Bass drop out at 75-55hz

[Dezoris]

I am recalibrating my audio setup, again.
RXV2500, Definitive BP10 Front, Definitive CLR2000, Definitive Supercube2.
PanasonicXP50, with Avia disk. Sub Crossover 80hz, all speakers set to small.

I have the warble test even accross the front, however, I can't get the bass sweep on the LFE channel alone from 100hz to 20hz even.

From about 100 to 80hz levels are even from 70-55hz bass drops off drastically.
From 50 to 35hz the level boosts by nearly 15db.
From 35hz to 22hz levels stabilize and drop off.

I am not so concerned about how boomy the bass is on the low end, but extremely agrivated by the drop off at 75-55hz.

The sub is in the front right corner of the room, I adjusted phase to get the warble even. But I cant get the sweep right.

 

[Ethan Winer]

> I can't get the bass sweep on the LFE channel alone from 100hz to 20hz even. <

Nobody can. Welcome to the crazy world of small-room acoustics. Most domestic size rooms have a disparity between peaks and nulls exceeding 30 dB. And it's not just one or two peak/null pairs but usually half a dozen or more. Excellent rooms decked out with the best bass traps and other acoustic treatment can sometimes get to within 10 dB.

> I am not so concerned about how boomy the bass is on the low end <

You should be!

--Ethan

 

[gene]

The sub is in the front right corner of the room, I adjusted phase to get the warble even. But I cant get the sweep right.

Sounds like you are dealing with a room node. However as an experiment, defeat the bass management of your processor by setting the crossover to 200Hz and seeing if the node from 55-75Hz goes away. If not, try repositioning your sub to the front center wall of the room.

You may need to add a second sub to provide more uniform bass to the listening area. Nodes are best dealt by multiple subs, better sub / listener location, and moderate passive treatments only. Electronic correction can help but you should never excessively boost especially since it wont help cure a bass node.

 

[Dezoris]

Thank you,

So if I defeat the bass management system, and it fixes the node. What next?

If I go two subs whats the best way? Split the monural LFE out into two.

 

[gene]

As far as the low end being boomy, is there any trick to helping that?

That could be caused by having the bass level set too high in your system, and/or too much gain at low frequencies between your main speakers and your sub.

If you are playing your main speakers full range as well as also having a dedicated sub, it gets tricky to calibrate and you may have too much gain below 30Hz. Moving the sub to a different location in the room, moving the listening position away from the back wall, and some active equalization may help your situation. Its hard to tell without measuring the response and actually seeing your room.

Update: If you are using BP10's up front, set all speakers to small and the xover of your processor to 80Hz. Then relocate the sub away from a corner and on the middle of the front wall and see what happens.

 

[Dezoris]

That could be caused by having the bass level set too high in your system, and/or too much gain at low frequencies between your main speakers and your sub.

If you are playing your main speakers full range as well as also having a dedicated sub, it gets tricky to calibrate and you may have too much gain below 30Hz. Moving the sub to a different location in the room, moving the listening position away from the back wall, and some active equalization may help your situation. Its hard to tell without measuring the response and actually seeing your room.

Update: If you are using BP10's up front, set all speakers to small and the xover of your processor to 80Hz. Then relocate the sub away from a corner and on the middle of the front wall and see what happens.

I changed my last post because I did not see your response. Sorry

I'll lay my questions out with numbers

1. So if I defeat the bass management system, and it fixes the node. What next?

2. If I go two subs whats the best way? Split the monural LFE out into two.

My entire system is set to small with the 80hz crossover based on your articles recommendation.

3. If I move the sub toward the middle which will be difficult would it be better to do two subs or.

4. Would setting the crossover lower to maybe like 60hz help or is that not recommended?

Here is the best image I could find of the front of my room

Notice the sub placement in the front right.

I can try to move it behind the equipment.

 

[Tomorrow]

> I can't get the bass sweep on the LFE channel alone from 100hz to 20hz even. <

Nobody can. Welcome to the crazy world of small-room acoustics. Most domestic size rooms have a disparity between peaks and nulls exceeding 30 dB. And it's not just one or two peak/null pairs but usually half a dozen or more. Excellent rooms decked out with the best bass traps and other acoustic treatment can sometimes get to within 10 dB.

> I am not so concerned about how boomy the bass is on the low end <

You should be!

--Ethan

Ethan,

Like many here, we have a multi-purpose (great) room in which we've put our 7.1 surround HT setup. There are WAF and design constraints on where equipment can go. I have gone to double subs (Hsu VTF-3s) and put them in opposing corners. I've found that the best levelling of some nasty room modes was done by switching sub phasing, and niggling the subwoofer placement (within WAF parameters). The use of room treatments, while desirable, is difficult....but still may occur.

Hopefully, some of this may help the OP overlook my hijack question....

My question regards the concept of "room gain". It is well known the placing a sub in a corner advances (enhances?) the sub output to a distinct degree. Is or is not this placement begging for aggravated room modes?

Thanks, in advance.

 

[bpape]

Yes. Putting a sub in a corner does maximize output. But, as you guessed, it also does the most to excite all of the room mode issues.

Bryan

 

[Tomorrow]

Yes. Putting a sub in a corner does maximize output. But, as you guessed, it also does the most to excite all of the room mode issues.

Bryan

Corner subwoofer placement seems almost the de facto suggestion by most folks. Thanks for the clarity you've given notion. This then becomes a great argument for multiple subs and room treatment. One corner-placed VTF-3 was way more than enough sub for serious rattling of my entire house...but not for linear frequency performance in the HT area.

I've already gotten the warden's blessing for the second sub...it's in place now. I'll just have to make her read this thread in preparation for Room Treatment Negotiations.

