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Lilmike's F20: Using the Dayton RSS390HF-4 - Official Thread

post #1 of 10
Thread Starter 
With the MFW-15s gone from circulation, I thought I would start a thread that speaks about specifically using the Dayton RS-15 HF (RSS390HF-4) in lilmike's F20 cabinet. This is the driver I have purchased for the four F20s that I am building. lilmike suggests only putting 300W through this 500W RMS driver due to bandwidth limitations of the cabinet. However, he has not had the opportinity to do actual testing with this Dayton driver, and thought it would be nice for anyone who has tested it to have a venue to help the rest of us in our amplifier and EQ selections. Thanks in advance to all who participate!

post #2 of 10
Thread Starter 
Post from lilmike on the subject on a different thread:

Power handling is related to the driver and cabinet combination. There are two limits, thermal and excursion. Thermal is simple - how much power does it take for the glue and varnish on the coil to melt. Been there, done that, don't recommend it. Excursion is more complicated, as it is sort of related to power, because more power = more excursion. It is also related to driver design - some drivers can handle it, some can not. It is also related to how you load the driver - what sort of cabinet is it in.

Excursion limits are typically discussed with two numbers, given in millimeters.

xmax = linear excursion, which is established by the driver's motor design or measured performance. Things tend to start sounding bad at this point, but you're not damaging anything by crossing this limit.

MFW = 13.02 mm per Eminence specs
RSS390HF = 14 mm per Parts Express

xmech = the point where moving parts hit stationary parts. Things go badly here - coils go clank, suspension makes noise, tinsel leads slap or break. This is a bad place to be, the driver may be irreparably damaged by exceeding this limit.

MFW = 20 mm per Mark Seaton, but this is suspension noise, not collision
RSS390HF = ?, but a web search suggests that 20 mm is appropriate

We can reach the power limit first, or we can reach the excursion limit first. That depends on how we load the driver. Simulations are invaluable here, but real world testing is what matters most, because the simulations I generally use are "nonresonant" and "lossless", whereas the real world is resonant and lossy. Simulations suggest that at 300 watts, I should be exceeding the point where the MFW-15 makes significant suspension noise. When I tested the MFW in the F-20, I did not reach the mechanical limit of the driver, and I exceeded the thermal limit by 33%. I certainly exceeded xmax, but I did not hear any complaints during high power sine wave testing. Honestly - I did not exactly wait around for it to happen, but we were looking for it and did not notice. High power sine waves are something that will kill drivers dead if done cavalierly. Hence - I concluded that when used in this cabinet, a 300 watt amp is a great match for the MFW 15, when used with a highpass at 20 Hz.

The F-20 was about getting the most out of the least. I targeted a 115 dB SPL at 20 Hz, measured at 1M in a groundplane setting, then worked backwards from there. I used the MFW because they were available, and provide a LOT of displacement for the dollar. I got a driver, measured the Thiele-Small parameters to make sure they were consistent with what was provided by Eminence, then modeled a bass horn to meet my goals. I folded the design into the simplest horn I could while minimizing the compromises wherever possible. I sacrificed size, and I limited bandwidth. Something had to give, I wanted low and loud, so I accepted large and I gave up the subsonics because huge was out of the question.

The fact that other drivers work at all in this cabinet is simply a matter of coincidence. The fact that a number do is a very happy coincidence. I'd power the RSS390HF with 300 watts personally. I'd also recommend a highpass at 20 hz, because in my opinion, applying watts of amplification outside of the operating bandwidth of a bandwidth-limited cabinet is a bad idea if you're after accurate, low-distortion reproduction.

SPL? Can't tell you what your room will give you, but four, in a cluster, outdoors in a groundplane setting should deliver in excess of 125 dB at a meter when fed with 300 watts each. This may not be enough for a huge room, but more power won't help things.

Funny thing about adding more power - it is a logarithmic progression. 1 watt to 300 watts nets you 24.75 dB of SPL increase. According to the math, increasing from 300 to 500 watts gets you 2.2 more dB, but exposes you to burnt or clanked coils, and does not account for losses due to voicecoil heating. A lot more risk for very little benefit in my opinion.

