Vented Enclosure - 15" or 18" drivers

[Ukwarrior]

Hi,
I'm hoping to build my first subwoofer before christmas; I'm based in the UK, and it seems that we have a ridiculously poor selection of drivers, amplifiers and parts. Germany isn't too far, but most of their products are high end, and indeed high priced. I would like to build a vented enclosure for my Hifi setup.

I've asked around but I haven't got a definitive answer yet - if this project will be 90%-95% Music oriented and at the most 5%-10% HT (if that!), then what sort of tuning should I aim for? I like the idea of a LLT enclosure, having read the brilliant article, but I'm not sure if it really applies to my intended usage.

I like some of the designs which a company called EPIK are producing ( I can't include the http link due to low post count), in particular their conquest unit. This is essentially a dual ported 18" driver enclosure driven by a 1000w RMS amp. I have been looking at the following options :

Elemental Designs LT 1300 Plate amplifier
Either dual RL-P15s
Or a single RL-P18
Custom Enclosure (I have full access to a 3 axis cnc mill, unlimited MDF, and all the woodworking tools a man could ask for)

However, I'm not sure if the RL-P18 unit would be able to withstand a thrashing from the LT 1300 on full blast. Bearing in mind that I have to ship these subs to the United Kingdom, I really want to avoid making any mistakes in my decisions. Is there any advantage in having two 15" subs over one, other than the increased power handling? Or is that not advisable, considering each sub would then only get 650w, when I should be aiming for 800w each?

I'm aiming for Music oriented bass; accurate, very loud and as low as I'll need for any track (1812 overture excluded!). I'm not bothered about dimensions, as long as they are not ridiculous (above 500 pounds and 6 feet by 6 feet and I'm going to have problems).

Are there any specifically music oriented drivers that you can recommend? If so, what are they, and what sort of price do they run at?

I apologize for the basic and probably inane nature of my questions, but it would be of great help to me if I could get some of the expert input that seems to be rife on these forums!

Cheers,

Ed.

[ISLAND1000]

My choice is the RL-p 18" and a vented box of about 12 Cu. Ft. and instead of the LT 1300 buy a Behringer EP2500 pro amp for power.
From what I've seen on this forum, that driver and amp combination will be as "musical" as you can find anywhere and still have uber gobs of ultra-low down cannon firing power.

But I'm NOT one of those experts you asked for.

[Sonnie]

I had a pair of RL-p15's in an LLT enclosure weighing over 500lbs and powered by an EP2500 bridged 4 ohms ... awesome on music, but it would do 12Hz on movies too...

[ISLAND1000]

Are you like doin a little braggin Sonnie? . . . . you should that was quite a project.

[buggers]

I second the RLP-18, EP2500, in a large ported box.

[Ukwarrior]

Thanks for the advice everyone; I'm definitely going for the 18 inch and an LLT. However, is the driver capable of running such a high RMS rating (From the EP 2500 amplifier) without damage to the unit? Would the LT 1300 be a suitable alternative? Apparently it puts out 1300w when connected up to a load bank - would that be enough for some serious bass?
Any input would be appreciated!
Ed.

[ISLAND1000]

Like with any amplifier and speaker combination, you don't turn the volume up until the cone flops out of the frame . . . . if it does, you've gone too far.

[Ukwarrior]

Thanks for the info, Island1000!
Would a Behringer EP1500 do the trick or should I opt for the more powerful model. Also, these amplifiers appear to have a LPF of 30/50 HZ. Assuming that this can be disabled, would I need a separate EQ (Elemental Designs EQ.2) to lower the subsonic filter (to around 10/15 hz)?

The Behringer amplifiers are capable of two channel or bridged mono operation. For a single driver, is it possible to run each voice coil from a separate channel or would that damage the driver? Would it be better to run each voice coil in series (4 ohm total impedance for the dual 2 ohm vc driver) from a bridge mono amplifier?

Thanks!

Ed.

[Mike P.]

Every sub has a specific power requirement for the size and tuning of a cabinet. Once you decide on the size and tuning, modeling can be done to determine at what frequency over excursion will occur. The use of a subsonic filter will protect the sub from the lower frequencies that cause the sub to exceed its Xmax.

Powering the sub can be done by each method you stated. The preferred way by many is bridged mono into a 4 ohm load. The dual 2 ohm RL-p18 can be wired for a series 4 ohm load, the dual 4 ohm one can only be wired for 2 ohm parallel, 8 ohm series or 4 ohms to each coil.

[ISLAND1000]

Since the EP2500 is so reasonably priced I would opt for it over the 1500. With that done you'll have more potential SPL available depending on your need to pressurize your listening room.
The voice coil RE of the driver for an amp like the 2500 should be around 4 ohms for best efficiency. Most pro amps like the 2500 produce most power with least distortion driving into 4 ohms.
Driving separate voice coils with separate amp channels will work but there's a chance that both channels may not have equal signal strength or quality which may cause some distortion.
I would link 2 (2 ohm in series) voice coils for a total 4 ohm load.
Before changing filters you'll need to run the driver and box combination in your listening environment along with your main speakers before determining what frequency you need to choose to filter. It's part of the listening/integration process.

