X-Omni's are missing midbass/bass

mojave · « **on:** 21 Jul 2009, 02:44 pm »

I just got a pair of X-Omni's from av123. According to the specs, they are -3 dB at 40 Hz. When listening with them fullrange I noticed that most of the bass and midbass was missing. Last night I did some measurements with REW and a Behringer ECM8000 microphone. On the chart, the left speaker is blue and the right speaker is green. Both speakers start to roll off just under 300 Hz and drop 12-15 dB. They rise at 90 Hz to a peak at 60 Hz before dropping off sharply again. I moved the speakers and measured and moved the listening position several times and measured and came up with similar results. I've had four other speakers in the same location with no problems. Is something wrong with the crossovers or the drivers?

fred · « **Reply #1 on:** 21 Jul 2009, 02:56 pm »

Anything's possible, but I think you should first determine how much your room is contributing to the response. I'd suggest taking near-field measurements, placing the microphone 3-4 feet in front of the speaker on a tripod if possible, at a moderate to low volume. This should mostly eliminate the room effects.

mojave · « **Reply #2 on:** 21 Jul 2009, 03:23 pm »

Thanks for the suggestion. I did use a tripod and take a measurement from 1 foot with the microphone pointed straight at the tweeter. Since the tweeter points horizontally and the woofer points vertically, I wasn't sure where I should point the microphone. I discarded the sweep because it also showed a dip in frequency response. Also, I wouldn't think that the X-Omni's would interact that much different with my room than the av123 ELT525T's that I had before.

corndog71 · « **Reply #3 on:** 21 Jul 2009, 03:32 pm »

Do you have them at least 3 feet from the walls? I understand that having them too close to the walls will mess up the sound.

mojave · « **Reply #4 on:** 21 Jul 2009, 03:35 pm »

Yes, they are 3 ft away from both the side and rear walls. I moved them closer to the walls to see if that would improve the bass response, but it didn't.

ebag4 · « **Reply #5 on:** 21 Jul 2009, 04:05 pm »

Probably a bit too obvious but have you verified the speakers are wired in phase?

Best,
Ed

Danny Richie · « **Reply #6 on:** 21 Jul 2009, 04:24 pm »

The first thing to do is to see if it really is the speakers or the interaction with the room.

To take the room out of the equation you can do a 1 meter measurement with the mic in line with the top edge of the speaker. But you'll have to gate the time window to about 4ms to eliminate the room reflections.

mojave · « **Reply #7 on:** 22 Jul 2009, 02:10 pm »

I moved an X-Omni to the center of the room last night and measured it at 1 meter with 6 ms gating. I also measured a small sealed bookshelf speaker (Atlantic Technology 170). The X-Omni started to roll off a little over 300 Hz. The bookshelf speaker was flat down to 167 Hz (which was as low as I could go with 6 ms gating using REW). This morning I realized that I had left my crossover turned on so I will redo the measurements tonight.

However, there was still quite a difference between the two speakers.

mojave · « **Reply #8 on:** 22 Jul 2009, 02:17 pm »

Quote from: ebag4 on 21 Jul 2009, 04:05 pm

Probably a bit too obvious but have you verified the speakers are wired in phase?

Best,
Ed

No, I haven't checked that yet. To do so would require that I remove the speaker base and then the bottom of the speaker to access the crossover. I'll probably have to check the crossover/wiring next, though. If the woofer was wired out of phase with the tweeter, wouldn't that cause a dip at their crossover frequency instead of lower down?

Edit: If you meant I should check that both speakers were connected in phase with each other, it shouldn't matter because I am only measuring one speaker at a time. However, they are both connected in phase.

Danny Richie · « **Reply #9 on:** 22 Jul 2009, 02:25 pm »

If the woofer was wired out of phase from the way it was designed to be then it would cause a dip at the crossover and not in the bottom end.

It sounds like you have something else pulling the bottom end out of it.

Here is one of my measurements of one of them:

mojave · « **Reply #10 on:** 22 Jul 2009, 02:38 pm »

Quote from: Danny on 22 Jul 2009, 02:25 pm

. . . It sounds like you have something else pulling the bottom end out of it. . . .

Nice measurement - you took it on my birthday.

