crossover suggestion for OB TB-1808, Eminence Beta 15?

Jeffs

Member
2011-10-14 12:55 am
Austin
Anyone have a suggestion on a crossover for an open baffle based on the PAP trio? (I've never built a speaker)

2x Eminence Beta 15A
Tang Band 1808

Purchased those parts yesterday but can't find any notes or bookmarks made some time ago and haven't had any luck with searches in the last day.

A year ago I purchased the Active Crossover Network for the diyaudiostore, but being as I don't have a computer that runs windows it is unlikely I will ever get around to using it.

Amps are a pair of F4 clones currently wired in parallel.

Any suggestions are welcome and most importantly may help with the WAF of spending money on parts for another project.

Thanks!
 

hweb

Member
2011-09-19 8:39 pm
MA, USA
IMHO use a miniDSP and go active cross over. It is very hard to do an OB any justice with passive XO. Some have succeeded, but it's much faster to good results with active XO (probably cheaper too, which you will notice once you see how expensive the big inductor you'll need for the woofers will be).
 
Hi Jeff,


for a passive XO, possibly it´s best to ask PAP directly. They seem to be very helpful to customers, and some of their XO´s have already been published here.
A crossover cannot be simply simulated or calculated. To work correctly, it must be measured and tuned to the loudspeaker. Without a measurement system, all what remains is guesswork.
If needed, I could guess some values, but after that, you´re on your own... sorry.


All the best


Mattes
 

Jeffs

Member
2011-10-14 12:55 am
Austin
active crossover starting point for DIY PAP inspired Trio TB?

Thanks for suggestions. It's probably past time to order measurement equipment (microphone and software).
Again, this is my first speaker build.

Is it correct to state active crossover requires multiple amps?

Looks like a multi-amp solution with miniDSP is how to get started, then take measurements, then build active crossover to match best DSP measurements?
First using the kit already on hand, then if good build another with "money-FET's"

The Eminence Beta 15A can be wired to provide 4 ohm load.
TangBand 1808 will be 8 ohm.

Options for amps on hand -
Option A: on channel of F4 to provide about 40w to woofers, one channel to provide 25w to TangBand.

option B: use adcom gfa-5300 to provide 125w to woofers, one channel of F4 for 25w to the TB. This is most reasonable for heat generated.

Future option C: use 2x F4 to provide 25w to each woofer at 8 ohms, build a 300B to drive the TB with ~8w. Least attractive option regarding heat generated, also time / money required to complete another amp.

Option D: ACA for the TB - I already have boards, JFET's, and 20V power supplies to do ACA around 5w, or spend ~$110 to get the 24V PSU's for 8wpc.

I'm just guessing on the amount of amp needed for the bass, and can guess based on other posts where the crossover points will be.
Thanks again.
 
Hi Jeff,


yes, getting some measurement equipment will be helpful. A UMIK microphone together with REW and a DATS doesn´t cost too much and is, once you´ve managed to operate it, quite helpful.
A miniDSP is an easy way into active solutions, and you´ll need multiple amps, my vote would be to start with option B.
Passive solutions with equal or better quality will require a lot more effort.


All the best


Mattes
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
What generally works best for OB is to low pass the woofer far below the acoustical point you've chosen for the crossover. For example if you are hoping to cross at 700Hz, you might be low passing the woofer at 100Hz.

This works because the woofer will have a pronounced rising response on open baffle, due to the front-back cancellation.(The bass is canceled out) To get a flat FR and the proper tonal balance, you have to trade away woofer sensitivity at the top end. This can often be 10dB, sometimes more. That's the trade off for having the open baffle. If you want proper tonal balance, the top end of the woofer can only be as sensitive as the bottom end.

Your woofer electrical crossover point will depend on many factors such as baffle size, woofer Q, room and your midrange driver. But using a very low low-pass is what works. Many OB speakers I've heard don't do this, being afraid of losing sensitivity. Consequently, they have no bass.
 

Jeffs

Member
2011-10-14 12:55 am
Austin
Have the baffles built PAP style. I get why people would pay for a pre-engineered frame.

The TB WB-1808 being driven by dual F4 mono blocks reaches higher SPL's than I was ever able to reach with speakers I've been using.

