Printable View
When modifying and reducing port size for a 825 or 828 A7 enclosure, are we also reducing the speaker's overall efficiency?
If so, about how much, stock opening versus different final openings ( 100 inches, 75 inches, etc. ) ??
Thanks, in advance.
Jeff Medwin....Low Ohms
I'm sure it does make them less efficient. But who cares about all the pesky numbers if it sounds good?:D
Its simple Hoffman's iron law. Trading efficiency for deep bass
Quote:
Originally Posted by Elitopus1
- - - - - - - - - - - - - -
I'd like to know " How much less efficient??"
- - - - - - - - - - - - - - - - - - - - - - - -
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
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
E1,
Thanks.
"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."
Thats what I would like to do, once I am ready to experiment. ( After I build my JJ 2A3-40 Mono amps ).
Jeff
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
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 diyaudioQuote:
Originally Posted by LowOhms
Quote:
Originally Posted by horndawg
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
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.
Altec A7 Voice Of Theatre Speakers
Quote:
Originally Posted by horndawg
Thanks, others will look to see that Pete Riggle A7 Web posting. I was already familiar with it.
Pete Riggle is a very capable and cool guy, as is his Seattle audio group. Look at that wood arm he offers, and his lovely VTAF !!
However, IMHO, what they would do with an A7, versus what I would do, are quite a bit different from each other. So, his results, and conclusions, which I do not doubt for a moment, will not necessarily be a model for my implementation, nor resemble my results.
Pete ( and his group we read about on the WWW ) will use a FIVE-stage McIntosh tube amp, ( with three cap couples ) or in Pete's case, his preferred-sounding 15 Watt Heathkit Push Pull amp, to power the ALTECS. He will use some sorta vintage wiring to connect-to and internally wire the A7s.
My wiring is very different, I am shooting for the absolute best wideband transfer function, to allow the use a 3 Watt amp easily, and with better dynamic contrasting - than any other combination.
High goals to shoot for.
I use a TWO STAGE, direct coupled ( no capacitor coupling ) triode Single Ended power amp. It uses a "fast ", low DCR power supply, and careful attention was paid to wiring in the ENTIRE chain, from the AC socket on the line cord, to the soldered connections on the driver's voice coil.
I use new technology capacitors, that only just a FEW people in audio have likely-yet-heard.
Some caps used ( both in the amp and crossover ) can do 1.500 Ampere instantaneous peak currents, so the " leading edge of the transient ", played-back information ( into the room)....... is very different from ANYONE else's in audio.
Additionally, I am multiple bypassing all-film cap positions with the latest-designed, most modern WIMA PULSE caps, to further enhance initial transient capability. Read up on WIMA's FKP1 series, and mentally grasp their state-of-the-art PULSE capabilities, on line. Better yet, HEAR them .
OK, so HOW did 'I" set up a A7 port size? Well, my goal is NOT to have the lowest bass, which is the realm of a 604/MLTL in a two-way system, IME, IMHO..
My goal on July 3rd and 4th, was to try to get the best sounding COMPROMISE port opening, for my system in my room, on familiar reference musical selections I hear.
Yes, I will LISTEN to drums and " bass shots " with the 515Bs, but I am also listening to how percussively-struck chords of a grand piano, in the bass registers, sounds to my ear, and how it is dynamically and spatially being displayed to me, at my seated position, in my room. I use " Uncle Stu's Pool Table Tweak " panels in my room, nine feet high by 18 inches.
It was WONDERFUL to be able to EASILY / QUICKLY move those Patio Stepping Stones, and change the 515B reflex port opening incrementally on MUSIC, and HEAR how it effected the presentation at the seated position .
I had never seriously tried to optimize the positioning of my newly corner-loaded 825s.
On July 3rd and 4th, I had the relaxed time to do this. My first move was 1 inch. My next move was 3/4s of one inch. My next move was 1/4 of an inch, and then, 1/16th of an inch. I listened to each move, with my reference music selections. I think I have to move my right-side 825 only about 1/32nd of an inch, to get it optimized and ( hopefully ) equal in performance to my left-side 825. NO RUSH to do that, will live with the system for a few days or a week, before doing so.
What a NEAT difference ( these less-than-an-inch 825 position-changes ) made in my overall enjoyment of the A7 system. In the 1980s, when I adjusted the big Fulton Premiers into a listening room, the same precision placement of the enclosures, was required, to optimize playback performance. I was HAPPY to be able to hear this in 2017, and be able to get it better into the room.
Perhaps these placement comments will spur some Forum people to try to self-optimize their A7s, A5s, etc., etc into the room. Be sure to measure carefully and record it, each iteration, so you don't get lost or confused !! You can do it !! Have fun, I do.
Low Ohms.....Jeff Medwin.