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Discussion Starter #1
Although I have been an audio "nut" for 48 years, I have only recently become interested in correctly applying room treatments. I have had first reflection absorption up for several years, but only after a phone call from Bryan of GIK this week have I become seriously interested in bass trapping.

My room is smallish for what I have in it. There are two pairs of Klipschorns (a 1998 vintage pair and a 1978 vintage pair; the 1978 pair was upgraded with the factory kits to better match the 1998 ones), a Belle Klipsch for center, a Velodyne FSR-18 sub, and a pair of Heresy IIIs on the side walls to round out the 7.1 setup. All driven from a Denon 5805 receiver, normally with Audyssey ON (that may change). The room is 12.5'x20.5'x8' with the L/C/R and rears along the 12.5' walls. The sub is between L and C.

Overall I have been very happy with the system, but always wondered what I was missing by not measuring the room and making compensation in the bass. Now that measurement tools are reasonably affordable, here I go. I have the ECM 8000 and the Behringer mixer on order as well as two of GIK's Monster traps with stands coming to get started.

Finding places for traps at the corners is tough. From the top of the K'horns to the ceiling is 42", so that means custom or DIY traps or horizontal 48" ones in the corners at the ceiling. Bryan suggested the Monsters on stands to put behind the listening chair and a pair of Tri Traps up front, located after taking some measurements. Since I needed to purchase the mic and mixer, I waited on the Tri Traps.

Some questions:

1) First, the K'horn's bass horn crosses over at 400 Hz. Seems that if I put Tri Traps on the floor near the mouth of the bass horn there would be near field absorption. Would that also happen with the traps at the ceiling corners?

2) The general consenus seems to be to cross over even full range speakers at 80Hz or so. Good idea also for the K'horns? Sure hate to lose that bottom 40Hz or so from the horns.

3) I have a Creative X-Fi Extreme Audio Notebook soundcard plugged into the ExpressCard slot of my laptop. It does not duplex (cannot simultaneously monitor). Is there a USB card that will? I have a workaround - moving a desktop PC into the room - but much rather carry the laptop.

4) Any other K'horn users that wish to share thier room correction stories?

Thanks.
 

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Tri Traps up high will be fine. Below, I wouldn't recommend.

The reason to cross over is to allow flexibility in placing whatever is generating 80hz down to allow smoother response without having to move mains. The lower you cross over, the less benefit there will be.

Several of the external Soundblaster USB units will work just fine.

Bryan
 

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Discussion Starter #3
Thanks, Bryan. The traps, mic, and mixer should be here early next week. I will post some before/after waterfalls as I get going with the room treatments.
 

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Discussion Starter #4
I don't have enough posts to add a photo file yet. I ran some measurements this afternoon using REW and the Denon mic (calibration unknown). Per the waterfall plots of the sub only, I have significant ringing at 25 & 57 Hz. The same ringing shows up when the left K'horn is driven. Not much I can do about the 25Hz one, but maybe the Monster traps will help on the 57Hz one.

FR plots of the sub only are MUCH smoother with Audyssey room correction OFF. Significant difference. Not sure what is going on with the mids and highs with Audyssesy - did not measure above 100Hz.
 

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Discussion Starter #5
I got the ECM8000 and Behringer mixer yesterday and the two Monster traps. Only had a little play time, but did notice that the Monsters have a positive effect even on the 26Hz room mode. I only slid them around to a few places, so lots more time needed to find the best place as well as the need to add more traps later on.

I did notice that the response irregularities in the bass were more pronounced when measuring with the ECM8000 than with the Denon Audyssey mic - guess that was to be expected since others have said that the Denon mic is not that linear in the bass.

Also noticed that the subwoofer FR plot is much smoother with Audyssey OFF (all room correction turned off). This is with the first generation Audyssey in the Denon 5805 - no dynamic EQ. Even the receiver's FLAT EQ position was worse than no correction. The mic was in the same position for all measurements and Audyssey is only averaging three chair positions, all in a straight row across the room. I will post some plots in a few days to illustrate what is going on.

