Is H-frame sub using GW-1858 "fast" enough for Maggies?

[tinnitusintx]

I'm very interested in Martin King's h-frame sub that uses the Goldwood 18" driver. Any chance a pair would integrate well with a pair of Magnepans (MMGs)?

[Pete Schumacher ®]

I'm very interested in Martin King's h-frame sub that uses the Goldwood 18" driver. Any chance a pair would integrate well with a pair of Magnepans (MMGs)?

I don't see why not. As long as you're not pushing them above 200Hz, you should be able to dial them in with the right LP filter.

[MSaturn]

No such thing as "slow" bass, really. A myth that's been propagated a long time.

My worry is just the "goldwood" part of the equation. 200hz might be too high.

I'd suggest a steep filter at 125-150Hz - the MMGs, full-range, claim to reach 50Hz - but distortion is likely high that low, and I certainly wouldn't use them to that depth.

[Bob Brines]

I just built a pair of those:



They are 19" baffles - 20.5" overall. There is a serious cavity resonance somewhere between 100-120Hz. I find these unusable above 100Hz. I have them crossed to the little TL's sitting on top of them at 90Hz and the TL's at 110Hz 2nd order LR. Works very well since the TL's will go to 40Hz on their own. The H-frames relieve the TL's of the heavy lifting and mve enough air to give the combination some real chest thumb.

If you would like to hear them, see you at LSAF in Dallas May 4-6.

Bob

[Deward Hastings]

There is a serious cavity resonance somewhere between 100-120Hz. I find these unusable above 100Hz.

It's the curse of H frames, and the price paid for the narrower (but deeper) footprint. That it is a problem, however, should be a cautionary for those who would use box (or pipe) resonance to "augment" bass . . . it's hard to come up with an "explanation" why resonance at 100-120 Hz is bad, but resonance at, say, 50-60 Hz. is "good" . . .

[Bob Brines]

It's the curse of H frames, and the price paid for the narrower (but deeper) footprint. That it is a problem, however, should be a cautionary for those who would use box (or pipe) resonance to "augment" bass . . . it's hard to come up with an "explanation" why resonance at 100-120 Hz is bad, but resonance at, say, 50-60 Hz. is "good" . . .

It's a really hollow sound over a narrow band width. It's not very noticeable in rock music, but I identified it loud and clear is a piece of Vivaldi. Three notes in the 'cellos just sounded horrible. Knowing the piece well, I knew exactly what frequencies to look at.

Bob

[martin]

It's a really hollow sound over a narrow band width. It's not very noticeable in rock music, but I identified it loud and clear is a piece of Vivaldi. Three notes in the 'cellos just sounded horrible. Knowing the piece well, I knew exactly what frequencies to look at.

Bob,

Are you sure the resonance is an acoustic mode generated in the cavity? Looking back at all of my calculations and measurements for my H frames, I don't see anything that would lead to a problem around 100 Hz. The cavity resonance I predict and measure is in the couple of hundred Hz and forms a broad rounded hump. A sharp narrow peak would set me looking at a structural resonance of the cabinet itself, maybe a wooden panel vibrating. Have you tried adding some dead weight that is very flexible (sand bags, cat litter, dog food, rice, ...) to the top of the H frame to see if that impacts the resonance?

[bbtk]

It's a really hollow sound over a narrow band width. It's not very noticeable in rock music, but I identified it loud and clear is a piece of Vivaldi. Three notes in the 'cellos just sounded horrible. Knowing the piece well, I knew exactly what frequencies to look at.

Bob

That sounds like it could be a phase issue to me, based on my limited knowledge.

I once built a test baffle of an H-frame subwoofer using 4 15" Pyle Pro woofers, after a discussion in diyaudio. I could not get a good integration with my Linkwitz Orions with the limited testing I did. I also called the bass "slow." The poor build quality of the drivers and the problems integrating made me send the drivers back. I tried searching for that thread, but couldn't find it. Here's another one I remember reading that is pertinent to the issue of "fast" or "slow" bass.

http://www.diyaudio.com/forums/subwo...-anyone-2.html

[Bob Brines]

I spent all afternoon trying to discover the problem with my H-frames. Yes, the problem is not a resonance. I ran a THD sweep to see if anything popped out. To my horror, the miniDSP is injecting huge amounts of 3rd order distortion into the signal. I don't know if I just got a bad item or it is endemic in the miniDSP. Attached are the traces. The first plot is the GW1858 driven directly through a DAC. The second is the GW-1858 driven through the miniDSP with everything set to bypass. The third is the Alpair 7.3 direct. The fourth isthe 7.3 driven through the miniDSP. WOW! Just for grins, the fifth plot is the GW-1858 FR and the sixth the A7.3 in the small TL I am using for this pairing.

