Tempest In-room Frequency Response - Needs BFD ? (1 Viewer)

[Joe Mihok]

House curve sounds interesting. Do you by any chance have a screenshot of a graph with a house curve ?

 

[GrahamT]

Here's my attempt, I have changed it a little since
http://clubpolk.polkaudio.com/forum/...&postid=192872

I think I now have a 2 octave filter at 366 Hz with 12 dB of cut.

 

[Joe Mihok]

Excellent. Seeing an existing chart makes it so much easier . I'll try your 2 octave filter at 366hz with a cut of 12 db's. I'll remove my +4 db boost at 25 hz first because I don't think it will be needed with the house curve.

 

[Brian L]

I may have lost the plot, but what is the purpose of the filter at 366 Hz?

BGL

 

[Ilkka R]

Almost 20dB up from 80Hz to 20Hz, that is too much! Try something like 7-8dB instead. Your max spl is very limited with that setup and your driver will easily bottom when listening loud.

 

[Mark Seaton]

Joe-

If you want to experiment with some contouring or sculpting of the response, I would point out that you have a very desireable looking response as is. So far as adjustments I would offer a few plans of attack:

1) Before you do anything, now measure with your center channel and the subwoofer on. If you put your receiver in Pro-Logic mode, splitting the test signal to both left and right will result in sound from the center and subwoofer if things are set up properly. Now look at how the center and left/right speakers integrate or fight with the smooth response. Adjustments of the virtual distance of the subwoofer as well as phase adjustments can help with cancellations. You may also find that your LCR's are producing too much low frequency in spite of the crossover. You can often get very good results by raising the crossover point in your receiver. I often find that you will need a crossover at nearly 100Hz to get an appropriate in-room curve to 80Hz where you have the sub crossed in. Note you might want to add a low pass in the FBD (not sure if that one allows LP filters), or use the one in your plate amp at about 80Hz. Smooth integration can take a lot of effort, but is very important to getting the best sound quality and most consistent results from many different recordings and soundtracks.

2) If you want to experiment with some sculpting of the response, I would take your current curve and look to increase the difference in the "shelf" you see occurring between say 28Hz and 50Hz. Right now it is maybe 3dB, where increasing this to 5-6dB will add some more excitement and power to exlposions, depth charges, and other ominous effects, while you can keep your mains at the same level. Note that you generally want the broad peak to the low end to be in the 25-30Hz range, where this range is what we generally percieve as the really loud and low, exciting bass.

3) Another option to contouring the response is to raise the subwoofer level a few dB (say 3-6dB). The key here is to look at the response with the mains engaged. Ideally you want a reasonably smooth transition which looks like a smooth ramp up to another level like a shelf. A combination of this and #2 will let you decide what you enjoy the most.

Finally, while your subwoofer is pretty potent, as soon as you start altering the response, you can quickly ask a lot more from it. 3dB is 2x the power, and 6dB is 2x the excursion. With your subwoofer design, the 25-35Hz region will be the point of highest excursion above the tuning frequency. A little less boost here may keep things within the limits if you are really pushing it. Many of these decisions will depend on how capable your mains are. This is also where the potential of a higher programmed XO in the bass management can be helpful in reducing the work your mains have to do, allowing them to play cleaner and louder. Note that with the response smoother it is generally easier to comfortably listen to higher playback levels. Similarly, at increasing playback levels, you will find that you need less contouring or elevation of the low frequencies. How much low frequency boost you need is both a matter of subjective preference which is related to the room acoustics. Smaller, more reverberant rooms will need subjectively less boosting at the same playback level as compared to a larger, more open and lossy room.

Enjoy!

 

[Joe Mihok]

I'll experiment with it Ilkka. Thanks for the suggestion. I'm gonna aim for a 10db dip from 20hz to 80hz. I have total confidence the Tempest will not "bottom out". I've pushed this sub VERY hard at 20hz frequencies and see no signs of it having a hard time. The entire house feels like it will break apart before the Tempest does .

 

[Ilkka R]

Actually I was commenting on graph that GrahamT posted. Your graph looks very good. No need to add anything, Mark already said it.
Btw. ALL drivers bottom out some day...

 

[Joe Mihok]

Thanks Ilkka and I hope I never have to hear that "clank" sound. I never heard it before with any sub *knocks on wood*


Mark - What a great response, thanks. I did some measurments with my mains hooked up last night and they are indeed producing too much bass in the 80-90 hz region. I had to set my xover to 100hz to flatten things out better (but I still have a small dip at 70hz and peak at 89hz). I should note that this sub is passive, and I'm using my old Kenwood AVR to power it. I'm running each channel to each voice coil. I have no phase control or low pass filter on the reciever.

I'm gonna play with the house curve a bit. I'll try Graham's 15db slope, then 10db's, and then 5-7db's. The flat response I have now sounds fantasic for music, but in movies, I' getting too much of the 70-90hz bass that I find slightly annoying. I'll start another preset on the BFD and go from there.

I regards to your advice that small rooms need less boosting in the 25-30 hz region couldn't be more true. I have a large loft type HT and there are many open spaces (even a 20ft ceiling at one point) and I really do need a decent low freq. boost to feel anything in my couch.

 

[GrahamT]

Ilkka,

Yeah that was the first attempt I plotted, not the one with 12 dB of cut. That was more than 20. 12 dB is more like 7-8 dB slope when the response is already flat.

 

[Mark Seaton]

With the crossover now set higher, try using another parametric cut on the BFD set up high, say 100Hz and cut it say 12-20dB with the width very narrow. Start widening the filter width while you take measurements of the 60-120Hz range. Call it a hacked low pass. You can cut more and/or move the center frequency higher to get the desired result.

 

[Joe Mihok]

Okay, I went with Graham's 12db cut @ 366hz and this is what I get:



Note: This is with my mains hooked up and taking Marks advice and increasing my xover. I had to increase it to 120hz though to flatten out a 6 db spike at 89 hz. No matter how hard I tried, the spike would not come down untill i increased the xover. I'll experiment and see if my sub is localized.

UPDATE: I managed to bring the xover back down to 100hz and tamed the 89hz peak by -4 db's. This is the best the sub has sounded for HT. The explosion in SW-EP2 is just insane. I switched the low freq boost from 25hz to 22hz and it brings up the natural decline in the 18-22hz range while leaving the 25hz level still fairly elevated. The sub is now IMO perfect for my tastes. I'm grining from ear to ear. Thanks guys .

 

[al lout]

Joe,

After reading this thread, I now want a BFD for my sealed tempest as well... I've measured my room FR. I need to cut the peak of 9db at around 40-50hz and maybe a lil boost at 22hz like u. The reason I'm holding out on BFD is because I live in a second floor apartment. The sealed Tempest did enough pounding on my neighbor. I'm just afraid of adding the BFD will get me in trouble w/ the neighbors... I'm glad to see you liking the result of ur new toy (BFD). Now, pop in "The Haunting" and watch it at reference level

Al,

 

[MikeDuke]

Joe, That looks fantastic.

All it takes is time to do it right

 

[Joe Mihok]

I don't have the DTS version of The Haunting. Is the DD5.1 version still good for performing a test at reference levels?

 

[JohnSmith]

Would the ULTRACURVE PRO DEQ2496 be a better alternative? Does it do everything the 1124P and more? How would you use the RTA and included mic?

http://www.behringer.com/DEQ2496/index.cfm?lang=eng

thanks