Speaker build with B&W units.

[peri]

Hi.

About 15 years ago I bought a set of B&W 305's from new. Last week I upgraded and bought a set of second hand B&W p4's - when I got them home I found the tweeters were totally shot (buy in haste and all that).

I'm a carpenter, and my idea was to build some nice cabinets, and use the woofers from the p4 and the 2 cones from the 305's.

I haven't much of a clue about speaker design, so before I start trying to learn I'd like to know if this idea actually sounds feasible - or am I on a hiding to nothing ?

Thank you.

 

[TLS Guy]

Hi.

About 15 years ago I bought a set of B&W 305's from new. Last week I upgraded and bought a set of second hand B&W p4's - when I got them home I found the tweeters were totally shot (buy in haste and all that).

I'm a carpenter, and my idea was to build some nice cabinets, and use the woofers from the p4 and the 2 cones from the 305's.

I haven't much of a clue about speaker design, so before I start trying to learn I'd like to know if this idea actually sounds feasible - or am I on a hiding to nothing ?

Thank you.

Even for the very skilled that would be a very difficult project. B & W are not OEM suppliers, so you won't know the specs of the drivers. You would have to measure them. You need the Thiel/Small parameters of the drivers you intend to use, and you need to measure the acoustic response of each driver.

You can't design the box and crossover until you have that information.

I would buy replacement tweeters for the burnt out ones, from B & W.

 

[peri]

Thanks for the reply.

Due to the age of the p4's, BnW no longer sell the tweeters - they have most other things in stock, but not tweeters or diaphragms for them.

Several threads I found suggested using Vifa OC25SC65-04 1" Textile Domes as replacements. I've ordered 2, but putting a £20 tweeter into a (when new) £700 cab just doesn't seem right to me.

 

[TLS Guy]

Thanks for the reply.

Due to the age of the p4's, BnW no longer sell the tweeters - they have most other things in stock, but not tweeters or diaphragms for them.

Several threads I found suggested using Vifa OC25SC65-04 1" Textile Domes as replacements. I've ordered 2, but putting a £20 tweeter into a (when new) £700 cab just doesn't seem right to me.

That tweeter will not work. It is a small tweeter with a resonance at 1380 kHz.
It is a high Qt tweeter also, so it can not be driven down through resonance.

That means it needs a second order filter at 6 kHz, or a third order filter at 4.5 kHz or a fourth order filter at 3 kHz. There is no way that will splice to those woofers precisely

The reviewer reports say the tweeter is harsh but break in. That is rubbish. They just learn to tolerate the harsh resonance peak at 1380 Hz, that is being caused by too low a crossover in the B & W speakers and crossover slopes that are too low.

The P4 uses a third order slope to the tweeter at 3 kHz.

There is also a severe sensitivity mismatch. You will need to modify the crossover to reduce the woofer tweeter output by 6db. Take out the crossover from the P4. You will find a 1.5 ohm resistor in series with the tweeter. Remove it and replace it with a 2 ohm wire wound resistor 10 watt. Now place a 6 ohm wire wound 10 watt resistor across the input of the Vifa Tweeter. That will give you optimal results from that tweeter. Without that L-pad I have designed for you it will sound really awful.

 

[lsiberian]

I can reverse engineer your box tuning if you can give me the dimensions of everything including the port, but lets not go buying tweeters just yet.

 

[peri]

Ok, I cancelled the tweeter order - the guy on the phone became quite terse when I explained the comments that TLS Guy had given. (I had originally phoned to enquire about getting the components mentioned).

Anyway, I removed the original tweeters, took them to bits (easily accomplished) and removed all of the ferrofluid that I could get out (not that easy). It had solidified, acting more like glue than a lubricant. They now sound 300% better. I have no idea if they sound anything close to what was originally intended, but at least they are 'listenable' now.

@Isiberian
If you want a new desk made or your kitchen redecorated, I'm your man. Speaker talk ....... not so much so haha.

Do you mean that if I was to give you all internal and external dimensions of both sets of speakers you could design a cab suitable for combining then into what I originally intended? (Sorry if thats a stupid question).


