rdale

Measuring the Effect of Extra Bass Traps

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I recently got a UMIK-1 measuring mike and installed REW on my Chromebook and iMac to use with it. I took my first measurements with my Chromebook using a stereo 3.5mm jack to twin RCA plug cable from the Chromebook headphone output to the input of my amp. That was a bit clunky and so I enabled AirPlay in Raspberry Pi running the Moode music player that drives my 2Qute DAC and then changed the default output of my iMac to AirPlay with the Raspberry Pi as a target. That worked a treat and it was way easier to take measurements with the iMac without needing to unplug RCA cables in my HiFi.

The initial measurements showed a large room mode peak between 40 and 50 Hz. I have a hallway in the left corner of the listening room next to the left speaker, and it was possibly aggravated by the port resonance of my Klipsch RP-600Ms at 48 Hz.

I wanted to take some new measurements of my system because I'd just got two extra bass traps; a Vicoustic Round Bass 360 and a Vicoustic Super Bass 90. I wasn't sure whether the acoustic foam bass traps would have any effect at frequencies below 60 Hz, and I already had a couple of 150mm thick GIK panels behind the speakers.

Here is a photo of the new bass traps, and extra Round Bass 360 on the right side, and an extra Super Bass 90 on the left hand side:

1702095846_ExtraBassTraps.thumb.jpg.e66d8cbc4f8afbd872fc53c9592fac5a.jpg

After adding the bass traps I played some music and thought it sounded a bit quieter and maybe more controlled, but I had been away for a day or two and couldn't be sure it was sounding any different. When I took measurements of the system I was quite surprised how much difference the extra bass traps had made though for an outlay of 72 euros. Here are the waterfall graphs from REW to show the differences:

left_speaker_before_extra_bass_traps.jpg.45e28823cdbbbd6bcc3db740858b151f.jpg

left_speaker_after_extra_bass_traps.jpg.d26035dda8020f1d0f014422968c59ad.jpg

right_speaker_before_extra_bass_traps.jpg.8ce670bb46dd316272d0fcf8fe710ca8.jpg

right_speaker_after_extra_bass_traps.jpg.e463417d13a6895b9b1a70a3d1a26f71.jpg

both_speakers_before_extra_bass_traps.jpg.8aece49d4be607067d8764adcc28926b.jpg

both_speakers_after_extra_bass_traps.jpg.490a4871b063ccb72ad3a004504989be.jpg

I think this is a great result. The bass traps have done a nice job in reducing the 40-50 hz peak in both the left and right channels and I actually wasn't expecting the traps to work as well as they have - bass trap pessimists take note!

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24 minutes ago, rdale said:

The bass traps have done a nice job in reducing the 40-50 hz peak in both the left and right channels and I actually wasn't expecting the traps to work as well as they have - bass trap pessimists take note!

It looks more like what the traps have done is to reduce the reverberation time at these frequencies, rather than to reduce the actual peaks? Still definitely an improvement though :^.

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4 minutes ago, MartinC said:

It looks more like what the traps have done is to reduce the reverberation time at these frequencies, rather than to reduce the actual peaks? Still definitely an improvement though :^.

Yes, you're right - I suppose I should have said 'reduce the reverberation peak' - that was that thing that had bugged me when I took the original measurements. When I get a miniDSP 2x4 HD and a couple of subwoofers I hope I'll be able to flatten out the frequency response a bit as well as extending the bass.

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Super Dealer

Difficult to treat  low bass passively, the Mini DSPs EQ will do the trick.

keith

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Super Wammer

You can generate from REW a filter to EQ this and then paste and copy it in to the MiniDSP .

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8 minutes ago, bencat said:

You can generate from REW a filter to EQ this and then paste and copy it in to the MiniDSP .

Yes, I've been reading about the miniDSP 2x4 HD capabilities and it sounds very powerful. The interesting question to me is whether or not it makes more sense to spend 700 pounds on a standmount speaker + 1300 pounds on subwoofers and miniDSP vs spending 2000 pounds on a pair of floorstanders.

