carl
Junior Member
Posts: 95
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4 Ohm
Jan 16, 2006 14:26:04 GMT -7
Post by carl on Jan 16, 2006 14:26:04 GMT -7
WOTW changes everything................. For a little background, I have a 4 Av 18 IB powered by a Behringer EP2500. The IB was callibrated with Avia, BFD'd and then callibrated by ear. All good so far. My mains are Klipsch (read efficient) so in order to keep my BFD out of the red, I've run the amp gain up considerably to balance the system. The drivers are wired for an 8 Ohm load. I'd like to see what WOTW sounds like at reference levels, but when I play it back at -15 the BFD hits the red noticeably in some scenes. I was thinking that I could rewire the drivers for 4 Ohms and drop the sub output on my receiver to achieve the same SPL as with an 8 Ohm configuration. This should keep the BFD from clipping. Thus my question. Can 4 2Ohm coils per side be wired somehow to equal a 4 Ohm load? Thanks, Carl
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4 Ohm
Jan 16, 2006 15:02:54 GMT -7
Post by ThomasW on Jan 16, 2006 15:02:54 GMT -7
Nope, you can get 2 ohm or 8 ohm if you want to run the amp in stereo.
You can do a series /parallel config and end up with a mono 4 ohm load
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4 Ohm
Jan 16, 2006 17:00:11 GMT -7
Post by jimlowe on Jan 16, 2006 17:00:11 GMT -7
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4 Ohm
Jan 16, 2006 19:27:05 GMT -7
Post by gottavtr on Jan 16, 2006 19:27:05 GMT -7
I must chime in here. I have read/heard on more than one occasion that it is not a good idea to series wire two or more none mechanically linked voice coils together. Inductive feedback was, I believe, the term used. If the two drivers are exactly the same, which is never the case, there is no problem. The problem comes when the slight difference in response in each woofer is fed back to the others through the voice coil moving through the gap differently than the other drivers. Or so that is how I understood it. It is no problem to wire two voice coils on the same woofer in series since they cannot respond differently. I have seen many people on here report that they are using series connections without problem so maybe it is not a big deal but let the debate begin. After looking at the Crutchfield page it looks like Fosgate doesn't believe me!
P.S. Thomas, I have a question to ask you and do not want to bring up an old post to do it. E-mail me at gottavtr@yahoo.com or if you can PM me through this site that would be great. Thanks, Zach
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ryans
Full Member
Posts: 132
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4 Ohm
Jan 16, 2006 21:25:44 GMT -7
Post by ryans on Jan 16, 2006 21:25:44 GMT -7
"it is not a good idea to series wire two or more none mechanically linked voice coils " I've heard this arguement before. its usually accompanied by the fact that if you wire 2 woofers in series to an amp and then push on one of them, the other will move in the opposite direction. Well, lets consider this for a minute. You're right that we're only only concerned with the slight difference in response between the 2 woofers (presumably of the same make and model). Nobody's going to be pushing on one woofer while its playing ... at least they better not be ... so there's no external forces involved. These deviations in response should be very small. But lets say it does happen to some degree and you're concerned about the possible consequences. First there's the extra excursion that is required from the woofer. Should be greatly dominated by the excursion that's required to reproduce the music signal. So unless you're right on the edge of bottoming the woofer already, this won't hurt you. Second there's the possible acoustic repercussions. This extra excursion must change the woofer's output to some degree, right? True, but the 2nd woofer is affected in (almost) exactly the opposite way. The extra output from each woofer will cancel each other out. If this were truly an issue we wouldn't see countless well-known and respected woofer manufacturers showing you how to wire them in series to achieve a desired impedence.
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4 Ohm
Jan 16, 2006 21:38:02 GMT -7
Post by ThomasW on Jan 16, 2006 21:38:02 GMT -7
Posting to the forum is the best way to communicate with me.
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4 Ohm
Jan 16, 2006 22:24:50 GMT -7
Post by dewardh on Jan 16, 2006 22:24:50 GMT -7
gottavtr:
That has always been my understanding as well . . . the series resistance of the 2nd speaker's voice coil reduces the amplifier damping factor. If the drivers are perfectly matched and misbehaving in exactly the same way the back EMFs should buck, and it all balances out, but they never are (perfectly matched). One finds very little discussion of how large the effect is, and it's not necessarily a bad thing anyway . . . some people prefer underdamped bass, and many commercially successful speakers are deliberately designed that way. Parallel wiring the drivers does not have that problem, but may present too low a load impedance to the amplifier (although the actual load impedance will be significantly higher than "nominal" around driver resonance). Probably the best solution is a separate small amplifier for each driver . . . for a number of reasons that's what Linkwitz recommends for the bass drivers in ORION.