Too many words... It took a few hours of warming up, and have never listed to OB speakers, so sort of having a moment

Cheers!
 

freddi

Member
Paid Member
2005-08-16 4:21 pm
probably not much help but fwiw look at Visaton's NoBox. Their woofer had a lot lower qts than Beta 15A. I've used 2nd order highpass on FR with low dcr shunt L across the driver and series R before the capacitor to match levels in order to keep FR excursion down when driving the woofer hard.

measurements really are helpful.

Bauanleitung | Visaton
 
Jeffs.... Your basic driver choice can work fairly well with a not too complicated passive crossover. The basic crossover layout can be surprisingly simple, not much different from my current Manzanita DIY project posted here: Fast, fun, Inexpensive OB project

Many designers over think the crossover topology required to enable the drivers you have selected sing. Pano previously posted the key design element, setting a usable woofer to full range driver electrical (-6 db) frequency. But, I am getting ahead of things... Need to know how wide your baffle will be and wing depth if you choose to use wings. Those physical aspects of the baffle set what is known as "path distance". This is where most of the crossover decisions begin. In addition, other crossover design issues include high pass crossover frequency for the TB8, correcting the frequency rise of the TB8, How much to pad the TB8 and building an effective trap to limit the horrible break up the Emi Beta 15 have. The only weakness I see is the Emi Beta 15. There are better choices for the money. J
 

Jeffs

Member
2011-10-14 12:55 am
Austin
I had the floors in my house replaced last week, and the general cleaning of the house really changed the acoustics of the room for the worse. Lots of dog beds, boxes and stacks of papers, more desk / workspace really made a difference.
I stayed up too late last night listening and drinking so have been suffering today.

Baffle width is 22.25 inches, and may reduce it to 21.25. I thought I could get away with it (WAF), being that my current speakers are 19"w x 49"h x 9"d, but the cloth grill is only 14"w and the rounded edges make the old speakers appear MUCH less imposing.
Right now I have mock-ups and will most likely use some oak I picked up on clearance a few years ago. The easiest thing to do would be to make 5.5" wings. If I get ambitious, I may make the sides start at 2" at the top then widen at the base to 5.5", or more oak scrap, glue and clamps to give up to 12" at the base. Base will most likely be an oak stair / step plank cut down to the width of the front baffle.

Here are a few photo's of approximations of what I have in mind.
First, a view from the top. I have the baffle isolated from the aluminum frame with buna washers. Don't know if it would help, hinder, or make no difference.
attachment.php


Next is if I go with a sloping wing, I don't know enough if this would decrease the sensitivity of the lower woofer while lowering the frequency. It's not deep like descriptions of U baffles I've read of.
attachment.php

Last is similar if I go with simple wings on the side with a depth of 5.5" + 0.25" for the spacing between the baffle and wings.
attachment.php

That bottle near the woofer is a bottle of bitter apple dog deterrent which he respects. I have a two year old that is curious enough to destroy the drivers, so a grill of some sort may be needed for the full range. He can hear things I can't, and is very inquisitive with his nose. His paws are strong enough to take down a deer, so not much to do if he decides a punch is needed to investigate.

It took some time and back pain to get all the holes drilled. Maybe it will make it easier to swap out individual baffles, but going with a single baffle would have involved much less labor. I'll try some dampening on the back as suggested eventually.

I would like to complete an XO, but have purchased a miniDSP 2x4HD with a matching microphone. Maybe will return the miniDSP, maybe not.

So far, I'm only listening to the TB8, and bass isn't too bad, but nothing like I am used to.
 

Attachments

  • topspacing.jpg
    topspacing.jpg
    106.7 KB · Views: 321
  • sideother.jpg
    sideother.jpg
    140.9 KB · Views: 317
  • sidea.jpg
    sidea.jpg
    99.4 KB · Views: 315
Jeffs.... thanks for posting pictures and approximate dimensional info. One thing about the design is the asymmetry of the woofer baffles in terms of path difference. The bottom woofer, as pictured, has a path difference of around 15"-16". This provides an F= of about 144 Hz. However, the top woofer path length is shorter at around 10"-12". This results in an F= around 195 Hz.

