How come "flat" sounds bad?

[fbwap]

I am new at some of this so please excuse me if these questions have been answered elsewhere.

I have played with stereo for 45 years. For many years, my speakers were Dahlquist DQ10s (acoustic suspension bass). They had decent sounding bass. I also have a Velodyne F-1200-B that I sometimes used with them.

Several years ago I replaced the DQ-10s with Aerial Acoustics 7Ts (rear ported). Everything above bass is better than the DQ-10s, but I have never been happy with the bass with the 7Ts in my room. A while ago, I bought an UMIK-1 and began playing with REW software and moving the sub around.

Last week, I received a Rythmik F12G and began further playing. Using both subs, I can obtain a nice flat bass response according to REW. But the bass sounds very weak.

I must be missing some basic psychoacoustic fact that maybe someone here can help me with. Why does a nice flat frequency response at my listening position, sound terrible in the bass region?

Thanks

 

[Sonnie Parker]

The Fletcher-Munson Curve can explain it pretty well.

EQ up to your transitional frequency with something similar to the Harman curve, which will give you a bit of a bump in the low-end.

 

[fbwap]

The Fletcher-Munson Curve can explain it pretty well.

View attachment 40742


EQ up to your transitional frequency with something similar to the Harman curve, which will give you a bit of a bump in the low-end.

Yes. Thank you. I guess I have been at it for too many years. I used to know about loudness contours, but I never heard them called Fletcher-Munson curves. For many years I used a Tandberg 3002 preamp which had a loudness button whose contour was supposed to change as the master volume control changed. I did have that button in most of the time and this probably contributed to my memory of bass with the Dahlquists.

I now have a Luxman CL-38uSE preamp and it has pretty flexible tone controls. I think I will try playing with those tomorrow, see if I can get things sounding good, then see what things look like with the REW software. Things do sound slightly less clear with the tone controls switched-in on the Luxman, but the trade off may be worth it. Looking at the curves you provided, I won't be able to "fix" things with the subwoofers alone. They can help somewhat below 100 Hz, but that will not cut it.

My system is still mostly analog except for the source, which is an Oppo BDP-105. I am using it as the crossover between the mains and the subs.

Thanks for reminding me of basics that I had forgotten about! I guess I fell into the purist trap, even though I resisted it for many years.

 

[DanDan]

Way back Bruel and Kjaer measured the frequency response of Hi Fi rigs in homes and dealers. Simply put the average is about +3dB at 100Hz. dropping to -3dB at 10Khz. Harmon came up with similar results as have Sonarworks in recent times. It's room gain. A combination of diminished clarity due to early reflections and reverb, plus room boom.
When we treat a listening space to mitigate those effects, we tend towards the anechoic. Nobody likes to listen to a flat response in anechoic conditions, e.g. audiometric headphones.
We have a sonic 'home' which we are used to. Music creators strive for translation, to achieve a tonality that sounds great in such spaces.
You can achieve LF boost by moving speakers close to a boundary.

https://www.bksv.com/media/doc/17-197.pdf

 

[Sonnie Parker]

Very true... I've always started with my subs in the corner, up until I got multiple subs... now I only have two in the corner... two on the side wall, and two out from the walls a bit... they all blend well. I still have a few PEQ filters on my subs where needed, so there's not much correction that has to be done to integrate them with the mains.

 

[DanDan]

I have seen some data. From memory 14 LF sources! Ruler flat LF. No treatment.... Heresy eh? But the continuing 'Flat' Heresy seems to roll on and on. The 'Pros' ridicule what the Listeners know well.
And I'm one of both!
Sigh.

 

[fbwap]

While playing around with various subwoofer configurations, I realized I had done something incredibly stupid. I was using the digital crossover in the Oppo so the Oppo was driving the subs directly, while there was a preamp between the Oppo and the mains. So the mains varied with the volume control on the preamp but the subs did not. I have not tried using the crossover in the Rythmik and the HPF out, yet. The idea of having an op-amp driving the nice electronics driving the mains does not thrill me.

After re-configuring so that the mains were running full bandwidth with the subs in parallel, I have the current observations....I can get a pretty decent curve on REW and it sounds pretty decent with only one sub (the Rythmik). BUT I have to have the volume knob on the Rythmik up like 90% to 95%. I cranked the music up louder than I would ever play it and I did not detect any distortion or breakup of the bass, but I wonder if having to run it with a 90%+ setting means I need a bigger sub. I bet that there are movies out there that have more bass content than the music I was playing.

The Rythmik is an F12G. I don't think the room (or the wife) will tolerate a 15 inch sub where it needs to be. My room is only 12 foot by 20 foot by 8 foot high. The AV system is on one of the long walls. The short wall to my right has a 45 degree fireplace where it joins the wall with the AV system. The Rythmik is between the right main and the fireplace opening. The wall to my left is only "half" there....it has a door to the kitchen and a window to the kitchen also. I don't play music or movies very loud and I thought a 12 inch woofer was more than enough.

I suppose my question would require someone to be familiar with Rythmik. Does anyone see a disadvantage running the sub volume at 90% (other than the possibility of maxing out one day during some movie?) Does bottoming out just once or twice cause permanent damage to a subwoofer?