Hope to have more time this weekend to do more measurements and post some graphs. I have a BFD on order to play with and to try a house curve as others suggest.

I can tell you that the subjective improvement in bass with the traps in the room is far greater than measurements show. The bass on 24 and House last night subjectively was much improved - likely due to positive effects on the mains above 100Hz (I only measured the sub and it only up to 100 Hz).

Bryan: Right now they are in your suggested position - behind the main listening position in front of the fireplace on the stands. I did shove them over to the side walls - not much difference. I also put them on top of the rear K'horns and the waterfall actually looked a little worse than in front of the fireplace, but they were not quite at the ceiling. I ran out of time before I could push them to the front of the room. One note about the Monster traps on the stands - they are not very stable when on carpet. Not much can be done, I suppose, due to the relative high center of gravity. Also was kinda disappointed with the screws for the stands into the soft side wood - never could get them very tight.
 

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Well, that's a good thing that the rear and the sides were not that much differen from a decay standpoint as they'll deal with different things from a frequency response standpoint.

Not sure what's up with the screws - we've not had problems with them.

Bryan
 

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Discussion Starter #7 (Edited)
I made a number of measurements today. First up are baseline plots without the Monster traps in the room and with Audyssey ON and OFF to see if LF FR is better with Audyssey OFF as I had earlier thought. First, here is Sub and Left Front with Audyssey's settings. I re-ran Audyssey to make sure I had an accurate baseline. Only the main listening, center recliner position is measured.

Speaker configurations as set by Audyssey are listed below. Channel levels are not listed, since they are not relevant to these measurements. All distances are in feet. Note that the tape measurements (below, in parentheses) are to the front of the speaker enclosures, not to the front of the horn drivers. If Audyssey primarily measures distance in the midrange, this can explain at least part of the differences (except for the sub) since the midrange drivers are at the rear of the enclosures. There is less of a difference between distances on the side surrounds; the midrange horns on the Heresys are not as deep as on the K’horns or the Belle. Sub is set as LFE+Main.

Front L&R: Large (no crossover set); distance: FL, 13.9 (tape measure: 12.2); FR, 13.4 (tape measure: 11.75)

Center: Large (no crossover set); distance: 12.3 (tape measure: 10.8)

Sub: On; Audyssey will not display the crossover freq. that it set for the sub. distance: 14.5 (tape measure: 11.08)

Side Surround: Large (no crossover set; this is odd - other times Audyssey has set them to small); distance L: 6.9 (tape measure: 6.25); R: 5.6 (tape measure: 5.2)

Surround Back: Large, 2 speakers (no crossover set); distance L: 10.7 (tape measure: 8); R: 9.8 (tape measure: 8.75)

Plot is of FR; green is Audyssey ON, purple is Room EQ off.
 

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Discussion Starter #8
Here is the waterfall for the FR plot above, but with Audyssey OFF. Should have mentioned that all measurements were made with ECM8000, 802 mixer, Creative X-Fi notebook soundcard and at 75db +/- (held volume control constant, but some plots are higher/lower SPL due to FR differences.
 

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Discussion Starter #9
Changing all crossover frequencies to 80Hz:
FR plot is subwoofer and LF on, no traps in room, audyssey ON with 80hz crossovers manually set: Red plot - Audyssey ON with 80Hz crossover; blue plot - Audyssey crossovers as above (all large); green plot - 80Hz crossovers, Room EQ OFF.
 

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Discussion Starter #10
Now, the two Monster traps are in the room; side walls, horizontally on the floor, front edge about a foot from the mouth of the front bass horns.

FR & waterfall, Audyssey OFF; subwoofer and LF on. Green FR trace with the larger dips is with traps; other green trace is without traps.
 

