A Question to show my lack of technical knowledge on Bass

bencat

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Right been reading a few of the threads on Sub Woofers and the crossover / filter points for them and have realised that I do not fully understand things . There are some on here who use Subs and seem very informed so as the only stupid quaestion is the one you do not ask here goes.

In my three way active system which is two pairs of KEF 103 Reference 70,s speakers per side . The top speakrr has the Bass/Mid and Treble unit active with the Bass unit acting from 290hz - 3000kHz when the Treble takes over . Now the bottom unit on each side only has the Bass/Mid driver connected and this is set from 20Hz - 290 Hz thus doing the low bass work of the system similar but i realise now not the same as a Sub . Now in my case I tried 48db CR points for the low bass starting at 250Hz and then increasing it by small increments and listening until I settled on the 290Hz as being the best compromise . Now in the Sub threads the CR point is given as being around 70Hz so as to not interfere with the main speaker .

So is what i am using just a three way active and this accounts for why the CR points are very different and sound best (to me at least) at the points i have set . Or should I be looking to have like a sub the low bass unit set to a much lower level ?

While this may seem obvious and have its answer in the different way that Subs work it is not obvious to me and would appreciate a little helpful education .
 
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Beobloke

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The bass/mid driver in your bottom cabinet isn't a subwoofer. It's a bass/mid driver. Hence why you need to run it up to a higher frequency than a dedicated subwoofer, which wouldn't normally go much higher than 70-80Hz.
 

Tony_J

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The bass/mid driver in your bottom cabinet isn't a subwoofer. It's a bass/mid driver. Hence why you need to run it up to a higher frequency than a dedicated subwoofer, which wouldn't normally go much higher than 70-80Hz.
Indeed...if you were building a 4-way, then it would make sense to have the bass drivers operating with a corssover around that point.

Andrew - a big difference between what you (and others of us that play with active systems) are doing and just adding a sub to a "normal" pair of speakers is that when you are just adding a sub, there generally isn't a true crossover between the sub & the speakers - at best, the sub will have its own (sometimes adjustable) low pass filter, but the speakers don't have a corresponding high pass filter - basically, their bass response will fall off naturally and you are aiming to supplement its bass performance by adding the output of the sub, and hopefully that will give you the desired bass extension. The potential problem is that there will be a considerable area of overlap between the speakers and the sub, so getting the two to work together seamlessly can be problematic - if you get unwanted cancellation between the two outputs it can make things sound worse, and the phase control on subs is used to get the best sounding result. This is of course why using a "proper" crossover to integrate a sub is generally better - much easier to engineer a smooth transition between midbass and bass, and you get to make a more considered choice of crossover point.
 

bencat

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Thank you both for taking the time to explain things what was confusing me was that some of the drivers I have seen in subs are quite similar in size to the 8 inch on the KEF and use an active amp to drive them . Presumably if I wanted to (no Tony I do not want to) I could add a sensibly rated 10 or 12 inch driver in a cabinet to my current three way and that could be classed over using a cr at say 10Hz - 70Hz then the current low base / mid could be cut off at 70Hz then cover up to 290Hz as it does now .
 
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Beobloke

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Thank you both for taking the time to explain things what was confusing me was that some of the drivers I have seen in subs are quite similar in size to the 8 inch on the KEF and use an active amp to drive them . Presumably if I wanted to (no Tony I do not want to) I could add a sensibly rated 10 or 12 inch driver in a cabinet to my current three way and that could be classed over using a cr at say 10Hz - 70Hz then the current low base / mid could be cut off at 70Hz then cover up to 290Hz as it does now .
8 inch?? Pah!

As an eminent British loudspeaker designer once said to me - “Anything below 12 inches is a mid/bass driver, not a bass driver”!
 
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bencat

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This may well be true but modern domestic harmony needs to be maintained .

Now you finished saying mines bigger than yours did what I say make sense and through you an Tonys advice have I learned a little something ?
 
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Lawrence001

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Andrew, the way you've added a second woofer which is the same as the first one is more like a 2.5 way speaker than a 3 way where the bass driver is usually different/bigger. I'm not sure how a 2.5 way crossover works but you might get better results if you do that and don't have a high pass filter on the first woofer, just rolling in the second one to help with the LF

Someone with more knowledge than me can hopefully advise.
 

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Andrew, the way you've added a second woofer which is the same as the first one is more like a 2.5 way speaker than a 3 way where the bass driver is usually different/bigger. I'm not sure how a 2.5 way crossover works but you might get better results if you do that and don't have a high pass filter on the first woofer, just rolling in the second one to help with the LF

Someone with more knowledge than me can hopefully advise.
2.5 way is different - you run the full bass plus midrange through the "mid" driver and just the bass through the "bass" driver. Andrew is running a 3 way, not a 2.1.
 

Tony_J

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Thank you both for taking the time to explain things what was confusing me was that some of the drivers I have seen in subs are quite similar in size to the 8 inch on the KEF and use an active amp to drive them . Presumably if I wanted to (no Tony I do not want to) I could add a sensibly rated 10 or 12 inch driver in a cabinet to my current three way and that could be classed over using a cr at say 10Hz - 70Hz then the current low base / mid could be cut off at 70Hz then cover up to 290Hz as it does now .
Yes.
 