And thank you both for your time - you've been far more helpful than I ever expected.

 

[monkish54]

Ok, I cancelled the tweeter order - the guy on the phone became quite terse when I explained the comments that TLS Guy had given. (I had originally phoned to enquire about getting the components mentioned).

Anyway, I removed the original tweeters, took them to bits (easily accomplished) and removed all of the ferrofluid that I could get out (not that easy). It had solidified, acting more like glue than a lubricant. They now sound 300% better. I have no idea if they sound anything close to what was originally intended, but at least they are 'listenable' now.

@Isiberian
If you want a new desk made or your kitchen redecorated, I'm your man. Speaker talk ....... not so much so haha.

Do you mean that if I was to give you all internal and external dimensions of both sets of speakers you could design a cab suitable for combining then into what I originally intended? (Sorry if thats a stupid question).


And thank you both for your time - you've been far more helpful than I ever expected.

If you want to take a trip to LA you are welcome to use my Dayton DATS System (for the T/S parameters). You are also welcome to use my measurement microphone, LspCAD 6 professional edition, Gedlee Speak, Bagby's PCD, WINPCD, and anything else I have that can assist you.

 

[peri]

If I could afford the airfare from the UK, I'd have bought new speakers instead of second hand (We could do with some Sun though).

 

[lsiberian]

Ok, I cancelled the tweeter order - the guy on the phone became quite terse when I explained the comments that TLS Guy had given. (I had originally phoned to enquire about getting the components mentioned).

Anyway, I removed the original tweeters, took them to bits (easily accomplished) and removed all of the ferrofluid that I could get out (not that easy). It had solidified, acting more like glue than a lubricant. They now sound 300% better. I have no idea if they sound anything close to what was originally intended, but at least they are 'listenable' now.

@Isiberian
If you want a new desk made or your kitchen redecorated, I'm your man. Speaker talk ....... not so much so haha.

Do you mean that if I was to give you all internal and external dimensions of both sets of speakers you could design a cab suitable for combining then into what I originally intended? (Sorry if thats a stupid question).


And thank you both for your time - you've been far more helpful than I ever expected.

The only tweeter I'd attempt in those speakers is a Dayton Reference tweeter because it is very verasatile. Unfortunately I don't think a 100 dollar bet is a good one. Though you could make a nice build with the tweeters if they didn't work in your B&Ws.

 

[monkish54]

The only tweeter I'd attempt in those speakers is a Dayton Reference tweeter because it is very verasatile. Unfortunately I don't think a 100 dollar bet is a good one. Though you could make a nice build with the tweeters if they didn't work in your B&Ws.

How funny you should say that, i was just looking at my pair of RS28As not a minute ago.

If you want to make speaker design a hobby you could buy a UMIK-1 from MiniDSP for around $100 with shipping and a pair of Dayton RS28A and we can help you.

 

[peri]

I've been in touch with a great guy at Wilmslow Audio here in the UK. I explained my original idea of combining the 2 sets of speakers and he agreed that its quite possible. He's willing to take all the cones and crossovers, test them to find the relevant specs and design new crossovers for the job.

Now all I need is to figure out a cabinet design. If I had the speaker specs used to design the crossovers, would that allow someone to suggest a design ? For simplicities sake I was thinking of a closed cabinet.

Thanks

 

[monkish54]

I've been in touch with a great guy at Wilmslow Audio here in the UK. I explained my original idea of combining the 2 sets of speakers and he agreed that its quite possible. He's willing to take all the cones and crossovers, test them to find the relevant specs and design new crossovers for the job.

Now all I need is to figure out a cabinet design. If I had the speaker specs used to design the crossovers, would that allow someone to suggest a design ? For simplicities sake I was thinking of a closed cabinet.

Thanks

Ask him to get the T/S parameters of the woofer/woofers you intend to use. We can use the T/S to determine the best type of box for the drivers, and how big it needs to be. You can pretty much make the box any shape you want as long as the internal volume remains the same, although some shapes work better than others.