Sealed Tempest results..... (1 Viewer)

[Boris]

Hi, I've been long time lurker, short time member.
It's excellent threads like these that gave me the insight, addiction and thirst for knowledge regarding DIY subs.
I'm a proud owner of a DIY Shiva. Probably quite rare here in the UK.
Great work Terry.
Cheers
Boris

 

[Stan Marcewicz]

Seems like you are making quite a number of changes/assumptions and ight be attempting to draw conclusions as if you did not. I mean you are comparing an underported mass 12 with no subsonic filter to a sealed sub not too far off from optimum. Which is okay if you draw onclusions with all of this in mind. But it's hard to draw conclusions about the drivers themselves from all of this stuff.
One thing I didn't see mentioned is what you are doing with the other subs when one is being tested. Are they in the room and off? This can lead to them acting as room acoustics devices at certain bass freqs. Try running some plots with the amp for the other nonused sub on and then off..it's not unusual to see a couple db or so diff at certain freqs. With the unused sub out of the room or at least with the amp on to restrain the cone you will cut down on this effect. With a little thought you can guess what effect each sub will have on the other. If you want absolute max output from a sub you need a subsonic filter with an optimized cutoff freq and slope. For sealed subs too, but ported subs need it the most.
Stan

 

[TerryC]

"Seems like you are making quite a number of changes/assumptions and might be attempting to draw conclusions as if you did not. I mean you are comparing an underported mass 12 with no subsonic filter to a sealed sub not too far off from optimum. Which is okay if you draw onclusions with all of this in mind. But it's hard to draw conclusions about the drivers themselves from all of this stuff. "
Yes you are 100% right Stan if you notice my very first post I mention I am comparing the completed subs more so than drivers although the driver obviously has a big impact on how each sub performs. Also I am going from the minute I plugged them in to now so I'm experimenting with their hookup and so on, if I had waited there would be less differences to the testing procedures.
To me the driver is almost inconsequential in these tests as I'm trying to see what kind of bass one can get in a smallish enclosure that many can use. Most people including myself have space limitations and spouses that limit the size of the sub we can use. Since this is my situation as well I'm trying to find the most amount of bass in smallish size. (Obviously PR's will be in involved in the future). Here is a good semi appropriate analogy, take your typical dragstrip and let’s pick the Ford Mustang outlaw class. You have many different years of cars with many different engines and setups such as Nitrous, Super Chargers, Naturally aspirated and Turbos. Its not what they are using that's important but the final time slip at the end. (no need for anyone to point out this analogy is not perfect, I already know that but I think it somewhat gets my point across)
That's why I'm not a big fan of comparing subs in their optimum enclosure as many always suggest including Dan W. To me its not how this driver performs in it's optimum enclosure as that enclosure could be huge and many can't use those. Take the Tempest for instance in a ported enclosure, its going to be 8.5 plus cubic feet and that's a very big box and not realistic to most people.
It's a tough call, as many want to see no holds bared designs but many don't have the option of doing that. That's the purpose of doing these tests to see if one can hit or come close to reference while not using the typical monster enclosures and I think these results speak for themselves.
"One thing I didn't see mentioned is what you are doing with the other subs when one is being tested. Are they in the room and off? This can lead to them acting as room acoustics devices at certain bass freqs. Try running some plots with the amp for the other nonused sub on and then off..it's not unusual to see a couple db or so diff at certain freqs. With the unused sub out of the room or at least with the amp on to restrain the cone you will cut down on this effect. With a little thought you can guess what effect each sub will have on the other. If you want absolute max output from a sub you need a subsonic filter with an optimized cutoff freq and slope. For sealed subs too, but ported subs need it the most. "
I had one sub totally disconnected, good advice to keep in mind I'll make sure to run a sweep with it in the room and without next time. I agree that a subsonic filter is a good idea I have that option on my Mackie, but in my frequency sweeps I can't see how it would have made much of a difference to the results other than to lower the output after the tuning?
Terry
PS- Since a sealed box is so inexpensive and easy to build would you think it's more fair to put the Mass in a sealed enclosure of the same Qtc? I'll be happy to do that if there is enough interest from people that want to see the drivers compared only on their own merits

 

[Charlie G]

If you just throw them in boxes with the same Qtc, I think the Tempest is going to beat the Mass handily (won't it's box be way bigger?)
Charlie

 

[Jack Gilvey]

If you just throw them in boxes with the same Qtc, I think the Tempest is going to beat the Mass handily (won't it's box be way bigger?)

