I had them moving +-0.2mm, they could move up to 2.5mm (+-1.25) easily. Noiselessly. They're nothing short of a modern feat of engineering! Can't forget the massive neodymium magnets that entirely and uniformly saturate the magnetic gap over 2T!

If you're wondering why I ran them in: I lived in a building. I did the same thing to the woofers, but instead of 10Hz +- 0.2mm for 40 hours they got 14Hz +-5mm for 60

 

[ROOSKIE]

I've been thinking of actively crossing one of my two way sets into three ways. The drivers are very high power and it'd be an inexpensive way to increase their power handling 3-4x, as well as get better low-end extension.

Their midbass driver is 5" with an underhung coil with linear excursion of +-6mm, acceptable excursion (Xmax) of +-10mm, and mech limit (Xlim) +-16 or 20mm (I forget)

I'm wondering, typically, for good performance in a wide range of rooms, how high can a woofer be crossed before its location starts to become problematic? My goal is to have a wide sweet spot. I think the largest potential problems of this design might be artificial vocal reproduction and altered (boosted/cut) frequency response at the top of the woofer's response (from boundary effect).

The woofer isn't planned to be placed like a subwoofer, I plan to have it below the midbass/tweeter some place between the floor and right below the midbass.
Anyone have experience with 3 ways crossed in the 100-300Hz range?
I've had a 3 way crossed at 900Hz and 4500Hz. The woofer was 10", and while it was located close enough to the midrange to blend with it well, directionality at its higher frequencies was a bit of a problem. When the towers were placed directly on the floor, the 100-300Hz range was smooth and present in a proper proportion, but also somewhat artificial sounding - I think from the floor reflection. Raising them a foot on stands lowered the artificial sound, but also level, which was problematic.

I'm also wondering - is there an optimal or minimal distance from the floor that a woofer should be for good sub-400Hz response (so the frequencies that are reflected are low enough in frequency that the small change in tone doesn't noticeably affect quality?

I make 2ways into 3ways all day long.
Many times.
In my case the subwoofers are the base & bass. Like towers. You can still have a separate sub(s) for the 20hrz stuff in some crazy location but the 3way design requires those 3 drivers to be reasonably near each other
So I can cross pretty high if needed 200ish hrz.
The main thing is that little is to be gained crossing a robust 6/6.5 driver above 125hrz. For a 5/5.25 some gains are made going as high as 150-175hrz.So start with that. Play to measure and experiment to get the blend you want and bear in mind many folks who have never done this will have some opinions that may or may not be relevant.

 

[mike7877]

If you already have a 12 dB slope (sealed), x-over at 80-100 Hz would be a start. Combine 18/30 dB with subs and you get 30 dB odd-order filter.

I am hesitant to x-over higher due to the voice region and introducing phase shifts in the more audible/sensitive region.

Ah, yes, 30dB is also odd order. With the 140Hz 24dB imposition by the KEF amplifier, 30dB at 110Hz would allow for even more power handling.

I don't necessarily need 3 or more times the power handling, I just want more power handling better bass that comes with proper integration.

110Hz allows for 5dB more than 80
140Hz allows for 10dB more than 80

140/24 and put a further 6dB, that'd be 30, also a match.

Maybe I can make a couple profiles - one for best integration and one for best power handling

 

[mike7877]

So I looked it up and the KEF Kube 10b is rated for 105dB continuous. I guess that means 108 maximum.
Not unreasonable - with its 300W RMS amplifier, driver sensitivity would need to be in the low 80s. Very probable.

Say the 5" cone in my speakers can move 6mm in either direction without the voice coil leaving the gap, without distorting (it can)
For it to make 108dB, and move no more than +-6mm, frequency is 136Hz or higher.

It looks like the 140Hz 30dB slope is the perfect combination between the two to maximize power handling, and minimize cone travel otherwise.

105dB continuous also matches with the ~100W RMS amplifier I currently have driving the SCM20 Pro PSL Mk 2s as well - they're 85dB/w

A perfect set! Who knew?