[Ukwarrior]

Sounds good to me, guys.
However, do you think the RLP-18 is better than a Maelstrom-X 18? I say this only because shipping of either sub to the Uk is going to cost a small fortune, so I'd like to make sure I'm buying the best subwoofer. For my needs (Vented, LLT, Musical), which would you advise?
Ed.

[ISLAND1000]

Performance wise there isn't going to be a great deal of difference between the two.
The Maelstrom X lists cheaper but you have to deal through their agent in Europe and I can't tell you anything about that. There's info about shipping on their website.
The Maelstrom X has one of the lowest Fs (cone resonance) I've seen . . . . good for low lows.
So from this point you're going to have to pick and choose which one has the best circumstances for you.

[SteveCallas]

Ukwarrior wrote:

I like the idea of a LLT enclosure, having read the brilliant article

Thanks. Based on some of the talk about amplification though, you may have missed this part:

SteveCallas wrote:

In terms of power, recent measurements performed by Ilkka and the realization that real world playback does not consist of continuous tones have caused me to reconsider my previous amp limiting guidelines. I used to think that one should aim for an amount of power that straddles the rated xmax of a driver in the given enclosure as seen in simulations without exceeding it. This guideline was faulty for three reasons. 1) The xmech, or mechanical limit of a driver's suspension, is much higher than the xmax, usually 1.5x or more. This means there is freedom for more excursion at the cost of nonlinearities, but that extra cushion of excursion is better put to use than having to clip your amp, as the resulting signal sent to the voice coil can be damaging. 2) Simulations show excursion used with a given amount of power based on a continuous playback of each frequency, like a sine wave. This is not an accurate representation of how the driver will behave with real music or movies, as few if any have extended continous tones. Excursion use will be less than the simulations predict with real material at a given power level. 3) A driver's suspension, even if very loose, will tend to resist movement more as it approaches its limits. This acts as another layer of protection.

Because of this, I now recommend using as much power as is economically feasible

In other words, don't be afraid of having a king kong amplifier, just know when enough is enough on your volume control. At the same time, if spending big bucks on an amp means you could really purchase a more modest amp and a second driver and enclosure, the better option will always be a second subwoofer, as your sensitivity increases and distortion at any given volume level decreases.

As for the driver, I'd personally go with the Maelstrom X. We haven't seen measurements of either that or the RL-p18, however, if the claims made for the Maelsrton X are true - proper utilization of XBL^2 and shorting rings, it should theoretically be the better performing driver. The RL-p18 comes from TC Sounds and they have a track record of drivers with very high Le, causing a rolled off FR at the top end of the subwoofer spectrum. And even if I'm wrong and the top end is fine, the Maelstrom is cheaper and not in jeopardy of becoming extinct anytime soon.

[Ukwarrior]

SteveCallas,
Thanks for the info; I didn't understand all of the LLT essay; this project is something of a learning curve for me! I'll be going with the EP2500.

Out of interest, what sort of gauge cable will I need to prevent them from being a limiting factor. I was trying to work out the sort of amps that would be traveling through the EP2500 to the subwoofer and judge an appropriate AWG accordingly. Having failed in this venture miserably, I considered 4mm2, or 11 AWG wiring to be a suitable compromise. I can easily source 10 and 8 awg copper strand wire - is this advisable? Will 11 AWG be a sufficient gauge to handle all of the EP2500's power? What sort of connectors would you recommend? I was considering wiring the cable up from the terminal outputs of the EP2500 to a pair of heavy duty binding posts at the back of the sub.

Also, I'm having trouble attempting to source a Maelstom X subwoofer in the UK - the European suppliers are all out of stock and can put me on a backorder but I'd really rather not wait. The US suppliers refuse to post outside of North America - not very helpful but a fail policy I guess. With this in mind, I'm still set on the RL-P18 unless I can find a way to get the Maelstrom X in the UK.

Thanks!

Ed.

[ISLAND1000]

11 awg will be MORE than adequate wire size. You could go lighter . . . . 16AWG and not burn anything down.
There is NOTHING wrong or insufficient about the RLP 18. It will out peform many of the top popular commercial subwoofers. It'll easily equal the units from EPIK you mentioned. With the EP 2500 and the RLP 18 in a 7 cubic foot box it'll have extraordinary power and the acoustic accuracy you're looking for because of it's lighter weight cone compared to the Maelstrom X, 66 grams lighter.

[Ukwarrior]

Thanks a load for replying - I'm sorry about the relentless questions; I really appreciate the time you take to answer them. I agree with you Island1000 with regards to the RL-P18; to me the unit seems very well made - the machining, finish and parts look top notch - from pictures alone perhaps better than the Maelstrom X? (This maybe incorrect). I'm glad the 11 AWG is sufficient (or even overkill!).