That may be, but I think that's the only way to compare the drivers themselves.
There are two ways to approach DIY,as I see it. One, the prospective builder identifies the performance goal (say,120db @ 20Hz at the seats), and decides how to best get there within budget.
Alternatively, our builder has a given size constraint, and tries to get the best performance given that restriction. Ultimately, everyone has some kind of size limit,if not for the "SAF", then just for practicality. I, for instance, simply couldn't fit a completed 30" sonosub through my den door (even though the "SAF" stops applying at said door).
It obviously comes down to a choice. "Driver A can do (insert performance stats) in this enclosure, but if I can go bigger, driver B can do (insert better performance stats)."
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[Mark Seaton]

As always, it comes down to the application at hand, and the design constraints we have to work within. This aspect of DIY subwoofers seems to cause quite a bit of confusion with those used to thinking in terms of retail subwoofers. They are 2 entirely different cases. With a retail subwoofer, you are attempting to find a sub which will "fit" your space and expectations. For a DIY design, you have many more tools at hand to maximize performance within your design constraints. Those of you who have designed a subwoofer for a friend likely can relate to my point. The constraints don't always make the most sense to everyone else, but you still have to work within them.
A good example of this is would be my car. What started as adding a simple subwoofer, quickly grew into a major project. My design constraints? I didn't want to take up my entire trunk with a large box, and the less space lost, the better (moving back and forth to school, and the desire to fit 2 or more sets of golf clubs in the trunk drove this constraint). So, I now have a PAIR of Tempests mounted to a baffle built behind my rear seats. The interesting part was that I KNEW that the response would not be flat in-car, in fact the response rises at 4-6dB/oct. below ~80Hz. Myself being a student of EE, I determinined this to be an easy thing to correct with a passive, line level filter, and a very attractive option to buying drivers costing 2-3 times as much which would have yielded a flat in-car response. For me, this met my design criteria of space, performance and even budget. I have too many projects for home audio to dump crazy cash into my car, especially with it being almost 15 yrs old.
The point here is that we have to keep our minds open to somewhat "unconventional" designs in the interest of helping more people meet the lofty deep bass performance groups like this have made more commonplace.
Regards,
Mark Seaton

 

[Mark Seaton]

Back on to the topic of the performance differences between these 2 designs, there is one detail of the max SPL plots which has me puzzled. If we look at the region between ~25Hz and ~45Hz, we see that the MASS subwoofer actually yeilded higher output. This being above the range where the port is complementing the output, I would expect the slightly larger Vd of the Tempest to have higher output limits.
I see 2 obvious possible reasons for the difference, first of course would be power. Based on the volume of the Tempest sub and the 500W available, I would expect output to be power limited above ~35Hz, so that's one possibility. The other could be the "loading" of the sub to the room. The MASS sub is downfiring, so the driver is very close coupled to the floor, along with being closer to the 2 corner walls. What I would suggest is for Terry to do 2 more measurements in the "good corner." First test would be to even more directly compare the subs by finding something to stand the tempest off the floor about 2-3" and determine max output and see if there are any real differences. The second test would be to spin the Tempest sub around and have the driver fire directly into the wall or corner, with probably 2-4" of clearance between the wall and the driver. For the frequencies in question I wouldn't think it would make that much of a difference, but would be interesting to veryify.
What do ya think Terry?
Mark Seaton

 

[TerryC]

Mark,
You gave me an idea, bottom to side firing comparison would that suffice? I'll try a down firing position this week. I'll just add the feet from the Sonosub test sub to the face of this test box.
Here are the results of the LED's on the mackie.
The LEDs on the mackie are the following:
Clip
-3
-6
-9
-20
I ran an each to produce 100hz signal until the channel the tempest is on read -20 and then can 2.5hz increments from 15hz up to 100hz to see how much power the Tempest required at those frequencies with the EQ.
15Hz- -6 flickering
17.5hz- -3 flicking
20hz to 25hz- -3 fully lit
27.5hz to 32.5hz- -6 flashing
35hz to 47.5hz- -9
50hz up to 100hz- -20
Maybe that will give you an idea of the power levels?
Terry

 

[Brian Fellmeth]

I somehow missed this thread and its a classic. I hope the mods forgive me for running it back to the top.