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Replace 3 way with 2 way + sub for better room correction?


May 19, 2020
I've recently got a mad idea of replacing my 3 way speakers with a 2 way bookshelf speakers + sub.

The reason behind behind this idea is that I cannot use 3 way active crossover + group delay because of my current speakers.
My current speakers are Martin Logan motion 40. They have two pair of pots at the back with two internal crossovers at 500hz and 2.6khz with pots being for 2.6khz.
I use them with a quad amping setup with an external digital active crossover at 2.6khz + group delay + room equalization.
Because the speakers have two pairs of pots and not three, I do not have separate control over the group delay and crossover for the low frequencies.

The idea is to replace Martin Logan with 2 way speakers + sub. I'll have then 2 active crossovers and separate control over low mids and highs.
I did check the Passive Speaker Recommendations but most of the 2 way speakers just have one pair of pots and I need two. so I started to lean towards DIY. Something SB Acoustic Bromo without crossover as I'll be using a active one plus a sub

Additional question arises about the room.
Yes I know reflections, window on the right etc, but unfortunately I cannot reposition anything (renting).
Are 2 way speakers (1 +6.5) will be enough to cover the area to the couch? Am I delusional and should just leave it as is or buy a 12 sub?

My room diagram:
Photo 14-5-2024, 08 30 35.jpg

Thank you

p.s. additional but not major reason for swap is that I might have to vacate the property and want something smaller
Then beside or behind the left speaker and to the left of the couch if the drawing is fairly accurate. I have done as much, and the results smoothed the the bass response remarkably well before DSP.
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Then beside or behind the left speaker and to the left of the couch if the drawing is fairly accurate. I have done as much, and the results smoothed the the bass response remarkably well before DSP.
Back to the main question then with all assumptions - is it viable to change to bookshelf speakers? are they are going to be enough giving the listening distance?
I can't answer your question. Normally, "active" means that the speaker's drivers are powered by internal amps. While many speakers have separate taps to be powered separately by power amps, I have only ever used speakers with single taps and am unsure of the benefits of supplying power to individual drivers with different, external amps. It sounds good though.

The use of larger, floor-standing speakers often comes down to how loudly one wants to play music, particularly in a large room. I own large speakers, but use small, 2-way speakers on stands (Revel M105s), which allow me more flexibility in placement, in one case, firing over the arm of a couch a 3-way would not allow.

I hope someone can answer your question. I'm interested.
I like the idea of 2 stand-mounted mains and in similar fashion to Elk above ^ recco minimum x2 subs to balance the room.
I'm a bit confused by your question, maybe you are confusing pots (potentiometers) with terminals?

Looking at the user manual for the Martin Logan Motion 40, I don't see any pots. I do see terminals that allow bi-amping between high and low frequency, but I don't see any option to defeat the internal passive crossover. The manual specifically says the passive crossover cannot be bypassed.

So I don't see how in your current setup how you are using an external active crossover with the Martin Logans. I also don't know what you mean by group delay in this context, are you just talking about adding delay?

My two cents, I don't see any reason to bi-amp the Martin Logans. Why not just add a sub to your existing setup?

You should play with REW's room simulator.


This is a sim of your room using the dimensions you provided. Top right is the predicted frequency response. REW assumes you own perfect speakers, have a rectangular room, and furniture isn't modelled - so your actual measured FR will be different. I have found that it is reasonably accurate in predicting bass response up to 80-100Hz.


And this is what happens if you add one sub and place it between your speakers.

I suggest you download REW and have a play. Placement of subwoofers is extremely important. Every listening room has limits on where subwoofers can be placed, e.g. you might need access to doors or cabinets or your partner might object. There is no point getting two subs if you can't place the second sub properly. It might provide negligible benefit or even make bass response worse.

You will need a plan on how you are going to use your subs. Proper placement is only one of the issues. Subs have to be time aligned, phase aligned, and ideally have some form of DSP to smooth out the peaks and dips that occur in every listening room. If you have DSP, you want to place your subs so that you have as few dips as possible. Don't worry about peaks, because DSP can cut those. But dips can not be boosted.

