Managed to get some time to play !!
Loaded the supravox 285 gmf's into the MLTL test cabinet - did not change anything else. Seem to get a similar tailing off LF response, for near field (4" in front of cone). However as you more back - ignoring the room interaction @ ~35Hz the response seems to flatten. I need to go and measure the port response to see if its working as it should.
I have also remeasured the Altec drivers T/S parameters using arta LIMP, seen abit different from before, however when putting them into MJK's sheet - did not notice big changes at the bottom end.
With respect to the question regarding the port its located why its not at the bottom, and it just being a hole in the cabinet, i have followed the recommendations of GM. I do not see from the MJK work sheet how the position of the port effects things, as the next step is to move the port to the front, an understanding of its position will be key.
Loaded the supravox 285 gmf's into the MLTL test cabinet - did not change anything else. Seem to get a similar tailing off LF response, for near field (4" in front of cone). However as you more back - ignoring the room interaction @ ~35Hz the response seems to flatten. I need to go and measure the port response to see if its working as it should.
I have also remeasured the Altec drivers T/S parameters using arta LIMP, seen abit different from before, however when putting them into MJK's sheet - did not notice big changes at the bottom end.
With respect to the question regarding the port its located why its not at the bottom, and it just being a hole in the cabinet, i have followed the recommendations of GM. I do not see from the MJK work sheet how the position of the port effects things, as the next step is to move the port to the front, an understanding of its position will be key.
5” dia. vent? The dims you confirmed awhile back is 5.5” dia, which tunes the cab a few Hz higher and could explain the impedance peak variance to the sim, though not the main problem.
What are the Supravox specs? How does its sim compare?
In a sim and in reality, in some alignments, moving the vent away from the bottom of a MLTL smooths out the mids response in room for a subjectively higher SQ, though some folks prefers this added ‘richness’ and why the Onken and Karlson is so popular in some audio ‘social circles’, i.e. reduces vent harmonics comb filtering with the driver’s output at the expense of slightly less ¼ WL pipe loading [damping] of the vent.
The vent’s BW in question has such large WLs [100–35 Hz = ~43.16”- 123.32” diameter sound ‘bubble’] that it’s hard to take the room’s reflections out of the ‘mix’ and why it should be measured with the mic slightly inside it, ergo in measuring the summed response < 1/4” in front of the dust cap [< a ~27,120 Hz reflection], moving the vent to the front should theoretically no impact on the <100 Hz BW’s measured response if not up against a wall or out at the room’s acoustic center.
That said, what little measuring I did long ago was very crude and done outdoors and haven’t yet bothered to learn how to use computer based programs and their many caveats beyond recalling that proper ‘gating’ was critical to accurately measuring LF in room, so if not a leak, then again I wonder how accurate the measurements are since the Petite Onken’s were so far off from the sim.
GM
What are the Supravox specs? How does its sim compare?
In a sim and in reality, in some alignments, moving the vent away from the bottom of a MLTL smooths out the mids response in room for a subjectively higher SQ, though some folks prefers this added ‘richness’ and why the Onken and Karlson is so popular in some audio ‘social circles’, i.e. reduces vent harmonics comb filtering with the driver’s output at the expense of slightly less ¼ WL pipe loading [damping] of the vent.
The vent’s BW in question has such large WLs [100–35 Hz = ~43.16”- 123.32” diameter sound ‘bubble’] that it’s hard to take the room’s reflections out of the ‘mix’ and why it should be measured with the mic slightly inside it, ergo in measuring the summed response < 1/4” in front of the dust cap [< a ~27,120 Hz reflection], moving the vent to the front should theoretically no impact on the <100 Hz BW’s measured response if not up against a wall or out at the room’s acoustic center.
That said, what little measuring I did long ago was very crude and done outdoors and haven’t yet bothered to learn how to use computer based programs and their many caveats beyond recalling that proper ‘gating’ was critical to accurately measuring LF in room, so if not a leak, then again I wonder how accurate the measurements are since the Petite Onken’s were so far off from the sim.
GM
I haven't measured the supravox drivers, but have the manufacturers spec sheet and claim to be fs=55hz and qts=0.33.
The port is around 5.25" diameter - as i have put some thin wall pipe up it so i can adjust the length. I have been using the formula from Dickinsons cookbook to calculate the length for a given diameter based on fs and cabinet volume, i assume this works for MLTL as well as BR's ?
Will try and get the port response measurements done this evening to confirm if whether it is acting like a BR or a BLH.
Its funny you should mention measurement accuracy- i have been wondering the same. Have only really used Holmimpulse with any confidence, when designing crossovers in the 1000+ Hz range. I have found if i make measurements at low volume the LF seems to be flatter. Also if you use the gated response its also much flatter. I suppose i could try another measurement piece of software.
Some room modelling software i have been looking at suggests opening all the windows will have an effect on room coupling. May measure with the windows in both condiftions to see if i can measure an effect.
