I had used this sub with the ob7's which are said to be 90.5db sensitive, and now trying it with the ob2x which I believe are 86-87db sensitive.
I have the peq off, and the xover set at a little above the 50 mark. 14 and 20 on the one switch, tried both mid and low damping, and set the low pass to ext/12.
I do have a large room these are playing into, but sit only 8 feet away.
I use a ps audio c-100 integrated amp, which has a seperate left and right output. It is unbuffered and I was told that the speaker level connections would be better for sound quality on any sub amplifier connection that was under 50ohms impedence. I don't know the gain because they didn't bother to specify it...probably 27db or more
The sub amp is the dual woofer option a370peq and the woofers are the 16 ohm version, in the w frame per Danny's plans.
How much break in time would you say that the woofers need?
Thanks for the help!
Please try 50hz/24db as you definitely need steeper slope so that the requirement for phase adjustment is not too dramatic. Even after you set to 50hz/24, I would set phase control to 11 o'clock to 2 o'clock position to see if that fills up the bass energy more. Since you don't have filtering on ob2x, your phase shift from the front speakers is 90 degrees phase lead. If you use a 12/ext setting, your sub most likely will have a 90degrees phase lag. That is a 180 phase difference. So how to add additional 180 degrees to the sub to get phase aligned? We have two options. First, turn the phase control to 180 degrees. However, the slower 12db roll-off means we expose the sub to a larger overlapped band that phase misalignment is more likely to happen. Second option is to use 24db roll-off instead of 12db roll-off. It will add 90 degrees by that, then use phase control to add another 90 degrees. So in my previous email, I should have added a case 3), that is, you may have volume control high because of phase misaligned. Since our hearing sensitivity increases from 20hz to 80hz fairly fast, if you have a null at say 50hz, you will definitely feel the bass energy less than adequate and hence turn up the volume. that means you need a lot of energy at the bottom end to compensate that effect and cause the volume to set higher. Phase alignment is the most difficult part of the setup. I am lucky because I have a data acquisition system and I can use close-mic technique to accurately capture the phase relation. You can achieve similar results by doing a bit more work using an SPL meter and a test tone CD. I use that method too. What you will do is:
1) record the response at the front speaker by placing the mic next to the front speaker woofer. It will accurately tell you where you -3db (or even -6db) point is. However, the limitation is it works only for sealed box speakers.
2) record the response at the sub only by placing the mic next to the sub. It will also accurately tell you where your -3db (-6db) is. In the case of OB, you need to add +6db/oct because of OB cancellation. Again it works only for sealed/ob sub.
3) record the response at the listening position of the response from front speakers only. It give you idea how serious the room mode and where they are. Also we need to use 1khz response to level set the reference level. All of the reading should be compared to the reading from 1khz. Reading from 1khz at close mic is not as reliable. The reason to pick 1khz is that it is found the room response above 300hz is way more reliable and less sensitive to wall reflections. A lot of people use 1khz as the reference level to level set subwoofer too.
4) record the response at the listening position of for sub only.
5) record the response at the listening position of sub plus front to find if they fill up the xover point well enough. and energy is 3)+4). If not, we have a phase misaligned.
Several trial-and-error iterations are needed and a spreadsheet will help us pick up which combination is best. Also I have found running the sub 3-6db hotter in general sound more full body and close to our live experience.
As for the argument that speaker level input sounds better, I would say it is case dependent. The input impedance of our plate amp is 24kohm which is very reasonable. If the interconnect distance is too long, one should consider XLR input. Using speaker level input adds the coloration from the power amp. Occasionally this coloration may sound better. But I cannot agree to use it as a general guideline. But that is just my 2cents.
