Active riser, bass trap?

[gatestick]

This is sort of a build thread with questions. I started an active riser project. It is 4 feet by 10 feet with 9 Dayton audio BST-1 bass shakers (tactile transducers) wired with 3, 12 ohm circuits to make the final load to the amp 4 ohms. I am powering them with the Dayton audio SPA-500 amplifier. I will need to take it apart and glue all joints as they buzz at certain frequencies. I have found with trial and error to make a filter to limit it to 50 Hz on the high side and I did 12 Hz on the low side. I really like the effect it produces. I don't need to crank up the volume to high levels to get the tactile feeling. The wife will hopefully complain less. I used rubber spacers around the perimeter of the top and bottom sheets of plywood. This was in order to decouple the subfloor to the frame. the gap on the top is .75 inch and the bottom is 1.5 inch. This is to allow air flow inside the frame. I then put R13 insulation inside the frame.

I have ben trying to find what carpet to cover it with, but am having a hard time finding much in black or dark grey. What I have found is automotive, boat carpet. I don't think it will work as it does not seem like air can pass through it. I am looking for suggestions on this. I would also like to hear from others what they would do differently if they were to build one again. I plan on using rope lighting around the perimeter. Debating on installing a 110 outlet in it.

I don't understand why, but the sound has changed in a negative way. For the most part all that has changed is that the seating position moved up 7 inches. The measurements I have taken show an average of a 6db drop across the entire spectrum. What I have noticed is the middle and high frequency's are less clear, quieter. I would like recommendations on how to correct this. I will add measurements from before and after the riser. the only DSP that has happened is time alignment and reducing a 42 Hz peak. I have no problem taking more measurements, however my understanding of the functioning of REW is pretty limited. I did have REW make a filter to put into the Mini DSP, but I didn't like the results.

Any and all suggestions, Information is welcomed.

By the way I highly recommend using the bass shakers.

 

[thothsong]

I only see measurements with the riser.

 

[gatestick]

Sorry, I thought I did both.

It wont upload for some reason. Prior REW build perhaps?

I will try another. This 1 the subs were inactive.

 

[thothsong]

REW build shouldn't matter for uploads. File too large?

For some reason the distortion has gone up, and the Clarity metrics have gone down, on the Center channel in the 1kHz-2kHz range with the riser in place. The early reflections have also shifted.

 

[gatestick]

Try this again from a different laptop.

 

[thothsong]

There's something very odd about the measurements. Left and Right channels pre-riser are indeed ~6 dB higher than with the riser, but Center channel pre-riser is ~6 dB lower than with the riser.

 

[gatestick]

Possibly reflections off of the un-finished plywood? I assume carpet even the low pile automotive boat carpet should help with that. Any suggestions for things to try moving around? Different measurements to do? I thought about turning off the amp to the riser and measuring again. I am thinking that the shakers are possibly causing interference, or distortion of their own.

 

[thothsong]

Hard for me to imagine anything about the room configuration that would cause that kind of SPL disparity in just the Center channel. If the Center had also been ~6 dB down instead of up, then I'd have guessed that the riser is simply acting as a very effective broadband absorber. Also hard to be sure, but it looks like with the riser there's more ringing at several frequencies below 80Hz. I would take a new set of measurements, to see if you get repeatable results with the riser.

 

[gatestick]

I took 2 sets of measurements tonight. 1 with shaker platform turned on, and the other with it off. That is the only difference. Microphone never moved. Volume set at -10. I can remove the platform completely and do another set of measurements if you like. I would rather not if possible, lots of work. When doing the sweeps, the center seems much louder than the rest. No idea why. I changed nothing.

 

[thothsong]

Those 2 new sets of measurements are pretty consistent with each other, with two differences that I see. With the shaker platform turned on, there's a fair bit more distortion in the 20-65 Hz range, and ringing is worse at ~55 Hz. Many of those measurements also have what looks like some sort of hum at ~118Hz, perhaps from equipment somewhere. Both sets otherwise look pretty consistent with your previous riser measurements, including the Center channel SPL disparity and the Center channel 1kHz-2kHz distortion. Are you sure there isn't some Center channel knob that got accidentally turned? At any rate, might as well re-level the Center channel to be consistent with the others.

