When I changed the port size on my 828's, I was powering them with a little 6bq5 amp. I didn't notice any change in the balance between the LF and HF drivers.
Maybe someone has made the change and measured it before and after.
I built a new board for the front of my cabs with the smaller port. That way I can go back to stock if I ever wanted to
Reduced the A7 port size from stock to 75 square inches, prefer the smaller port as it seems to produce a tighter, more focused bass. As far as efficiency, did not perceive any change.
The XO has gone through extensive upgrades since the port was reduced; wonder what they would sound like reverting to the stock port? Look into it when I have more time.
Cheers
For good reason E1, my audio world is low-powered tube amplification, typically about 3 Watts, direct coupled SET..
I have GONE to Altec speakers, high efficiency, specifically so I can use such amps, which I typically DIY build. I have shown you some photos.
I always have considered amplifiers, and not speakers, as being the weakest link in the audio playback chain.
Thanks in advance.
Jeff Medwin .... Low Ohms
Output reduction in going from 182 in^2 to 78 in^2 occurs basically bellow 100 Hz, where the room dominates and so in practical terms efficiency is not affected. The attached sim assumes a 13 cu. ft. box and the port sizes are 7"x26" and 3"x26". Driver is the GPA 515-16C Alnico and the T/S parameters used are from measurements taken and posted by Gary Dahl over at diyaudio
Output reduction in going from 182 in^2 to 78 in^2 occurs basically bellow 100 Hz, where the room dominates and so in practical terms efficiency is not affected. The attached sim assumes a 13 cu. ft. box and the port sizes are 7"x26" and 3"x26". Driver is the GPA 515-16C Alnico and the T/S parameters used are from measurements taken and posted by Gary Dahl over at diyaudio
Thanks so much !!
Over July 3rd and 4th, after living with stock reflex ports for two full years, I FINALLY took the time to reduce my stock 825 ports and give a listen.
Very interesting to hear !!
I used two regular 12 by 12 inch Patio Stepping stone 16 pound concrete bricks, each placed vertically against the front of the 825 and resting on top of a regular building brick ( to get needed height). This nicely blocks off any part of the stock 825 Bass reflex port.
So, I got a chance to critically evaluate what opening sounds best to me, into MY room, while playing music.
At this moment, subject to change and future re-evaluation, I am at about 75 square inches of open port.
The concrete stepping stones have a 45 degree bevel, about 5/16ths wide, on one side, and THAT is the side I placed against the box, to avoid a sharp 90 degree corner at the port's transition.
I LIKE using the concrete stepping stones use, to block the ports as its
(a) inexpensive ,
(b) EASY to make adjustments and
(c) NON invasive as far as keeping the 825 stock.
Heartily recommended to HEAR the effects of port size in one's room, and to one's ears.!
LOW OHMS....Jeff Medwin
Last edited by LowOhms; July 5th, 2017 at 12:15 PM.
Glad you were able to experiment and found the port area that best suits your system / room. The following link contains in part a write-up by Pete Riggle on his A7-500 experiments with port area. I found the entire article an interesting read. For the port size experiments, scroll down to about the middle of the page.
Originally Posted by Elitopus1
I'm sure it does make them less efficient. But who cares about all the pesky numbers if it sounds good?
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