When you say a 7 foot enclosure, do you mean ported or sealed?
Also, I'm wondering if LLT or any Ported variant is really the best way to go if I'm heading for a really nice musical setup - HT is not really something I need to consider for this project - what would you recommend for the best sound quality? Having said this, the idea of a ported enclosure appeals to me - I'm sorry to be so vague but I haven't enough experience to make a proper judgment.

Regards,
Ed.

[ISLAND1000]

SoundSplinter recommends 7 cubic feet for the optimum SEALED box for home use. And in my opinion, as a former symphony musician, the "sound signature" of a sealed box system is more accurate than any other box design. Other people always prefer the sound of ported boxes. It's really a personal decision.

SoundSplinter recommends a 12.8 cubic foot box tuned at 18hz for a ported design for home use or an 18 cubic foot box tuned at 14hz for more infrasonic response. (DVDs and movies)
These are some of the decisions only you can make according to your available space, your own ability to move and place these units, and your own sound preference.

[SteveCallas]

LLT offers the most balanced performance and the most accurate reproduction. Accuracy comes down to linear FR, non liner FR, and headroom - a LLT bests a sealed in all of these areas.

Have you considered dual Mach5 IXL 18s, or are you wanting one beefier driver in a single enclosure?

[Ukwarrior]

I was hoping to use a single driver in one enclosure - It fits my needs best (room size may be a limiting factor). SteveCallas, what sort of volume LLT enclosure would the RL-P18 require for optimum performance? I hope to build the enclosure shortly after christmas (I'll be waiting for the driver to arrive in the United Kingdom), and I'll have access to a cnc router which will make building the unit easier and more precise. Would I need more than one 6 inch port or would a single 8 inch do the job? I've ordered an EP2500, and I'm hoping to order the subwoofer as soon as I'm sure what sort of enclosure I'm going with.
Regards,
Ed.

[SteveCallas]

With the RLp18 you would probably want to target ~650 liters and an 8" diameter port that is ~27" long, though you might be able to get away with a 10" diameter port. I'm away and don't have access to modeling software at the moment, but I'd imagine if the tuning was ~14hz and the enclosure was maybe a little bit larger you could probably get away with a 10" diameter port coming in ~40" in length.

Can somebody confirm that?

[Ukwarrior]

Sounds excellent; I'll be looking into sourcing some 8 inch pvc piping for the port. Would I need to integrate some sort of flare into the port, or can that only be determined after modeling? If so, I'd probably construct the front face of the enclosure (the driver face) from two sheets of 3/4" MDF, and use the cnc router to create a nice sloping flare over perhaps an inch of the combined sheets. The remaining half inch could then be routed from the reverse face to the external diameter of the port material, so the port could slide into the material ensuring a better fit and seal. Is a 650 litre enclosure as large as it sounds? I'm looking forward to this project and I sincerely appreciate the time you take to offer your advice!
Regards,
Ed.

[Mike P.]

Can somebody confirm that?

A 10 inch diameter port 40 inches long will tune 650 liters to 14 hz, and will 1000 watts input the port air speed reaches a maximum of 24 m/s at 12.5 hz.

Air speed with the 8 inch port is 38 m/s at 12.5 hz withe same cabinet size and input power.

[SteveCallas]

Thanks Mike, I'm visiting family and didn't really want to have to download and install WinISD on their computer It looks like if you want a super low tuning you'll want to stick with 8" diameter, but if 14hz is plenty low for you (and it should be), 10" diameter would be better.

UKwarrior wrote:

Would I need to integrate some sort of flare into the port

Yes, and the way you described is what most of us do. If the driver is going to be mounted to that same side of the enclosure, and you will be making a ~650 liter sub, you may want to seriously consider using 3 sheets of MDF.

Is a 650 litre enclosure as large as it sounds?

It's quite large.....I have two of them You can see one in the attached picture - I went with sonotube, 28" diameter and 70" length.

[Mike P.]

There are subs in the Database in that size range. Have a look to give yourself an idea.

http://www.hometheatershack.com/foru...-database.html

[Ukwarrior]

They all seem huge
While that's not a bad thing, I think I'm going to have a hard time convincing less subwoofer friendly family members that an enclosure that large is suitable. In an ideal world, I'd love to use an LLT design but maybe for now it's just too big. I've been looking at the intended room, and a sonotube isn't really an option - I've got about 30 inches width to play with, four feet (48 inches) height, and maybe 35 inches depth. That's a raw 825 litres. Factoring in the driver, port(s) & bracing, this figure may be well short of the 650 mark. Even these measurements are larger than I'd ideally want them.
The soundsplinter website recommends an 18 cubic feet enclosure tuned to 14hz - If I settled for this would it sound ok, or would the magic be lost?
I'm sorry for being so indecisive, and to those who have helped me, contradictory and vague!
Ed.