 

[Anatoliy Gavrilov]

All files open well, but I did not like the high unevenness of the frequency response graph.

For example, my bookshelf speakers, 2-way :

 

[gatestick]

Do you mean the difference in sweeps between each channel, or the unevenness in each channel sweep? Other than Audyssey I have no EQ for anything above 80 Hz. I have a Mini DSP 2x4HD for the sub channels. I don't own any other DSP devices.

My original purpose of the thread was to get some help/advice about the riser. I have since found some other issues. If I need to move to another thread for this someone please tell me.

#1 Center channel got much louder for some reason. I attempted to get all channel levels to about the same DB with test tones. This works as it should using the tomes from the processor. I can get them all within .5 DB. When using an external source for the tones, REW, a test disc, or YouTube clip the center channel trim is at -12. All other channels are near 0 to +2. I need ideas of things to check.

#2 Added distortion with the platform on, and ringing at 118HZ. I still need to disassemble the platform to glue all joints. This is in the hope of stopping some of the ringing or other negative things that have happened since building this. I see the distortion percentage numbers are higher, but I am not sure what to look for at the 118HZ. I do see a null at that frequency. Time alignment between the channels possibly?

#3 At this point I am unsure that keeping the riser is worth it. I can install the shakers directly to the chairs. The next step with it is carpet. I haven't received any suggestions on that part. Also should I put padding under the carpet? If so what kind? If I put the carpet on it I am committed to keeping it. It will be near impossible to take it apart again after the carpet is installed.

I really enjoy the tactile feeling of the shakers, but not at the expense of the rest of the system sounding poorly. I fail to grasp how going up 7 inches could cause all of this.

Thank you to everyone. I want any more info/suggestions you might have.

 

[thothsong]

The 118 Hz isn't ringing, it's hum from some sort of equipment. 118 Hz is 7080 RPM, which is the nominal speed for some kinds of motors and fans. It doesn't seem to be present in all of your measurements, so it's something that's not always running at speed. Does your PC have any internal fans? Or is there something else in/near the room with an intermittent motor or fan?

My bet is the internal test tones generated by your processor are bypassing Audyssey, so the difference you are seeing with external sources for Center is due to some Audyssey configuration.

 

[gatestick]

I agree with audyssey changing things. I just don't know what would have changed with adding the riser. Previous trims were within 4, excluding the Atmos speakers. They have always been boosted a bunch.

There is a deep freezer in the next room of my basement. Probably about 25 feet from the theater area. No wall between them. L shaped room. Also possible that the washing machine was running the spin cycle.

 

[Anatoliy Gavrilov]

Do you mean the difference in sweeps between each channel, or the unevenness in each channel sweep?

I converted all your REW measurements to 1/3 octaves and compiled them into one averaged measurement.
All measurements have a different level of signal amplitude, this also affects the uniformity of the average frequency response.

Try this again from a different laptop.

Here it is already a little better, but there is a dip from 2 to 3 kHz. :

 

[gatestick]

How can that be fixed?

 

[JStewart]

#2 Added distortion with the platform on, and ringing at 118HZ. I still need to disassemble the platform to glue all joints. This is in the hope of stopping some of the ringing or other negative things that have happened since building this. I see the distortion percentage numbers are higher, but I am not sure what to look for at the 118HZ. I do see a null at that frequency. Time alignment between the channels possibly?

The 118 Hz isn't ringing, it's hum from some sort of equipment. 118 Hz is 7080 RPM, which is the nominal speed for some kinds of motors and fans. It doesn't seem to be present in all of your measurements, so it's something that's not always running at speed. Does your PC have any internal fans? Or is there something else in/near the room with an intermittent motor or fan?

@thothsong is correct, the 118Hz is in the environment and not your audio system. You can see it in the noise floor, which is really low, by the way. If the noise floor is really that low it shouldn't be audible anyway.and as also pointed out, not always on.