So before you spend any money, come up with a plan. Think about where you are going to place your subs. Use REW's room sim. Think about how you are going to incorporate DSP into your system, or at the very least some form of PEQ.

And BTW I agree with @mdsimon2, there is no need to change your speaker unless you want a smaller speaker in case you have to vacate. Like him, I am also confused by your use of the term "pots". The normal meaning is "potentiometer", some kind of volume control. I am assuming you mean "speaker binding terminals".


I am also not sure what you mean by "cover the area to the couch". If you mean volume, well that depends. You can not make a generalisation about 3 way speakers being louder than 2 way speakers. It depends on the speaker.
Some people are more sensitive when it comes to sub localization than others. Depending on the room having sub on one side could sound really bad, as it did in my tests. I also couldn't stand having the subs on my side walls for some reason. The only place where they made sense were corners, but only where there was symmetry and then I also preferred them in stereo rather in mono. At this point, for music, I prefer just full range speakers with all of their downfalls, to sub or subs with their downfalls. So I encourage you to try it first before any commitment, as all of the setups I tried came out fine in measurements (all of them were room corrected, phase aligned, delayed etc. to the same target), but some of them were just unacceptable, whereas full range speakers were always at least good enough to not be bothering
I am assuming you mean "speaker binding terminals".
Yes sorry speaker binding terminals. English is not my first language.
My two cents, I don't see any reason to bi-amp the Martin Logans. Why not just add a sub to your existing setup?
I can add subs to my existing setup easily and if the subs are active (which most of them are) I can do 3 way output from my preamp, but It makes the set up too bulky. That's what I'm trying to understand what's technically (assuming I measured the room, got two subs, and got bookshelf speakers) better.

I've also measured (using Iphone as I'm too lazy to use umk and rev for it) the loudness I need at the couch and It is around 72-75db, adding 10% just in case, it appears that I need 80-83db of distortion free at the distance of 2.5 meters from the speakers.
Assuming I get\build something like Bromo (I want ceramic speakers frankly speaking) which is close to philharmonic ceramic mini, I guess it should be enough considering that Erin states that "My max volume was about 95dB @ 3m before the woofer would “plop” and I need 83db at 2.5m
Just FYI, my friend calibrated his iPhone SPL meter with my SPL meter. His iPhone 12 was 7dB too low. Then there is the possibility that iPhones don't have flat responses.

If I understand you properly, you want more bass output. But if you add 2-3 subwoofers to your existing setup with your ML floorstanders, it will take up too much space. This is why you are considering bookshelf speakers + subwoofers?

I don't think you would save much space by changing to bookshelf speakers. Bookshelf speakers need to be placed on stands anyway to get the best performance. Once you do this, they eat up as much floor area as a floorstander. The only way to save space compared to your existing setup is to place your bookshelf speakers on top of the subs, but now you are limited by where you can place your subs. As mentioned, subwoofer placement is extremely important.

I think that for now, if your priority is to get bass whilst eating up as little room space as possible, get one sub and find a proper location for it with REW's room sim.
I don't think you would save much space by changing to bookshelf speakers. Bookshelf speakers need to be placed on stands
Bookshelves + stands + subs are more packable than a floor standing.
My main concerns are
If the sound will be better (that’s why I don’t want to add sub to my current speakers really)
If I’ll get enough distortion free volume range.
Is the sound going to be better? Don't know. To answer that question, you need to know (1) how your speakers currently perform in your room (this means take some measurements), and (2) what speaker you are proposing to replace them with. You then look up the measurements of the proposed replacement speaker, and compare them with what you currently have. This will help you predict whether your proposal will be an improvement or not. Right now, we simply do not have enough information.

Will you get less distortion? If you are adding subs and removing bass from the mains, the answer is most likely yes. But if you are not removing bass from your mains, the answer is likely no.
Because it's easier. You might be interested in following Geddes' 3 sub method. I haven't tried it so I can not tell you what it sounds like.
Thank you. I will definitely have a read for learning purposes although three subs looks like a bit to much at least at this stage.
it is what Wilson Audio does with the Watt plus Puppy An exceptional speaker indeed
i would use two subs one per channel to avoid problems
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