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8 minutes ago, rdale said:

Yes, I've been reading about the miniDSP 2x4 HD capabilities and it sounds very powerful. The interesting question to me is whether or not it makes more sense to spend 700 pounds on a standmount speaker + 1300 pounds on subwoofers and miniDSP vs spending 2000 pounds on a pair of floorstanders.

The floorstanding speakers would still have a very uneven bass response, like you have above, just presumably extending a bit lower. 

(I'll post up what I've achieved with my miniDSP, floorstanding speakers and sub sometime soon. I'm getting there with the optimisation.)

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8 hours ago, PuritéAudio said:

Difficult to treat  low bass passively, the Mini DSPs EQ will do the trick.

keith

Yes I agree. But the miniDSP would not have been able to sort out the bass reverberation peak at 40-50 Hz in the waterfall graph, it would only be able to correct the frequency response as far as I know. But my 72 euros worth of acoustic foam bass traps have had an important and measurable effect at 45 Hz. So in contrast to what you say, it isn't that difficult to treat low bass passively. But I don't think it is one or the other, you need both room treatment and bass DSP to get the best bass sound.

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Posted (edited)
8 hours ago, rdale said:

Yes I agree. But the miniDSP would not have been able to sort out the bass reverberation peak at 40-50 Hz in the waterfall graph, it would only be able to correct the frequency response as far as I know. 

Yes and no.

If you have a play about with the EQ in REW for one of your measurements you'll be able to compare before/after waterfall plots to give you an idea.

EQ will improve the waterfall plot dramatically in that the decaying signal from a resonance peak will now take much less time to drop to the noise floor.

The actual reverberation time (RT60) I think does not improve but the change relative to the other signals is still significant. (The RT60 is how long it takes the amplitude to drop by 60 dB, so following EQ this is 60 dB down from a lower amplitude reference).

16 hours ago, rdale said:

Yes, I've been reading about the miniDSP 2x4 HD capabilities and it sounds very powerful. The interesting question to me is whether or not it makes more sense to spend 700 pounds on a standmount speaker + 1300 pounds on subwoofers and miniDSP vs spending 2000 pounds on a pair of floorstanders.

Thinking back to this question I just thought that I'd add that I don't think it's a slam dunk that you'll like the results of the strategy you're thinking of, in particular by not applying a crossover to the main speakers. Have you given any thought to picking up a second hand sub to two that you could experiment with? That way if you weren't happy with the results you should be able to sell them on for little loss. That's what I'm doing with my current sub. 

For my own situation I think I'm getting there but I'm not quite at the point where I'll say I'm definitely sticking with a sub long term, and it is definitely extremely easy to make a complete mess of things with adding a sub and getting a result that is frankly poor. 

Edited by MartinC

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Super Dealer
Posted (edited)
8 hours ago, rdale said:

Yes I agree. But the miniDSP would not have been able to sort out the bass reverberation peak at 40-50 Hz in the waterfall graph, it would only be able to correct the frequency response as far as I know. But my 72 euros worth of acoustic foam bass traps have had an important and measurable effect at 45 Hz. So in contrast to what you say, it isn't that difficult to treat low bass passively. But I don't think it is one or the other, you need both room treatment and bass DSP to get the best bass sound.

What do you think causes the long reverberation , read around the subject , your bass ‘trap’ has had very little if any effect as your plots corroborate.

Keith

Edited by PuritéAudio

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34 minutes ago, PuritéAudio said:

What do you think causes the long reverberation , read around the subject , your bass ‘trap’ has had very little if any effect as your plots corroborate.

Keith

I think the reverberation at 45-50 Hz is caused by the hallway in the left corner of the room by the left speaker. To me the plots show a worthwhile improvement in flattening the reverberation peak between 45-50 Hz which is what I was hoping they might do. The extra bass traps have had virtually no effect on the in room frequency response though and I'm hoping the subwoofers + DSP might be able to flatten it.

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1 hour ago, MartinC said:

Yes and no.

If you have a play about with the EQ in REW for one of your measurements you'll be able to compare before/after waterfall plots to give you an idea.

EQ will improve the waterfall plot dramatically in that the decaying signal from a resonance peak will now take much less time to drop to the noise floor.

