PSW350 vs. Hsu STF-2 in room FR

pjdami

I had some time to play around the past couple of days before Santa came and plotted the in room frequency response of my PSW350 vs. my Hsu STF-2. I used the 41 bass test tone cd that Dr. Spec generously shared with the forum a while back. Both subs were calibrated to be about 2 - 3 db hot using the Sound & Vision DVD with my left LSi 15 main at 85 db.

Each sub was tested individually, and placed in the same exact location (moved the other sub away) in my living room.

I used the analog Radio Shack decibel meter and set-up a spreadsheet which interpolates the "in-between" frequencies which are not listed on the correction factors.

Crossover frequency on my receiver was set at 80 hz, all speakers set to small, sub yes. 0 degree phase switch setting on both subs. I tried 180 degrees on the STF-2 but bass out was significantly lower during the first few readings I took so I went with the 0 degree phase numbers.

The first test tone is a ten second tone at 100 hz which is used to set the volume on the receiver. Since the correction factor for the RS analog meter is +2.0 db at 100 hz, I adjusted the volume on my receiver until I got 83 db on the sub from my listening position.

The plot is below. I'm kind of new to analyzing these things but know that obviously flat is better. The STF-2 has more grunt in the low end and doesn't drop off below 30 hz like the PSW350 does. I'm kind of surprised at the "hump" with both subs at 35 hz. I was expecting this from the PSW350 but not the Hsu. Must be room - induced?

Even though I started off at 85 db corrected with the 100 hz test tone, it looks like both subs are trying to average around 80 db which is 5 db down and I'm sort of puzzled by this as well. As you can see from the graphs, the Hsu doesn't have nearly as severe of dip that the PSW350 exhibited. But they both share the "hump" but in listening the Hsu is not "boomy" like the PSW350. Perplexing... like "riddle me this Batman".

Any thoughts? The subs were not corner loaded and placed along the longest wall (same wall as mains) and this is one of the walls with an opening to my foyer area in the front of the house.

Thanks for any analysis.

Paul

Loud & Clear

Couple nasty dips with the 350, but overall not a slaughter, imo.

Oh, and has been reported, I believe by Doc, the 350 in essence says goodbye at 32Hz, which is fine for most of the music that I listen to.

Dr. Spec

I love this kind of stuff - great write-up. That hump at 35 Hz is probably a room mode considering both subs did the same exact thing.

That is exactly the kind of thing the PEQ in the PB1+ can tame - you pick the worst hump in the room and knock it down.

Mic placement is critical - try the 30-40 Hz tones in a few different spots (even 2 feet away) and see what happens.

Also, try moving the subs around a little and see what happens to the curve - you might be able to tame that hump yet.

I always look at the 80 Hz response when selecting phase because that will be the frequency where both the sub and mains are playing equally. The PB1+ has 0-180 continuously variable, which is nice. I have found the SVS responds well at 180 actually, and you might find this too.

Neither of them are bottom dwellers, but the Hsu clearly has more low end, being up about 10 dB over the 350 at 25 Hz. That should be very noticeable on certain passages.

The difference in SQ might be attributable to harmonic distortion - something you can't measure unless you have an RTA. Woofer generated harmonics sound fuller and richer, something many people actually prefer.

Finally, I don't know what the weather looks like over there, but ground plane testing with such small and light subs is easy. If you have a sub cable extension and an extension cord, you can place it outside on a towel or sheet and run the sweep again. Place the mic at one meter and equally split the distance between the woofer and the ports and keep the mic about mid-height of the sub. Ground plane will show you the quasi-anechoic response of the sub and you will see if that hump at 35 is designed in, or a room mode.

Doc

pjdami

I always look at the 80 Hz response when selecting phase because that will be the frequency where both the sub and mains are playing equally.

Doc, so are you saying chose the phase setting that is the loudest of the two at 80 hz (at the same volume setting)?

P.

Dr. Spec

Originally posted by pjdami
Doc, so are you saying chose the phase setting that is the loudest of the two at 80 hz (at the same volume setting)?

P.

Yes, I have noticed a 8-10 dB gain/drop at the xo point by varying the phase control.

If all the speaks are set to small, the phase setting becomes less significant in the lower registers, because none of the other speakers are producing any bass.

pjdami

Yeah. 10 db drop at 80 hz for me at 180 degrees. I charted the 180 phase FR and it looks terrible compared to 0 degrees.

This is an easy way to figure out if you are in phase or not but I had it right the first time "by ear" prior to plotting FR curves. Of course, I had a 50 percent chance of being lucky... but I only wish I was that lucky!:D

Dr. Spec

Actually, without some type of test rig (meter, spreadsheet, CFs, graphing capability) like you now possess, determining the correct phase setting really is a guessing game.

I suspect you will find the SVS works best at 180 - it has been my experience with the first two I've owned. But double check to be sure.

walk

Since both curves look very similar I'd say you are graphing room response more than the sub's abilities. Except for maybe at the sub-30hz range which clearly shows a difference.

As for comparing levels to your Left channel speaker, remember the RS meter's freq. response isn't flat - it will read significantly down (-3/5db) at the low end.

pjdami

As for comparing levels to your Left channel speaker, remember the RS meter's freq. response isn't flat - it will read significantly down (-3/5db) at the low end.

