Adventures in Room Equalization Part II (1 Viewer)

[Larry Chanin]

Thanks again for your advice, and I apologize if it sounded as if I was "blowing off" your suggestions.
However, the fact is that in order to experiment with the placement of my mains would require me to abandon an attractive, expensive and very functional entertainment center. As I said I don't disagree with you that placing mains against the walls is not the preferred arrangement, nor is placing speakers in cabinets, or placing large projection TVs between the mains, or placing speakers on top of TVs, or putting aquariums in home theaters, etc. However, these are audio compromises that I have made to fit in with my lifestyle, after all its all about home entertainment which is a broader objective than just audio.
When I move to a new home I'll revisit the advisability of abandoning the entertainment center along with the other "mistakes" I've made when designing my next home theater, but I'll probably commit a whole new set of mistakes.
Thanks again for your interest.
Larry

 

[Michael R Price]

Oh, I see. That makes more sense...

What kind of crossover are you using with your mains and surrounds again?

 

[Larry Chanin]

Hi Steve:
Thanks very much for your input.
Despite having made the investment in room equalization, I am trying to maintain a healthy objectivity to the pros and cons of this approach, and I continue to experiment.
The aspect of Mr. Hardesty's arguments that resonates with me (pardon the unintended pun) is the fact that our ears (even my untrained ears) can differentiate between direct sounds and echos and we can identify different voices regardless of the acoustics of a room. Therefore, room equalization techniques which do not differentiate between direct sounds and reflected sounds are bound to be less accurate than the human ear. Of course the big question is, "Is it so inaccurate to be more of a hindrance than a help"? I think it still can help, but as everyone agrees it has the potential of making things worse if we are not very careful.
Despite the pain and suffering I'm still having fun experimenting with equalization and, thanks to people such as yourself, I'm learning a bit in the process.
I've done some casual reading on some of the high-end room correction products, but I must admit my interest starts to wain when the costs get close to $10,000. I've got a Lexicon MC-1 processor and of course I like to see where Lexicon is going. The Lexicon MC-12 has future connections for four microphone inputs and it is generally thought that a future Lexicon upgrade may involve digital room correction without a lot of extra D/A conversions.
Thanks again.
Larry

 

[Larry Chanin]

Hi Michael:
Well, I continue to experiment, but for my mains I currently have my high pass crossover set to 40Hz and my LFE subwoofer low pass crossover set to 40Hz.
The connection to the surround subwoofer from the surround decoder sends the same signal to the subwoofer as is being applied to the surround channels. For my surround subwoofer I have its internal crossover set to 125Hz and the surround channel is set to small with a high pass crossover set to 40Hz. So the LFE subwoofer is handling everything in the surround channels below 40Hz. The surround subwoofer is handling everything in the surround channel from 40Hz to 125Hz, and the surround speakers are seeing everything from 40Hz to about 25kHz. The specs on my surround speakers have a lower and upper -3dB point of 50Hz and 25kHz respectively, so I'm pushing them a bit in the 40Hz to 50Hz range, but I haven't heard any noticable distress.
Larry

 

[Stephen Dodds]

The TACT units correct both frequency and time, and would be ideal for your situation as they are most useful when speaker or room isn't ideal. But they are expensive. I got mine used, but you are still looking at $1500-$2000 for the cheapest one.

I'm not sure I'd hold out for room correction for the MC-1, I hear there is a replacement coming out that is a baby MC12. Still, they might bring out a magic box.

Steve

 

[Larry Chanin]

Hi Steve:

I'm sorry I wasn't clear. I was thinking that I might be able to trade-up from the MC-1 to a future version of the MC-12 that had room correction. Chances are I still won't be able to afford it. The Baby MC-12 of course should be more affordable, but I doubt it will have room correction. All this of course is speculation since the Lexicon folks don't release too much information on future products for competitive reasons.

Larry

 

[Michael R Price]

Larry, have you tried using higher crossover frequencies? Or can you localize the subwoofer too much? 40Hz seems very low and with multiple sources, you may have some extra anomalies in the 40-120Hz range.

 

[Chris Tsutsui]

I always thought that up to 80hz in the mid-bass region is non-directional though I do know audiophiles who will disagree. This leads me to believe that a subwoofer in the rear will give you the same effect as 2 or 1 subwoofer in the front.

I agree with Michael in that if you are adding another subwoofer such as a surround woofer it could be detrimental to room EQ if not placed right.

I also didn't know that you had an entertainment center that limited the speaker positioning. We are talking more about home theater and not critical listening so I wouldn't be concerned about it.

 

[Larry Chanin]

Quote:

Hi Guys:
You guys might be right. My reasoning might be a little "seat of the pants", but let me attempt to elaborate. The decoder with the surround subwoofer connection is a SMART Circle Surround processor. Before I connected the surround subwoofer I contacted the Chief Engineer and designer of the device and asked him how I should set the crossovers to take advantage of this feature. His response was to set the surround channel to large, and it had been his experience that most surround speakers don't have a problem with this. I was uncomfortable treating a surround speaker as if it were a full range speaker, so I compromised and set the crossover to 40Hz. Since the speaker's -3dB limit went down to 50Hz, I felt fairly certain that I wouldn't be exposing it to too much danger.
With regard to anomalies and hurting equalization, in my first posting I posted the before and after frequency response at the primary seating position. These plots are measuring the surround subwoofer/surround speaker combination. The plots show a distinct improvement in overall frequency response for both channels. There is an 8 dB dip at about 160Hz on both channels that resisted correction. However, I doubt that raising the crossover frequency from 40Hz to 80Hz would have any effect on an anomaly occurring at 160Hz, but I certainly can try it to see what happens.
Chris, if you have the time or interest you can take a look at my room by clicking on my signature below and then clicking on "Photos of Larry's Home Theater".
Thanks again to both of you for your thoughts.
Larry

 

[Michael R Price]

Larry, if your main and surround speakers have a flat unequalized response down to 40Hz, that's great and I think you might want to stay with that setup. I would try to avoid any EQ boost to those channels under 80Hz.

