For the benefit of @Fatmarley, the following graph compares the response of the my MG12 drivers in free space (i.e. not mounted in any baffle or enclosure) and the response when installed in the Edinburgh enclosures, both measured from 1 metre. I have averaged the left & right drivers in both measurements to remove some variance. These measurements were taken in 2017/2018. Comments welcome .
Is that with respect to the nearfield measurement in post #25 or the listening position measurement in post #1?Are you sure the problem isn't 70hz to 200hz?
Is that with respect to the nearfield measurement in post #25 or the listening position measurement in post #1?
I know that measuring from 1 metre helps to reduce room effects, but by how much? i.e. I'm wonder if the elevated response at 70Hz is due to the speaker's position in the room (as you can see from post #1 they're very near the corners of the room), so perhaps that's corrupting the nearfield measurement below 100Hz?
I don't know exactly what the port tuning of the Edinburgh enclosure is as it's a distributed port system with narrow 'slots' rather than a conventional round port (the gothic-style detailing down each side of the cabinet are the ports). Altering the port tuning is therefore very difficult.
If you fancy some light reading I've uploaded some literature on the Edinburgh's design here, perhaps you can make more sense of it than I?
The Edinburgh was originally fitted with Tannoy "3149" 12-inch hard-edged drivers, which have an Fs=38Hz when new. One of the reasons I removed the 3149 drivers is the Fs rises significantly with age and when I last measured my Edinburghs with 3149 drivers installed the bass started rolling off at 125Hz! More importantly though I preferred the sound of the mid and high frequencies of the MG12 over the 3149, it was more phase coherent to my ears.
The hard-edged MG12 has an Fs=49Hz when new, though again this apparently rises with age. I haven't measured the Fs of mine, but I'm assuming it hasn't risen by as much as the 3149, given I'm still getting strong bass output from it down to 40Hz in the Edinburgh enclosure.
I have a pair of rubber-surround MG12 drivers in the cupboard still waiting to be installed somewhere. I wonder if these may fare better in the Edinburgh enclosure given they have a much lower Fs=27Hz? I can see a busy summer ahead of me!...
Is there a smallish panel on the enclosure or something that you can remove to reveal a hole? Thinking off the top of my head - blocking ports will lower the tuning frequency, so you need to add them. They don't actually have to be a tube or tunnel, just an opening would do.
Continuing on from what I was saying on the other thread. I've uploaded some graphs to try to explain what I was talking about:
This first graph is the ideal enclosure size and tuning for a flat response with this driver (56ltr). Imagine we design a crossover to work with this tuning and that's going to be our crossover for the next examples I upload. In other words everything from 200hz and up, stays at the same level because the tuning doesn't affect the driver output, only the port output.
Next we increase the enclosure volume to 100ltr and also keep the port the same diameter and length.
The lowest of low midrange, midbass/bass is now down in level compared to the rest of the frequency range. The crossover needs to be adjusted to bring the midrange (200hz and up) down to be inline with the bass from the port (or maybe corner loading would work?)
Next graph is the same but with a higher tuning to fill in that missing bass/midbass (what I was suggesting you try as a quick experiment)
Midbass is now fine, but we have a peak at the tuning frequency that's going to annoy on the odd track. Some will put this down to room, or just how ports sound, or the recording etc. You can stuff the hell out of the enclosure to reduce the peak (make sure there is a clear pathway for air to move through the port), Or you reduce the volume to 56ltr like in the first graph.
It may be possible to make the second graph sound OK with corner loading but it's not something I've ever looked in to.
You can go even smaller than 56ltr and tune higher. That is exactly what I did with the Deltalite 2510 (42ltr) because I wanted to hear what it sounded like when you took a large driver and tuned it like small standmounts are often tuned. It gave incredibly tight, fast bass that you could feel but obviously lacked a bit of depth. Thought they were fantastic fun but I have a speaker building addiction and no room for storage, so they had to go
Yes, funnily enough when I installed the MG12 drivers I removed the Edinburgh's binding posts backplate so I could feed the MG12 cable out to its crossover externally. The rectangular cutout, 125mm x 65mm x 19mm, is currently covered over with a piece of thin plywood I blu-tacked on, leaving just a small hole for the cable. I did run FR sweeps before and after covering the hole and observed no change in the bass response (though I probably wasn't looking at frequencies above 100Hz at the time in these tests). I wonder if this is because there's also internal foam damping covering the cutout, which is preventing or at least impeding the airflow?
I see what you mean about the dipped upper bass response, but from the graphs you posted I'd expect this to be inaudible above 150Hz or so?
Reducing the Edinburgh's internal volume from ~200L to ~60L would take some doing! I'd probably be better off just putting the MG12s in smaller cabs? Given that I have stereo subwoofers, I could probably even forego the added complication of ports and just go with sealed cabs? They would take up less space and should make subwoofer integration easier too.
I assume making the 200L Edinburgh enclosure a sealed design wouldn't increase the lower midrange output anyway, it would simply provide a smooth 12dB/oct roll-off and push the -3dB point quite high up?
I'd be interested to see the Fs=27Hz (rubber surround) MG12 modelled in a 200L distributed port enclosure. I don't suppose either you or @cooky1257 could give me an idea of the bass curve I might expect to see?
Regarding your comment on tuning the crossover to account for different baffle step and enclosure volumes, all of the graphs I've posted on this thread are pre-EQ. I do tweak all of my speakers with EQ to provide my desired response at the listening seat. Rather peculiarly though, the 100Hz-400Hz recession shown in the first graph in post #1, suggests it's down by 4dB or 5dB from where it should be. Yet when I apply EQ to this area, I find that boosting it by more than 1.5dB or 2dB just sounds plain wrong, so I do think that particular graph is somewhat misleading, either that or I have been conditioned over time to prefer a leaner balance in this area!...
Thanks, I'll try that with the rear plate blocked and open and see what the difference is.Forgot to say - To find out the port tuning frequency, put your microphone about 5mm away from the centre of the woofer and run a sweep. The notch in the frequency response is the tuning frequency.
I then tried taking a measurement with the mic against one of the enclosure's side vents. This time I expected to see a response peak, but there's no peak, only a notch. What does this mean?