[Moonfly]

Out of interest, do you know what the system Q of the Ultra box sub in sealed mode is, did you ever measure that. Whatever it was, the resulting sound gave me an opinion that it was quite low, and probably too low for my tastes.

Should I take a guess, maybe the Qtc was .6 or under. Totally out of the hat, I'm gonna guess at .575, just in case there is an actual answer, based really on how it sounded to my ears. Finding out the true answer should clarify a few things in my own mind :T

Honestly, I wouldnt be surprised if it was lower, even much lower, but if its much higher then that really would be a surprise and not what I expected at all. If the answer is getting too close to the TSP's (therefore not something tat would become public knowledge maybe), then I understand, but I would really be interested in the answer.

Cheers

 

[Ed Mullen]

The system Q of the PB13U in sealed mode can be estimated by looking at the roll-off profile (refer to Ilkka's test results elsewhere on this website). You are correct, the anechoic system Q is probably around 0.5.

Each tune switch setting has a specific EQ curve, and the anechoic roll-off profile in Sealed mode was designed to provide a flat in-room response when the subwoofer is placed in a small to mid size room which provides some room gain. It works beautifully, as the PB13U in Sealed mode does indeed measure flat to ~10 Hz in several smaller rooms we tested.

The in-room FR of the system (anechoic + room gain) is really all that should matters to the end user; the PB13U in Sealed mode will sound balanced and accurate in a smaller room, but when placed in a large room (with minimal room gain), it might sound a bit thin on the really deep stuff when compared to the vented tunes (which were designed for a flatter response to the system knee).

 

[Moonfly]

Exactly what I was looking for Ed, spot on with this :T

Everything you say is true. The system Q value (in room Qtc) is something Ive taken great interest in with sealed subs, and sealed designs are my favourite and have been for some time, despite their cost.

My only gripe with the PBU was in fact a sound I could only call a low Q sound, and for me you have confirmed this was exactly true. My ears identified a Qtc lower than my tastes prefer. Its very accurate for sure, but a little to much one way for my personal liking. It certainly met your targets though, as flat to 10 hz was a reality in my room, although the 10hz tune also attained this and was preferable to me.

I must stress, the points I make are in no way negative towards the PBU, its a fantastic sub, just not quite right for me personally.

This is one thing I will look towards your new sealed subs for, as IMO most ported subs suffer this low Q type sound if their aim is to go deep and clean. IMO, with a ported sub, you struggle to go deep and clean as well as maintain a higher Q style sound. Its also why I knew the SB13 driver would be a modified version of the PBU one, and not the same one, although the PB13 driver could go in a very small cab at the expense of depth, probably too much though, especially for you guys.

A lot of things have made sense to me here, and confirmed some of the things I thought I had learned and understood. Its also shown me that for one particular aspect of a subs design, ears remain the number one judge. The possibility of targeting a system Q to where you want makes sealed subs the most attractive IMO, as long as budget doesnt stand in the way, as less budget obviously means less clean depth and spl.

Thanks for your input Ed, I look forward to seeing the new SB subs roll out :T.

 

[Moonfly]

The in-room FR of the system (anechoic + room gain) is really all that should matters to the end user; the PB13U in Sealed mode will sound balanced and accurate in a smaller room, but when placed in a large room (with minimal room gain), it might sound a bit thin on the really deep stuff when compared to the vented tunes (which were designed for a flatter response to the system knee).

Just a heads up on this comment though. For me personally, the statement is wrong, as the in room FR isnt the only thing that matters. I'm not sure how many people out there are like me, but it might be a useful bit of market info to know there are people out there with a view like mine. If the sound had been more like that of a sub with a higher Qtc, I would probably still own it.

All the best

 

[Ed Mullen]

Well, the system Q can certainly be changed with the application of external EQ. It only takes a very small change in the FR to subjectively alter the sonic signature of the subwoofer, so if you want to move toward a slightly warmer sound, then you could raise the anechoic Q of the system.

I don't know how your dual AV15 system is aligned, but a close-mic (like 1/2" from the center of the dust cap) sweep of the woofer will provide a very good approximation of the anechoic FR and we can see the system Q value. Assuming you like the sound of this sub system better, it might be more like 0.6-0.7 but that is pure speculation on my part until I see the FR.

 

[gperkins_1973]

Dan,

The PB13 sounded a bit lack luster in my room after running Audyssey. As you know my room is 17 feet by 17 feet. I am guessing that counts as a medium sized room. In ported mode it sounded alot better and I mean alot. I don't seem to get alot off low end gain in my room hence why a ported sounds so much better. My dual being a qtc off 0.9 sounded great with music and still pretty good with films but no where near as good as the ported I currently have. I loved the PB13 sub. It is a truely great sub and by far the best I have owned prior to my diy ones.

Does the room comp help with the sub in sealed mode. I know it does alter the crossover frequencies with the ported set ups but does it help with gain in the lower frequencies with the sealed mode.

This is one thing I will look towards your new sealed subs for, as IMO most ported subs suffer this low Q type sound if their aim is to go deep and clean. IMO, with a ported sub, you struggle to go deep and clean as well as maintain a higher Q style sound.

Dan, from my experience off my low tuned ported subs, this is somewhat true but only to a certain extent. Yes it is very clean down low and music does sound very good but I still feel I am missing something. It leaves you a bit, well, um, I dont know really attitude. There's something missing, maybe its a bit off punch. My MA RS6's even though are crossed over at 80hz still don't give enough much in those frequencies but yet if I up the crossover off the sub it tends to sound a bit muddled. This is why I have decided to do the 3 tuned sub. I think you loose something going really low. Going low is great for films and playing low bass tracks with now middle content but how often do we do that. I am very interested to see how the 21.5hz tune sounds.



cheers

Graham

 

[Moonfly]

Well, the system Q can certainly be changed with the application of external EQ. It only takes a very small change in the FR to subjectively alter the sonic signature of the subwoofer, so if you want to move toward a slightly warmer sound, then you could raise the anechoic Q of the system.

I don't know how your dual AV15 system is aligned, but a close-mic (like 1/2" from the center of the dust cap) sweep of the woofer will provide a very good approximation of the anechoic FR and we can see the system Q value. Assuming you like the sound of this sub system better, it might be more like 0.6-0.7 but that is pure speculation on my part until I see the FR.

Hi Ed, I have another question for you.

How does one interpret the response into system Q. I dont have a near field of my DIY subs, but I certainly preferred the sound of it. I aimed for about .65 to .675 according to the model in WinISD, but that probably raised slightly in room, perhaps not :dontknow:

My DIY subs is being replaced with an IB at some point, and I would like to get a measure of the system Q if possible (and probably some other subs too) so I can dig a little deeper into this area for myself.

Graham, the room comp simply applies a filter to the low end response of the sub to counter room gain. The function of that was basically there for eq'ing, which I used it for and it did a pretty decent job :T