Ricci

I voted 3 stars. This was primarily a slow burning dialog driven movie as expected. I wanted LFE effects to end all LFE effects when the bomb was finally detonated. It didn't quite deliver that to say the least. Good movie though. 

Hello Lex,

I'm glad that you like the design and that the front plate appears to be solid enough. The modeling for it only ever indicated a modest amount of gain in the kick and upper bass region. Does look cool and provide driver protection as a bonus. 

Unfortunately a 21" cabinet can only be so small / light. Physics grrrrrrr. Did you happen to weigh the finished product with the driver installed? It looks like you measured the weight as about 52 kg without the driver. 70kg with the driver? This should be about right. A little big and heavy for a one man lift. You could add wheels or a dolly system. 

The 18" design you are thinking of is probably what I tested the BMS 18N862 in. It is much smaller and lighter but that cab is tuned a little lower and was intended for a heavy duty bass guitar rig using AE TD18H+ Apollo's. Traditional BR designs aren't that difficult. You could probably design your own. 

What country are you in? The bike systems seem interesting and fun. This would be a lot of sub on a bike!

I'm much in the same boat MM. Behind on movies.  I've been watching mostly docu series and sports lately. 

I did watch Godzilla Kong and Minus One, both in the theater. There was plenty of bass for sure but whether either truly dug deep or not I can't tell at the local Plex. 

Excellent job Lex. The cab looks solid and well built. Nice pictures of the process too.

What driver are you using? The 4 ohm or 8 ohm 21sw152?

Give me a day or two and I'll go through the measurements and formulate a reply. Apologies for the extra extra  late reply. I've been on hiatus from audio for quite a spell. Overall the measurements look about as expected with the vent pipe resonance causing the blip at about 150Hz. Looks like the tuning may have come in a smidge lower than the target, but that isn't unexpected given the size of the vents and the cramped space inside of the cab.

Any thoughts on the sound and structural solidity of the cab? The driver cap plate? Are there issues with vibration or noise from it during loud playback? That's been a concern since day one of the design. Secondarily I'm not sure if the acoustic effects of it are worthwhile. At least it's a glorified driver grille if nothing else.

I'll have to give this a watch John. Haven't seen it yet. 

I'm really out of the loop on the latest bass movies. Have there been many solid 4 to 5 star films in the last couple of years? Most everything seems to be lacking in the really deep stuff lately.

Jami,

Thanks for the cnc files and sharing them! I'm sure it will be a huge help to some other builders. I know it probably took some time to put those together. 

Hello Andyman3k. Nice work and thanks for the measurements. 

QSC eh? I've used my share of QSC amps and speakers over the years. 

The impedance plot suggests that the tuning of the vents is near 30hz or so. That's right about where it should be. The corner drooping a little is probably due to the 8 ohm 21sw152 having a little lower motor force than some of the other drivers used. That's one effect is that the vents aren't loaded as aggressively which results in a little bit of a roll off before the tuning. Not the end of the world in the scheme of things.

In general you'll get a sharper more aggressive low corner with drivers having more motor force ( BL^2/Re) / lower qts.  My cabs are usually a bit undersized vs extension and thus require extra energetic drivers. 

That indoor measurement rig sounds intriguing. Too bad it's not for public consumption. Am I correct that the polar work was conducted outside but the FR and Imp were on the inside rig? 

Nice measurement rig. Again thanks for sharing your info. More data is always welcome.

Dude. You're nuts. Haha. Definitely keep us updated on your journey.

Kyle you da man! 

8 hours ago, rolo95 said:

Can this design be split in to a half cabinet with 1 driver only for easier transportation ?

 

See the Skram subwoofer thread.

Nice build pics STE.

I'm still around.

I have similar thoughts based on the design work and simulations. In a lot of ways they do seem to be a vintage type of design, but taking advantage of modern driver advancements. Big, leverages a lot from one driver, should be loud and efficient over a narrow band, cabinets do not lend themselves to going low especially considering the considerable size, potential upper response phase and ringing issues could limit the upper range usefulness. Note: I've not actually seen good measurements on a top end example and have not heard or used any examples my self yet. YMMV.  

Kyle let's have a conversation soon. I can take over the payments for some time. I'd really hate to lose everything at either the main site or the forum, but since I've been spending times with other endeavors for a few years and don't have time to post like I used to the traffic has gone downhill. Perhaps there is an interested party at another website or forum that would be interested in taking over? 