I'm going to send an email to av123's tech support, but since you designed these do you have any idea what might be pulling down the bottom end? Are the drivers the same as in the X-CS Encore? I could swap drivers and measure again to determine if I have bad drivers. That would be ironic, because the X-CS came with non functioning tweeter. A replacement is supposed to be shipped this week.

Danny Richie · « **Reply #11 on:** 22 Jul 2009, 02:49 pm »

Quote

Are the drivers the same as in the X-CS Encore?

Yep, same drivers, sort of. The CS has dual 16 ohm woofers.

Quote

I'm going to send an email to av123's tech support, but since you designed these do you have any idea what might be pulling down the bottom end?

My first thought would be that the electronics are pulling it down.

Their tech support would likely be just as stumped and would fire it over to me.

I wonder how they are insolated?

mojave · « **Reply #12 on:** 22 Jul 2009, 03:14 pm »

What if av123 accidentally put in 16 ohm woofers into my X-Omni's? Are the woofers marked so I tell which woofers are in the X-Omni's?

The X-Omni's are rated at a lower sensitivity that the ELT525T's (86 dB vs 87 dB). However, my X-Omni's play like more sensitive speakers. I had to lower the subwoofer output by 6 dB's from their setting with the ELT525T's. Does this provide an additional clue?

Danny Richie · « **Reply #13 on:** 22 Jul 2009, 08:28 pm »

Quote

What if av123 accidentally put in 16 ohm woofers into my X-Omni's?

Then the woofers would play up to high into the tweeter.

Quote

Are the woofers marked so I tell which woofers are in the X-Omni's?

They will look the same. You can stick a volt meter to it though and check its DCR.

Quote

The X-Omni's are rated at a lower sensitivity that the ELT525T's (86 dB vs 87 dB). However, my X-Omni's play like more sensitive speakers. I had to lower the subwoofer output by 6 dB's from their setting with the ELT525T's. Does this provide an additional clue?

Okay, that's odd.

emac · « **Reply #14 on:** 22 Jul 2009, 11:03 pm »

Yikes!!! Those are impressively bad measurements. Obviously, Danny's the best person to help you out. My first and main thought is bad drivers. I've had 2 tweeters from AV123 speakers die on me, so it wouldn't be the first time.

Good luck.

mojave · « **Reply #15 on:** 23 Jul 2009, 01:10 pm »

Here is a chart of the X-Omni taken with the speaker in the middle of the room, the microphone at 1m and 6 ms gating using Room Equalization Wizard. I've also included a picture of the crossover.

Danny Richie · « **Reply #16 on:** 23 Jul 2009, 03:15 pm »

That looks pretty good.

Turn the speaker slightly off axis and the top end will flatten out.

You are likely picking up a little floor reflection in the lower end too. Cut the window down a little more and you'll drop it out. If you can look at the impulse response then you can see when the first reflections arrive.

This would lead me to believe that the dipped area in your first post was room related cancellation. Try another room response of that speaker with it out in the middle of the room.

mojave · « **Reply #17 on:** 23 Jul 2009, 04:07 pm »

Here is an overlay of two measurements. The green trace is the right speaker measured in its normal position with the microphone at the listening position pointing vertically. The purple trace is with the speaker in the middle of the room with the microphone 1m in front of the speaker and pointed at the top of the speaker. Both traces have 1/3 octave smoothing.

The next chart is that of the X-Omni speaker (purple) and the small, sealed bookshelf (red) taken in the middle of the room at 1m. This is with 1 octave smoothing. The sealed bookshelf is rated at 3 dB low at 100 Hz so the measurement from the middle of the room looks appropriate. My ELT525T's are at a friends house, or I would have measured one of those in the middle of the room.

Danny Richie · « **Reply #18 on:** 23 Jul 2009, 04:17 pm »

Okay, this line threw me a little. Before I get deeper into this please clarify this line.

Quote

The green trace is the right speaker measured in its normal position with the microphone at the listening position pointing vertically.

Are you saying that the microphone is pointed vertically (aimed at the ceiling)?

mojave · « **Reply #19 on:** 23 Jul 2009, 04:40 pm »

Quote from: Danny on 23 Jul 2009, 04:17 pm

Are you saying that the microphone is pointed vertically (aimed at the ceiling)?

Yes, it was aimed at the ceiling when measuring from the listing position. Per the ECM8000 microphone measuring techniques and usage thread at hometheatershack.com, below 1kHz, there is no difference between vertical or horizontal placement.