My RS180 MTM Design

[PWR RYD]

Re: My RS180 MTM Design

My only concern would be the difference in sensitivity between the RS28F and the original shielded version RS28AS that Jeff used. I don't remember Jeff needing any padding on his tweeter. The F version may not be able to keep up with the two RS180's in parallel.

[kraigo]

Re: My RS180 MTM Design

Thanks for your reply. The sensitivity of the RS28F-4 is pretty much the same as the sensitivity of the RS28A-4. Was the shielded RS28AS-4 more sensitive? Since the parallel RS180-8's and the RS28x-4 are both four ohms, shouldn't the RS180's combine to add 3dB over a single RS180? You get no boost for going from eight ohms to four ohms, the combined RS180's can be thought of as having a sensitivity of 90 dB as does the RS28F-4. Is my math or understanding wonky?

As far as the crossover, I'm mostly wondering if those caps are what people tend to use. The cost of the crossover components is almost $100, which I'm willing to pay and is cheaper (due to low component count) than almost any other crossover you'll come across for the MTM's that use this configuration. OTOH, if I'm way over spec-ing things or I've made a rookie mistake, I really want to know before I put out the dosh.

Thanks again for the reply and any help you guys can give me.

KO

[Jeff B.]

Re: My RS180 MTM Design

Thanks for your reply. The sensitivity of the RS28F-4 is pretty much the same as the sensitivity of the RS28A-4. Was the shielded RS28AS-4 more sensitive? Since the parallel RS180-8's and the RS28x-4 are both four ohms, shouldn't the RS180's combine to add 3dB over a single RS180? You get no boost for going from eight ohms to four ohms, the combined RS180's can be thought of as having a sensitivity of 90 dB as does the RS28F-4. Is my math or understanding wonky?

As far as the crossover, I'm mostly wondering if those caps are what people tend to use. The cost of the crossover components is almost $100, which I'm willing to pay and is cheaper (due to low component count) than almost any other crossover you'll come across for the MTM's that use this configuration. OTOH, if I'm way over spec-ing things or I've made a rookie mistake, I really want to know before I put out the dosh.

Thanks again for the reply and any help you guys can give me.

KO

Your component list is fine, and probably in line with what others use.

A parallel pair of 8 ohm drivers increases sensitivity by 6 dB. We give most of this back in the form of baffle step compensation though.

I believe as advertised the shielded version is listed as more sensitive, but, and I'm going by memory here, but I believe this is correct, when actually tested head to head both versions of the RS28a were the really the same sensitivity.

[PWR RYD]

Re: My RS180 MTM Design

Yes the shielded version of the RS28A was more sensitive than the currently available unshielded version. I have both and the shielded are 91 and the unshielded are only 89. My RS28F-4 are 89.2. Not saying your project is undoable, just something to consider. Hopefully others here can add personal experience and insight.

[PWR RYD]

Re: My RS180 MTM Design

Looks like Jeff and I were posting at the same time. I'm sure he has more experience with these drivers than me so go with his recs.

[Jeff B.]

Re: My RS180 MTM Design

Looks like Jeff and I were posting at the same time. I'm sure he has more experience with these drivers than me so go with his recs.

Actually, it was a test that Paul Carmody did that showed the two identical except in the are of Fs where the difference in their Q's showed up.

[kraigo]

Re: My RS180 MTM Design

OK, one more rookie question: Someone in some thread or another posted that this (http://www.parts-express.com/speaker...lared--260-480) is an appropriate port for this cab, but my modelling in WinISD show that as not even being close to right to getting a 1ft^3 box tuned to 40 Hz. A single 3" port somewhere between 9.5" and 9.75" looks to work ("9.66" according to WinISD), but now I'm second guessing my school-of-hard-knocks speaker skills. If anyone can give me a confirmation, I'd appreciate it. That port gives (by my work) about a 53.5 Hz tuning.

Added: Or someone could just tell me what the appropriate dimensions are (bonus points for why)! :-)

If it helps, enter the following text into Notepad, save it as a .WSD file and load that into WinISD.