Also, you may want to see if you still like the sound if you raise to crossover frequency. The reason for this is, even if your main speakers could produce better quality 40-80Hz bass than your subwoofer (which they most likely can't), the loud bass signals can stress the speaker and cause distortion in the midrange. If you cut the bass load from the speakers, they will play cleaner and louder. Just food for thought, though trying to change the crossover could open a new can of worms.

 

[Manuel Delaflor]

Larry,
In your opinion the ETF software resulted accurated? I tried to find that specific answer in your posts, but I couldn't find it. And as the subject you are dealing with is very complex, I prefer to ask rapidly

 

[BruceD]

I have been using ETF for the last three years and find it more than accurate enough for any HT purpose.

The FFT mathematics and MLS based test signals plus a full duplex sound card almost guarantee accurate results as long as you minimize the background noise level (

 

[Greg Monfort]

> always thought that up to 80hz in the mid-bass region is non-directional though I do know audiophiles who will disagree.
====
It's a matter of being room dependant and where you're sitting. True omni LF is only down where the particle density is ~uniform, i.e. in the room gain BW. Once the WL is completely developed it has directivity. ~(1130/80)/pi = ~4.5ft dia., so if you're sitting where you can hear a reflection or are sitting partially outside the WL you may be able to hear its source if the room's effect on it doesn't alter it too much, IOW, if the room's transfer function begins at 80Hz or higher, then it may not be perceived as directional, but in a large room with a single sub stack in the corner...... and why in theaters they array a number of subs across the stage rather than a single large stack, to get more uniform horizontal coverage.

This is also why folks like me accept the comb filtering of 'stereo' subs since our rooms are acoustically large enough for single subs to be pinpointed, and for one reason or another, putting the sub equidistant between the mains isn't an option.

GM

 

[Larry Chanin]

Quote:

Replacing or repositioning the sub wasn't feasible at this time.
With regard to mid range distortion concerns. Each of my main speakers have 4-6.5 inch mid range drivers and a 12 inch passive driver. So my reasoning was that the mid range should be minimally effected by a 40Hz crossover since they are not being called upon for double-duty, i.e., mid-range and deep bass.
Even if there was increased distortion, I'll bet my untrained ears wouldn't be able to pick it up in my movie environment.
Thanks again for your comments.
Larry

 

[Larry Chanin]

Hi Manuel:
I can't blame you for not wanting to wade through the previous posting for an answer. But to answer your question, I was never in a position where I could definitively prove that the ETF5 software was as accurate as the Behringer RTA. However, I believe that it is likely to be more accurate. As I suggested in responding to Stephen Dodds' question, I could try to infer the frequency response by trying to capture the positions of 31 dancing LEDs on the Behringer RTA, or I could try to figure out the response by looking at an ETF5 graph with hundreds or thousands of data points. ETF5 is not perfect because it also will show different curves for the same equalizer setting, but on the whole it is a lot easier for me to use. Remember I have a home theater computer permanently attached to my A/V equipment so I'm not inconvenienced by lugging the computer from the den over to the home theater. In addition I get almost real-time results, whereas the Behringer requires switching back and forth between equalizer and RTA modes.
Finally, I respect the opinion of BruceD, and I had been following his comments in the prior thread which was supportive of using ETF5. (Bruce: Thanks for responding here as well.)
Larry
PS Manuel, I know that you plan on buying the Behringer mixer. zzounds.com has a current sale for $60. I doubt if you will ever be able to beat that price.

 

[Larry Chanin]

To BruceD and Greg Monfort:
Welcome back to Part II of this thread. I feared that you may have given up on me and my bubbling through equalizerland.
Would you mind terribly if I put you on the spot and asked for your opinions regarding Mr. Hardesty's criticism of room equalization?
The Audio Perfectionist Journal
Thanks again for your contributions.
Larry

 

[Greg Monfort]

Hey Larry,

I haven't been posting much here or following threads much for quite awhile. I did look at Polk's info on your speakers though. I'd forgotten about his phase correction design. These aren't speakers that should be EQ'd IMO, but then your room is so compromised acoustically that it boils down to what sounds entertaining and screw what's accurate.

I'm kind of short on time, what's the 'bone of contention' in RH's article that you're curious about?

GM

 

[Stephen Dodds]

Hardesty believes room correction above bass frquencies is the spawn of the devil, mainly due to timing issues.

Steve

 

[Greg Monfort]

I agree with the caveats that just like in the LF, above ~7kHz we don't hear phase well enough for EQ to be an issue unless it's a major correction, and then we perceive it only as a change in amplitude, just like in the LF; and if you're using a typical speaker with an XO in the 2-3kHz BW it's already audibly screwed up enough that adding EQ may help it. .
GM

 

[Larry Chanin]

Hi Greg:
At your convenience:
Here's what I'm curious about. For purposes of discussion suppose we are in a home theater with a really bad echo that even I can hear . (You know like in a large bathroom.) Apparently our hearing is smart enough to differeniate between the direct and indirect sound in this case. So in this extreme case if I didn't like what it sounded like obviously I would change the room treatment to kill the echo not try to change the frequency response of the speakers to fix the sound.
In rooms with less extreme reflections (echos) aren't we doing basically what I described above, unnecessarily changing the speaker's response, when we attempt room equalization above bass frequencies?
Thanks.
Larry