I think 300 watts will be safe based on the simulations, but I have not actually tested the RSS390HF in this cabinet, nor have I measured the Thiele-Small parameters of the RSS390HF. Comparing modeled results at 300 watts suggests that at the same drive voltage, the RSS390HF (gray) has a lower excursion than the MFW (black).

post #3 of 10
Thread Starter 
Post from Looneybomber on the subject from a different thread:

As shown in this picture, excursion will be a problem for the Dayton HF <22hz and 35-45hz.
The black line shows the excursion of the driver (MFW) with 250w of power. Frequency is along the x-axis. The Dayton HF will have a similar excursion profile due to the horn and is limited to 14mm with a hard bottom somewhere beyond that. But I don't know if it's 18mm, 22mm, 1000mm... Suffice it to say, staying within xmax is the game plan.

You'd have to have lilmike model the HF to see how much power it can take at 40hz because with a lowpass XO set in the low 20's, that will be the only area it'll be excursion limited (nearly the same limitation the MFW driver has). Maybe 325w? Otherwise, it should be able to handle 500w everywhere else.
*edit* It's worth noting that at the excursion minimums (~27 and 63hz), the lack of movement means there's little air being moved past the voice coil and greatly increases the chances of thermal failure if pushed. In layman's terms, don't feed it gobs of power.
post #4 of 10
Dutch: Are you also going to use this thread as a "build thread". I can't remember if you have one or not. I probably should have searched before posting...what a n00b mistake.
post #5 of 10
Thread Starter 
Originally Posted by Looneybomber View Post

Dutch: Are you also going to use this thread as a "build thread". I can't remember if you have one or not. I probably should have searched before posting...what a n00b mistake.

No; click here to see the build thread for both my F20s and my 4pis. In order to keep the continutity of the pictures, I will just be adding pictures and commentary to the original post, but will post questions and other such dialogue as new posts in that thread.

I wanted to create the thread on this page for others who have used the Dayton RS-15 HF in their F20 cabinets so that the rest of us who are still considering how to power them and what amps/equalizers to use can have a resource for that in one spot. I suspect this driver as well as the DVC will get used a lot more now that the MFW-15 is no longer available.
post #6 of 10
The really simple answer is use an Oaudio 500w amp (one for each F20), and set the subsonic filter to the desired setpoint to get you all the clean bass you can get, and not have too many headroom problems above 30Hz...

The 300w amp they offer would be good too, but only has a highpass that begins cutting at 20hz....no adjustability.

I use Reference HF drivers in my THTs (very similar to F20), and I have used both the Oaudio 300 and 500w amps. Both do their job well, but i prefer the adjustability of the 500w version.

If ultimate adjustability is needed, pro amps and minidsp.

post #7 of 10
Nice post, DutchSwan.
post #8 of 10
Thread Starter 
I opened a dialogue with Alex and Elemental Designs in Newton, IA where MkTheater had the F20 programmed into a CNC. Alex is going to provide me with a few quotes depending on which wood I want to go with. While everyone knows that baltic birch is the best, it might be past the point of diminishing returns on quality of sound for me since these subs will be concealed behind a wall in our application. Fortunately for me, Elemental Designs is a mere 5 MINUTES out of my way as I drive to our winery from my house. So I will not have any shipping cost, whereas others who might order a "flat pack" from ED would have associated S/H. For the benefit of everyone, I will post the pricing on lilmike's original Cinema F20 page once I have the prices for the various woods that ED can get.
post #9 of 10
any updates to this? no one else using this driver in this enclosure with findings to report?
post #10 of 10
Originally Posted by thaddeussmith View Post

any updates to this? no one else using this driver in this enclosure with findings to report?

i'm still a few weeks out from going to pick this up ...but here's the progress on mine, which is built around the HF-4. 3/4" MDF, using pocket hole screws to minimize external screws and filling etc. Corners will be rounded, and a second panel is going to be attached on the bottom - both to help with bracing around the mouth and to give the 5 rubber feet something to screw into.

final panel being glued on..

access panel, still needs some work to be a tight and tidy seal...

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