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Discussion Starter · #1 ·
I had some polyfil left over from a sub build and decided to try adding some to my DIYSG Fusion 8 Alchemy Towers. They were already lined with egg crate foam. I took a big handful of polyfil and stuffed the entire area around the compression driver. Sort of blocked off that whole top section. None behind the woofers or anywhere else in the cab. I then took some sweeps of one of the towers with the stuffing added vs the other without. Tested with UMIK-1 and REW. Mic stayed stationery 3 feet from speaker pointed at the mid point between the top woofer and the CD. Based on what I see in the measurements the stuffing either did nothing or hurt overall. I hear the distortion results in REW might not be trustworthy but the stuffed speaker had more THD and what looks like a more jagged distortion graph. Then just for the heck of it I decided to test my Pioneer andrew jones tower in this same test setup. The pioneers needed 7db more volume to get an overlapping graph. Surprisingly the pioneers look to measure considerably flatter up until a rising top end. The distortion graph from the pioneer also looks better. I'm sure if I ran this test at reference the distortion on the pioneers would be alot worse. But this backs up my earlier impression that the pioneers sound better to me at low volume. These sweeps were done at -25db. It won't let me upload the mdat.

Here is the stuffed vs unstuffed: (unstuffed in red)




Here is the averaged response of the two alchemys vs the single pioneer: (pioneer in red)

 

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Discussion Starter · #3 ·
Sorry, I'm not sure what "gate the measurement" means? Are you suggesting that these measurements are not done in a way that would produce useful results? If they're rubbish then I'll try again tomorrow. I really just want to make sure what I'm doing is correct and the modifications to the speakers are done in a meaningful way. And maybe it will save some other members the trouble of worrying about adding stuffing. I also have more stuffing if anyone thinks adding even more might be worth checking. Although I'm not sure how many times I can take these screws in and out, lol. :)
 

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Gating removes the room effects from the measurement, but only above a certain frequency. I'm not sure how it is done on rew, but typically you will be able to look at the impulse response and see were a bunch of little spikes are after the initial speaker response. Like this example



To see the low frequency response below the gate you can move the mic an inch or so from the woofer dustcap and measure. That response will be good up to around 500hz, so where they overlap and blend gives you a full range quasi anechoic response.
 

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First, stuffed vs not stuffed: if it's a different speaker with each measurement, you're also showing the differences between the speakers. Could you show a measurement of the two speakers before you changed the stuffing in one?
Also, are those two measurements both in the same location in the room? Exact same position, same mic position?

Where's the distortion measurement? I see frequency responses.

Is your receiver using the same auto eq correction filters for both the Fusions and Pioneer? If so, you should disable for the measurements.

What does the frequency response of Fusion and Pioneer look off-axis? Not only will some of your audience sit off-axis, but actually the majority of the sound you'll hear has been reflected off of a room surface. Can you move the mix 30 degrees to horizontal off-axis when speaker is in center of room?
 

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Discussion Starter · #6 ·
I turned off all eq for these tests.

The speakers were placed as close as possible to the same spot but they were not in identical locations due to human error and a non scientific method.

I don't have before measurements that were done the same way. Only MLP sweeps.

I tried uploading the mdat for distortion but that's not allowed apparently. I'll take screen shots.

I put all the gear away so my wife could watch her shows :(

I'll try sometime this week with the other tower. I can do before and after and some off axis. But that will be tough to get the mic and speaker back in the same spot for before and after tests. I can mark my spots but aiming the speaker is tricky on shag carpet.
 

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Discussion Starter · #7 ·
Distortion:

To be honest I'm not sure exactly what to look for in these. I originally was looking for the lowest THD line, in relation to the bottom. From what I can tell the higher the line goes the higher percentage of the sound is distortion. Maybe I'm way off here?

unstuffed:




stuffed:




pioneer:

 

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You're right - higher distortion is worse.

It is a simplistic distortion measurement. IMD can be more of a problem (two or more simultaneous tones) and even order (octave doublings) is less harsh than odd order (you plot 2nd, which is even).

And as you suspected earlier, you would see long term distortion in power handling, where one speaker's drivers would change impedance after playing loud, so the frequency response would change.

