Getting Bass from TD15M in a 5.5 ft³ Cabinet

[skywave-rider]

DT, why are you measuring woofer nearfield at cone edge? Is it because this woofer has a phase plug? I would think you want the most pistonic measurement you can get for the nearfield, or at least an average between the 2. Wouldn't closer to the center be better> Does it matter?

 

[dumptruck]

Beats me, but I measured in the middle of the cone surface, i.e. between the phase plug and the surround, not the edge. From previous measurements [I think] I know that the entire cone works pretty much the same way until above ~500Hz.

 

[RayW]

You're right it does, but phase is as measured (exported min. phase), and now shown above (without delay added). :scratch2:

Is the phase actually measured or derived with a H-transform?

RayW,

Thanks for posting this, I'll try to measure mine that way to compare with DT's data.

You seem to be one of the real knowledgeable speaker guys around here,

Thanks. I kinda do this as a career.

what do you think of a vent located at the bottom of the cab, right at the floor boundary versus one of the same size located most anywhere else, does it really have higher output efficiency as I remember reading? And for the above measurement technique, is it valid for me to measure the vent located right next to the floor and would there be anything to modify in the calculation?

az

By putting the port right at the ground plane you extend the effective length by a bit but I wouldn't think it would be a drastic difference. I don't remember the correction factors for stuff like that, I'd have to look it up. As far as efficiency, I guess a case could be made for 2pi vs. 4pi space but with a 20' wavelength, unless you have a really tall speaker with the port at the top, you're going to be radiating into 2pi effectively.

Measuring might be a little funky because you'd be getting a pressure doubling with the mic at the floor. You would have to apply a correction factor like you do with ground plane measurements. I've never done something like that in the near field. When I do ground plane stuff I usually measure at 2m which cancels the gain from the pressure doubling and you end up with the same as a 1m measurement in free space but with less noise.

 

[audiozaz]

Thanks. I kinda do this as a career.

By putting the port right at the ground plane you extend the effective length by a bit but I wouldn't think it would be a drastic difference. I don't remember the correction factors for stuff like that, I'd have to look it up. As far as efficiency, I guess a case could be made for 2pi vs. 4pi space but with a 20' wavelength, unless you have a really tall speaker with the port at the top, you're going to be radiating into 2pi effectively.

Measuring might be a little funky because you'd be getting a pressure doubling with the mic at the floor. You would have to apply a correction factor like you do with ground plane measurements. I've never done something like that in the near field. When I do ground plane stuff I usually measure at 2m which cancels the gain from the pressure doubling and you end up with the same as a 1m measurement in free space but with less noise.

Thanks for the info. If I get pressure doubling that way, would it be pertinent to then go with 2*20*log(vent_csa/Sd) to get the appropriate offset? Alternatively, I could not be lazy and flip the 110lb monster on its head to have the port ~38" up from the floor.

az

 

[dumptruck]

Is the phase actually measured or derived with a H-transform?

, I am taking MLS impulse measurements, and I think how it works is the phase in generated from that, and the minimum phase is extracted when I click the checkbox (edit: confirmed, H-transform calculated from DFT, and min phase then extracted is supposedly accurate <12kHz). This is what's been working for me for crossover simulation, but phase measurement is something I'm continually struggling to understand these days. If this is not an appropriate method for what I'm trying to do here, you'll have to tell me.

AZ, you could also put it on its back on the floor pointing up, but your port is a slot at the very bottom of the cab, right? It probably acts longer there, so moving the cab would move the tuning.

 

[audiozaz]

AZ, you could also put it on its back on the floor pointing up, but your port is a slot at the very bottom of the cab, right? It probably acts longer there, so moving the cab would move the tuning.

Yeah, I had decent results measuring bass for a cab lying on its back a while ago, sealed box though. Mic was ~30-40cm above woofer.

Bottom slot, yes. It might increase Fb by a Hz or two if I move the mouth away from floor plane, I'll try to check this also for interest.

az

 

[donprice]

Keep up the good work! I should have my TDM15-4 in 2013. :yes:

Did you ever get to measure it with a woofer tester to see what the impedance peaks (and tuning frequency) look like?

 

[dumptruck]

I measured it with LIMP, apparently with reasonable accuracy since the crossover sims worked. I am considering doing that again, although now I'm distracted by trying to figure out how to measure phase of port output and what it's supposed to look like. I removed some more lining around the ports (which are just holes now, still), and it's not really too shabby sounding, but I'm not done here.

