RS100 or RS52 for midrange - A to B

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There is no such thing as a woofer doing too much, or a midrange doing too little. In fact getting the woofer to do more, all things being equal, will reduce the average power and thus the power compression on the midrange without greatly affecting the same of the woofer as most of the energy within music is centred lower down than higher up.

After balancing the pros and cons you would consider it better to have 2 x 8" woofers covering the frequency range 400-800 Hz rather than a light, efficient, short stroke 5" midrange designed to cover the range? If so, why do you think the tower speakers from the established commercial home audio companies might opt to use 4" or 5" midranges with their 2 x 8" woofers and 1" tweeters and not a 2" upper midrange driver?
 
And the power required?

Okay this is confusing, on their website Dayton state that the RS100P-4 has a 2.83vRMS voltage sensitivity of 88.5dB, yet in the datasheet it says it's 84.1:confused: I think there's an error in the datasheet where it should be displaying the 1 watt dB level.

Either way if we take the 88.5dB figure for the 4 ohm voltage sensitivity, then to hit 106dB we need a gain of 17.5dB. This is around 21.2vRMS which is well within the voltage swing capabilities of a standard 100 watt @ 8 ohms amplifier. Into 4 ohms this = 112 watts, which obviously exceeds the RS100P-4s power handling, but this is assuming continuous excitation, which music is not. Tweeters, with their 5-15 watt continuous power handling, only survive at high SPLs due to musics low average power at higher frequencies.

After balancing the pros and cons you would consider it better to have 2 x 8" woofers covering the frequency range 400-800 Hz rather than a light, efficient, short stroke 5" midrange designed to cover the range? If so, why do you think the tower speakers from the established commercial home audio companies might opt to use 4" or 5" midranges with their 2 x 8" woofers and 1" tweeters and not a 2" upper midrange driver?

It's got nothing to do with blanket statements and everything to do with considering the individual drivers in question.

The RS225 has exemplary performance up till around 1kHz with pure pistonic behaviour and very low harmonic distortion.

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It is not going to be a limiting factor vs crossing up that high with regards to individual driver performance and the overriding concern would be achieving the kind of off axis performance that you wish for in the vertical plane. This, as was touched on before, is governed purely by the driver C2C spacing and is absolutely worth looking at, but with close driver spacing and the rather large flange of the RS52 you'd still be under 1 wavelength if you used an 800 Hz xover. Given the fact that you could go lower than this with the RS52, down to say 700Hz, only makes things even better.

If you went with a 3-4" cone driver instead you'd be able to cross even lower and get the C2C spacing closer to boot. The trouble with this is finding a decent candidate for the midrange of this size. As was pointed out before you've got plenty of surface area in a 3" driver for hitting high SPLs at relatively high frequencies (400Hz), the trouble is finding one with a high enough sensitivity to mate with the RS225s. This isn't so easy as most small drivers are aimed at mid/bass duty where they sacrifice sensitivity for bass extension. The RS100 is a prime example of this, which is why it'd require using the 4 ohm version to bump the voltage sensitivity up high enough otherwise you'd be stuck.

I am reminded of the good old Audax HM100Z0 which was a dedicated midrange driver with ~93dB sensitivity and 8 ohm impedance, it would work well in this application although its absolute distortion isn't as low as newer stuff. It's a shame that manufacturers ignore this kind of application.
 

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Dayton Audio RS100P-8 4" Reference Paper Midwoofer 8 Ohm
Sensitivity 86.2 dB @ 2.83V/1m

Dayton Audio RS100P-4 4" Reference Paper Woofer 4 Ohm
Sensitivity 88.5 dB @ 2.83V/1m

I would like to keep this project simple, ideally I would like to just keep it TMW(W). I've never been impressed fully with any TM design, and just like the full sound across the range that a good 3 way provides in an average size room with high ceilings etc. My goal is to pick the best option from the available RS drivers (to keep the look and price of the project uniform, and possible even "voicing" of the drivers being from the same family). No doubt RS125 and RS150 are both very good drivers, but it doesn't make sense to me to use RS150 as the "midrange" in the passband when at the top you have RS28 that can cross low and at the bottom you have RS225 pair that can go easily to 700-1000hz. Negating the need to use a midrange/midbass hybrid driver like the RS125 or RS150 that was designed to do both things GOOD, but not any one thing REALLY good? In my mind I keep thinking that a driver that was designed to be neutral, low on distortion in the passband (dome or cone) would be a better choice for a specific frequency range. We are talking specifically what, 650-900hz to 2000-3000hz range.

Am I just thinking about this wrong?

I don't want to make the same mistake I did with my previous design where I used a 6" mid/midbass driver as my midrange. I want a better midrange integration in a 3 way setup.

Padding a tweeter down is fine, but I don't want to add resistors in series with the woofer section.

Keep the feedback going guys! :)
 
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There's nothing inherently wrong with using a larger driver as a midrange, but you do have to think about how you're going to maintain a good off axis performance as the drivers start to beam earlier.

The ubiquitous 6" + 1" design became really popular simply because it married decent bass extension with decent midrange. Most 1" domes are comfortable crossing to a 6" driver without making the off axis a complete disaster, but nevertheless most 6"+1" designs leave quite a lot to be desired where the off axis comes in.

To get around this you need to cross over below 2kHz and preferably as low as the tweeter can go. Most neglect this, some don't and some even ignore it completely, crossing over ridiculously high and creating an off axis nightmare.

