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1st Open Baffles; Need help!

MJKing said:
Right now I am listening to expensive dipole drivers, four AE Dipole 15 woofers in H frames that are almost U frames (baffle shifted forward almost to the front of the box). These are paired with Lowther PM2C full range drivers. The bass goes deeper then my two low cost woofers and the Dipole 15 definitely can take more power without struggling. They are a step up from the Eminence and Goldwood woofers but not so large a step that I could not still enjoy or recommend the lower cost alternatives.

Martin
Click to expand...


Outstanding news! I just happened upon four AE IB15's and was hoping I could use them in a design that would offer a significant improvement over my Alpha 15 h-frames (wonderful contribution you made there, BTW...thank you) and wondered if a dipole h or u-frame with two per side was a worthwhile design consideration for these drivers (my understanding is they are very similar to the Dipole 15 in terms of performance characteristics and fine for OB use). Based on your testimonial it sounds like a tree worth barking up. Do you have any information detailing this OB sub design yet available for perusal?

Thanks,
Michael
 
rogerfederer said:
i'm hoping to set up the baffle to switch in and out different drivers, like in the MJK design. thus, his use of a crossover setup would make the most sense so you could adjust the mix between the FR driver and the alpha. so you add the crossover to your path. and many of the pro crossovers are XLR so you need XLR adapters. seems to get complicated fast. am i making this too hard?

if like you i would use a SET amp for the FR driver and another amp for the alpha then you have inputs > preamp > crossover > 2 amps (SET and SS) > OB

or could i have inputs > preamp > y-splitter > 2 amps > OB, where 1 of the amps is a plate amp (like you use) which has an adjustable cut-off?
Click to expand...

Yes, you are. :D Here's what makes it easy...

http://www.monoprice.com/products/p...=11509&cs_id=1150902&p_id=4783&seq=1&format=2

I use them in my system that is all Audioquest when I don't have my Ashly active xover in the chain (and no XLR connection is required) and hear no noise from the Monoprice cables at all. I got noise when using adapters.

- Michael
 
FWIW getting comfortable with active multi-amping opens up lots of doors and I recommend it to anyone who is a little more than half-way serious about their audio hobby and likes to tweak and DIY. As far as Behringer's reliability....I'm a musician and almost all of my exposure to Behringer products has been in that arena. I think it's a roll of the dice if you elect to use their products...some out there have had zero issues and others nothing but. I can say this....if I see Behringer gear being used at a gig I'm playing or helping out with sound I get concerned and always make the Behringer piece one of the first things on my troubleshoot list when and if things go wrong. Ashly, Rane, and dbx (in order of my personal preference) are brands I'm more comfortable with.

- Michael
 
From experience I learned never to buy a used electronic crossover as they are often abused by stoned sound guys. I have the cx2310 and it works well in my main system but the 3 way, well I returned it to P.E.

A 2 way OB doesn't require a preamp as you can use Y cables from your CDP/source and split the output between two amps. If you have an older AVR with a internal DAC you can send the digital output from your CDP to it and let it drive your bass woofers with a low pass filter. The CDP analog outs would then send it's signal to your main amp.
 
thanks, michael for the info re crossovers

mr. geist, in this system i have multiple inputs running to a control preamp. i was then running that to a tube buffer before my SET amps (2 in rotation).

so i could do inputs > control preamp > crossover > 2 amps (SET and SS)

that is not too messy. would use the monoprice adapter cables. could slip the buffer back in if it helped out the sound.
 
I currently run pre > tube monoblocks > passive crossovers > coaxials and then pre > plate amps > bass drivers

My pre has 2 pairs of outputs so bi-amping is easy.

Poultrygeist has suggested removing the passive crossovers and using an active crossover but I'm not sure I really want to do that. maybe if I could come across one cheap to try out for comparisons sake.
 
as an experiment i plugged my forte IIs back into the same rig and sure enough there was a lot more bass that i had been missing.
so i'm pretty sure i'm going to try the 2 way option even though it balloons my budget.
thanks again for all the advice. any more suggestions welcome!
 
