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Multi-Way Conventional loudspeakers with crossovers

3.5-way with combined closed and vented enclosures
3.5-way with combined closed and vented enclosures
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Old 10th January 2018, 06:56 PM   #1
karha096 is offline karha096  Sweden
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Default 3.5-way with combined closed and vented enclosures

Lately I've been considering building a 3-way floorstander. Something along the lines of the smaller Sonus Faber floorstanders. My primary candidate for the bass enclosure is to use 2 x Scanspeak 18W/8531. For midrange I'm considering the Scanspeak 15M/4531K and on top I'll likely go for the 6600 AirCirc tweeter. Crossovers will be DSP.

The 18W/8531 is typically used ~30 liter vented enclosures (I've been looking into Troels Gravesen, John Krutke among others, who have nice designs posted online).

To keep the volume down (or rahter to allow some really excessive bracing with maintained WAF ), I've come to consider putting the top woofer in a separate closed enclosure around 15 liters and the bottom woofer in a 30 liter vented enclosure. This would make it a 3.5-way I guess.

Would this type of design achive "the best of two worlds" with good transient response from the top woofer and deeper bass from the bottom woofer? Or would I run into problems?

I'v never seen any designs like this. All of the 2.5-ways and 3-5 ways I have seen have both woofers in the same enclosure or in separate but equally designed enclosures.

Has anyone tried it?

Last edited by karha096; 10th January 2018 at 06:59 PM.
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Old 11th January 2018, 09:14 PM   #2
BlueWizard is offline BlueWizard  United States
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What makes a speaker a HALF-Way is when one of the drivers share PART of the range of the other driver.

Click the image to open in full size.

In this case Bass-1 and Bass-2 share PART of a frequency range.

A 4-way with the same drivers gives a isolate frequency range to the Bass-1 driver or in some cases the Bass-1 might actually be a Subwoofer -

Click the image to open in full size.

I suspect in your case, if you could set it up as a Low-Bass (30liter vented) and a Mid-Bass (15liter sealed). But the output of those two drivers in those diverse cabinets will not be the same.

Also -

To keep the volume down ...I've come to consider putting the top woofer in a separate closed enclosure around 15 liters and the bottom woofer in a 30 liter vented enclosure.

How does this keep the volume down? The only thing that keeps the volume down, is that very large knob on the front of your Amp.

The Scanspeak 18W/8531 is a 7" Bass Drive (US$218) -

ScanSpeak Revelator 18W/8531G-00 7" Mid Woofer 8 ohm

The Scanspeak 15M/4531K is a 5.25" Mid-Bass Driver (US$204) -

Scanspeak 15M/4531K Revelator 5.5" Midrange

The Tweeter is a ScanSpeak Illuminator D3004/6600 AirCirc Tweeter (US$194) -

ScanSpeak Illuminator D3004/6600 AirCirc Tweeter Textile Dome

Given the Frequency Response of the drivers, it seems clear you are building a Low-Bass/Mid-Bass/Tweeter system, not a more standard Woofer/Midrange/Tweeter system.

If you want to make the 7" bass drivers into a HALF-Way system that can certainly be done. Typically the crossover is at the Baffle Step of the Cabinet. But you are already building a Low-Bas/Mid-Bass system (7" Low-Bass, 5.5" Mid-Bass).

Though other here are more expert than I am, I question whether you can make a effective Crossover between the 15M/4631 and the 6600 AirCirc. The 15M/4631 has a large bump in the response above 1khz, that is going to have to be dealt with using additional Crossover components. That implies that the Mid/High Crossover is going to have to be pretty low. Too low to effectively merge with the Tweeter. Though others may disagree, but I don't think so.

The 18W/8531 7" Low-Bass look good up to 1000hz, but they also have a resonance bump above 1khz. Again, that is going to have to be dealt with in the crossover. And the Low/Mid crossover is also going to have to be pretty low.

The most critical aspect is the Mid-Bass to High Crossover. I'm not sure that is going to work. The Mid-Bass won't go high enough, and the Tweeter won't go low enough.

But then ... that's just my opinion.

Steve/BlueWizard

Last edited by BlueWizard; 11th January 2018 at 09:18 PM.
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Old 12th January 2018, 02:27 AM   #3
eriksquires is offline eriksquires  United States
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Fast transient response is a function of room matching, not driver size.

Also, I find the 18W/8531 or 4531s exceptional mid-woofers, but they require a lot of volume sealed, more so vented. Given you'll be using active/DSP, I would suggest sealed. Smallest size, best transient response.

