tag:blogger.com,1999:blog-8689487740107692135.post7432505445792424682..comments2024-01-15T04:39:32.375-08:00Comments on Red Spade Audio: Do small foam traps actually work?Paul Spencerhttp://www.blogger.com/profile/07514836858344391753noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-8689487740107692135.post-66310761320004684962011-08-29T00:39:47.072-07:002011-08-29T00:39:47.072-07:00I suggest calculating the RT60 from the impulse re...I suggest calculating the RT60 from the impulse responses you measured. Surely, increasing the decay rate of individual modes is important. But by using broadband absorptive devices you also increase th effective absorption coefficient, thus lower the RT60 above the 200Hz limit of your plots.<br />Referring to Toole's latest book; their is a lower limit of RT60 below which the listener envelopment and apparent source width decrease and adversely affect the subjective quality of reproduction.svenrnoreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-19298196121340627192011-08-29T00:29:23.726-07:002011-08-29T00:29:23.726-07:00I use REW which by default also includes reverb ti...I use REW which by default also includes reverb time, but it's not something that I pay a lot of attention to. I'm more interested in the decay plots because they show how well modal ringing has been damped. In some of my more recent measurements, the in-room waterfall plots start to look like nearfield measurements.Paul Spencerhttps://www.blogger.com/profile/07514836858344391753noreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-49792656273783908552011-08-29T00:21:22.117-07:002011-08-29T00:21:22.117-07:00When comparing the effects with / without the corn...When comparing the effects with / without the corner foam traps, did you also measure the reverberation time over the entire bandwidth?svenrnoreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-58211570764654812512011-08-28T06:36:49.121-07:002011-08-28T06:36:49.121-07:00This one was take later:
http://redspade-audio.blo...This one was take later:<br />http://redspade-audio.blogspot.com/2011/04/bass-measurement-update.html<br /><br />However there are more recent measurements that I had a look at when considering adding membrane traps. These aren't on the blog, but they suggest no real benefit.Paul Spencerhttps://www.blogger.com/profile/07514836858344391753noreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-6796680998120971012011-08-28T06:20:34.078-07:002011-08-28T06:20:34.078-07:00I may not have seen the measurements you meant. Wh...I may not have seen the measurements you meant. What's the name of the entry?svenrnoreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-74382215162218480002011-08-28T04:22:57.817-07:002011-08-28T04:22:57.817-07:00svenr, I can't agree with any of your points. ...svenr, I can't agree with any of your points. <br /><br />The traps have excellent measured performance and are effective down to 25 Hz; more recent versions have very little room for improvement. <br /><br />That some absorbers are narrow band is certainly not a desirable feature. Their strong point is their low profile. Their narrow bandwidth means that more of them are required to cover a wider bandwidth. Typical rooms already have pressure based absorbers built in.Paul Spencerhttps://www.blogger.com/profile/07514836858344391753noreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-52506459542569324212011-08-28T01:46:49.814-07:002011-08-28T01:46:49.814-07:00A saw the measurements. The large foam traps did s...A saw the measurements. The large foam traps did something - but not what one actually wants. You achieved absorption above 120 Hz over the entire bandwidth, but none at low frequencies. So your reverberation time curve simply shifted down in time with an even more pronounced exaggeration at low frequencies. I'm sure you heard significant differences, but you didn't get a better controlled reverberation time.<br /><br />Absorption at low frequencies needs to act frequency selective. Foam, due to its broadband absorption, is not suitable for that. Feasible solutions include plate absorbers, Helmholtz absorbers or stud walls of very low flexural rigidity backed by absorptive material.svenrnoreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-10922912922488964752011-08-26T00:16:51.241-07:002011-08-26T00:16:51.241-07:00Hi Svenr,
I have used foam traps and shown meausu...Hi Svenr,<br /><br />I have used foam traps and shown meausurements elsewhere on my blog. The small ones fail due to their size. Large foam traps can be very effective.Paul Spencerhttps://www.blogger.com/profile/07514836858344391753noreply@blogger.comtag:blogger.com,1999:blog-8689487740107692135.post-19352215595312420582011-08-26T00:08:26.129-07:002011-08-26T00:08:26.129-07:00Open cellular foam is characterised by its flow re...Open cellular foam is characterised by its flow resistivity, i.e. how much energy does the foam absorb by hindering the flow of air through it. This definition reveals that if the flow is zero, no energy absorption can occur. This placing foam near a reflective boundary where the particle velocity (i.e. the flow) is zero by definition will not result in any absorption.<br /><br />If foam is to be used for low frequency absorption, it needs to be placed at the room modes' nodal lines, not at the walls. That's why acoustic engineers never use foam for low frequency absorption.svenrnoreply@blogger.com