FWIW, I use two Behringer CX3400 crossovers and have had zero problems with them. I'm sure DBX and Rane are better but the 3400 is pretty functional for hifi use. You can sometimes catch one at a Guitar Center, open box, for less than a C-note. I bought one new for $125 and the other off CL for $50.

Cool to see MJ King contributing here at AK. If you haven't read anything at Quarterwave.com, you need some skoolin'.:D
Also, better get some learnin' at Linkwitz Labs.
 
tomlinmgt said:
Do you have any information detailing this OB sub design yet available for perusal?
Click to expand...

Hi Michael,

Nothing documented yet, I am listening and tweaking and am waiting to measure the final configuration. I have posted a few details via e-mail and will copy and paste them below.

The H frames are 11.75" deep and 17.25" square (outside dimension) with the baffle offset 2" from the front, so it is an offset H frame that is almost a U frame. I did this primarily to protect the AE woofers.

The AE woofers presented a different crossover challenge compared to the Alpha 15A woofers. The AE driver has a lower fs and Qts which when combined with a 12 dB/octave crossover, my standard recipe for the Alpha 15A woofers, resulted in a rolled off low frequency response which did not reach very deep. The 6 dB/octave dipole roll-off starting around 200 Hz really attenuated the deep bass output. I ended up using a 6 dB/octave low pass crossover set at 30 Hz and then boosted the power to the paralleled AE woofers. The calculated SPL response is very flat with -3dB points at 25 Hz and 240 Hz. The Lowther PM2C has a 12 dB/octave LR crossover at 300 Hz. The driver SPL responses cross at 320 Hz.

Martin
 
Active crossovers are extremely flexible and can be used over and over again in different systems, but one note on active crossovers. Many entry level active crossovers tend to have only one slope option, mostly 24 dB/octave. I have found that the ability to use different slopes 6, 12, or 24 dB per octave and even different high and low pass slopes and frequencies to be very powerful. I have almost always ended up using 6 or 12 dB/octave crossovers with very different frequencies on my dipole systems. My personal crossover is a dBx DriveRack PA but there are many other options like miniDSP or Behringer.

While the cost of an active crossover can look prohibitive you need to recognize that the large passive crossover parts for frequencies in the 200 Hz range are also going to be expensive. A passive two way 12 dB/octave filter can cost as much as the budget woofer drivers, then if you want to tweak or try something different rhe costs start to rise quickly if you do not have a large stash a parts to raid. If you want to change drivers ...... Pretty soon an good active crossover can be a cost savings. Check the budget for all the parts you want to use and then decide.

One other thing I see people do to cut cost is to only use a crossover on the woofer and let the full range driver run wide open. This was recommended to me and I did try it once. At first the sound of the system was very pleasing but after a while I found that the large SPL hump around 200 Hz that was created by the added output of the full range driver and woofer to sound off, A/B comparisons convinced me that a crossover on both drivers sounded more natural. Neat idea but I am not sure it works well in reality. Maybe in some special cases with different drivers then I had on hand.

Martin
 
thanks for the excellent advice!

there are a couple of active crossovers on BT that i am looking at. will put up a WTB for the eminence on BT as well. maybe someone has some sitting around...
 
MJKing said:
Hi Michael,

Nothing documented yet, I am listening and tweaking and am waiting to measure the final configuration. I have posted a few details via e-mail and will copy and paste them below.

The H frames are 11.75" deep and 17.25" square (outside dimension) with the baffle offset 2" from the front, so it is an offset H frame that is almost a U frame. I did this primarily to protect the AE woofers.