Best,

E
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Old 12th January 2018, 08:27 AM   #4
karha096 is offline karha096  Sweden
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Yes, indeed the volume knob is the best way to keep the volume down, but I hope you understand that I was referring to the cabinet volume in liters.

With regards to the 15M midrange, the bump is just a shelf, which is simple to compensate with a DSP filter. The rollof is as smooth as they come. Practivally no cone breakups at all. Is see no problem using the 15M up to 2500Hz LR2.

A lot has been written about the 18W and how it requires a large volume. I have been simulating it using both the specs from Scanspeak and measured TS posted online and I agree that it would not fit well in a tiny box, especially not considering measured Qts of 0.55 (www.audioexcite.com).

I do have some hope that putting one driver in a closed or aperiodic enclosure and the other driver in a ported enclosure would work though. If that does not work, perhaps one big aperiodic enclosure with some DSP bass attenuation would work. Since I have dual woofers, the excursion is limited. Any thoughts on that?
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Old 12th January 2018, 08:50 AM   #5
BlueWizard is offline BlueWizard  United States
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Quote:
Originally Posted by karha096 View Post
Yes, indeed the volume knob is the best way to keep the volume down, but I hope you understand that I was referring to the cabinet volume in liters.
Eventually that thought did occur to me.

Quote:
With regards to the 15M midrange, the bump is just a shelf, which is simple to compensate with a DSP filter....
Above 1khz there is a 5db or 6db bump. Though if you have active crossovers, and/or EQ, that can perhaps be dealt with.


Quote:
A lot has been written about the 18W and how it requires a large volume. I have been simulating it using both the specs from Scanspeak and measured TS posted online and I agree that it would not fit well in a tiny box, especially not considering measured Qts of 0.55 (www.audioexcite.com).

I do have some hope that putting one driver in a closed or aperiodic enclosure and the other driver in a ported enclosure would work though. If that does not work, perhaps one big aperiodic enclosure with some DSP bass attenuation would work. Since I have dual woofers, the excursion is limited. Any thoughts on that?
I can only tell you what I see from a quick look at the frequency response graphs. The 15M is really only good up to about 1khz, but again, DSP is a possibility for compensation. It can certianly respond quite a bit higher, but it is going to take some fancy crossover work to make this happen.

Steve/bluewizard
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Old 12th January 2018, 09:10 AM   #6
TMM is offline TMM  Australia
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Bad idea. The woofer in the smaller sealed enclosure will have a different phase response to the one in the ported enclosure, they won't sum together properly and make for a strange low frequency response. They may also unload badly at very low frequency as they become completely out of phase - a closed speaker is a 2nd order system and heads towards 180deg at DC and a ported speaker is a 4th order system and heads towards 360deg at DC. Run them in the same enclosure.

Last edited by TMM; 12th January 2018 at 09:13 AM.
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Old 12th January 2018, 09:58 AM   #7
giralfino is offline giralfino  Italy
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Quote:
I've come to consider putting the top woofer in a separate closed enclosure around 15 liters and the bottom woofer in a 30 liter vented enclosure. This would make it a 3.5-way I guess.
This is not a 3.5 way. A x.5 way is when 2 drivers share the lowest part of their FR, and one is crossed over earlier than the other. It is often used to counteract the baffle step effect, using two woofers in the 4pi region and switching gradually to 1 woofer alone in the 2pi region. In a baffle good to accommodate a 6.5" driver this transition occurs at some 100s of Hz, and you can use the crossover point between bass and midrange to handle the baffle step effect.

Quote:
Would this type of design achive "the best of two worlds" with good transient response from the top woofer and deeper bass from the bottom woofer? Or would I run into problems?
Even without what TMM says about phase, you won't achieve that, you'll have an anemic bass under the closed woofer. Run them both closed or vented for the best and only one possible summation.

You should be aware that John Krutke suggests to run the 2 woofers in a roughly 40L closed or 60+L vented box, since you are planning to use an active crossover you can probably also use it to gain some bass extension from the smaller closed box.

Quote:
The Scanspeak 15M/4531K is a 5.25" Mid-Bass Driver
It is not a bass, its parameters make it inadequate to produce bass. Its FR is not flat above 1KHz, but this is only the infinite baffle response, once you factor in the baffle effect, and specifically the bump above the baffle step transition, the on-baffle FR can be much nicer, and should be easily crossed over to the tweeter. I won't cross it over higher than 2KHz LR4 thou, it starts to beam earlier than other 5" drivers, but this won't be a problem with the chosen tweeter.

Ralf
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Old 12th January 2018, 12:38 PM   #8
karha096 is offline karha096  Sweden
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I understand the phase response issue, thanks for pointing that out.