Unfortunately for the future I  don't know if or when I'll have time to do testing like I used to. I have far too much on my plate. 

I have no web developer or programming skills and no time to learn it either so that's another piece of the problem. 

See my reply in the other thread. The physical dimensions of the driver make mounting it in a horn that models well acoustically a particularly tough challenge. 

Good job Mike. Those look excellent. 

That is the problem with using these drivers horn loaded. They want a compression ratio that is quite high and the drivers themselves are huge with a massive frame and surround . Typically back mounting is used for horns but these do not have a frame designed for back mounting. Logistically it isn't feasible to use the drivers like this. This is part of the reason that I didn't pursue a horn for this driver myself. You could try a compression chamber...Or a bandpass which the MAUL already is sort of. 

I'd agree with Peniku8 on that comparison based on the available info. 

Isobaric doesn't really give much extra output. You are still limited by the xmax of 1 driver. it was a way to get extra motor force and a smaller cab back in the day. The modern 21's don't lack for motor force. It's a huge money sink for not much gain. The CKRAM is already small for a single 21. 

Hello DJimbo and welcome. 

As far as assembling the cabs go. Clamps and more clamps are your friend. Other options that help are a brad nailer, or a pocket screw kit. 

If using the 21SW152 drivers best results will probably be with 2 to 4kw of amplifier rating per driver. Any more might get sketchy over long periods of time. Less would leave some of the dynamic capability on the table. I prefer to run fully bridged amp channels on bass when possible. 

Smoothing out the corners might help with airflow in an ideal scenario but it has drawbacks. It reduces the internal volume utilized by the driver. With bass size (air volume) is king. The Skram is a vented cab on the back side so it's a traditional ported arrangement there. Large flares and circular vents would be beneficial ideally but would greatly increase the size of the cab and its complexity. The front is a short horn/expanding slot. The same applies here. Ideally it would be a totally smooth, straight path, but packaging it into the cab dimensions requires compromises. At best these would be small gains in output / noise reduction, even if it was built ideally with a totally different (much uglier and unwieldy) form factor. I hope this explains why most bass cabs do not bother with dramatic smoothing of the air path. It comes with other tradeoffs. 

On 7/24/2022 at 10:35 AM, jngggggggg said:

Has any fine folks on this thread had the chance to run impedence measurements on the skram? I thought about using the skhorn measurements as a close approximation if none were available but it would really help me for sizing up the right amplifier.

I am looking to run two Eminence NSW6021 (nominal 6 ohm) per amplifier and an considering two options:

1. operating a 2 channel amplifier in bridge mode with 2 drivers hung in parallel (net 3ohm). However, this would theoretically put a 1.5ohm load per channel (which is below the rated 2ohm minimum per channel) - that is unless the cabinet loading (acoustic impedance) raises the effective impedance to something more tolerable for the amplifier. 

2. Purchasing a 4 channel amplifier and also running it in (dual) bridge mode. Here I would hang one driver off each 'stereo bridged channel' and therefore only impose a 6 ohm load per bridged channel (ie: 3ohm spread across 4 channels which is more tolerable for the amplifier). +whatever cabinet effects may impart on the impedance the 'amplifier sees' 

First option is a bit more budget friendly so that would be my first pick. 

Amplifier is Wasi W15K or W15K4 respectively 

A pair of the NSW in parallel should be closer to a 2 to 2.5 ohm min at the vent tuning once cable resistance and cabinet effects are factored in. Most of the freq range will be much higher in impedance but this would be pretty low for most amps bridged. I'd suggest the 4 channel amp method, or running the drivers in series which should present a 8 to 10 ohm min load to the bridged amp. Most touring amps are happiest at about 4ohms per channel. 

On 9/6/2022 at 3:51 AM, Shayne32 said:

I’m in the process of building an skhorn right now, love the design, straight beast

Just ordered up a pair of sw152 4 ohm drivers and I was planning on running them 1 channel each off my crown itech 12000hd, should get about 4000 watts per driver.

is this too much power per driver or for the box itself?

Hello Shayne. That is a lot of power. Whether it is too much depends on a few factors. I'd suggest doing a bit of experimentation before running it wide open for long periods of time. Remember doubling power is only 3dB in an ideal case. 

Yes. If using all vents open a 25Hz HPF is recommended.

Sure...Please see the following link back to the Articles section under the heading "Equipment"

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