2-Way W/Dual Subs Vs 3-Way

[Brian Walter]

I'm planning on building an MTM using the RS180 and RS28 drivers, likely either the Modula or Natalie or similar. I would like to build the MTM in the same box as the sub or bass bin. Now I could cross the MTM over at a standard sub/sat frequency of say 80hz, or I could cross over at a higher frequency of say 250hz, making it more of a 3-way design. In either case, I will be crossing over actively between the bass bin (1 or 2 RS265HF) and the MTM. I could also use a separate box for the MTM and the bass bin, but my preference would be the single box approach.

My question is what are the advantages and disadvantages of each approach? and what would you suggest? I've got all the drivers (only 2 - RS265HF at the moment) and I hope to finalize my design and get started fairly soon. Unfortuneately, my day job has been getting in the way of starting, or I probably would have already done so.

Brian Walter

[ThomasW]

You'd use a higher XO point for the bass bin. The idea with a bass bin is to let it run as high as possible, taking the workload off the smaller midwoofers

If your bass bin is going to function as your sub then you certainly want a pair of drivers in each box, and to have the bin as a separate box....unless you have access to a fork lift ....

[Brian Walter]

From a sound quality standpoint, what do I gain by crossing at say 300hz versus 80hz?

So, with the RS265HF's your suggesting I should be looking at running them up to around 250 to 300hz I would guess. If I do this, how does this effect the crossover of the Natalie P or Modula, or doesn't it? I mean, can I use the existing passive crossover and simply create a 24 db/octive HP & LP active crossover at 300hz and call it good or do I need to modify the passive crossover?

Other than the Wilson Sofia, etc, do you have any examples of designs using separate boxes that I could look up to get construction ideas from?

Brian Walter

[ThomasW]

From a sound quality standpoint, what do I gain by crossing at say 300hz versus 80hz?

You get the bulk of the lower midbass workload off the midwoofer. That allows them to play louder/cleaner.

No you don't need or want to rebuild the passive crossover. Just get something like the $90 Behringer CX2310. That way you can experiment with various XO points.

I don't follow what's being offered in the retail speaker world. Most of the time they're into so called 'fill-range' systems with everything in one box. Those are visually impressive, expensive, and heavy.

With a bass bin you can align the acoustic centers should you so choose, and they don't require a forklift to reposition. In addition you can upgrade the sections independent of each other as technology or your tastes change..

[Mark K]

Hi Brian,

I agree with Thomas. If you look at my Usher sealed 2 ways and some of the distortion plots, you can see, even a 7" midwoof of high quality is strained at 80 Hz at high spls. More than is generally appreciated. So moving the xover to 250-300 is much better for the mids, and can help with smoothing the floor bounce. It's a clear advantage of a true 3 way.

[cjd]

I'll chime in here as yet another "I agree with Thomas"

Particularly if you're looking at something like the Natalie P which pushes the upper limits of crossover on the midrange, keeping bass away will help keep it in the more ideal range and limit distortion artifacts that creep in.

I'm crossing the big 3-ways to the RS180's at ~300Hz. I think.

C

[Brian Walter]

Part of the problem I'm having with the design is that in order to use the 10" woofers, I need a box say at least 11" wide, and the Modula and Natalie are designed for 9" - 10" wide baffles. I realize that the MTM box doesn't need to be the same width as the bass bin, but I think it would certainly look better if it was. That's why I was asking about seeing other designs, to see how others did it. Maybe there is a design out there I could copy (visually).

At any rate, it seems that everyone thinks I need the extra 10" woofer per side, so I'll go ahead and order them while they are still on sale.

I'm sure I'll have more questions as I get into this.

Brian Walter

[ThomasW]

It's pretty much standard procedure for really high-end companies to bevel the front of the bass bin. That way you can keep the nose of the bin very close to the width of the MTM section.

Or....

Make a facade for the MTM with grill cloth. The will give you the look of a wider baffle without the acoustic penalty.

[Hdale85]

Could you side mount the subs? im no expert at all on this lol so that may alter the SQ so dont ask me just asking as i was thinking of building a floor standing speaker with a sub mounted on the side lol

[ThomasW]

Side mounting limits the usable XO point to no higher than ~100Hz, so that's not a viable option for a woofer.

[Brian Walter]

Thomas,

As you mentioned, a side mounted woofer really only works for a sub-woofer. That's what I have right now is a side mounted sub with a front facing MT. This combination works fairly well, but I'm looking to improve it. One of my options has always been to simply replace my drivers, and crossover with the RS stuff and use the same box (would need to change the front baffle). I could actually fit the MTM into the same box, but I would be limitted to using a single RS265HF. I have a removable baffle, so it wouldn't be too hard to make the internal changes.

The main reason I was asking about the bennefits of going to the higher crossover frequency was to help me decide if I could justify the additional work and expense of building a new set of cabinets versus simply modifying my existing speakers.

Thanks for you input,

Brian Walter

[cjd]

Here's the thing.

Complete speakers are generally easier to sell than components.

On a vaguely related note, our local Menards has actually started stocking real live Baltic Birch plywood in 4x8 sheets! ~$56/sheet IIRC.

C

[JonMarsh]

From a sound quality standpoint, what do I gain by crossing at say 300hz versus 80hz?

So, with the RS265HF's your suggesting I should be looking at running them up to around 250 to 300hz I would guess. If I do this, how does this effect the crossover of the Natalie P or Modula, or doesn't it? I mean, can I use the existing passive crossover and simply create a 24 db/octive HP & LP active crossover at 300hz and call it good or do I need to modify the passive crossover?

Other than the Wilson Sofia, etc, do you have any examples of designs using separate boxes that I could look up to get construction ideas from?

Brian Walter

If you're keeping the same baffle width on the MTM, then I'd keep the same passive crossover, which includes BSC, and use the active crossover in the 200-250 range. A little lower is OK, too.

These used a 180 Hz active crossover.




This is the crossover. Jensen transformers, custom DIY analog PCB's (mine).






It used fairly high grade opamps in conjunction with high power video buffer amps (ones capable of driving several 75 ohm loads in parallel- they look like the so-called "chip amps".

I still have that unit.

~Jon