This difference needs to be included in the crossover design because the woofers will exhibit a different frequency response characteristic.

In other words, each woofer will have to be corrected differently to yield a flat response. A dicey situation. We need them to sing together.

Lets assume we target the system to play flat to around 50 Hz. We have to correct the bottom woofer by around 8-9 db. The top woofer however, will require 10-12 db. The top woofer will be 3 db less efficient acoustically.

So we need to increase the top woofer path to match the bottom woofer with a 5" wing across the top (rear of baffle).

Once the two woofers are roughly equal path wise, we need to work out the woofer pair low pass crossover component(s). Which gets to the next question, how low do you need your system to play before it starts to roll off?
 

Jeffs

Member
2011-10-14 12:55 am
Austin
I'll be going with 3.75" deep "wings", rearward facing ends of the wings will be rounded over.

I'm not sure what "path" means but have some guesses. To use what I have on hand, is 7" good? Suggestion was 5", but am guessing that was a minimal figure.

How low do I want to go? As low as possible! But there must be a trade-off.

For the last few days I've been using the miniDSP 2x4 HD1 software and haven't experimented much, but went with their 200Hz 12dB suggestion for FAST / woofer assisted full range. Once I have a remote and a few variations setup I'll start trying other values. It seems good for learning, but needs some work and time.
My measurements with REW are done blind, without reading suggestions, without RTFM. They are definitely doing 45Hz. Sometimes there is not much above 10K Hz showing up. I can only guess that the miniDSP assumes amps are of equal power. Far from it, I'm powering the full range with 25 watts, and that is more than the full range likes (brassy distorted sound) the woofers are killing an amp with something in the neighborhood of 125 watts into 4 ohms, not even guessing what impedance they are seeing with only sub 200Hz signal. I can't listen to it at anywhere near full volume. I get some 110dB peaks at listening position, where with previous speakers I could never get to 100dB with 25 watts. Closer to a 92dB average with the loudest music the system could produce. My ear doctor wasn't the least bit concerned with those numbers.
It's nice to have the headroom, I would definitely like 105dB peaks. I would like to have the ability to listen at 96dB for when it's appropriate. Most evening listening is in the mid 80dB range. These are not great for daytime listening... so far.

I've seen a review stating the commercial model I'm copying (for modularity, once frame is completed) are about 95dB sensitive, and somehow produce an 8 ohm load. Same reviewer was also content with a couple of different First Watt 25 watt models. Same review states the XO is at 500Hz.

Best news is there is not a WAF issue with the prototypes!
 
Last edited:
Good to see you are making progress... Open Baffle can be a steep learning curve. As for "path". This is the shortest distance between the center of an OB woofer and effective baffle edge. I say effective because of potential wing and floor influences on the total (net actually) path. You can use a simple tape measure to validate your configuration. Linkwitz discusses this at his web site and includes a EXEL based SPL worksheet. Very informative and super useful. Electro-acoustic models

A typical OB will actually do a bit better than the predictions. A number of reasons for this, but a bit too much to get into here. It will be interesting to monitor your progress with your build. J
 
Help With Open Baffle Speaker

I noticed that the last activity on the thread was in May 2020. I hope that members can help me. I built a 3 way OB speaker as seen below. I made the mistake of using the Eminence Beta 15A in lieu of the Eminence Alpha 15. I like the speaker build but disappointed with the bass output. I am considering either using an active crossover or replacing the Beta 15 with the Alpha 15 (possibly adding active crossover with the Alpha 15's). Below is my current build. Would appreciate members recommendations on what to improve the sound (particularly increase bass output). If there are members that recommend an active crossover, I would appreciate a brand recommendation for a 3 way speaker. Thanks for considering to help.


I built the following open baffle speaker.

<image.jpg>




<image.jpg>







Using the following components:


Tweeter

Dayton Audio PT2C-8 Planar Tweeter

Mid-Range

Tang Band W8-1808 8" Neodymium Full Range Driver

Bass Woofer (2 bass drivers for each speaker)

Eminence Beta-15A 15" Driver

This is the crossover design:



<image.jpg><image.jpg>





Sincerely,

Greg Edwards