dewardh
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 17, 2006 6:44:27 GMT -7
Post by carl on Jan 17, 2006 6:44:27 GMT -7
Nope, you can get 2 ohm or 8 ohm if you want to run the amp in stereo. You can do a series /parallel config and end up with a mono 4 ohm load Wouldn't this require bridging the amp? Any other thoughts on a way to solve my predicament? Thanks, Carl
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4 Ohm
Jan 17, 2006 9:01:30 GMT -7
Post by ThomasW on Jan 17, 2006 9:01:30 GMT -7
If you want a 4 ohm load the amp must be bridged. If you wire the drivers in pairs the options are 2 or 8 ohm for the amp running in stereo. What input operating level switch settings are you running for the BFD?
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 17, 2006 9:25:22 GMT -7
Post by carl on Jan 17, 2006 9:25:22 GMT -7
Without looking on the back(I'm at work now) I don't recall, but I think it's at the +4. I do remember however at one point I was curious as to the function of the switch. I took a reading at my normal position with a sine wave. I then toggled the switch and left everything else the same. My second measurement was the same the first. I couldn't figure it's function at that point and kinda forgot about it as it seemed like it didn't do anything. As a last resort, I don't have a problem rewiring at 2 Ohms if I can hang onto my SQ. Carl
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 18, 2006 19:14:28 GMT -7
Post by carl on Jan 18, 2006 19:14:28 GMT -7
I checked tonight. The input switch closest to the sub cables is set at the -10dB. Now I'm beginning to doubt myself. I'm wondering if I toggled the correct switch when I tested the output (as described in my last post). Should there be a 14dB swing when toggling that switch and measuring SPL when receiver and amp settings remain the same?
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4 Ohm
Jan 21, 2006 10:41:13 GMT -7
Post by ThomasW on Jan 21, 2006 10:41:13 GMT -7
Sorry I missed you last question. This is dBV, it's an increase in voltage. This is completely different from +14dB of acoustic output
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 21, 2006 14:27:15 GMT -7
Post by carl on Jan 21, 2006 14:27:15 GMT -7
If you want a 4 ohm load the amp must be bridged. If you wire the drivers in pairs the options are 2 or 8 ohm for the amp running in stereo. What input operating level switch settings are you running for the BFD? I checked and it is in the -10 setting. Placing it in the +4 gives no more output. What is the purpose of this switch?
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4 Ohm
Jan 21, 2006 14:58:04 GMT -7
Post by dewardh on Jan 21, 2006 14:58:04 GMT -7
Carl:
The switch tells the device what signal level to expect on its input (and to provide on its output), +4 being "pro" and -10 being "consumer". If you set it -10 in a "pro" system you'll get clipping, if you set it +4 in a "consumer" system you under drive (waste resolution) in the digital converters (but with a 24 bit device probably won't hear any difference). RCA (phono) connectors on your pre-amp, amp, or elsewhere in the system strongly suggests using -10 . . .
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 24, 2006 8:58:46 GMT -7
Post by carl on Jan 24, 2006 8:58:46 GMT -7
Thanks for the explination. Back to my original quandry (original post): Is the only way to keep the BFD from clipping going to be re-wiring for 2 Ohms, or am I still missing something? My assumption is that rewiring will enable me to lower the receiver's sub output (and amp gain), while still maintaining the same relative output at the drivers. Will I notice a difference in SQ with a 2 Ohm config versus 8 Ohm?
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4 Ohm
Jan 24, 2006 11:38:57 GMT -7
Post by ThomasW on Jan 24, 2006 11:38:57 GMT -7
If you rewire for 2 ohms that just means the power amp has the potential to deliver more power. If you're clipping the BFD, that's a separate issue from running out of amplifier power.
Those really aren't 'gain' controls on the power amp. Those are adjusting the level of the input signal coming from the BFD. On your power amp those should probably be turned all the way up.
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carl
Junior Member
Posts: 95
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4 Ohm
Jan 25, 2006 9:58:42 GMT -7
Post by carl on Jan 25, 2006 9:58:42 GMT -7
So turning the amp up the last 2 or three clicks will increase the SPL of the subs relative to the mains correct? I then reduce the sub out signal in my receiver to lower the SPL on the subs to realign them with my mains? At that point the signal to the BFD would less likely to clip as the receiver signal has been reduced?
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4 Ohm
Jan 25, 2006 11:30:06 GMT -7
Post by ThomasW on Jan 25, 2006 11:30:06 GMT -7
Certainly.
The EP2500 level controls limit the input voltage coming from the BFD. Turn them up and more voltage drives the amp so it plays louder.
You do what you need to do to balance out the system. Since no one else has your specific setup, experimentation is the name of the game.
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