Low SPL at 20hz for 12" XLS Peerless - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 27 Old 12-26-07, 10:31 AM
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Steve
 
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Re: Low SPL at 20hz for 12" XLS Peerless

1. Chances are its the room and how its interacting with it.

2. If you were not clipping the amp or sending allot of power to the sub it should be just fine.

na, keep this thread goin.

if you are really worried about maybe you did something wrong i still say you bring it outside and test it where reflections and what not have little effect.

p.s. its not SLP its SPL.
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post #22 of 27 Old 12-27-07, 05:14 AM Thread Starter
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Re: Low SPL at 20hz for 12" XLS Peerless

Yes, I've been doing some reading over at the Home Audio Acoustics forum and I think I need base traps. Any suggestions?

So far I've found Ecopink (Batts) Permastop 436 75mm thick fiberglass insulation with a foil facing on one side - apparently this is the best cheapest way to start bass trapping? This brand seems the best choice so far because it's the only one where I could find acoustic absorbing specs online. Are there any other brands that are commonly used here in Australia? The stuff Bunnings or Hudsons sells has no acoustic specs given as far as I'm aware.

Can't get any till the new year as suppliers are on holiday - bunch a slackers . OK, I know I'm on holiday, but that's beside the point.

Yes, I will test outside (somehow) sometime. But at the moment I think I'll concentrate on the in-house performance. Now with everyone's feedback I'm starting to think the sub's performing ok (the next door neighbour says it vibrates the opposite side of his house no problem at all when I crank up War of the Worlds - and it sure shakes my seat ). Re your question as to how loud I ran my sub with sine waves, I don't think I heard any clipping - I had the sub running loudish, but not really loud.

I'm starting to wonder if it's even worth getting the BFD I ordered as the acoustics forum seem to recommend that tuning the room is more beneficial than eq-ing. What do most people find - a combination of both works best?

Yes, SPL, but SLP (Sound Liberation Party? I like the sound of that.) is what comes out when I type around midnight. Sorry.

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post #23 of 27 Old 12-30-07, 09:58 PM Thread Starter
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Re: Low SPL at 20hz for 12" XLS Peerless

Have decided to go with the BFD over the bass traps since bass traps appear to predominantly work at the 60-80hz range and are much more expensive than a BFD.

Due to difficulty in measuring the sub outside I decided to measure the sub's SPL using this method as suggested by Terry:

1. placed the sub in the middle of the room away from walls (main speakers off, crossover at 80hz on receiver).
2. set SPL meter 1/2" away from the bottom of the driver and set measurement level to 75db. Took a 4 sweep reading.
3. repeated the setup and measurement procedure for each PR, at 75db
4. Used RoomEQ averaging feature to average the 3 readings (see top graph).

I have also moved the sub position and been able to get a much flatter response curve at the listening position (see bottom graph). However, both the room response and the 'anechoic' response show a rapid decline at approximately 24hz. Could it be the tuning I need to check (i.e. could that notch in the top graph at 24hz indicate incorrect Fb)? Any suggestions as the cause/remedy?

Cheers,
Blue
Attached Thumbnails
Low SPL at 20hz for 12" XLS Peerless-mean-slp-across-drivers-prs.jpg  

Low SPL at 20hz for 12" XLS Peerless-sub-rear-right.jpg  


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post #24 of 27 Old 12-31-07, 04:13 AM
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Re: Low SPL at 20hz for 12" XLS Peerless

looks a lot better now we can see what the PR's add.

Personally I wouldn't worry about any discrepancy between the '24 hz' result you get and the '20 hz' claimed design....that could very well be within tolerance y'know?

I little tweak at 25 and 55 hz would make it a very flat response indeed, a lot better than many rooms seen here!

What results did you get from changing the weights on the PR's? There might be a bit of gain there, but again personally I would take what you have, it's all too easy to try chasing tiny gains and lose the good you have!

I assume that you will be using it for HT, given the nature of the site. Then I would understand trying to get maximum bass extension, me I'm purely stereo guy, and so find it actually irritating for the subs to go much lower than you have (very unmusical to just be shaken, OK for movies, great the first time for music, fine the second but annoying after that..for me anyway).

Out of curiosity, how do the graphs 'swap' in output between the driver and PR's? From what you saw did it explain the points you raised initially? If so, it is just that bit more collective knowledge on the shack and helps all of us better answer questions like this in the future.
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post #25 of 27 Old 12-31-07, 09:29 PM Thread Starter
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Re: Low SPL at 20hz for 12" XLS Peerless

From memory, there was little difference in overall SPLs (over the response curve) with the changing of the PR weightings, it mostly seemed to effect the dip (tuning) at fb (20hz).

I am curious about the drop at 25hz then slight peak at 23.5hz - any idea what's causing that? Have I got the PR weighting 'massively' (excuse the pun) wrong, and that dip is the dip that should be at fb?

Yes, I'm using the sub for HT so chasing that extension. However, maybe I have done something wrong with my measurements? I calibrated the soundcard and loaded the RS meter compensations. I'm measuring at 75db, would measuring at a louder volume make any difference?

In the accompanying graph, the top two lines are the passive radiators, the third line down is the averaged line (PRs & driver), and the bottom line is the driver. I'd still like to know if this is a legitimate way of measuring the sub's SLP output. If it is, it's pretty handy if it's difficult to take the sub outside.

Happy new year,
Blue
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Low SPL at 20hz for 12" XLS Peerless-mean-slp-across-drivers-prs2.jpg  


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post #26 of 27 Old 12-31-07, 11:49 PM
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Re: Low SPL at 20hz for 12" XLS Peerless

As I say, I'm out of my comfort zone so I can't really answer your questions, others around here are pretty good with sub stuff.

Looks like the PR's and driver swap right on 40 hz, interesting to see the swap unfold.

Maybe the dip at around 24 hz or so IS the fB? Rather than still follow the 'projected' design results, it is the actual measurements that tell you how YOUR sub is performing. Don't forget everything has tolerances, maybe this is what your collective tolerances add up to.

Perhaps that rise after the dip is more 'noise' than sound...what I mean is I know in a normal vented box the driver can 'unload' below the critical point..whether that has any truth or applies to PR's as well I don't know. Just wondering if the dip tells you all you need to know about the sub.

I'm reasonably sure that a close mic measurement is fully valid for bass stuff, by extension I also assume it's therefore valid to measure the outputs of the PR's too....having just typed that I do recall people measuring both the driver and ports outputs in BR subs, and summing them so yeah, I reckon it is a valid measurement.

If I've led you astray hopefully s/one who knows their stuff will correct it for us all.

Good luck with it all, hope the HT you are also discussing ends up a beauty.
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post #27 of 27 Old 01-01-08, 01:18 AM Thread Starter
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Re: Low SPL at 20hz for 12" XLS Peerless

Thanks Terry,

"Good on ya mate!" (translation: well done)

Cheers,
Blue

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