Regarding the center channel relative volume, I may have missed it, but has the center channel dialog adjust been looked at in the Marantz? From the 7702 Web Manual. It explicitly states it raises and lowers the center channel volume:

 

[gatestick]

I disassembled glued and re assembled the riser this weekend. I haven't done any measurements yet. The wife wants to watch a movie. I won't say no. I built this system to enjoy it. Feels more like work at the moment.

I checked the center channel dialogue adjustment. It was on with a trim of +1. I turned it off. I then watched about 5 minutes of a TV show. I couldn't tell a difference. My center channel was the only speaker I had bi-wired, so I ran a single run to eliminate that as a possibility. I don't think it would be that as it has been setup bi-wired since 2004. Also 1 of the connections on the connection plate to the crossover inside the cabinet had vibrated loose. I tightened then soldered the connection.

I think that I will reset all settings and then run audyssey again. Not sure when that might happen. I need the wife and kid to be elsewhere.

 

[gatestick]

I finished the riser with the exception of finding a 30 foot piece of dimmable rope light for the perimeter. I did do a factory reset of the Marantz 7702mk2, and re ran audyssey. I also found a video from GR research

for doing a crossover modification for my Klipsch RF7 version 3. Its a rather expensive, so it will need to wait for a bit. In the video he explains that the image center is very large and that the vertical off axis is pretty terrible. He gave a tip to tip the speaker backward to help with this. I put a 3/4 spacer under the front feet for now. I haven't taken any measurements to confirm anything yet. Overall I am pleased with how the riser turned out and performs. I do wish I didn't create other problems.

 

[thothsong]

Nice job!

 

[gatestick]

New measurements with the finished shaker platform. Fronts and surrounds tilted back with 3/4 inch spacers I also boosted the subs PEQ at 20hz a little. No other changes. First 1 is platform on, second is platform off. Audyssey is on for all of it.

Still sounds as if I am listening with cotton stuffed in my ears.

When doing the test tones for room correction or REW sweeps in the surround channels I can hear the heat ducts humming after the tone is done. I don't remember hearing this before the riser.

 

[thothsong]

The platform on is producing a bit more distortion between 32 and 46 Hz, but otherwise platform on now looks pretty much the same as platform off, so that's good.

 

[JStewart]

Still sounds as if I am listening with cotton stuffed in my ears.

What's it sound like with mains running full range in stereo? Wondering about that 15dB low end rise. Maybe a bit much? Any pre-riser measurements to compare to?

 

[thothsong]

I change my opinion about what's going on at 118 Hz. There's too much consistency between your latest two sets of measurements for it to be equipment hum, but there are also curious differences between speakers. The resonances I see in your latest measurements:
Left: 119 Hz
Right: 113 Hz
Center: 119 Hz
Left Sur Back: 119 Hz, 130 Hz
Right Sur Back: 118 Hz
Left Sur: 113 Hz, 118 Hz, 130 Hz, 180 Hz
Right Sur: 113 Hz, 180 Hz

 

[gatestick]

What's it sound like with mains running full range in stereo? Wondering about that 15dB low end rise. Maybe a bit much? Any pre-riser measurements to compare to?

I played with this for quite some time. I turned the subs off through the Marantz, and ran he fronts in full range. If I have the Audyssey MultiEQ set to L/R bypass it sounds best. As I remember it used to be. I expected the Audyssey off setting to sound the same as bypass, but it is not at all the same. The MultiEQ reference setting is by far the worst at this time. Listening to music like this is good. I have yet to try a movie or tv show. I would prefer to have the subs active. Pre riser measurement included has the sub off, and audyssey off.

I change my opinion about what's going on at 118 Hz. There's too much consistency between your latest two sets of measurements for it to be equipment hum, but there are also curious differences between speakers. The resonances I see in your latest measurements:
Left: 119 Hz
Right: 113 Hz
Center: 119 Hz
Left Sur Back: 119 Hz, 130 Hz
Right Sur Back: 118 Hz
Left Sur: 113 Hz, 118 Hz, 130 Hz, 180 Hz
Right Sur: 113 Hz, 180 Hz

I also noticed the traces were different at each respective speaker. I guess I don't know what to look for to find the resonances. Specifically I thought that the Rt front might actually be defective at the 91 to 116 Hz range. I have no clue how to fix any of these issues.