Parts Express Subwoofer Plate Amps on Sale Now

JoshK · « **Reply #20 on:** 27 Feb 2007, 03:23 pm »

If you ceiling slopes for 8' on the sides and 10' in the middle, then it averages 9' everywhere. This may be simplistic but its a good start. Try using your center freq corresponding to 9' with a higher Q (wider bandwidth). Your hanging panels likely don't kill all the standing waves but probably dampen it a bit, this should lower the amount of EQ needed.

This is my simpleton approach to your problem.

Housteau · « **Reply #21 on:** 27 Feb 2007, 04:08 pm »

My suggestion is that you take good independent measurements using test tones. You can download these from here: http://realtraps.com/test-cd.htm Just use a simple portable sound meter like what is available from Radio Shack. These tones are 1 Hz at a time and you will get a very accurate understanding of what your room is really doing. A 1/3 octave analysis, or similar will not help you.

John Casler · « **Reply #22 on:** 27 Feb 2007, 04:43 pm »

While the slopes will certainly "sum" in the room over all, I have a feeling that the pertinent elements are the speaker position, and the listening position.

I don't think the standing waves will be "exactly" the same throughout the whole room, so the "measurement" at the listening position is likely the only way to get the true response.

In all likelyhood, the frequency will correspond to the ceiling height at the listening position.

The good thing, at least it looks so from the pictures, is that you have a large opening behind you. This reduces the return bounce, and has a tendency to produce less interuption to the direct bass waves.

In the end, measuring is the most accurate way, and even then it is far less accurate than we would like, due to the "dynamic quality" of the frequncies during playback.

tbrooke · « **Reply #23 on:** 27 Feb 2007, 08:07 pm »

You may want to try the REW software available at the hometheatershack Forum: http://www.hometheatershack.com/forums/bfd-rew-forum/

It is free but you will need a Radioshack SPL meter and an external soundcard. It will give you a pretty good picture of what your sub is doing in the room and will even figure out the equalization settings for a behringer 1124P or else 2496. I have been using it and I have the 1124BFD and frankly I'm not sure using a sub would make any sense without it.

Tom

RGordonpf · « **Reply #24 on:** 28 Feb 2007, 05:45 am »

I would like to thank Housteau for his suggestion to use the Real Traps 1Hz test tones. I spent 2 1/2 hours this evening playing the 1 HZ test tones. My initial run from 20 to 120Hz showed a very minor hump centered at 80Hz +/- 10 Hz. There was a major hump centered at 35 Hz +/- 15 Hz. If you divide 35 and 80 into 565 you get lengths of 16.14 feet and 7.06 feet. Neither of these lengths match any real dimension in my room which is 23 feet by 21 feet with a peaked ceiling that is 10 foot at the peak and 8 foot at the sides. Strange.

By adjusting Gain, Crossover Frequency, Equalizer Center Frequency, Q, and Cut I was able to shrink the large hump so that it is now centered at 30Hz +/- 10 Hz and the amplitude has been cut by 2/3rds. I think that this is a major achievement. I think if I spend some more hours that I can reduce the 30Hz hump even further.

Because it was getting late, I only had time to play a few cuts off of a bass heavy CD before shutting off the system. There was a noticeable improvement in the bass.

Thank you for all of your suggestions. Now if I can just figure out what the 16.14 and 7.06 feet relate to. That is really puzzling me.

PLMONROE · « **Reply #25 on:** 28 Feb 2007, 11:55 am »

Why were these humps not detected when you used the PAA2???

Housteau · « **Reply #26 on:** 28 Feb 2007, 02:10 pm »

You are welcome. I was shocked and surprised with what I had found in my room as well. The modes were different than expected. Using standard 1/3 and 1/6 octave charting had completely missed them. I have found the acoustic information on Ethan Winers site very informative and helpful.

RGordonpf · « **Reply #27 on:** 28 Feb 2007, 04:29 pm »

Quote from: PLMONROE on 28 Feb 2007, 11:55 am

Why were these humps not detected when you used the PAA2???

