FBT Verve 12mA Frequency Response

merlin17

merlin17

Power User
Hi!

I just measured the Frequency Response of my 3 wedges (unscientifically with a 31band t.meter), and it proved what I am hearing...

The QSC K10 was relatively flat when the Bass switch is set to Ext.Sub - in the normal position everything below 120Hz is way too much.

The LD Systems Mon121a is also relatively flat, the bass does not go as deep and the treble is slightly rolled off from about 4k up.

The FBT Verve 12mA has a 8-10db (!) dip centered at about 2.5kHz and ca. 3db too much at 8-12kHz!
This should be the cause why it sounds so "nice" but almost unusable without a LPF set around 6-7kHz...
I'll try to compensate the dip with an EQ block, but I doubt it will sound "real"...
 
Wow. Can some of you speaker design experts weigh in on this? For those of us who are contemplating the 12ma (like me), is this cause for concern?
 
I heard that dip without tools. The Verve sounds to me like a boombox with fake "Hyper-Bass" turned on. I tested it next to the QSC, which had a slight plasticky quality to my ears, and the Atomic, which as you see in my sig, I now use (with a bit of low end rolloff in the global EQ).
 
Yes, I heard that before I measured, too, that's why I said the measurement proves what I heard. ;-)
I also find the K10 to sound a bit "plasticky" (hard to describe).

BTW: EQing the Verve helps. I'll continue testing in the next days...
 
I'm a bit confused. How wide is the curve at 2.5k? 8-10db is hard to believe. Doesn't that basically cut the levels of those frequencies in half? Also, are you saying that you essentially defeat the frequencies above 6k? If these are true, it's hard for me to view this as a good solution. I played through some 12m's the other day and it didn't seem like there was this much of a drastic hole in the sound. But I didn't listen to any music through them so I don't know. Could this be a characteristic of the mA specifically?

Can you post images of the meter's display during the test?
 
merlin17 said:
The FBT Verve 12mA has a 8-10db (!) dip centered at about 2.5kHz...
Click to expand...
That's a significant dip. It's also only about 1/3 octave away from the crossover frequency. That raises the possibility that the mic position resulted in some destructive interference between woofer and tweeter. I wonder if a different mic position would give different results. I also wonder how much had to do with room response and the placement of the speaker in the room. You'd have to get the mic pretty close to the speaker to minimize room response, but there's no accurate place to close-mic a two-way speaker — even a coaxial one..
 
Rex said:
That's a significant dip. It's also only about 1/3 octave away from the crossover frequency. That raises the possibility that the mic position resulted in some destructive interference between woofer and tweeter. I wonder if a different mic position would give different results.
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If that is the case, it would mean that the single greatest advantage of a coaxial layout had somehow been defeated.
 
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Jay Mitchell said:
If that is the case, it would mean that the single greatest advantage of a coaxial layout had somehow been defeated.
Click to expand...
Help me understand that. At some distance, I can understand the advantage. But miked up close, wouldn't it be tricky to find a spot where the mic isn't significantly closer to the tweeter (which is eclipsing the woofer) or closer to the woofer but significantly off-axis for the tweeter? Where would the ideal close-miked position be on a coaxial design?
 
I know that Jay has cautioned that it is not a simple thing to interpret polar plots. However, it appears that if you measure 20 degrees off-axis horizontally, you would get approximately the results given above, based on the plots published by FBT.
 
That could be true, but if you're close-miked to minimize room response, and you've got the mic in a spot where it can "see" the woofer, you'll be much more than 20­­º off axis
 
Not sure what you mean, Rex. I haven't seen a Verve up close, but isn't the tweeter behind the woofer?
 
Rex said:
At some distance, I can understand the advantage. But miked up close, wouldn't it be tricky to find a spot where the mic isn't significantly closer to the tweeter
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The B&C coax assembly used in the Verve has the HF driver mounted on the woofer backplate and firing through a bore in the the pole piece which is contoured to form a small horn shape. There is no shadowing. Even in a nearfield (~1M) measurement, you can place the mic on axis and get a similar response to farfield.

Where would the ideal close-miked position be on a coaxial design?
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If you're measuring the speaker's response, you don't close-mic it. A distance of a meter will give you a reasonable approximation, and it is trivially easy to get the speaker far enough off the floor that you can do a non-windowed response measurement at a test distance of one meter that is not significantly affected by the floor reflection.
 
Jay Mitchell said:
The B&C coax assembly used in the Verve has the HF driver mounted on the woofer backplate and firing through a bore in the the pole piece which is contoured to form a small horn shape. There is no shadowing. Even in a nearfield (~1M) measurement, you can place the mic on axis and get a similar response to farfield.
Click to expand...
I didn't know that. I haven't looked closely at a coaxial design in years. I figured they were still mounting the HF driver in front of the LF driver. Thanks for the update.


Jay Mitchell said:
If you're measuring the speaker's response, you don't close-mic it. A distance of a meter will give you a reasonable approximation, and it is trivially easy to get the speaker far enough off the floor that you can do a non-windowed response measurement at a test distance of one meter that is not significantly affected by the floor reflection.
Click to expand...
How close do you have to be to avoid significant effect from room response?
 
Rex said:
I didn't know that. I haven't looked closely at a coaxial design in years. I figured they were still mounting the HF driver in front of the LF driver.
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The verve layout precedes the one you describe, at least in sound reinforcement loudspeakers and studio monitors. The Altec 601 was introduced in the early 1940s and was soon followed by the 604. Versions of this speaker remained in production until some time in this century, and it was used in the UREI 809 and 813 studio monitors.

How close do you have to be to avoid significant effect from room response?
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That depends on too many things to list here. I am able to take measurements with no room effects at distances up to 4 meters in my test environments.
 
Those with a Verve12mA, try this EQ last in your chain, it will compensate for the dip and flatten the exaggerated highs (not fully, but in a way that sounds more natural).
2431Hz, Q: 0.707, +5.01db
7513Hz, Q: 0.707, -2.93db, shelving
There may still be room for tweaking it further, I'll do so in the next days, but it seems to be a usable starting point...
 
merlin17 said:
Those with a Verve12mA, try this EQ last in your chain, it will compensate for the dip and flatten the exaggerated highs (not fully, but in a way that sounds more natural).
2431Hz, Q: 0.707, +5.01db
7513Hz, Q: 0.707, -2.93db, shelving
There may still be room for tweaking it further, I'll do so in the next days, but it seems to be a usable starting point...
Click to expand...

Very interesting info, thanks. I'll try these out tomorrow. Is it possible that your speaker is faulty? they are some pretty serious EQ settings. A few people on these forums have sent their speakers back with a similar sounding problem and they have been repaired. It's possible.

Spence

Spence
 
xpenno said:
Very interesting info, thanks. I'll try these out tomorrow. Is it possible that your speaker is faulty? they are some pretty serious EQ settings.
Click to expand...
OTOH it may explain why Verve users have been able to use nearfield IRs without PEQ.
Interested to see how this develops.
 
merlin17 said:
Those with a Verve12mA, try this EQ last in your chain, it will compensate for the dip and flatten the exaggerated highs (not fully, but in a way that sounds more natural).
2431Hz, Q: 0.707, +5.01db
7513Hz, Q: 0.707, -2.93db, shelving
There may still be room for tweaking it further, I'll do so in the next days, but it seems to be a usable starting point...
Click to expand...

I don't have the 12mA but I tried those setting on one of my presets (Shiva sim 412 recto R121 mic) with the 12m/SLA combo I have and it made the upper mids way harsh.
 
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