[warnerwh]

These measurements were taken with a Rives cd with a Radio Shack meter:
20/ -8
25/ -2
31.5/ 0
40/ -10
50/ -12
63/ -12
80/ 3
100/ 3.5
125/ -1.5
160/ -6
200/ -8
250/ -6
315/ -5
400/ 0
500/ -8
630/ -7
800/ -10
1000/ -1
1250/ -1
1600/ 2
2000/ -1
2500/ 0
3150/ -3
4000/ -10
5000/ -5
6130/ -5
8000/ -5
10k/ -6
12.5k/ -4
16k/ -6
20k/ -10

The speakers are RM 30's and the amplifer is a Butler hybrid(tube output stage) and a Modwright preamp.  Overall the room isn't too bad except between 40-63. This is a very broad dip. Anybody have any ideas? Thanks

[ekovalsky]

Hi Warner,

Were you using a sub when you made these measurements ?  If not, the output you measured below 40hz is spurious.  Also did you use "C" weighting on the meter ?

Between 40-63hz, you are probably seeing the combined effect of the RM30's natural bass roll off and a room null.  You have about a 15dB swing from nulls to peaks in the bass range which is quite typical for speakers in an enclosed space.  You can try moving the speakers and/or listening position to get a little more output in the 40-63hz range, which is where a lot of the perceived low bass resides.

If you have some extra time (who does ?) and are a bit masochistic, get the test CD file from http://www.realtraps.com/test-cd.htm, burn to CD, and repeat your measurements 1hz at a time.  What this will reveal is that you have closely spaced nulls and peaks that aren't detected when using typical test signals that are averaged over fractional octaves.

Getting flat bass in-room basically requires a sophisticated correction system -- DEQX, TacT, Behringer, Meridian, etc. -- regardless of speaker manufacture.  If you are fortunately enough to have an exceptional room, meaning there are just a few problematic frequencies, then traps may be the answer if they are of the proper design and size.  In typical rooms traps can help but they are not a complete fix.

It seems that there are some other issues you may want to explore.  Your treble is quite rolled off, but this may sound okay as it matches the bass response (rule of 400,000 applied).  Also you are measuring output  that is up relatively 10dB at 1khz-2.5khz compared with the adjacent 500-1khz and 2.5khz-5hz bands.  This is quite similar to what I (and others) measured with our VMPS so it may reflect the output characteristics of the planar driver.  

You can be assured that the response issues you have found are a function of the loudspeakers and their interface with the room; it is not caused by your electronics or cables.

Eric

[warnerwh]

Eric: A sub had not been used during this test. The person just received an Innersound ESL SS amp from the Butler and will retake measurements with the SS amp. I do suspect the Butler's amp tube output stage as making bass softer than what the Innersound will be. We will have to wait for mca to tell us as he's the only one who has heard both.

The fact that he is flat at 31.5 and only 2db down at 25hz makes me also think that room position and some bass traps will help significantly. I also agree that digital room correction will help. I bought a Behringer DEQ 2496 due to a comment you'd made a while back and love it.  I recommend it regularly.  I'd almost go so far as to say at minimum everybody should at least have the DEQ 2496 in their system.

His room is odd due to an alcove in the left front corner and I wonder if this is causing the wide null.  The null being where it is has to make the bass  weak.  I'd like to help him if we can as he has worked hard to get the best sound he can but there are a couple of obvious problems to address.  I believe if the bass can get straightened out then the rest will be easy.  He's also stated he's had a bass problem with all the speakers he's used in that room.

Thank you for the link for the 1hz tones. I've been wanting to at least do an accurate test through the bass range.

[Rob Babcock]

It's probably time to ditch my BFD and step up to the DEQ 2496.  It's pretty cheap, so there's not much risk involved.  Mostly I'm apprehensive about having to learn how to set the thing up.  Behringer isn't noted for their high quality manuals or instrutions.

[ctviggen]

Did you also apply the RS weighting to this?  I once had my Linn speakers  near two "alcoves" -- on the left, a hallway and open area and on the right an entrance into the house.  The bass response sucked.  When I moved the system to the neighboring wall, the bass response improved dramatically.  The 31.5 could be a room mode.  The realtraps site also has a room mode calculator, which is of some benefit though only an estimate unless you have a perfectly rectangular room.  You definitely need a better measuring system/tool because you're note getting many measurements per octave.  For reference, here's a frequency response using one of my Rm40s and using ETF:



Now, this isn't a valid response, as I've had some problems using ETF, but it shows you how radical these things can be.

[ctviggen]

I should note that I think the only thing "invalid" about that frequency response is 60Hz leaking into the measurement.  Other than that, I believe it's a valid reponse.  Not a very nice looking response, but valid.

[ctviggen]

I should also note that the Linns have rear-firing woofers, which means that in the spot with the alcoves, the woofers fired directly into the alcoves.  As the RM30s have side-firing woofers, you might want to move the woofers to fire into the room.