The AE woofers presented a different crossover challenge compared to the Alpha 15A woofers. The AE driver has a lower fs and Qts which when combined with a 12 dB/octave crossover, my standard recipe for the Alpha 15A woofers, resulted in a rolled off low frequency response which did not reach very deep. The 6 dB/octave dipole roll-off starting around 200 Hz really attenuated the deep bass output. I ended up using a 6 dB/octave low pass crossover set at 30 Hz and then boosted the power to the paralleled AE woofers. The calculated SPL response is very flat with -3dB points at 25 Hz and 240 Hz. The Lowther PM2C has a 12 dB/octave LR crossover at 300 Hz. The driver SPL responses cross at 320 Hz.

Martin
Click to expand...

I'll preface this post with an apology to the OP for a quasi-hijack...but I think we can all agree an opportunity to harvest a little of MJK's wisdom should not be missed and any information he has to share will likely be relevant to many....including the OP in this instance.

Thanks for the reply, Martin. And thanks for joining us here on AK and chiming in. It's quite the luxury to get input in these parts from someone with your level of experience. It certainly bolsters one's confidence to know information is coming from an accomplished source...especially if said individual's foray into loudspeaker DIY is just getting started.

So, you've touched on something I've already identified as a potential obstacle for me....being locked into the 24 db/octave slope of my Ashly unit. And you mentioning the h/u-frame sub build with the AE Dipole drivers benefits from a 6 db/octave slope and the Alphas a 12 db/octave slope prompted me to check and see what the slope is on my Dayton plate amps. Turns out they're 24 db/octave....so not only am I not going to realize the most potential from any efforts with my AE IB15's in an h or u-frame if using these plate amps, but I've already been compromising the performance potential of these Alphas I've been using in H-frames. :headscrat

Adjustable slope is clearly the way to go and the dbx driverack PA unit looks to be a nice piece with a price of admission that's quite reasonable...especially when one considers all the other features it offers. My concern with the digital xovers has always been my already-converted-through-an-external-tube-DAC signal going through another d/a converter which is likely inferior to the external DAC I have upstream. But, I'm going to have to assume since you're using one it hasn't proven to be much of an issue for you. I understand the next model up in the chain, the driverack 260, has better converters. I'd appreciate hearing any comments you may have on this.

- Michael
 
tomlinmgt said:
I'll preface this post with an apology to the OP for a quasi-hijack...but I think we can all agree an opportunity to harvest a little of MJK's wisdom should not be missed and any information he has to share will likely be relevant to many....including the OP in this instance.

Thanks for the reply, Martin. And thanks for joining us here on AK and chiming in. It's quite the luxury to get input in these parts from someone with your level of experience. It certainly bolsters one's confidence to know information is coming from an accomplished source...especially if said individual's foray into loudspeaker DIY is just getting started.

So, you've touched on something I've already identified as a potential obstacle for me....being locked into the 24 db/octave slope of my Ashly unit. And you mentioning the h/u-frame sub build with the AE Dipole drivers benefits from a 6 db/octave slope and the Alphas a 12 db/octave slope prompted me to check and see what the slope is on my Dayton plate amps. Turns out they're 24 db/octave....so not only am I not going to realize the most potential from any efforts with my AE IB15's in an h or u-frame if using these plate amps, but I've already been compromising the performance potential of these Alphas I've been using in H-frames. :headscrat

Adjustable slope is clearly the way to go and the dbx driverack PA unit looks to be a nice piece with a price of admission that's quite reasonable...especially when one considers all the other features it offers. My concern with the digital xovers has always been my already-converted-through-an-external-tube-DAC signal going through another d/a converter which is likely inferior to the external DAC I have upstream. But, I'm going to have to assume since you're using one it hasn't proven to be much of an issue for you. I understand the next model up in the chain, the driverack 260, has better converters. I'd appreciate hearing any comments you may have on this.

- Michael
Click to expand...

Thanks for the positive feedback. But please recognize that I am not the ultimate expert, I have only followed one recipe for designing dipole speakers. John K and SL have a very different approach for designing dipole speakers and both feel very strongly that their method is better. The down side is that it must be active and more complicated with the various filtering required, they put a lot of effort into the filter design work. The advantage of my approach is that it is simple and can be done passively with the right combination of drivers. Since I have never heard the two design approaches side by side I don't know if one inherently sounds better.

