[Mike Cason]

I lost my Maelstrom 21" due to a burnt voice coil. I saw a ding on the end of the coil and couldn't find a suitable replacement driver so Mark is building me a pair of the Pi-18s. He will ship Monday.

I have 13 cubes, an Exodus 21" Pr to replace the Maelstrom and also have will have one AE 2100 gram 18" passive on each side. I'll mount each of the Pi-18s on either side of the cabinet and am shooting for a cabinet tuning of 15 hz or lower. Attached is Mike P's graph on the ported twin drivers simulated at 15 hz tuning.

I think this is going to be a very nice improvement from the single 21" driver. Notice the 3 dB gain in the graph. Going with Prs instead of the ports, I expect a better performance and low box tuning. I'm driving it with the Face Titanium TS1200 bridged to mono at 8 ohms for 2000 watts of clean power. I am series wiring the 4 ohm drivers.

Looking for comments...I plan on putting my drivers in the bottom PR location on either side for early floor reflections and deeper bass. Does anyone have a comment for the active driver placement either on the top or the bottom pr location. I'm always eager to listen to other points of view on new builds. That is what DIY is all about.

 

[Moonfly]

Re: New Mach 5 Audio Pi-18 Driver

Is mixing pr's a good idea?

It will be a very interesting project for sure. 2 drivers, 2 x 18 pr's and a single 21 pr up front, thats a wild mix if ever I heard one. I think it will likely act like a multi tuned cabinet though, so I would model the enclosure volume with 2 drivers and the dual pr's, and again with the single pr, then overlay the graphs to see what it looks like. I think that would likely be a more accurate simulation of the cone excursion on the pr's too.

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

There is a ton of work in this cabinet build and is my only option at this point, so I have to give it my best shot by using the mix. The drivers are dumb and don't know what type of passives I'm using or what the internal cabinet pressure is.

I don't have a modeling program and I think by doing an "overlay", it will be pot luck at best on what the final results will be. Remember Teflon? It was an accidental test.

I haven't started the loading on the 21" PR. I think the fs is around 23 to start. I'm going to start adding mass and not exceed 2200 grams. This number is what has been suggested by Kevin as nearing maximimum and I don't want to damage the suspension with too much weight either. I have the huge washers to add and 2200 grams is equivilant to 4.8501 lbs of weight. If I can reach a cabinet tuning of 15 hz with 1500 grams or less, I'll stop there and be quite happy with the results giving my 21" PR more life with the lighter suspension duty. I'll have to see how much those 18s are moving at tuning frequency too. I don't what them flying around and the 21 not working very hard. It is going to be a "cabinet tuner's challenge" for sure.

With the Maelstrom tuned at 15 hz, it was the best sounding subwoofer I've ever built, owned, or auditioned, bar none; so with the extra gain I'll realize with the two Pi-18s, it should be even better.

It is definately a wild mix for sure, but one I'm hoping will work out quite well.

How well did your PR project work out for you Dan?

 

[Moonfly]

Re: New Mach 5 Audio Pi-18 Driver

I am still waiting for the driver for my build, so it wont get completed till around christmas time now. My thread is upto date with all the latest pictures though.

I will model this sub for you and do the overlay to show you what I mean. What is the exact drivers models and the exact pr models. The AE pr's are obviously fixed, so they are easy, but the 21" will be variable, so I can model it with different weights and see how things look, but will use the info from Kevin and his stated weight to begin with. We should be able to run a model that is as close as your going to be able to get IMO.

Do you know the xmax of the 21" pr, or its weight limit?

Edit: fwiw, initial modelling isnt that positive, and shows the 21" pr tuning to be up around 30hz with no weight added, but hitting xmax with only 100 grams, which doesnt bring the tune down nearly enough IMO (depending on what your actually trying to achieve). Of course, predicting how the pr's will affect each other is very difficult, and for sure this model wont be entirely accurate, but I think its as good as you could hope for.