[lkosova]

you might want to try this program:
http://www.rhintek.com/tutorial/aura.php

Especially if this is an odd shaped room. You might be able to pinpoint areas that need fixing better.

Larry

[Jose R.]

 Your treble is quite rolled off, but this may sound okay as it matches the bass response (rule of 400,000 applied). Also you are measuring output that is up relatively 10dB at 1khz-2.5khz compared with the adjacent 500-1khz and 2.5khz-5hz bands. This is quite similar to what I (and others) measured with our VMPS so it may reflect the output characteristics of the planar driver.
 

I would agree with Eric's comment - the measurements you show are typical of the planar drivers and are similar to what I measure with the Tact 2.2x at the listening position.  My RM30C's benefited greatly from room correction, not only in the bass region ( I use corner subs) but also in the midrange.

Regards

Jose

[warnerwh]

Bob: Those measurements were taken with the Radio Shack correction values on the Rives cd. I asked to make sure.

Thanks for the info on the bass problems in your room with the alcoves. He said he's had bass problems with various speakers and I'd suspected the alcove may be doing something odd.  Maybe it's like a black hole for bass.  Moving his system around is another issue altogether.

[ctviggen]

In my room (with my Linns), simply moving the system to a different wall improved by bass response immensely, on the order of 10-20 db.  If he doesn't have that option, then I'm not sure what you can do about the alcove, short of drywalling it in!  

[warnerwh]

Here are two new sets of measurements. The first is using the Innersound amp and leaving the speakers as they were. The second is taking the speakers off the 4" blocks and facing the woofers inward(still with the Innersound). Kind of weird as all three came out very different. One weird thing I noticed is with the Innersound the different frequencies wavered up and down a couple of db. It was a little hard to get a read and I ended up just taking the average. Pots were left the same.

20/-4/-6
25/1/0
31.5/3/2
40/-9/-10
50/-12/-11
63/-12/-11
80/5/3.5
100/6/3.5
125/1/2
160/1/2.5
200/-1/-1
250/-3/-9
315/-5/-6
400/-1/-6
500/-10/-11
630/-1/-4
800/-5/-4
1000/-3/1
1250/5/4
1600/0/4
2000/-6/-3
2500/6/-10
3150/0/-12
4000/0/-10
5000/5/0
6300/-4/0
8000/6/3
10k/1/0
12.5k/0/-9
16k/-10/-5
20k/-3/-4

[Bill Baker]

Before you take your measurements too seriously, keep in mind that the Rat Shack analog meter is not the most accurate at either extreme. If I recall, below 80 Hz and above 10kHz, I would not start serious renovations based on results gathered from this meter.
 It is a great meter to get a general idea of whats going.
 Jyust trying to save you some headache chasing measurements that may not be very accurate.

[warnerwh]

Thanks Bill.  I'm aware it's not very accurate but he did use the Rives CD.  This person has had bass problems consistently though with various speakers.  These are the first time he's measured his room though.  I suggested he block that alcove behind his system with either plywood or try putting some large acoustic panels in front, preferably double thickness and see what happens.

[ekovalsky]

Maybe give your Behringer a try to see what it can do for the bass in your client's room.  I still suspect that the speaker's bass is rolling off fast below 60hz and there is little usable output below that to equalize.  Output detected at 31.5hz and below is likely spurious.  All the true room nulls I have seen are very high Q -- in my case about 53-57hz.  I've never seen one stretch over half an octave.  

In my room, the RMX dropped off fast below 40hz (measured @ 4m), and that is with 10" and 12" active woofers and the 12" passive radiator driven by two 600w into 4ohm amp channels.  Putty adjustments didn't make a difference either.

As Jose and I found, the tonal balance can be greatly improved by implementing some form of speaker correction in the midrange (particularly 1khz-2.5khz).  The planars are fast and can take a lot of power, but their response curve is not flat.

As Bill said, above 10khz the accuracy of the meter is very questionable, as it is with most cheap microphones.

Good luck!

[warnerwh]

I'm sure you're right that the Behringer would help, i'm convinced it will help most any system.  Unfortunately he lives 250 miles from here.  I'm sure the bass can be better as I have another client with the RM 30's with the same exact options and he's getting good measured bass down to the 40's and although he bought a sub he didn't think they needed it. He also has four very large bass traps in each corner.

I'm convinced that like ctviggen that the alcove in the corner behind his system sucks up the bass as he's had this problem with a number of different brands/designs of speakers although this is the first time he's measured his room.  Maybe he should get long lengths of cheap speaker cable and put his speakers at the other end of the room and see what happens.

[mca]

I tried stacking up three panels in front of the alcove, this pretty much blocked it off  except for a couple of feet near the ceiling. I also tried swapping the speakers to the opposite wall. In both cases the low bass response did not change.

I have a Behringer on order now, so we'll see what effects it has on the room/system.