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#1
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Relocating Speaker Ports
Hi Friends,
I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? Assuming I use the same size and length port, any major downside, soundwise, to doing this? Regards, Joe |
#2
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Joe Kramer wrote:
I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? It won't sound exactly the same, because at some frequencies there will be significant sound coming from both the cone and the port, and moving the port to the front alters their relative timing (the rear port has extra delay due to the distance 'twixt front and back) so they will have a different phase relationship. -- Anahata -+- http://www.treewind.co.uk Home: 01638 720444 Mob: 07976 263827 |
#3
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anahata wrote:
Joe Kramer wrote: I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? It won't sound exactly the same, because at some frequencies there will be significant sound coming from both the cone and the port, and moving the port to the front alters their relative timing (the rear port has extra delay due to the distance 'twixt front and back) so they will have a different phase relationship. Thanks for your reply. I won't have a problem with them if they sound different; I will have a problem if they sound bad though. As far as the phase relationship goes, there are plenty of speakers similar to PBM-8s out there but with front-firing ports. Is the design of those speakers (in general) really all that different, aside from the port location? Regards, Joe |
#4
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Joe Kramer wrote:
Thanks for your reply. I won't have a problem with them if they sound different; I will have a problem if they sound bad though. The Tannoys would have been designed with that delay included in the calculations for flattest forward frequency response. If you move the port and keep everything else the same, I doubt if the frequency response will be so flat. Just how bad that will be, I really don't know. Maybe not very different. Given I think you said you're in a small room and putting the speakers with their back to the wall, that's not the optimum position unless they are designed to be mounted that way, and with rear ports they probably aren't. Your room is probably having more effect on the overall response than which way the ports are facing. As far as the phase relationship goes, there are plenty of speakers similar to PBM-8s out there but with front-firing ports. Is the design of those speakers (in general) really all that different If there's any truth in my theory, then yes - the optimum tuning for the port will be different. You'd have to do the whole calculations (driver Thiele-Small parameters, box volume etc.) to work out the best reponse and that still might not be as good - I suspect that a rear-firing port enables more extended bass than forward-firing for a given box size but don't ask me for mathematical proof! -- Anahata -+- http://www.treewind.co.uk Home: 01638 720444 Mob: 07976 263827 |
#5
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On Thu, 24 Mar 2005 22:50:01 +0000, anahata
wrote: If there's any truth in my theory, then yes - the optimum tuning for the port will be different. You'd have to do the whole calculations (driver Thiele-Small parameters, box volume etc.) to work out the best reponse and that still might not be as good - I suspect that a rear-firing port enables more extended bass than forward-firing for a given box size but don't ask me for mathematical proof! I doubt it will make any difference as there's no parameter for port location in any of those models. Kal |
#6
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It seems to me there is some rule of thumb on port placement that says
it should be 2 to 3 times its diameter away from any obstacle, like a wall or brace. It would seem that there is not much room on the front available that would meet this criteria. Maybe on a side, if the port is not too long... As to phase and delay issues, I think if you look at the length of bass waveforms, its placement should be a fairly minor impact. Then again, I'm not sure I'd want to cut up my monitors... --Peter Joe Kramer wrote: Hi Friends, I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? Assuming I use the same size and length port, any major downside, soundwise, to doing this? Regards, Joe |
#7
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#8
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"Peter Sylvester" wrote in message
... As to phase and delay issues, I think if you look at the length of bass waveforms, its placement should be a fairly minor impact. Only the lowest frequencies are produced at any volume through the ports in the first place, so I agree that phase issues would minor at least, possibly not even measureable. Frequencies that are coming through both the ports and the woofer may not be masked as much coing from the rear, but I would expect would be closer to being in phase if the port was moved to the front. I think there would be audible differences between the two placements, but whether it was better or worse would be subjective. Then again, I'm not sure I'd want to cut up my monitors... It would make more sense to replace the Tannoys for something that fit the location better. Sean |