If you want to go 6" mid range, you either cross low, or use a wave guide for a good directivity match. This means you end up using a 6" wave guide with a 1" tweeter and end up crossing over around 2.5kHz. This is a much better way to use a 6" as a midrange and as there are loads of 6" drivers out there you've got a ton to choose from, although the high xover frequency of 2.5kHz does require that your 6" have a soft cone and be well controlled through its breakup region.

The 6" Satori would make for an excellent mid range driver as would the far cheaper SB17MFC35-8.

Certainly the vertical off axis in such a design would suffer as the C2C spacing of two nominal diameter 6" drivers (the mid and the wave guide) would clash a little with the target xover frequency of 2.5kHz, but there is not a lot you can do about that. It's a sacrifice you pay, poorer vertical off axis performance but superb horizontal.

Naturally if you're not going to go down this route then using a smaller mid range is definitely the best bet. This is usually the number one thing that people want to do when going for a three way. That is throwing away the good old 6" mid/bass and using a smaller driver that is inherently more linear (hopefully) higher up in frequency with less issues to deal with off axis.

There are many choices to make when deciding on the diameter of your mid driver, but the smaller it is the better its off axis response will be and the higher up it will operate before any serious breakup issues start to occur. As you're using an 8" bass driver I'd ideally want to use a 3-4" mid, providing its sensitivity is high enough to keep up with the paired bass drivers and cross over around 2.5kHz. Why 2.5kHz? To give you an extremely even horizontal off axis response and a very wide primary listening lobe in the vertical axis too.

I recently designed a tiny fully active two way using a 1" neo tweeter, 4" mid/bass with a DSP xover. I placed the xover as low as the tweeter could comfortably go, in this design a 4th order 2kHz acoustic. Yes it's very low, but what was gained from this was an extremely smooth and even presentation.

Padding down a midrange or tweeter is par for the course, padding down the woofer section is a complete no-no.

One RS225 sits at around 88.5dB half space. Two of them make that up to around 94.5dB half space. Then factor into things baffle step losses and you're back down around 5dB, providing free wall placement, so 89.5dB. You will lose a little bit from that due to the series resistance of any inductor placed in series with the drivers, so you'd be at around 89.2dB net sensitivity for the bass section.

If you cross over around 600-800Hz and 2.5-3kHz you will get around 1.5-2dB of bandpass gain. This is sensitivity added onto the mid range drivers and relaxes the requirement placed on the midrange driver for its required sensitivity. Still, I'd err on the side of caution and go for a solid 88.5-89dB driver.
 
Thank you 5th element for detailed reply. You've pretty much nailed it, and some of the areas you've touched on is probably why I've been happy enough with my current speaker for so many years, the xo point I have between ss9500 and pl18wo is just under 2200hz. I can listen to it for hours and there is no ear fatigue, it can play plenty loud. But we always want to improve something , and see how much better it can still get right ? :) Otherwise we wouldn't be on this forum DIY'ing.

I think what I'll do is order a pair of the RS52 drivers, as they are pretty cheap and go from there. I am thinking I'll mount the RS52+RS28 on a baffle and mount it on top of my existing 8565 sealed cabinet (pl18/ss9500 is in it's own sealed cabinet that sits on top of the 8565), and I'll just start playing with a new crossover and see how I like the RS52/RS28. If I like what I hear, then I can either make a new cabinet for two RS225s to keep this modular or scrap the RS52 idea for something else.
 
Jean has similar thread at Tech Talk Thinking about putting the RS drivers to a good use (RS28 + RS52/100 + 2 RS225s))

Some thoughts that seem like being missed,
- mid is naturally ok with less sensitivity, because of overlapping spl from W and T specially with LR2 topology and good symmetry (duelundish acoustic roll-off)
- RS52 with closed chamber gives more freedom for baffle design
- RS100P must be a very nice driver and it's frame is smaller that RS52, but requires a well damped closed box
- Putting two RS225 in series should be investigated, baffle width might take care of bsc!
- baffle width and driver positioning should be examined with simulations

My choice would be a WWMT speaker with 2xRS225, RS100P and RS28, xo around 400Hz/3500Hz all LR2 (physical time-aligning for M and T)

I had a very similar proto a year ago, with 2x SEAS 8", Audax HM100Z0 and Fountek NeoCD3.5H (without horn). I had minidsp xo+delay+eq wich is a nice way to test configurations "live". A single 8" is in trouble (distortion) first, serial pair halves distortion%, but with parallel BSC can be handled easier. I have zero competence for passive xo design...
 
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Too many possible projects to do, too little time/room to do them all :)

My two projects at this time are to put these RS drivers to use , hence my post .

Another one is to upgrade or re-design my 10 year old 3 way scan speak project with another TM section (maybe 3/4 tweeter and newer scanspeak mid).

I've done the active route before, and just don't want to deal with that again, would like to keep it basic with only 2 amplifier channels (maximum 4, two channels for W and two for the TM section).
 
I have designed two speaker using the RS52 (as a kind of filler) and the Seas DXT tweeter, crossed at -6dB 800Hz and roughly 3k. It's the best combination for the money I can imagine, excellent clarity, blending very well :D

I think the waveguide of the DXT is an advantage over the rs28, but this is also a question of personal preference...

I've used either two 7'' (Seas ER18) or two 8'' (Eton 8-502) symmetrical to the RS52, crossing in a "kind-of-D'Appo" manner. I#ve thought of using the rs225, but didn't do it for reason, which are now incomprehensible to me... ;)

If you are interested, I can add more details and crossover schematics.

Best
Leif
 
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