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This may well be true but modern domestic harmony needs to be maintained .

Now you finished saying mines bigger than yours did what I say make sense and through you an Tonys advice have I learned a little something ?
Yes it does.
 
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Lawrence001

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2.5 way is different - you run the full bass plus midrange through the "mid" driver and just the bass through the "bass" driver. Andrew is running a 3 way, not a 2.1.
Oops I wasn't very clear, I meant his driver configuration is more like a 2.5 way speaker but he's doing it 3 way which is sub optimal, it would work better as a 2.5 way as 2 woofers are the same on each side. What I'm not sure is how you could take some of the bass work off one woofer and add it to the second as they are in seperate boxes. There will be a way I'm sure.
 

Tony_J

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Oops I wasn't very clear, I meant his driver configuration is more like a 2.5 way speaker but he's doing it 3 way which is sub optimal, it would work better as a 2.5 way as 2 woofers are the same on each side. What I'm not sure is how you could take some of the bass work off one woofer and add it to the second as they are in seperate boxes. There will be a way I'm sure.
There is certainly a way if you are using miniDSP as the basis of the crossover.

Not entirely clear that 2.5 way is necessarily better than 3 way. Even with two (identical) drivers covering the mid and bass ranges, making one of them cover both mids and bass may well compromise what it does - it may do the mids better on its own than if it has to do mids and bass.
 

bencat

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8 inch?? Pah!

As an eminent British loudspeaker designer once said to me - “Anything below 12 inches is a mid/bass driver, not a bass driver”!

Why do you restrict the mid range driver to 290hz? Is there any reason that you don't go down to 80Hz and then over to the other bass driver?
The two drivers are identical and I am trying to create a three way were one driver the mid range one is used in it's best range without stress and all low has is then handled by the other driver . I am not sure the driver as used is good for really low base . As it sounds spot on and works I think I am doing some thing right .
 
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MartinC

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Now in the Sub threads the CR point is given as being around 70Hz so as to not interfere with the main speaker .
Not sure if this may be a reference to a post I made this morning? There was a poster whose main speakers I checked and their output was -3 dB at 72 Hz, which is why I referred to 70 Hz in my reply.

When adding a subwoofer but not applying a high-pass filter to the main speakers the optimal crossover point is governed by whatever the in-room response of the main speakers is. This is very different to what you're doing with your active speakers, with your 290 Hz figure sounding entirely reasonable to me.
 
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bencat

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Thanks Martin I was not doubting your advice or knowledge in fact the opposite i knew you would be right in what you were saying . As per the the title it was my lack of understanding that needed the help and my confusion over fully active integrated set ups like mine and Sub woofers which is a different set up and so rules and filter design . While I will never be fully sure about these things i am much clearer in my mind with the instructive posts that have been made .
 
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MartinC

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Thanks Martin I was not doubting your advice or knowledge in fact the opposite i knew you would be right in what you were saying .
Don't worry, I didn't read your post as some sort of criticism, just I'd guessed I may have lead to possible confusion. Plus please do challenge things I say if they don't make sense too as I wouldn't remotely claim to always be right! One reason I like posting on forums is discussing things with others and having ideas challenged is a great way for me to learn. When I'm wrong I want to know 🙂.
 
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Tony_J

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The potential problem is that there will be a considerable area of overlap between the speakers and the sub, so getting the two to work together seamlessly can be problematic - if you get unwanted cancellation between the two outputs it can make things sound worse, and the phase control on subs is used to get the best sounding result.
At the Harrogate show, I had a pair of Lowther "full range" speakers running with Ed's sub, using Ed's DSPeaker Antimode unit to integrate the two. We found that the best way to set this up was to deliberately set the sub's output much too high and then do a DSPeaker correction sweep; because the combined bass output was too high, the DSPeaker dropped the bass output to something sensible, but because the DSPeaker signal was feeding both the Lowthers and the sub, and the sub was set to output much more bass than the Lowthers, this had the effect of suppressing the bass output of the Lowthers in the area of overlap between the two. Worked remarkably well!
 
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Lawrence001

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There is certainly a way if you are using miniDSP as the basis of the crossover.

Not entirely clear that 2.5 way is necessarily better than 3 way. Even with two (identical) drivers covering the mid and bass ranges, making one of them cover both mids and bass may well compromise what it does - it may do the mids better on its own than if it has to do mids and bass.
As I understand it, if the driver is optimised for running both mid and bass, it doesn't do much harm to operate it down to its natural limit, but adding a second one at the lowest frequencies effectively behaves like a 10" bass driver, which should have better bass. I'd certainly try it if it was me.
 
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bencat

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Just to say that I have tried leaving the bass/mid down to 20Hz and also tried the Low Base unit up to 350Hz and in both cases they were not as musical and natural sounding as what I have it set to now . MiniDSP does allow a very wide option for how you use drivers and were they cut off so you are free to experiment . Strange but true the way most active speakers in production are set up often turns out to be the best sounding . At some stage I may well build a lower unit with a single larger bass unit in it and give it a try but just not right now .
 
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