True, but I generated a spreadsheet that will compensate for these shortcomings. There are correction factors that one can incorporate to adjust. Still not the most accurate thing in the world (the Radio Shack meter) but it is something that is repeatable and still worth the effort in my honest opinion.

We'll see. I'm about to move the sub over to my two channel rig in my office and take data in that room. This is where the sub will eventually be anyway so its worth the effort here too. Besides this is kind of fun, interesting, and educational.

Paul

Hz data (db) Corr (db) Final
100 83 2.000 85.0
94.4 77 1.860 78.9
89.1 78 1.728 79.7
84.1 76 1.603 77.6
79.4 75 1.500 76.5
75 78.5 1.500 80.0
70.8 83 1.500 84.5
66.8 80 1.500 81.5
63.1 79 1.500 80.5
59.6 79 1.500 80.5
56.2 79 1.500 80.5
53.1 76 1.500 77.5
50.1 75 1.500 76.5
47.3 77.5 1.770 79.3
44.7 78 2.030 80.0
42.2 80 2.280 82.3
39.8 84 2.512 86.5
37.6 85 2.641 87.6
35.5 82 2.765 84.8
33.5 80 2.882 82.9
31.6 78.5 2.994 81.5
29.9 77 3.492 80.5
28.2 75 4.015 79.0
26.6 74 4.508 78.5
25.1 72 4.969 77.0
23.7 71 5.650 76.7
22.4 69 6.300 75.3
21.1 66 6.950 73.0
20 61 7.500 68.5
18.8 59 8.700 67.7

pjdami

well, the data looks like crap on my post above, and I tried to cut and past the data image into a jpg file and its to big to post.

ah well. At least I can post the graph which is the most important thing from a visual perspective.

Dr. Spec

You should notice more room gain in a smaller room - it will have a flatter low end with less roll-off.

Doc

pjdami

I have plotted the in room FR of the STF-2 in my office. Much better low frequency response and sounds really good there listening to that Classical Organ Music cd that was distributed thoughout the forum about two months ago.

-10 db down (approximately) at 18.8 hz and pretty strong down to 20 hz. I may have to increase the gain on the sub amp just a tad because I had to calibrate using the test tone cd at Track #5 (@ 80 hz). My B&K PT5 preamp does have a sub out RCA and High level output RCAs that I am sending to the mains.

Glaringly obivious is the huge dip at 50 hz. I've tried several different sub positions (within a couple of feet) and it is still there. I've also read of some people on the Hsu forum complaining about output in this region. Amazingly, the dip is much less severe in the much larger room. I will try out some more positions with the sub and mic.

Paul

pjdami

Here's the graph. Office vs. Living room response. Office is a much smaller room. Office is the blue line. Had to edit to get it to fit.

Dr. Spec

Wow, nasty null at 50 Hz. You might have to find an unconventional location for the sub to eliminate that.

Otherwise looking good, much flatter overall and better extension - probably sounds quite good in that regard - flat to 25 Hz as advertised - nice. A small room works wonders for a small sub, no doubt.

Try some of these links for sub location and null elimination.

http://www.harman.com/wp/index.jsp?articleId=1003

http://www.harman.com/wp/pdf/Loudspeakers&RoomsPt3.pdf

pjdami

Thanks for the links Doc. Looks like I have a lot of reading to do. Cool stuff.

A little moving around and experimentation yielded the below graph which is better. At first I thought it might have been crossover related or "double-filtering" but it wasn't. My B&K also has a full range RCA output L + R that is none filtered and the Hsu has a crossover switch to allow the sub to do the filtering but looks like it yielded similar results with the null. I didn't plot that graph though.

The null is definitely room related. I went down to 75 db for the measurements this time. 85 db was rattling too many things in here. The worst null is now only 6.5 db lower than the starting point which isn't too bad.

I'm envious of your response that you got on the 20 - 39 PC+. Now that's a flat and nice response you had there.

goingganzo

the best way to get a flat responce is to have it in a basement. but sometimes a flat responce you dont get as much output sometimes. where i located my sub was in the center of the left wall so i dont get any corner load but i do get a bit of gain from my rear platform. too bad polk stoped makeing the 1200 that was a sub.

Dr. Spec

Nice job experimenting with placement. It makes a huge difference. A PEQ could knock down that 50 Hz hump, but overall much flatter; nearly a 15 dB taming of than null - good work.

A cheap PEQ like the BFD for $120 could really help if you want to get crazy and get a really flat response. Some people swear by them. They are a **** to figure out, but luckily there is an internet support community for the BFD that really helps out.

pjdami

So Doc, in your opinion, what is good placement and room tuning performance from a sub? +/- 5 db? +/- 2 db?? I know flatter is better but without a PEQ what is a realistic expectation that one can expect to attain in a sub FR?

Dr. Spec

I'd say +/- 5 should be the limit, but it's more what the curve looks like. A bunch of moderate bumps evenly spaced apart is better than a +5 and a -5 right next to each other.

goingganzo

if you want bass check this link out a motor that can do 80 mm of x max and can be made to do 12in of x max at olny 4-5k

http://www.adireaudio.com/Files/Dan/Parthenon/