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Old 5th July 2008, 02:12 PM   #1
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Default Rear port and front port

Hi, I thought this might be of interest. I decided to convert my old eltax floorstanders to something a bit nicer. I replaced the drivers with good quality JMP's and fitted a Kef 3 way crossover. Much better, but because they are rear ported cabinets and are fairly close to the walls I decided I would change them to front ports.
The rear ports are at the top behind the tweeters? OK, I drilled a big hole in the bottom front and put in plastic port fittings from the JPM boxes. Out of interest I thought I would try the one I had modified before I blanked off the rear port. It sounded great. I tied a book to the rear port, and gues what? It wasn't as good. After several lash ups, I now have speakers with a rear port at the top and a front port at the bottom, with what seems to me as superior sounding boxes. No booming or resonance at any volume. I'm driving them with a Quad 33/303 set up with Meridian MCD and Nakamich MR-1 casette player. I wonder if anyone else has tried twin ports like this. I would be interested inany comments, for or against. Thanks for reading. Good listening. Barry
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Old 23rd February 2009, 11:39 PM   #2
robmc52 is offline robmc52  United Kingdom
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Hi Barry
I came across your post after searching the forum for threads on Eltax speakers. Interesting that I've (accidently) discovered how to improve the sound of my "Eltax" floorstanders by leaving the terminal plates hanging out of the boxes, thus ending up with two bass ports The speakers themselves are cheap Richersounds jobbies that I bought about ten years ago. I think they are badge engineered rubbish that RS's seem to sell a lot of nowadays, similar to the TDL's that are advertised by the bucket load on ebay. I thought I'd try modifiying them just for the hell of it, they didn't sound horrible to be honest but the base output was poor and the treble muffled, so the first thing I tried was making two separate boxes to house the tweeters which were originally in the front baffle between the two mid/base drivers. The tweeters now sit in rectangular boxes atop the main cabinets with small spikes keeping them apart. I forgot to replace the round terminal plates when I stood them back in the corners where they normally sit. The difference in the sound when I tried them out was quite something. There was so much more bass that at first I couldn't work out what had happened, it was only when I pushed the terminal plates back in and all the bass disappeared that the eureka! moment occured. I tried blanking off the original front port and discovered that it made no difference at all so I cut a 60mm hole in the back of each cab just underneath the terminal plates and now, with the front ports uncovered they are producing decent bass for the first time. The treble seems much improved as well, certainly clearer and better defined than before. I think I might try glueing some braces inside the cabs now, just because I can
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Old 24th February 2009, 08:36 AM   #3
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Hi Rob, that is most interesting as I thought no-one would ever reply to this stread. Interesting you mention the tweeters as part of my mod was to add a second tweeter. That made no improvement so I braced of the internal one with mdf inside the cabinet and bingo! more improvement. I'm now running them with a gainclone amp and linn sondek turntable and they zre greeeeeeeat. Barry
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Old 24th February 2009, 06:22 PM   #4
robmc52 is offline robmc52  United Kingdom
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I think some internal bracing will be very benificial for my speakers as they are made from 12mm chipboard by the look of it, what's the worst that can happen? Luckily I make fitted bedroom and office furniture which means there's a workshop full of MDF lying around. In fact, I'm sitting here now wondering why on earth I haven't thought of doing this before. As a matter of interest my cheap and cheerful system at the moment consists of Planar 3/ Nagaoka MP11 and Planet cd player feeding a Rotel RC980bx pre amp/ x2 RB971 power amps. Now I've realised how duff the speakers are I'm getting quite excited thinking about what else I can do with them.
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Old 25th February 2009, 08:53 AM   #5
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There is an inexplicable effect with ported enclosures I've observed.

A friend of mine has a system that uses a ported midbass minimonitor underpinned by a big woofer tower much like Wison watt-puppy combo. The mini monitor runs full rage with the woofer tower which just comes in underneath.

Blocking up the rear facing port on the top produces no audible tonal change to the system, but the soundstage shrinks markedly.

Could this be a polar respose related effect, or a backwave phenomenon? There is more than just bass coming from the average port. I've never come up with a satisfactory explanation!
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Old 25th February 2009, 05:00 PM   #6
robmc52 is offline robmc52  United Kingdom
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Hi Simon
Thats an interesting point re. the sound stage effect, I hadn't given any thought as to whether that had changed, I'm still recovering from novelty of listening to deep bass! I'm going to try stuffing some cardboard tubing into the holes I've drilled and then vary the length of them to see what difference it makes. It's like rocket science isn't it?
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Old 25th February 2009, 05:05 PM   #7
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Well Rob, whatever works for you.. lol
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Old 26th February 2009, 01:00 PM   #8
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I havn't found any noticable difference in the soundstage, but maybe there is a little which is compensated by a better stereo image. I did find that the front port was improved by fitting a proper port with a sleeve. It improved the bass end even more. I tried to upload a picture but it was too big. Barry
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Old 26th February 2009, 11:26 PM   #9
Pano is offline Pano  United States
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You might want to look at my sims in the Onken thread.

http://www.diyaudio.com/forums/showt...76#post1753776

Front low vs. Rear high port.
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Old 27th February 2009, 09:28 AM   #10
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Thank you Panomaniac. Now that is a very interesting thread. I will have to take my time over it. I'm also interested in the Onkyo design, so will have a delve there also. I like to add that although my cabinets a big they are on stands, so the ports are nowhere near the floor. It was suggested in the thread that there is or maybe some relationship between low ports and the floor. This must have been a very time consuming project for you to present these simms. Well done, I have nothing but admiration for such work. Have a pint on me!! Barry
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