The actual reverberation time (RT60) I think does not improve but the change relative to the other signals is still significant. (The RT60 is how long it takes the amplitude to drop by 60 dB, so following EQ this is 60 dB down from a lower amplitude reference).

Thinking back to this question I just thought that I'd add that I don't think it's a slam dunk that you'll like the results of the strategy you're thinking of, in particular by not applying a crossover to the main speakers. Have you given any thought to picking up a second hand sub to two that you could experiment with? That way if you weren't happy with the results you should be able to sell them on for little loss. That's what I'm doing with my current sub. 

For my own situation I think I'm getting there but I'm not quite at the point where I'll say I'm definitely sticking with a sub long term, and it is definitely extremely easy to make a complete mess of things with adding a sub and getting a result that is frankly poor. 

There isn't much HiFi in Gran Canaria and so buying and selling second hand subwoofers isn't really possible. Any subwoofers I buy, I will keep. I'm mainly thinking of REL T0s or T5is as that is a conservative choice and would probably have better resale value than the lesser known sort that you recommended the other day. Richer Sounds were doing the REL T0 for 50 pounds off, and the T5i for 100 pounds off, and I was about to pull the trigger on two T5is and one T0, but the offer stopped the day before I tried to order and I just missed it.

I agree it is a bit of a concern that I could take a system that I am actually perfectly happy with, spend a lot of money and then make it worse. But playing with DSP room correction just sounds like a lot of fun, and I don't think I can resist having a play. On studio sound forums from discussions I've read, it seems to be a pretty normal thing to do, just not so common in HiFi circles.

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1 hour ago, rdale said:

There isn't much HiFi in Gran Canaria and so buying and selling second hand subwoofers isn't really possible. Any subwoofers I buy, I will keep. I'm mainly thinking of REL T0s or T5is as that is a conservative choice and would probably have better resale value than the lesser known sort that you recommended the other day.

I'm not going to check back but I suspect I suggested a BK XXLS400? If so, in the UK I'd actually say it is easier to resell these than REL subs, and with better retained value, specifically via AVForums (where they have a very good reputation). However, given where you live your own situation is obviously rather different!

1 hour ago, rdale said:

I agree it is a bit of a concern that I could take a system that I am actually perfectly happy with, spend a lot of money and then make it worse. But playing with DSP room correction just sounds like a lot of fun, and I don't think I can resist having a play. On studio sound forums from discussions I've read, it seems to be a pretty normal thing to do, just not so common in HiFi circles.

Don't get me wrong I'm very much in favour of the 2x4 HD and experimenting with bass frequency mode correction but for balance I'm keen to not present it as the quick and easy simple fix that it sometimes is. I'm also very conscious that what you have in mind is different to what would more commonly be done, which will likely make it more problematic.

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Posted (edited)

Just in case it's of interest, a different way for you to experiment with the sub plan without a big financial loss if it doesn't work out would be to get a pair of Arendal Sub 1s. They have a good reputation and have a 60 day 'buy and try' policy, although you would have to pay 149 Euros for return postage if you didn't want to keep them.

https://www.arendalsound.eu/products/1723-subwoofer-1

Just a different option to be aware of. Although I'm guessing the subs themselves are more expensive than you're prepared to pay.

Edited by MartinC

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2 hours ago, MartinC said:

Just in case it's of interest, a different way for you to experiment with the sub plan without a big financial loss if it doesn't work out would be to get a pair of Arendal Sub 1s. They have a good reputation and have a 60 day 'buy and try' policy, although you would have to pay 149 Euros for return postage if you didn't want to keep them.

https://www.arendalsound.eu/products/1723-subwoofer-1

Just a different option to be aware of. Although I'm guessing the subs themselves are more expensive than you're prepared to pay.

I can't say I've heard of those before. I think they are a bit too big and expensive. I have an old Mana rack to the side of my equipment stand and the right sub woofer really needs to be able to fit under that, otherwise I'll have to start rearranging everything. I'll probably get the miniDSP 2x4 HD and newer Tisbury preamp first. I've just noticed the Cranage Hall show is on at the end of June and I'll be in the UK then. Maybe there will be some subs there to listen to and discuss with the dealers.

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