 

[audiozaz]

Seems like the driver's phase will wrap (180°) at Fb, so I guess the port phase should then be 0°?

Did not have time to measure my stuff last night. :/

az

 

[djnagle]

OK Dump....you've inspired me. Today I am going to finish my speakers!!! I got the day off, the weather is crap, my wife is gone for the day, and all my friends are at work. After reading all these posts, I hope my bass is good. I'll let you know by the end of the day. Off line until then.

 

[dumptruck]

Go for it! Did I read somewhere you have the X version? You should get a lot more bass from those, one way or another.

 

[djnagle]

Taking a break before tackling the second speaker. Yep, I have the X version. WinISD show a strong f3 at 40hz. Then there is boundry gain so I should be good to go. I do have 4 good subs if need be so no issue there. Breaks over, back on your heads!

 

[dumptruck]

Here's the impedance. I confirmed everything was working as reliably as it was the last time I was taking this type of measurement, calibrated to several resistances, and the result includes a bazillion averages. I'm pretty sure it's reasonably accurate.

It doesn't match WinISD, but neither does anything else about this. I am also re-posting the most recent sim/measurement combo because that was the same cabinet config. Something happening at 50Hz - that's new. The resonant stuff you see higher up is intrinsic to the woofer and not going anywhere. I promise. Any thoughts?

 

[Jeffery]

Man I swear I didn't know these things sucked so bad. They had a good following, I just thought they were decent gear...but I never tried them out. Now I just cringe every time you put up another plot. Luckily the TD18s were destroyed in shipping and the TD12s will never see the light of day, but I just feel terrible about these TD15s.

I'll say one thing, you've sure given it a hell of a try!

 

[dumptruck]

Heh, I feel fine about them Jeffery. Not sure how I'd feel if I paid full price instead of your price . I don't really have any experience with expensive 15" drivers. This <100 Hz stuff is my problem, in any case.

 

[Jeffery]

That's very gracious of you! I'll just sit over here and cringe in the meantime.

 

[djnagle]

Man I swear I didn't know these things sucked so bad. They had a good following, I just thought they were decent gear...but I never tried them out. Now I just cringe every time you put up another plot. Luckily the TD18s were destroyed in shipping and the TD12s will never see the light of day, but I just feel terrible about these TD15s.

I'll say one thing, you've sure given it a hell of a try!

Hi Jeff. They really are great woofers. I've been messing with them for a number of years now and have not seen what DT is seeing. Are you having issues with your 15s? I would not judge them just from this situation. There is only one woofer that comes close to these and that is the TAD 1600 (or 1601, can't remember the number off hand)

What are you doing with your 12s that they won't see the light of day?

 

[Jeffery]

Hi Jeff. They really are great woofers. I've been messing with them for a number of years now and have not seen what DT is seeing. Are you having issues with your 15s? I would not judge them just from this situation. There is only one woofer that comes close to these and that is the TAD 1600 (or 1601, can't remember the number off hand)

What are you doing with your 12s that they won't see the light of day?

My whole experience with AE has just been misery. I don't have any issues with the 15s, I sold the speakers and their issues to dumptruck. I won't be repeating that experience with the 12s.

I don't know much about the TAD woofers, but I have some cloth surround JBL 1501FE 15s that I might use some day.

 

[audiozaz]

Here is a bit of data from my set, for comparison's sake.

Just to have the info here for newcomers, I have the AE Lambda TD15M 8ohm in internal golden ratio cabinets of 5cu.f, with a bottom slot-vent totaling 190sq.cm in area, tuning the cabinet to ~32Hz.

I measured the following with the cab on its head, thus the vent was up in the air. Mic was placed mid-cone, ~1cm away, and very close to the baffle plane for the vent measurement. Vent output was adjusted by -13dB, as per 20*log(190/855).

Blue trace = woofer, near-cone

Red trace = near-vent, -13dB adjustment

Green trace = summed response

This is fairly close to simulation, with a f10 point in the mid-30ies. It sounds good in my small room.

Disregarding the fact that DT's woofer is 4ohm, the major differences are the cabinet shapes and tuning frequencies, his more squat/stout and mine taller/leaner, which I'm hoping helps give a bit of punch around 90-100Hz, as it verges on an MLTL, can't really prove this though. His Fb is mid-40ies while mine is low-30ies. I would expect this to give stronger output from 40-60Hz versus my cab, which trades this for some reach sub-40Hz.

az

 

[djnagle]

The 1500 is another great driver. I think they are discontinued now, but still very good.