Color cod for the THD plots: 1=white, 2=white, 3=red, 4=blue, 5=green, 6=yellow.

As a backup, I setup a crossover and a graphic EQ in Foobar2000. The results are promising, but not quite there. From the plots at least, the GW-1858 is good up to ~500Hz. I would up with the low-pass at 150Hz and the high-pass at 200. I hope I can get this worked out by LSAF.At the moment, the W8-1772 MLTL sounds better on all counts except slam on rock.

Bob

[Bob Brines]

Just for grins, the first plot is the GW-1858 FR and the second the A7.3 in the small TL I am using for this pairing.

Bob

[martin]

Thanks for the update Bob.

For me this is a nice result, the H frame measurements seem to correlated well with the MathCad calculations.

[r-carpenter]

Bob, are you using S&L software for all your needs? How is it? Do you like acoustic measurement suite?

[Bob Brines]

Bob, are you using S&L software for all your needs? How is it? Do you like acoustic measurement suite?

Yes, I use WTPro for everything. I suffered through Speaker Workshop and SoundEasy (which I haven't used in ~5 years) and each measuring session started out with an hour or so getting the jigs right. WTPro just works. Plug it in and measure. Period. My only gripe is that pretty-printing can be a pain. I still have a copy of SW to play with presentation. If I get off the dime, I could do this in MathCAD or even Excel, but I haven't cared enough yet.

Bob

[Pete Schumacher ®]

I spent all afternoon trying to discover the problem with my H-frames. Yes, the problem is not a resonance. I ran a THD sweep to see if anything popped out. To my horror, the miniDSP is injecting huge amounts of 3rd order distortion into the signal. I don't know if I just got a bad item or it is endemic in the miniDSP. Attached are the traces. The first plot is the GW1858 driven directly through a DAC. The second is the GW-1858 driven through the miniDSP with everything set to bypass. The third is the Alpair 7.3 direct. The fourth isthe 7.3 driven through the miniDSP. WOW! Just for grins, the fifth plot is the GW-1858 FR and the sixth the A7.3 in the small TL I am using for this pairing.

Color cod for the THD plots: 1=white, 2=white, 3=red, 4=blue, 5=green, 6=yellow.

As a backup, I setup a crossover and a graphic EQ in Foobar2000. The results are promising, but not quite there. From the plots at least, the GW-1858 is good up to ~500Hz. I would up with the low-pass at 150Hz and the high-pass at 200. I hope I can get this worked out by LSAF.At the moment, the W8-1772 MLTL sounds better on all counts except slam on rock.

Bob

You've hit on something that may explain why DoubleTap and I dumped the miniDSP in favor of a line level analog filter for bass duties.

[DoubleTap]

Wow, interesting Bob! I'll hook my MiniDSP up and see what I get. Right now I know it sounds like hammered sh*t, just don't know why.

[tinnitusintx]

With the MMG's I will be actively biamping and will likely limit their LF extension to 80-100 hz. So according to your findings, Bob, that should work out just fine. I will absolutley be attending and would very much like to hear those rascals. Do you have any idea yet where you'll be set up?

- Michael

[MSaturn]

If you're going active, you can get rid of the ~100-120Hz bump, too - the sort of thing mistaken for "slow bass" (read: poor integration)

[ROTECH]

If you're going active, you can get rid of the ~100-120Hz bump, too - the sort of thing mistaken for "slow bass" (read: poor integration)

Slow Bass; Read- descriptive wording of what somebody hears
Fast Bass; Read- descriptive wording of what somebody hears


Beating down the use of the words fast and slow is just as old an argument as people who use the words fast and slow. They are both easier to type and say in general conversation that going into a 14 page dissertation about response and integration.

[Bob Brines]

With the MMG's I will be actively biamping and will likely limit their LF extension to 80-100 hz. So according to your findings, Bob, that should work out just fine. I will absolutley be attending and would very much like to hear those rascals. Do you have any idea yet where you'll be set up?

- Michael

It's an absolute crap shoot. I reserved a double queen, but those are scattered about. Last year I got stuck down one of the corner aisles. Hope that doesn't happen again!

Bob

[generic]

No such thing as "slow" bass, really. A myth that's been propagated a long time.

My worry is just the "goldwood" part of the equation. 200hz might be too high.

I'd suggest a steep filter at 125-150Hz - the MMGs, full-range, claim to reach 50Hz - but distortion is likely high that low, and I certainly wouldn't use them to that depth.

Isn't it just a way to describe distortion and or cone break up? I've heard subs that were so muddy that they actually sound slow. Even if that isn't the correct term. Doesn't bother me as much.