FR Graph - questions...

[droht]

My 2 channel set up resides on my desk top. Throughout many different amp and speaker combos one thing has been somewhat consistent. A boomy sound on certain recordings - maybe 10 - 15% of what I listen to. Very annoying at anything but moderate volume. Almost sounds like someone hummng loudly over recording.

Anyway, tried to "test" this today. I have RS analog sound level meter in my listening position. Played various test tones (3 second sine waves). Played each tone twice. They were very consistent. But when I put together a very crude graph it looks ugly (to my very untrained eyes at least). dBs on Y axis (not adjusted - raw #s from the RS meter) and Hz on X.

Not really sure what to expect with my test method and equipment, but the peak at 135Hz is the tone that is annoying me on some recordings. I'm using foobar2000 for playback. Using it's EQ function I knocked down the output at 110 and 156HZ by 6dB. Pretty nice imrovement to my ears. I ran through a handful of songs that have that boomy hum and only one still has a fair amount of it.

Any feedback on this from anyone? Do my results make any sense? Current speakers are Ref1s, but the issue is not unique to them. In fact, to my ears, they may be the best speakers I've had in terms of this issue. I'm planning to repeat the test with other speakers and another amp. Is there a better SOP for this test? (there has to be :))

I'm sure the obvious reply is that the room/placement is the issue. I thought so originally, as the speakers are pushed back on corners of desk way too close to the wall. But I have played with that. I stuffed soft pillows behind speakers and heard no change. I moved speakers out to front edge of desk and heard no change.

[django1]

I'm amazed you haven't gotten any commentary on your nice squiggly line. I know less than nothing about this and even when I'm told something I promptly forget it. That notwithstanding and in the spirit of participation here's my advice: try making the line less squiggly :eyebrows:. Hope that helps...

[Eric D]

Question: did you apply correction factors for the RS SPL meter readings? Here's just one source:

http://diyaudioprojects.com/Testeq/RadioShack_33-2050/33-2050.htm

Is there a better SOP for this test? (there has to be :))

Yes. TrueRTA, Acoustisoft ETF, or Room Eq Wizard (REW) software. I'm a new convert to REW, and the price is right. Any of them will take a little study, but IMO it's worth it.

good luck,

P.S. Django is right - make the line less squiggly. :)

[droht]

Question: did you apply correction factors for the RS SPL meter readings? Here's just one source:

http://diyaudioprojects.com/Testeq/RadioShack_33-2050/33-2050.htm

Yes. TrueRTA, Acoustisoft ETF, or Room Eq Wizard (REW) software. I'm a new convert to REW, and the price is right. Any of them will take a little study, but IMO it's worth it.

good luck,

P.S. Django is right - make the line less squiggly. :)

The correction factors don't do much for the squiggles, but thanks for the link. I will have to try REW when I have some time to spend with it.

[lngbruno]

droht,

This just caught my eye.

Please provide some further information, so I can take a stab at answering your unique issue.

What are the dimensions of the room?

Is the floor carpeted?

Speaker location? (from each other, from the front wall, from you, toe-in, stand, etc.)

Any other room treatments besides the pillows? :lame: attempt at humor...

Are you using a sub? If so, what crossover frequency are you using and how are the Ref1's used (full frequency or ??)?

Have you ever used a sealed cabinet speaker in your current set-up and room?

Do you have another system to use as your reference point?

OBTW, I used a different method to measure the low frequency levels. I use a test tone cd and the RS meter (taking into account the corrections) and just keep trying different things...eventually it snapped into place.

Lou

[bunnyma357]

Pictures would help, but here's my guess based on your description.

If the speakers are on the desk surface and not a tiered riser that brings them closer to ear level, it seems there would be three things effecting what you're hearing.

Reflections off of the desk surface.
The desk resonating.
Being off-axis vertically.

You could try Auralex Mo-Pads to isolate the speakers or a DIY isolation tweek. Desktop stands that raise the speakers so that you're more on axis and don't get immediate reflections from the desk. Or you could try floor stands next to the desk to raise them to an appropriate height and isolate them from the desk.

I'd also suggest using REW for testing. Good Luck.


Jim C

[droht]

Lou: In response to your questions:

room: 12x13x8; carpeted; speakers are on longer wall, right speaker is about 3' from corner

Speakers are ~ 3.5' apart; 28" from listening position. They are toed-in ~ 40 degrees. Center of back of speaker is 3.75" from wall. Speakers are on Auralex Mo-Pads on desk.

No room treatements - the pillows were just a test.

I do use sub, off and on, crossed at 90 Hz. That helps a bit, but does not fix the problem. I tried cranking crossover up beyond where problem seems to be. That helps the boominess, but the overall sound quality is not as good.

I have never used a sealed speaker, just a variety of front and rear ported. Port location does not seem to make a difference.

I have used the same Ref1s in my HT; no issue whatsoever.

Pic below; the sub is not usually in that position. :)

Thanks!

[droht]

Jim, thanks for the thoughts on this. Picture of set up is in previous post.

I am using Mo-Pads, and they were actually a great improvement, though not a complete one. Speakers are angled up slightly, and tweeters are on line with my ears.

I think I've ruled out reflections off the desk surface, by moving speakers to front edge and by placing pillows all around speakers. The desk resonating is my best guess at this point. The desk is a cheap Ikea deal, so that can't help. I've toyed with pulling desk out a bit and putting stands behind it, but just have never gotten around to it. I've also thought about going with smaller speakers and wall mounting them. Might also be a good excuse to get a nicer desk! How's that for a system tweak?

[lngbruno]

droht,

Thanks for the photo, I forgot to ask for it but I saw that Jim had my back on that one.

That was funny about the sub not being located where you had it in the picture. :goodvibes:

Here are my thoughts:

1. The room dimensions may be a big issue, due to being a square room. But it is what it is, so let's focus on location and some room treatments. My office is very similar in size to yours, with my desk on the long wall too.

2. Since the Ref1's are rear ported, they are too close to the front wall. I know you said you had tried front ported speakers and netted the same results, but I think you need to experiment with sealed speakers. OBTW, you also need something more substantial than the pillows to experiment with too. A 2" or even 4" thick 2' x 4' rigid fiberglass panel would be the preferred item of choice. Make two 2' x 2' panels and put them directly in front of your desk with about a 18" gap between them (do this as a temparary thing to see if the gap needs to be smaller or wider depending on the amound of toe-in you end up using). This may cause you to pull the desk out a few inches and this is a good thing too. In my case I use a smaller two-way sealed speaker with a small sub. There was no need for the acoustic panel behind them.

3. The other thing to experiment with is toe in. You may need to toe them out instead of in. It is all trial and error. For me, I have the L speaker parallel with the front wall and the R speaker toed in about 10 degrees. The sub is set about 80 Hz and out of phase.

4. The other thing is break up the corner reflections. I use book cases in each of the front corners. They are functional for my books and they perform the much need break up. If you are limited in doing this, then another acoustic panel should be used in the corners. I have a small frabric faced love seat in the rear R corner of the room and a door entrance in the rear L corner.

What I have learned over the years is that no two rooms are the same, so there is not one solution. It truely comes down to trial and error and the time to play with the variables.

Good luck and have fun experimenting, :thumbsup:
Lou

[droht]

Thanks again Lou. It's funny, I have a small fabric covered love seat in back right corner and door in back left corner as well.

I really thought that near-field set up minimized a lot of room issues. Interesting that your experience says otherwise. I never tried anything but symmetrical toe-in. I will play around some more with it. Good thing I wasn't planning on getting any work done anyway. :D