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

Dan, from an earlier post in this thread:

Fp: Resonance frequency (in free-air with no added mass) - 20.5 Hz
Qmp: Mechanical compliance loss - 6.8
Mmp: Moving mass - 300g
Cms: Suspension Compliance - 0.20 mm/N
Vap: Stiffness of driver scaled by cone size - 391L
Sd: Area of the cone - 1182 cm^2
Suspension Travel - 35-38mm one way. Somewhere around 70- 76mm peak-peak, depending on how far you stretch the suspension.

The graph Mike P did was for ported and the the Exodus PR loaded to 2100 grams. I've also got 13 cubic feet to work with too.

The drivers are a pair of the Pi-18s, 4 ohms and will be series wired to 8. I think Bob Reimer said maximum loading would be 2200 grams from what info he got from Kevin.

Thanks....

 

[Moonfly]

Re: New Mach 5 Audio Pi-18 Driver

Hmm, I got a slightly different set of params from here:

Sd: 1550 cm^2.
Qms: 3.9,
Mmd: 285g,
Cms: 1.8 x 10 -4 m/N,
Vas: 605L,
Fs: 22.2 Hz (just starting mass...no washers).

I can only see vented models in Mikes graphs below, do I need to look further back. Also,is the goal here to get all pr's to work to the same tune? With 2100 grams it looks to work well and not be far off the 18's.

 

[gperkins_1973]

Re: New Mach 5 Audio Pi-18 Driver

Mike,

If the different PR's work out then they will be a totally different animal. Its a shame you can't model different PR's in winisd. I don't think you can in bassbox pro either. Its a shame you are not just using 3 AE PR18 1200 PR's as they model perfect in a 13 cu ft box tuned to around 14.64hz.

And you'd be good for around 1900 watts input power too.



cheers

Graham

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

Hmm, I got a slightly different set of params from here:



I can only see vented models in Mikes graphs below, do I need to look further back. Also,is the goal here to get all pr's to work to the same tune? With 2100 grams it looks to work well and not be far off the 18's.

Vented was the only sim Mike could do using mixed passives. That is the only graph I have.

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

Mike,

If the different PR's work out then they will be a totally different animal. Its a shame you can't model different PR's in winisd. I don't think you can in bassbox pro either. Its a shame you are not just using 3 AE PR18 1200 PR's as they model perfect in a 13 cu ft box tuned to around 14.64hz.

And you'd be good for around 1900 watts input power too.



cheers

Graham

I have the extra 2 passives now, but they are all epoxied and fixed at 2100 grams. I would have to build a reducing bushing for the 21" hole too.

Thanks for modeling it out for me..

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

Seeing as how unusual this build is and because it is DIY, there is the thought of adding an Aperiodic stuffed venting on the rear to releive some of the pressure from the drivers.

It is something that could be easily patched up and not noticed. I have a beautiful cabinet now and would hate to see this one get away.

This could get really crazy....

 

[Moonfly]

Re: New Mach 5 Audio Pi-18 Driver

Mike, this is the passives overlay I did (see below). With the twin 18's, a single 21, and the 2 mach drivers, with 2KW of input power, I think the system will work very well. The tune of all the pr's is almost identical, as is the excursion behaviour of the pr's. The drivers behave very similarly as well, so all in all I think you are onto a winner with the 3 pr and 2 driver setup.

Personally, I think you should go for it. If you can use REW, you could confirm all the results via that program as well.

 

[Mike Cason]

Re: New Mach 5 Audio Pi-18 Driver

Thanks Dan,

That is one of the best performances in a subwoofer graph I've seen. Those numbers are awesome. So you are projecting a cabinet tuning frequency of about 12.5 hz? Wow...

Passive radiator designs usually roll off fairly quickly and this one shows a nice gradual taper all the way to the 12 and 13 hz frequencies.

Again, thanks for your time working this up. I'm not set up for REW but I do have a great set of ears and some test cds. The end result is what counts!

I'll post the results when the project is finished.
Mike

 

[Mike Cason]

Because I have so much money and time building this 1.25" thick monster, I just ordered another 21" PR from Bob for a spare. Soon there won't be any more available. I divorced and sold my home and shop, so I really don't have the room or place to build another one right now.

I have a date this afternoon, so before ordering our dinner I need to ask her if she likes really deep bass! It is a requirement...

