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Post by MartinT on Jun 27, 2014 19:33:57 GMT
If you have a pair of large speakers, as I have, it's very easy to overload your listening room. Take a few frequency plots and you'll see how scary the bass lift can be in a real room, as opposed to an anechoic chamber. I think this is why large floorstanders are not generally popular in the UK, due to our smaller room dimensions and many dealers' reluctance to recommend anything other than stand-mounters. However, if you have ported speakers, there is something you can do to help tune the speakers to the room by the simple expedient of stuffing or partially stuffing the bass ports.
Celef were one of the first speaker manufacturers, I remember, to use resistive port stuffing (using drinking straws) to lower the absolute bass augmentation and widen the port's frequency band. So I bought some lambswool and experimented with different amounts of stuffing in one or both bass ports (there is a single mid port too, left untouched) at the rear of the speakers, just listening to the effect when playing music I know well. I have settled on one roll of about 17cm in length into each port. This exactly used one pack of Monacor damping material.
On my known bass heavy recordings (Jewel: Spirit, Sarah McLaghlan: Afterglow, Kraftwerk: Minimum/Maximum) the effect is remarkable. The bass is still there, sounding even deeper due to the lack of pressurising of the room into one-note tendency, while the midrange comes through in even greater detail than before. The overall effect is to clean up the sound tremendously without apparently losing anything, although first impressions are that it sounds bass lighter. In fact, there is less overhang and the bass just sounds faster.
Showing plots before and after port stuffing. Although the reduction of the 40Hz peak doesn't look that much, the sound tells a different story.
I can hear quite clearly that overall the open sound has improved significantly while deep bass is more tuneful and textured than before.
Showing the rear of an Usher Be-20 and the two large bass ports.
My recent experiments with RDC cones under my preamp and power amp have yielded further tightening and apparent lightening of the bass. I may remove just a small amount of the stuffing to compensate, which is a very handy adjustment to be able to make. |
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Post by MikeMusic on Jun 28, 2014 14:43:53 GMT
Assuming you can get a few weight lifting mates around....
How about supports (!) under the Ushers ?
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Post by MartinT on Jun 28, 2014 17:40:59 GMT
They have a plinth with their own adjustable cones going through the carpet into the concrete.
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Post by pinkie on Jun 28, 2014 17:48:00 GMT
Its a sound idea Martin. The Kef R900's I tried recently ship with foam bungs for the ports, and my precious Ventricals also shipped with 2 guages of cavity bung for the rear port (a quarter wave Helmholtz loading on the Ventricals). You can further fine tune by using a lighter foam. Personally I fell that the room is the trickiest, and most often neglected component in any HiFi (and have been slapped down before for suggesting it) so its refreshing to see someone else pointing it out. I have recently had a big "relearning" of the room effect with the Lowthers, and I know Gordon had similar issues with his German speakers (we are both ESL boys at heart, where the speaker positioning ideal is a bit different from most moving coils, so may have been unusually slow on the uptake) Keep stuffing!  |
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Post by MartinT on Jun 28, 2014 18:25:10 GMT
I have a lot of room treatment in my room, which has dramatically reduced the slap echo, but it does next to nothing for the bass. Yes, I have tamed my Ushers in a rather pleasing way. Some more experimentation required, but I'm getting there  |
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Post by danielquinn on Jun 30, 2014 6:13:45 GMT
It would seem you have inadvertently discovered the "superiority" of sealed box's Martin  |
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Post by John on Jun 30, 2014 6:45:04 GMT
Its great when you can find cost effective ways to improve sound
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Post by MartinT on Jun 30, 2014 7:20:58 GMT
It would seem you have inadvertently discovered the "superiority" of sealed box's Martin Hah! There is actually air movement if I put my hands to either port, so they have become resistive ported, but it suits my room well. |
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Post by danielquinn on Jun 30, 2014 8:48:23 GMT
Romm for further improvement then !
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Post by MikeMusic on Jun 30, 2014 9:24:06 GMT
They have a plinth with their own adjustable cones going through the carpet into the concrete. That makes very good sense |
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Post by MikeMusic on Jun 30, 2014 9:27:12 GMT
Its great when you can find cost effective ways to improve sound Agreed 100% says Cheapskate no.1 |
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Post by walpurgis on Jul 13, 2014 9:51:56 GMT
Putting anything into a reflex port effectively makes it smaller, raising the port/system resonances with unpredictable results, but that's not to say it shouldn't be tried.
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Post by MartinT on Jul 13, 2014 22:13:18 GMT
Are you sure, Geoff? From what I've read, it widens and lowers the peak but, for values much less than fully resistive, does it change the centre frequency?
In any case, I like what it's done for my speakers in my room. Fully reversible, too, for when I move house.
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Post by walpurgis on Jul 13, 2014 23:17:48 GMT
Are you sure, Geoff? From what I've read, it widens and lowers the peak but, for values much less than fully resistive, does it change the centre frequency?In any case, I like what it's done for my speakers in my room. Fully reversible, too, for when I move house. Yes Martin, the laws of physics says it has to. However, with speakers with a well extended bottom end such as yours, I suspect the improved bass amplitude control will help, without any audible compromise. |
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Post by MartinT on Jul 14, 2014 5:24:39 GMT
Hmm, a thought experiment says that you're right. My plots hardly show any movement in centre frequency (actually, there is, from about 41Hz to about 44Hz), but my ears detect a significant improvement in bass response. Result!
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Post by RFGumby on Jul 15, 2014 16:58:40 GMT
Hmm, a thought experiment says that you're right. My plots hardly show any movement in centre frequency (actually, there is, from about 41Hz to about 44Hz), but my ears detect a significant improvement in bass response. Result! Ahh, the old sock trick! There might be an amplitude change at or around the port frequency, which would tend to show a broader flatter band of output around the port, but it shouldn't change center frequency. It's more like a variably controlled acoustic suspension. Aside from the obvious effective alteration of the port size, which in conjunction with the cabinet volume might make that 3 Hertz shift. So, acoustically, not electrically. |
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Post by MartinT on Jul 15, 2014 17:04:19 GMT
Indeed, if you look at my graph in the first post, there is a small movement in frequency. What amazes me is how much better it sounds, far more than the plots would suggest.
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Post by MartinT on Jul 21, 2014 18:49:20 GMT
On further listening, I am even more pleased with the effect of bringing the Usher's performance down to the limiting size of my room. Changes elsewhere (change of power cable, further use of RDC support cones) have tightened up the bass even further to give an overall effect of massively restrained potency. The great thing is, there is all that additional power to unleash should/when I move to a larger listening room. For now, I have a sound very close to ideal where the room is minimally loaded up even when generating some serious SPLs. |
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Post by MikeMusic on Jul 22, 2014 8:13:43 GMT
For a check on room size why not sling them in the boot and bring them round to my place for a quick listen |
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sb6
Rank: Starter
Posts: 2 
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Post by sb6 on Aug 3, 2014 20:26:32 GMT
I can hear quite clearly that overall the open sound has improved significantly while deep bass is more tuneful and textured than before.
Showing the rear of an Usher Be-20 and the two large bass ports.
Hi all, new member to this forum. I think it's great that by loading the ports you are achieving a more linear low freq. response and most of all, better bass. However, I think what's really hurting you is a speaker-room boundary condition. I also have the BE-20s and they really need to be significantly further away from the front wall. You would get better imaging, a fuller wider sound stage and much less bass bloat. Even 6" would make a big improvement I'd wager.
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