#9
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On 3/24/05 2:51 PM, in article
et, "Joe Kramer" wrote: Hi Friends, I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? Assuming I use the same size and length port, any major downside, soundwise, to doing this? Regards, Joe As Mike said, Getting them away from the wall is good. There IS the option of stuffing the port with foam or cloth. It WILL change the lo end but a simple broad lo end tone control boost might compensate. |
#11
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Mike Rivers wrote: writes: As far as the phase relationship goes, there are plenty of speakers similar to PBM-8s out there but with front-firing ports. Is the design of those speakers (in general) really all that different, aside from the port location? Have you looked inside the box to see how the port is constructed? (I haven't) Typically, a port in a small speaker isn't just a hole in the panel, there's a tube that projects into the box and establishes the proper phase of the port signal (at least within the frequency range of interest). When moving the port to the front, if you also moved the tube, I'd think that it would work pretty much the same other than you didn't have the delay of the port sound associated with the depth of the cabinet. You could certainly try it. The worst that could happen is that it sounds worse and looks ugly when you put it back the way it was. -- I'm really Mike Rivers ) The smaller the box the more critical the size _and length_ of the port is to the low end response. Change this and your bottom will go away. If you can duplicate the size and length of the port when you relocate it, you should be OK. good luck rd |
#12
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In article ,
"Sean Conolly" wrote: "Peter Sylvester" wrote in message ... As to phase and delay issues, I think if you look at the length of bass waveforms, its placement should be a fairly minor impact. Only the lowest frequencies are produced at any volume through the ports in the first place, so I agree that phase issues would minor at least, possibly not even measureable. Frequencies that are coming through both the ports and the woofer may not be masked as much coing from the rear, but I would expect would be closer to being in phase if the port was moved to the front. I think there would be audible differences between the two placements, but whether it was better or worse would be subjective. There are reasons some monitors are only ported to the rear, of which the manufacturer has already thought out. IMO It's not a very good idea. In a high-end 2way speaker system, the midbass driver is regularly crossed over as high as 3k. Changing the port location *may* make a difference as there is sound resonating from the port after all. As far as phase, once again changing port location *may* make a difference. Without knowing the exact specifications of the drivers much less the xo, of which the manufacturer will probably not disclose, who's to say what can happen. And on top of all this, the OP may or may not even notice a difference if he changes it so all this would be moot. Then again, I'm not sure I'd want to cut up my monitors... It would make more sense to replace the Tannoys for something that fit the location better. Sean hth, -- Cyrus *coughcasaucedoprodigynetcough* |
#13
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et, "Joe Kramer"
I have a pair of Tannoy PBM-8s which are right up against the wall because of the size of my room. Can I improve on this situation somewhat by moving the rear-firing ports to the front on the cabinets? Assuming I use the same size and length port, any major downside, soundwise, to doing this? Blocking the ports is the LEAST of your worries with the speaker stuffed up there. Don't you notice the low end is kind of... well... flabby? --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#14
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Hi All,
Thanks for all the thoughtful replies. Scott Dorsey wrote: Blocking the ports is the LEAST of your worries with the speaker stuffed up there. Don't you notice the low end is kind of... well... flabby? --scott I suppose I'd notice the low end was flabby if I had much opportunity to hear other other rooms with my speakers, or other speakers in my room. As it is, I don't. In this very subjective situation, the bass I'm getting isn't too bad, but yes, maybe a little reserved dynamically. I've already rebuilt the crossover with better parts and filled the box with polyfill, both of which moves were marked improvements. The only stock part now is the rather cheap and flabby woofer, which I also intend to replace some day. There are some 4" thick foam panels on the wall behind the speakers, and if as Mike says, the ports being blocked might be a good thing considering the small size of my room, this foam is probably helping filter some low end that would otherwise be an even bigger problem. You've all helped me come to the conclusion that I better put away the hole saw for now. Instead I'll spring for some better woofers and see how that works out. Thanks again for all your help. Regards, Joe |
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