The port is around 5.25" diameter - as i have put some thin wall pipe up it so i can adjust the length. I have been using the formula from Dickinsons cookbook to calculate the length for a given diameter based on fs and cabinet volume, i assume this works for MLTL as well as BR's ?
Will try and get the port response measurements done this evening to confirm if whether it is acting like a BR or a BLH.
Its funny you should mention measurement accuracy- i have been wondering the same. Have only really used Holmimpulse with any confidence, when designing crossovers in the 1000+ Hz range. I have found if i make measurements at low volume the LF seems to be flatter. Also if you use the gated response its also much flatter. I suppose i could try another measurement piece of software.
Some room modelling software i have been looking at suggests opening all the windows will have an effect on room coupling. May measure with the windows in both condiftions to see if i can measure an effect.
I think you should still do this and do another woofer nearfield, no smoothing, maximum time window.
As requested i have remeasured without any stuffing, with the responses unfiltered.
I also had a little play with the cabinet today - i added 3.5" to the height, so 7" on the line, and 0.6 cft on the volume. I was expected to see some differences from this action, - at least 3 hz drop on the vent tuned freq. As you can see from the attached, very little has changed.
What i don't understand from the port trace is why it is not decaying faster - it should have almost no response by 300 hz, but as you can see it keeps going > 1000Hz. I know people will cry leaky cabinet - i have caulked and recaulked. The only source being the speaker surround, as far as i can see but i cannot believe both the Supravox and the Altecs leak.
I also had a little play with the cabinet today - i added 3.5" to the height, so 7" on the line, and 0.6 cft on the volume. I was expected to see some differences from this action, - at least 3 hz drop on the vent tuned freq. As you can see from the attached, very little has changed.
What i don't understand from the port trace is why it is not decaying faster - it should have almost no response by 300 hz, but as you can see it keeps going > 1000Hz. I know people will cry leaky cabinet - i have caulked and recaulked. The only source being the speaker surround, as far as i can see but i cannot believe both the Supravox and the Altecs leak.
Without any damping, Fb should rise and the vent's decay will primarily be a function of the system's tuning and since the the lower the tuning, the wider its harmonic BW, the slower it will decay away, so my Q is why it's tuned so low? This is the opposite of a leaky cab. It's like the cab's net Vb is much < than sim's.
GM
GM
I'm confused, you say you expected a 3Hz drop in tuning frequency, and it looks like that's what you got? Anyway, response looks pretty much like a standard bass reflex box of 8.6ft³ tuned to 30Hz, with a little bit of a resonance around 35-40Hz. Actually matches a bass reflex sim with whatever parameters I have saved on my PC for this driver just about exactly.
Since I admittedly don't really understand what the point of MLTL cabinets is supposed to be, I'll limit my comment to that.
The out-of-band port output doesn't look surprising for a cabinet without any absorption. It may also be running into your noise floor to some extent.
Since I admittedly don't really understand what the point of MLTL cabinets is supposed to be, I'll limit my comment to that.
The out-of-band port output doesn't look surprising for a cabinet without any absorption. It may also be running into your noise floor to some extent.
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In my limited experience with MJK sheets, it has a significant effect on driver impedance and response. While i can see it being possible to get similar response, the impedance does play a somewhat significant role in the playback of music in a system, with lesser impedance providing an easier load to the amp. In the box I have designed for an Altec 416, the BR saddle has been reduced to one basically insignificant peak and another of lesser value than found in BR design. This is based soley on Win ISD and MJK sheets.
A bit of a "curve ball" i have the oppotunity to aquire a pair of 416z's - remagged with new GPA cones, on this side of the pond ( no $300 + shipping and customs costs). The question is for a given cabinet size ( ~ 8 cft) will these offer better LF performance than the 414z's, in a MLTL or similar BR cabinet. Worth a gamble?
Perhaps your question should be directed to Lynn Olson and Gary Dahl aka g3dahl over in Beyond the Ariel thread. They have GPA416's in a tapered transmissin line
Back of vacation ( for a few days until the next !!)
I passed up on the 416's as no positive vibs. Looking around the GPA stable of drivers - the 515 LF's are may be what i need to watch out for.
Back to the tuning of the 414'z - should i tune to 45hz (rule of thumb for TL low qts driver = 10hz higher than fs) currently tuning to 45hz is a problem as the cabinet has a 5" hole in it without any tube its @3/4" long is around tuned @ 35hz ( dependant on level of stuffing) Increasing the length just takes the tunning freq lower. Not understanding if a MLTL is a TL or a BR is there a problem with tuning lower?
I passed up on the 416's as no positive vibs. Looking around the GPA stable of drivers - the 515 LF's are may be what i need to watch out for.
Back to the tuning of the 414'z - should i tune to 45hz (rule of thumb for TL low qts driver = 10hz higher than fs) currently tuning to 45hz is a problem as the cabinet has a 5" hole in it without any tube its @3/4" long is around tuned @ 35hz ( dependant on level of stuffing) Increasing the length just takes the tunning freq lower. Not understanding if a MLTL is a TL or a BR is there a problem with tuning lower?
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