 

[Eric SVL]

Flat is what you want. But tilt it a little so you get 3-6 dB more at 20 Hz.

We would need to know more about your system. It sounds like you aren't using an AVR with bass management, correct? Are you using a crossover at all?

 

[fbwap]

Flat is what you want. But tilt it a little so you get 3-6 dB more at 20 Hz.

We would need to know more about your system. It sounds like you aren't using an AVR with bass management, correct? Are you using a crossover at all?

When I say I have a "decent" curve, I mean that it has a pretty good bass tilt.....much more than the 3-6 dB you suggest

When I wrote my second post above, I was using the digital crossover in the Oppo to drive the subwoofer. That appeared to work because I was only doing REW sweeps (and manual tone sweeps) at a constant level. Once I started playing music and varying the pre-amp gain, I realized my dumb mistake.

At the moment (and for the curve above), I am not using a crossover at all. I am just running one sub (the Rythmik) in parallel with the mains, which are running full bandwidth. My only option for a crossover right now would be the one built into the Rythmik, which is fixed at 80 or 85 Hz. Rythmik literature says they have a nice Op Amp for that filter but right now I don't think I need to reconfigure the system again. My only concern is that the subwoofer master volume is up "high." The system is:

Oppo BDP-105 - source feeding.....
Luxman CL-38uSE - pre-amp feeding.....
Threshold T200 - Amplifier feeding.....
Aerial Acoustics 7Ts
Rythmik F12G - driven off the pre-amp in parallel with the main speakers

The subwoofer setting are currently:
PEQ ON - around 60 Hz, a wider bandwidth, +3dB - needed to fill a hole and make the bass part of the curve smoother
Master volume around 75% to 80% - Was a little higher yesterday, maybe 85% - REW curve above was taken when the knob was at 85%.
Crossover dial approximately 55Hz
Delay (phase) approximately 4ms
Damping HI
Extension Filter 14Hz
Rumble Filter OFF
Low Pass Slope 50Hz/24

I have several more permutations to try during my 30 day evaluation period, but this one seems pretty good. The only thing that is not ideal is that the master volume on the sub needs to be so high in this configuration. I suppose if it never "bottoms out" that it is not a problem, but I am just looking for experience from the forum about running a sub with the mater volume up this high.

Thanks

 

[Jack1949]

The Rythmik design/support team (Brian and Enrico) participate in the Official Rythmik Audio Subwoofer thread on AVSForum. You can ask Enrico (enricoclaudio on AVSForum) about your master volume concern and get his input.

https://www.avsforum.com/threads/official-rythmik-audio-subwoofer-thread.1214550/

 

[DanDan]

The Harmon and B&K curves are not at all flat. The elevated level at 30Hz is a result of the overall tilt which is about 6dB across the spectrum.
There is something about the unbalanced input on the Rhythmik webpage of that speaker. You may be able to get a 6dB change by changing the XLR wiring, or they also mention a Y lead. In the PA world most rigs are worked with the Power Amps up full.

 

[MediumRare]

I can get a pretty decent curve on REW and it sounds pretty decent with only one sub (the Rythmik). BUT I have to have the volume knob on the Rythmik up like 90% to 95%. I cranked the music up louder than I would ever play it and I did not detect any distortion or breakup of the bass, but I wonder if having to run it with a 90%+ setting means I need a bigger sub. I bet that there are movies out there that have more bass content than the music I was playing.

The Rythmik is an F12G. I don't think the room (or the wife) will tolerate a 15 inch sub where it needs to be. My room is only 12 foot by 20 foot by 8 foot high. The AV system is on one of the long walls. The short wall to my right has a 45 degree fireplace where it joins the wall with the AV system. The Rythmik is between the right main and the fireplace opening. The wall to my left is only "half" there....it has a door to the kitchen and a window to the kitchen also. I don't play music or movies very loud and I thought a 12 inch woofer was more than enough.

FBWAP, you're on a journey of discovery now - good to ask all the questions and challenge assumptions! IMO, your Rythmik sub is an excellent choice and is plenty big enough for that room. Together with your Velodyne (I have a DD18) you should have an outstanding system. You may have heard that multiple subs is better because the respective standing waves cancel each other out and you will have even smoother response. Of course, the subs will also work less hard, have less distortion, and strain their amps less.

An easy way to tell if your subs are working very hard is to play some music overall at a volume you enjoy, then switch off the mains. You will then hear the subs on their own. The bass should sound only moderately loud. If it is shaking your doors and buzzing the items on your bookshelves it's too loud.

Most likely, the sub volume is set over 90% but the signal coming in is rather low, so the sub is still playing only at a moderate level. Those subs are easily capable of over 100 db each, which would be very loud indeed. If the subs ARE playing very loudly, it would be because they are improperly placed. Play around with the Room Sim tool in REW and you can find good approximate locations for the subs to complement your main speaker locations.

They key is you should never hear the bass separately from the music. It should sound like it's coming naturally from the same soundstage as the main speakers.