>>
[Driver]
Brand=Dayton
Model=RS180-8
Manufacturer=Dayton
ProvidedBy=kraigo
DateAdded=20150807
DateModified=20150807
Qts=0.31154861916003
Znom=8
Fs=35.54549813519
Pe=0
SPL=86.268920766928
Re=6.4
Le=0
fLe=0
KLe=0
BL=7.82
Xmax=0.006
Cms=0.00112
Qms=1.22
Qes=0.41839257817385
Rms=3.27685838851422
Mms=0.0179
Sd=0.01247
Vas=0.02470560978984
Dia=0
Vd=0.00007482
no=0.0025789727626
Dd=0.12600514720775
EBP=84.9572865043019
numVC=1
Hc=0
Hg=0
SPLmax=0
SPLmaxLF=78.0447656770847
USPL=87.2428497375749
alfaVC=0
Rt=0
Ct=0
gamma=436.871508379888
Rme=9.5550625
Mpow=3.09112641281459
Mcost=0
Gloss=0.03276728653333
VCCon=1
c=343.684120962152
roo=1.20095217714683
Thick=0
Depth=0
MagDepth=0
Magnet=0
Basket=0
Outer=0
Vcd=0
DVol=0
ParState=ECNCENNNEENEECCCEECCNCCENNNCCNNNCCCCNCNNN NNNNNNCC
<<

[kraigo]

Re: My RS180 MTM Design

FWIW, when I get these done, the first album I'll be playing through them is XTC's "English Settlement". Well done in terms of production, but my #1 Desert Island album for most of my life.

[Chris Roemer]

Re: My RS180 MTM Design

All of these port observations of yours seem valid to me.

[Mike220]

Re: My RS180 MTM Design

I have 4 of the shielded woofers I've been wanting to build these but am missing the aluminum shielded rs28A's. I really don't want another build with the RS28's as im coming up to my 3rd of 4th one with rs28's (its a great woofer im just tired of using it) but these woofers seem kind of fickle with the high levels of cone break up. Any other builds that use these or a potentially equal tweeter that can be used? Perhaps a sb acoustics tweeter like the SB26stnc or something else. Anyone have another tweeter suggestion?

[PWR RYD]

Re: My RS180 MTM Design

That SB tweeter is fantastic and one of my favorites. But I wouldnt push it any lower than 2kHz. I think the RS180 needs a tweeter that can cross lower like the RS28 can.

[bullittstang]

Re: My RS180 MTM Design

I disagree slightly in that I've used the SB26STCN and have crossed as low as 1600-Hz, currently crossing at 1800-Hz and 2nd and 3rd order distortion is very low and at almost 95-db it doesn't show any signs of distress. I really like this little tweeter and it's easy to work with too. Also Jeff used in his Sopranos and mentioned he is crossing at 1750'ish as well and noticed no issues. To get the same look as the RS, you could use the SB26STAC which gives you a lower FS, but similar flat response and easy to work with. Just my $0.02.

[kraigo]

Re: My RS180 MTM Design

The drivers and boxes arrived yesterday. It should be good. I'll probably order the rest of the parts tomorrow.

One more sill question: I bought the curved 1 ft^3 boxes. They are 4.5" wide in the back. Everything I'm seeing in WinISD suggests I want a 3" port - it gives me good air flow and is still short enough to fit nicely in the cabinet. In my bass cabs I've always just used a PCB tube and it's been fine for my needs. Looking at the flared tubes, the flares are bigger than my 4.5". Two 2" tubes would also work, but the placement gets more sketchy and the flares are still too big for the 4.5".

So it looks like 3" PCB is my only realistic choice.

So the question: Given not extreme volume levels, how much does one really get out of flared ports?

KO

[fastbike1]

Re: My RS180 MTM Design

It depends on the velocity through the port. If you're in the 20m/s or less area with your max power you should be fine. Rear mounted ports also help.

[kraigo]

Re: My RS180 MTM Design

I am at 25 m/s at excursion limit for the woofer (~120 watts) at 35 Hz. I'm not worried about that because I won't have 120 watts and this is mostly for music where there is not much content at 35 Hz. Thanks for the confirmation.