 

[bpape]

As long as you're negotiating, see if you can talk her in to putting those 2 subs centered on each side wall. That'll help smooth things out.

Bryan

 

[Ethan Winer]

My question regards the concept of "room gain". It is well known the placing a sub in a corner advances (enhances?) the sub output to a distinct degree. Is or is not this placement begging for aggravated room modes?

Yes, room "gain" is exactly that. It's a real increase in level over what you'd have outdoors. In this case the room resonances are a physical equivalent to boosting those frequencies electronically with an equalizer.

I think sub makers recommend corner placement because it gives the biggest "wow factor." Since corner placement really does increase the SPL at those frequencies, it also lowers distortion because the speaker requires less power and less cone motion to achieve the higher levels. But as Bryan pointed out the increase is frequency selective. You get an increase at some low frequencies but not others. Larger rooms have more modes that are also close together, so corner placement in a large room is better than in a small room.

That said, I have my big SVS sub in a corner and it's fabulous there. I also have 40 bass traps in my room, which makes all the difference. This way I can get very high output levels to below 20 Hz, with low distortion, and also have a very flat bass response.

--Ethan

 

[Nick250]

I have not used bass traps so far, bearing that in mind my experience is with powered subs (6 years) is that corner placement has always way too boomy for music. Currently my VTF-2 sits about two feet into the room from the left side wall midway between the sweet spot and the left front speaker. Not everyone is will to have a sub just sitting there in their living room, but I am. Bass traps are next on the shopping list.

Nick

 

[Ethan Winer]

Nick,

> corner placement has always way too boomy for music. <

Yes, but ...

> Bass traps are next on the shopping list. <

Exactly.

--Ethan

 

[Vaughan Odendaa]

Ethan, could you please post your in room frequency response for all of us to see ?

--Sincerely,

 

[Ethan Winer]

Vaughan,

> could you please post your in room frequency response for all of us to see? <

Glad to. All I have prepared and handy is the first graph below which shows the low frequency response (only) in my 25 by 16 living room home theater. Since I added the 40 traps over time, and bought ETF after at least a dozen were in place, I don't have a graph of the room sans treatment. But the second graph below is typical of small untreated rooms.

As you can see, besides the flatter response with bass traps, the decay times are also much shorter and more consistent, and the peaks are much broader. Having wider peaks and less ringing is at least as important as a flat response.

--Ethan

 

[Dezoris]

I moved my sub left center.

It smoothed out the drop out, but excited the 40-25hz boom.
I spent hours smoothing out the fronts response. After the move, its much better. I can't say I am 100% happy with it but its better.

 

[gene]

It smoothed out the drop out, but excited the 40-25hz boom.
I spent hours smoothing out the fronts response. After the move, its much better. I can't say I am 100% happy with it but its better.

At this point you have two practical options:
1) use active equalization to cut the low frequency bass modes
2) add an additional sub along with #1

 

[Vaughan Odendaa]

Ethan, thank you for posting your results ! Very, very good. Have you used any extensive EQ (or mild EQ) to achieve the results you've posted ?

I experienced something strange. On a disk that I regularly use, with an expensive, very expensive HT system, no bass traps, but extensive absorbtion, I noticed that dialog is extremely clear.

However, in the lower dialogue range, notes can boom. Literally. It's as if the singer put his voice too close to the microphone, and dialogue reverberates and just clouds everything. I can't make out this dialogue clearly.

Strange, because I never thought that dialogue would be affected in the lower bass range. The room that this test was done in is extremely small, like 5 m x 4 m. Then I took the same disk and put it in a budget system, in a huge open area, and I mean very big, where the walls are spaced practically 10-12 meters apart facing the long way, and that dialogue was much easier to hear with far less boom.

Very interesting for me. I guess the most interesting thing for me is that I learned how much bass can affect things like dialogue. Never really thought about that too much until now.

--Sincerely,

 

[Ethan Winer]

Vaughan,

> thank you for posting your results ! Very, very good. <

And it sounds simply amazing too. Many of my friends are professional musicians and recording engineers, and they all consider my system and room to be state of the art. And some of these guys have mixed gold records.

> Have you used any extensive EQ (or mild EQ) to achieve the results you've posted ? <

Yes, I use the one-band cut-only EQ that's built into my SVS PB12-Ultra/2 subwoofer to cut the 2nd order length mode a couple of dB. As regulars here know I'd never use an equalizer to boost, but for cutting below, say, 50 Hz it makes sense. In my case it's around 40 Hz. But even without the EQ engaged the graph still looks pretty darn flat just from all the bass traps.

> in the lower dialogue range, notes can boom. <

Oh sure, that's common. Deep male voices have content down to below 100 Hz. If you have a computer with audio software, you can use an FFT plug-in to analyze all sorts of interesting stuff like this.

> I learned how much bass can affect things like dialogue. <

We just treated a vocal booth for a semi-famous NY Producer. He'd had a bunch of one- and two-inch foam in there so the sound was dead enough at mid and high frequencies, but the room still boomed like crazy on male voices. Even though it's a small booth we squeezed bass traps into each corner, and the improvement was immediate and very obvious just talking in there.

--Ethan

 

[Vaughan Odendaa]

What disappoints me, I guess, is that it's going to be extremely difficult to persuade my superiors to purchase bass traps to put in the room.

And as I said before with the cheap system that I used, the results were great in a massive room with no bass traps. Obviously, with traps the results would have been much better. But the big point to make is that one does not need an expensive system to reap the benefits of clear sound.

Even a budget system, and I mean budget, can sound amazingly clear, clearer in fact than many high-end systems in a proper acoustic situation.

Thank you for posting your results again. I just wish I could actually have the pleasure of listening to music in a room with as many traps as you have. Unless one day. . .

--Sincerely,