I used a borrowed PAA2 and a CD of 1/3rd octave test tones when I first set up the room a year and a half ago. I had to return the PAA2 to its owner (darn). I ordered my own PAA2 last week, but it has not arrived yet. The frequency curve that I obtained with the 1/3rd octave test tones (and the PAA2) showed a hump that was broader and not as high as the one I obtained using the 1Hz test tones last night. I suspect that using a different crossover, with a different low pass frequency, with different amps and with a different amount of gain might have something to do with the large change in the frequency curve from then to now.

PLMONROE · « **Reply #28 on:** 28 Feb 2007, 05:55 pm »

Yes, it seems that anything changes everything. I am coming to think think that you really need 1/12 octave steps to get a reliable picture. I also have a PAA2 on order although I understand that they have been discontinued .

Housteau · « **Reply #29 on:** 28 Feb 2007, 08:44 pm »

Measuring one Hz at a time is very time consuming, but I think it is worth it. Anything less is just an average between measured points.

For example, here is a graph taken with a 1/3 octave analysis

Now, here is the same room measured in exactly the same way, just one db louder and one Hz at a time.

PLMONROE · « **Reply #30 on:** 1 Mar 2007, 01:04 am »

290 readings but WOW!!!!! What a difference!

RGordonpf · « **Reply #31 on:** 3 Mar 2007, 05:08 am »

I have spent another 4 1/2 hours trying various settings on my two 540 watt plate amps for a total of 7 hours and have arrived at what I think is the best compromise. I have a 5dB hump centered at 30Hz +5/-10Hz and another 5dB hump centered at 80Hz +/-10 Hz. The 30Hz hump does not affect orchestral music, except pipe organ. It would be noticeable on soundtracks and other music with synthetic bass. Treating that hump would take a very large Helmholtz resonator.

John, you have a lot of experience moving the Largers around. From the picture I posted you can see the position of the Larger. It is on its side with the active drivers facing out and the bottom plate on. Based on your experience, any recommendations as to the positions/orientations/height that I should try first when moving the Larger to try to eliminate the 30Hz hump?

With regards to the 80Hz hump, I think the first step will be to switch the RM30Ms from having the woofers face out to facing in. That will change the reflection patterns, but will it change the standing waves? Any thoughts? I guess I can only try. If that fails I suppose the next step would be a Helmholtz resonator tuned to that particular hump. I have neither the time nor the tools to make a slot Helmholtz resonator. Anyone know of a source that will make a helmholtz resonator to your specifications?

The ASC Subtrap http://www.asc-home-theater.com/subtrap.htm is another possibility. Has anyone tried one?

John Casler · « **Reply #32 on:** 4 Mar 2007, 02:34 am »

Quote from: RGordonpf on 3 Mar 2007, 05:08 am

I have spent another 4 1/2 hours trying various settings on my two 540 watt plate amps for a total of 7 hours and have arrived at what I think is the best compromise. I have a 5dB hump centered at 30Hz +5/-10Hz and another 5dB hump centered at 80Hz +/-10 Hz. The 30Hz hump does not affect orchestral music, except pipe organ. It would be noticeable on soundtracks and other music with synthetic bass. Treating that hump would take a very large Helmholtz resonator.

John, you have a lot of experience moving the Largers around. From the picture I posted you can see the position of the Larger. It is on its side with the active drivers facing out and the bottom plate on. Based on your experience, any recommendations as to the positions/orientations/height that I should try first when moving the Larger to try to eliminate the 30Hz hump?

With regards to the 80Hz hump, I think the first step will be to switch the RM30Ms from having the woofers face out to facing in. That will change the reflection patterns, but will it change the standing waves? Any thoughts? I guess I can only try. If that fails I suppose the next step would be a Helmholtz resonator tuned to that particular hump. I have neither the time nor the tools to make a slot Helmholtz resonator. Anyone know of a source that will make a helmholtz resonator to your specifications?

The ASC Subtrap http://www.asc-home-theater.com/subtrap.htm is another possibility. Has anyone tried one?

Hi Roger,

I forgot what requency are you rolling this sub into the mix?

If you are adding it too high, then that in itself might be the simple solution. Check your slope and the roll off of the RM30's and you might just be doubling at 30Hz.

Actually I am not 100% sure where it is. Is that it on the left wall firing "in"?

If so it should (I think) be run 90 degrees out of phase. + or - a few degrees since it is not in an ITU plane.

I might also try Lying it on its back, firing UP to the ceiling to see what that produces.

