Seas Froy Mk3 modify

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Hi Folk,

I just completed the DIY Project about Seas Froy Mk3 (MTM design ) and with listening experience does not satisfy.

1) 3-D and atmosphere not enough
2) Middle band a bit dull and not bright
3) Low band and extension not enough (I will add sub-woofer later)


a) Any modification on the original xover to solve 1) and 2) ?
b) If I add the sub-woofer with Scan-Speak 18WU in 7 liters box to parallel the Froy Mk3, what the xover is required and such drive should be 4 or 8 ohm selected ?
Well, re your points, in order

1/ It rather depends how you define '3d' and 'atmosphere' as these are subjective matters that vary between different listeners and different opinions. Various technical characteristics can connect to this, but which will depend on what, exactly, you are referring to. The MTM configuration is also quite directional, vertically, so you need to be on the tweeter axis for optimal results.

2/ It's not designed to be bright, althought there is a slight lift between 2.5KHz - 5.5KHz, according to D'Appolito's measurements (taken in 2003). Personally, like D'Appolito, I have some reservations about the crossover as I'd rather have greater suppression of cone modes from the midbass units, but those aren't likely to make it sound dull.

3/ Nothing you can do about this without adding bass assistance / subwoofers. You can get more LF out of the midbass units, but you'd need to completely change the enclosure & go to a quarter-wave floorstander.

In essence I suspect you're going to have to decide what characteristics you want, and change the whole crossover to suit, as far as possible. If you want to try something simple, you could see if reducing R2 to 1.5ohms & increasing R3 to 15ohms helps. That should give roughly another 1.5dB or so from about 5KHz upward. I'd rather change the whole filter, but without knowing exactly what you want & optimal in-box measurements, that's far from straightforward.
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1) 3-D and atmosphere not enough
With this kind of design you have to listen exactly on the tweeter axis so each woofer has the same offset. I find the D'Appolito design flawed for this reason.
2) Middle band a bit dull and not bright
Mag units can be a bit 'dark' sounding but ultimately revealing with the right front end.
3) Low band and extension not enough (I will add sub-woofer later)
They don't seem to have much below 100hz. I'd recommend an active sub for the best integration and extension.
I think they are showing some wrong measurements of the low section or better they did not show the combind curve from the port and the woofer, just the woofers themselves...

Because if you model the speaker with the network and the portlength and size plus the volume (roughly 9 liters netto) you get something like this for the "bassresponse" (black curve)
But when you model the woofer with the network in a closed box by given size, (the red curve) than the curve goes a little more in the direction of the measurements shown in the file of the "assembled speaker" in the pdf.
But this is in both cases no bass at at...
Just to show that the woofers are capable of producing significant bass i simulated it with an other internal volume and a bigger port (the blue curve)

To put it simply the given box is way to small for the two woofers and should be rebuild to a bigger size which can be added juts by making it to a "small" floorstander without changing the width!!! because than you have to redo the network!
The simulation of the blue curve is for box with 32 liters and a port size (same port place) doubled the actual (2,6 cm instead of 1,3) and about 0,7 cm shorter than he original.

That should fix the problem of the lacking bass and for the lower middleband because now you just have a oversounding pseudo bass with a to reset lower middleband.


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I'd certainly agree that you need to be on the tweeter axis. Assuming you don't actually want the greater vertical directionality (some do) an issue with MTM designs is that they're often crossed too high, which often results in a duller sound off the vertical.

Re magnesium cones sounding 'dark', I can't say I've ever found that myself; assuming their cone modes are sufficiently stamped on, the cones themselves don't have any sound as such: that's the point, they're working more or less as pure pistons and any colouration from the driver is caused by other factors e.g. motor design / distortion, power compression &c.

LF support is pretty much required with these enclosures as-is.
I don't use the Froy myself. I simply ran a brief simulation of the Millennium tweeter on the Froy baffle & noted a couple of things you might want to try adjusting with its high pass. It's essentially just level / EQ adjustment via altering the resistor values; a wholesale redesign would be a different matter. For that you'd need accurate on-baffle measurements of the drive units to do it properly.
Hi Scottmoose,

After I evaluate to remove C5 and R3 then change R2 to 3R3 ohm, high band is fine to me. About adding the subwoofer, my plan is set the cabinet size in 7.5 liters net volume (20cm high x 18cm wide x 21cm deep), then the MTM sit on top of it.
Can you give me advice how to design the sub-woofer crossover, which I want it cut-off at 180Hz or 240Hz with external switch control ? And its port design like following box at front panel with rectangle shape or else use a sealed box design.

These are three woofer models that I want to use. Can you advise me which one is suitable for my case, thanks in advance !
Morel Supreme SCW636 Carbon Fiber Cone Woofer
ScanSpeak Revelator 18W/4531G 7" Mid-Woofer 4 ohm
ScanSpeak Revelator 18W/8531G-00 7" Mid Woofer 8 ohm
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