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Discussion Starter · #1 ·
OK,


I've been thinking about building a Rythmik servo kit for a while and I finally got around to it. My goal is to compare it to my Velodyne HGS-12 over the next couple of weeks and see how the two match up. For testing, I put the Rythmik in a 2cf Parts Express pre-made box.


I ordered the parts last week; they were all here by wednesday. Unfortunately I was out of town for a few days. I got back this afternoon and started working around 2.00. Here's how it went.


The boxes arrived.



I took out the parts.



I cut two holes in the box.



I put in the driver and amp, and about 1/2 pound of polyfill. Here's the assembled kit:



And here's the HGS-12:



"I want a good clean fight..."



Anyway, the whole process of building the Rythmik couldn't have been much simpler. It took about 3 hours from start to finish. I cut out the holes in the box with a jigsaw, using the shipping materials as a template. I put the Rythmik in the Velodyne's old spot in the corner and tried it out. It seemed to be working fine, so I set the Velo on top of the Rythmik (so they form a little stack in the corner), and set things up like this:


Velodyne: 20Hz highpass, crossover off, phase 180

Rythmik: 20Hz Extension (to match the Velo), High damping (my best guess as to how to match the Velo), crossover as high as possible, phase 180


I set levels with my RS digital SPL meter, played a few music tracks, the Intro sequence and "Bridge of Khazad-Dum" from LOTR, and A/B'd the two. I won't say much yet, other than they are both nice sounding subs. I don't want to get subjective until I'm reasonably confident that the subs are set up optimally and level-matched. Anyway, I'll keep this thread updated over the next few days as I measure and listen.
 

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Start putting in your bets, boys!


I'll chip in for the Rythmik since I'm already biased (but honest!)





Let's set some basic rules to keep it fair:


-Always level matched

-Both subs have REW run

-Both subs are tested from same exact location, do not move the mic, do not move the subs, both subs share the same location


Can anybody else think of some ways to keep this a fair fight?








[Oh, yeah, subscribed to the thread I don't want to miss any of this!]
 

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My bets are on the Rythmik as well. BUT, I will keep an open mind and wait for the results.


It is an interesting comparo, with the different enclosure sizes, amps, excursions, servo methodologies, etc.
 

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At matched levels both should be close in SQ.If there is a winner it is the less expensive sub.


Interesting comparo,that is for sure.Do some max SPL 80,60,50 down to 20Hz.The smaller Velo should hold its own and only lose below 30Hz in output.


My quick guess.
 

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Quote:
Originally Posted by TheEAR /forum/post/0


At matched levels both should be close in SQ.If there is a winner it is the less expensive sub.


Interesting comparo,that is for sure.Do some max SPL 80,60,50 down to 20Hz.The smaller Velo should hold its own and only lose below 30Hz in output.


My quick guess.

A was also thinking he could just do REW at progressively higher levels.... Like do -20dB, -15dB, -10dB, -5dB to find out when compression is taking place and how it affects both subs.
 

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Quote:
Originally Posted by crackyflipside /forum/post/0


A was also thinking he could just do REW at progressively higher levels.... Like do -20dB, -15dB, -10dB, -5dB to find out when compression is taking place and how it affects both subs.

I like that idea!
 

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Discussion Starter · #9 ·
Sounds good -- I agree it'd be a good idea to see when compression becomes a factor; I'll do what I can to bring out the differences, and I'll steal liberally from test methods developed or suggested by others.
My plan for tomorrow is to spend some time doing nearfield measurements to establish a baseline for what each sub is putting out, and also to try get good in-room response by positioning and use of bass traps (I've got a bunch of OC 703 panels and traps in my recording room, which I'll move downstairs for this). I'm not opposed to the use of EQ in real life; I'd just prefer to do this test with acoustic treatment if I can. We'll see how realistic that is after a few sweeps.
 

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Quote:
Originally Posted by poormanq45 /forum/post/0


Usually nearfield measurements are taken at ~6" from driver and/or outside away from walls

I still have the paper of "Low Frequency Loudspeaker Assessment by Nearfield Sound Pressure Measurement" by D. B. Keele Jr when he was with EV , published in Journal of Audio Engineering Society, April 1974. Yes, the technique is already 30 year-old. In the paper, there is no mentioning it "has" to be done with 6" distance though, nor it is normally done that way (in other words, there is nothing magic about the number 6, or 6.0, or 6.00
). In the photo he showed how he did his measurement, his mic is almost on the cone. In the distance he had used in his figures, the closest one is 0", I repeat 0. The near field he implied is 0 distance (or as close to 0 as possible). Of course he also showed the result of 0.9", 2.1", 4.05", 7.5", .... I can fax it to any one who is interested to read the paper. I don't recommend 0" because it would damage the cone. But it should be close to 0" as much as possible and without the possiblity of damaging the cone.