 

[gperkins_1973]

Personally for me I would try and model the PR's so they stay within their xmax. You have got to treat them with greater care personally as you are relying on them to do a harder job. I always model my PR subs so they stay within xmax off their abilities.

This is why I suggested 3 PR's for this sub so there is much less stress on th PR's excursion.

A much better model in my view. The previous looks like it was modelled on 2 PR's

 

[Mike Cason]

I don't have a way to open your .wpr file.

I think Dan did figure in the two 18s in one overlay, and the 21" in another. Othewise there would be a huge difference in the plot lines.

My original intention was to tune the cabinet to 15 hz with the prs. My two 18s are fixed at 2100 grams, but I'm going to load the 21" pr in incriments until I get a good response from all of the prs working together. I'm not going to run this at full power anyway and I have the Reckhorn B1 to help control the subsonic frequencies to help keep the PRs in check. At 8 ohms, this should also be very clean power to the drivers and should not push them to their limits, thus making it easier on the PRs.
Thanks..

 

[gperkins_1973]

Mike I just used winisd. I find situations like this very interesting. I think its great fun trying new things to see how they turn out. I reckon the cone excursion on the exodus and AE pr's should be pretty similar so it will probably work out really well. Can't wait to see how it turns out.

cheers

Graham

 

[Mike Cason]

Hey Graham,

Thanks for double checking the numbers in WinIsd. I wouldn't have chosen to mix and match for such an unusual project, but when the Mael 21 failed, I was left with a very fine cabinet build, lots of cu ft, and not many choices to restore my subwoofer. Long term, I think I'm going to like it better than the Mael build. The 18s being smaller should be more linear, have lower distortion, and have more cone area combined than the single 21". I'll let you know my results with a couple of progress pics.
Thanks

 

[Moonfly]

Personally for me I would try and model the PR's so they stay within their xmax. You have got to treat them with greater care personally as you are relying on them to do a harder job. I always model my PR subs so they stay within xmax off their abilities.

This is why I suggested 3 PR's for this sub so there is much less stress on th PR's excursion.

A much better model in my view. The previous looks like it was modelled on 2 PR's

A pr is at is highest excursion around tune like a port so will show increased excursion, if you want to reduce it, then alter the tune, reduce input power or add more pr's or change the cabinet volume.

You have modelled with 3 x 18" prs which ignores the parameters set out by Mike due to his unique circumstances, and as such is entirely irrelevant unless Mike decides to modify his cabinet, something he has repeatedly stated he wants to avoid if possible. The model I did is a model of what he will actually build, and the overlay is required due to mixing different pr's. The model I did shows that the pr's will behave very similarly and as such should work well together.

Mike, I wouldnt be so sure about changing the weight on the 21" pr. Less weight will tune it higher which IMHO will mess up the sound, although of course you might really like it like that which I couldnt possibly predict, so by all means experiment. Currently, my model shows the system as a whole is tuned to about 12hz with usable output to 15hz (due to pr excursion behaviour). You would need a filter to ensure the pr's were protected if you want to err on the safe side at about 14hz or so, but implementing that would allow you to use the full power handling capability of the driver. I would ensure the pr's are all tuning to the same frequency, because otherwise you will get a the kind of result you would from mixing different subs in a setup as the system wouldnt be acting in unison, it might work, but I think it would be increasing the chances of it not doing. Another issue with the higher tune is that hitting the excursion limit occurs at higher frequencies.

 

[Mike Cason]

I had originally decided to load the 21" pr to 2100 grams. Mike P. recommended that I start low and add up to tune the 21". Bob told me the Prs were capable of 2200 grams and perhaps a bit more. I do want the lower box tuning and I have the Reckhorn B1 equalizer and subsonic frequency protection.

Do you think I should just load the PR like I planned or work up with the weighting? I like to epoxy the washers in due to their extreme movements. (You do realize I'm using two Pi-18s?)
Thanks for your inputs.

 

[Moonfly]

You could start low and add weight to lower the tune, but as I said, according to the model the higher tune impacts negatively on the system as cone excursion with higher power is raised. This would then limit what you can achieve from the lower tuned pr's which may reduce their output to the point they dont contribute effectively enough, and the system could effectively end up sounding like the higher tune is the limit of its ability.