While this might sound strange, I might also try moving it 3 feet out from the wall and try it both facing the listener (as in angled right at them) and facing the side WALL. And while your at it try having it face the "front" wall. All of these will lengthen the path a bit.

As well

Obviously the 30Hz bump is not caused by the ceiling, and is likely one of the long dimensions, but the comb filtering of the angled ceiling, might be changing the energy distribution.

Since it is a "hump/bump" that means two major waves are "summing" (one direct original and one reflected) when they reach your listening position.

Let me think about it a bit more. I might come up with a few other thoughts.

RGordonpf · « **Reply #33 on:** 4 Mar 2007, 05:55 am »

Hi John,

I appreciate your thoughts. The subwoofer is on the left side of the fireplace against the wall, behind and inside of the left speaker. It is turned on its side with the active drivers and the open slot facing into the room. The Eagle monoblock amps are sitting on top of it. My RM30Ms, being from the first production run, are -3dB at 37Hz. So I don't know if they would contribute much to the 30Hz hump. My crossover frequency is 60Hz. I tried 30, 40, 50, 60 and 70Hz as the crossover frequency. If I dropped it below 60Hz I got a large suckout between 45-75Hz. So 60Hz is a compromise. If I was only worried about the 30 Hz hump I would drop the XO to 25Hz and crank up the gain. I agree that moving the subwoofer around and changing its orientation is the first thing to try. Art Noxon of ASC believes that moving the sub off of the floor is also beneficial as it breaks up the vertical mode and gets the sub out of the floor reinforcing boundary. That is why I was interested in the ASC Sub Trap.

Maybe my problem is that I am trying to solve two problems at once: the 30 Hz hump and the 45-75Hz suckout. With the equalizer I can cut the 30Hz hump by 2/3rds and fill in the 45-75Hz suck out. However that still leaves me with the 5dB hump at both 30Hz and 80Hz. Maybe I should just use the equalizer on the plate amps to solve the 30Hz hump and find other solutions for the suckout and the 80Hz hump, though I don't know what they would be.

And all of this listening to test tones is keeping me from the doing the really important stuff - listening to music. I have not listened to Beethoven or Rammstein for over a week now. ARRGHHH!!!

John Casler · « **Reply #34 on:** 4 Mar 2007, 08:54 am »

That 60Hz crossover means there is a lot of ground covered by both the RM30s and the Sub.

RM30 side firing woofers face "in" or "out"?

I'd consider reversing which ever one you are using and then try lowering the sub LP filter to more like 40 or below.

The "suckout" is no doubt caused by the RM30's interacting with the room.

And I like raising SUB off the floor too. Old Steamer Trunks and Cedar Chests filled with sandbags, cat litter bags, or anything similar are good.

I have my RM30s raised 8" and the subs are as high as the top of the RM30's.

You might want to forget measuring for a while and just listen. aa

RGordonpf · « **Reply #35 on:** 19 Mar 2007, 03:04 am »

"You might want to forget measuring for a while and just listen."

Hi John,

I took your suggestion and quit screwing around with test tones. I started listening to music again while I searched E-pay for ASC tube traps. Today I drove up to LA to pick up part of my winnings: an ASC Tower Trap (14.5 x 14.5), two 3' x 16" Tube Traps and two 3' x 16" Super Traps (Tube Traps with Helmholtz resonators inside). Two 4' x 13" Tube Traps and two 4' x 13" Super Traps should be arriving this week via freight. When you pay less than 50 cents on the dollar, the ASC stuff is not that expensive for what you get.

It is amazing the difference in the sound with today's five traps installed in my room. The warmth caused by the bass peaks is gone. The midrange is cleaner and clearer. Bass is tightened up with more detail.

Once April 17th has come and gone I will start creating some waterfall plots with Acoustisoft software and my trusty laptop. That should help me position the traps in the optimal spots. According to Ethan Winer at RealTraps, you keep adding bass traps until your room fills up or the bass drops off. It will be interesting to see how many traps I will need to remove the worst of the peaks and valleys in the bass frequency response.

geraldedison · « **Reply #36 on:** 22 Mar 2007, 01:24 am »

Seeing this post got me thinking as I have been looking to purchase a pair of amps to drive the woofers in my 2003 vintage RM40. I saw a "rack mountable" version of the Dayton amp mentioned in this listing in parts express.

