Tannoy Edinburgh 3149 become Tannoy Edinburgh Monitor Gold 12 !!!

[Fatmarley]

I took a measurement with the mic literally 1mm from the dust cap, expecting to see a deep notch in the response like the graphs in @Fatmarley's post #24, but there's nothing apart from a tiny dip at 46Hz.

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?

FYI - No smoothing has been applied to either measurement.

Starting to think that maybe the Bose 301 measurements are right. If you look at the Stereophile B&W 802D port measurements, they look similar. You just seem to have a lot of output around 1khz and down. Not sure why there's a double dip in the near-field woofer response though.

As for the Tannoys, It's not a conventional port, so I'm not completely surprised by the result (I didn't know what to expect tbh). I don't know why there's not a descent notch in the woofer measurement. Maybe it's because it's a DC driver?

I've built three ported speakers so far, and always got a clean notch at the tuning frequency when measuring the woofer near-field.

 

[ToTo Man]

I’m only partially understanding this thread and what you are trying to achieve, but surely taking separate/independent close-mic measurements of the cone (front-wave) and the port (backwave) will miss or dramatically negate any phase-cancellation that will happen in reality when you are listening to the whole. The key is how the port interacts with the direct sound.

Post #25 and onwards relates to another thread where it was suggested that installing a woofer in an enclosure that's ported at too low a frequency for the driver's T/S parameters will cause a shelf in the bass response before it peaks back up again at Fb. I was wondering if this might be what happening with my MG12(HE)-equipped Edinburghs, but I do not know what frequency the Edinburgh's distributed port system is tuned to (the literature doesn't say). Fatmarley suggested I could determine Fb by taking a frequency sweep very close to the driver's dustcap and looking for a notch in the bass response, the notch revealing the Fb of the enclosure. That was the plan anyway.

 

[ToTo Man]

Starting to think that maybe the Bose 301 measurements are right. If you look at the Stereophile B&W 802D port measurements, they look similar. You just seem to have a lot of output around 1khz and down. Not sure why there's a double dip in the near-field woofer response though.

As for the Tannoys, It's not a conventional port, so I'm not completely surprised by the result (I didn't know what to expect tbh). I don't know why there's not a descent notch in the woofer measurement. Maybe it's because it's a DC driver?

I've built three ported speakers so far, and always got a clean notch at the tuning frequency when measuring the woofer near-field.

The excessive mid and high frequencies from the Bose's port measurement are perhaps caused by the tweeter cones that are positioned/angled near the port and thus being captured by the mic?

 

[Fatmarley]

The excessive mid and high frequencies from the Bose's port measurement are perhaps caused by the tweeter cones that are positioned/angled near the port and thus being captured by the mic?

Oh yes, could well be. When I take my measurements, I usually do it with the raw driver. No crossover or tweeter connected.

 

[Tony L]

I was wondering if this might be what happening with my MG12(HE)-equipped Edinburghs, but I do not know what frequency the Edinburgh's distributed port system is tuned to (the literature doesn't say). Fatmarley suggested I could determine Fb by taking a frequency sweep very close to the driver's dustcap and looking for a notch in the bass response, the notch revealing the Fb of the enclosure.

I don’t have any math or design knowledge to back it up, but to my ears once you move away from traditional tuned port tubes to large slots, aperiodic loading like the Lockwoods, things like big Onkens etc etc different rules seem to apply.

As most here know by now I tend not to like ‘ported’ cabs much at all, i.e. the sort of cab that has a hole with a tube stuffed up it that is (to my ears) aggressively tuned to a note with the aim of bass reinforcement. They just tend to sound hollow, chuffing and boomy and I try to avoid them. I’m sure the classic big Tannoys tend to work in a different way where it is more a ‘vent’ to lose excess pressure from within the cab rather than to generate any additional bass. I’m certain this is how the Lockwoods work anyhow, i.e. the thick felt is to lose mid-band information before it gets to the lower part of the cab which has a huge hole to remove internal pressure, but isn’t there to add bass. As such they sound agile and just don’t have that ‘hollow’ or ‘thuddy’ character. I’ve felt the same when I’ve heard Canturburys which have the long variable slot vents similar to your Edinburghs.

It is a different thing somehow, maybe conceptually as much in common with an open back guitar amp than a highly tuned modern ported hi-fi speaker. Another way to articulate it is that with even a really, really nice ported speaker like a ProAc, MEG or whatever you can take a bass guitar or synth and play a bass run and find the port frequency, whereas you can’t with a very gently vented big Tannoy.

 

[darkmatter]

@Fatmarley

Could you tell me what simulation programme was used here? Looks interesting as it can take account of room gain?

Thanks

DM

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

 

[Fatmarley]

@Fatmarley

Could you tell me what simulation programme was used here? Looks interesting as it can take account of room gain?

Thanks

DM

Here you go - http://audio.claub.net/software/jbabgy/WBCD.html

 

[darkmatter]

@Fatmarley

Splendid!
Thanks
DM