I consider the Eminence Alpha 15A a great candidate for an OB system because of its fs of about 40 Hz, Qts of 1.3, and efficiency of 92.5 dB/W/m. In an infinite baffle this means that the SPL response is rising as you go from 100 Hz down to 40 Hz, there is a small peak at fs, and then the response drops at 12 dB/octave. This is not a great SPL curve for a boxed speaker, the response will ring. But when you combine this driver with the dipole response of a 20" wide baffle that exhibits a hump above 100 Hz and rolls off at 6 dB/octave below the hump the summed response looks really good for a bass system that gets down to 40 Hz. I like to use a 12 dB/octave low pass crossover to further flatten the response and smoothly combine with a full range driver. But a 24 dB/octave low pass would also be OK if the frequency is set higher. The Eminence Alpha 15A is a very flexible and affordable driver that works pretty well in almost any sized OB or dipole speaker system.

When you start to consider a more expensive driver like the AE IB 15 or Dipole 15 a different problem rises that needs to be solved. The dipole hump still exits above 100 Hz and then rolls off at 6dB/octave below the hump. The fs and Qts are in the range of 22 Hz and 0.8 to 0.9 respectively. The dipole response has rolled off the woofer's bass output by 12 dB by the time you get down to 25 Hz (two octaves below 100 Hz). This is why I use a 6 dB/octave low pass filter set to about the driver's fs, it counters the dipole roll off to create a flat resposne but the penalty is it also lowers the SPL output a lot. The AE drivers are not so efficient to start with at about 90 dB/octave, so you need to use an active crossover and boost the low end to match the output of the next driver up in the system. I do not believe a passive crossover approach will work well for the AE drivers.

Two very different drivers requiring two different low pass crossover approaches,

Martin
 
ready to start the build!

thanks for all the great advice, i have settled on a 2-way OB based on the MJK project 9, http://www.quarter-wave.com/Project09/Project09.html

now for some practical questions:

1. choice of wood: most of the OB threads i have read suggest MDF or plywood as there are no voids or knots. however, with the 2 way design i will be relying on the baffle itself much less sonically than in a single driver design. is the choice of wood that important with the 2-way?

here is the question my builder sent this AM:

"I was at Lowe's yesterday picking up plywood for my guinea pigs when I saw some really nice 3/4 edge-glued panels. I believe they were Aspen (not pine) and had a very light grain with no knots. The choice would be one more of aesthetics than sonics, I would imagine. The edge-glued panels are cheaper (by maybe half) but you will get a sort of basketball/chopping block look instead of the even veneer on the ply. The Baltic ply is also heavier and that may be a factor."

2. placement of the drivers: earlier in the thread there was a lot of discussion of driver placement to avoid a comb filter effect. also i asked questions re the edge (tolvan) software and its application to driver placement on a baffle (context wasy 1-way baffle). my builder is suggesting using a sort of cardas/fibonacci approach to the placement of the drivers. my attachment sketches out how he proposes to do it. would love any comments re this!

happy 2nd day of spring!
 

Attachments

I made my first OB using Alpair 10.2 and alphas 15. I have some problems and I would appreciate any help. I use 24x48 baffle with 11" from the bottom to the center of the alpha and 8.5" from the top for the 10.2, two inches from a center line. I've tied different types of filters: 1st and 2nd. Different x-over points. My impressions so far:
1) I have no idea why, but the speaker is so inefficient. I have troels PMS clones and they are so much louder. It was the most important point for me: make efficient easy to drive speakers.
2) I just can't mate Alpair10.2 and alpha. It doesn't sound coherent, fils like some part of lower mid is missing. Maybe they are too far apart? Or maybe you need something bigger to match 15".
Here is the photo:
ImageUploadedByTapatalk1367177400.804017.jpg
 
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