Another difficulty you mentioned was away from walls, it should have been away from "walls and floor". Floor is a major source of reflection. This is one of the main reason I won't recommend it in indoor. It is always a good thing to try. If it does not work, then move it to outdoor. It also depends on the type of resolution we want. For ruler flat type of curve, we can only get it outdoor.



Brian


Rythmik Audio
 

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All you get is the bone of contention.
 

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SpectralID,


Thanks for doing this. Don't forget to let the Rythmik driver break-in before the comparison, unless Brian thinks it doesn't need too.


Looking forward to reading your findings.
 

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Discussion Starter · #16 ·
OK, I know, I know... Things aren't quite the way I expected so I want to be cautious. I think this will take longer than I thought to do a real comparison. But one thing is clear after only a couple of days: there are definite differences between these subs. If you're looking for a DIY Velo, this is not it; it's got a different personality.


I guess I'll talk a little about some preliminary measurements I did. I was just working in-room, mostly to choose location and level-match things. I haven't done much testing of max SPL, but from some in-room preliminary measurements, I don't think the results I get will surprise anyone. So far it appears they will be more-or-less as they were predicted above.


One difference in these subs is that as you approach max SPL, the Velo produces only small increases in distortion and eventually the limiter engages and it refuses to get any louder. The Rythmik, on the other hand, will allow THD to creep up more and continue to get louder. However, the max SPL seems roughly the same, if you stop the Rythmik at around 10% thd. On the Velo I measured 110db in-room, 1m, with around 5% thd using a 70Hz test tone. It was quite impressive; the thing gets louder until it hits the limiter, but THD barely moves. The Rythmik produced around 10% 2nd harmonic distortion (I was just using room EQ wizard at this time, so I didn't have access to THD measurements) by around 108db under the same circumstances. I spoke with Brian about this over the weekend; it's possible I was simply seeing the beginnings of the amp clipping. I need to find time and location to really do quality measurements to see what's going on here; I'm planning to take them outside and measure THD vs. SPL at a few representative frequencies. Please, please take all of this as nothing more than preliminary results to get some rough idea of what these things look like. I fully realize the difference between right and wrong ways to do a technical review; I'm mentioning these preliminary results since I thought some might find them interesting.


On the other hand, the sound quality is starting to become a little clearer to me. I watched a few scenes from LOTR again, and then chose a few 30-second clips of different songs. I exchanged the position of the two subs a few times to see if it made any difference in my perceptions and it did not seem to. Both subs sound very good with music. I calibrated the subs using room EQ wizard and my RS SPL meter; I tried to find a location where the curves in room EQ wizard were virtually identical and the SPL was equal. I will attach my in-room responses (I have an ugly peak at 40Hz) when I get home. Anyway, with music the Velo is extremely clean; the Rythmik kit does not seem quite as clean but sometimes seems more dynamic. Both subs are excellent at producing crisp attacks and there's no sense of boominess or ringing decay from either. The drums on John Hiatt's "Riding With The King" have a very tight kick sound and the rest of the mix is sparse; on this track the Velo was virtually invisible. The DS-12 conveyed the same sense of impact when the batter hit the head, but I felt it was adding some color which I didn't hear with the Velo. The bass guitar and the kick drum were not as clearly separated anymore. On the other hand, with movies I felt there was perhaps more definition in loud, low scenes (e.g. Bridge of Khazad-Dum from FOTR) with the Rythmik, whether I set it to 20 or 14hz tune. I need to measure the peaks I'm seeing from both subs; it's possible it's just a headroom issue but it may be more than that. I simply don't know yet. I need to do some testing with impulse-type sounds like kicks or burst tones and see what each sub does.


Anyway, I really like both subs. I need to reserve the right to change all my opinions as I do more listening
; I've had the Velo for a year and I'm very used to its sound.
 

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Thanks for the analysis so far SpectralD!
It is turning out to be very interesting.


We will be looking forward to you upcoming measurements and other tests...


Thanks!
 

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For me, this is one of the most interesting threads I've seen on AVS for quite some time. Thanks for doing the buying, building and testing!


PS: I have no experience with the Parts Express cabinets. Are they as well-braced as the Velodyne cabinet would be, and do you believe that would be an issue here at all?
 

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Likewise, I had been hoping someone would actually do this! I even started a couple of threads asking if anyone had compared the Ryhtmik servo to Velo servo and got no replies.


There are pictures of the PE box in the first post. They have only eve had one small cross brace in them. I doubt SpectalD has pulled the driver out of his Velo, but if I remember correctly there are no braces in the 12" DD cabinet.
 

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The PE cabinet is 3/4 MDF with the one brace connecting the side walls. Also with the 2cf cabinet your more likely to be around 1.7-1.8 cf after driver,amp and brace displacement. And yes, PE doesn't factor in the brace. A little off of Brian's 2.1cf recommendation.
 
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