I will try out vented around 65 liters, closed around 40 liters and also try an aperiodic alignment and see which plays better in my room.

I am aware of the beaming related to driver diameter, stiffness and cone geometry. Perhaps the 12M/4631-G00 4.5" Midrange would be a better choice...
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Old 13th January 2018, 12:30 AM   #9
BlueWizard is offline BlueWizard  United States
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Two 7" bass drivers, are not that big. In my day, 10" bass drivers were for amateurs, and most had 12" or 15". Though I also realize that those days are pretty much gone.

Get some design software (WinISD, or Bass Box Pro) so you can model the response relative to cabinet size. 30 Liters is only about 1.05 cubic feet, that's a small cabinet.

You should be able to put two 7" bass drivers in the same cabinet with out any problem and come up with a reasonably sized floorstanding speaker.

Though I still question the use of the 15M (5.5") for either mid-bass or midrange. I would suggest a midrange with a wider frequency range and higher crossovers. Given the bump in the 15M response above 1khz, it is going to take an odd crossover to compensate for that bump.

If you want midrange, you are going to have to go with a smaller Mid-Range driver, perhaps 4".

For example, here is a $120 Arum Cantus AC-130F1 - 5.25" - check the frequency response on that -

https://www.parts-express.com/pedocs...ions-45624.pdf

Aurum Cantus AC-130F1 5-1/4" Woofer

Pretty much flat from 100hz to over 5khz.

Here is an 8" Aurum Cantus AS-200-MKII - pretty much flat to 1kzh, and workable out to perhaps 2khz. Though there is a peak around 3.5khz.

https://www.parts-express.com/pedocs...ions-45628.pdf

Aurum Cantus AC-200MKII 8" Carbon Fiber Sandwich Woofer

This Aurum Cantus Ribbon Tweeter - G3Si - though it has a slight peak around 20khz, that probably not going to be a problem as most people can not hear that high at normal volumes. Response is roughly 1.5kzh up to 30khz

https://www.parts-express.com/pedocs...ifications.pdf

https://www.parts-express.com/aurum-...eeter--276-410

Those speakers will blend together much easier than the original speakers suggested. I would suggest in a 3-way, Low/Mid crossover in the roughly 300hz to 500hz range. That puts the Mid/High in the roughly 2400hz to 4000hz range all well within the working range of the each driver. Though not etched in stone, you generally allow 3 octave per driver range. 300hz to 2400hz is 3 octaves, and 500hz to 4000hz is 3 octaves. Though that is simply a guideline, when it comes to the specifics of a given design, those numbers can certainly change. But the point is, those particular drivers will easily blend together in the 300hz to 500hz range and in the 2400hz to 4000hz range.

Next you need to decide what you are designing? 2.5-way, 3.0-way (W/M/T), or a 3.0-way (LB/MB/T), or a 3.5-way, or some other configuration?

Generally Woofer/Midrange/Tweeter have higher crossover, typically 500hz and 4000hz or 800hz and ~5000hz.

Low-Bass/Mid-Bass/Tweeter
usually have lower crossovers. Metaphorically they are like a 2-way speaker with a Low-Bass driver added. So the crossover might be in the 200 to 300hz range, with Mid-Bass/Tweeter in the 1600hz to 2400hz range.

I just can't see your original speakers in a Woofer/Midrange/Tweeter configuration. The best you can hope for is a Low-Bass/Mid-Bass/Tweeter, and even that is going to be a stretch.

I'm sure there are those here who are far more familiar with Seas and ScanSpeak that can advise you of better combinations of drivers. But, I see those you have originally chosen as being difficult.

But then ... that's just my opinion.

Steve/bluewizard

Last edited by BlueWizard; 13th January 2018 at 12:33 AM.
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Old 13th January 2018, 12:58 AM   #10
BlueWizard is offline BlueWizard  United States
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Best guess, a single cabinet that is 10" wide x 40" high x 18" deep (254mm x 1016mm x 457mm) is going to be about 4.17 Cubic Feet or 118 Liters, which is a fairly sized cabinet for 2x7" or 2x8" bass drivers.

Now I'm not specifically recommending the Aurum Cantus, simply using them as a example of how similarly sized speakers can blend together much better.

My speakers (Diamond 9.6) which have 2x8" bass drivers and a 3" Dome Midrange in a 3.5-way configuration, are about 43" H x 10" W x 12" deep (1092mm x 254mm x 305mm).

Steve/bluewizard

Last edited by BlueWizard; 13th January 2018 at 01:01 AM.
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