And with brief loud signals, you'd push the drivers to where they're less linear and you'd see more of a difference.
 

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The distortion on the pioneer looks worse in the upper mids lower treble, where it'll matter more.

I'm not sure I agree with Jay about gating these measurements, as you're just measuring a difference and it should be in the bass region. If you redid the test I might make one change and that would be to put the mic 1' from the woofer and ports and ignore the tweeter. There shouldn't be any changes to the tweeter, and if there is I'd be shocked. If this is the MTM then it's trickier. So hopefully it's the MT.

Do you have any photos of how you did the stuffing? Stuffing up in the horn area isn't an area I'd expect much to be required. The horn provides a bit of diffusion on its own. Directly behind the woofer would be an area of concern. But if you already have egg crate foam it might already be adequate for this ported speaker. With ported, stuffing can reduce output, so keep that in mind.

That said, I think the stuffing did slightly smooth things out.

As for the flatness of the speakers, the pioneer does look better. Dome tweeters have an advantage here. Usually not that much of a difference though. I'm on my phone, are the graphs 5db scale or 10db? I'm not sure what to say about that, could ask the designer. He doesn't come on AVS often though.

Edit - had a better look on my phone. It's 5db so that's good. The differences aren't dramatic. But I also misread it and I take back what I said, the stuffing did seem to make it worse.
 

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How loud were these done? If you weren't sufficiently above the noise floor in your room that can skew the measurement. I typically don't bother with distortion measurements in room unless they are so bad that something is broken. I also look at higher order odd distortion rather than thd when I do.

I will say that I have data on the smaller Pioneer bookshelf and I would hope the Alchemy can do better. Typical widening of the tweeter response off axis at the xo, though not as bad as most cone and dome speakers (that's not to say all cone and dome speakers are bad).
 

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The distortion on the pioneer looks worse in the upper mids lower treble, where it'll matter more.

I'm not sure I agree with Jay about gating these measurements, as you're just measuring a difference and it should be in the bass region. If you redid the test I might make one change and that would be to put the mic 1' from the woofer and ports and ignore the tweeter. There shouldn't be any changes to the tweeter, and if there is I'd be shocked. If this is the MTM then it's trickier. So hopefully it's the MT.

Do you have any photos of how you did the stuffing? Stuffing up in the horn area isn't an area I'd expect much to be required. The horn provides a bit of diffusion on its own. Directly behind the woofer would be an area of concern. But if you already have egg crate foam it might already be adequate for this ported speaker. With ported, stuffing can reduce output, so keep that in mind.

That said, I think the stuffing did slightly smooth things out.

As for the flatness of the speakers, the pioneer does look better. Dome tweeters have an advantage here. Usually not that much of a difference though. I'm on my phone, are the graphs 5db scale or 10db? I'm not sure what to say about that, could ask the designer. He doesn't come on AVS often though.

Edit - had a better look on my phone. It's 5db so that's good. The differences aren't dramatic. But I also misread it and I take back what I said, the stuffing did seem to make it worse.

I'm just a fan of when you post measurements that are supposed to represent a speakers response they should be accurate. If he didnt compare the measurements with the pioneer I likely wouldn't have mentioned it, but that imo took the results in a different direction.
 

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Discussion Starter · #13 ·
No photos of the stuffing, but I'll describe it like this: if you take the top woofer out, you now see a wall of white stuffing instead of the back of the CD. You cannot see through or around the stuffing at all.

The tests were done at -25 for the Alchemy towers and -18 for the pioneers. I had to raise the level for the pioneers to get the graphs to overlay. There might be a better way to do that, but I'm not aware of it. I guess the higher volume on the AVR could introduce more distortion.

I will take more measurements when I remove the stuffing from the tower I added it to. Since it appears that it either didn't help or maybe even hurt, I'm not going to add it to the other. So I'll set up a proper test somehow and do before and after, and toss in some more pioneer tests.

These tests might not have been done in the ideal way, but they are measurements of these speakers. Taken with a calibrated mic at seated ear height 3 feet from the speaker. Take it for what it's worth.
 
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