Am I being naive to believe that I can use this rack mountable 500w amp to drive my bass by just setting the high pass to 200hz which is above the 166hz cutoff for the RM40 if I am correct. This seems to be simple and reasonable way to pump up the bass with a volume and phase control.

I know the draw back would be that bass signal is really going through 2 sets of filters both in the sub amp and the crossover. So the signal path is definitely sub-optimal. Assuming that the degradation is reasonable, does anyone see an issue with this approach.

As I look at the info on the paper glue to the back of the RM40, it warns not to use any external electronics on this speaker and a sub woofer amp seems to qualify as external electronics.

Would anyone who knows more than me about the RM40 and crossover circuitry comment on this thought.

Any opinion would be appreciated.

Gerald

John Casler · « **Reply #37 on:** 22 Mar 2007, 01:44 am »

Quote from: geraldedison on 22 Mar 2007, 01:24 am

Seeing this post got me thinking as I have been looking to purchase a pair of amps to drive the woofers in my 2003 vintage RM40. I saw a "rack mountable" version of the Dayton amp mentioned in this listing in parts express.

Am I being naive to believe that I can use this rack mountable 500w amp to drive my bass by just setting the high pass to 200hz which is above the 166hz cutoff for the RM40 if I am correct. This seems to be simple and reasonable way to pump up the bass with a volume and phase control.

I know the draw back would be that bass signal is really going through 2 sets of filters both in the sub amp and the crossover. So the signal path is definitely sub-optimal. Assuming that the degradation is reasonable, does anyone see an issue with this approach.

As I look at the info on the paper glue to the back of the RM40, it warns not to use any external electronics on this speaker and a sub woofer amp seems to qualify as external electronics.

Would anyone who knows more than me about the RM40 and crossover circuitry comment on this thought.

Any opinion would be appreciated.

Gerald

Hi Gerald,

Interesting observance, and maybe you can get B. to comment regarding the how it might work.

We use that amp (or one very much like it) for the PBS system (powered bass system) but because the x-over is now set higher (in the 240-280hz range) B, has to mod the amps to get them to do what we want. That is why they cost more in the PBS app.

Could be a pretty good improvement (for sure would have enough juice).

I would think that you would "not" want to use the x-0ver in the amp (run it stright through the LFE input, so that it "by-passes" amps filter, and the RM40 passive system would do the filtering and you don't have a "double filter" effect.

geraldedison · « **Reply #38 on:** 22 Mar 2007, 02:31 am »

John,

Thanks for the LFE suggestion, I didn't even think of that>

That would eliminate the double filtering!

SInce my RM40's are the 2003 version, the cutoff was below the 200hz range. So I thought this may be a cheaper bi-amping solution. As all the other amp's I can find with this power range are either way too expensive or I would have to settle for one of the amps for cars. This seem like a nice compromise.

Now if I can find a way adjust the upper range crossover point to that which has been done for the newer RM40's where the mids only go up to 6.9Khz. My version, the mids still go to 10khz and I can sense a bit of clutter in that range. But if I can pump up the bass with passive bi-amp, I'll be a happy camper

Gerald

RGordonpf · « **Reply #39 on:** 4 Apr 2007, 03:11 pm »

My ASC sub trap arrived yesterday. I put it under my Larger with the Larger in normal position (it previously had been on its side with the slot facing out). Raising the Larger 22" off of the floor puts the centers of the two drivers pretty much at ear level for me. The sub trap contains a Helmholtz resonator tuned to 70 Hz as well as other damping material to attenuate bass. So the change in sound that I heard was due to both lifting the Larger off of the floor as well as adding additional bass absorption. My listening room already had an ASC tower trap, two 3' x 16" tube traps, two 3' x 16" super traps and four 4' x 13" super traps. So the bass was already damped. Inserting the sub trap into the system made a noticeable tightening of the low bass with additional clarity in high bass/low midrange. Flight of the Cosmic Hippo was mesmerizing.

John Casler has previously recommended getting the subs up off of the floor to remove the floor boundary reinforcement. He is definitely correct. Put your sub(s) up on some crates and see if you notice an improvement. It is a cheap, reversible tweak.