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Discussion Starter #12
Here is the waterfall for moving the two traps to the rear corners, on the floor. For this measurement, I had to move the rear K'horns out of the corner (I have only 42" from the top of the speaker to the ceiling.) I am sure that moving them out of the corners affected FR and decay to some extent. The green overlay is the waterfall for the traps at the rear center of the room as described above - I did this to see the difference that the location made.

This was an attempt to predict the decay improvement of putting custom 42" Monster traps on top of the rear speakers.

Sub and LF mains on, 80Hz crossovers, Audyssey OFF.
 

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Discussion Starter #13
Whew! This is more work that these worn out knees and back can handle. Maybe the system is good enough just like it is.... NOT!

Sure looks like more traps are in my future. Later on, I will post plots with the BFD inserted to see how much better the FR can be.
 

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Nice job of looking at the options. Each has it's advantages and shows differences in FR and decay times. As you're seeing, 2 is helping but more are needed due to the room size and multiple items needing to be addressed.

As you add more, you'll also see a cumulative improvement in decay time down low.

Bryan
 

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Discussion Starter #15
I put three more Monster traps on order yesterday with the custom height needed to go on top of the K'horns, so we will see how much difference that makes. Two are going in the back corners; the third was planned to go in the front left corner, but may end up elsewhere.

Bryan: I did not see your e-mail about symmetry until after I placed the order. I can always use the third one elsewhere if there is an obvious imbalance between the fronts. BTW, I asked about GIK's health during the recession - glad to know that you folks are doing OK! Many places closing their doors around here... including Hoopers, where I purchased most of my HT gear over the years.
 

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Let me know if you need anything Harry. Sorry for the email timing.

As for business, well, Christmas wasn't as good as it usually is but it was certainly better than the average time of the year. January started a bit slow but is picking up very nicely. The factory in the UK is coming along. That just takes a while to get the word out.

Bryan
 

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Discussion Starter #17
Bryan: In reading Ethan's excellent primer on acoustic treatment, I see that he recommends filling the cavity behind a trap with absorbent material. For corner mounting of the Monsters would there be any discernable improvement in <100Hz performance by filling the cavity with "pink stuff"? Gut feeling is no since the density is low.

Again, thanks for all your patience with us folks that are just now learning about room treatment. As I said in an earlier post, the subjective improvement of just adding the two is far greater than the numbers would suggest.

No problem on the 3rd trap. I know that I have a long way to go, so I will certainly find a place for it. There is a chance that a Tri Trap will fit on the window side, so that may be a better option later on. Wife reminded me this morning that I was spending way too much on this stuff, so I suppose a truly excellent Valentine gift is in order:bigsmile:
 

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Discussion Starter #18
Forgot to mention that I did play around with the BFD this weekend. The primary benefit that I saw (and hear) is the ability to flatten out the sub response when Audyssey is ON. I don't recall the boost/cut db, but I ended up with 4 filters, one to re-gain a rolloff that Audyssey is introducing below about 25Hz or so.

I still like what Audyssey does for EQ in the mids and highs, so being able to leave it on and still have the smooth sub FR is beneficial.
 

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If you add a bit of standard insulation behind the Monsters, it will help a little. It's not going to be a ton but down really deep, it will help some - certainly worth the very small expenditure to buy a roll of insulation.

Bryan
 

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Discussion Starter #20
Bryan: The other 3 Monster traps arrived today and I have a question. Based on your comments about symmetry, I put two up front on top of the K'horns, including on the right side at the window. This leaves about 3" of the right side of the trap not pushed up to the wall - actually it is spanning the window. I think I read that corner traps should be against the wall and that an air gap would reduce performance. Your opinion, please.

The options that I have with the 5 traps (no budget for any more for a while) are two vertically up front in the corners, two horizontally in the back corners at ceiling level and the 5th in front of the fireplace in the rear center.

No time to run plots tonight, but should be able to post more on Saturday.

Thanks.
 
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